The PIN Diode is a semiconductor device that acts like a variable resistor at microwave frequencies. The resistance of the diode is controlled by varying the dc current used to forward bias the diode.

PIN diodes are used in numerous microwave and wireless applications, including those listed below.

- Microwave switching.

- Variable attenuators. PIN diode attenuators can be designed as matched or reflective.

- Amplitude modulation and leveling of microwave signals.

- Microwave phase shifters.