Theoretical Design And Optimization Of Phase-Shifting-Surface Array Antennas

A Phase shifting Surface (PSS) array, composed of patch or aperture elements in different working statuses, is a two-dimensional array antenna periodically arranged in a rectangular grid. PSS elements act as spatial phase shifters by imposing phase delay on the incident tangential electric field to form the demanded wave front. Considering the electromagnetic wave propagation direction after the phase modulation, PSS antennas can be divided into reflectarrays and transmitarrays. Based on microstrip structures, planar PSS antennas com-bines advantages of both reflectarrays and transmitarrays, such as low profile, volume, mass and cost, easy folding and conforming with carriers, and flexible beam control by large degree of freedom. It has become a well-known fact that the PSS array antenna is a new potential alternative to the conventional curved aperture antenna and the planar phased array.This dissertation keeps its eyes on the design and optimization of PSS array antennas. With research of different optimization algorithms, efforts are made to improve the typical per-formance indicators of several PSS antenna designs. The author’s major contributions are summarized below:1. The improved Alternative Projection Method (APM) algorithm. Aiming to overcome the drawbacks of APM, typically being sensitive to starting point and easily trapping in local optimum, a new multi-step convergence strategy described as the gradual variation of the target pattern is applied in the iteration process. This strategy distributes the convergence pressure into each step to avoid prematurity. Furthermore, to promote the efficiency on de-sign procedure, a co-simulation process is developed to link the numerical optimization in MATLAB and the electromagnetic simulation in HFSS together, including calculating the element scatting parameter, optimizing phase distribution, determining element status, mod-eling and simulating the PSS antenna.2. The design and optimization of large sized reflectarrays with shaped beams. As the phase response is highly consistent in the work band, as well as the element status can be cal-culated analytically, the circularly polarized rotational element is potential in beam-shaped PSS antennas. A dual split loop element is designed by the multi-resonance technique to acquire wide band circularly polarized reflection. Using this element, three reflectarray an-tennas with different shaped beams are designed and studied, including a sectored cosecant square beam antenna, a contour beam antenna and a multi-beam antenna. The multi-beam PSS array has been manufactured and tested. All the simulations and measurements of the beam shaping examples suggest the design method to be correct and effective.3. The design and optimization of small sized transmitarrays. The multi-layer technique is usually adopted in the transmitarray antenna to broaden the phase range, which is com-monly less than a cycle due to the narrow bandwidth characteristic of microstrip structure. However, this approach leads to a contradiction between profile height and phase range. The Particle Swarm Optimization (PSO) algorithm is applied to address this phase only syn-thesis problem with a limited range. The measurement results verified the approach by a low insert loss of the proposed transmitarray. Then, a rotational transmitting element with multi-layer of parallel dipoles is designed for a high gain circularly polarized transmitarray antenna. Finally the PSO method is employed to realize broadband optimization for a circu-larly polarized transmitarray. This approach compensates the spatial phase errors in different frequencies, resulting in gain variation in the work band meeting with the requirement.4. Study of dual-aperture PSS array antenna. To develop the application of PSS in dual-aperture antenna area, as a classic dual reflector antenna, a dual reflectarray configuration is analyzed according to the Side-Fed Offset Cassegrain antenna structure. The incident tan-gential electric fields on both the sub-reflectarray and the main-reflectarray are calculated using geometric optic and far field superposition approaches. Based on above analysis, a linearly polarized dual reflectarray antenna is presented. The demanded element statuses of both array are limited less than a cycle by properly designing the dual reflectarray configu-ration, which is of benefit to reduce spatial phase error for a good bandwidth. The simulated results indicate a high gain and wideband radiation performance. At last, a new concept of dual mode PSS array antenna is proposed, i.e., introducing a polarizing grid as the ground plane in PSS element. A triple-layer dual mode PSS antenna is designed for verification, in which the incident wave parallel to the grid works in reflecting mode and the vertical one transmitting mode. Both sides of the PSS array are available for radiation, which enhances the integration and functionality of the antenna system.