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Amateur Radio

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  • $\begingroup$ Hello Jonathan, and welcome to this site! :-) $\endgroup$ Commented Mar 17, 2022 at 22:39
  • $\begingroup$ So basically, directivity is not array gain, am I getting it right? $\endgroup$ Commented Mar 19, 2022 at 6:39
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    $\begingroup$ Hi JW and welcome, your input will be super useful to this stack site. What you say is correct but it's for real-world phased arrays. For eg. two antennas a reasonable distance apart do give double the gain&directivity (ignore coupling&overlap). The spirit of the question is "N isotropic radiators" so I started by assuming they're well spaced out. In the limit I think it's N, but of course lots of real-world effects start to happen in real arrays. If I'm wrong about ideal N please explain, and especially if it's more (not considering weird coupling stuff). I can't open that book page. $\endgroup$ Commented Mar 20, 2022 at 19:59
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    $\begingroup$ Hi Tom and thank you for the welcome. I see that you are a long-time contributor and work on large radio telescope arrays. I think that leads to the difference in our thinking, as I interpreted the question in terms of a planar phased array and not a sparse array such as what you work on. My formulas technically still apply, but as the array becomes more sparse (elements move away from each other by a factor of many wavelengths, the illumination of the "array" is no longer unity and therefore the directivity goes down. I need to put some thought into the sparse situation, frankly. $\endgroup$ Commented Mar 21, 2022 at 17:02
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    $\begingroup$ Thanks JW. I'm an antenna guy, so was thinking more along the lines of Lossless Passive Splitter -> Several Antennas, neglecting all coupling etc. This I think is the way it would have been treated in Kraus or Balanis. Your answer brings some rigour to the answer, better covering a real phased array today. $\endgroup$ Commented Mar 21, 2022 at 23:44