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I'm working on a passively scanned phased array radar project, as a concept and hopefully design.

One of the things that bugs me is that antenna patterning used. The vast majority of radar arrays I've seen employ a hex grid pattern, with a small minority using an orthogonal grid.

What would be the benefits of using a hex grid like this: enter image description here

As opposed to a square orthogonal grid like this:

enter image description here

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    $\begingroup$ Idle speculation: I would guess it depends on the design of the individual element antennas. If their largest element (presumably a horn or reflector) is circular, then a hexagonal grid is the most efficient packing. If it is square, then a square grid is most efficient. $\endgroup$
    – Kevin Reid AG6YO ♦
    Feb 17, 2016 at 15:09
  • $\begingroup$ Interesting idea. Intuitively though I would think it complicates the phase difference calculations. For azimuth control (horizontal sweep), its the elements line up neatly so each new column has a different phase delay. For the attitude control (vertical sweep), the rows do not line up and you end up with every other element in a line. Although perhaps this is moot since even with an orthogonal array, if you steer the beam in diagonals you'll get irregular antenna element spacing anyway. $\endgroup$
    – Oliver
    Feb 17, 2016 at 15:29
  • $\begingroup$ Found this paper which considers both briefly and settles on an orthogonal (or linear lattice as they call it) array because it means they can turn the whole thing over to swap linear polarisation. They do however use square shaped antenna. $\endgroup$
    – Oliver
    Feb 17, 2016 at 15:32
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    $\begingroup$ Worthy of thought, the orthogonal-array's elements line up cleanly in 2 axes (0/180 and 90/270 degrees). Meanwhile, the hexagonal-array's elements line up cleanly in 3 (0/180, 60/240 and 120/300 degrees). When scanning/beamsteering through a 3D, hemispherical space, having 3 steering axes would simplify the equations over having only 2, as any chosen direction would be on average 50% closer to a "natural" axis for the array. $\endgroup$
    – Robherc KV5ROB
    Mar 13, 2016 at 19:34
  • $\begingroup$ @SDsolar, I rejected your edit suggesting the "maintenance" tag because there is no mention of "maintenance" in the original question. Your answer gives clear reasons why the original poster might have included the tag, but I concluded that you were "putting words in his mouth" so to speak, and so therefore you were making changes incompatible with the author's intent. $\endgroup$
    – rclocher3
    Feb 21, 2017 at 2:22

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The hex grids can fit more transmitter/receivers into the same space, resulting in greater power output per square meter.

But more importantly, the one you pictured also has independent transceivers so they are individually field-replaceable.

The computer that runs it all does diagnostics on startup and can flag the bad ones so they can be fixed right away without having to have access to the back of the array. That is key.

No disassembly required - just pull out the bad one(s) from the front and slide in a new one, right on the flightline. No need to pull it into a shop.

Just one bad TRX can cause unwanted sidelobes which can defeat the LPI (low probability of intercept) property of those arrays.

Addressing what you said about passively: All I can mention is that the old phased arrays used switched delay lines in order to generate the pattern. But they were very limited in the switching speed, and could not transmit during the switching.

The unit you pictured can probably track more than two dozen targets "at once" - of course it is scanning, but it is so fast it seems to be simultaneous.

Good luck with your project. I am sure you are learning a lot.

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