[amsat-bb] Cupping a patch feed

["Bill Acito" <w1pa@xxxxxxxxxxx>]

Assuming an offset fed dish (sometime I wished I lived in Europe, where
the small f/d dishes are so prevalent...):

f/d is +/- .6
therefore, illumination angle about 70 deg.
Matched helix feed gives proper illumination, but some side lobes and
the axial ratio is not as good (per my reading).
A patch over-illuminates (+/- 130 deg), but better axial ratio (less
QSB) and no side lobes.

Not knowing all the physics and the math of the pattern, if I cup the
patch enough so it only "sees" the offset dish (effectively cutting off
part of the "volume" of the patch's pattern), will I effectively reduce
the gain of the patch?...

In other words, some practical experiences describe a patch on an offset
dish having the same relative signal strength for signals vs a helix,
less QSB, but more background noise. If I cup the patch, can I reduce
the noise component, and keep the same QSO signal strength, when I have
effectively cut off the outer ring of the pattern?

Bill
W1PA

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org