A microstrip array of concentric annular rings

Analysis of an array of concentric annular ring microstrip antennas is presented. The feasibility of such an array is based on the observation that annular rings with different mean radii can be designed to resonate at the same frequency for the TM12mode. The ring array can be excited by means of a single feed by interconnecting two consecutive rings with an impedance transformer. The design procedure for the rings and the impedance transformers for a particular amplitude distribution is discussed. An experiment with an array of two rings has been performed and is found to agree with the theoretical predictions.