Improved implementation of wideband 90° hybrids

Wideband micro wave 3 dB, 90° hybrids [1] are used to split signals equally between two outputs over a broad bandwidth with quadrature phasing independent of frequency. They are often also called symmetrical couplers, 90° directional couplers or quadrature couplers. Typical uses include microwave mixers, phase shifters, sinuous antennas, antenna feed networks, reflectometers and frequency discriminators. Approximately equiripple wideband performance can be achieved by cascading multiple coupled line sections with varying coupling coefficients. Numerous synthesis techniques exist to design a coupling profile for a desired frequency response. Continuously tapered coupling profiles typically have to be used at higher frequencies to overcome the performance degradation caused by the step discontinuities. 3 dB couplers are almost always implemented in a tandem configuration of two 8.34 dB couplers to overcome the requirement for very high coupling factors.