A standing-wave microstrip array antenna

A single-layer resonant-type microstrip array feeding technique is proposed where feed lines act like a cavity within which standing waves are excited. No quarter-wave transformers or power dividers are needed in the proposed design and so spurious radiations can be minimized. The radiating patch elements are designed to accept the power leaking from the feed line cavity. The feed line can now be considered a long patch operating at a higher order mode. A simple cavity model is developed to compute the resonant frequency, return loss, and impedance behavior. The cavity model provides excellent physical insight that helps the designer assess the mode of operation, the 50Ω feeding point, and the branch tap positions for array element connections. Comparison of the model with Ensemble 5.0, a full-wave numerical technique, is provided for validation of the results.