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° 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.