frames but has now been ported over to PCs via EZNEC.

For modeling simplicity, the initial runs assumed "perfect" ground and a car body made of an aluminum alloy. The initial use of "perfect" ground allowed the azimuthal patterns to be compared at 0° elevation angles regardless of the presence or shapes of various lobes at higher angles. I introduced "real" ground and steel car body in later runs.

Overall Results

The initial runs discussed below demonstrate that near-horizontal azimuthal radiation patterns from an aluminum bodied car over a "perfect" ground are not circular. Their shapes vary with the antenna location on the car. This confirms basis of this paper.

Subsequent runs show that replacing the "perfect" ground with a typical "real" ground has the expected effect of reducing gain at low elevation angles but has essentially no effect on the symmetry of the patterns. Additional runs show that modeling the car body as low-carbon steel instead of aluminum changes the drive-point impedance somewhat, again as expected, but has virtually no effect on the radiation pattern.

Asymmetrical patterns remain so regardless of the ground quality or the metal of the car body.

Location Dependence

Fig 2 shows the azimuth and elevation patterns for the four locations of the A/4 vertical whip using "perfect" ground and an aluminum car body.

Center of Roof—The main lobe is horizontal, over the hood of the car and has a gain of about 8.9 dBi. Various side lobes and high-angle lobes are evident with gains of 2 to 7 dBi. Gain to the rear is -3 dBi, giving a front-to-back ratio (F/B) of about 12 dB. For this configuration, turning the car around can have a significant effect.

Front-Center Roof Edge—This pattern is almost the reverse of that above. The main lobe is horizontal, but over the rear of the car. The gain is about 9.3 dBi and the F/B is 9 dB. Clearly, the almost complete absence of ground-plane immediately in front of the antenna (over the windshield), curtails radiation in the forward direction.

Left-Front Corner of Roof— The only path for ground-plane current forward from, and to the left of, the antenna is along the highly inductive

Fig 3—These patterns show the effects of antenna height on radiation pattern. See text for details of the models.

Elevation Plot through Main Lobe

Efevatipn Plot through Main Lobe

« dB

36 7 Front on Car

Genter of Roof

Elevation Plot through Main Lobe

Elevation Plot through Main Lobe

Corner of Roof + Hood

Corner of Roof

Corner of Roof + Hood

Fig 4—Radiation plots for vertical antennas at the center and at the corner of an isolated roof and for a combination of a roof and hood.

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