[Antennas] True Ground Plane?

2002年3月28日 00:57:57 -0500 (EST)

Sure Ron.
As Bill Orr described, a ground plane is a vertical halfwave antenna, fed at the center, with the bottom half of the dipole divided into separate sections which are swung up to the horizonal plane. The vertical section acts as an antenna and the horizontal portions, or radials, form an artifical ground plane. The horizonal radials of the ground plane antenna perform two important jobs. First, they provide a return system or image for the radio field of the vertical quarter wave antenna. The engery field flows between the antenna and the radials. Secondly, the radials shield the ground plane from the nearby ground with its attendant ground losses. The degree of shielding and the amount of ground loss depend upon the number of radials used and the electrical height of the ground plane above the surface of the actual ground.
As I stated earlier, the higher you elevate your radials the less ground loss you should experience with the antenna. According to the ARRL antenna book, "There is no advantage to using more than four or five radials if the [ground plane] antenna is elevated a half wavelength or more above the ground." As you can see, it's all about avoiding ground losses. If you are not avoiding ground losses, you have something less than a "true ground plane."
If you are still puzzled, suggested reading would include the empiricial evidence found in an article written by KB8I in August, 1988 for QST entitled, "Elevated Vertical Antenna Systems" and "Elevated Radial Systems" by K0CS in Vertical Antenna Theory - The Low Band Monitor (7/94).
Ron W7MRR

--- On Wed 03/27, Ron Evans wrote:
> Ron, while I agree with nearly everything you said, I find the term 
> "true ground plane" puzzling. Perhaps you can share with the
> list 
> members your authority for the assertion that a ground plane must be at 
> least 1/2 wavelength off the ground to be...a "true ground
> plane."
>> The ARRL Antenna Book imposes no such restriction. Straighten us out?
>> 73,
>> Ron - K5MVR
>>>> "What you have now is a vertical with elevated radials. You have to
> go 
> at least 1/2 wavelength off the ground on your chosen band to be able to 
> categorize the antenna as a true ground plane."
>>>>>> - - - 
>> Your moderator for this list is:
> Larry Wilson KE1HZ [email protected]
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