RF Waveguide Phase Shifters

RF waveguide phase shifters are two-port waveguide modules that alter the phase of an output signal in response to an external signal. They are made of aluminum, brass, bronze, copper or silver waveguides and have rectangular, circular, or elliptical cross sections. There are two basic types of RF waveguide phase shifters. Analog phase shifters use an analog signal, usually voltage, to change a signal’s output phase. By contrast, digital phase shifters use a digital signal that consists of two discrete stages. For both types of devices, phase shift change is the most important specification to consider. Typically, RF waveguide phase shifters can change the phase of an input signal from a minimum of 0° to a maximum of 90°, 180°, 270°, or 360°. Variable devices apply a variable control signal and used mainly in digital products.  

RF waveguide phase shifters use flanges to connect waveguide sections or terminate waveguide components. Most flanges are square, circular, or rectangular in shape and plated with cadmium, nickel, rhodium, silver, or tin. Union guide (UG) is the military standard MIL-DTL-3922 for a range of flange types. Cover or plate flanges are flat, square UG-style flanges. Choke flanges are UG-style devices with an O-ring groove and choke cavity. They are often used to minimize the effects of flange discontinuity. Connector pressurized rectangular (CPR) flanges meet Electronic Industry Association (EIA) specifications and are used in many non-military applications. CPR variants include miniature (CMR), grooved (CPRG), and flat (CPRF) flanges. Mill-back flanges are made with the opening of the flange face equal in size to the inside of the waveguide, which is soldered into a larger milled opening at the rear of the flange.   

Performance specifications for RF waveguide phase shifters include operating frequency range, EIA waveguide size, length or height, insertion loss, average power, and voltage standing wave ratio. Operating frequency range is the range for which RF waveguide phase shifters meet all guaranteed specifications. EIA waveguide sizes have a prefix of WR and indicate the widest inside dimension of the waveguide in hundredths of an inch. For example, WR650 is 6.50 in. wide, WR90 is 0.90 in. wide, and WR75 is 0.75 in. wide. Length or height is also measured in inches. Insertion loss is the measured in decibels (dB) and defined as the ratio of power output to power input. Average power is measured in watts (w). Voltage standing wave ratio (VSWR) is a unit-less ratio ranging from 1 to infinity that expresses the amount of reflected energy at the input or output of the device. A value of one indicates that all energy passes. Any other value indicates that a portion of the energy is reflected.

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