A novel microstrip bandpass filter using lumped resistor-loaded configuration

A new bandpass filter (BPF) with a good frequency selectivity using lumped resistor-loaded element is proposed. The filter is composed of a parallel-coupled line shunted with a folded open-ended stub and a coupled line loaded with lumped resistor. The proposed filter has been designed, simulated, optimized for wireless communication system, and the obtained frequency responses have demonstrated a good filtering properties including -3 dB fractional bandwidth (FBW) of 11.2% at the central frequency 8.9 GHz, the maximum insertion loss less than 0.8 dB and the minimum return loss more than 15 dB within the passband frequency range, and two transmission zeros close to the lower passband edge and three transmission zeros close to the upper passband edge. The filter exhibits an excellent band-pass property and a high attenuation characteristics nearby the lower and upper stopband. Thus, a high selectivity of the proposed filter is achieved.