We have been developing a double size (8 times the volume!) 200mm square lower frequency RAM tile.... Taking 18 months to do, much of the work has been done by our toolmaking apprentices.
Initial sample look surprisingly flat, and the spike are sharp enough to be painful: Parts of this sort of structure breaks all of the rules of Injection mounting - where constant wall thickness are strongly desired, and gas can get trapped in the tips of the spikes.
Scaling our 100mm tile, we are hoping to get useful performance down to X-band..... Watch this space for Sxx measurement results.