Influence of the antennas on the ultra-wideband transmission

Spectrum is presently one of the most valuable goods worldwide as the demand is permanently increasing and it can be traded only locally. Since the United States Federal Communications Commission (FCC) has opened the spectrum from 3.1 GHz to 10.6 GHz, that is, a bandwidth of 7.5 GHz, for unlicensed use with up to -41.25 dBm/MHz EIRP, numerous applications in communications and sensor areas are showing up. Like all wireless devices, these have an antenna as an integral part of the air interface. The antennas are modeled as linear time-invariant (LTI) systems with a transfer function. The measurement of the antenna's frequency-dependent directional transfer function is described. Quality measures for the antennas like the peak value of the transient response, its width and ringing, as well as the transient gain are discussed. The application of these quality measures is shown for measurements of different UWB antennas.