antenna-theory.com

[jmcguckin]

Why does a bigger dish give more gain? If the feed irradiates both dishes evenly without spillover, wouldn't both antennas radiate in the 'forward' direction.

How can you have a beam width of 2 or 3 degrees with a parabolic antenna? Shouldn't any size parabolic antenna have a beam width close to zero?

[admin]

this is possibly the worst question, or least thought out query, I've ever read. at least put some effort into reading the basics

[jmcguckin]

Thank you for your illuminating response.

[hagster]

Because RF behaves as waves. The gain is caused by the constructive interference of the waves being reflected off the dish. The less wavelengths the less sharp the constructive interference.

Don't think about it as infinatly small particles bouncing off the surface. In such a case there reflected particles would not diverge.

[jmcguckin]

Well, I understand why a larger parabolic dish acting as a receiver produces more gain: larger aperture. But when used for transmitting, why is bigger better?

If constructive/destructive interference is the answer, I'd expect nulls in gain as reflector size gets bigger, probably at multiples of wavelength...

[hagster]

Antennas are reciprocal. So the Tx gain and Rx gain patterns are equal.

Yes you get side lobes and nulls with dish antenna. But they are small for dishes that are large compared to the wavelength.

[phamlindan]

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