rf launch pin
I notice on sample demo boards you get from the likes of Hittite, they always have a large pad where the edge mount SMA is soldered. Way bigger that the (usually) CPWG line.
I'm assuming this is to reduce discontinuties, and to match the soldered pin to the 50ohm line.
Can I model this in microwave office (MWO-100) to calculate what size launch pads I need on my boards?
Or is there an online reference doc I can read up on it in?
I have seen the footprints you are discussing on Hittite demo boards. I suspect that they were experimentally determined.
Getting a footprint to match a particular connector is a challenge. The connector suppliers usually do not make recommendations, claiming that there are just too many variables in the various PCB's, thickness, dielectric, trace dimensions, plating, frequency, performance requirements, and the list goes on.
I generally use HFSS to model the connector interface and PCB footprint. I suspect that you could get similar results from other software. The next step is to build a set of coupons to confirm the simulation's results. The goal here is working hardware. Getting things working still often includes some time with copper tape and a sharp knife.
I have found reference material to be relatively sparse in this area. I suspect it is because each application is very specific and unique.
The odd thing is that this "launch pad" is not common among various vendors and in fact you may see them on one Hitite ref, board yet another from them doesn't have the same approach and may in fact launch directly off of the pin, however universally, all of the vendors seem to favor using a vertical mount connector adapted to edge launch rather than using an connector designed for the application.
SiGiNT
I liked the comment about using the wrong connector above. That happens all the time (and of course, I would never do that). Below 2 GHz things are relatively forgiving, above that it gets dicey. If you are working in X or Ku or higher the fine grain details are significant.