A power combiner is an electronic device used to combine the output power of multiple radio frequency (RF) or microwave signals into a single output signal. Power combiners are used in various applications, including radar systems, communication systems, and microwave test equipment.

There are several types of power combiners, including:

1. Wilkinson power combiner: A popular passive power combiner that uses a quarter-wavelength transmission line and a resistor to provide isolation between input ports. It is known for its low insertion loss and good isolation between input ports.
2. Resistive power combiner: This type of combiner uses resistors to combine input signals. While it has a simple structure, it is less efficient due to power loss in the resistors.
3. Hybrid coupler (90° or 180°): A hybrid coupler is a four-port device where two input ports are combined into two output ports. The coupling can either be 90° (quadrature hybrid) or 180° (rat-race hybrid). They offer good isolation and low insertion loss.
4. Waveguide power combiner: This combiner uses waveguides to combine high-power microwave signals. It is suitable for high-frequency applications and can handle large amounts of power.

The choice of a power combiner depends on factors such as the required frequency range, power handling capability, insertion loss, and isolation between input ports.