Differences of Time Domain Gating Implementions in Vector Network Analyzers

Time domain gating in vector network analyzers (VNAs) is used widely in EMC and other RF measurement applications. Conceptually, it is straightforward - the analyzer first converts frequency domain data to time domain via inverse Fourier transform, and a gate is applied to include or exclude certain time periods. Because gating is provided as a built-in function in commercial analyzers, a user typically does not concern himself with the details of the mathematical process. However, the actual implementations are different in different VNAs, especially in the gate designs and band edge treatments. Even with the same measurement, gated results can vary. The lack of documentation on the specifics from VNA manufacturers further clouds the issue. In this paper, we provide detailed discussions on the gating process, and illustrate the differences of the gating functions from different VNAs. We aim to promote a better understanding of the gating process and its impact on measurement uncertainties.