Calculation of frequency domain parameters by time domain methods (for antennas)

By adequate postprocessing it is possible to extract many frequency-domain results out of sampled time-domain data. For the calculation of far-field patterns in the frequency domain one needs to determine the harmonic field amplitudes near the radiating structure. This is accomplished by a time-domain calculation with time harmonic excitation sources. As an example the far-field pattern of a corrugated horn is calculated and compared with results obtained by a mode matching method. Boundary conditions and mode amplitudes for the calculation of filter characteristics are computed by mode expansion and a convolution technique. These modes are calculated by solving the 2-D waveguide eigenvalue problem. Broadband characteristics of a commercially available hyperthermia treatment set are calculated by a pulse stimulation technique together with CW SAR patterns.>