A Compact Reconfigurable Coupler with Tunable Coupling Coefficients and Frequencies

A compact microstrip coupler with tunable frequencies and coupling coefficients is presented. The calculation equations for capacitances under two different reconfigurable situations are derived. The design procedures are also given upon different requirements. To demonstrate the design strategies, a prototype with center frequency of 2 GHz is fabricated and measured. The measured results show a tunable frequency range from 1 to 3 GHz with 3 dB coupling, and a tunable coupling coefficient range from 0.86 dB to 9.5 dB at center frequency.