Antenna Selection Guide

　　Brief Antenna Theory The antenna is a key component for reaching the maximum distance in a wireless communication system. The purpose of an antenna is to transform electrical signals into RF electromagnetic waves， propagating into free space （transmit mode） and to transform RF electromagnetic waves into electrical signals （receive mode）。

　　A typical antenna is basically an air core inductor of defined wavelength. As can be seen in Figure 2， the AC current through an inductor lags the voltage by 90 degrees so the maximum power is delivered at ¼ wavelength. The λ/2 dipole produces most power at the ends of the antenna with little power in the centre of the antenna. 3.1 Dipole （λ/2） Antennas A dipole antenna most commonly refers to a half-wavelength （λ/2）。 Figure 3 shows the typical emission pattern from a dipole antenna. The antenna is standing in the Z plane and radiating energy outwards. The strongest energy is radiated outward in the XY plane， perpendicular to the antenna.