Handbook of Antenna Technologies

One of the objectives of this presentation is to illustrate how Maxwell came to his mathematical constructs of the work done before him by OerstedOersted, H.C., Ampère, Faraday, Gauss, and so on, into a concise and precise mathematical form. In addition, the chapter addresses two specific topics which are fundamental in engineering electromagnetic education: how did Maxwell reached the conclusion that light was electromagnetic in nature and thereby revolutionized the last-century physics and the concept of displacement current? Maxwell first published his famous equations 20 in number in the early 1860s, and yet they were not accepted by the scientific community and were not put in the proper form till the early 1880s. The question is why it took over 20 years for the scientific community to grasp Maxwell’s ideas. One of the reasons why Maxwell’s theory was so difficult to follow was due to the development of Maxwell’s thought process through different times. This made Maxwell not to identify his physical pictures with reality. Maxwell felt free to discard one picture and adopt another as often as expediency or convenience demanded. Maxwell’s theory over the years evolved in two different steps. That is the other subject matter of this chapter.Maxwell never believed that light could be generated electromagnetically. In fact, he was always silent about electromagnetic waves and their generation and detection. It took almost 25 years before Hertz discovered electromagnetic waves, and his ingenious experiments confirmed Maxwell’s theory. Maxwell’s ideas and equations were expanded, modified, and made understandable by the efforts of Hertz, FitzGerald, Lodge, and Heaviside. The last three are being referred to as the “Maxwellians.” The early history of electromagnetic waves, up to the death of Hertz in 1894, is briefly discussed. The work of Hertz and the Maxwellians is briefly reviewed in the context of electromagnetic waves. It is found that historical facts do not support the views proposed by some, in the past, that Hertz’s epoch-making findings and contributions were “significantly influenced by the Maxwellians.” Finally, Maxwell’s macroscopic theory was transformed to the microscopic theory based on electrons as its discovery came 18 years after Maxwell’s death.

The objective of this chapter is to illustrate that an electromagnetic macro model can accurately predict the dominant component of the propagation path loss for a cellular wireless communication. The reason a macro model can provide accurate results that agree with experiments is because the trees, buildings, and other man-made obstacles contribute second-order effects to the propagation path loss as the dominant component that affects propagation is the free-space propagation of the signal and the effect of the earth over which the signal is propagating. It is demonstrated using both measurements and an analytical theoretical model that the propagation path loss inside a cellular communication cell is first 30 dB per decade of distance, and later on, usually outside the cell, it is 40 dB per decade of the electrical distance between the transmitter and the receiver irrespective of their heights from the ground. This implies that the electric field decays first at a rate of ρ─1.5 inside the cell and later on, usually outside the cell, as ρ─2, where ρ stands for the distance between the transmitter and the receiver. This appears to be independent of the frequency of operation in the band of interest and the parameters of the ground. It is also illustrated that the so-called slow fading is due to the interference between the direct wave and the ground wave as introduced by Sommerfeld over 100 years ago. All these statements can be derived from the approximate integration of the Sommerfeld integrals using a modified path for the steepest descent method and also using a purely numerical methodology. Finally, an optical analog is described based on the image theory developed by Van der Pol to illustrate the mechanism of radio wave propagation in a cellular wireless communication system.

Antenna design traditionally relies on physical understanding of electromagnetic radiation, intuition, and experience, as well as trial-and-error experimentations. With the advent of computers and increasingly sophisticated numerical methods, however, computer-aided design tools play a central role in today’s antenna design and optimization process. This chapter presents a summary of commonly used commercial antenna design simulation tools and their underlying computational electromagnetics methods.

The principal computational electromagnetics techniques for solving antenna problems are reviewed. An introduction is given on a historical review of how antenna problems were solved in the past. The call for precise solutions calls for the use of numerical methods as found in computational electromagnetics. A brief introduction on differential equation solutions and integral solutions is given. The Green’s function concept is introduced to facilitate the formulation of integral equations. Numerical methods and fast algorithms to solve these equations are discussed.Then an overview of how electromagnetic theory relates to circuit theory is presented. Then the concept of partial element equivalence circuit is introduced to facilitate solutions to more complex problems. In antenna technology, one invariably has to have a good combined understanding of the wave theory and circuit theory.Next, the discussion on the computation of electromagnetic solutions in the “twilight zone” where circuit theory meets wave theory was presented. Solutions valid for the wave physics regime often become unstable facing low-frequency catastrophe when the frequency is low.Due to advances in nanofabrication technology, antennas can be made in the optical frequency regime. But their full understanding requires the full solutions of Maxwell’s equations. Also, many models, such as perfect electric conductors, which are valid at microwave frequency, are not valid at optical frequency. Hence, many antenna concepts need rethinking in the optical regime.Next, an emerging area of the use of eigenanalysis methods for antenna design is discussed. This can be the characteristic mode analysis or the natural mode analysis. These analysis methods offer new physical insight not possible by conventional numerical methods.Then the discussion on the use of the domain decomposition method to solve highly complex and multi-scale antenna structures is given. Antennas, due to the need to interface with the circuit theory, often have structures ranging from a fraction of a wavelength to a tiny fraction of a wavelength. This poses a new computational challenge that can be overcome by the domain decomposition method.Many antenna designs in the high-frequency regime or the ray optics regime are guided by ray physics and the adjoining mathematics. These mathematical techniques are often highly complex due to the rich physics that come with ray optics. The discussion on the use of these new mathematical techniques to reduce computational workload and offering new physical insight is given.A conclusion section is given to summarize this chapter and allude to future directions.

Design of small antennas is challenging because fundamental physics limits the antennas performance. Physical bounds provide basic restrictions on the antenna performance solely expressed in the available antenna design space. These bounds offer antenna designers a priori information about the feasibility of antenna designs and a figure of merit for different antenna designs. Here, an overview of physical bounds on antennas and the development from circumscribing spheres to arbitrary shaped regions and embedded antennas are presented. The underlying assumptions for the methods based on circuit models, mode expansions, forward scattering, and current optimization are illustrated and their pros and cons are discussed. The physical bounds are compared with numerical data for several antennas.

The concept of receiving mutual impedance is introduced through derivation from a method of moments (MoM) analysis. The theoretical and experimental methods for the determination of the receiving mutual impedance are given and illustrated with typical examples of dipole and monopole antenna arrays. The fundamental difference, namely, the truly isolated state between the receiving mutual impedance and the conventional mutual impedance, is explained. Typical examples for the application of the receiving mutual impedance are given to demonstrate the validity and accuracy of using this concept. These examples include applications in direction of arrival (DOA) estimation, in interferences suppression, in magnetic resonance imaging (MRI) phased-array design, and in multiple-input and multiple-output (MIMO) communication systems.

A variety of antennas have been engineered with metamaterials and metamaterial-inspired constructs to improve their performance characteristics. Interesting examples include electrically small, near-field resonant parasitic (NFRP) antennas that require no matching network and have high radiation efficiencies. Experimental verification of their predicted behaviors has been obtained. This NFRP electrically small paradigm has led to a wide variety of multiband and multifunctional antenna systems. The introduction of active metamaterial constructs further augments the antenna designer’s toolbox and leads to systems with many interesting and useful properties.

