What Is a Phase Shifter?

A phase shifter is a device that can alter the phase angle of a radio frequency or microwave signal. Most phase shifting devices are compatible with signals no matter their direction, classifying them as reciprocal networks. Phase shifters can be controlled electrically, mechanically, as well as magnetically. They are available in analog form to allow for a variable phase or time delay that occurs continuously, and digital devices with a set of phases or delays. Different types also include a variable phase shifter or switched-line, loaded-line, reflection phase, and microwave phase shifters.

When signals go in to the input port of a phase shifter, a command causes the output signal to be changed. Most often phase shifters are digital and also include voltage control that provides immunity to noise, or interference. The phase states of the signal are controlled using digital phase bits. Each successive phase is half the angle of the last, so a 2-bit device would be a 90 degree phase shifter, being that 180 degrees is the highest in the range and categorizes a signal moving in a straight line. The off-state of the device is determined by the phase length covering the shortest distance, while the longest phase length is the on state.

Analog phase shifters offer continuous phase change with continuous shifting. A variable control input, which supports an unlimited phase resolution, can also be included. Even a microwave phase shifter can be analog or digital and controlled by a semiconductor device such as a diode. The circuit itself is designed to shift the microwave signal to a maximum level, so one must consider the specifications of the device and the circuit before adding it to the system. A phase shifter is chosen based on the requirements of the application and mathematical calculations of what qualities are needed in the signal.

As with most electronics, saving power is an important characteristic of a phase-shifting device. No power is consumed by a passive phase shifter, which performs the required operation automatically without outside control. Low loss is another power saving trait, and the loss can be diminished even more by including an amplifier stage in the phase shifter. Variations of the device include a switched-line shifter, which includes two single-pole double-throw switches to switch two electrical lines of different lengths. Loaded-line phase shifters are configured for shifts of less than 45°, while reflection phase shifters use line lengths that switch to change the length of electrical paths.