Design of a Superstrate Module for Simple Resonant Frequency Tuning

This paper proposes the design of a dual-band circularly polarized antenna with an exchangeable superstrate module to compensate for the unwanted frequency shift without the re-fabrication process. The proposed antenna consists of inner and outer circular ring patches printed on the same layer of a substrate, and the mushroom-shaped superstrate is inserted to the substrate hole placed in the middle of the inner ring patch. The proposed superstrate structure adaptively adjusts the resonant frequency by selecting appropriate heights of the superstrate module. By inserting the superstrate module with the height of 2 mm, the maximum frequency shift of 20 MHz was obtained with the improved gain of about 0.9 dB at 1.42 GHz without any deteriorations on the AR and radiation patterns.