A theoretical investigation of IMPATT diode integrated microstrip low-pass filter and band-pass filter is proposed. In which the cutoff frequency of low-pass filter and bandwidth of band-pass filter is tunable by means of bias voltage of IMPATT diode without changing the dimensions of the microstrip lines. This work can satisfy the day by day increasing demand of tunable filters for microwave applications. This work presents the design, simulation and synthesis of IMPATT integrated microstrip low-pass filter and band-pass filter using coupled microstrip line through Advanced Design System (ADS). The microwave filter is designed by using insertion loss method. Simulation of the filters verifies that the final output response is correct in terms of s- parameter.