Stacked 6-Element Log-Yagis

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k6sti
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Joined: 20 Oct 2014 17:27

Stacked 6-Element Log-Yagis

Post by k6sti » 28 Feb 2016 14:50

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To obtain a narrow main beam along with low backlobes, I optimized a stacked pair of 6-element log-Yagis. The booms are 114" long and spaced 78". Forward gain is 8.8-10.2 dBd, and secondary forward lobes and rear lobes are down 30 dB.

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I was inspired to do this when Glenn sent me this photo of stacked 5-element Yagis. I love the construction. I wanted to improve forward gain and rear rejection, and I figured that a longer boom shouldn't be that difficult to accommodate.

http://ham-radio.com/k6sti/ly.htm#6

http://ham-radio.com/k6sti/curves.htm

Brian

k6sti
Posts: 63
Joined: 20 Oct 2014 17:27

Re: Stacked 6-Element Log-Yagis

Post by k6sti » 03 Mar 2016 16:38

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k6sti
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Re: Stacked 6-Element Log-Yagis

Post by k6sti » 05 Mar 2016 14:34

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The azimuth pattern is more sensitive than usual to ground proximity. To improve it at practical installation heights, I added a design optimized at 30 feet over ground.

Brian

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Julian Hardstone
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Re: Stacked 6-Element Log-Yagis

Post by Julian Hardstone » 05 Mar 2016 17:01

Brian - Perhaps you could explain the six-element log-Yagis you used in the H-plane stack: The reflector has gone back to staright, and what's that feed arrangement around the three elements?
Re Glenn's stacked array, is he using some PVC in the stacking boom structure?
- Julian

k6sti
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Re: Stacked 6-Element Log-Yagis

Post by k6sti » 05 Mar 2016 18:11

Yes, that looks like PVC near the Yagis. Without it, the crossboom would affect the element currents. One of the disadvantages of horizontal stacking is the need to use a nonconductive crossboom, at least in the vicinity of the antennas.

I just redesigned the vertical stack using my latest optimizer. I added an image of the phasing lines for the log-Yagis. When stacked with elements parallel, mutual coupling is very high and it can really degrade the pattern. You must optimize the array as a whole to try to mitigate the unwanted coupling. But when stacking so that the elements are colinear, you can get pretty good results using antennas that are individually optimized, not as part of an array, because the coupling is much lower.

Brian

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