Synthesis techniques for some tunable notch filter topologies

Synthesis techniques are described for two different tunable microwave notch filter topologies with two resonators. Notch is obtained by first forming an All Pass circuit by cross-coupling input and output ports of either a BSF or a BPF with a transmission line and then detuning capacitors of the two resonators. The previous works on such designs were involving manual tuning and optimization. In this paper systematic design approaches are developed enabling the designer to get control of all the parameters affecting the responses. Both BSF and BPF approaches lead to realizable notch filter circuits having sharp and deep notches. It is shown that with this approach the stop bandwidth remains essentially constant over a broad tuning band while the notch depth is almost independent of the Q of resonators.