> At 4.5% above design frequency, the difference in the pattern
> of the single dipole is negligible, and the gain rises 0.04 dB.
> At 4.5% below design frequency, the difference in the pattern
> of the single dipole is negligible, and the gain drops 0.04 dB.
OK, so you've confirmed that the main lobe hasn't shifted up or down as you
varied the frequency a nominal amount for a single element, no suprise
there.
Now take four of those dipoles arranged colinearly, spaced at 0.9 lambda at
450 MHz, and feed them all in phase. You should have a nice major lobe
right on the horizon at about +6 dBd. Now change the frequency to 430 MHz,
leaving all of the phystical characteristics of the array the same. You
should see a slight reduction in peak gain in the major lobe, but the main
lobe still stays on the horizon. Then go up 20 MHz to 470 and repeat.
Heck, go 40 or 60 MHz in either direction if you want. Whaddya see? You
should see that the sidelobes change, the beamwidth and gain of the major
lobe will change, but the elevation angle of the main lobe will always be
perpendicular to the array.
--- Jeff WN3A
