Electronic – How to know the phase shift or phase delay of the SMA connector and RF port

connectorphasephase shift

I am now doing a project to measure the phase difference in my circuit. Figure 1 is my circuit. My target is to know the phase difference between the output of the DAC and the input of the ADC. I have known the phase of the output of the DAC, phase shift of the analogue circuit and that the modulator has no phase shift. And the output signals from the DAC is lower than 20kHz.

My questions are:

what phase shift would the SMA connector cause normally?(SMA connector is 5-1814400-1 from TE connectivity) And

How about the RF port? What phase shift would it cause?

Does anyone have idea about my questions or idea about how can I solve the problems?
(I will try my best to update all information in need)

Thank you very much!

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1.

More information:

The cable between the SMA and RF port is about 30cm long. But I can`t find any more detail about it. The modulator and analogue circuit are connected through fibre and PD. The analogue circuit, SMA connector and MCU are inside one PCB board.

Best Answer

At 20 kHz, the phase shift of the SMA connector is negligible. The length of the signal path is maybe 5 mm. The dielectric constant of the PTFE (Teflon) material in the SMA connector is about 2.0. So the delay through the connector is about 23 ps. That's about 20 microradians of phase delay at 20 kHz.

Even at higher frequencies, the delay through the SMA connector is probably quite small compared to the delay through the cable that's connected to the connector, which you've said nothing about.

If you were working at a higher frequency where 20 ps made a difference, then you'd have a problem. Because the delay induced by a connector like this depends on the footprint on the PCB where you mount it as well as the construction of the connector itself. And because the two sides of the connector aren't the same type of waveguide.

The best way to determine the characteristics of the connector would probably be to build two additional "test coupons" onto your pcb. Each coupon would be a length of trace with a connector on each end. The two traces would be different lengths. By measuring the S-parameters of the two coupons with a network analyzer, you'd have enough information to cancel out the affect of the traces and determine the characteristics of the connector.