Enhanced vector network analyzer time domain measurement using normalized superimposition

The measurement of the complex scattering parameters of a device under test (DUT) in the frequency domain using a Vector Network Analyzer (VNA) is common practice. Further investigation in the time domain is often obtained where the Inverse Fourier Transformation of the measurement results is examined. Thus, the impulse and/or step responses of the DUT can be obtained, which give another form of representation of the characteristics of the DUT. One of the main problems in this scheme is the introduction of unwanted side lobes that are caused when applying FT or IFT to measured signals that are band-limited. One technique to reduce side lobes is windowing, but this has a broadening effect on the main-lobe. The Spatially Variant Apodization (SVA) and superimposition (SI) techniques have been seen to address these issues in the past, and in this paper an enhancement to the SI technique through a normalisation process is investigated. The SI technique is seen to preserve the position, amplitude and phase of the main lobe responses from a DUT in simulated and measured data, while reducing side lobes and therefore confusion in the time domain representation of the DUT. In that sense a better approximation to the ideal impulse response of the DUT can be obtained.