Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
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Gain and bandwidth - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
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Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
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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
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
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.