Performance of a band reject tunable microwave filter in the face of frequency-modulated interference

This paper presents the theory of a microwave band reject filter (BRF) performance when the input signal to be rejected is accompanied by an adjacent channel frequency-modulated interference. The BRF is designed in the X-band at 10 GHz. The 3-dB bandwidth of the BRF is calculated to be 1.485 GHz. We have calculated the FM interference power of the output of the BRF as a function of input interference power to rejected input signal power ratio. From analysis, it is seen that the normalized output interference power level is down by 55 dB to 37 dB relative to the input interference power to signal power ratio in the range -20dB to -3 dB, the FM interference carrier lying above the BRF centre frequency by 155 MHz.