A 90° hybrid coupler has four ports and is a tool that’s used to either equally split input signals or combine two signals while retaining high isolation between ports.
When power is brought to the IN port, half of the power flows to the 0° port while the other is coupled to the 90° port. Anything that comes from mismatches is sent back to the output ports and will flow right to the ISO port. That’s why hybrid couplers are used so frequently to split high-power signals when unnecessary reflections may damage the driver device.
3dB 90° degree hybrids are also referred to as quadrature hybrids since two equal amplitude signals that are 90° apart will result when a signal is applied to any input. It doesn’t matter which port serves as the input because the relationship at the outputs stays the same. Such a configuration makes sure that a high degree of isolation exists and is maintained between the two output and input ports without any interaction among them.
An electronically tuned, low-loss notch absorptive filter can be obtained with a four-port quadrature hybrid coupler.
3dB, 180° Hybrid Ring Couplers
Also referred to as “rat race” couplers, 180° hybrid ring couplers are four-port devices that are used to equally split an input signal as well as sum up two combined signals. A key advantage to these types of couplers is to offer equally-split but 180° phase-shifted output signals.
The center conductor ring is six ¼ wavelengths in circumference and every port is separated by 90°. Such a configuration helps create a lossless device with low VSWR, impeccable phase and amplitude balance, match output impedances, and high output isolation. Because of the low loss construction of these 3dB, 180° hybrid ring couplers, they make the ideal choice for blending high-power mixed signals.
Common Applications of Hybrid Couplers
Carriers often have to deal with the difficulty of incorporating next generation services while attempting to limit CAPX equipment expenses. A more cost-effective solution is to mix a couple of transmitters along with a hybrid coupler that share an antenna and therefore free up another antenna. Hybrid couplers offer fantastic isolation between receivers and limit group delay so that it has no impact on current receiver operation or calibration.
Hybrid couplers are also useful for carrying multiple carrier inputs for in-building distribution systems because a high degree of isolation exists between the two output and input ports with no interaction between carriers.