Isolation Improvement Techniques for Wideband Millimeter-Wave Repeaters

Two passive approaches for improving the isolation between flush-mounted transmitting (TX) and receiving (RX) antennas over 45-110 GHz are investigated. Both configurations exploit a reactive impedance surface (RIS) that suppresses TM polarized surface waves propagating on the ground plane between the TX and RX antennas. Quarter-wavelength corrugated one-dimensional (1-D) RIS is shown to improve isolation by similar to 20 dB in an octave bandwidth (45-90 GHz), whereas concentric corrugations around the antennas improve isolation over the same bandwidth with better antenna radiation characteristics at the low end. On the other hand, an isolation improvement of similar to 15 dB over the entire bandwidth is obtained with an array of grounded circular patches 2-D RIS. Computational studies are validated with measurements of quad-ridge horns with 3-D printed corrugations and printed circuit board 2-D RIS patches.