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Gain and bandwidth - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


Qacer
Post subject: Gain and bandwidth
Unread postPosted: Thu Apr 28, 2005 1:11 am
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Captain

Joined: Sat Apr 23, 2005 2:09 pm
Posts: 17
Location: Tampa, FL
Hi all,

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.

Thanks!


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Jeanalmira
Post subject:
Unread postPosted: Thu Apr 28, 2005 1:25 am
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General
User avatar

Joined: Tue Mar 15, 2005 11:43 pm
Posts: 65
Location: Singapore
Hi,

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,
Jean


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Guest
Post subject:
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.


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Guest
Post subject:
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.


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Guest
Post subject:
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.



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