Mixer measurements with a Vector Network Analyzer
February 27, 2023
Mixers are typically 3-port devices that produce the sum or difference of two input frequencies. Most of the mixers are active ones require external power supply. But there are also passive mixers like audio mixer that doesn’t require any power because it doesn’t have an amplifier.
A typical mixer is shown in Figure 1, the RF and LO are two input signals, while the output is IF. The relationships of their frequencies are as follows.
fout = fin + fLO (1-1)
or fout = fin– fLO (1-2)
For example, if we have fin = 1 GHz, fLO = 500 MHz, then fout = 1.5 GHz or 500 MHz.
Engineers often need to evaluate mixer performance, including conversion loss, phase and group delay, the 1 dB compensation point, isolation between ports and port VSWR. Phase and group delay can be measured with a VNA equipped with Vector Mixer Measurement function. While the others can be achieved with Scalar Mixer Measurement function. In this application note, we give brief introduction about scalar measurements.