Formulas & Data:
- Electronics
- Mathematics
- Physics
- RF & Microwaves

Parts Vendors:
- all hand-selected

- Amateur Radio
- Vintage Articles:
- Electronics World
- Popular Electronics
- Radio & TV News
- Radio Craft
- Short Wave Craft
- Wireless World

- Events Calendar
RF Cafe Homepage
Copyright 1999-2015   •−•  ••−•    −•−•  •−  ••−•  •   "RF Cafe" in Morse Code  >> Listen to It <<
- EW & Radar Handbook
- Quizzes       - Software
- App Notes
- Calculators
- Advertise on RF Cafe
- About RF Cafe™
- RF Cafe Shirts & Mugs
- RF Cafe Archives
RF Cafe Book Contest
- RF Cafe on Visit RF Cafe on Facebook Visit RF Cafe on Twitter Visit RF Cafe on LinkedIn
- Tech Humor
- Forums Archive
- Job Board
- Donate to RF Cafe
- Kirt's Cogitations
Custom Search
More than 10,000 searchable pages indexed.
Greetings: There is so much good stuff on RF Cafe that there is no way to list or link to all of it here. Please use the Search box or the Site Map to find what you want - there is a good chance I have it here. Thanks!

Parabolic Reflector Cross Polarization levels - 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: Parabolic Reflector Cross Polarization levels
Posted: Wed Jul 05, 2006 7:25 am 
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
I confess to being rather mystified as to how a parabolic reflector and feed horn radiator combination can produce a cross polar isolation of -28dB or better (some firms claim -34dB) across a wide angle around boresight axis.

The theoretical level for a perfect uni-polar feedhorn at the focus and an edge taper of -10dB is two "rabbit ears" at about -27dB relative to main beam boresight level, at an angle corrsponding to the first zero in the copolar level.

So how do the manufacturers beat the physics?

 Post subject:
Posted: Fri Jan 12, 2007 8:31 am 

Joined: Fri Jan 12, 2007 8:22 am
Posts: 2
The way I design systems is as follows:

Introduce higher order modes into the feed, such as TE21. These change the the feed X-pol pattern to produce two X-pol lobes. The feed X-pol is set up to be in anti phase to the X-pol lobes from the dish. Using this method I can get get better than 32dB X-pol off a reflector in the 13.75-14.5 frequency range.

The Doctor

 Post subject:
Posted: Fri Jan 12, 2007 9:46 am 
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Thanks very much for that solution. But how does one determine the relative level of TE21 to main dominant mode?
Or is it by trial-and-error?

 Post subject:
Posted: Thu Feb 01, 2007 7:09 am 

Joined: Fri Jan 12, 2007 8:22 am
Posts: 2
I am sure that it would be possible to generate a set of design curves for TE21/TE11 mode content and I have, in the past, run series of parameter studies looking at this. In all the designs I have done at Ku band, which, for what I am involved in is the biggest market for this type of feed, the higher order mode generating section is a fairly standard design and dimensions tend to be similar.

The Doctor

Posted  11/12/2012

Your RF Cafe
Progenitor & Webmaster

Click here to read about RF CafeKirt Blattenberger… single-handedly redefining what an engineering website should be.

View the YouTube RF Cafe Intro Video Carpe Diem!
(Seize the Day!)

5th MOB: My USAF radar shop

Airplanes and Rockets: My personal hobby website

Equine Kingdom: My daughter Sally's horse riding website