Millimeter Wave Radar
Hardware and Signal Processing
- Open Access
- 2025
- Open Access
- Book
- Authors
- Christian Waldschmidt
- Christina Bonfert
- Timo Grebner
- Publisher
- Springer Nature Switzerland
About this book
This open access book covers millimeter-wave radar technology as used today in advanced applications such as automated driving and industrial sensor technology. Each topic is discussed from a comprehensive systems perspective, thoroughly addressing both signal processing and hardware aspects, along with their interconnections. After a solid introduction to the basics and applications of radar sensors, the focus shifts to the fundamental operating principles of these sensors. Separate chapters then cover signal processing and hardware concepts in detail. Finally, the book concludes with an in-depth discussion of specialized radar techniques, including imaging radar.
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Table of Contents
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Fundamentals
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Frontmatter
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Chapter 1. Introduction
- Open Access
Download PDF-versionThis chapter delves into the widespread use and advantages of radar sensor technology, highlighting its robustness against weather, lighting, and other environmental factors. It begins by explaining the basic principle of radar, where an electromagnetic wave is transmitted, reflected by a target, and received back by the sensor. The chapter then explores the historical development of radar, from its inception in 1904 to its modern applications in automotive, industrial, and safety technologies. A significant portion of the text is dedicated to the frequency bands used in radar sensors, particularly in the millimeter wave range, and their respective applications. The radar equation is derived and explained for both point targets and infinitely extended area targets, providing insights into the factors affecting the received power and range of a radar sensor. The concept of radar cross-section (RCS) is introduced, discussing how different materials, shapes, and viewing angles influence the backscatter properties of targets. The chapter also covers the measurands detected by radar, including range, relative radial velocity, and spatial direction, and explains how these measurements are made. Finally, the text explores wave propagation phenomena in the millimeter wave range, including multipath propagation, diffraction, scattering, and clutter, and their impact on radar sensor performance. By reading this chapter, professionals will gain a comprehensive understanding of radar sensor technology, its applications, and the underlying principles that govern its operation.AI Generated
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AbstractRadar sensor technology has spread immensely over the past decade and is now indispensable in many applications. This is mainly due to the fact that the costs of radar sensors have fallen tremendously and radar sensors have strengths in areas that are not covered by many other sensor principles. For example, radar is extremely robust against environmental influences such as weather, lighting, the position of the sun, dirt or other environmental influences in which the radar sensors are used. In addition, radar is one of very few sensor principles that allows direct velocity acquisition. Radar is an active sensor principle: A radar sensor transmits an electromagnetic wave that is reflected by a target in the radar channel and received back by the radar sensor. By comparing the received signal with the transmitted signal, various information about the target can be obtained. The most important properties are the range of the target to the radar sensor, the radial velocity of the target in relation to the radar sensor, and the direction in which the sensor detects the target. The comparison of the received signal with the transmitted signal contributes to the robustness of the system, as interference or signals emitted by other electronic devices are not mistakenly interpreted as part of the received signal. In this chapter, the fields of application frequently used and discussed today and the corresponding frequency ranges are presented. This is followed by the basics of radar sensor technology with a derivation of the fundamental radar equation and an introduction to key terms and measurable variables. The chapter concludes with a brief insight into wave propagation in the millimeter wave range, which includes the influence of the atmosphere and multipath propagation. -
Chapter 2. Applications
- Open Access
Download PDF-versionThis chapter delves into the diverse applications of millimeter wave radars, highlighting their integration and advancements in various fields. It begins with an exploration of automotive radar, detailing its evolution from early implementations to current highly integrated systems. The chapter then discusses the use of radars in rail, air, and water vehicles, emphasizing their role in enhancing safety and efficiency. Another key focus is on radar applications in mobile robotics and automation technology, showcasing their robustness and cost-effectiveness. The chapter also covers the use of radars in civil security technology, particularly in body scanners for security checks. Additionally, it explores quality assurance applications, where radars are used to detect inhomogeneities in materials. Lastly, the chapter touches on medical applications, including the measurement of vital parameters and the detection of certain medical conditions. The conclusion highlights the rapid advancements in radar sensor technology and the potential for further differentiation in sensor performance, particularly in the context of automated driving and other emerging applications.AI Generated
