g86
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flatulent said:It would be easier to make the circular at the lowest level in your system (individual antenna element). Then the combining networks and lines to make a phased array are not as critical and only have one line.
dowjones said:Hi,
4) I implicitly assume that the subarray is 2x2, which gives broad XP cancellation along the main cuts. please indicate if this assumption is correct.
regards
dowjones said:well, in fact no. i was assuming a linear array of 4 subarrays (2x2 each one)- in other way a 4x1 array of 2x2 subarrays-, following your first post.
what you say however (4x4 of 2x2 subarrays) will give much broader XP cancellation than the linear case.
flatulent said:If the basic elements are exactly circular, it should not make any difference how they are combined. What you two seem to be discussing is the case where the basic element is really elliptical and the design of the overall array is done to reduce this effect by rotating the elements. If this is the case, I would suggest that making the overall pattern very fine would work the best. As an example. AAABBB is no as good as ABABAB.
dowjones said:ok g86,
my thoughts were in the direction which indicates flatulent, in the sense that the sequential rotation improves the axial ratio of a single element (elliptically polarized). I was not considering lineal elements because there is a 3db gain loss with respect to an array made with circularly polarized elements.
dowjones said:other thing is the array configuration. any seq.rot. configuration gives ideal 0 crosspol (XP) at boresight. This is got because the crosspol adds out of phase at theta=0. however the cancellation depends on the spatial delay between elements, and worsens with the angle. that is what i meant when talkin about broader XP cancellation. by the way, g86 in your first post you talken about a linear array (to me this means Nx1), while now it seems that your interest is a planar (MxM). that confused me and maybe my comments have confused you.
dowjones said:on the other hand, and as flatulent notices, if the array is composed of circ. pol. elements with ideal XP, it has no sense to use seq. rot. since it does not provides any improvement.
dowjones said:ok g86, ill try to explain the 3db loss issue. I recognize that I think usually on patch antenna elements (meybe this is not your case, but it is useful for my explanation).
suppose that your patch elements have a single feed and radiate linear polarization. if the linear polarization gain is G(dB), your circular polarization gain is G-3 (dB).
Extending this, if you have 2 elements rotated 90deg, the gain of your array will be 3 + (G-3), i.e. G dB referred to a circular polarization standard.
dowjones said:On the other hand, suppose that the patch element has 2 inputs so that it generates a CP (circ.pol) wave. Then the gain of your single element is G (dB) in CP, and if you make an array of 2 elements (rotated or not), the gain of your array is 3 + G.
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