A multi-functional coupler of four-port crossover and continuously tunable power divider

A multi-functional coupler combing the properties of crossover and tunable power divider has been presented. The coupler is designed by cascading two branch-line coupler (BLC) with two varactors in between. By applying even-odd mode analysis, explicit design formulae are provided. Return loss and isolation are independent from the value of varactors. A multi-functional coupler with tunable power ratio from −8.8 dB to 9.0 dB was realized. The measured return loss and isolation are larger than 20 dB. In addition, the crossover property of the proposed structure was verified.