"Ian White GM3SEK" wrote
Richard Harrison wrote:
My original comment was in support of Arnold B. Bailey who said something
about increasing antenna gain by 3 dB every time you double its size.
Precisely, that`s not true, but I gave an example from Kraus where he did
much the same thing.

+3dB is a valid generalization, based on sound physics - but it is only a
generalization. At the time those Grand Old Men were writing their
textbooks, such generalizations were the best that anybody could manage.
_______________

No doubt the 'GOM' knew the exact gain changes from successive doublings of
an antenna aperture, or could calculate them if they wished to. The
difference between the two isn't very important except when it is part of
the equation to arrive at some legally required ERP, such as in commercial
broadcasting.

Below are the gains of a series of commercial FM broadcast transmit arrays
to illustrate the point. The elements (bays) in these arrays all are one
wavelength apart, and driven with equal power and phase.

# Elements C-pol Gain (dBd)
1 -3.55
2 -0.21
4 3.09
8 6.34

Starting with the gain of the 1-bay and adding exactly 3 dB per doubled
aperture in this example would result in 5.45 dBd gain for the 8-bay,
meaning that FM ERP when using this approach would be more than 18% below
its licensed value (illegal).

RF