Chapter 5: Timedomain modeling of antennasIntroductionNumerical modeling of antennas in the frequency
domain is effective if the antenna parameters are desirable in the narrow band
of frequencies. If the wideband analysis is desirable, it is better to use
timedomain analysis. However, this one is suitable only for the structures
with low Qfactor, otherwise, the computed response is too long, and the
analysis is time consuming.
For modeling in the time domain, an analyzed structure is excited by a desired pulse [37], and a transient response
is computed. From the excitation pulse and the computed response, we can obtain
properties of the analyzed structure at those frequencies which the excitation
pulse contains. It is wideband modeling which can be used for the wideband
analysis of antennas, scatterers, or in the area of the electromagnetic
compatibility (EMC), or electromagnetic interference (EMI).
The
timedomain modeling has several advantages in the comparison to the
frequencydomain one:
 The wideband response is obtained by one run of an analysis.
 The frequencydomain analysis can not be used for the time variant or nonlinear systems.
 By the time domainanalysis, only the beginning of the transient responses can be computed, and the rest of the responses can be ignored.
Due to the above advantages of the time domain modeling, the basic principles of the timedomain modeling will be described in this chapter. Again, as in the frequency domain, the formulations which come out from Maxwellâ€™s equations in the differential or integral form are solved.