Optimization strategies have been heavily used in the antenna design community for many years. Oftentimes, the details of the strategies and optimization configurations are left out of the designs in open literature. The goal of this chapter is to inform the reader of many of the algorithms currently being used in the antenna design community, give a detailed operation of four of the most commonly used algorithms, and compare their performance on test functions and an example antenna design problem. Additionally, several recent examples of complex antenna designs which made use of these algorithms will be examined.

In this chapter, transmission-line-based metamaterials are presented, and their application to the design of passive and active antennas is outlined. Transmission-line metamaterials, also termed negative-refractive-index transmission-line (NRI-TL) metamaterials, are formed by periodically loading a transmission line with lumped-element series capacitors and shunt inductors, and it is shown that they can support both forward and backward waves, as well as standing waves with a zero propagation constant. These rich propagation characteristics form the underlying basis for their use in many antenna applications, including leaky-wave antennas, compact resonant antennas, and multiband antennas. The resonant characteristics of the NRI-TL metamaterial structures reveal how these structures can be designed to offer multiband responses whose resonant frequencies are not harmonically related while offering large degrees of miniaturization. Design equations for rapid prototyping are presented, enabling the simple design of metamaterial antennas to a given specification using standard microwave substrates and loading elements in either fully printed form or surface-mount chip components. A number of passive metamaterial antenna applications are presented, including examples of zeroth-order resonant antennas, negative-order resonant antennas, epsilon-negative antennas, mu-negative antennas, metamaterial dipole antennas, and metamaterial-inspired antennas. Active non-Foster matching networks for small antennas are also presented using negative impedance converters (NICs) and negative impedance inverters (NIIs), and it is demonstrated how these can be applied to metamaterial-inspired antennas. Finally, a new method of implementing reactive non-Foster elements using loss-compensated negative-group-delay (NGD) networks is presented that exhibits improved stability, dispersion, and achievable bandwidth.

Transformation optics provides a bridge between the electromagnetic functionality of the device and the material properties of the custom-engineered media. This chapter includes an overview of transformation optics theory and their application in antenna engineering. The basic theory of transformation optics is analyzed, including the general transformation and quasi-conformal mapping. Reviews are focused on the planar lens antenna, the multibeam antenna, the Luneburg lens antenna, and the metasurface Luneburg lens.

Traditionally, frequency selective surfaces (FSSs) comprising structures with periodicity in two dimensions have important applications as spatial filters in microwave and optics. Due to the manufacturing process, they are usually in the form of printed patches on a dielectric substrate or apertures in a conducting screen. Multiple FSS screens and dielectric layers can be stacked together to meet desirable spectral filter responses. For these structures, a surface discretization of the unknown currents and/or electric fields is more convenient, and efficient integral equation solutions are sought thereafter. Recent developments in manufacturing processes, material properties, and new wave phenomena call for periodic structures with three-dimensional (3D) unit-cell elements. There are situations that a volumetric discretization of the unit cell is more appropriate, and differential equation solutions are preferred. The advent of powerful commercial simulation tools allows effective FSS designs with more flexibility. Compounded with the popularity of 3D printings, some previously unimaginable FSS structures can now be cost-effectively realized. Exploitation of transmission and reflection information obtained from FSS also paves the way for better antenna designs.

An overview of the field of optical plasmonic antennas is presented in this chapter. After a brief introduction and historical review, the theory of surface plasmon polaritons which leads to a set of overall observations as to the requirements and restrictions placed on the operation of plasmonic waveguides and antennas is presented. Both a single metal-dielectric interface and two interfaces between a metal sheet with dielectrics on either side are considered. In the second section the physical principles of operation and mathematical design criteria are presented for several common optical antennas including on-surface metallic structures and free standing particles. The third section covers the basic theory of aperture radiators along with a more detailed description of some popular designs. Current applications of optical nanoantennas are presented along with a discussion on some future directions in optical nanoantenna research.

In the first part of the chapter, an introduction to localized waves (LWs) is presented as polychromatic superposition of propagation-invariant beams (PIBs) with specific spatiotemporally coupled spectra. In the second part of the chapter, the focus is shifted towards some of the peculiar characteristics of electromagnetic LWs that distinguish them from other types of electromagnetic waves. In the last part, a presentation of the state-of-the-art techniques and experiments to generate electromagnetic PIBs is illustrated. Since PIBs are near-field phenomena, the electromagnetic structures that generate them differ significantly from conventional radiating antennas.

Terahertz technology has been receiving expanding interest in the recent years. With the help of newly invented terahertz sources, terahertz systems have been developed for various applications. One important technology for terahertz systems is the design of efficient antennas for terahertz wave transmission and receiving. Accordingly, the terahertz antenna measurement technology is of equal importance as terahertz antenna design. This chapter gives an overview of the state-of-the-art terahertz antenna design and measurement for a range of applications including the photoconductive antennas and radioastronomy/remote sensing antennas.

Additive manufacturing (AM), or often referred to as three-dimensional (3D) printing, is an important emerging research area which has received much attention recently. It allows 3D objects with arbitrary geometry to be printed automatically layer by layer from bottom to top. This technology offers several advantages compared to conventional manufacturing techniques including the capability of more flexible design, prototyping time and cost reduction, less human interaction, and faster product development cycle. 3D printing techniques have been applied in many different sectors including mechanical engineering, electrical engineering, biomedical engineering, art, architecture, and landscaping. This chapter reviews state-of-the-art 3D printed antennas from microwave to THz frequencies and offers practical and futuristic perspectives on the challenges and potentials of 3D printed antennas. An overview of various 3D printing techniques relevant to antenna applications is presented first. A number of 3D printed antenna examples categorized by different AM methods are then described. Finally, technical challenges and possible solutions of 3D printing technology specific to antenna application, as well as new and revolutionary antenna design/realization concepts enabled by 3D printing technology, are discussed.

This chapter shows the basic characteristics of a linear wire antenna in time-harmonic electromagnetic fields. The application of the method of moments is explained briefly to obtain the current distribution on the antenna. For a transmitting antenna, input impedances, current distributions, and radiation patterns are shown for four typical antenna lengths. For a receiving antenna, current distributions and reradiation patterns are shown when the complex conjugate of the input impedance is loaded at the receiving point. The received and reradiated power of the loaded receiving antenna is shown for three different plane-wave incident angles. Also the application of the Thevenin equivalent circuit is discussed for the calculation of the received power. Characteristics of a Yagi-Uda antenna are shown where the optimum gain of a reactance-loaded Yagi-Uda antenna is compared with that of an end-fire array.

This chapter on loop antennas covers implementation aspects of both electrically small and electrically large loops which have a wide range of applications. On one side, they are still a part of the old broadcasting systems such as analog radios, and, on the other side, they are increasingly gaining attention for the contemporary high-definition video transmission and reception. The chapter begins with electrically small loops and coil antennas and covers its different aspects of radiation and losses, tuning, quality factor, and matching. Subsequently, resonant full-wave loops and their polarization are presented. A technique is shown on how loops can be placed in closed vicinity of a communicating device conducting surface without losing efficiency. In the final part, single-element beam steering loop antennas and their arrays for enabling devices to achieve high throughput and high-gain wide scanning range are discussed.

