Electrical-Balance Duplexer RF Front-End with a Commercial Wi-Fi Antenna and a Chebyshev Circuit Load-Balancer

This paper presents a new Chebyshev response load-balance (LB) circuit for electrical-balanced RF front-ends targeted for simultaneous transmit-receive (STR) applications. TX reflection of a commercial Wi-Fi antenna that barely supports a 3:1 VSWR and direct TX leakage of a commercial quadrature-hybrid are considered and canceled concurrently in simulations and tests. We analyze the reflective LB as the RF front-end optimal load and propose a theoretically lossless impedance-matching network that achieves SIC performance over more than ± 5 % bandwidth relative to the carrier. A load balance PCB design with two transmission lines and lumped RLC elements is realized to demonstrate the potential of our architecture. The implemented design achieves > 25 dB of total TX-RX isolation over 300 MHz around 2.65 GHz where the antenna reflection is 7 dBr. This is the first published work that cancels real antennas employing a low-cost LB circuit to the best of our knowledge.