Design, Simulation And Properties Of A Three-dimensional Woven Conformal Load Bearing Microstrip Feeding Antenna

Intelligent system is mainly composed of sensor, actuator, information processor and signal propagation device. As a kind of wireless signal transmission device, antenna is very critical role in the intelligent system. Therefore, to make an ideal intelligent system, designing of a proper signal transmission device is the first priority. With the development of aerospace engineering, information technology and social needs, tighter requirement on the electromagnetic and mechanical properties of the antenna is very necessary. Due to the better performance on invisibility and reliability, microstrip antenna was widely used in multiple applications.Most of the intelligent antenna systems utilize the laminated fiber reinforced composites or sandwich composites as their substrate material. However, these kinds of antenna systems are easily delaminated during mechanical loading, which lead to the malfunction of the antennas. Three-dimensional (3D) woven composites, with the binding yarns in thickness direction, are of extraordinary structure integrity and delamination resistance. Three-dimensional integrated microstrip antenna (3DIMA) is the combination of 3D woven composites and microstrip antenna. It provided a better performance both on electromagnetic and mechanical properties, which is a great improvement compare with traditional and other novel antenna. Study on 3DIMA is very significant for the developing on the stealth technology of the aircrafts, as well as the detecting of public security.In this thesis, electromagnetic and mechanical properties of the 3DIMA fabricated with microstrip feeding were systematically investigated through theoretical and experimental study.Objective:1. Simulated model building of the 3DIMA and systematical study on influence of the structure parameter and other factors to the antenna performance.2. Manufacture the 3DIMA with microstrip feeding and study its electromagnetic and anti-impact properties.3. Based on the simulating and analyzing on the influencing factor of the antenna, modify the designing of the 3DIMA to enhance its gain property.4. Systematically study the mechanical properties and failure modes of the 3DIMA.The specific study and results are stated as follows:Firstly, the structure of 3DIMA was designed according to the antenna theory and its performance was simulated by High Frequency System Simulator. Based on the simulation results, 3DIMA was fabricated and tested. During the simulation, two-dimensional strip grid model, three-dimensional cuboid and cylinder grid model were established independently. The strip grid model is the simplest with less computation and easy solution; cuboid model is capable of modeling the interlaced structure of the copper yarn and simulating the influence of the copper yam along the thickness direction; cylinder grid model is most similar with the morphology of the copper yarn and results in a most accurate simulation. After the analysis of different modeling, two kinds of 3DIMAs with glass fiber/vinyl ester composites and arimid fiber/vinyl ester composites as substrates were made accordingly. The tested results showed the glass fiber/vinyl ester 3DIMA had its Voltage Standing Wave Ratio (VSWR) of 1.18 at the resonant frequency of 1.31 GHz; the arimid fiber/vinyl ester 3DIMA had its VSWR of 1.05 at the resonant frequency of 1.32 GHz. Both VSWRs met the VSWR requirement of the antenna. Radiation patterns of the two 3DIMAs showed similarity with the traditional microstrip antenna, and fine directionality. However, the tested gains of the two antennas are-4.7 dB and-5.9 dB respectively, requiring for a further improvement. The VSWR test was also conducted after 15 J impact and turn out to be 1.25, which confirmed a better structural integrity and impact resistance of the 3DIMA in this study than other conformal load-bearing antenna.Secondly, to optimize the performance of 3DIMA, we studied the different influence factors of the antenna through simulation and experiment. The influence factors include:waving orientations, waving density and waving structure of the conductive yarns in radiating patch; and the existence of the resin cover on the patch. When the copper yarn was woven along the feeding direction, the antenna demonstrated a VSWR of 1.4 at resonant frequency of 1.39 GHz and gain of-3.7 dB. When the copper yarn was woven transverse the feeding direction, the antenna demonstrated a VSWR of 1.2 at resonant frequency of 1.35 GHz and gain of-5.3 dB. It was indicated that the antenna with the conductive yarns which woven along the