Please don't think I'm trying to be contentious, but your comment
challenged my established view of what "dBi" represents. That led me on
a literature search starting with my (very old) Masters Degree notes,
antenna engineering reference books, and web sites. I can't find any
material where the Isotropic reference power density is defined as
anything other than the transmit power spread over a *complete sphere* -
not a hemisphere - even where the antenna being compared is over real
ground. In other words, consistent with EZNEC.
In some cases the interpretations were explicit - for example "......
compared with the power density of an isotropic radiator in Free Space";
in others it could be inferred from the underlying maths.
That's the interpretation I was taught, and yes it would certainly lead
to a 3dB higher figure than your interpretation.
I'm trying to understand whether your view is commonly held, or rather
something you feel strongly about; if it's a commonly held view perhaps
you could point me to some literature. I presume that someone like IEEE
must have an unambiguous definition?
On 06/01/2011 17:07, Dr. Gerald N. Johnson wrote:
> As for the effects with ground planes and my claim of error. I base it
> on this: Model a quarter wave vertical on a perfect ground plane. It
> will show 3 dB more gain than a half wave dipole in free space. Yet the
> theory of images in the ground plane insists that the quarter wave
> vertical on the ground plane has a image of the other half making it the
> exact equivalent of a half wave dipole. I claim that while the program
> in free space is comparing the signal intensity from the antenna to that
> of a perfect isotropic radiator located at the 0,0,0 origin of the axes,
> that when the ground plane is present it cuts that isotropic radiator in
> half, shielding half of its radiated power and so the reference to a
> full isotropic radiator is 3 dB in error. 3 dB too much gain.
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