I have been struggling to obtain the Bode plot of common-mode response of a filter. I first simulated it using LTspice, then I used a USB network analyzer. Both do not match each other and to the given plot of the filter.
Here is the general datasheet of the filter. The specific model I have is called FN2060-10-06. Below is the components parameters for this model:
And below shows the circuit diagram of this filter and the frequency response plots:
First I want to show how I simulated this circuit in LTspice and what Bode plots I have obtained:
Secondly, I used a USB network analyzer where it has the following pin-outs:
Above 1+ and 1- are differential input terminals for channel 1; 2+ and 2- are differential input terminals for channel 2. W1 is one of the signal generator output.
So I set Ch1 as the reference channel using this software and made the wiring between the filter and this USB network analyzer as below where 220 Ohm is to limit the current:
And the network analyzer plotted the following between 1Hz to 30 MegHz:
So something I'm doing is not correct because neither the simulation nor the network analyzer results do not match the datasheet at all. All I wanted was to find a simple method to obtain the common mode response of this filter. Does anybody have experience with such setup? If wrong, how can I correct the simulation and/or the network analyzer setup?