An ultra-wideband microstrip bandpass filter which operates from 3.1 GHz to 10.6 GHz, with high selectivity and sharp notched band is presented and experimentally verified. The filter is composed of a square loop shaped defected ground structure, metal faces, and microstrip lines. By adding two short stubs connected by a short circuit point on the microstrip lines, the filter achieves an attractive capacity in out-of-band rejection. By placing open stubs in microstrips, the filter realizes a notched band in passband. To illustrate the possibilities of the new approach, an ultra-wideband microstrip bandpass filter is designed and fabricated. Measured results agree well with the predicted counterparts.
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