[time-nuts] GNSS Antennas (was: Rooftop antenna and splitter)

[Bob kb8tq]

Hi

If you take a hammer to one of these antennas, they seem to mostly play games
with transmission lines on pc boards. The number of components involved is pretty 
small. 

If hammering one apart does not sound like a great thing to do, there are pictures 
here and there. I have yet to see a picture that shows enough to actually make sense 
out of. I’d bet that is intentional. 

Looking at network analyzer sweeps, it becomes pretty apparent that whatever 
combination of things are involved, they only work inside each of the target sub-bands.
Once you get to the edge, it all falls apart. It comes back together once you get to
the edge of the next sub-band. Some of that is intentional filtering so sorting it out 
that way … not so much. 

Bob

> On Jan 30, 2019, at 11:33 PM, Peter Monta <pmonta at gmail.com> wrote:
> 
> Hi Attila,
> 
> 
> The "good" patch antennas thus
>> employ a four point feed, but this makes the whole antenna quite a
>> bit more expensive, as a 0°/90°/180°/270° phase spliter/hybrid is
>> needed. Of course, any such circuit is rather difficult to make
>> wide-band and thus becomes the bandwidth limiting element.
>> 
> 
> Mini-Circuits has such a 4-port phase splitter, part number SCQ-4-1650+.
> It's $25, which is not super cheap, but it's unclear one could implement
> such a network with a planar circuit for less, and the planar circuit would
> be more bulky.  I've been thinking of picking up one of these to give an
> untuned 4-filar helix a try (not a fancy resonant backfire quadrifilar
> helix, which are hard to make broadband, but just a plain set of 4 helices
> and the combiner).
> 
> From the data sheet it's clear they have GNSS in mind, and it is quite
> broadband:
> 
> https://www.minicircuits.com/pdfs/SCQ-4-1650+.pdf
> 
> Cheers,
> Peter
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