TIME-DOMAIN ANALYSIS OF MICROWAVE NETWORKS: AN EDUCATIONAL APPROACH

Telecommunication and electronic engineers are used to a frequency-domain (FD) based analysis and design of electronic circuits and systems. The reason is that, due to the extremely complex environment of practical communication systems, a complete physics-based time-domain (TD) analysis of any subsystem is usually not considered in any of the subjects that lead to the engineer degree.

However, TD analysis of systems such as microwave two-port networks (i.e., filters, amplifiers, etc.) or one-port networks (i.e., antennas, resonators, etc.) can be of great help to understand their behaviour and in some cases to improve their functionality, and is widely employed in the research environment. The reason is that physical phenomena actually occur in TD, and therefore it is easier to isolate the behaviour of each part of a certain subsystem when studying it in TD. This is why several commercial software tools are based on TD simulation such as Finite-Difference Time-Domain (FDTD) or the Method of Moments in time domain (MoMTD). Also, TD simulation and analysis has been employed in the research of broadband antenna design and ultra-wide band (UWB) systems such as Ground-Penetrating Radar (GPR).

In the microwave and RF frequency range, the most widely used instrument is the Vector Network Analyzer (VNA), which allows the measurement of the FD response of an n-port network, both in module and phase. As time and frequency domains are related by the Fourier transform theory, which is one of the basic pillars of the Telecommunication and Electronic Engineering degrees, the students of the last courses of any of them are capable to perform a full TD analysis of a microwave subsystem as long as they have accurately characterized its FD characteristics.

In this work, we present two laboratory experiences developed to allow the engineering students to understand the TD phenomena, by studying the transitory response of one and two-port networks. For the first of them, which is intended for students who are not experts on the Fourier theory, we have codified a software tool to automatically control the VNA and analyze and transform the measured data to TD. In the second experience, prepared for students with advanced knowledge in signals and systems, the transform is directly performed by the students using mathematical tools (i.e., Matlab, MathCAD, etc.) and also the VNA has to be properly configured in order to be able to obtain a correct TD response.