Fixed and Steerable Beam Dual-Polarized Lens Antenna With High Tx to Rx Isolation

A co-polarized, co-channel simultaneous transmit and receive (STAR) antenna system utilizing a two-layer spherically stratified lens with nominal directivity of 24.3 dBic is demonstrated in the 27-29 GHz frequency band. The STAR operation is achieved with a WR28 waveguide-implemented balanced circulator beam forming network (BC-BFN), which relies on two 90 degrees hybrids and two circulators along with antenna symmetry to cancel the circulator leakages and achieves theoretically infinite isolation between the transmit and the receive ports. The sensitivity of the BC-BFN to alignment imperfections is studied and it is found to be robust to this kind of error. To comply with the BC-BFN's symmetry requirements, a highly symmetric WR28 waveguide orthomode transducer (OMT) is developed. Transmitted (Tx)/receiver (Rx) isolation of 30 and 34 dB is measured with and without the lens, respectively; indicating acceptable impact of the lens on the system isolation. To demonstrate the STAR with the beam steering, the proposed configuration is modified into a mechanically rotated half spherical lens over a ground plane. The experiments show that the isolation of the rotating half-lens system degrades when compared to the full-lens counterpart due to the break of the geometrical symmetry. However, respectable isolation greater than 27 dB and high-quality circularly polarized radiation patterns are still maintained over the operational bandwidth.