RF Power Measurement

Power Measurement in the RF and Microwave Range

Power measurement of high-frequency signals requires special techniques, which are usually realized with two possible basic systems:

• Combination of microwave power meter and measuring head (RF power sensor, designed for specific frequency ranges), which is connected to the meter by cable. The power sensor converts the microwave power into an analog voltage. It is converted into a power measurement value by the measuring instrument.
• RF power sensors with interface (USB or Ethernet/LAN). They generate a digital signal that is transmitted via interface to a PC, which then serves as the power measurement device.

The second, PC-connected technology with USB and Ethernet (power supply for the sensor via USB or PoE) is the more modern one. For power measurement, power sensors/transducers use different techniques depending on the type - the most common ones are thermal sensors or diode-based sensors.

RF Power Sensors with Thermal Sensors

• Are based on thermocouples or thermistors.
• Measure the heat rise resulting from the absorption of energy from RF or microwave signals in a load.
• Detect actual average power of signal, whether pulsed, CW, or modulated.
• Relatively linear.
• Fast response time.

Diode-based Power Sensors

• Diodes rectify incident microwave power.
• Diode provides output voltage proportional to incident RF power.
• Extremely fast response time.

RF/Microwave Power Measurement is Usually Done in Two Ways

• Average power meter: Actual average power of the signal, similar to a digital voltmeter.
• Peak and average power power: Envelope power of the signal over time, can make triggered measurements, similar to an oscilloscope. Often other measurements besides peak, average and peak-to-average power possible, for example automatic pulse measurements of a pulsed RF signal (pulse width, duty cycle, average pulse power, rise and fall time, pulse repetition rate, overshoot, etc.).

RF Power Sensor Applications

Power measurements in...

• ...mobile handset, base station, wireless backhaul, satellite components and calibration applications.
• ...manufacturing tests.
• ...long-range antenna test.
• ...field applications.
• ...satellite receiver tests.
• ...power amp chipset manufacturing test.
• ...satellite in-orbit-test (SED systems).
• ...TVAC test setup (thermal vacuum): Power measurements in in base station and satellite ground station application who required thermal vacuum compliance for minimal outgassing (requires special TVAC power sensor models from Keysight).