Integrated Designs of Filtering Circuits Based on Adjustable Dielectric Waveguide Resonators

This paper presents a new kind of adjustable dielectric waveguide resonator (DWR), based on which integrated designs of filtering circuits are conducted. The DWR is composed of a dielectric part as the main resonating body and a printed circuit board (PCB) part as the cover. An unmetallized blind hole is carved at the upper surface of the dielectric part. A tuning screw is installed on the PCB and inserted into the unmetallized blind hole to adjust the resonant frequency the DWR. This adjusting method is flexible and reversible. By using the proposed adjustable DWR, a fourth order bandpass filter (BPF) is designed, fabricated and measured. The measured results show that the BPF is with an in band insertion loss of 0.8 dB and an in band return loss better than 19 dB. A capacitive cross coupling structure is constructed on the PCB so that two transmission zeros are introduced close to the passband to improve the filtering selectivity. In addition, a Wilkinson power divider is realized on the PCB and integrated with the above BPF, forming a filtering power divider. The measured in band insertion loss of the filtering power divider is 1.1 dB. The isolation is better than 24 dB and the maximum phase imbalance is 1circ in the passband.