circular outer corrugated waveguide - RF Cafe Forums

RF Cafe Forums closed its virtual doors in late 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2012, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts. Here is the full original RF Cafe Forums on Archive.org

-- 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