Novel Synthesis of Generalized Strongly Coupled Resonator Triplet Filters With Complex Reflection Zeros

Complex reflection zeros (CRZs) are introduced into generalized strongly coupled resonator triplet (GSCRT) filter synthesis for the first time to reliably eliminate negative couplings, thus facilitating physical implementation. CRZs bring more flexibility in synthesis and can be preassigned and regulated as needed to guarantee nonnegative couplings in different topologies and achieve varying electrical performance. Besides, CRZs bring the advantage of self-suppressed spikes, which can save extra band-stop modules in the system. To provide useful guidelines for designers, the selection of suitable CRZs is discussed in detail. With the introduced CRZs, the responses of GSCRT filters feature nonideal “in-between” performance, which shows a tradeoff between electrical performance and physical realization. Also, a comparison between the performance of GSCRT filters, extracted-zero, and path filters is given, which aims to help designers choose the most suitable configuration in practical use. Finally, the good measurement results of an anti-interference satellite filter have strongly validated the proposed theories.