Microwave signal transition between PCBs. SIW, castellation RF modules above 2.4 GHz

[Terminator3]

Is it possible to obtain low insertion loss in case of castellation PCB rf module LO output path transition? Or maybe use a pad and mimic RF surface mount RF IC? Currently I designed SIW transition, but pcb area used is a little too big - around 1x2 cm. S21 is good, an bandwidth is good, but any small gaps between PCBs worsens S11 alot. (-20dBm ideal, -7dBm with a narrow gap). I considered to solder SIW transition between boards, because there are a lot of vias which can absorb excessive solder paste. Then I thought about using castellated PCB transition, size is much smaller, kind of VIA transition style. But siw have advantage of filtering lower harmonics.

I tried to use thin enameled copper wire put in VIAs between PCBs, but think it is not optimal design, requires too much non-automated work, Also PCBs can "pop" and destroy wire connection. Enamael must be removed, etc. Coaxial connection is not very convenient too: hand work, good ground soldering, or metallic plate between PCBs to form coaxial outer metallic wall. Coaxial with metallic plate have better repeatability.

I search for some solution that would not require additional technological process. So PCBs could be connected with screws or soldered as modules with castellation. Multilayered PCBs considered, but currently is too expensive for me, especially if using good microwave substrate.

 

[FvM]

Via plugging is an industry standard process to avoid solder being drained off. If the vias are not in small pads, economic non-conductive plugging can be applied.