Compact size microstrip coupled resonator band pass filter loaded with lumped capacitors

A compact band pass filter based on microstrip coupled resonator is presented. The proposed structure consists of two microstrip open- loop resonators with electrical coupling. The reduction of the size of the proposed bandpass filter is achieved by combining the microstrip resonator with the lumped capacitors. The insertion of lumped capacitors within resonator was designed at maximum electric field.The insertion of lumped capacitors within resonator increases the effective capacitance and reduces the resonant frequency, so the dimensions of the filter will reduce and the performance of the filter will improve by enhancing the energy stored in the resonator. The design represents size reduction of more than 30 % compared to conventional filter without lumped capacitors. The filter has the characteristics of compact structure and low insertion loss. A second order band pass filter has been designed with rejection higher than 20dB and insertion loss lower than 0.7dB has been achieved within pass band.