Compact microstrip lowpass filter with wide stopband using nonuniform radial stubs

A compact microstrip lowpass filter with a wide stopband is proposed in this paper. To achieve wide stopband suppression and compact size, nonuniform radial stubs are adopted. The proposed lowpass filter is composed of four nonuniform radial stubs, four transmission lines, and two standard ports. A filter with the 3-dB cutoff frequency of 900 MHz is fabricated and measured. The fabricated lowpass filter is able to suppress the ninth-harmonic frequency response with a stopband rejection from 1.65 GHz to 8.5 GHz better than 20 dB. In addition, there is a good agreement between the simulated and measured results.