Bandpass Filters Based on Dual-Disparate-Mode Dielectric Waveguide Resonators With Dual Port-Excitations

this brief, a novel dual-disparate-mode (DDM) dielectric waveguide resonator (DWR) is proposed for bandpass filter (BPF) designs. It is constructed by hollowing out a square ring in a traditional square DWR and plating a half-wavelength microstrip resonator in the hollowed part. The two modes are the TM110 mode of the DWR and the TEM mode of the microstrip resonator. Unlike the common dual-mode DWRs, the proposed one is smaller in volume since the two modes used are both fundamental modes. In the BPF designs, a probe is inserted into the DWR and connected with the microstrip resonator so as to feeding the TM110 mode and the TEM mode simultaneously. Consequently, dual port-excitations are realized to form a cascaded-trisection (CT) coupling topology together with the coupling between the two modes. By controlling the two CTs at the input and output ports, transmission zeros (TZs) can be generated aside the passbands and controlled to be at the lower side or at the upper side. Based on the proposed DDM DWRs, three BPFs are designed: the first one owing one TZ at the lower side, the second one owing one TZ at the upper side, and the third one owing two TZs (one TZ at each side). The third BPF is manufactured and measured for the purpose of verification. The measured results have good accordance with the simulated ones. A total size of 30.86 mm
$\times14.38$
mm
$\times5$
mm, an insertion loss smaller than 1 dB and a return loss better than 19 dB are observed.)