Time-domain simulation and characterisation of TEM horns using a normalised impulse response

A common way of describing antennas in the time domain is by means of their impulse response. When the time-domain antenna equations are expressed in terms of the normalised impulse response (normalised IR), they become very simple to use, because all frequency-dependent antenna characteristics are included in the normalised IR. This paper describes a method for measuring the normalised IR experimentally, using a vector network analyser. The normalised IRs of different air and dielectric-filled TEM horn antennas are compared and discussed. The normalised IR is found to be a powerful tool for simulating antenna behaviour directly in the time domain. Thanks to the introduction of the virtual source, (i.e. an apparent point in the antenna from which the radiated field degrades by a factor 1/r), the time-domain antenna equations can also be used near the TEM horns, although still in the far field of the antenna. Some examples of time-domain simulations and system modelling using the normalised IR are presented. In each example, the simulations are compared with measured data.