The literature contains solutions for the patterns of a number of antennas. Figure 1 shows the meshing of a commercial standard gain horn analyzed and compared to measurement. The horn operates from 8.2 to 12.4 GHz. The horn has a radiating aperture that is 110mm wide and 79mm high and a bell length of 228 mm. The 51-mm
length of the input waveguide and the details of the feed probe were included in the model.
Placing a perfectly magnetic conductor through the midsection of the horn uses symmetry to halve the number of cells to a uniform mesh of 519 × 116 × 183 Yee cells. Ten cells were used on the outside for the ABCs around the sides of the horn and 40 cells for the front ABCs in the maximum radiation direction. The model placed 20 cells between the edge of the horn and the equivalent current surface used for pattern calculations. The longest side of the grid determined the number of time steps at 10 times the number of cells = 5190 time steps. The model contains approximately 11M Yee cells that require 330 Mbytes of computer storage. Assuming that the problem takes 60 flops per cell for each time step, the solution required 3.43 Tflops of computer calculations.
FIGURE 1 FDTD model of a standard gain horn.
FIGURE 2 FDTD calculated electric field in the vertical symmetrical plane of a standard gain horn: (a) early time with a pulse in the throat; (b) pulse leaving the mouth of the horn.
The initial calculation used a differentiated Gaussian pulse excitation with τp = 15.9 ps that centered the response at 10 GHz. The calculation produced patterns that matched measurements. A second calculation used a sinusoidal modulated Gaussian pulse with the time constant 79.6 ps. This pulse time constant gives a normalized frequency of 2 GHz for the Gaussian pulse. The −3-dB frequency is 0.83 times the normalizing frequency. The pulse is centered at 10 GHz with a 3-dB bandwidth of 3.32 GHz. Figure 2 shows the fields when the pulse reached the horn aperture. Note the high fields in front of the horn and the amount of fields still radiating beyond and behind the aperture. By using a sinusoidal modulated pulse, the visual display contains nulls that improve its clarity.
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