I'm highly skeptical of the 60% efficiency figure being any sort of end-to-end metric. I suspect that was poorly phrased, and the receiver/rectifier was operating at 60% efficiency (which is reasonable for RF rectifiers), of power incident. But the vast majority of power loss is happening along the path before reaching the receiver.
Some ballpark numbers: 1km at 10GHz is ~110dB of path loss. Those look like feasibly 40dBi antennas at both ends. That still leaves -30dB link budget, i.e. 0.1% of energy reaching the target.
Some ballpark numbers: 1km at 10GHz is ~110dB of path loss. Those look like feasibly 40dBi antennas at both ends. That still leaves -30dB link budget, i.e. 0.1% of energy reaching the target.