Novel compact wideband based on square ring short stub loaded resonator

This letter presents a novel compact microstrip wideband bandpass filter (BPF) based on square ring short-stub loaded resonator (SRSLR). The SRSLR is able to generate three resonances over the wide frequency band, while the fourth resonance is far away. In this design, by tuning the lengths of square ring and short-stub, the filter has an adjustable fractional bandwidth from 29.8 to 71.9%. Moreover, two transmission zeros are created to improve the filter selectivity. A prototype of wideband BPF with high performance is designed and fabricated for demonstration. Good agreement can be found between the measured and simulated results.