Circular antenna

　　Circular antennas are very similar to the human body, with ordinary monopole or multi-stage antenna functions. In addition, the small size and high reliability of the small circular antenna

　　And low cost makes it an ideal antenna for miniaturized communication products. A typical circular antenna is composed of an electrical circuit consisting of copper wires on a circuit board, or it may be a section of wire made into a circular shape. 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 energy emitted by a circular antenna, and the power it consumes is the transmission power of the circuit.

　　Assuming the current flowing through the antenna circuit is I, the power consumption of Rrad, i.e. RF power, is Pradiate=I2 · Rrad. The resistance Rloss is a resistance model of the energy consumption of a circular antenna due to heat generation, and the power it consumes is an inevitable energy loss, with a magnitude of Ploss=I2 · Rloss. If Rloss>Rrad, then the power loss is greater than the actual transmitted power, so this antenna is inefficient. The power consumed by an antenna is the sum of the transmission power and the loss power. In fact, the design of a circular antenna can hardly control Ploss and Prad, as Ploss is determined by the conductivity of the conductor used to make the antenna and the size of the wire, while Prad is determined by the size of the area enclosed by the antenna.