VE4MA and Chaparral feeds with Septum Polarizers
Paul Wade W1GHZ ©2006 [email protected]
Tommy Henderson WD5AGO [email protected]
This started out to be a simple project – optimize the VE4MA feedhorn1 with a septum polarizer2 for
circular polarization. Some unexpected results have led to a larger analysis with conclusions that may
differ from the prevailing wisdom, but have been verified by measurements made by WD5AGO.
Some improved variations of the VE4MA and Chaparral feedhorns are described which show some of
the highest calculated and measured efficiencies to date for a prime-focus dish.
What we often call a “feedhorn” includes several separate elements: an antenna which shapes the
beam for improved dish illumination, a waveguide section (round, square, or rectangular), perhaps a
circular polarizer, and an excitation region (waveguide, probe transition to coax, or other transition).
While these elements may interact, each has a separate function and may be analyzed independently.
It is not necessary to exactly replicate all the dimensions from end-to-end, but it would be foolhardy to
make changes without considering possible interactions....
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