An I/O Coupling Multiplier Circuit and Its Application to Wideband Filters and Diplexers

Abstract

In this paper, a novel input/output (I/O) coupling multiplier circuit for conveniently increasing I/O coupling of a wideband coupled-resonator filter/diplexer is proposed. The multiplier circuit consists of a shunt capacitor and a negative phase shift. By appropriately shunt connecting a capacitor in the vicinity of an I/O port, the I/O coupling can be effectively increased. Compared to conventional approaches of increasing I/O coupling for a wideband application, using the multiplier circuit allows much less perturbing the resonant frequency of the first resonator. For many resonator configurations such as helical resonator, to which the tapping probe could not be adjusted continuously, the multiplier circuit provides a convenient way to control I/O coupling. In this paper, the working mechanism of the proposed circuit is well proved theoretically. The usefulness of the multiplier circuit has been demonstrated for coaxial combline cavity resonators and helical resonators, both for filter and diplexer applications. As a practical example, the multiplier circuit is applied to a wideband UHF helical resonator diplexer.