Impulse TDR and its Application to Characterisation of Antennas

Abstract

Passive microwave systems are traditionally characterised in the frequency-domain with a vector network analyser (VNA). The measurement of antennas typically takes place in an anechoic chamber where the interference from spurious reflections and outside noise is minimised. Despite the high level of accuracy achieved with this approach, such facilities have high costs associated with them. Recent publications have demonstrated the characterisation of antennas using a step-function time domain reflectometer (TDR) along with frequency-domain processing techniques. Localisation of the measurement in time prior to transformation allows for the dismissal of unwanted spurious reflections, eliminating the need for an anechoic chamber. An alternative technique is proposed whereby an impulse generator is employed in place of the step generator in a TDR. The advantage conferred by "impulse TDR" (ITDR) is that more energy is available at higher frequencies than with conventional step TDR, leading to a higher bandwidth and signal-to-noise ratio (SNR). The theoretical result is compared with measurement.