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Author Topic: triangle stacked array  (Read 3645 times)
KU7I
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Posts: 267




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« on: July 04, 2012, 05:55:49 AM »

Just wondering....has anyone ever used or is anyone aware of a triangle stacked array of antenna? For example, three yagis all stacked in the form of a triangle.It would be two yagis side by side with the third one stacked vertically above the two horizontal ones? It would look like this:

                                                                                              ant 1
                                                                                                 !
                                                                                                 !
                                                                                    ant 2-----!------ant 3

If you were looking at it broadside.

They would all be equidistant with compromised spacing to where it would be effective from 10 meters down to 20 meters. I figure this would be max 3/4 wave spacing on ten would be about a half wave on 17 and a bit more than a 1/3 wavelength on 20. I figure on 20 it would still offer decent benefits over a single antenna and 17 to 10 it should work well. I am thinking three 5 band hex beams.

Again, just thinking. Feedback please. Thanks. Lane Ku7i
« Last Edit: July 04, 2012, 06:04:44 AM by KU7I » Logged
WB6BYU
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Posts: 17352




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« Reply #1 on: July 04, 2012, 07:35:39 AM »

I've seen an array with 4 antennas in a diamond configuration - similar to what you
propose but with a 4th antenna below the bottom pair.  And wider horizontal spacing
accordingly.

Is your spacing dimension center-to-center or between adjacent ends?  3/8 wave
boom-to-boom spacing on 20m puts the ends of the antennas pretty close together:
they would overlap with full 1/2 wave elements, and I would expect considerable
interaction between the tips of the elements even with the shorter hex-beam
dimensions.

Depending on your priorities for performance on different bands, I'd suggest using
wider spacing if at all possible, particularly for the side-to-side antennas.  That
shouldn't compromise performance much on the higher bands.
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K3VAT
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Posts: 860




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« Reply #2 on: July 04, 2012, 09:24:58 AM »

Just wondering....has anyone ever used or is anyone aware of a triangle stacked array of antenna? For example, three yagis all stacked in the form of a triangle.... Again, just thinking. Feedback please. Thanks. Lane Ku7i

No, never have come across anything like this.  What exactly are you trying to accomplish?  Seems to me that this is very problematic from the onset.  Are these rotatable yagis or fixed?  It looks like that one would require 3 separate towers.  If constructed as some time of an array, then how would you feed it? Rich, K3VAT
« Last Edit: July 04, 2012, 09:58:12 AM by K3VAT » Logged
KU7I
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Posts: 267




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« Reply #3 on: July 04, 2012, 12:36:13 PM »

Rich, The whole array would be rotatable. Hexbeams are the considered antenna due to lighter weight. Since it is a broadside array they would all have to be fed in phase. Also if a triangle is too hard physically I would consider three antennas in line in the horizontal still broadside array.

Like this:     ant 1 ------------ ant 2 ---------------ant 3

 Lane
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KU7I
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Posts: 267




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« Reply #4 on: July 04, 2012, 12:39:26 PM »

Also, a long boom connects ant 1 to ant 3. Would have to be re-inforced. Again, physically this might not be practical but it seems somewhat possible.

Lane
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K4SAV
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Posts: 2428




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« Reply #5 on: July 04, 2012, 01:14:15 PM »

The real way to figure this out is to model it on NEC.  I don't have a model of a hex beam handy any didn't feel like generating one, but I did take a quick look at stacking 2 element Yagis like that.  A single 20 meter Yagi at 40 ft height had 11 dBi gain at 24 degrees elevation.  The Yagi I used had 7 ft boom.  Stacking a second one horizontally to the first at 0.6 wavelength spacing gave a gain of 13.4 dBi, also at 24 degrees elevation.  (You can't stack Yagis horizontally at 0.5 wavelength spacing because the antenna would touch.)  Stacking a third Yagi at 0.6 wavelength higher and centered between the two bottom ones gave a gain of 15.2 dBi at 15 degrees elevation.  The azimuth beamwidth dropped from 73.4 degrees for the single Yagi to 50 degrees for the 3 Yagi combo.  I would expect a little less gain with a hex beam, but there could also be some surprises with a hex beam.  I would recommend modeling it before building it.

For comparison, stacking only two Yagis at 0.6 wavelength spacing (same heights as before) one over the other gave 13.9 dBi gain at 14 degrees elevation with a beamwidth of 72 degrees.  Notice that this elevation angle is lower than any of the other combinations and the beamwidth is much wider.

Stacking antennas horizontally is a pain mechanically and can put a lot of stress on a tower depending on the antennas, however it is one method of adding gain when you don't have a tower that is tall enough.  The down side is that even though the gain goes up, the  elevation angle stays the same as for only one antenna, and the beamwidth decreases.

The whole subject of stacking antennas depends a lot on what you are trying to accomplish.  People that do this are concerned with the elevation angles for max gain, beamwidth, where the nulls are, minimum height for the lower antenna, tower height available, compromise stacking for more than one band, and what the local terrain is.  HFTA is a good tool for playing games with antenna stacking, but it won't handle this weird 3 stack.

Jerry, K4SAV
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KU7I
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Posts: 267




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« Reply #6 on: July 04, 2012, 10:03:04 PM »

Jerry,
Wow, great info. Thank you for taking the time to look at this. I am a bit concerned about the physica challenge of running a triangle formed three stack. I might look at a simple two antenna horizanal pair or a pair stacked in the vertical plain. Not sure yet but again, thanks for the helpful into.

Lane
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WB6BYU
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Posts: 17352




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« Reply #7 on: July 05, 2012, 08:30:05 AM »

Horizontal stacking is problematic for horizontal polarization because the boom is in the
plane of the elements.  (Unless the antennas are vertically polarized.)  That's why
vertical stacking is preferred - it also maintains a wider azimuth pattern so aiming isn't
as critical.

If you use the 2 x 2 configuration you can build an H frame so each antenna is connected
to a vertical mast that is secured to the tower by cross arms some distance from the
antenna.  This minimizes the interaction between the antenna and the cross arm.

Unless you really need the narrow beamwidth, you probably will have better results
(and fewer issues with wind loading, etc.) by just using higher-gain yagis and stacking
them vertically on a single mast rather than trying to put them side-by-side.
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KU7I
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Posts: 267




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« Reply #8 on: July 05, 2012, 06:22:35 PM »

I agree. Extensive internet research since my original post for this thread has shown that vertical stacking is so much easier. Also, I would not want to narrow the horizonal beamwidth, that is not the desire. The desire is max gain. Appreciate all of the comments. Lane
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