Lothar
Ok guys this is not directly related to agilent t+m but im
banging my <br> head on the wall with this !<br>
Im looking for material on how to design and build a turnstile <br>
polarization converter, i googled up and down but cant find anything <br>
usefull , not even in the books i have.<br>
The problem i have requires me to design and build a 36GHz circular <br>
polarized horn antenna, the antenna needs to have two ports one for <br>
right and the other one for left turn polarization .<br>
any help would be appreciated <br>
There are number of ways of doing this, but at 36GHz there's a rather more
limited number of choices. Techniques such as the use of coax hybrids are
definitely not usable, and the septum polariser becomes tricky to make above
about 10GHz. My suggestion would be to split the problem: use an
otho-mode-transducer to launch two orthogonal linearly polarised waves into a
length of circular waveguide, and then delay one polarisation by 90degrees
using a suitable polariser. I don't think there's a simple 'recipe' for a
feed that I could recommend - frequency scaling of a waveguide component is
often quite complex. However, the late Dick Turrin, W2IMU, (of Bell Labs)
wrote an interesting paper describing such a system for amateur 10GHz EME
back in the 1980s which might scale reasonably easily. That's on my ham radio
web site:
either <www.christopherbartramrfdesign.com/blaenffos/indexgw4dgu.html> or
<www.blaenffos.org/indexgw4dgu.html> should get you there.
There is a book: 'Waveguide Components for Antenna Feed Systems' by Uher,
Bornemann & Rosenberg. (Artech House) which is very good, but rather
expensive. ($200?) You may be able to find it in a library, though. In the
UK, most university libraries allow public access, if you ask nicely...
If you are doing waveguide design, I'd also strongly recommend that you try to
get access to a 3D electromagnetic simulator such as HFSS. That can save
considerable hair loss, although in my case that's less of a consideration
than it used to be!
BTW. Thanks for the ongoing observations, tips and transferred knowledge. I
find your posts to this group very useful. There are some very bright
contributors to the group, and it's on my daily 'must read' list!
Best wishes
Chris Bartram
(actively playing 10GHz Moonbounce as GW4DGU)
