Two Types of Trisection Bandpass Filters With Mixed Cross-Coupling

In this letter, a comparative analysis of two types of trisection bandpass filters (BPF) with a mixed cross-coupling is carried out. It is shown that a mixed cross-coupling results to the vanishing of a transmission zero in a trisection BPF of the first type (with a central reflection-type resonator). In a trisection BPF of the second type (with a central through-type resonator), mixed cross-coupling leads to two transmission zeros. A condition under which these transmission zeros are equidistant with respect to center bandpass frequency f0is determined. A position of these transmission zeros with respect to f0is expressed in terms of the coupling coefficients. The results of the measurements and the simulation are presented.