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AbstractRadars in the millimeter wave range are used today in a variety of different applications that were unthinkable ten or more years ago. Radar circuits are now available highly integrated in silicon, very robust and mass-produced assembly and interconnect technologies are available and frequency regulation allows many new applications, especially in the ISM bands. The main fields of application are briefly presented in this chapter. However, as development in the field of radar sensor technology is currently progressing very rapidly, it is hardly possible to provide a complete overview of all applications. -
Chapter 3. Resolution, Separability, Accuracy and Unambiguity of a Radar
- Open Access
Download PDF-versionThis chapter delves into the crucial properties of radar sensors: resolution, separability, accuracy, and unambiguity. It begins with a discussion on the role of sinusoidal and periodic signals in radar signal processing, setting the stage for understanding these properties. The chapter then defines and distinguishes these properties, explaining their significance in various radar applications. Resolution is explored in detail, with a focus on range, velocity, and angle resolution, and how they are influenced by factors such as signal bandwidth and observation time. The concept of separability is introduced, highlighting its close relationship with resolution and its role in target detection. The chapter also examines accuracy, discussing how noise and other disturbances affect measurement precision, and provides insights into the maximum achievable accuracy. Lastly, the principle of unambiguity is explained, emphasizing its importance in system design to avoid target detection ambiguities. By the end of this chapter, readers will have a solid understanding of these fundamental properties and their impact on radar sensor performance.AI Generated
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AbstractProperties such as resolution, separability, accuracy, and unambiguity are important for describing the performance of a radar sensor. These properties are introduced and explained in this chapter. They form the basis for the following chapters, in which different implementation concepts for radar sensors are discussed.
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Radar Types, Modulation Schemes and Radar Imaging
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Frontmatter
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Chapter 4. Radar Types and Modulation Schemes
- Open Access
Download PDF-versionThis chapter delves into the world of radar sensors, focusing on their ability to measure ranges and velocities. It begins by explaining the radar equation and the challenges of using signal amplitude for range measurements due to various influencing factors. The text then explores different modulation methods, starting with the classic pulse modulation and moving on to continuous wave (CW) methods, which have become more prevalent due to their cost-effectiveness and efficiency in the millimeter wave range. The chapter also discusses the advantages and disadvantages of analog modulation schemes, such as FMCW and chirp sequence radars, and their applications in measuring range and velocity. Additionally, it introduces digital modulation techniques like OFDM and PMCW, highlighting their flexibility and the potential to replace analog-modulated radars in the future. The chapter concludes with practical examples and performance parameters, providing a comprehensive overview of the latest developments in radar technology.AI Generated
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AbstractIn order to determine the target range, the transmitted radar signal is modulated. There are many different modulation methods known for this purpose. The classic pulse modulation, in which short pulses are transmitted in the time domain, was used frequently in the past but is now rarely used in the millimeter wave range because this method cannot be implemented cost-effectively in modern radar circuits. Instead, analog modulation methods in which transmission and receiving are continuous, so-called continuous-wave methods, have become established. With these methods, the measurement of the radial target velocity is also taken into account: this is always achieved by evaluating the Doppler frequency shift between the transmitted and received signals. Since the mid-2010s, the use of digital modulation techniques for millimeter-wave radars has been widely discussed, at least in the research community. These radars offer enormous flexibility in the modulation design, but also require the processing of enormous amounts of data. Since it is becoming apparent that these radars are likely to replace analog-modulated radars at least in part in the medium run, they are presented in this chapter, as well. -
