It wouldn't help. Focusing requires a concave surface, and the inside of the sphere is the only concave bit. Coating the outside would create an omnidirectional

It wouldn't help. Focusing requires a concave surface, and the inside of the sphere is the only concave bit. Coating the outside would create an omnidirectional reflector, but it'd be super low-gain. We actually tried exactly this with Project Echo. https://en.wikipedia.org/wiki/Project_Echo https://en.wikipedia.org/wiki/Project_Echo Also, "one-way reflectance" is largely a myth. One-way mirrors in police stations and stores are actually just partially reflective mirrors with a dark room on one side. A true one-way reflector would involve an optical circulator, which tends to be a small, sensitive, expensive component, not something you can coat over a flexible surface. https://en.wikipedia.org/wiki/Optical_circulator https://en.wikipedia.org/wiki/Optical_circulator Lastly, the main advantage is cost and simplicity. Phased arrays use fancy semiconductors. This gives you a lot of features and benefits, but comes at significant cost. This antenna is more or less a Mylar party balloon, it would not surprised me if it's orders of magnitudes cheaper.