Conversion of Scattering Parameters to Time-Domain for Imaging Applications: Rules and Examples

Marcelo Perotoni,Kenedy Santos,Claudio Junior

doi:10.14209/jcis.2021.6

Abstract

This article discusses the conversion of scattering parameters from an antenna input port to time domain for imaging applications. Frequency-domain measurements offer some advantages to time-domain methods, and the complex data encoded in the scattering matrix convey target geometric and material information which can be later used to reproduce the scene image illuminated by the antenna. Three different examples using the inverse discrete Fourier transform are discussed. Trade-offs in the data acquisition, bandwidth, sampling and topics related to the antennas used as probes are covered.

Highlights

C OMPLEX scattering S-parameters are measured in Vector Network Analyzers (VNAs) and provide an understanding of the behavior and performance of linear passive and active elements and systems
Though provided as a complex-valued vector uniformly spread across a frequency range, they encode useful information when analyzed in time-domain, in applications such as TDR, radar [1] [2], near and far-field imaging [3] applied in areas such as breast cancer detection [4], ground-penetrating radar [5] and even non-destructive concrete characterization [6]
This paper reported the conversion of S-parameter data to time-domain employing Hermitian Processing, where the original frequency-domain S-parameter represents some physical measurement

Summary

INTRODUCTION

C OMPLEX scattering S-parameters are measured in Vector Network Analyzers (VNAs) and provide an understanding of the behavior and performance of linear passive and active elements and systems. Despite FFT/IFFT routines (Fast Fourier Transform / Inverse Fast Fourier Transform) and Chirp-Z Transforms [10] [8] being available in network analyzers and field solvers alike, sometimes a deeper understanding is needed to implement own codes and better design systems that make use of time-domain signals transformed from frequency-domain data sets. Processing resources such as zero-padding, oversampling, filtering, and windowing might be used in addition to the IFFT, which might not be quite clear to the instrument or field solver user.

COMPUTING THE INVERSE FOURIER TRANSFORM OF A

EXAMPLE I - BAND-PASS UNITARY AMPLITUDE

EXAMPLE II - SHORT CIRCUITS IN TRANSMISSION LINES AND FREE-SPACE

CONCLUSION