LAUSR

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.