The ATc3.7-4.2 from Narda-ATM is a RF & Microwave Circulator with Frequency 3.7 to 4.2 GHz, Average Power Forward 2 W, Peak Power 20 W, Insertion Loss 0.1 to 0.15 dB, Isolation 23 to 26 dB. Tags: Coaxial Circulator. More details for ATc3.7-4.2 can be seen below.