X-Band Isoflux Concentric Circular Antenna Arrays for Image Data Download from LEO Satellites to Ground Stations

摘要

A circularly polarized isoflux beam synthesized by concentric circular arrays of printed microstrip patch antennas is proposed for X-band transmission of image data from land-imaging LEO satellites to the ground stations. This beam has a wide coverage angle of about 100 degrees of uniform illumination. The paper introduces a novel design of a compact righthand circularly polarized microstrip patch as an element for the concentric circular arrays. The patch antenna has impedance matching bandwidth of about 600 MHz and axial ratio bandwidth of about 170 MHz at 8.1 GHz. A prototype of the proposed patch antenna is fabricated for experimental measurements. The electromagnetic simulation and experimental results show good agreement. A computationally efficient particle swarm optimization (PSO) procedure is developed and applied to find the distribution of the excitation magnitudes over the array elements so as to generate an isoflux beam in all the elevation planes with circular symmetry in the azimuth planes. The phase of excitation is the same for all the array elements. The method proposed to apply the PSO reduces the computational resources to about 6.5% of those required by the conventional method of application. Moreover, the proposed iterative PSO procedure is shown to be very fast convergent.