[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: focal point of the dish?



At 06:23 AM 3/30/2003, Tyler Harpster wrote:
>My question is this:   The helical feed is a few inches long.  The focal 
>point of a dish is theoretically a point.  Where should that point be in 
>relation to the feed?  Along the centerline of the feed, yes, but at the 
>reflector, the end of the helical, or somewhere in the middle?

The point you are searching for is called the "phase center" of the 
helix.  Ye Olde rule-of-thumb is one fourth of the helix length from the 
helix's feed point.  (So claims Antenna Engineering Handbook, by Richard C. 
Johnson.)

For the archeologists:
S. Sander & D.K. Chang, "Phase Center of Helical Beam Antennas", IRE Conv 
Rec, Part I, 1959, pp 138-146.


----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home