If you look at the feedhorn design in many parabolic antennas they have a dipole element at the feed point.. So basically you are taking an omni-directional dipole radiator and making it directional (high-gain) by placing it at the focus of a parabolic reflector dish..
But if you want high gain over 360 degrees things are no longer this simple.. You see, in stacking multiple elements to build a high gain omni, you have already squished the radiation pattern into a 7 degree or so slice of radiation.. it is not radiating much up or down, so adding a reflector above or below it wouldn't give you much return.. The more elements you stack, the more surface area to catch a signal, but also the more squished the pattern is.. Until it becomes unusable.. That is why many times you get better coverage out of a lower gain omni than a high gain omni.. Unless you live in a 2D world, the lower gain omni will fill in the 3D hills and valleys better than high gain one will at close distances. In the end it is very difficult to get gains over 14db in an omni setup. At to get 14db in an omni setup you are getting such a narrow radiation pattern that it is hard to work with.. To get gains higher than this in an omni configuration, you need to move to arrays of high gain sector panels.. which means multiple radios, lots of wind load, etc.. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Robi Sent: Friday, September 20, 2002 12:27 PM To: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: Re: [BAWUG] goofball comments about reflectors Wouldn't it be possible to passively amplify a signal on an omni antenna by building a 360 degree parabolic reflector. Imagine a parabolic cone dog collar shield thing with the small opening exposing the omni antenna piece orthogonal to it then another cone on the other side symetrical to it (small opening to large). That way a weak signal coming to the omni would get extra coverage from the reflecting parabolic picking up more of it. Ultra Small Diagram: \ / )) | (( / \ where | = omni exposed )(= signal /= one slice of the parabolic (imagine it's curved just right) -- Robi -- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless -- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