The basic geometry of a microstrip patch antenna (MPA) consists of a metallic patch which is either printed on a grounded substrate or suspended above a ground plane. The antenna is usually fed either by a coaxial probe or a stripline. In the coaxial case, the center conductor is directly connected to the patch and the outer conductor to the ground. In the stripline case, energy is coupled to the patch in several ways: by direct connection, by proximity coupling, and by aperture coupling. The patch antenna idea appeared to be originated in the early 1950s, but there was little activity for almost two decades, mainly due to its inherent narrow bandwidth. It began to attract the serious attention of the antenna community in the 1970s, as antenna designers began to appreciate the advantages offered by this type of antennas, which include low profile, conformability to a shaped surface, ease of fabrication, and compatibility with integrated circuit technology. In the last three decades, extensive studies have been devoted to improving the bandwidth and other performance characteristics. This chapter begins with a brief description of the modeling techniques and basic characteristics of the MPA. Methods for broadbanding are then discussed, followed by dual- and multiband designs, size reduction techniques, circularly polarized patch antennas, and frequency-agile and polarization-agile designs. The chapter ends with some concluding remarks.

Reflector antennas are in widespread use in communications and radar applications in the twenty-first century. They are seen on towers for point-to-point telecommunication links, on houses for pay tv and in news items of spacecraft travelling to distant galaxies. This chapter provides an introduction to reflector antenna fundamentals for design and analysis. The history of the focusing properties of reflectors extends back to ancient times, but some of the more intricate properties such as defocusing have not been realised until recent times. Some basic reflector geometries are considered initially through a review of geometric optics. The basic design principles of a reflector are established from a rigorous point of view through a study of the paraboloid geometry, its radiation pattern and focal region fields. Practical reflectors have imperfections due to surface errors or misalignments, and how these impact the reflector radiation pattern is outlined. The means of feeding a parabolic reflector is outlined through a description of the dipole, waveguide and horn feeds. Some other reflector configurations are discussed including the offset parabolic reflector, the symmetrical and offset Cassegrain geometries and the spheroid. An introduction to reflector shaping is given through a description of two techniques. The chapter concludes with a description of three typical reflector applications in satellite communications, weather radar and radio astronomy.

Various antennas radiating a circularly polarized wave are reviewed on the basis of numerical techniques. The method of moments, the finite-difference time-domain method, the beam-propagation method, and the finite element method are employed to clarify the operation principles of spiral, helical, and rod antennas. A novel type of spiral antenna (a metamaterial-based spiral antenna) can provide a dual-band counter-circularly polarized wave. Since the operation principle of an endfire-mode helical antenna is very close to that of a dielectric rod antenna, the so-called discontinuity-radiation concept of a surface-wave antenna is discussed using a dielectric rod. Modification of the dielectric rod is studied to achieve a higher gain. A rod antenna based on an artificial dielectric is also investigated using a periodic structure of circular metal disks.

Over the past 30 years, many interesting developments have been seen in the field of dielectric resonator antenna (DRA). Analytical and numerical models for different shapes of DRAs were established in the 1980s and 1990s to understand their radiation properties. A couple of excitation schemes have also been proposed so that the DRAs can be excited efficiently. With the rapid advancement of dielectrics and microfabrication technologies in recent years, the DRA can now be made very compact for applications in portable wireless communication and millimeter-wave systems. In the first part of this chapter, miniaturization techniques of the DRA are discussed. It is found that the DRA can be integrated with power dividers for designing the circularly polarized and differential DRAs. Use of ground miniaturization technique has enabled realization of the omnidirectional CP DRA and the quasi-isotropic DRA for the first time. A review of the recent achievements in millimeter-wave DRA is then given. In this chapter, different dielectrics such as polymer and glass are also explored for designing the DRA. Transmission lines such as microstrip and substrate-integrated waveguide are deployed for exciting the DRA in the millimeter-wave spectrum. Elucidation is made on the design procedures and other considerations of the miniature and millimeter-wave DRAs.

Dielectric lens antennas are attracting a renewed interest for millimeter- and submillimeter-wave applications where they become compact, especially for configurations with integrated feeds usually referred as integrated lens antennas. Lenses are very flexible and simple to design and fabricate, being a reliable alternative at these frequencies to reflector antennas. Lens target output can range from a simple collimated beam (increasing the feed directivity) to more complex multi-objective specifications.This chapter presents a review of different types of dielectric lens antennas and lens design methods. Representative lens antenna design examples are described in detail, with emphasis on homogeneous integrated lenses. A review of the different lens analysis methods is performed, followed by the discussion of relevant lens antenna implementation issues like feeding options, dielectric material characteristics, fabrication methods, and a few dedicated measurement techniques. The chapter ends with a detailed presentation of some recent application examples involving dielectric lens antennas.

This chapter is focused on circularly polarized antennas. Key definitions and governing equations of circular polarization are given. Infinitesimal dipole sources are considered to establish circularly polarized radiation. First, radiation patterns of cross dipoles are mathematically reviewed, from which the condition of circularly polarized waves is concluded. Later, the idea is extended to four displaced sequentially rotated dipole antennas, resulting in circularly polarized waves within a wide angular range in space. The extension of the concept to the magnetic source counterparts and Huygens sources is briefly discussed. Other than point sources, also known as one-dimensional current sources, sources of circularly polarized radiation are further investigated for two-dimensional cases, such as microstrip patch antennas, and three-dimensional structures, such as volumetric current sources existing in dielectric resonator antennas. For these cases, the creation of circularly polarized radiation using single-feed and dual-feed, perturbed structures and sequentially rotated method is described. As a design example, numerical and measurement results of circularly polarized square patch ring antennas are extensively discussed and presented in this chapter. The square-ring microstrip antenna is selected as it closely approximates the sequentially rotated currents, and also it has not been widely studied in the literature.

This chapter explains the fundamental issues in designing phased array antennas (PAAs). At first, the structure and functions of the PAAs are introduced. Pattern synthesis, which is a feature of array antennas, and array calibration methods are explained. It includes some methods, minimax algorithm, element thinning algorithm, and genetic algorithm. For array calibration, rotating element electric field vector method is also explained. Digital beam forming (DBF) including signal processing and MIMO (multiple input multiple output) techniques are shown in a later part of this chapter.

Frequency independent and broadband antennas are reviewed form the view points of the self-complementarity and self-similarity. The theory of self-complementary antenna, original and modified self-complementary antennas, and so-called log-periodic antennas are discussed. Then the frequency independent antennas based on the self-similarity and other broadband antennas are presented.

The classic Fresnel zone plate has the advantage of being a flat, two-dimensional structure with a small thickness, light and easy to manufacture compared to the bulky refraction lens. In some cases, however, the zoned plate can be fabricated as a three-dimensional curvilinear assembly standing alone or conformal to some man-made or natural formation.This chapter is devoted to aperture antennas based on flat or curvilinear Fresnel zone plate lenses or reflectors. It is written as a self-sufficient text, which brings together most of the standard knowledge and recent research on the Fresnel zone plate antennas.

Grid antenna array (GAA) is a kind of planar array antenna with multiple rectangular loops. It can flexibly function either as a traveling-wave or non-traveling-wave antenna. This chapter lists clearly the different variations of the GAA and reviews briefly its theory development as well as applications. With a focus of the resonant GAA for 60-GHz millimeter-wave applications, the basic theory and operation are explored for the basic single-feed, dual-feed, and sub-array structures. More importantly, the further integration of the GAA as an antenna-in-package (AiP) module is presented with the design, fabrication, and test details at 60 GHz. The chapter finally reviews the state-of-the-art GAA millimeter-wave applications showing that the GAA really has wide applications from low microwave frequencies even to 120-GHz millimeter-wave frequencies.

