Dual-mode dual-band bandpass microstrip filter design

In this paper, by using microstrip resonators having dual-mode characteristics, a novel dual-band bandpass filter with elliptical filter characteristics is presented. Designed resonator structures have been formed by placing a couple of open-circuit ended edge lines to the corner points of a square loop resonator. By means of movement of the gaps between the open ends, by constituting a perturbation effect, two degenerate modes are excited and by this way mode frequencies and transmission zeros can be controlled. Two resonators which represent two different passbands are fed by only one feed-line. Designed dual-band microstrip filter has totally 14.2mm × 14.2mm surface area and by configuration it has been gained a compact structure. Proposed structure has been fabricated by serigraphy and it has been observed that simulated results are compatible with measured results.