Study Of The Conformal Microstrip Array Antennas

Conformal arrays have been widely used in wireless communication systems due to their distinctive features such as low-profile, compactness and wide-angle-scanning performance. However,the analysis and synthesis methods for conformal arrays are complicated and difficult. Most of the studies available are concerned with conformal arrays mounted on the regular surfaces. Synthesis method for the conformal arrays mounted on the irregular surface is still an open problem. As the main part of a national research projects, this dissertation is mainly concerned with the analysis and design method for the microstrip conformal antenna arrays mounted on the irregular surface. The author's major contributions on the subject can be summarized as follows:1. Optimization methods for the microstrip antenna design are investigated. An optimization design method for patch antennas is proposed by combining particle swarm optimization with standard software IE3D (PSO/IE3D). Patch antennas with complicated structures can be optimized using the proposed method without causing overlap problem in IE3D. Besides, the optimization procedure of the PSO/IE3D method can be suspended and resumed at spare time, which makes it possible to design complicated patch antennas in an effective,convenient and flexible manner. Two microstrip antennas are designed using the PSO/IE3D method and the modified PSO/IE3D (MPSO/IE3D) method respectively. Simulated and measured results of the optimized microstrip antennas show the accuracy and utility of the proposed method. A optimization method using particle swarm optimization base on Finite Difference Time Domain (FDTD) method is also studied for designing wideband and dual-frequency microstrip antennas. A dual-frequency microstrip antenna is designed using the PSO/FDTD method. The measured results of the optimized antenna agree well with the simulated results.2. Interpolation methods for the approximation of three dimensional (3-D) antenna radiation patterns are studied. A modified approximation method for the reconstruction of three dimensional (3-D) antenna radiation patterns from two cuts (vertical and horizontal) is presented based on the investigation of other existing approximation methods. The performance of the proposed method is compared against other existing extrapolation algorithms, which shows the advantage and usefulness of the proposed method. Three-dimensional radiation pattern of an antenna can be accurately reconstructed using the proposed method from two cuts (vertical and horizontal), and its directivity can be easily achieved by the integral method.3. The microstrip elements for conformal arrays are studied. A modified H-shaped microstrip antenna is designed using the PSO/IE3D method. The optimized antenna has a wider frequency span than that of the normal H-shaped microstrip antenna. Besides, the antenna has a relative high gain as well as a compact size. The optimized antennas mounted on cylinders with different radiuses are studied and the resonant frequency and the radiation pattern of the antenna versus the radius of the conformal cylinder are also investigated. A conformal low-profile E-shaped patch with unequal thickness substrate mounted on an irregular surface is also investigated.4. Mutual coupling effects of the modified H-shaped microstrip elements in planar and conformal arrays are analyzed. RF simulation software IE3D and CST are used to study the mutual coupling effects in planar and conformal arrays respectively. Cylinder conformal arrays with different radiuses are implemented and the characteristics of the conformal elements in the cylinder array are measured to investigate the mutual coupling effects.5. Analysis and synthesis method for circular and elliptical arrays are studied. Circular array antennas are analyzed using the phase mode method. An approximation formula is presented for the omni-directional circular array composed of the directional elements. Omni-directional circular array composed of the directional elements can be properly designed using the approximation formula. Fitness distance ratio based particle swarm optimization (FDR-PSO) algorithm is also used to synthesize the circular arrays, when the requirement of the approximation formula can not be met, as well as the elliptical arrays. Radiation patterns with low ripples are obtained by optimizing the phases of the arrays using the FDR-PSO method.6. Design method for the conformal array mounted on the irregular surface is studied. Three conformal array antennas are designed using FDR-PSO algorithm. Mutual coupling effects of the elements and the effect of the conformal platform are considered in the conformal array design by adjusting the return loss and using the measured radiation patterns of the elements mounted in the array. The conformal arrays are successfully implemented and the measured results show that the proposed synthesis method is effective and efficient.