COMPACT QUAD-BAND BANDPASS FILTER USING OPEN- AND SHORT-STUB-LOADED RESONATORS

This paper presents a planar quad-band bandpass filter using open- and short-stub-loaded resonators. The proposed filter consists of two sets of resonators. One set of resonators is embedded in the other, thus the filter is compact in size. The outer resonators are the open-stub-loaded resonators, and the inner ones are short-stub-loaded resonators. The former is designed not only to generate the third and the fourth passbands, but also feed the inner resonators. The latter operates at the first and the second passbands. All the passband frequencies can be conveniently tuned to desirable values by altering the corresponding resonator dimensions. On each side of each passband, at least one transmission zero is realized, resulting in high skirt selectivity. To validate the proposed idea, a demonstration filter is implemented. The design methodology and experimental results are presented.