what is phase shifter

phase shifters are twin-ported devices that alter the phase of an output signal in response to an external signal. Variable phase shifters change the output signal phase by applying a variable control signal. There are two basic types of variable phase shifters: analog and digital. Analog phase shifters change the output phase with a continuous signal, usually voltage. In turn, the control voltage determines the voltage range used to change the phase of the output signal. Digital phase shifters use a digital signal as the control element. The number of bits in this signal determines the number of steps in each phase change. If n equals the number of bits in the digital control signal, then the number of output states (phase changes) is 2n .

Performance specifications for RF phase shifters include frequency range, phase shift range, insertion loss, input voltage standing wave ratio (VSWR), and input power. Frequency range is measured in megahertz (MHz) and indicates the range of frequencies for which devices meet all guaranteed specifications. Phase shift range is measured in degrees and indicates the maximum phase shift that devices can produce. Common phase shift ranges are 90°, 180°, 270°, and 360°. Insertion loss, the measured power loss through the device, is calculated as the ratio of power output to power input. Typically, insertion loss is measured in decibels (dB). Input VSWR is a unitless ratio ranging from 1 to infinity that represents the amount of reflected energy at the input of the device. A value of 1 indicates that all of the energy passes. Any other value indicates that a portion of the energy is deflected. Measured in watts (W), input power is the maximum amount of power that can be applied to RF phase shifters without causing excessive heating.