What is a hybrid coupler?
A hybrid coupler is a four-port directional coupler that splits the input signal equally between the two output ports with a 3 dB attenuation. The signals at the output ports have a 90-degree or 180-degree phase difference. A 90° hybrid coupler is a four-port device that splits the input signal equally with a 90° phase shift between the ports. To illustrate its operation, the signal at the input port (port 1) is split between the two output ports, with half the power going to the 0° port and the other half going to the 90° port. Any reflections from the mismatch at the output ports go to the isolation port (port 4). This is one reason hybrid couplers are used to split signals in applications where unwanted reflections could damage the circuit. This type of coupler is also called a quadrature coupler.
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180° Hybrid Coupler
A 180° hybrid coupler is a four-port device used to split an input signal equally between the ports with a 180° phase shift, or to combine two signals with a 180° phase shift. A 180° hybrid coupler typically consists of a central conductor loop with a circumference of 1.5 wavelengths (six quarter-wavelengths). Each port is separated by a quarter-wavelength (90° apart). This configuration results in a device with low loss, low standing wave ratio, and excellent phase and amplitude balance. This type of coupler is also known as a "rat coupler."
