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circular outer corrugated waveguide - RF Cafe Forums
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| bstrt
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Post subject: circular outer corrugated waveguide
Posted: Wed Apr 18, 2007 8:46 pm
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Joined: Wed Apr 18, 2007
7:48 pm
Posts: 1 |
I am trying to figure out Ku-band antenna consisting
a prime focus parabolic reflector à sub-reflector-->circular
outer corrugated waveguide à omt. It is backfire
feed so that feed assembly ( OMT) is located behind
of reflector. I am having a hard time to understand
what is function of outer corrugation of waveguide.
The corrugation looks like rings. Does anyone
has any clue of the function of outer corrugation
of waveguide ?
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nubbage |
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Post subject:
Posted: Thu Apr 19, 2007 3:42 am
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| General |
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Joined: Fri Feb 17, 2006
12:07 pm
Posts: 218
Location: London UK
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Hi
It is called a choke feed arrangement, and
is widely used in sat TV antennas.
The purpose
is to equalize the E and H plane beamwidths of the
exciting circular waveguide. Without the choke the
beamwidths are different for the two vectors, leading
to a poor cross-polar discrimmination. The OMT selects
horizontal polarization in one port and vertical
in the other, but if the discrimmination is poor
due to the fundamental properties of the feed aperture,
then there will be ghost carriers of H pol sources
in the V pol port and vice versa.
The corrugations
act as chokes that restrict the pasage of unwanted
currents across the aperture, and slightly increase
the aperture diameter for the broader lobe (E vs
H) so it is narrowed and more closely equals the
narrower plane width. I know that is a rather vague
explanation, but without a lot of math, what you
see is what you get
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Posted 11/12/2012
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