Method and system for testing device under test (dut) over long distance

A system for testing a device under test (DUT) over a long distance, the system comprising:

• (i) a first vector network analyzer (VNA), comprising:
• a signal generator configured to generate a radio frequency (RF) signal at an RF frequency;
• and
• a first reference clock configured to provide a first reference signal at a first reference frequency to at least the signal generator;
• (ii) a second VNA configured to receive and measure the RF signal from the first VNA via the DUT, the second VNA comprising:
• a second local oscillator (LO) configured to generate a second LO signal having a second LO frequency;
• a second mixer configured to mix the measured RF signal and the second LO signal to output a second intermediate frequency (IF) signal;
• a second analog to digital converter (ADC) configured to digitize the second IF signal;
• a resampler configured to resample the digitized second IF signal;
• and
• a second reference clock configured to provide a second reference signal to at least the second LO and the second ADC, wherein the second reference clock operates independently of the first reference clock;
• and
• (iii) a processing unit programmed to:
• determine a reference error ratio between the first reference clock and the second reference clock;
• and
• adjust the second LO frequency at the second LO to a corrected second LO frequency by applying the reference error ratio to a desired second LO frequency,
• wherein the second mixer is further configured to mix the measured RF signal and the second LO signal at the corrected second LO frequency to output the second IF signal, and
• wherein the resampler is configured to resample the digitized second IF signal at an adjusted sample rate to output a corrected second IF signal corrected for the reference error ratio, such that the second VNA appears to use the second reference signal at a second reference frequency equal to a first reference frequency of the first reference signal without adjustments having been made to the first reference clock or the second reference clock.

A method of synchronizing a first vector network analyzer (VNA) and a second VNA for testing a device under test (DUT) over a long distance, wherein the first VNA includes a first local oscillator (LO) for generating a first LO signal having a first LO frequency and a first analog to digital converter (ADC), wherein the second VNA includes a second LO for generating a second LO signal having a second LO frequency and a second ADC, and wherein the first VNA and the second VNA do not share a reference clock or a trigger signal, the method comprising:

• receiving and measuring at the second VNA a radio frequency (RF) signal from the first VNA, wherein the RF signal is a continuous wave (CW) signal;
• mixing the measured RF signal and the second LO signal at the second VNA to output a second intermediate frequency (IF) signal to the second ADC, wherein the second IF signal has a second IF frequency;
• determining a reference error ratio between a first reference clock and a second reference clock, wherein the first reference clock is configured to provide first reference signals to at least the first LO and the first ADC, and the second reference clock is configured to provide second reference signals to at least the second LO and the second ADC;
• adjusting the second LO frequency at the second LO to a corrected second LO frequency by applying the reference error ratio to a desired second LO frequency;
• mixing the measured RF signal and the second LO signal at the corrected second LO frequency to output the second IF signal;
• digitizing the second IF signal;
• and
• resampling the digitized second IF signal at an adjusted sample rate to output a corrected second IF signal corrected for the reference error ratio,
• wherein the second VNA appears to be operating with the second reference signal at a second reference frequency equal to a first reference frequency of the first reference signal without adjustments having been made to the first reference clock or the second reference clock.