dbic gain of a Patch feed

[G1BVI]

Hi All
I have just finished my patch feed and mounted it on a 60 cm dish.
The patch gain is suposed to be 8.5dbic.

The dish I am using has an f/d ratio of 0.35 which has a gain of 21 dbic.

Am I right in saying that the whole gain with patch is then 29.5 dbic?

If so I think this equates to 26.5 dbi

Is my ERP then nearly 60W assuming no losses?

Thanks and 73
Nick
G1BVI

[g0mjw]

No you are not correct. Only the dish gain counts and that depends on how well it is illuminated. Your patch will have a beamwidth of about 85 degrees. That seems quite narrow for a 0.35 f/D. It would be good for low noise but I assume this is for the uplink where gain is what matters. You are illuminating less of dish area so an efficiency of 50% seems likely. However, I suspect that is already in the calculation as a perfect 60cm dish on 2.45 GHz would have over 23dB gain, so 21dB seems reasonable, perhaps a little high. Most definitely not 26.5dBi

How much less requires some maths. See http://www.qsl.net/n1bwt/chap6-0.pdf for the theory.

It would appear perhaps you have Jim Millers' AMSAT feed? http://www.jrmiller.demon.co.uk/products/patch.html ?

Mike

[G1BVI]

Hi Mike
Thanks for that .
I have the RUH dish, I have had it sitting in the original box since AO40.

The patch I fabricated myself some years back and recently checked it on a network analyser.
After all this time of sufffering house moves and being thrown about in boxes it has survived Hi hi,

Looking at the maths now.........

73

Nick