RF Test Equipment Series: RF/Microwave Power Sensors and Power Meters (Wattmeters)

July 15, 2019

RF/microwave power sensors/meters, or wattmeters, are one of the simplest and most commonly used test instruments for diagnostics and repair of radio systems. These devices essentially extract a portion of the energy from an RF device or antenna, and using calibrated and traceable standards, present a power reading. RF Power sensors/meters are often used in the field to determine if radio transmitters are functioning at appropriate power levels, and more complex and sophisticated power analyzer systems are used for R&D and device characterization.

RF Power meters vary widely in the design and format, from simple in-line and analog wattmeters, to very sophisticated spectrum analyzer and power analyzer types. There are also several benchtop, handheld portable wattmeters with digital readouts, and even USB/Ethernet Power Meters that connect to a standard PC. Though many common power meters use coaxial interconnect, there are waveguide-based power sensors that operate at millimeter-wave frequencies.

The simplest form of power meters extract a small portion of RF energy from the transmission path, absorb this energy in a calibrated transducer, and provide a measurement of the overall signal power. For these instruments, the energy they measure is frequency independent within the operating range of the device. Moreover, these devices tend to provide some form of averaging, as the transducers don’t respond instantly to the variations in signal power. There are other types of power meters which use more responsive transducers and high-speed sampling techniques to provide better capture of the power envelope through the transmission medium. Moreover, there are many sophisticated power analyzer systems that measure power over a range of frequencies and time, providing metrology-grade measurement accuracy over a high dynamic range for R&D purposes.

Power sensors/meters are often either peak sensors, or average sensors. Meaning that some RF Power sensors will continuously capture the peak power passing through the transmission medium, while others will provide some type of averaging depending on the device and technology, such as thermocouple, thermistor, or diode power sensors. There are power sensors which are able to perform both functions, and these are called peak and average power sensors.

Most common power sensors are either connected in-line to the transmission medium, or are used as absorptive terminations. Power meters are often used to calibrate electromagnetic energy sources, and hence are commonly equipped with coaxial or waveguide interconnect. This being the case, interconnections between sensors and DUTs typically requires high precision and low loss cables or adapters.

RF/Microwave Power Meter Compatible Components and Accessories

Pasternack Waveguide Interconnect & Components

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