Chapter 5. Signal Processing Principles
- Open Access
Download PDF-versionThis chapter delves into the principles of radar signal processing, focusing on estimating range and velocity information from signals received by radar sensors. It explores different signal processing chains, each involving similar steps such as windowing, range estimation using DFT, velocity estimation, angle estimation, and target detection using a CFAR detector. The chapter discusses two commonly used processing chains and provides detailed explanations of key quantities and terms like the range-velocity matrix and the CFAR detector. It also covers various window types and their significance in signal processing, as well as the estimation of range and velocity information for different radar modulation schemes. Practical examples, such as measurements of a passing car and a target in an anechoic chamber, illustrate the concepts. The chapter concludes with an overview of target detection using CFAR algorithms, highlighting the importance of adaptive thresholding to minimize false detections and missed targets. By reading this chapter, professionals will gain a deeper understanding of radar signal processing techniques and their applications in various radar systems.AI Generated
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AbstractThis chapter focuses on the signal processing of the various radar types and modulation schemes. Here, the range and velocity information is estimated from the signals received by the radar sensors and assigned to the targets. For this purpose, different signal processing chains are used, each involving similar signal processing steps. Often, a 2D Fourier transform along the frame’s fast time and slow time is first used to generate the so-called range-velocity matrix. If the radar has sufficient range or velocity resolution, range and velocity information of potential targets can be extracted in the range-velocity matrix using a threshold filtering via a constant false alarm rate (CFAR) detection algorithm. Subsequently, an angle estimation is carried out for these targets using the individual radar channels or receiving antennas. The following chapter explain the individual processing steps in detail: First, various window types and their significance in signal processing are introduced. After that, the estimation of the range and velocity information for the analog and digital modulation methods is presented. Finally, target detection using a CFAR detector is introduced. -
Chapter 6. Fundamentals of Antennas and Antenna Arrays
- Open Access
Download PDF-versionThis chapter delves into the fundamentals of antennas and antenna arrays, focusing on their application in modern millimeter wave radar systems. It begins by explaining how antenna arrays determine the angle of a target relative to the radar, highlighting the advantages of electronic scanning systems over mechanical ones. The text then introduces key terms and coordinate systems used in the context of millimeter wave radars. It provides a detailed description of antenna arrays from both an antenna engineer's and a signal processing perspective, emphasizing the duality and differences between these approaches. The chapter also discusses hardware influences on array signal processing and calibration, which are crucial for accurate angle estimation. Furthermore, it presents the concept of a beamformer, which focuses signal power in a specific direction during transmission or reception. Finally, the achievable resolution and separability of one- and two-dimensional arrays are derived, providing practical insights into the performance of antenna arrays in radar applications.AI Generated
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AbstractIn many modern radar applications in the millimeter wave range, the radar must determine not only the range and velocity of a target, but also its angle at which it is located in relation to the radar. For this purpose, antenna arrays are required, i.e. a group of antennas. By evaluating and comparing the signals at different receiving antennas, the angle of incidence, i.e. the angle of the target, is determined. The larger an antenna array is in relation to the wavelength, the better its angular resolution and separation capability. For this reason, the millimeter wave range is interesting for angle estimation due to its small wavelengths. The absolute size of the sensors remains in the range of a few centimeters for most applications, even with high demands on angular resolution. While in the past, radars often employed mechanically rotating antennas with strong beam focusing to determine the angle of incidence, nowadays only electronically scanning systems are used in the millimeter wave range. Thus, a mechanical scanning system for the antenna is no longer required. The electronic approaches, known as beamforming, can be realized in both analog and digital domains. In this chapter antenna arrays are described both from the point of view of an antenna engineer and from the point of view of signal processing to show the duality and differences of both approaches. Additionally, hardware influences on array signal processing and calibration are discussed and the concept of a beamformer is presented. Finally, the achievable resolution and separability of one- and two-dimensional arrays are derived. -
Chapter 7. Methods for Angle Estimation
