Antenna Fundamentals

We shall discuss here only the fundamental concepts needed to understand the role of an antenna as a power-coupling element of a system. Figure illustrates the elements of a communication

system that involves antennas (with no conductors in the propagation medium) and the following nomenclature:

P_t Power generated by the transmitter

L_t, L_r Transmitting-path loss (representing the power reduction caused by the transmission line or waveguide that connects to the transmitting antenna) and receiving-path loss

L_ta, L_ra Transmitting antenna loss and receiving antenna loss

R Distance of separation between the antennas

S Signal power available at the lossless antenna output

S_r Signal power available at the receiver input

Radio transmission consists of antennas at the source and at the destination. It requires the signal to be modulated on a high-frequency carrier, which usually is a sinusoid. Driven by an appropriate carrier, the transmitting antenna launches an electromagnetic wave that propagates through space without the help of a transmission line. A portion of the radiated power is collected at the receiving antenna.