How to use these SMA connectors?

[Andrey_irk]

It is supposed to go into a milled enclosure with a wall thickness equal to the length of the PTFE insulator. The center conductor lands directly on a 50 Ohm PCB stripline.
If everything is made precisely, this could have an VSWR of 1.2 or less up to 18GHz.

I've just modeled the transition in CST just to illustrate my point better (some of the people don't get it by the looks of it).
There is a rear part of the connector with the dimentions from the drawing (first post), then the center pin goes onto a pcb. There are two simulations with two different PCBs. The substrate material is Rogers RT5880 (it is basically PTFE) in both cases. The thickness of the first board is 0.254mm, of the second board - 0.508mm. Microstrip widths are 0.77mm and 1.56mm accordingly.
The results show significant capacitive discontinuity (as to be expected, see TDR plots). In the second simulation it is significantly smaller due to wide microstrip.  Although it is possible to further compensate the second transition by narrowing down the microstrip under the pin, it is not much one can do to get even 1.3 VSWR in the first case. If, however, we choose a substrate with higher dielectric constant (in case of, say, RO4003 or 4350) then the track width will be even more narrow thus making the problem even bigger. Imagine what happens if the substrate E is as high as 10.

The background material of the model is PEC, there is some air over the PCB (there is a hidden cube made of vacuum) and the upper boundary is open, the others are conductive.

Am I missing something? How would you compensate the transition in the first case?

Have you tried removing some of the ground plane under the transition/pin? I haven't read the thread fully but if I understand correctly that you are trying to optimise the coax to microstrip transition then that might help.

Just removing the gound plane won't help much as the PCB is supposed to be soldered on a metal surface. But if I remove the ground and create a cavity under it  - this might work. I'll give it a try!
Although this approach may add some problems during the assembly process (you need a good contact between the PCB and the enclosure and it is hard to make sure the solder doesn't get into the cavity).

[Andrey_irk]

Coaxial to microstrip transitions should allways be carefully simulated. Sometimes you place a small gap between the pin dielectric and PCB edge for stray capacitance compensation.

Is not something the connector manufacturer can do for you, as there are too many variables.

I'm not asking them to enumerate every possible configuration or detail.  I just want them to tell me the test conditions under which their performance numbers were measured.  If they don't want to do that I think they shouldn't put VSWR in the datasheet at all -- I think that is dishonest.

I bet they dont take the coaxial to microstrip transition into account in their specs. It's probably just the VSWR and loss of the coaxial structure.

I'm aware of this actually. Nevertheless, how would you connect together the ones from my first post achieving good VSWR? Tricky, huh? And wil it have anything to do with reality?

[ejeffrey]

Coaxial to microstrip transitions should allways be carefully simulated. Sometimes you place a small gap between the pin dielectric and PCB edge for stray capacitance compensation.

Is not something the connector manufacturer can do for you, as there are too many variables.

I'm not asking them to enumerate every possible configuration or detail.  I just want them to tell me the test conditions under which their performance numbers were measured.  If they don't want to do that I think they shouldn't put VSWR in the datasheet at all -- I think that is dishonest.

I bet they dont take the coaxial to microstrip transition into account in their specs. It's probably just the VSWR and loss of the coaxial structure.

How would they measure that?  And why would I care about that?