On 1/22/13 9:08 AM, Joe Leikhim wrote:
John;
You might look into building your own, _scaling up_ from a G3RUH design
(2.4 GHz)
note that they were illuminating a 60 cm dish in those experiments,
that's not a very big reflector for 12.5 cm wavelength at 2.4 GHz. not
even 5 lambda. I'm not sure you can really model that system by physical
optics.
the OP wants to illuminate 120 cm for 1.5GHz, 20 cm lambda.. that's 6
lambda. Still a pretty small dish, wavelength wise.
Both will have issues with diffraction around the edges, so if you're
worried about noise temperature, you'd want to seriously under illuminate.
I'm assuming the F =0.375 is the F/d ratio? so the focal point is 18"
(45cm) from the dish? That's going to require a very low gain feed to
illuminate all that area. (HPBW on the order of 100 degrees).
I'd take a look at what they use to receive HRPT signals at 1.6-1.7 GHz
for design ideas. They use 3-4 foot dishes for that. Timestep uses a
helical feed.
here's some design info for a HRPT system
http://members.inode.at/576265/
He has all the design equations AND a lot of nice pictures of various
helical feeds for various dishes, and recommendations on design (how
many turns given the f/d)
http://homepages.ihug.co.nz/~jpsl/a_simple_patch_antenna_feed.htm
that's an air dielectric patch, which is nice, because it will have
wider bandwidth, but it's still pretty close to the ground plane.
Would anyone happen to have a LHCP patch antenna, with or without
preamp,
they would be willing to sell? I want to use it as the feed for a 4
foot
diameter F: 0.375 dish antenna for a dedicated WAAS receiving set up.
Thanks,
John Franke WA4WDL
4500 Ibis Ct.
Portsmouth, VA 23703
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