[time-nuts] LHCP patch antenna

Jim Lux jimlux at earthlink.net
Wed Jan 23 01:08:11 EST 2013


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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