An Analytical Design Method for a Novel Dual-Band Unequal Coupler With Four Arbitrary Terminated Resistances

A new design concept of a generalized dual-band branch-line coupler with unequal power division and four arbitrary terminated resistances is proposed in this paper. By using an external frequency-dependent impedance transformer, a novel dual-band branch-line coupler is obtained with a detailed analytical design method. For ease of design, maximum power-dividing ratio with varying frequency ratio for different terminated impedance values is provided. Owing to the additional design freedom, the calculation of parameters becomes much more flexible. Finally, for experimental validation and convenient measurement, a dual-band unequal microstrip branch-line coupler with four standard ports is designed, fabricated, and measured. Good agreement between the simulated and measured results can be observed.