Then, I tried to implement it on pcb (RO3210), but its S21 response is really different from the results I have seen on momentum simulation. I expected some difference of course but I didn't expect such thing. What can be the reasons?
Try a Monte Carlo analysis on EM Sim , if possible.
I see a certain weakness in the "lonesome" ground vias connecting the ports. The ground pads are no low impedance ground, we can expect some crosstalk between the ports and an effect on S11/S22.
Can you describe it more? Do you mean soldering the coax gnd to the lower pcb and the inner conductor to the signal pad by drilling a via?The idea to use small semi rigid cable from the back side is great, this should give a much better transition from the coax to the PCB. Also, we don't need the bad ground pad with the lonely via then.
Yes, too far away from the port ground pads. The via distances are in a range where you can even get pretty resonances. One would expect a via fence around the square opening and particularly at the port ground pads.Still lack of vias?
Can you describe it more? Do you mean soldering the coax gnd to the lower pcb and the inner conductor to the signal pad by drilling a via?
The whole pcb is like this, https://obrazki.elektroda.pl/7856431500_1407956039.jpg
Still lack of vias?
I will put a photo with coaxes. It is like the gnd of coax is soldered on gnd pads, and inner conductor is soldered to the input and output pads of the filter. It is actually huge considering the filter size.
Thank you for all you for comments.
The whole pcb is like this, https://obrazki.elektroda.pl/7856431500_1407956039.jpg
Still lack of vias?
Can you describe it more? Do you mean soldering the coax gnd to the lower pcb and the inner conductor to the signal pad by drilling a via?
I will put a photo with coaxes. It is like the gnd of coax is soldered on gnd pads, and inner conductor is soldered to the input and output pads of the filter. It is actually huge considering the filter size.
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Can you also offer me some documents/books about these practical issues?
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