Calculaticn and Use of Time Domain Response From Vector Network Analyzer Measurements

The translation of frequency response measurements to the time domain has become more popular. In our engineering facility, the requests for time domain information have been increasing since its introduction. Engineers have become aware of the wealth of information that can be found in time domain plots. Implementation of time domain calculation is not difficult. Usually a 100-line program is all that is needed to calculate band limited impulse response using a Fast Fourier Transform (FFT). To accomplish this, some study of transform theory is involved, supported with information on sampling. An intuitive approach will be used to help in explaining the digital Fourier transform. Once the basic transform methods are understood, certain methods for conditioning data will be presented to improve the resolution and sensitivity of the transform. Once the basic FPT package has been developed, it can be used in the low pass mode to obtain a TDR type display. This is done by measuring the network in a certain way and inputting the data to the FFT so as to obtain a real-time function. The traditional TDR step response is obtained by using the FFT to compute the inverse Laplace transform after an appropriate data manipulation.