A wideband tunable quadrature coupler with flat coupling

Abstract

This paper presents a wideband reconfigurable coupler with tunable coupling ratios. It consists of two 3 dB quadrature couplers and two varactor-based continuously tunable reflection networks. The instantaneous bandwidth is enhanced by adding matching networks at all four ports. The proposed four port with reflection symmetry offers a return loss greater than 15 dB and an isolation greater than 20 dB through a fractional bandwidth of 23 % while exhibiting a very flat response. The coupling ratio can be tuned from −9 dB to 0.1 dB.