H-shaped aperture-fed bidirectional circularly polarized antenna using dual rotated patch

A multilayer bidirectional circularly polarized antenna for underground communications is presented in this letter. The antenna consists of two slot-coupled back-to-back arranged rotated patches and a T-type strip feed-line. The H-shaped aperture is adopted to provide a favorable axial-ratio (AR) bandwidth. Identical left-hand circular polarization in the front and back of the radiating antenna is important in avoiding the undesired polarization mismatch for point-to-point connection. The proposed antenna combines the attractive features such as compact size, high aperture efficiency, as well as easiness of manufacture. Simulated results show that the antenna achieves a - 10 dB impedance bandwidth of more than 26% and a 3-dB AR bandwidth of 9% with a peak gain of 5.7 dBic.