The 21000 3500-4200 from Microwave Filter Company is a Waveguide Filter with Frequency 3.780 to 4.2 GHz, Insertion Loss 0.46 to 0.6 dB, Rejection 25 to 85 dB, Rejection Frequency 3.57 to 4.47 GHz. Tags: Band Pass. More details for 21000 3500-4200 can be seen below.