Antennas
An antenna is a device designed to accept RF power from a transmitter and radiate it into its surroundings, or alternatively to extract energy from a passing radio wave and deliver it to a receiver. Considering transmitting first, an antenna is ideally designed to present a resistive load Rt = Rr + R1 (a pure resistance equal to the design load impedance of the transmitter, usually 50 Ω, if perfectly tuned and matched) and it is to this resistance that the transmitter delivers power. If the antenna is also loss-free, all the power delivered to it goes into the radiation resistance Rr and is radiated; if not, a proportion of it is converted into heat in the antenna’s loss resistance R1. The efficiency η of an antenna is given by η ...
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