design of cassegrain antenna, help!

[saras]

Hi

i have to design a cassegrain antenna, with a circular horn feed.
i read in a paper that the design of cassegrain antennas has 8 parameters.
I just have the diameter of the main reflector and the f/D.
could you please tell me about the procedure for finding the other parameters?
and is it possible to simulate the design by hfss?
thanks a lot in advance
sara

 

[G4BCH]

Hi Saras
A good place to start would be
http://www.w1ghz.org/antbook/contents.htm
There is a lot of good practical information there.
A cassegrain antenna is regarded as being any dish type antenn that is rear fed with a sub-refelctor. Strictly speaking a caassegrain reflector has, if I remember correctly a spherical primary mirror and hyperboloidal secondary. and this is probably where all the other parameters you mention come from; shape of primary and it's F/D and the matching secondary.
You can make the antenna apear to the feed to have almost any F/D you like by suitable shaping the seconday refelctor. Look at Schmidt cassegrain telescopes, very short tube with F/D of 10.
Designing a reflector antennna is basically an optical problem.
When designing your antenna you may have to take into account the facat that the secondary is of the same order of a magnitude in size as the wavelength you are using, not as when dealing with light where it is many orders larger so you may have to look at diffration around it.

Hope this helps a bit. ther are plenty of antenna design sources out there particularly on those sites devoted to microwave amateur radio.

Peter