I got some of the modeling I want to do done, here is what I have so far.
All of these are models of just the antenna, one in free-space, one at 20 feet above earth, and the last one at 30 feet above earth. None of these have mast or feed line, or any form of ground plane attached, that is something I intend to add later.
First the free-space model.
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In this case, the capacitor is making the antenna slightly more efficient (99.57% compared to 99.37%), and has a higher directivity (2.49 compared to 1.98), both of which help it over the non-cap version when it comes to gain.
Another point of note, the version with the capacitor has a 6° angle of peak radiation and a 3dB beam-width of 70° (40° to -30°). The version without the capacitor has a peak gain between 13° and 14°, and a 3dB beam-width of 50° (25° to °-25). This suggests that the version with the capacitor will perform better in local situation, assuming you have absolutely no currents on the mast and feed line, although not so much that you would notice the difference.
Next the 20 foot high models.
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When it comes to efficiency, this time the model without the capacitor is more efficient at 57.74% compared to 56.18% for the model with the cap. The model with the cap also has a directivity of 6.08 dB, while the model without the cap has a slightly lower directivity of 6 dB. In this case, the added efficiency of the non-cap antenna noticeably exceeds the gains of the slightly higher directivity of the cap antenna for 0.18 dB more gain.
When it comes to the angle of peak radiation, the non-cap version is slightly lower at 23° compared to the version with the cap at 24°. The version with the cap has a 33° beam-width (39° to 6°) while the version without the cap has a 25° beam-width (39° to 14°).
Finally the 30 foot high models...
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When it comes to efficiency, again without the capacitor is more efficient at 61.94% compared to 59.52% for the model with the cap. The model with the cap also has a directivity of 6.88 dB, while the model without the cap has a slightly lower directivity of 6.49 dB. These combine to give the antenna with the cap a 0.22 dB high gain.
When it comes to the angle of peak radiation, here they have the same angle of 11°. The version with the cap has a 33° beam-width (39° to 6°) while the version without the cap has a 11° beam-width (5° to 14°).
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So, if you look at the data, you will notice that at free-space and 30 feet above the earth the antenna with the capacitor is both more efficient, and has more gain. However, the model at 20 feet neither of those things are true. I'm curious on any thoughts as to why and/or how this happened.
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I do intend to make more models that have things like a mast and even two different radial configurations in the future, when I get a chance.
The DB
