Problem in measuring the phase shift in VNA

[Dines]

We are implementing the below circuit as follows. We are giving M1 at 108 MHz and the splitting SUM 1 at 3 dB with 90 deg phase shift and SUM 1 at 3 dB with 0 degree.

At the input of SIG_MOD_1_I at 1.348 KHz with zero degree and the SIG_MOD_I_Q at 1.348 KHz with 90 degree phase. It is driving in to AD834AR (four quadrant multiplier).

We are trying to measure the phase difference in the Vector network analyzer at 6th pin (TCM4-6T) but we are getting constantly fluctuate phase or not stable to measure. In theoretically it should be same phase either 0 or 90 degree at the input of power divider (SBTC-2-10) to combine.

Kindly let us know how to measure the measure the phase at pin 6 from TCM4-6T and what output should expect ?

 

[FvM]

A standard VNA measures phase and magnitude of signals with it's internal generator as reference. It can't measure the phase of signals modulated by a second external signal or even being frequency shifted. More advanced signal anylyzers may be able to.

You can measure the multiplier output with VNA, if you DC couple the modulation input and apply constant DC level.

 

[BigBoss]

An oscilloscope can measure the phase differences between the signal, VNA is not necessary.
Why don't you use standard , cheaper IQ Modulator IC for that purpose ?
Like this

https://www.analog.com/en/products/ltc5598.html#product-overview

 

[biff44]

those four quadrant multipliers were a little funky to use, as i recall. there is a reason Analog Devices no longer produces that AD834 chip.

what are you trying to do? Are you trying to make a vector 360 degrees phase shifter? are you trying to make a SSB transmitter for a 1.3 KHz data signal? Maybe your circuit would make more sense if we know the intended function