mmWave Measurements with a Low Frequency VNA
Using the right equipment for the right measurement is crucial to getting accurate results. Precision millimeter-wave (mmWave) measurements normally require a VNA with built-in capability, or mmWave extenders to augment the frequency range. This equipment may be used to evaluate mmWave mixers, which are commonly used to up-convert or down-convert 5G signals back and forth from baseband frequencies.
The CobaltFx mmWave frequency extenders operate in conjunction with a Copper Mountain Technologies 9 or 20 GHz Cobalt series VNA. The S5243 Compact VNA supports measurements from 10 MHz to 44 GHz with 2.4mm NMD connectors, which can be used to make measurements without an extender. Brian discusses using a lower frequency VNA to perform mmWave mixer measurements using two mixers driving the base-band ports. He goes over the use of the image filter, how the reference mixer is characterized, the creation of de-embedding data, and introduces example measurements. He then covers measurement accuracy, along with a practical demonstration of the concepts discussed.
This video demonstrates vector mixer calibration to evaluate an mmWave mixer. The expectation of error on conversion loss measurements of a MUT (mixer under test) is approximated from the formula, which is then used to create the reference mixer de-embedding file. Conversion loss of the reference mixer should be 10 dB or less to measure the conversion loss of the MUT with reasonable accuracy, as conversion loss above 16 dB or so would give poor results. The device used in the practical demonstration is the S5065 6.5 GHz VNA, along with a 2520 2-port 20 GHz ACM (automatic calibration module).