Waveguide Power Sensor (26.5 GHz to 40 GHz)
The Keysight R8486D and Keysight Q8486D are diode power sensors. They measure power levels in a range from –70 dBm to –20 dBm (0.1 nW to 10 μW).
The power sensors measure the power dissipated in a 50 Ω load place on the microwave source. The power is determined from the AC voltage developed across the 50 Ω load. The diodes convert this AC voltage to DC. The DC voltage produced is the square of the AC voltage. This low-level DC voltage requires amplification before it can be transferred on standard cables to the power meter.
The amplification is provided by an input amplifier assembly which consists of a chopper (sampling gate) and an input amplifier. The DC voltage is routed to the chopper circuit which converts the low-level DC voltage to an AC voltage. The chopper is driven by a 220 Hz square wave generated by the power meter. The result is an AC output signal proportional to the DC input. The AC signal is then amplified by the input amplifier. The relatively high-level AC signal output can now be routed by standard cables.
In application, the power sensors are connected between a microwave source and a compatible power meter. The power sensors provide a matched load to the microwave source for very low SWR. The power meter indicates the power dissipated in the load in μW, nW or in dBm.
Included with each power sensor is the Keysight 11708A 30 dB reference attenuator. To calibrate the power sensors, the reference attenuator must be used to reduce the 1 mW calibration signal provided by the power meter to 1 μW. Also included is a hex ball driver plus the waveguide mounting screws.