RF Test Equipment Series: Programmable Phase Shifters

Aug. 5, 2019

Controlling the phase of RF/microwave signals is an essential aspect of most modern communications, radar, and testing applications. Phase adjustments can be used to create a variety of effects, including combining, subtracting, and aligning signals, as well as part of phased-array antenna technology. Moreover, phase variations in a radar response can be used to distinguish important characteristics of a radar target. Hence, there is a need during testing and for deployed systems for phase shifting hardware.

A key instrument for prototyping, testing, and deployed systems is the programmable phase shifter.

There are several types of phase shifter technologies. These include mechanically or electrical phase shifting. Mechanical phase shifter is done by physically manipulating structures within the phase shifter to cause a delay, such as changing the length of a transmission line. Electrically controlled phase shifters can be implemented with a variety of electronic technologies, including varactor diodes, Schottky diodes, PIN diodes, switched filters, or other active electronic methods.

A programmable phase shifter is a phase shifter that can be digitally programmed (via parallel or serial communications) or even computer controlled. Typically, phase shifters are either bench-top instruments, rack-mountable instruments for automated-test equipment (ATE) applications, or connectorized modules that can be integrated inline to a testing or hardware system. Recent advancements have also led to compact surface mount package phase shifters that are more readily integrated into dense and complex devices, such as phased-array antenna transmit-receive (TR) modules. The programming cable for these devices can be as simple as an SPI interconnect, GPIO, RS-232, Ethernet, TTL, or even USB.

Generally, the critical parameters for a programmable phase shifter, are switching speed, phase control range, frequency range, phase resolution, phase flatness, insertion loss, power-handling, phase noise, VSWR, and noise figure. These factors are largely influenced by the specific phase shifter technology as well as the packaging/housing for the device.

As programmable phase shifters may be bench-top, rack-mount, in-line connectorized, or surface mount components, there is a wide range of interconnect, both coaxial and waveguide, that may be used with these devices. This includes coaxial cable assemblies, waveguide interconnect, and coaxial/waveguide adapters. Moreover, a programmable phase shifter is often used alongside a variable attenuator to either create modulation or to manipulate the antenna pattern of a beam steerable antenna.

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