feeding direction had better resonant frequency and gain property. The simulation results of the antenna with radiation patch made by different weaving density showed that when the ratio between the yarn diameter and the separation distance (S/D ratio) is 1 and the resonant frequency of the antenna is 1.49 GHz, it has a VSWR of 1.4 and a gain result of 2.9 dB; When the S/D ratio became 1/4 and the resonant frequency of the antenna is 1.31 GHz, it has a VSWR of 3.9 and a decreasing gain of 1.5 dB. This indicated that when the ratio between the conductive yarn diameter and separation distance was less than 1, the VSWR and radiation pattern property will be impaired with the decreasing of the weaving density. It also suggested that higher patch weaving density is very critical to the performance of the 3DIMA. After we systematically investigated the influence of the thickness, dielectric constant and dielectric loss tangent of the superstrate resin on the antenna performance by simulation.3DIMA without superstrate resin covering on the patch was obtained by a modified vacuum aided resin transfer technique. The results showed a more accurate resonance frequency of the antenna without superstrate resin cover. Meanwhile, the gain of the antenna increased to 0.5 dB comparing with the resin-covered antenna (-3.6 dB). Due to most of the textile structural antennas integrate the conductive yarn into the structure by weaving methods; our study not only optimized the performance of the 3DIMA, but also provided reference and instruction to other type of textile structural antenna.At last, to study on the mechanical properties of the structural material of the 3DIMA, the tensile, bending, compress and impact performance of the glass fiber and copper wire hybrid composite was tested. Three types of composites were tested, including the glass fiber/copper wire/vinyl ester resin 3D woven composites with the copper wire in double faces (3DIMA-DFC); glass fiber/copper wire/vinyl ester resin 3D woven composites with the copper wire in single faces (3DIMA-SFC); copper clad laminates based on glass fabric/polytetrafluoroethylene composites (PTFE-CCL). The tensile testing results showed that 3DIMA-SFC achieved normalized tensile property with strength of 1614 MPa, which was 25% and 92% respectively higher than the strength of the 3DIMA-DFC and PTFE-CCL. Normalized tensile modulus was 112 GPa,60% and 155% higher than the modulus of the 3DIMA-DFC and PTFE-CCL. The outstanding tensile properties of the 3DIMA was contributed by the straightened yarn of which reinforcement effect can be fully utilized, and a better interfacial bonding between the glass fiber and vinyl resin. The compressing test results showed the normalized compressing strength of the 3DIMA-SFC and 3DIMA-DFC are 633.9 MPa and 721.8 MPa, both of which were much higher than the compressing strength of 3DIMA-DFC (266.4 MPa). Because of the binding yarns in the thickness direction,3DIMA structure presented good integrity and strain dispersion. In a contrast, the laminated PTFE-CCL structure was easy to delaminate under compressing. Furthermore, the bending testing of 3DIMA-SFC showed a normalized strength of 963.6 MPa, which is 26% and 31% higher than the strength of the 3DIMA-DFC and PTFE-CCL respectively. The normalized bending modulus of the 3DIMA-SFC and 3DIMA-DFC are 60.3 GPa and 60.9 GPa, almost 25% higher than of the PTFE-CCL. The better binding property of the 3DIMA structure was also results from the better structure integrity and interfacial bonding. The impact toughness of PTFE-CCL,3DIMA-DFC and 3DIMA-SFC was 206.3 KJ/m2,74.7 KJ/m2 and 31.1 KJ/m2 independently. It is suggested that the impact property of the 3DIMA structure can be enhanced by utilizing the thermoplastic resin such as PTFE. Apparently, the 3DIMA showed very good mechanical property, delaminate resistance and structure integrity.In conclusion, the design and manufacture of the conformal load-bearing microstrip feeding antenna based on the structure of 3D woven composites are definitely feasible. The 3DIMA in our study demonstrates enhanced structure integrity and delamination resistance than the traditional antenna and other conformal load-bearing antenna. This antenna performance was also optimized by analyzing different factors, such as weaving direction and weaving structure and weaving density of the conductive yarn in the radiation patch. It provides the theoretical reference for the similar textile structural antenna. Besides, the study on the mechanical properties and failure mode of the antenna also benefits the optimizing and investigation of other composites structural conformal load-bearing antenna.