Steering the Focus: Programmable Phase Shifters

Posted on Wednesday, October 05, 2016
By Scott Blanchard

Phase shifters are used in countless applications, with one of the most popular being phased array antennas. These antennas do not require a gimbal to keep the beam stabilized. Without this technology the antenna and/or satellite would have to physically adjust itself in three dimensions to simply stay on target—which can prove to be a difficult task, especially where some applications require accuracy within a fraction of a degree. Instead, beams are formed by shifting the phase of the signal emitted from each radiating element in the structure. This provides interference to steer the beams in the desired direction. Phase array antennas have been primarily used in military radar platforms, however, this technology has recently been adapted for a few commercial satellite applications, including satellite television on planes and in vehicles such as RVs, as well as general mobile data-intensive applications that require fast downloading and uploading capabilities. This type of commercial satellite technology also enables automated highway system platforms such as intelligent cruise control, collision avoidance radar, and electronic tolling. On average, phase shifters account for around 40% of phase array antenna technology.

 

The Choices in Phase Shifters

Phase shifters are RF components that use a control to output a varying insertion phase (S21()) which is the change in phase of a signal as it propagates through a transmission line &ndash often measured in degrees or radians. Phase shifters are created to provide variable insertion phase without changing the path length and can be controlled electrically, magnetically or mechanically.

 

These devices can operate passively or actively, where the passive components have attenuation from input to output and the active components have a gain associated with them. Analog phase shifters provide a continuously variable delay, while digital phase shifters work in discrete increments. 

 

The controlling elements leveraged in phase shifters vary depending on the application. For instance, in high-speed applications, semiconductor devices, such as PIN, Schottky and Varactor diodes are leveraged as they offer a faster switching time. In applications that require high power handling at the expense of switching speed, ferrites are typically employed.

 

Phase Shifter Type Control Type Controlling Element Materials Material Pros Material Cons
Analog Electrical Semiconductor:
  • Varactor Diode
  • PIN Diode
  • Schottky Diode
  • Silicon
  • Gallium Arsenide (GaAs)
  • Low Loss
  • Fast Response Speeds from Control
Limited Power Handling
Ferrite Ferroelectric Materials:
  • Barium Strontium Titanate (BST)
  • Yttrium Iron Garnet
  • Low Loss
  • High Power Handling
  • Slow Response Speeds from Control
  • High Power Consumption
Digital Digital Micro-Electro Mechanical Systems (MEMS) Silicon
  • Fast Response Speeds from Control
  • Small Size
  • Low Current
  • Low Loss
  • High Losses at high frequencies
  • Limited power-handling
  • High Production Cost & Limited Yield
Monolithic Microwave Integrated Circuit (MMIC) Gallium Arsenide (GaAs)
  • Fast Response Speeds from Control
  • Low Current
  • Small Size
  • Limited power-handling
  • Expensive to manufacture
  • High Loss
PIN Diode
  • Silicon
  • Gallium Arsenide (GaAs)
  • Low Loss at High Frequency
  • Commercially Available
Limited Power Handling

*Note: Table above ignores analog phase shifter technology that is mechanically controlled.

 

The typical parameters phase shifters are designed around are frequency range, attenuation or gain, switching time, power handling and accuracy/resolution. The controlling elements are arranged to provide the optimal output given the design specifications. There are also several design topologies of phase shifters that are leveraged towards optimizing particular parameters. Some of these designs include: Switched Network, Switched Line, Hybrid Coupled, Switched Path, High-Pass/Low-Pass, Loaded-Line, and Switched Filter designs. 

 

Vaunix Lab Brick Phase Shifters

Vaunix phase shifters offer 360-degree phase control with 1 degree phase resolution. The maximum switching time is 10us with a typical insertion loss of 5 dB and a maximum of 7 dB. All Vaunix Lab Bricks are controlled and powered through the USB port of your computer. The PC-driven capabilities, along with the small portable size, make this phase shifter a desirable option for certain test bench set ups, both in the lab and on the go. The software offers a simplified graphical user interface (GUI) for automated phase sweeps, or allows for a more easily controlled phase angle output.

Digital phase shifters are typically controlled and programmed over GPIB. This type of interface can come with the challenge of specialized programming and involved rigging for complex automated test equipment (ATE), which can be especially involved since many phase shifters are controlled with transistor-transistor logic (TTL) where troubleshooting test systems can involve a balancing act of tracking discrete bits of input to the phase shifter. USB power and control have the benefits of automated detection from the PC/laptop and much higher data rates making it a desirable alternative. USB also allows for each phase shifter to have a specific serial number, which allows for multiple phase shifters to be controlled over one USB simultaneously, simplifying the troubleshooting of the automated test system.

 

The Lab Brick Phase Shifters come in four different models with four different frequency ranges of 1-2 GHz, 2-4 GHz, 4-8 GHz, and 8-12 GHz. Prices range from $755 to $885 and are priced according the to frequency range of interest. Vaunix phase shifters are composed entirely of solid-state components with no mechanical parts to wear out, extending the operating lifetime and reliability of these components. Vaunix also has the ability to customize the phase shifter according to certain customer specifications.

 

Ease of Use

All phase shifters are calibrated in house at Vaunix to operate at their peak performance once shipped to the customer. Vaunix phase shifter Lab Bricks come with preconfigured user-friendly software for “plug and play” capability. The phase sweeps can also be customized by configuring the dwell time, idle time, and phase sweep to vary the phases in specified order. This can be done by creating text file (.txt) or profile file (.prf) and loading it through the “File” then “Load” option in the GUI. Each phase shifter stores settings in internal memory to allow the devices to power up in a specific phase state. These products have been used for a variety of tests, including beam forming for phased antenna array systems, signal cancellation, phase modulators and multiple-input and multiple-output (MIMO) test platforms for LTE and WiFi. Vaunix readily answers questions presented by the various customers in regards to their test components, visit our Q&A blog series to see some of these questions and the offered solutions.

Vaunix Phase Shifter Lab Brick
GUI Functions Description Units
Frequency Frequency Point of Interest MHz
Phase Shift Step Size Increments of Phase Shifting: 1 deg, 10 deg, 90 deg, Other: Degrees
Phase Shift Customizable Phase Shift Step Size Degrees
Dwell Time The period between each step ms
Idle Time The time between repeating steps ms
Bidirectional Sweep Enables a bidirectional sweep (start to finish then finish to start again)  
"Bidirectional" Dwell Time The period between each step on the return sweep in bidirectional sweep mode. ms
"Bidirectional" Hold Time Time of pause after a bidirectional sweep is completed ms
One Time Sweeps only once  
Repeats Repeats sweep  
Stop Halts the sweeps  
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