Single Layer, Differentially Driven, LHCP Antenna With Improved Isolation for Full Duplex Wireless Applications

This paper presents a unidirectional, left handed circularly polarized (LHCP), single layered antenna array with improved interport isolation for simultaneous transmit and receive (STAR) or in-band full duplex (IBFD) wireless applications. The proposed IBFD antenna is comprised of three identical and sequentially rotated LHCP radiating elements where two Rx patches are symmetrically placed with respect to a single Tx patch. The symmetry of proposed antenna structure results in same amount of coupling or self interference (SI) from Tx element and differentially driven Rx patches achieve effective suppression of resulting SI to obtain improved Tx-Rx interport isolation required for STAR applications. The deployed feed network for differential-driven Rx operation is composed of a simple 3dB/180° rat-race coupler (ring hybrid coupler) with nice in-band amplitude and out-of-phase balance characteristics. The implemented single layer, compact (antenna elements and feeding network etched on single-layered PCB) antenna array achieves 10dB return-loss bandwidth ≥ 75MHz for both Tx and Rx ports. The prototype achieves ≥ 47dB interport isolation in 75MHz bandwidth and 3 dB axial ratio beam-width is ~ 60° for implemented antenna.