What is the RF design of a wireless charging system using focused microwave beams?

The RF design of a wireless charging system using focused microwave beams transmits power from a transmitter to a receiver over distances of 1-100+ meters using a directional microwave beam, achieving higher efficiency than radiating power omnidirectionally. The system consists of: a transmitter (a high-power RF source (magnetron, klystron, or solid-state GaN amplifier) generating a continuous or pulsed microwave signal at 2.45 GHz, 5.8 GHz, or 24 GHz (ISM bands); the power level ranges from 1 W (for short-range device charging) to kilowatts or megawatts (for long-range power beaming); the transmitter feeds a directive antenna or phased array that focuses the beam toward the receiver), a transmit antenna (a phased array or reflector antenna that creates a focused beam aimed at the receiver; for near-field power transfer (receiver within the antenna's near-field, distance less than D^2/lambda): the beam can be focused to a spot smaller than the antenna aperture, achieving high power density at the receiver; for far-field transfer: the beam diverges as lambda/D (antenna diffraction limit)), a free-space path (the microwave beam propagates through the air; atmospheric attenuation at 2.45 GHz is less than 0.01 dB/km (negligible); at 5.8 GHz: approximately 0.02 dB/km; at 24 GHz: approximately 0.1 dB/km; rain attenuation can be significant above 10 GHz), and a receiver (a rectenna array that converts the incident microwave power to DC (see rectenna design); the rectenna's area determines how much of the beam power is intercepted; efficiency: greater than 80% for high-power rectennas at 2.45 GHz).