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Design >> RF Design >> Matching problem
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Message started by jefkat on Jun 25^th, 2007, 7:58am

Title: Matching problem
Post by jefkat on Jun 25^th, 2007, 7:58am

Hi guys,
I have a resistor capacitor parallel combo (100ohm || 8pF). I have to match it to 100 ohm with a return loss of atleast 19dB from 1M to 400M.
Its a challenge. Can anyone float an idea here please ? What are the theoretical limits in such cases ..any clues?? hope to hear some wisdom :-)
Cheers
Shaf

Title: Re: Matching problem
Post by mg777 on Jun 25^th, 2007, 9:33am

Where does the 19 dB come from? Is this for pulse transmission?

Off the top: the bandwidth range 1:400 is way too high, in fact the 8 pF has a 100 Ohm reactance only at 200 MHz. So you're probably looking at 100 MHz to 400 MHz, or a Q close to unity. For starters, try a series inductor of 10,000*8e-12 = 80 nH, which also gives a resonance in the right range. Or fix the resonance and fiddle the Q.

If you want a tighter performance, try a higher order Chebyshev LC ladder. But it's not worth the effort, I think.

M.G.Rajan

Title: Re: Matching problem
Post by jefkat on Jun 25^th, 2007, 11:59pm

yes ,Its about pulse transmission.!
Thanks for your input.