Design Of The Antennas System Layout On The Airborne Platform And Antennas For The Special Applications

The subject of this dissertation is chosen according to scientific research projects.It mainly focuses on the designs of antenna system layout on the airborne platform and antennas for special applications.This thesis is divided into two main parts.The first one presents the layout of the antenna system on the airborne platform,which utilizes electromagnetic simulation and experimental test to study the electromagnetic compatibility for specific airborne platform.The second part is the researches on antennas for special applications,including wide-band low-profile stacked Yagi and wide-beamwidth circularly polarized microstrip anenna.The specific contents are listed as follows:1.Simulation design of antenna layout on the airborne platform.First,determine the layout scheme design and simulation software according to the performance requirements and design difficulties.Secondly,design the isolated antenna model to meet the electromagnetic characteristics.Thirdly,establish the special airborne platform model.In accordance with the performance and application,two antenna pre-layout schemes are achieved.Fourthly,the patterns and isolations of the airborne antennas are simulated and analyzed under the schemes.And with repeatedly tuning the location of the airborne antennas on the basis of the simulation results,an optimal layout which meets the performance requirements is achieved.Finally,the electromagnetic environment and the shielding effectiveness of the cabin are carried on the simulation analysis and evaluation.2.Electromagnetic compatibility measurement on airborne antenna system.In order to verify the correctness of the layout design on the airborne platform antenna system,the measurement schemes of the electromagnetic compatibility are designed.The measurement schemes include the measurement of the electromagnetic properties of airborne antennas,the measurement of the electromagnetic environment and the shielding effectiveness of the cabin,the measurement of the short-wave radio communication distance,and the manufacturing requirements of the special airborne platform model.The electromagnetic properties include the radiation pattern on the vertical and horizontal plane and isolations between different antennas.The measurement of the electromagnetic environment and the shielding effectiveness of the cabin is used to measure the electric field in the cabin when the electromagnetic waves with the different work frequencies and different polarizations irradiate the airborne from different directions.The measurement of the short-wave radio communication distance is mainly aimed at the max communication distance of the short-wave radio antenna.Finally,the main structure,supporting structure,structure installed antenna and cable hole of the airborne prototype are discussed.3.Research on wide-band low profile stacked Yagi antenna.To reduce the profile of the antenna,a reflector modified with six slots,two?₀/4 meanderline-shaped slots and four straight short slots,is employed.Furthermore,a ladder-like director is designed to overcome the mismatch loss caused by the diminution of the height between the reflector and driven dipole.The|S₁₁|?-10 dB bandwidth is widened to 20%,and a FTBR of 18dB is achieved within the bandwidth.As shown in both simulation and measurement,the proposed compact Yagi can achieve stable performances.These make the proposed Yagi a good candidate for airborne communication applications where compact size and wide bandwidth are needed.4.Research on wide-beamwidth circularly polarized microstrip antenna.A wide-beamwidth circularly polarized asymmetric microstrip antenna is proposed by etching four novel unequal fan-shaped notches at the vertexes of the square radiator.A bandwidth of 1.5%and a beamwidth of 172°are well achieved for an axial-ratio?3 dB?3-dB AR?.To widen the bandwidth,the asymmetric microstrip antenna is further expanded with the construction of a antenna array using sequentially rotated feeding technique.Moreover,by properly optimizing the distance between each two neighboring elements and the radii of the fan-shaped notches,the 3-d B AR bandwidth of the sequential-rotation array?SRA?is approximately extended to 7.8%with a wide-beamwidth.In addition,the gain variation within the bandwidth is less than 1 dB.Finally,a laboratory model of the SRA has been fabricated and acceptable agreement of the simulated and measured results make it a good candidate for applications where wide-bandwidth,wide-beamwidth and small gain variation are needed,specially for the comprehensive application of GPS and CNSS systems.