The reflectarray is a novel type of high-gain antennas, which combines some of favorable features of reflectors and arrays. It consists of a space-feeding primary source and an array of reflecting elements with individually predesigned phases to collimate or shape the high-gain beam in the desired direction. In this chapter, the operating principles of reflectarray antennas will first be introduced. Then the design procedure and analysis methods of both reflectarray elements and systems will be explained in detail and some practical design considerations will be discussed. Finally, some latest developments and applications, such as broadband and multiband techniques, reconfigurable reflectarray designs, shaped-beam and multi-beam reflectarrays, etc., will be presented.

This chapter first provides basic treatment of small antennas (SAs), beginning with overview; definition, giving four types; discussions of the limitation related with the size and Q or the bandwidth; and significance of SA, in which a short history is included. Then, principles and methods of making antennas small based on those principles are described for four types of SA. Representative examples of practical SAs are introduced for the four types individually by referencing recent technical journals. Finally, the future prospective of SA is discussed.

At first, the history on studies on waveguide slot antennas and arrays is described briefly. Then the components for the waveguide slot antennas are explained. Various configurations of the waveguide slot antenna are described, and the equivalent circuits for some configurations are given. The procedure to design a waveguide slot array antenna is explained, and also the analysis model to design the element is discussed as well as the scattering matrix in connecting the equivalent circuit with a transmission line. Finally, the design examples for one-dimensional and two-dimensional arrays of the waveguide slot antennas are explained.

An omnidirectional antenna which radiates electromagnetic wave uniformly in a specific plane (often in the azimuth plane) is one of the most popularly used antennas in wireless applications. This chapter illustrates the basic principles and recent development of the omnidirectional antennas. The discussion is carried out based on a category of polarization of the omnidirectional antennas. The polarizations of the omnidirectional antennas include linear polarizations of vertical polarization and horizontal polarization, dual linear polarization, and circular polarization. A brief literature review about omnidirectional antennas is also presented along with state-of-the-art designs.

Recently, multiple-input multiple-output (MIMO) technology and diversity have attracted much attention both in industry and academia due to high data rate and high spectrum efficiency. By increasing the number of antennas at the transmitter and/or the receiver side of the wireless link, the diversity/MIMO techniques can increase wireless channel capacity without the need of additional power or spectrum in rich scattering environments. However, due to limited space of small mobile devices, the correlation coefficients between MIMO antenna elements are usually very high, and the total efficiencies of MIMO elements would be degraded severely due to mutual couplings. In addition, the human body causes high losses on electromagnetic waves. In real applications, the presence of users may result in significant reduction of total antenna efficiencies, and the correlations of MIMO antenna systems are also highly affected. In this chapter, the performance of some basic MIMO antennas as well as recent technologies to improve MIMO antenna performance of portable devices and mobile terminals are reviewed. The interactions between MIMO antennas and human body are also addressed particularly in mobile terminals application.

This chapter provides a broad discussion on the progress in low-profile antenna design and their applications. The antennas are divided broadly into dipole-based antenna designs, slot antennas, loop antennas, and microstrip patch antennas. In addition to the basic concepts, a literature review that outlines state-of-the-art designs along with recent trends in this field is incorporated. The objective of these discussions is to enrich the readers with conceptual knowledge in this marvelous field of engineering.

On-chip antennas feature the integration of antennas with other front-end circuits on the same chip in mainstream silicon technologies such as CMOS and SiGe. This chapter describes the basics, technology, and applications of on-chip antennas with particular emphasis on their circuit modeling, radiation efficiency, and integration as well as their crosstalk mechanisms with other circuit elements.

Research and development progress in the area of millimeter-wave antennas has been associated since recent years with substrate integrate waveguide (SIW). SIW was proposed and studied as a class of efficient integrated transmission lines compatible with planar technologies, offering incomparable self-consistent shielding and high-quality factor performances. SIW can be designed as open wave-guiding structures and energy leakage will take place when the uniformity of those guides is perturbed or they are not excited in an appropriate mode. This leakage effects may be used positively for the design of antennas by deliberately introducing perturbations in these guides so that they radiate in a controlled fashion. With the advantages of broadband, efficiency, and high gain, a specific benefit of such antennas is their compatibility with SIW from which they are derived, thus facilitating an integrated design. In this chapter, H-plane horns, leaky-wave structures (long and periodic) and tapered slot antennas are presented. Special attention is given for tapered slot antennas and arrays with their application in the design of passive imaging systems.

The focus of UWB antenna research activity has matured in recent years and currently mainly concentrates on applications such as biomedicine and security. Early UWB antenna designs were driven by the FCC allocation of spectrum in 2002 and focussed on obtaining wide impedance bandwidths with reasonable group delay characteristics. Many of these were simple planar monopoles antennas with canonical geometries. The emergence of new applications channelled the emphasis towards miniaturisation and integration into devices. This required optimisation of the antenna geometries to ensure that good system performance is achieved from the integrated antenna. Many optimisation techniques are available including the spline technique to generate the outline of the antenna element and ground plane. Simple methods based on genetic algorithms are employed and evolutionary algorithms which are capable of optimising for multiple goals are beneficial when multiple antenna parameters are simultaneously investigated. These techniques have proven advantageous especially when time-domain performance is critical and provide solutions for both single-ended and differential feed arrangements. The main applications using UWB channels in the 3.1 GHz −10.6 GHz spectrum are localization and tracking applications, mainly employing impulse radio UWB imaging, and generally using linear polarization. However circularly-polarized UWB antennas have been developed, both directional and omnidirectional and are being investigated across various systems.

This chapter presents the basic principles and recent developments of beam-scanning leaky-wave antennas. The single radiating element is realized by modifying waveguides to leak along the structure producing radiated beams that scan as the operating frequency is varied. This unique characteristic distinguishes leaky-wave antennas from other types of antenna. Leaky-wave antennas are broadly classified into three classes: uniform, periodic, and quasiperiodic. In the following sections, each class will be explained and compared. Samples of novel design techniques and potential applications are also highlighted.

In this chapter, a summary of the various components, categorization, and design process of reconfigurable antennas is presented. The various applications where reconfigurable antennas have been implemented and the association of various antenna properties with new communication applications are discussed. The chapter takes into consideration new and evolving applications and associate novel antenna designs with these applications. The control, modeling, and optimization of reconfigurable antennas are also detailed and multiple mechanisms are presented. Finally this chapter emphasizes on the development of reconfigurable antennas to service futuristic and evolving practical wireless communication applications and propose optimal solutions for more efficient and holistic designs.

This chapter presents the development history of radial line slot antenna. The antennas are used for circular polarized high-gain antenna in microwave and millimeter wave bands. Linearly polarized arrays are also provided by changing slot array arrangement. The feeding structures are given by a coaxial probe and cavity resonators, which is presented in detail. The applications of radial line slot antennas are satellite communication antenna, plasma etching, and high power use. This chapter also describes these applications.

The growing interest associated with exploiting the millimeter-wave spectrum for future wireless communication devices and networks has rendered the ensuing need for in-depth research and development of advanced millimeter-wave antennas. This chapter provides an overview of the background and motivation of ultrafast, low-latency millimeter-wave wireless applications as well as key characteristics of the spectrum. Major antenna design considerations and techniques are introduced and discussed in detail. The discussion is followed with state-of-the-art millimeter-wave antenna design techniques applicable to next-generation wireless devices. The chapter is concluded with discussions of future directions.

