Dual Null Steering and Limited Beam Peak Steering Using Triple-Mode Circular Microstrip Patch Antenna

A compact triple-mode circular microstrip patch antenna capable of creating two nulls in the upper hemisphere and steering them independently is presented. The antenna consists of a central circular patch supporting TM11 mode, a TM21 mode shorted annular ring around it and another shorted annular ring supporting TM31 mode encompassing the other two radiators. Each mode is fed using two feed points to create right-handed circular polarization. Analytical and simulation studies show that by controlling the individual mode amplitude and phase ratios, radiation pattern can be reconfigured. Especially, two nulls can be generated in upper hemisphere and can be steered independently based on the ratio of applied excitation to each mode. This is a highly desirable feature for satellite receives antenna system with antijamming capability. To calculate the required modes excitation ratios, a MATLAB optimization code using a hybrid method of particle swarm optimization and pattern search was used. To apply the calculated excitation, an analog beamforming network consisting of digital variable gain attenuators, digital phase shifters, and low-noise amplifiers was used. This antenna was fabricated and tested for radiation patterns showing full hemispherical null steering along with limited beam peak steering.