"Emanuele Colucci" wrote in message
...
Thanks to James for the advices and to Jerry and Jim for the news.
Jerry: I'd like to know more about your solution, if you agree. 
Jim Lux ha scritto:
There's a set of articles in IEEE Antennas and Propagation Magazine (not
the transactions) a few years back that has all the equations and design
rules for all of the various reflector configurations.
Where I can find these articles?
Best wishes,
Emanuele Colucci
Hi Emanuele
I submit that, if you intend to actually build an antenna for L-Band and
are restricting its diameter to 3 meters, you need not consider a cassegrain
feed. The reflector at the focus is too small to allow the primary feed to
illuminate it with a high percentage of the available source at the rear of
the dish.
For one example, let the cassegrain reflector be 1/2 meter diameter and be
spaced 1meter from the apex of the dish. Wouldnt that suggest that the
primary beam, from behind the dish will have a beamwidth of about 30 degrees
(at -3dB)??
If the cassegrain reflector is made bigger, that blocks more of the
parabolic dish apperature. If the cassegrain reflector is made smaller,
that increases the need for a high gain primary feed.
It is my contention that, if you want to research Cassegrain antennas,
that is a worthy project. If you want to build a functing L-Band telescope
with 3 meter dishes, dont include cassegrain feeds in the project.
Jerry KD6JDJ