Shaped Beam Circularly Polarized Circular Array for SAR and Satellite Applications

Circular arrays for circularly polarized radiation are considered for satellite and synthetic aperture radar (SAR) applications. Planar microstip circularly polarized antenna elements are arranged uniformly around a circle with equal spacing to produce the desired radiation pattern at 4GHz. The microstrip elements of four axial slots and four circular cuts at the corners are selected as the antenna element for such arrays. At first, four elements of such antenna are arranged without rotation around the centre of the circle, and again with regular successive rotation to form a simple circularly polarized array. It has been shown that the array with rotated elements is having a much better performance with wide axial ratio frequency bandwidth relative to the array without rotation. Another array of eight elements uniformly spaced and successively rotated has been proved to produce higher gain than the simple four element array. These two arrays are not suitable for beamforming. So, a sixteen elements uniform circular array with successive regular angular rotation is investigated. It has been used to apply beamforming using the particle swarm optimization algorithm (PSO) to produce flat-topped beam in one of the principle planes with relatively low side lobe level in the same plane.