Gain and bandwidth - RF Cafe Forums
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Post subject: Gain and bandwidth
Unread postPosted: Thu Apr 28, 2005 1:11 am
Joined: Sat Apr 23, 2005 2:09 pm
Location: Tampa, FL
I was just reading the Pozar book and on p.553 it mentions that "it is preferable to design for less than the maximum obtainable gain to improve bandwidth."
Is there a formal derivation to this statement? I'm curious why.
Unread postPosted: Thu Apr 28, 2005 1:25 am
Joined: Tue Mar 15, 2005 11:43 pm
I think it's related to this condition "Gain-Bandwidth is equal to constant", which derived from Bode-Fano Theorem.
Therefore, by designing for less than the maximum obtainable gain, wider bandwidth will be obtained.
Thanks and Regards,
Unread postPosted: Mon May 02, 2005 1:30 pm
The last post is absolutly correct. Fanos limit shows that for wider bandwidth, the gain will be reduced.
Unread postPosted: Tue May 03, 2005 8:49 am
Aint Bode-Fano's criterion showing the VSWR-bandwidth product that a matching network can have for a given quality factor mostly for passive devices shuch as antenas?
I always had the impession that remplacing VSWR by GAIN was an oversimplification. In my mind it only work as stated if the device in unilateral.
Second, what is this GAIN-Bandwitdh tradeoff? What gain? A flat gain or the Maximum available gain over frequency, whatever value or rolloff it shows?
Very often people will design matching network to autocompensate the gain rolloff and obtain a flat response, by sacrificing the VSWR.
I see Bode-Fano as a good starting point to sea if a matching is feasable.
Unread postPosted: Tue May 03, 2005 11:43 am
You are correct , it is a criterion for passive networks. The matching networks are passive, therfore, the wider the bandwidth the higher the loss, hence lower gain.