The upper bound on the amount of heat that can be radiated per unit area of the antenna and the efficiency of the microwave generator then determine how much microwave power can be radiated per unit area of the transmitting antenna. These relationships are shown in Figure 3 where contours of radiated microwave power density are shown as a function of efficiency and radiating temperature. The relationships in Figure 3 assume an emissivity of unity (black body radiation) and radiation into a 0 degree Kelvin environment. The radiated microwave power density is very sensitive to efficiency. If there is an upper bound to the radiated heat density, then a conversion efficiency from DC power to microwave power of 80% will produce four times the radiated microwave power density as operation at 50% efficiency. And operation at 90% efficiency, a distinct possibility at 2.45 GHz and already achieved at 890 MHz, will produce nine times as much power output as operation at 50% efficiency [3], In addition, the radiated microwave power density is sensitive to the temperature at which waste heat is radiated. A device operating its allowable heat disposal area at 300 degrees
RkJQdWJsaXNoZXIy MTU5NjU0Mg==