Phase shifters are devices utilized in high frequency RF designs to provide a phase shift to the signal by adding propagation delay. They are used in applications including satellite communications, beamforming modules, phase cancellation, communications antennas and phased-array radar. Phase shifters can be analog or digital, active or passive. RF micro-electrical mechanical systems (MEMs) phase shifters are available for passive high performance antenna arrays for Ka-band (26-40GHz) applications that exhibit superior performance to solid state alternatives.

Phase shifters change the transmission phase angle (the phase of the forward gain S21 scattering parameter). Analog phase shifters are controlled by a voltage. An example of a device that can do this is a voltage variable capacitance varactor diode. By using a varactor diode as a component in an all-pass filter topology, the phase shift of the network can be controlled. Digital phase shifters are the most common phase shifter ICs. They provide a discrete set of phase shift sections that can be switched in series to provide for various phase delays controlled by phase bits. Digital phase shifters are specified with a bit precision related to a phase shift at a frequency or over a frequency band. For example, a 1.4-2.4GHz 6-bit digital phase shifter with 360^o coverage and a least significant bit (LSB) of 5.6^o.

An important characteristic of a phase shifter is low insertion loss. Passive phase shifters are reciprocal (bidirectional) networks and the most common available. Each phase section adds to insertion loss of the device. Active phase shifters are available to compensate for losses through phase delay stages but these are non-reciprocal (only one direction) and the active stages can introduce distortion and noise. Their contribution to a systems noise figure (NF) must be accounted for.