The coupling coefficients of disk-shaped dielectric resonators interacting through a two-conductors stripline resonator placed in the rectangular diaphragm of a metallic case have been studied. It has been found that the capacitive interaction of the resonators changes to inductive when the eigenfrequency of the stripline resonator is lower than those of dielectric resonators. This feature makes it possible to design small-size multicavity bandpass filters with additional capacitive and inductive couplings, which are expected to offer a high selectivity and a small spread of the group delay time in the passband. Using the electrodynamic analysis of a 3D model, a small-size 12th-order filter with center frequency f0 = 3.925 GHz of the 45-MHz-wide passband has been synthesized. The width of the passband was measured at a level of 1 dB from the minimal loss level. In the designed filter, a two-conductors stripline resonator is used to provide differing-in-sign additional couplings between disk-shaped resonators and couple feed lines at the input and output. This improves the filter manufacturability and raises the mechanical strength of the device. The characteristics of the filter confirm that the proposed design is promising for creating small-size frequency-selective devices for space communication.
Belyaev et al. (Sat,) studied this question.