- Open Access
Download PDF-versionThis chapter delves into the essential digital angle estimation methods employed in modern radar sensors operating in the millimeter wave range. It begins by examining the two fundamental approaches to angle determination: correlation and Fourier transform. The correlation method is noted for its robustness and practical relevance, although it requires a high measurement effort for creating a calibration matrix. The Fourier transform approach, on the other hand, offers simple implementation and low computational complexity but has limited angle resolution. The chapter then explores advanced beamforming techniques, including the Bartlett beamformer, Capon beamformer, and the high-resolution MUSIC algorithm. Each method is discussed in terms of its principles, advantages, and limitations. The Bartlett beamformer is highlighted for its noise robustness, while the Capon beamformer and MUSIC are praised for their superior resolution. The chapter also provides a comparative analysis of these methods, illustrating their performance under different conditions. Practical considerations, such as the impact of noise and the trade-offs between resolution and computational effort, are thoroughly addressed. By the end of the chapter, readers will gain a comprehensive understanding of the available angle estimation techniques and their applicability in real-world radar systems.AI Generated
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AbstractNowadays, only digital angle estimation methods are used in modern radar sensors in the millimeter wave range. The most important approaches to digital angle estimation are therefore presented in this chapter. First, the two basic approaches to angle determination by correlation or alternatively by a Fourier transform are discussed. These two approaches have an high practical relevance, as they are used very often. These approaches are often combined with more powerful but also more complex approaches to achieve high-resolution and at the same time robust, i.e. reliable, angle estimation. Here, Bartlett and Capon Beamformer as well as MUSIC are discussed. -
Chapter 8. MIMO Radars and Antenna Array Design
- Open Access
Download PDF-versionThis chapter delves into the world of MIMO radars, focusing on their unique ability to create a virtual aperture that significantly enhances angular resolution without the need for large physical apertures. The text begins by introducing the concept of the virtual aperture and explaining how it is formed through the convolution of transmit and receive antenna arrays. It then explores the generation of orthogonal signals, crucial for distinguishing transmit signals at the receiver, through methods like Time Division Multiplexing, Frequency Division Multiplexing, and Code Division Multiplexing. The chapter also compares MIMO radars with phased arrays, highlighting their performance differences and similarities. It provides a detailed analysis of array design and evaluation criteria, including the array ambiguity function and its role in assessing angular resolution and potential ambiguities. Additionally, the chapter addresses the compensation of near-field effects, which is essential for maintaining accuracy in applications where the far-field condition is not met. The text concludes with practical insights into the design and optimization of MIMO radar systems, making it a comprehensive guide for professionals looking to leverage the advantages of MIMO technology in their projects.AI Generated
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AbstractMIMO radars have multiple transmit and receive channels. Such multichannel radars have been used in different configurations for many decades. On the one hand, the detection probability can be increased compared to a single channel if the antenna spacing is very large and many receivers are used. The fusion of many channels leads to a lower probability of failure than a single channel if the channels have different fading characteristics. On the other hand, especially with small antenna spacings, in the range of \(\lambda /2\), many channels can be used for classical transmit or receive beamforming. This approach leads to so-called phased arrays. However, the MIMO systems presented in this chapter address a completely different mode of operation where the numerous channels are used to make the receive aperture appear larger than it actually is. In this context this is called a virtual aperture. Since the virtual aperture is larger than the real aperture, this approach leads to radars with an improved angular resolution. An important requirement for MIMO radars is that all transmit channels and all receive channels must be coherent, i.e. phase-locked to each other. This is the only way to create the virtual aperture, since the phase relationships between the antennas are evaluated. In addition, all transmit signals of each transmit channel must be orthogonal to each other to guarantee that the transmitted signals can be separated at the receiver. This chapter begins with an introduction of the virtual aperture and the creation of orthogonal signals. This is followed by a performance analysis of MIMO radars, along with a description of how to design and evaluate MIMO radars. Finally, the compensation of near field effects of large antenna arrays in the millimeter wave range is addressed.
