The U3931 from Mercury Systems is a Low Pass RF Filter with Frequency 405 to 460 MHz, Stopband Frequency 2200 to 2400 MHz, Insertion Loss 0.3 dB, Rejection 60 dB, Upper Rejection 60 dB @2200 to 2400 MHz. Tags: Module with Connector. More details for U3931 can be seen below.