RF 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.
There are several mounting styles for RF phase shifters. Surface mount technology (SMT) adds components to a printed circuit board (PCB) by soldering component leads or terminals to the top surface of the board. Through hole technology (THT) mounts components by inserting component leads through holes in the board and then soldering the leads in place on the opposite side of the board. Flat pack (FPAK) devices have flat leads and are available in a variety of body sizes and pin counts. Connectorized devices attach with coaxial or other types of connectors. Waveguide assemblies consist of a hollow metallic conductor with a rectangular or elliptical cross-section. Some conductors contain solid or gaseous dielectric materials.
RF phase shifters use several types of connectors. Bayonet Neil-Concelman (BNC) connectors are used in applications to 2 GHz. Threaded Neil-Concelman (TNC) connectors are similar in size to BNC connectors, but feature a threaded coupling nut for applications that require performance to 11 GHz. Miniature coaxial (MCX) connectors provide broadband capability through 6 GHz and are used in applications where weight and physical space are limited. Ultra high frequency (UHF) connectors are designed with non-constant impedance for use in comparatively low voltage and low frequency applications. Subminiature-A (SMA) connectors directly interface the cable dielectric without air gaps. Subminiature-B (SMB) connectors snap into place and are used for frequencies from DC to 4 GHz. Subminiature-P (SMP) connectors are rated to 40 GHz and, depending on detent type, can withstand from 100 to 100,000 interconnect cycles. Other connectors for RF phase shifters include MMCX, Mini-UHF, Type F, Type N, 1.6/5.6, and 7-16 connectors.