Couplers and hybrids are devices in which two transmission lines pass close enough to each other for energy propagating on one line to couple to the other line. A 3dB 90° or 180° hybrid splits an input signal into two equal amplitude outputs. A directional coupler normally splits an input signal into two unequal amplitude outputs. This terminology “directional coupler”, “90° hybrid”, and “180° hybrid” is based on convention. However, the 90° and 180° hybrids could be thought of as 3 dB directional couplers. Despite these similarities, the parameters used to describe signal flow in directional couplers and the application, in actual use, is sufficiently different to warrant separate considerations. A 180° hybrid is a reciprocal four-port device which provides two equal amplitude in-phase signals when fed from its sum port (S) and two equal amplitude 180° out-of-phase signals when fed from its difference port (D). Conversely, signals input into ports C and D will add at the sum port (B) and the difference of the two signals will appear at the difference port (A).