The 3700BL15B200 from Johanson Technology is a Balun with Frequency 3.4 to 4 GHz, Amplitude Balance 1.0 dB, Phase Balance 20 Degree, Insertion Loss 1.2 dB, Power 0.1 W. Tags: Ceramic, Surface Mount, Unbalanced to Balanced. More details for 3700BL15B200 can be seen below.