The 21000 3720-4200 from Microwave Filter Company is a Waveguide Filter with Frequency 3.72 to 4.2 GHz, Insertion Loss 0.88 to 1 dB, Rejection 25 to 90 dB, Rejection Frequency 3.6 to 6.45 GHz. Tags: Band Pass. More details for 21000 3720-4200 can be seen below.