On 5/24/11 7:08 AM, pehaire wrote:
> I agree with you.
>
> In Beer's article on using different verticals in a 2 element phased array
> by varying the lenght of the feed line to each vertical, he uses radials and
> he pointed out that when radials crossed he bonded them together.
>
> It looks like to me that a half square could be thought of as 2 verticals
> each with one radial and the 2 radials attached or bonded together at their
> ends. Thus 2 verticals spaced a halfwave apart.
>
> Noll in his book describes 2 verticals spaced almost a half wave and fed
> with 300 ohm line and has a switch in the center of the 300 ohm line that
> he can go from end-fire to broadside. The close spacing I guess is to
> reflect the velosity factor of the 300 ohm line. The close spacing causes a
> slight loss in gain. But who cares about plus or minus one db. That is one
> sixth of an S unit. Or you could increase power by one fourth and more than
> make up for the loss.
>
In most phased array schemes, you're not looking for forward gain as
much as reverse null depth. You can have huge phasing errors with small
effect on gain: The gain (in dB) is 20*log10(1+cos(theta)) where theta
is the phase error.
10 degrees is 0.05 dB gain decrement
45 degrees (an 1/8th wavelength!) is only 1.35 dB decrement.
You can do better than 45 degrees without a tape measure by just pacing
the distance between antennas.
But that same 10 degree error in phase changes an infinite null to -36
dB, and the 45 degree error changes the null to only -10dB.
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