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Radar Hardware
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Frontmatter
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Chapter 9. Hardware and Technology
- Open Access
Download PDF-versionThis chapter delves into the critical components of radar hardware in the millimeter wave range, with a particular focus on Monolithic Microwave Integrated Circuits (MMIC) and antenna systems. It explores the unique challenges posed by high frequencies, such as transmission line losses and tolerance requirements, and the innovative solutions developed to overcome these obstacles. The text discusses various system partitioning concepts, including MMIC and antenna system detachment, Antenna in Package (AiP), Antenna on Chip (AoC), and System on Chip (SoC), each with its own advantages and limitations. It also provides a comparative analysis of different semiconductor technologies used in the millimeter wave range, including GaAs, Si CMOS, and SiGe CMOS, highlighting their unique properties and applications. The chapter concludes with an exploration of signal synthesis in millimeter wave systems, discussing the use of Phase-Locked Loops (PLL) and Direct Digital Synthesis (DDS) circuits, and the challenges posed by large multiplication and divider factors. By the end of the chapter, readers will have a comprehensive understanding of the latest advancements in radar hardware and the unique challenges and solutions associated with operating in the millimeter wave range.AI Generated
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AbstractRadar sensors in the millimeter wave range usually consist of an antenna system, a radar circuit, a digital processor for signal evaluation and a power supply. The radar circuit is monolithically integrated and is referred to as MMIC. The antenna system used is either an array consisting of many individual antennas, as described in Chap. 6, or a single antenna, which is often designed as a primary radiator together with beamforming lenses. This chapter focuses on the two components MMIC and antenna, as the processing unit and power supply are usually available as standard components. -
Chapter 10. Hardware Effects on System Level
- Open Access
Download PDF-versionThis chapter delves into the critical hardware effects that influence system-level design in millimeter wave radar sensors. It begins by examining the link budget, highlighting how the unique properties of millimeter waves, such as high channel attenuation and antenna gain scaling, impact the power balance of radar sensors. The chapter also explores the challenges posed by leakage, including the parasitic coupling of transmit signals and its detrimental effects on short-range performance. Additionally, it discusses phase noise and its implications for signal synthesis, particularly in coherent sensors. The chapter concludes by emphasizing the importance of suitable sensor architectures and technologies to mitigate these challenges and enhance sensor performance. Readers will gain valuable insights into the practical aspects of designing and optimizing millimeter wave radar sensors, making this chapter an essential resource for professionals in the field.AI Generated
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AbstractThe implementation of a sensor in the millimeter wave range entails not only the hardware-related challenges described in Chap. 9, but also affects the overall system design. Selected topics are therefore discussed in this chapter which illustrate the impact of hardware on system level and play a crucial role in the millimeter wave range.
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Advanced Radar Topics
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Frontmatter
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Chapter 11. Radar-Based Grid Maps
- Open Access
Download PDF-versionThis chapter delves into the creation and application of radar-based grid maps for robotic and automated driving applications. It begins by outlining the basic structure of millimeter-wave radar sensors and the associated signal processing methods for detecting, localizing, and determining the velocity of targets. The chapter then describes methods for transforming sensor data into a global map and localizing the sensor within this map. Grid maps, which segment a map into a uniform grid, are highlighted for their simplicity and effectiveness in storing, processing, merging, and presenting environmental information. The chapter compares two primary grid mapping methods: amplitude grid maps (AGM) and probabilistic occupancy grid maps (OGM). AGMs are noted for their computational efficiency but suffer from issues like information loss for weak or distant targets and the permanent storage of false information. OGMs, while more complex, offer a probabilistic representation of the environment, providing clearer contours and reducing blurring and range dependency. The chapter also explores the Simultaneous Localization and Mapping (SLAM) method, which enables self-localization within the global map. Two approaches are presented: dead reckoning based on ego-motion estimation and scan matching. Dead reckoning, though prone to cumulative errors, is suitable for short trajectories, while scan matching offers higher accuracy for long trajectories. The chapter concludes by discussing graph-based SLAM, which fuses information from dead reckoning and scan matching to ensure robust localization for both short and long trajectories.AI Generated
