How loop antennas work

The loop antenna is very similar to the human body and has the functions of a common monopole or multi-pole antenna. The small size, high reliability
and low cost of the small loop antenna make it an ideal antenna for micro-miniature communication products. A typical loop antenna consists of an electrical loop composed of copper traces on a circuit board, or it may be a wire made into a loop. Its equivalent circuit is equivalent to two series resistors and an inductor in series (as shown in Figure 1). Rrad is the resistance model of the actual energy transmitted by the loop antenna, and the power it consumes is the transmission power of the circuit.

Assuming that the current flowing through the antenna loop is I, then the power consumed by Rrad, that is, the RF power is Pradiate=I2·Rrad. The resistance Rloss is the resistance model of the loop antenna consuming energy due to heat. The power it consumes is an inevitable energy loss, and its size is Ploss=I2·Rloss. If Rloss>Rrad, then the power loss is greater than the actual transmitted power, so the antenna is inefficient. The power consumed by the antenna is the sum of the transmitted power and the loss power. In fact, the design of the loop antenna can hardly control Ploss and Prad, because Ploss is determined by the conductivity of the conductor making the antenna and the size of the wire, while Prad is determined by the size of the area enclosed by the antenna.

Loop Antenna Equivalent Circuit