Scalar Design

[nelson61]

I'm deep into building a custom offset antenna and am now exploring lnb modifications that may be incorporated into the design.

In looking at KU scalars, I can't find design data on the net (some pictures of larger KU scalars and nothing else)

I can see and understand the geometry that is capturing the antenna area and excluding the area outside of the antenna.

When I rip apart some standard KU lnb's, I think I am seeing that the scalar rings spacing is related to the wavelength. The tips of each ring appear to be in the plane of a cone extended from the initial cone and depth appears to have a comparable dimension.

If that is true, I ask myself why the designers did not just extend the cone sufficiently to match the "cloud" area one is trying to receive. Or, is it a mechanical design to provide sufficent attaching area for the protective cover?

 

[Anole]

When I rip apart some standard KU lnb's, I think I am seeing that the scalar rings spacing is related to the wavelength. The tips of each ring appear to be in the plane of a cone extended from the initial cone and depth appears to have a comparable dimension.

Regarding just this one point of your post . . .
I had been looking at the designs of an offset scalar for C-band, recently.
Yes, I believe the tips of the rings do form a cone which includes an angle just big enough to see the dish.

And, given a round set of scalar rings, the dish must appear round from the perspective of the LNB.
For typical offset dishes, that makes them a little taller than wide, and their aperture is the width, not height, of the dish.
So, if your dish is 30" wide and 36" tall, it's not really a 36" dish, it's a 30! -
This is not in keeping with the way imported dishes are measured, but if you compare their performance with commercial dishes, I think the answers will be clear.

Now, as to the scalar spacing...
The only document I could find, suggested scalar rings be spaced no less than 1/4 wavelength apart, and no more than 1/2 wavelength.
The same measurement applied to their height.
Measuring ring height in an offset scalar wasn't clearly documented.

Hope you can confirm the info on the scalars.
Working at Ku sizes will probably require considerable care and accuracy.
C-band on the other hand, is something I'd be a lot more comfortable dealing with.

 

[nelson61]

Regarding just this one point of your post . . .
I had been looking at the designs of an offset scalar for C-band, recently.
Yes, I believe the tips of the rings do form a cone which includes an angle just big enough to see the dish.

And, given a round set of scalar rings, the dish must appear round from the perspective of the LNB.
For typical offset dishes, that makes them a little taller than wide, and their aperture is the width, not height, of the dish.
So, if your dish is 30" wide and 36" tall, it's not really a 36" dish, it's a 30! -
This is not in keeping with the way imported dishes are measured, but if you compare their performance with commercial dishes, I think the answers will be clear.

Now, as to the scalar spacing...
The only document I could find, suggested scalar rings be spaced no less than 1/4 wavelength apart, and no more than 1/2 wavelength.
The same measurement applied to their height.
Measuring ring height in an offset scalar wasn't clearly documented.

Hope you can confirm the info on the scalars.
Working at Ku sizes will probably require considerable care and accuracy.
C-band on the other hand, is something I'd be a lot more comfortable dealing with.

Thank you - I am moving in uncharted territory here and may just fabricate some and see what happens. Just puzzled and don't understand why they did not extend the solid cone.

And yes, when one goes thru the design process, one finds that even though a standard offset dish (designed for one focal point) does not have a 1/1 height/width ratio, the area seen by the lnb is "1/1 and round" and matches the diameter (width) when the dish is placed in it's "offset" position.

 

[Larry1]

Quite a while ago there was some posts with pictures of a home made cone feedhorn. The idea, I believe, is to keep out the signals from other satellites and allow the signals from the satellite you are pointed at to enter.

 

[nelson61]

Quite a while ago there was some posts with pictures of a home made cone feedhorn. The idea, I believe, is to keep out the signals from other satellites and allow the signals from the satellite you are pointed at to enter.

As I dig deeper, as usual, the European professors seem to have posted the best info. It leads me to suspect the scalar designs are empirical in nature.

 

[Othea]

tin can

I don't know if will help, but there is an article in Tele-Satellite n° 194 (2006: 0609) on using a vegetable can as as feed for c-band.