Quasi-elliptic triple-mode filter

A quasi-elliptic triple-mode resonator filter is proposed in this paper. The filter is realized by having a capacitive coupling between the input and the output of a proposed triple mode resonator with one transmission zero at the high side of the passband. With the mentioned coupling, additional two transmission zeros are obtained at both sides of the passband which yields a quasi-elliptic response. Consequently, the selectivity of the triple mode filter is improved. Moreover, a very wide stopband rejection is achieved which underlies the major advantage of a spurious free performance of the filter. Theoretical analysis together with experimental prototypes is presented in this paper.