Compact Lowpass Filter with Stopband Using Radial Patch Resonators
A compact elliptic-function low-pass filter using microstrip radial resonators and their equivalent circuit model are proposed. This filter is composed of multiple radial resonators and open stubs. To achieve wide stopband suppression, two symmetrically open stubs are adopted. Also equivalent circuit of the proposed filter is calculated according to high-low impedance lossless line, bend and open-end. A demonstration filter with 3 dB cut-off frequency at 1.64 has been designed, fabricated and measured. The results show that a relative stopband bandwidth of 175.3% (referred to suppression degree of 20dB) is achieved, while obtaining high figure of merit of 33250.