A Coupler with Simultaneously Tunable Phase, Frequency and Coupling Coefficient

A novel coupled-line coupler with tunable frequency, coupling coefficient and phase difference is proposed with a reduced number of varactor diodes. The proposed coupler consists of two weakly coupled lines cascaded using varactors and two highly tunable coupled lines loaded with varactors. By varying the cascading capacitances between two weakly coupled lines, the phase difference between the output ports can be tuned with little effect on frequency and amplitude. More importantly, the operating frequency and coupling coefficient can also be independently controlled by choosing the proper combination of the loading capacitances between and on the highly tunable coupled lines. For demonstration, a highly reconfigurable coupler was designed, fabricated and measured. It exhibited a tunable operating frequency ranging from 1.15 GHz to 1.85 GHz with a relative bandwidth larger than 18%. The power division ratio and phase difference between the output ports are also tunable from 0 dB to 7.4 dB and from 65° to 130° respectively.