Use of time domain gating in spherical near-field measurements

Time domain gating has been widely used in antenna measurements for many years. The technique has proven useful in gating out extraneous signals from the range that can be uniquely separated from the primary desired signal. The well known process involves collecting data in the frequency domain and then transforming the data to the time domain for processing. In far-field antenna measurements the technique is limited in its applicability by factors such as antenna bandwidth and pattern shape vs. frequency, and internal time delays within the device under test. Spherical near-field presents additional challenges to the effective use of time domain gating. These challenges of performing time domain gating in spherical near-field measurements are presented along with measured results from a small spherical near-field range. These results show the significant reduction in stray signals and the resulting increase in accuracy that can be achieved via time domain gating. Finally, the paper concludes with measurements made on a large spherical near-field arch over a ground plane system. Additional challenges of such a system will be highlighted.