The history, including the theory and the technology, leading to today’s conformal array antennas (nonplanar array antennas) is discussed. Since the apertures of these antennas are curved (usually convex), the traditional methods for planar array analysis and design cannot be used. An important aspect is the mutual coupling between radiating elements due to the diffraction along the curved surface. Beamforming, phase modes, geodesics, and polarization are concepts that are dealt with.Several applications of conformal array antennas are mentioned including wide angle (360°) coverage antennas for mobile base stations, antennas built into the skin of vehicles such as aircraft and satellites, spherical arrays for simultaneous tracking of signals from many directions, etc. Compared to planar arrays, the steering and control of conformal arrays is more complicated. However, the rapid growth in computer power (software and hardware) opens up for new solutions. In particular digital beamforming (DBF) looks promising for the future.

This chapter begins with a brief introduction of basic concepts in antenna arrays which is followed by slightly advanced concepts including smart antennas and related systems. This helps the readers to acquire basic knowledge necessary to understand the concepts of multi-beam antennas and various beam-forming networks outlined in the sessions that follow. The world of engineered materials which become an important research area is also outlined to broaden the knowledge of the readers. This chapter concludes with some recent multiple-beam antenna design examples with metamaterial technology.

Reduced surface wave (RSW) microstrip antennas are a class of microstrip antennas that excite much less surface wave fields than do conventional microstrip antennas. Furthermore, they have a greatly reduced amount of lateral (horizontal) radiation that propagates outward from the antenna along the ground plane. This results in less edge diffraction from the edges of the ground plane or supporting structure, which in turn results in smoother front-side patterns and less back radiation. The RSW antennas also exhibit less mutual coupling when the antennas are widely spaced, due to the reduced surface wave field and lateral radiation. This chapter reviews RSW antenna design and the different methods for realizing such antennas, and illustrates their main performance features.

The magnetoelectric (ME) dipole antenna is a type of complementary antenna. The basic antenna geometry includes a planar electric dipole and a vertical shorted quarter-wave patch antenna. Traditionally, a proximity coupled feed is utilized to excite the antenna which performs as a combination of an electric dipole and a magnetic dipole. As a result, the antenna exhibits a wide impedance bandwidth, a stable gain, and a stable radiation pattern with low cross-polarization and back radiation levels over the operating frequencies. After the discourse of the fundamental magnetoelectric dipole design, several studies are devoted to antenna height reduction and alternative feed methods. And then some research works, focusing on designing magnetoelectric dipoles with different polarizations, are presented. The magnetoelectric dipole antenna is also modified for the fulfillments of various applications, such as UWB and 60-GHz wireless communications. Other than the magnetoelectric dipole, several other types of complementary antennas are also introduced.

Measurement is an important and necessary way to characterize the performance of an antenna and verify the design of an antenna. This chapter aims to give a brief overview on the basic setups of antenna measurement instead of detailed discussion of measurement techniques for each antenna parameter. The typical setups of far-field and near-field antenna measurements as well as the different antenna test ranges are reviewed. In particular, the setups for the impedance measurement of differential antennas, the on-wafer measurement of antennas, and the measurement of special absorption rate (SAR) are introduced.

An anechoic chamber usually involves a substantial investment both financially and in building space. Hence, there is much interest to attain the required technical performance with lowest possible investment. The screened room must be designed to provide an environment free of extraneous signals. The suitable type of RF absorber must be chosen to line the entire inner surface of the shielded room in order to simulate a free-space environment with no reflection from the walls, ceiling, and floor. Using a suitable computer simulation tool together with the appropriate model which characterizes the absorber scattering behavior, the chamber geometry may be optimized to achieve the cost-effectiveness target. Upon completion of the construction, the performance of the anechoic chamber should be evaluated using the standard acceptance test methods.

An EMI/EMC anechoic chamber represents a substantial investment. A number of careful considerations must be weighted in an anechoic chamber project. The screened room must be designed to provide an environment free of extraneous signals. The suitable type of RF absorber must be chosen to line the entire inner surface of the shielded room in order to simulate a free-space environment with no reflection from the walls, ceiling, and floor. The test site must meet the required performance specified in EMC standards. For frequency range below 1 GHz, the normalized site attenuation (NSA) method is specified by CISPR 16 and ANSI C63.4 for validation of semi-anechoic chamber where the floor is not covered with RF absorber. The reference site method is recently added to the standards as a better option to improve the site validation accuracy. For frequency range above 1 GHz, EMC radiated emission measurements require the use of full anechoic chamber where the floor is also covered with RF absorber. The site voltage-standing-wave ratio (SVSWR) method is specified by CISPR 16-1-4 for test site validation. A time-domain reflectivity (TDR) method proposed by ANSI C63.4 offers numerous benefits compared to the CISPR method. It can produce equivalent values of SVSWR without physically moving the antenna, potentially more accurate in validating the chamber quietness performance, and the measurement process is much less time consuming.

A complete description of the near-field antenna measurement techniques is provided in this chapter. After a discussion of the state of the art, the key steps of the classical near-field–far-field (NF-FF) transformations with plane-rectangular, cylindrical, and spherical scannings, in their probe-uncompensated and probe-compensated versions, are summarized, by also providing some analytical details on the wave expansions commonly adopted to represent the antenna radiated field. The nonredundant sampling representations of electromagnetic field are then introduced and applied to drastically reduce the number of required NF data and related measurement time with respect to the classical NF-FF transformations. At last, the NF-FF transformations with innovative spiral scannings, allowing a further measurement time saving, are described.

This chapter deals with a range of antenna radiation efficiency measurement methods and techniques: from the traditional to the state-of-the-art. The most widely used methods are discussed in details, along with their backgrounds and scientific foundations. The relevant measurement setup, procedure, and data processing techniques are also given. A comparison of these methods is made at the end of this chapter, and their advantages and limitations are identified.

This chapter deals with mm-wave and sub-mm-wave probe-fed antenna measurements. First, worldwide state-of-the-art measurement solutions are presented. Then, the most interesting solutions to achieve the RF and mechanical parts of an mm-wave probe-fed measurement setup are described. In a second subpart, the focus lies on possible measurements and associated techniques to perform accurate characterization of probe-fed mm-wave antennas. Special attention is given on reflection coefficient measurements, gain measurements and associated calibration techniques, novel phaseless techniques developed for the characterization of circularly polarized antennas, hybrid total efficiency computations from simulation and measurements, near-field and phase measurements, and possible source of errors taking place in those mm-wave probe-fed measurement setups. A last subpart deals with measurements above 110 GHz as today no coaxial connection exists, and therefore rigid waveguide connections have to be employed at those frequencies. Lastly, open problems are discussed, and future directions for the coming years are proposed.

Recently, body-centric wireless communications (BCWCs) have become a very active area of research because of their numerous applications such as security, electric money, smart homes, personal entertainment, and identification systems. Most BCWCs systems have been focused on the development of wearable antennas for on-body and off-body communications and implantable antennas for in-body communications. These antennas are evaluated with different kinds of human-body phantoms. Particularly, it is almost impossible to use a real human body to evaluate implantable antennas experimentally. Instead, human-body phantoms are inevitable for experiments.This chapter describes evaluation of wearable and implantable antennas with human phantoms. As for tested antennas, two compact wearable dual-mode (on-body mode at 10 MHz and off-body mode at 2.45 GHz) antennas and two UHF band implantable antennas are exemplified in this chapter.

