mmWave noise figure considerations were briefly covered earlier, in the receiver offset section. As loops are not available in the mmWave modules (usually), the 3744A-Rx module was created that is receive-only and does not have a coupler, so the noise figure is roughly equivalent to that of the loop access ports on the base MS464XX VNA. This Rx module is normally connected in place of the port 2 module for noise figure measurements and the same (conceptually) pre-amp filter combinations in front of this module are required for all but the highest gain DUTs.

One complication relates to the power calibrations done as a precursor to the receiver calibration. The noise receiver (with all of the added gain) will compress at a relatively low power level and mmWave power sensors with range below about -25 or -30 dBm are often not available. For this reason, the receiver offset discussed earlier in this chapter is available. There are cases when the accuracy of this approach is not enough because of the harmonic content of the source leading the power sensor concept of integrated power differing from the heterodyned tuned power measured by the receiver (note that the PowerMaster series of USB sensors are also heterodyne-based and do not suffer from this problem). A more advanced version of the receiver offset process is discussed in the Application Note “Procedure for a Higher Accuracy Receiver Calibration for Use in mmWave Noise Figure Measurements” (11410-00878) that can help correct for harmonic contributions.