I guarantee you that these rectennas will not work if their temperature is equal to that of the source radiation, and that they will generate waste heat which h

I guarantee you that these rectennas will not work if their temperature is equal to that of the source radiation, and that they will generate waste heat which has to be removed. As for slaves to the Carnot cycle, no one has ever built a Carnot cycle; it is merely an ideal which these rectennas might help us approach more closely.