The loop antenna is very similar to the human body and has the function of a common monopole or multistage antenna. Coupled with the small size and high reliability of the small loop antenna.
And is an ideal antenna for micro communication products. A typical loop antenna consists of an electrical loop consisting of copper traces on a circuit board, or it can be a piece of wire that is made into a loop. Its equivalent circuit is equivalent to the series connection of two series resistors and an inductor (as shown in figure 1). Rrad is a resistance model of the actual transmitting energy of the loop antenna, and the power it consumes is the transmitting power of the circuit.
Assuming that the current flowing through the antenna loop is I, then the power consumed by Rrad, that is, RF power, is Pradiate=I2 Rrad. Resistance Rloss is a resistance model of loop antenna, which consumes energy due to heating. The power it consumes is an inevitable energy loss, and its size is PLOSS = I2 RLOSS. If Rloss & gtRrad, the lost power is greater than the actual transmitted power, so this antenna is inefficient. The power consumed by the antenna is the sum of the transmitted power and the lost power. In fact, it is difficult to control Ploss and Prad in the design of loop antenna, because Ploss is determined by the conductivity of conductor and the size of wire, while Prad is determined by the area surrounded by antenna.