Compact Lowpass Filter With Sharp Roll-Off and Ultra-Wide Stopband Using Polygonal Patch Resonators

A compact microstrip lowpass filter (LPF) with sharp roll-off and ultra-wide stopband using polygonal patch resonators is proposed in this article. The filter is composed of a main meander high impedance transmission line, three types of cascaded polygonal patch resonators, and four attenuation cells employing stepped impedance stubs. A demonstrated LPF with 3-dB cut-off frequency at 2.76 GHz is designed, implemented, and tested. The experimental results demonstrate that the filter processes a sharp roll-off of 203 dB/GHz, an ultra-wide stopband from 2.9 GHz to 22 GHz with a rejection level greater than 20 dB, and a small size of 8.15 mm × 17.43 mm.