ANTENNAS ON A CADILLAC ANTENNAS ON A CADILLAC This example illustrates the usage of ALDAS in selecting a position on a car for an antenna.
A CADILLAC de Ville has been modelled with monopole antennas on its roof. Two positions were used, both on the roof centre line. One antenna was sited at the centre of the roof and the other antenna was placed well forward and near the top edge of the wind-screen.
Figure 1 shows the geometry of the model with the positions of the two antennas indicated. The antennas were quarterwave monopoles with a centre frequency of 1.9 GHz.
Mercator contour plots have been used to illustrate the installed performance of the antennas. In these, the vertical axis is Elevation with 0.0 degrees in the centre of the plot as a horizontal line. The Elevation scale is shown on the right hand side of the plot and runs from +90.0 degrees (zenith) to -90.0 degrees. Azimuth is the horizontal axis with 0.0 degrees (staright forward from teh car) as the vertical line in the centre of the plot. The Azimuth scale is along the top of the plot.
Figure 2 shows the contour plot of radiation from the monopole mounted centrally. Figure 3 shows the plot for the same geometry but higher order interactions have been added in.A diffraction at an edge followed by a reflection from a flat surface is a typical higher order interaction. There is reasonable coverage in both case with no deep nulls between 0.0 degrees Elevation and 40.0 degrees Elevation.
Figure 4 shows the contour plot of radiation from the forward monopole. Figure 5 shows the same geometry but higher order interactions have been added in.A diffraction at an edge followed by a reflection from a flat surface is a typical higher order interaction. In this case, there is a noticeable change when the higher order interactions are included. The results are poor compared with the centrally sited antenna. This is caused by additional reflections and diffrcations from the bonnet of the car and can be witnessed in the fringes which occur between Azimuths 315 and 45 degrees and Elevation 0.0 to 40.0 degrees. There are deep nulls here of up to -14 dB.
Thus of these two positions, the centrally mounted one gives superior performance. This could be repeated for other sites on the car and a trade-off made between the RF pattern performance and other factors such as convenience, utility and appearance of the car.
Figure 1 Geometry of CADILLAC de VILLE with two antennas mounted on the roof
Figure 2 Mercator contour plot for the antenna at the centre of the roof.
Figure 3 Mercator contour plot of the antenna mounted at the centre of the roof. Higher order interactions have been included
Figure 4 Mercator contour plot of the antenna mounted forward on the roof.
Figure 5 Mercator contour plot of the antenna mounted forward on the roof. Higher order interactions have been included