Base station antenna systems have undergone a dramatic development within the last decades: in the early days of cellular communications, the cells where more or less of similar size and circular shape, having a base station in the center. This base station typically was equipped with a passive omnidirectional antenna illuminating the whole cell. Since then, the cell topology has become more and more diverse, using different cell sizes and also cell sectorization of higher orders. Moreover, the increasing demand on dynamic control and adaptation of the cell size and of the cell capacity results in complex requirements for both the antenna structure and the transceiver system. Therefore, it makes sense to consider the base station antenna system as a whole, comprising the antenna radiators, the transceiver system, and the data preprocessing.This system design approach is the basic idea of this chapter: it starts with basic antenna considerations, then different system topologies are described including their functionality and their development over the years, and finally, an outlook into future challenges and design aspects is given.

MIMO technology has facilitated tremendous performance improvements in wireless communications, allowing the data rate to increase linearly with the number of antennas used, at no additional expense in transmit power or spectrum. However, the tremendous performance gain can only be achieved by multi-antenna designs that provide low coupling and correlation, as well as high total efficiency. Such design criteria are especially challenging for small terminal devices. The situation becomes even more complicated with increasing bandwidth requirements for terminals in existing and upcoming mobile communication standards. Beginning with the history of MIMO terminal antenna and its evaluation methods, this chapter is geared towards providing useful guidelines to researchers and practitioners alike on how to design efficient MIMO antennas for terminals. The focus is on decoupling and decorrelation techniques, including RF circuit level decoupling, antenna structure decoupling and characteristic mode based decoupling. Future directions in MIMO antenna design and some corresponding open problems are also described.

The antenna is one of the most critical components in wireless charging systems since the power transfer efficiency of the system is largely dependent on the antenna performance. In this chapter, the modeling and analysis of antennas are introduced with a focus on increasing the power transfer efficiency. The relationship between wireless power transfer efficiency and antenna parameters like antenna geometry, ohmic loss, impedance matching circuits, and distance between transmitting and receiving antennas is studied analytically and numerically by using circuit theory and full-wave electromagnetic analysis, in order to provide some fundamental and theoretical knowledge to develop antennas for highly efficient wireless charging systems. Finally, challenges and recent studies of antennas for wireless power transfer systems, as well as standards on this field, are briefly introduced.

The exponential growing demand of electricity has stimulated the manufacture of electric equipment with high rated powers withstanding tens and hundreds of kilovolts. These devices have to be insulated to ensure a safe and reliable service while their size and cost are reduced. Unfortunately, insulations deteriorate over time by being in operation under load and exposed to harsh environments that can degrade their behavior and lead to unexpected equipment outages and failures. The continuous monitoring of these assets is paramount in the operation of electric power systems, and one of the most popular methods to evaluate the ageing is the detection of partial discharges. Partial discharges are ionization processes that take place in voids filled with gas or oil inside the insulation, in dielectric surfaces, and in the proximity of sharp metallic objects. The chemical and physical structure of the insulation is changed, and eventually weakened, by the continuous action of the discharges. Then, their apparition can be directly a signal of problems in the insulation, but they can also be the consequence of other degradation processes. Partial discharges can be measured with a wide range of detectors including inductive, capacitive, acoustic, and light sensors. Because partial discharges occur in extremely short times, well below 1 ns, the radiofrequency measurement of the phenomenon in the HF, VHF, and UHF bands is also part of the unconventional methods used for their detection. EM sensors or antennas have the ability of performing a complete study on the measurement of partial discharges. They can detect pulses, localize the partial discharge site, and, to some extent, classify the type of partial discharge online. However, one of the most important challenges when using antennas in the diagnostic of insulations is the difficulty of relating the RF emissions to the severity of the PD. Another determent in the wide application of antennas as partial discharge detectors is the sample rate needed to obtain information from the signals in the time and frequency domains. The chapter also explores the most common configurations of antennas used in the detection of partial discharges as well as how they are installed and used in different electrical machines.

Automobile radars are under investigation since the 1960s. The first operational systems are on the market since 1992 for buses and trucks and 1999 for passenger cars, both in the frequency range around 24 as well as 76.5 GHz; a new frequency band for medium- and short-range sensors from 77 to 81 GHz has been allocated recently in Europe. Requirements for the sensor antennas are high gain and low loss combined with small size and depth for vehicle integration. Great challenges are due to the millimeter-wave frequency range, and a great cost pressure for this commercial application determines design and fabrication. Consequently, planar antennas are dominating in the lower frequency range, while lens and reflector antennas had been the first choice at 76.5 GHz, partly in folded configurations. With increasing requirements toward a much more detailed view on the scenery in front or around the vehicle, multi-beam antennas or scanning antennas have been designed. For actual systems, digital beamforming with a number of integrated antennas is in use or under development, and also MIMO concepts will be exploited. With such development, antennas for automotive radar no longer can be considered as stand-alone devices, but will be part of an “imaging” system including multiple transmit/receive units and digital signal processing.General antenna concepts, partly including system aspects, as well as several realized antenna and sensor configurations will be described in detail in this chapter.

The mobile reception of satellite services on vehicles places high demands on the antennas in many regards. Due to the high path loss because of the great distances, low signal levels are experienced on the ground.The following chapter gives an overview on antennas which can be used for the mobile reception on vehicles. The main areas of application in this regard are systems for global positioning and for satellite radio services. At first an overview of the requirements on the antennas imposed by the different services is given. Thereafter some basic antenna types are discussed regarding their advantages and disadvantages as far as the reception of satellite services are concerned including dipole and ring structures. More advanced antenna designs are also presented which are specifically optimized for different satellite systems.In reception scenarios with severe signal impairments like multipath propagation resulting in deep signal fades, a single antenna is not sufficient for satellite reception. The mechanisms which lead to these scenarios are shortly introduced followed by a discussion of antenna diversity techniques which are an effective means to reduce these impairments. Special consideration is given to scan-phase diversity which efficiently combines the advantages of a simple system design with high signal quality improvements. Measurements obtained in real fading scenarios are presented for single antenna as well as scan-phase diversity systems. They show that antenna diversity can significantly improve the audio availability in adverse reception scenarios compared to single antenna systems. Furthermore, diversity can even allow for using antenna mounting positions which are unsuitable for single antennas like the dashboard or single side mirrors while still outperforming a rooftop mounted standard antenna.

Smart antennas are important for satellite communications because they can increase the channel capacity, spectrum efficiency, and coverage range of the communication systems. This chapter reviews the technology for smart array antenna design with examples. Applications of smart antennas for satellite ground stations and direct broadcast satellite systems are also presented in this chapter. A detailed list of references is given in the end of this chapter.

This chapter presents antennas used in access points of WLAN/WiFi systems. The frequency spectrum for these systems based on the standards is described first. Antenna parameters to understand the WLAN/WiFi antennas are also explained. The antennas are classified into outdoor, indoor, and built-in antennas in this chapter, which are presented in detail.

