Miniaturized microstrip lowpass filter using cylindrical-shaped resonators for integrated applications

A novel compact microstrip lowpass filter is presented in this paper. The structure uses stepped impedance and radial patches and it has the − 3 dB cut-off frequency at 4.39 GHz. The proposed lowpass filter has a wide rejection band from 6 to 30 GHz with rejection level more than − 20 dB. It has also other advantages such as: low insertion-loss < 0.1 dB and high return-loss more than 22 dB in 80% of the passband. The circuit size of the presented filter is about 90 mm2. Such important advantages make the proposed lowpass filter applicable to be integrated in many high frequency circuits such as power amplifiers, oscillators, couplers and power dividers. It also can block the unwanted video transmitter interference nearby 4 GHz such as implementing between transmitter and antenna. The lowpass filter has simulated and fabricated and a good agreement was seen between the simulation and fabrication results.