[TowerTalk] Analysis of phase errors for transmit phased arrays

[Rick Karlquist]

Jim Lux wrote:
>  In numbers, if you control the phase to within 45
> degrees, in 99.7% percent of the cases, you'll lose less than a half dB.
>
> The writeup and graphs are at:
> http://home.earthlink.net/~w6rmk/antenna/phased/txtol.htm
>
> > Thanks
> Jim, W6RMK
>

I didn't see in the report details of what the arrays were
other than # of elements, but the 3rd paragraph says it all:
"doesn't necessarily apply to superdirective arrays".
There are enormous differences in phase sensitivity of different
commonly used amateur arrays.  I can certainly give you plenty
of examples where you need to control the phase to a lot better
than 45 degrees to lose less than 1/2 dB.  Try end fire arrays
with 3/16 wl spacing, binomial amplitudes.  Not too bad with cophasal
currents, but as you increase the phase gradient to get more gain, (and
enter the superdirectivity regime) the array gets extremely sensitive
to phase and amplitude errors.  The gain you can get is directly
related to accuracy.  On the other hand, broadside arrays will still
work even with fairly large phase/amplitude errors, especially
if you don't care about sidelobes.

Rick N6RK