Compact Co-Linearly Polarized Microstrip Antenna with Fence-Strip Resonator Loading for In-Band Full-Duplex Systems

A compact co-linearly polarized microstrip antenna with identical radiation properties is proposed and validated for in-band full-duplex systems. By exploring a fence-strip resonator (FSR) in the central plane of a patch, good isolation is achieved between the transmitting and receiving ports. The proposed FSR consists of a metallic vias fence and a strip with a distance away from the ground, performing as a pair of distributed inductor and capacitor. When the FSR is resonating, the radiating current is concentrated in the half part of the patch, performing at its half-TM10 mode with high port isolation. To validate the proposed antenna, a prototype with the size of $0.25\lambda _{0} \times 0.25\lambda _{0} \times 0.04\lambda _{0}$ ( $\lambda _{0}$ is the free-space wavelength at center frequency) has been fabricated and characterized, with experiments consistent well with simulations. A measured port isolation higher than 20 dB is achieved over the operating bandwidth of 2.40-2.52 GHz with the maximum of 30 dB. The proposed antenna is with the merits of compact size, low profile, simple feed, and planar-integrated structure for in-band full-duplex systems.