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AbstractIn this chapter, radar-based mapping of the environment for robotic applications or for automated driving is presented. The generation of a map of the environment is the basis for a wide range of applications in the field of robotics and autonomous systems, including the planning of driving trajectories, obstacle avoidance, or finding parking spaces. Grid maps have been known since the 1980s and provide a simple and effective method for storing, processing, merging and presenting information about the environment. The two-dimensional visualization of a grid map from a bird’s eye view allows an intuitive interpretation of the maps without in-depth technical knowledge. The efficient generation of grid maps makes them a fundamental basis for a wide range of applications. Grid maps segment a map into a uniform grid, either in two-dimensional or three-dimensional space, in order to create a corresponding image of the environment.In this chapter, amplitude grid maps (AGMs) as well as probabilistic occupancy grid maps (OGMs) are presented, and compared. Subsequently, the SLAM method is presented, which enables self-localization within the global map. -
Chapter 12. Synthetic Aperture Radar (SAR) for Millimeter Wave Applications
- Open Access
Download PDF-versionThis chapter delves into the principles and applications of Synthetic Aperture Radar (SAR) for millimeter wave applications, focusing on enhancing angular resolution for high-precision environment modeling and radar imaging. It explores how SAR leverages the motion of a radar platform to create a synthetic aperture, significantly improving resolution without the need for additional hardware channels. The text discusses the fundamentals of SAR, including resolution in range and azimuth directions, and compares it with grid mapping techniques. It also details SAR processing methods, particularly the backprojection algorithm, which is widely used in the millimeter wave range. The chapter highlights the advantages of probabilistic SAR processing, which ensures amplitude-independent imaging, and its integration with SLAM for autonomous, high-resolution mapping. Practical applications in robotics, autonomous driving, and automation are also examined, showcasing SAR's capability to distinguish weak-reflecting targets and provide robust environmental models.AI Generated
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AbstractIf an application requires angular resolution capabilities, radar images or environment models that have a significantly better resolution than what is possible with MIMO radars or grid mapping approaches, the principle of the synthetic aperture radar (SAR) can be utilized. In many applications in robotics and autonomous driving, very accurate environment models or radar images with resolutions in the range of a few centimeters are required. Radar images with millimeter-range resolutions are also used in automation and safety engineering applications. In all these applications, the SAR principle is used. SAR enables the generation of a synthetically enlarged aperture with high angular resolution by sequential spatial sampling the beat signal. This is done by utilizing the motion of the transmitter and receiver of a radar platform that, for example, is attached to a moving vehicle or robot and moves along a known trajectory. Alternatively, radar sensors are mounted on linear rails, for example in automation technology, so that the movement of the radar sensor allows a spatial synthesis of the aperture.SAR improves the quality of the angle estimation without using additional hardware channels. -
Chapter 13. Coexistence and Interference of Radar Sensors
- Open Access
Download PDF-versionThis chapter delves into the coexistence and interference of radar sensors operating in the millimeter wave range, a common scenario in modern traffic environments. It begins by outlining the conditions under which interference occurs and the unique characteristics of interference signals compared to regular radar measurements. The chapter then examines the specific impacts of interference on analog and digital radars, including the increase in noise floor and potential saturation of the receiver. Various countermeasures are explored, such as zeroing and smoothing in the time domain, adaptive frequency spectrum adjustments, and beamforming techniques in the angular domain. The chapter concludes with a discussion on the effectiveness of these countermeasures and their practical implementation. Readers will gain insights into the complex dynamics of radar interference and discover advanced strategies to mitigate these issues, ensuring reliable radar performance in congested environments.AI Generated
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AbstractDue to the widespread use of radar sensors in the millimeter wave range, multiple sensors are often used in close proximity or in the same application scenario. This can lead to interference between the sensors. In road traffic in particular, many vehicles are nowadays equipped with one or more radar sensors, so that in dense traffic scenarios, interference can occur between sensors on different vehicles. This chapter first presents an overview on interfered signals in radar applications and then provides a more specific description of the impact of interference on analog and digital radars. Additionally, a selection of countermeasures is presented.
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- Title
- Millimeter Wave Radar
- Authors
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Christian Waldschmidt
Christina Bonfert
Timo Grebner
- Copyright Year
- 2025
- Publisher
- Springer Nature Switzerland
- Electronic ISBN
- 978-3-031-89118-2
- Print ISBN
- 978-3-031-89117-5
- DOI
- https://doi.org/10.1007/978-3-031-89118-2
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