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circular outer corrugated waveguide - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


 Post subject: circular outer corrugated waveguide
Posted: Wed Apr 18, 2007 8:46 pm 
 
Lieutenant

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 ? :?:


 
   
 
 Post subject:
Posted: Thu Apr 19, 2007 3:42 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
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




Posted  11/12/2012
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