Circularly Polarized Planar Antenna Array Using Linear Polarized Microstrip Antenna with Beamforming for SAR Applications

Abstract

Circular polarization is so important for satellite and SAR applications. Therefore, a relatively large planar array of 10 × 10 building blocks is proposed to get a high gain and to have the possibility of beamforming for such applications. The individual antenna element used in this array is a linear U-slotted microstrip patch. This allows for simplicity, lightweight and low cost. At first, a subarray of these microstrip antennas is constructed and analyzed to become a building block for the large array. This subarray is formed of four U-slotted microstrip antenna elements arranged in a cross form with 90° sequential rotation in orientation in space, and 90° sequential phase shift between adjacent microstrip elements. The distance between the centers of two opposite microstrip elements is selected to be 0.53λ0. A linear array is formed of ten of these subarrays and analyzed to become one row or one column in the final planar array. The distance between subarray centers is kept to be 0.53λ0, which implies a new arrangement technique using the superposition of elements of the adjacent subarrays. The phase and amplitude relations of this linear array are developed for beamforming using the particle swarm optimization algorithm. Finally, the planar array is formed and simulated. It also implies using the superposition theorem to get the final array form. This planar array has proved to produce a cosecant-squared radiation pattern in the φ = 0° plane normal to the array plane, and a flat-topped pattern in the other perpendicular plane of φ = 90°. This type of array is very suitable for SAR side looking applications.