I am not sure what senso is going to do after all. Perhaps it make sense to make small 4 layer breakout board and solder it on top of 2 layer if going 4 layer for entire design is not justified.
When people say "popper equipment" I wonder what do they mean specifically in cases like this? Thing is so tiny. Suppose I have 6GHz VNA and want to "tune it". How do I even approach measuring/tuning it? I sometimes solder pieces of RG405 with SMA connectors at other end right to the track, but here even that won't fit well.
Whoever has the "proper equipment" how exactly do you guys do it in cases like this? Please share. Even few photos would mean a lot.
Other guys who do this for a living have commented about using products like Sonnet to model the circuit using the s-param files published by the component manufacturers. The free lite version of Sonnet doesn't allow this which is a shame as it would be perfect.
(You can download the s-param model for the antenna from the Johanson website.)
There are quite a few free options which may be able to do it, like Qucs, openEMS, Z0lver,.... I can't comment on them as I have not used them.
One other point that hasn't been mentioned yet - the differential traces into the balun should both be the same length. Probably not a big enough mismatch to matter though.
I don't see any reason why a 4 layer board is _required_ for this.
FWIW, simulating the current board with a free simulator is the approach you could take without any test gear. Then build it and test it and tweak it and repeat...