A Pin diode controlled dual-mode branch-line coupler

In this paper, a dual-mode branch-line coupler is proposed to adapt to different multi-beam network application. Controlled by the PIN diode, a grounded distributed capacity may be selectively introduced into the coupler. And then this coupler can have the pass-through mode and power divider mode to tune coupling ratios and get two kinds of output responses. The center frequency of the coupler is 2GHz. The circuit simulation shows both return loss and isolation are better than 20dB from 1.9GHz to 2.1GHz, and the amplitude imbalance is less than 0.5dB. And then the microstrip line model is also established and simulated. This coupler has a good engineering application scenario because of its simple structure, easy processing and broadband performance.