Andy,
One of the minor drawbacks of a 4-square is the high angle rear lobe you are
seeing. With optimal phasing, you should be able to get a pattern where that
rear lobe is down 25 dB or more. This may, or may not, be acceptable for
your performance objectives.
[This is one of the reasons my future plans include a 4-sq of K9AY loops
instead of the simpler verticals. The built-in F/B of the loops virtually
eliminates the back lobe, resulting in a very high array F/B.]
73, Gary
K9AY
> Many thanks Chris and Ken for your responce to mail below:
>
> I trust that a brief description of the array will answer your questions.
>
> The proposed antennas will be receive only 1-2m active Vertical (
> FET/Bipolar buffer amp) hence there will be no element mutual interaction.
> The centre element is run in anti-phase compared to the outer elements,
> the amplitude is the sum of the outer elements also. All 3 elements are
> combined using zero delay for Element 1; 0.73x40m (95ns) for the centre
> (2) Element and 0.73x80m (190ns) for the Element 3.
>
> The delaylines provide near optimum phasing for reduced rear vertical lobe
> from 0.53MHz to 2.65MHz. Going above 2.65MHz or 0.35Lambda spacing the
> Gain and F/B starts to reduce.
>
> The array was modelled at 0.53,1.06,1.59, 2.12 and 2.65MHz using the
> degrees phasing calculated from the delaylines i.e. the correct phasing
> tracks the frequency range.
>
> Eg. for 0.53MHz the phasing is 0, -162, -324 degrees and for 1.06MHz the
> phasing 0, -143, -286 degrees. The delaylines were determined from a
> similar model for a 3 Loop phased array.
>
> I have used a similar phasing scheme for the MW 2 Element Phased loop
> array and a Phased Vertical array.
>
> 73
>
> Andrew
>
>
>
>
>
>
> "Hello Guys
>
> Having struggled to model an 3 element endfire Active Vertical array using
> the same Phasing lines from 0.53MHz to 2.12MHz. I find that I can achieve
> a very good elevation plot with very low rear lobes (-30dB). Even the plot
> at 2.65MHz only shows 2 small (-22dB) rear lobes!!! Also this model is
> very tolerant of several dB amplitude difference on the outer elements
> providing that the centre element is the sum of the 2 outer ones.
>
> I have tried to do the same with the 4 Square, but there is always a large
> rear lobe on the elevation plot 10-15dB higher than the 3 element endfire,
> no matter how I adjust the phase. Am I doing something wrong or is there a
> fundamental problem with the 4 Square?!
>
> Both arrays have 40m Element spacing.
>
> 73
>
> Andrew G8LUG (not active)"
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