Co-Circularly Polarized Planar Antenna With Highly Decoupled Ports for S-Band Full Duplex Applications

This work presents a unidirectional, co-circularly polarized (CP), printed antenna with highly decoupled or isolated transmit (T-x) and receive (R-x) ports for 2.4 GHz in-band full duplex (IBFD) applications. The presented antenna topology is based on four similar and sequentially rotated trimmed patches with right hand circular polarized (RHCP) characteristics. The symmetrical placement of two T-x patches with respect to both R-x elements results in equal levels of self interference (SI) which was suppressed through balanced excitation of T-x mode. This mechanism results in effective suppression of SI at each R-x patch. The residual SI is suppressed further through a second balanced feeding network deployed at R(x)port of proposed antenna topology. The employed balanced feeding networks provide superior performance of <= 0.5 dB and 6 degrees magnitude and phase imbalances respectively between the two balanced output ports over the bandwidth of interest. The measured results for prototype of presented antenna achieve -10 dB bandwidth of better than 100 MHz for both T-x and R(x)ports. The measured interport coupling for validation model <= -70 dB across the entire bandwidth of 100 MHz. As per best of authors' knowledge, the presented antenna is the first one to report such reduced levels of interport coupling over the whole impedance bandwidth of planar antenna with unidirectional radiation patterns and co-RHCP characteristics for both T-x and R-x modes across the overlapped bandwidth.