Owing to the increasing use of a variety of wireless networks, gauging antenna performance has become something of a black art. In general, however, antennas are still characterized by basic parameters like efficiency and gain. Operating-frequency range also must be considered. For certain antennas, the operating frequency partially determines the choice of material for the antenna. In a five-page white paper titled, "Radiated Efficiency: A True Measure of Antenna Performance," Pulse Finland's Jouni Liflnder provides an overview of basic antenna characteristics and their definitions.
For example, one way of measuring antenna performance is with resonance bandwidth. Initially, this bandwidth can be verified with a network analyzer by doing impedance matching. Yet a more accurate antenna-efficiency measurement can be gained by doing the evaluation in an anechoic chamber. In terms of radiated efficiency, Liflnder notes that a good antenna generally will radiate 50 to 60 percent of the energy fed to it (-3 to -2.2 dBi). Even if an antenna has good efficiency, its radiation pattern can have a null in some specific direction or directions.
Gain combines the antenna's efficiency and directivity into one figure, with directivity showing that the antenna radiates with greater efficiency to one particular direction. As a result, gain does not measure the antenna's overall efficiency. Increasingly, the signal emitted from the antenna needs to be equally strong in more than one direction, making gain a poor measure of performance. More companies are therefore choosing radiated efficiency as their preferred test method.
