Analysis of gating errors in time domain antenna measurements

Although relatively new, the principle of measuring the radiation pattern of an antenna using the time domain rather than frequency domain is well known and relies on gating out unwanted reflections. Time domain measurements on horn and spiral antennas illustrate the need for error criteria and in this paper the nature of the gating error, and its relationship to the anti-interference enclosure size and the antenna frequency response, are investigated by both analytical and computer simulation methods. The results show that a lower frequency antenna can be expected to require a larger enclosure for a given gating error and that, for small enclosures, the time domain method has advantages over the conventional frequency domain method. The practical implementation of time domain measurement involves other factors such as the effects of aliasing, the need for a high quality reference channel for calibration, matching and noise levels. It is concluded that, in the time domain method, the amount of absorbent material in a chamber may be reduced but at the expense of a fast signal processing facility and, to some extent, a more critical equipment installation.