Here's another little board I quickly spun up and sent off to the fab tonight. It's just a really simple breakout board for the HMC431 VCO, which can just be used as a simple connectorised "building block" for rapid prototyping and quick, agile, flexible prototypes and experiments with further RF concepts I might play with in future.

I might also build similar building blocks such as MMIC amplifiers, mixer, LNA etc later. The key differentiating factor compared to existing connectorised modules and evaluation boards that you can get commercially from Hittite and Mini-Circuits etc is cost - they can be surprisingly high in price for what they are. For example the little Hittite HMC431 evaluation board costs 400 freaking dollars at Digi-Key - for a board essentially identical to the one shown below, with a $20 VCO chip and a pair of SMA connectors. And I think that huge difference in price is something valuable to address - but there is also merit in having a connectorised sub-board for each individual device, allowing re-usable prototyping of different designs, the agility to reconfigure new experiments, etc.

I'll just be using cheap, standard FR-4 instead of specialized RF substrates, but the RF loss in the dielectric isn't likely to be a huge dealbreaker.