The 21000 3720-4220 from Microwave Filter Company is a Waveguide Filter with Frequency 3.72 to 4.22 GHz, Insertion Loss 0.92 to 1 dB, Rejection 45 to 85 dB, Rejection Frequency 3.5 to 4.4 GHz. Tags: Band Pass. More details for 21000 3720-4220 can be seen below.