Arbitrary Terminated Coupler with Tunable Negative and Positive Group Delay Responses

This paper presents a design of arbitrarily terminated coupler with tunable negative group delay (NGD) response and power division ratio. The proposed coupler provides tunable NGD through port 3 and 1 whereas positive group delay (PGD) through port 2 and 1. The analytical analysis shows that the power division ratio and NGD are controlled by a junction resistance of parasitic compensated PIN diode. Perfect matching and infinite isolation are obtained at the center frequency $(\pmb{f}_{\mathbf{0}})$. The proposed coupler is validated by fabricating circuit at $\pmb{f}_{\mathbf{0}}=\mathbf{2.14}$ GHz. Measurement results are well agreed with simulated and predicted results. The experimental results show that NGD is varied from −0.2 to −1.3 ns with NGD fractional bandwidth (bandwidth of $\mathbf{GD} < \mathbf{0}$) of 21.14 % to 15.88%.