A High-Isolation Dual-Circularly-Polarized Antenna for Simultaneous Transmit and Receive Based on the Differential-Mode and Common-Mode Coupling Cancellation Principle

In this paper, an improved co-aperture, dual circularly polarized (CP) microstrip patch antenna with good isolation for simultaneous transmit and receive (STAR) applications is proposed. The antenna consists of a slot-loaded cross-shaped patch with four slots embedded around the patch to adjust impedance matching and a rectangular slot in the center of the patch to achieve dual CP. In addition, the transmitting (Tx) to receiving (Rx) isolation of the antenna is improved through the differential-mode and common-mode coupling cancellation theory. Simulation results show that the final antenna has compact overall dimensions of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.43\lambda \times 1.43\lambda \times 0.033\lambda$</tex>, where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\lambda$</tex> is the guided wavelength at the center frequency. The antenna operates over a bandwidth of 4.21 GHz-4.32 GHz with isolation higher than 15 dB and up to 33 dB. At the same time, it has a consistent radiation pattern. Compared with similar antennas, this antenna has the characteristics of small aperture size and a simpler feeding structure, which is suitable for STAR systems.