Orthogonal hybrid couplers, also known as 90-degree hybrid couplers, are passive RF/microwave components that split or combine electromagnetic signals with a 90-degree phase difference between output ports. These couplers are widely used in communication systems, radar modules, and antenna arrays, where balanced signal distribution, phase control, and isolation between ports are critical.

The design typically features four ports: an input port, two output ports, and an isolated port. When a signal is applied to the input port, it is split equally between the two output ports, with one output lagging the other by 90 degrees in phase. The isolated port is designed to absorb reflected power, ensuring that any mismatch at the output ports does not affect the input signal—a feature measured by isolation (typically >20 dB), which quantifies the power leakage between non-adjacent ports.

Orthogonal hybrid couplers can be constructed using various transmission line technologies, including microstrip, stripline, or waveguide structures, depending on the frequency range and application. Microstrip designs are common in low to medium power applications (up to 100 W) and operate efficiently from 1 GHz to 100 GHz, while waveguide-based couplers are used in high-power, high-frequency systems (above 10 GHz) due to their low loss and high power handling capabilities.

A key advantage is their ability to combine signals with minimal interference. For example, in antenna systems, they can combine two signals into a single output with a 90-degree phase shift, enabling circular polarization—a critical feature for satellite communications, where signal stability is affected by atmospheric conditions. In radar systems, they facilitate phase comparison between signals, enhancing target detection accuracy.

Performance parameters include amplitude balance (difference in power between output ports, ideally <0.5 dB), phase balance (variation from the 90-degree shift, typically <5 degrees), and return loss (reflection at the input port, >15 dB for efficient operation). These parameters are tightly controlled during manufacturing through precision machining of transmission lines and careful selection of dielectric materials (e.g., high-frequency laminates for microstrip designs).

Orthogonal hybrid couplers are essential in systems requiring phase-coherent signal processing, offering a reliable means to split, combine, and manipulate RF signals with precision and isolation. Their versatility across frequency ranges and applications makes them a cornerstone of modern RF engineering.

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