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Re: Disparaging Helical Antennas: Use a DSS Dish for a reflector?


I don't want to dissuade you from experimenting, but I think you will find
little advantage from using the DSS as the reflector for a long helix beam.
 First of all the surface curvature of he DSS is designed for the feed to
be at the bottom edge of the dish not in the center of the surface.  From
comments on this bb, a simple shallow can reflector will act as a cavity
and do a better job of rejecting sidelobes.  Don't ask me for the
dimensions as I have not seen the literature on this.  Maybe others can
supply the dimensions [or place them on their web page].

PS:  I think it has already been pointed out that a single long helix of
even an array of four helices will have a hard time equaling the
performance of a single dish with the proper feed.  A helix of 7-WL [the
max length that more gain can be had] will approach 17 dBic, four of them
will equal 5.5 dB more gain after subtracting the loss for the cabling and
dividers [needed for the impedance transform].  So you might get 22.5 dBic
if you get it all right.  A single 60cm dish will do this!

>From: Christopher Cox <chrisc@coboxinc.com>
>Hi Jerry,
>I guess my post must have been confusing. The idea was to use a DSS dish 
>as a reflector for the helix. Placing your rather long helix at the base 
>of a DSS dish would put at least some if it at the focal point. Being 
>concave would help eliminate those pesky 45 degree lobes.
>Perhaps this combination would offer the best of both worlds, maybe the 
>worse as well...:-)
>Christopher Cox
>Hey look  ~~~~~~)    This is what I am talking about!

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