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Flat (planar) parabolic gain vs Dish gain?

 
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xrcv
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Joined: 02 Apr 2016
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PostPosted: Sat Apr 02, 2016 9:22 am    Post subject: Flat (planar) parabolic gain vs Dish gain? Reply with quote

Hi everyone,

Calculating the gain of a dish parabolic antenna is easy and there are many calculators around. However, I can't find anything on planar parabolic reflectors, does anyone know the difference in gain between the two?

Thanks!

I want to make a long-range wifi connection and I have an old satellite dish, which works perfect. However, it's heavy and unpractical, and I was wondering If I make a flat parabolic shape out of acrylic or heavy cardboard and cover it with aluminum foil, how much lower gain will I have compared to the dish, provided that the length of the flat parabolic is the same as the dish diameter?

There's a common flat parabolic pattern around the internet, which you can print and make a little reflector for the wifi antenna (2.4GHz) and it gets around 9dbi of gain. Imputing it's diameter into a dish parabolic gain calculator returns about 9db as well..But a dish should have a larger gain, no?


Also, what is the minimum height(same plane as signal polarization) of a flat parabolic reflector for it to act as a reflector? I'm guessing half a wavelength, as that's what yagis use for their reflector? Anything shorter will direct the signal back 180 degrees?
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S^3
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Joined: 01 Apr 2016
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Location: Dallas, Tx

PostPosted: Mon Apr 04, 2016 8:52 pm    Post subject: Reply with quote

In a Yagi the reflected signal is added to the signal transmitted by the Tx element using thereby the component which would have been wasted behind the TX element.

So the TX element transmits the signal in the intended direction of antenna. That is the fundamental difference in Yagi and a Parabolic antenna wherein the feed does not point in the intended direction. ( Cass antenna feed does not directly transmit to space even though it is pointed to that direction.. the beam is intercepted by the subreflecter. )

In parabolic reflector all the components falling on parabola are collected and vectorially added to each other .. not to the signal being transmitted by feed . Therefore its position w.r.t. reflector is not dictated by wavelength but by the mutual characteristics of feed and reflector such that the feed illuminates the full surface of reflector and all the rays maintain the transmit phase in a single plane in transmit beam.
==

I doubt whether it is economically worth designing and fabricating a new printed antenna for a single piece requirement.
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