This chapter concentrates on embroidered textile antennas for body-centric wireless identification and sensing systems. Methods for modeling and characterization of embroidered UHF RFID tag antennas, creating totally embroidered wearable patch-type antennas, and co-designing textile-based transmit antenna and mm-size implant antenna for challenging wireless brain-machine interface systems will be presented. Wireless body-centric identification and sensing systems hold an enormous potential to revolutionize wearable intelligence by extending the functionality of advanced garments. There are several specific requirements for on-body and implant antennas and their communication: on-body antennas have to be lightweight, conformal, easy to integrate into clothing, and as immune as possible to the performance-degrading effects of human body. When implanted systems are considered, communication link between the on-body and implant antennas has to be as efficient as possible, but at the same time SAR regulations must be obeyed. Moreover, implants and thereby implant antennas are intended to be as small as possible, and therefore the on-body textile antennas have to be able to efficiently communicate with mm-size implant antennas. Approaches to solve these challenges are presented in this chapter. Additionally a comprehensive and organized list of references is provided to assist the readers in identifying most pertinent publications about this very important and timely subject.

Biomedical telemetry permits the measurement of physiological signals at a distance, through either wired or wireless communication technologies. One of the latest developments in wireless biomedical telemetry is in the field of implantable medical devices (IMDs). Such devices are implanted inside the patient’s body by means of a surgical operation and can be used for a number of diagnostic, monitoring, and therapeutic applications. Implantable antennas, i.e., antennas which are integrated into RF-enabled IMDs, exhibit numerous challenges in terms of design, fabrication, and testing and are, therefore, currently attracting significant research attention. Contributions from researchers of various disciplines build a rich pool of background information, while highlighting future prospects.

In recent years, various types of medical applications of electromagnetic techniques have been investigated. We have also been studying several medical applications of microwave techniques, which can be classified into diagnosis techniques and therapeutic systems. In this chapter, radio frequency techniques in magnetic resonance imaging (MRI) are discussed from the point of view of biomedical electromagnetic compatibility as an example of medical diagnostic devices. Moreover, therapeutic systems that employ the microwave thermal effect of biological tissue are also introduced. These systems are the thermal treatment of cancer and surgical devices using high-power microwave energy.

The holographic theory known from optics can also be used to describe the functionality of a special kind of leaky-wave antennas. Within the so-called holographic antenna, a hologram builds the radiating aperture, which is fed by surface-wave modes traveling on thin substrates. The hologram can be described as the interference pattern of the superposition of the traveling surface wave and the radiated plane wave. Therefore, it is possible to control the beam direction and beam shape of the holographic antenna by a modification of the hologram form. Compared to other kinds of leaky-wave antennas, the holographic antennas have also advantages in manufacturing and system integration, which make them to be a very promising antenna type for different millimeter-wave applications, e.g., radar systems.

Microwave radiometry is concerned with purely passive sensing of naturally generated microwave radiation of thermal origin. Microwave radiometers are corresponding measuring devices typically designed and built as a very low-noise receiver followed by a signal recording unit. Usually, radiometers contain an antenna as the first reception component collecting the incoming radiation, and they measure radiation power expressed in an apparent temperature called brightness temperature. The observable brightness temperature of any object or surface depends on various chemical and physical quantities, whose concurrence is expressed by the objects’ emission (absorption), reflection, and transmission properties and its true temperature. Since the Earth has a temperature typically close to 300 K and the universe close to 3 K, a nearly arbitrary mixture of these two extreme temperatures can be expected. Consequently, our environment can show quite different brightness temperature values depending on the direction of actual observation.On the one hand, radiometer measurements are carried out stationary with respect to the antenna pointing direction in order to observe time-dependent variations of the brightness temperature. On the other hand, the brightness temperature of a whole scene is scanned in order to acquire locally changing one- or two-dimensional profiles, while the latter ones are assembled as a two-dimensional image comparable to a conventional photograph. Depending on the specific application, various antenna types are considered, where usually hard requirements with respect to beam width, side-lobe level, scan capability, and losses have to be addressed (chapter “Transmission Lines”). Radiometric measurements are performed for Earth or planetary observation in space (chapter “Space Antennas Including Terahertz Antennas”), from aircraft platforms on the Earth’s surface and the atmosphere, or on the ground, either sensing the environment or sensing the universe, the latter being performed in radio astronomy (chapter “Antennas in Radio Telescope Systems”). Usually, the brightness temperature is rarely used as the physical quantity of interest. More often, it is transferred via adequate physical models to other secondary or third quantities for more direct use in the case of Earth observation (e.g., soil moisture, ocean salinity, rain rate, snow cover, etc.), being performed already since the 1950s of the last century. However, in the last decades, microwave radiometry is as well used in many safety- and security-related applications, for which often only sufficient temperature contrast between an object and its surrounding is required besides spatial resolution for detection and recognition purposes.In this chapter relevant fundamentals of microwave radiometry are outlined for better understanding of antenna requirements, followed by an overview of typical types of radiometer antenna systems. Some existing antenna systems are discussed in order to illustrate the variability with respect to applications. A section on basic antenna quantities addresses key figures for practical design and verification and illustrates the results exemplarily for selected cases. Finally, a brief summary and an outlook on possible future implementations and other frequency ranges are given.

Antenna sensors have received considerable interests in recent years due to their passive wireless operation, simple configuration, compact size, multiplexing capability, and multimodality sensitivity. Based on the principle of antenna backscattering, an antenna sensor can be wirelessly interrogated at middle range distances without an onboard battery. Since the antenna serves the dual function of sensing and communicating, an antenna sensor can be implemented with minimum number of components. As narrowband resonators, antenna sensors can be easily multiplexed based on the principle of frequency division multiplexing. In addition, different types of antenna sensors that are sensitive to a variety of physical measurands have been demonstrated. Due to these unique features, antenna sensor technology could play a vital role in our drive toward ubiquitous sensing. This chapter provides a comprehensive review of this exciting technology with detailed descriptions on the operational principle and wireless interrogation of batteryless antenna sensors. Four application examples of using antenna sensors for moisture, dynamic strain, temperature, and crack sensing are discussed. Future research directions and open problems are suggested.

Today the Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging are very well-established methods for noninvasive investigations of live objects, substances and materials. The radio frequency (RF) coil is the first component where the Magnetic Resonance (MR) signal is stimulated and received and therefore is one of the most important components of a Magnetic Resonance Imaging (MRI) system. The design of properly developed RF coils is the key to achieve the best clinical, preclinical or experimental result for MRI scientists or clinicians. In this chapter a detailed overview on RF-coil concepts for MRI is presented. This article contains some results of my personal work and the study of many articles, reference textbooks, and other people’s work. The intention of this chapter is to give the reader a rough summary of the state-of-the-art knowledge and physical background of MRI RF coils engineering in an easy-to-understand format. This chapter contains three main sections. The first section is a simple introduction to MRI and will provide a basic understanding of MR physics behind the detection of RF signals for MRI for students who do not have any knowledge of MRI or NMR. The RF engineer must be familiar with these basic principles in order to design and build successfully a MRI RF coil. The next section is related to the basic types of RF coils. It is divided in multiple subsections covering volume coils and their basic design principles, local RF coils including their arrangement for so-called array RF coils, and last but not least cryogenically cooled RF coils. The last section discusses further directions and challenges in the field of MRI RF coil engineering and gives a brief description of active shaping of the RF field within a given volume and its challenges. While this section gives only a rough overview about the topics of MRI RF coil engineering, the interested reader will find the most interesting textbooks and articles in the reference section.

