Novel Method for Characterizing Filtering Antennas

Ultra-wideband systems show promise in high-data-rate radio communications. However, these systems interfere with other communication protocols, such as WLAN. To solve this problem, current work proposes the insertion of thin half-wavelength slots in the antenna´s structure, thus creating filtering antennas. Many criteria were used to characterize the filtering of these antennas, such as the measurement of the VSWR, the return loss, and the maximum gain of the antenna as a function of frequency. In this paper, we show by studying the three-dimensional gain pattern of these antennas that their filtering is not just dependent on the frequency, but that it also depends on the radiation direction, due to the radiation of the slots. We then propose efficiency measurement as the best way to quantify the filtering of these omnidirectional antennas, independently of the radiation direction. Two filtering antennas were characterized using a modified wideband Wheeler-cap efficiency-measurement method.