Visit RFCafe.com Thanks for visiting RFCafe.net Thanks for visiting the RF Cafe Archives Thank you for visiting RF Cafe Thank you for visiting the RF Cafe Archives!

circular outer corrugated waveguide - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam.

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

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews
-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

bstrt
 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 ? :?:


 
   
 
nubbage
 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
RF Stencils for Visio v3.1 by RF Cafe
RF Cascade Workbook 2018 (GS) - RF Cafe
About RF Cafe Archives
Kirt Blattenberger - RF Cafe Webmaster
Copyright: 1996 - 2024
Webmaster:
    Kirt Blattenberger,
    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:  AirplanesAndRockets.com

spacer