Wide stopband lowpass filter based on defected microstrip structure

A microstrip lowpass filter based on the defected microstrip structure with sharp roll-off characteristics and wide stopband is proposed. The filter is composed of S-shaped and H-shaped slots. Based on the proposed structure, a lowpass filter with a 3dB cutoff frequency at 4.05GHz, a simple structure, a compact size and a sharp transition band is designed. The passband insertion loss is less than 0.3dB, the stopband width is 15.7GHz, and the roll-off rate is 81dB/GHz. Both the simulation and the experimental results are provided which have good agreement, and the circuit only occupies 23 × 5 mm2.