TM dual-mode pseudoelliptic filters using nonresonating modes

This paper presents a new class of very compact pseudoelliptic dual-mode filters. The basic idea consists of using a pair of resonant TMmn0 modes, while nonresonating modes are exploited so as to produce a direct coupling between the input and the output of the cavity. In this way, a single cavity can provide two reflection and two transmission zeros, thus leading to Nth order dual-mode filters having N transmission zeros. In addition, the proposed configuration yields very compact and geometrically simple structures that can be properly analyzed by a fullwave mode-matching technique, thus dramatically easing the design procedure. The analysis technique has been validated by comparison with commercial EM tools and by the measurement of a manufactured prototype. Several filter examples are proposed showing the design flexibility of the proposed filter class.