Compact microstrip lowpass filter with ultra-broad stopband

A microstrip lowpass filter (LPF) with ultra-broad stopband is demonstrated. The proposed microstrip LPF is designed with simple microstrip bandstop structures realized essentially using simple short-stub and open-stub structures. Compared to the reported microstrip LPF designs, the upper stopband frequency of the proposed LPF is about 15 times greater than its 3-dB cutoff frequency, and the rejection is greater than 20 dB over the entire stopband. Additionally, the LPF is relatively compact in size- 0.3 wavelength by 0.18 wavelength at the 3-dB cutoff frequency.