Gates and domains [time-domain measurements on antennas]

There are several reasons that one may wish to characterise a system, or analyse it, in terms of its response in the time-domain (TD). The reason for choosing to measure systems directly in the time-domain, rather than choosing to use subsequent computation from frequency domain measurements, may be different and the situation has changed with the availability of synthetic TD instruments. The HP8720A (130 MHz to 20 GHz), is a recent introduction to the scene. Some of the compromises and approximations in changing from one domain to the other are noted before discussing results of direct TD measurements on antennas