This chapter deals with the analysis of several kinds of space antennae with a special section devoted to THz antennae. In particular, horn antennae, either corrugated as spline profiles for data downlink and uplink communications and TT&C applications are developed. More innovative antenna designs based on the use of Electromagnetic BandGap (EBG) or Metamaterial structures (MTM) are included. These ones exhibit very promising properties to be used in applications such as TT&C or Navigation. Finally, due to the increasing interest in scientific missions operating at THz frequencies, a section including the last results of using MTM technologies for implementing antennae at THz bands for imaging space applications is presented.

Radio astronomy is the study of the universe by measurement of radio frequency emission at frequencies ranging from a few MHz to the far infrared. Signals of interest are typically extraordinarily weak, necessitating large effective aperture and resulting in some of the world’s largest antenna systems. Technologies now commonly employed include reflector antennas (“dishes”) using horn-type feeds or feed arrays, beamforming arrays consisting of elements ranging from dipoles to large dishes, and interferometry. Many problems in radio astronomy also require very fine angular resolution, leading to aperture synthesis imaging instruments consisting of antennas distributed over apertures ranging from hundreds of meters to intercontinental distances. This chapter provides a brief review of antenna systems used in operational modern radio telescopes and in anticipated new radio telescopes.

With the capability to dynamically change their radiation characteristics, reconfigurable antennas will become indispensable parts for the next-generation wireless communications and sensing systems where the RF front-ends are required to be cognitive in nature. Compared to traditional antennas whose characteristics are fixed, reconfigurable antennas pose new challenges to antenna researchers and designers, such as tuning the operating frequency of an antenna whilst maintaining its radiation pattern. In the last two decades, substantial progress has been made in the development of reconfigurable antennas from both academia and industry. This chapter provides an overview of the state-of-the-art of reconfigurable antennas by elaborating the basic concepts of different reconfigurable antennas and practical techniques to realize them. It is focused on both reconfigurable antenna elements and arrays, and outlines some directions for future research.

The transmitting and receiving antenna designs for the microwave wireless power transmission (MPT) systems are illustrated in this chapter. After introducing a brief history, this chapter describes the components of a MPT system and the operation band selections. Several rectennas and arrays with different structures and performances are designed after analyzing the special considerations of the receiving antennas. To obtain the maximum DC-DC (direct current to direct current) system efficiency, the aperture level distributions of the transmitting antenna are investigated with consideration of the receiving rectennas. A MPT system design operating at C-band is explained based on the above discussion and the summary is made finally.

This chapter gives a general overview of the antennas used in mobile phones for wireless cellular communications. The evolution of the antenna structures is discussed in combination with the evolution of cellular communication standards. Some common antenna types widely used in mobile terminals are presented, some of them being examples from commercial products. The antenna design techniques that are used to achieve broader operating bandwidths with smaller antenna dimensions are addressed. Tunable and reconfigurable antennas are mentioned and their advantages and disadvantages versus passive antennas explained. The most important metrics that quantize antenna performance in mobile phones are presented. Some simulation and measurement results as well as data from previously published papers are used to support the claims and information in the chapter. The chapter is finalized with some forecast for the future cellular standards, and some challenges that antenna designers might face for the fifth generation are mentioned.

An array feeder for a reflector or a lens provides considerable flexibility in the beams that can be produced. A single beam could be obtained by combining all elements; multiple beams can be created with clusters of subarrays or the elements combined in such a way that a beam is steered by adjusting the phase and amplitude of the elements. A variety of applications of array feeders are possible from satellite communications, radar, and radio astronomy. The latter application is described here through fixed arrays, and individual horns of the cluster are excited step-by-step to produce multiple beams at radio observatories such as Parkes, Australia, and Arecibo, Puerto Rico. A full phased array solution is described for the Australian Square Kilometre Array Pathfinder (ASKAP). For fixed arrays, an optimum excitation is described. It is shown that without coupling effects, the excitation should be the complex conjugate of the focal field. The size of an array is defined and the sensitivity of a multibeam feed is shown to be proportional to N$$ \sqrt{N} $$ where N is the number of elements of the array. The theory relating to phased array feeding of reflectors is developed, and the definition of sensitivity is extended to phased arrays. The survey speed of a phased array feed interferometer is defined, and conditions are developed for survey speed as a function of the number and spacing of the beams. The application of fixed arrays as multibeam feeds for radio telescopes is described for the 13-element multibeam feed for the Parkes radio telescope and for the phased array checkerboard feed for ASKAP in Western Australia.

This chapter presents the theory of transmission lines, which are essential for the design of radiofrequency (RF) circuits associated with antennas and transmission-line-based antennas. It includes the transmission-line equations and important transmission-line parameters such as characteristic impedance, propagation constant, phase velocity, effective relative dielectric constant, dispersion, loss, distortion, impedance, reflection coefficient, etc. It also presents synthetic transmission lines, a class of transmission lines that can be implemented using only lumped elements, which could be useful for RF circuits needed for on-chip antenna interface. Moreover, the chapter covers the most commonly used printed-circuit transmission lines for RF systems, which also include those that can be realized in multilayer structures that are attractive for printed-circuit antennas and associated RF circuits.

The coming years will show new applications of wireless communications at higher frequencies (30 GHz and above). Modern wireless technologies like massive MIMO and gigabit transmission will become a reality. The industrial winners will be the companies that can provide the hardware at the lowest cost. This requires new waveguide and mmWave packaging technologies that are more cost-effective than normal rectangular waveguide technology and are more power efficient (lower losses) than PCB-based microstrip and coplanar waveguides. The gap waveguide has this potential.The present chapter gives the historical background of gap waveguide technology until its invention in 2008 and how it has evolved since then to include many different kinds of gap waveguide types. Several useful waveguide components have been developed for integration in complete RF front ends. Passive gap waveguide parts and components like filters, couplers, and transitions have been realized very successfully, and active microwave electronics have been packaged. The chapter contains also an overview of the gap waveguide antennas that have been developed during the last years.

In this chapter, the subject matters of impedance transformation and BALUNs are studied, which should be designed for inclusion in the input ports of transmitter and receiver antennas. The Smith chart is commonly used for the design of lumped and distributed circuits for impedance matching in the technical journals and textbooks. Its explanations and usage are readily accessible in the available textbooks. However, the method of least squares is developed here for the design and optimization of various circuits of impedance transformers for microwave and higher-frequency circuits.The topics discussed here include the following:The concept of impedance, transmission lines, power gains, varieties of matching networks, impedance transformer design by the method of least squares, the quarter-wave line, theory of small reflections, multi-section transformers, design of step-line transformers, design of taper lines, devices and components for impedance matching, and BALUNs including waveguide and planar circuit implementations.

The future of wireless technology is stressing the development of ubiquitous, low-cost, highly specialized wireless devices, where both the design and fabrication of wireless antennas have an essential role. This chapter presents four modern fabrication processes used for the development of advanced wireless antenna structures, both present and emerging: MEMS, LTCC, LCP, and ink-jet/three-dimensional printing. Each fabrication technique is investigated historically and analytically, discussing early achievements, process development, and several state-of-the-art demonstrations. The strengths and challenges of these additive and subtractive methods are highlighted, outlining the cost, processing time, scalability, and dimensional resolution of each method. Throughout the discussion of these electronic fabrication techniques, an emphasis is placed on the realization of highly efficient, robust antenna structures for a variety of applications, including conformal sensor networks, radar systems, low-cost RFID, and on-chip/on-package integration.