High Spurious Suppression Bandpass Filter with Singly-Step Impedance Transmission Lines Compensation

A simple technique to suppress spurious responses of microstrip bandpass filter is presented. This is achieved by employing the step impedance transmission line (SITL) compensated parallel-coupled line with enhance isolation/directivity to synthesis and implement the proposed bandpass filter. The optimum values of SITL parameters can be derive from the proposed closed-form expressions. To demonstrate the technique´s applicability, the compensated parallel-coupled lines are used to design resonator and bandpass filter and compare with an uncompensated bandpass filter. The proposed SITL compensated bandpass filter operating at 1.8 GHz is obviously show the excellent results than the unconventional bandpass filter.