Effect of adhesive bonds on electrical performance in multi-layer composite antenna
Introduction
Research has been undertaken in the last 15 years on the embedding of antennas in load-bearing structural surfaces of aircraft, to improve structural efficiency and antenna performance [1], [2], [3]. Structural, material and antenna designers have combined to develop the new high payoff technology known as CLAS (Conformal Load-bearing Antenna Structure) [3]. Integration of antenna elements, amplifiers and the ground plane should improve the quality of reception and improve manufacturability. To develop the load-bearing antenna structure, we have proposed the use of antenna-integrated composite structures of sandwich construction [4], [5], [6]. The adhesive that bonds the different layers and provides mechanical strength has an effect on antenna performances, however. The effect is marked for epoxy adhesive, which is used because mechanical rigidity is important. The structural integrity of any sandwich construction depends on the quality of the adhesive bond between skin and core. In honeycomb cores, the cell walls provide a relatively small area for bonding. Structural strength depends on the formation of an adhesive fillet at the interface between the cell wall and skin, so that the fillet is involved in load transfer between the two components of the sandwich [7]. Fig. 1 shows a typical adhesive fillet. The adhesive layer cannot be taken into account in simulations of the antenna design, because of the formation of a fillet in the actual fabrication process. The effect of the adhesive fillet should therefore be considered at the design stage, using an experimental correction.
In this paper, the adhesive effect is studied experimentally in a multi-layer composite antenna. The composite antenna is composed of several composite laminates and Nomex honeycombs, and microstrip antenna elements are inserted between layers with designed configurations. Changes in the antenna performance were determined after the bonding process. In new designs, corrections are introduced to allow for the effect of the adhesive, and electrical performance is then measured to verify the corrections.
Section snippets
Composite antenna technology
The composite antenna is an integrated composite sandwich panel and multilayer microstrip antenna (the SSFIP concept; see [8], [9]). This structure is shown in Fig. 2. It consists of three composite substrates, two honeycomb cores and the antenna and feed elements.
A composite antenna substrate of low electrical loss, and the upper honeycomb, prevent surface wave propagation and increase the bandwidth. The antenna patch is deposited on the underside of the substrate which acts as a protective
Design of antenna elements
The antenna design is based on three different resonant frequencies, at 7, 10 and 12.5 GHz. A computer-aided design tool (Zeland IE3D) was used to select strongly interacting parameters by providing integrated full-wave electromagnetic simulation. The honeycomb between antenna layers is regarded as air for this purpose, since it has the same electromagnetic properties. A square-shaped antenna patch, a rectangular-shaped slot and microstrip line of characteristic impedance of 50 Ω are used, as
Experimental results
Manufacture of the composite antenna is a sequential process. First, the antenna substrate (top face) is processed by a photolithographic method to allow for the radiating patch. The feed substrate for the slot in the ground plane and feed line is then prepared. The honeycombs and every layer must be aligned before permanent bonding. The layers are bonded to the top and bottom of the honeycomb cores with epoxy film adhesive. The assembly is then cured under pressure in an autoclave, using the
New design for adhesive bonds
A frequency shift is observed after the bonding process in the composite antenna. When the microstrip line is covered by adhesive bonds, the characteristic impedance, the phase velocity, losses, and the Q factor of the line all vary with the dielectric constant, loss tangent and the geometry of the layer. The change in resonant frequency of the composite antenna can be determined if the effective dielectric constant of the structure is known before and after the bonding process. The change in
Conclusions
We have investigated experimentally the effect of adhesive bonds in multi-layer composite antennas. The measured electrical performances show that all antennas have a shift in their resonant frequencies, and a reduction in the gain, after the bonding process. The change in resonant frequency implies a change in the effective dielectric constant, and the gain falls due to loss in the adhesive. Corrections so as to compensate for the effect of the adhesive bonds were introduced in a new design,
Acknowledgement
This research was supported financially by the Ministry of Education, Science Technology (MEST) and Korea Industrial Technology Foundation (KOTEF) through the Human Resource Training Project for Regional Innovation.
References (10)
- et al.
An investigation of the skin/core bond in honeycomb sandwich structures using statistical experimentation techniques
Composites: Part A
(2006) - et al.
Design and development of a conformal loadbearing smart-skin antenna: overview of the AFRL smart skin structures technology demonstration (S3TD)
SPIE Smart Struct Mater: Ind Commercial Appl Smart Struct Technol
(1999) - et al.
A qualitative assessment of smart skins and avionics/structures integration
SPIE Smart Struct Mater: Smart Mater
(1994) - Tuss J et al. Conformal loadbearing antenna structure. In: 37th AIAA SDM conference, Salt Lake City, UT,...
- et al.
Design of microstrip antennas with composite laminates considering their structural rigidity
Mech Compos Mater
(2002)
Cited by (29)
Inspection of antennas embedded in smart composite structures using microwave NDT methods and X-ray computed tomography
2024, Measurement: Journal of the International Measurement ConfederationDeformation sensing and electrical compensation of smart skin antenna structure with optimal fiber Bragg grating strain sensor placements
2019, Composite StructuresCitation Excerpt :The antenna structure provides a new paradigm where the structural surface becomes an antenna [1–3], and it will play an increasingly key role in future radar and wireless communication of mobile vehicles such as the aircraft, high-speed train, car, and ship. Many researchers have dedicated to the design and fabrication of the antenna structures, and proposed different concepts such as conformal load-bearing antenna [1,4,5], structurally integrated (embedded) antenna [6,7], skin antenna [3,8–10], 3D integrated microstrip antenna [11], and composite antenna [12,13]. The structural configuration of these antennas is usually a sandwich construction consisting of factsheets, honeycomb cores and printed antennas.
Glueless Multiple Input Multiple Output Dielectric Resonator Antenna with Improved Isolation
2023, Electronics (Switzerland)Research on Manufacture of the Lightweight Antenna Reflector Based on Carbon Fiber Reinforced Polymer
2022, Lecture Notes in Electrical EngineeringDamage tolerance-based design of conformal antenna composite structure
2022, Mechanics of Advanced Materials and Structures