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Jeanalmira Post subject: Resonant cavity combiner Q factor Posted:
Wed Feb 07, 2007 1:52 am General Joined: Tue Mar
15, 2005 11:43 pm Posts: 65 Location: Singapore Hi All :
I have a question regarding resonant cavity combiner. As it is mentioned
that this combiner disadvantage is narrow-band as it has high Q (Quality
factor). By formula : BW = (fresonant)/Q But I am not
sure how to determine/ derive Q? It is my guess that it derives
from permittivity and conductor properties? I am trying to relate
that Q= (1/R) * (sqrt (L/C)) ? and I also read that the Q somehow
related to eigenvalues or number of waves? I am not sure about this.
and how exactly it is related? Any advice is appreciated.
and please recommend good textbook on waveguide combiners Thanks
and Regards, Jean Top nubbage Post subject:
Posted: Wed Feb 07, 2007 10:31 am General Joined:
Fri Feb 17, 2006 12:07 pm Posts: 218 Location: London UK The
formulas you need are a) for a cylindrical cavity length L diameter
D in TMlm0 mode Q = (lambda0/skin depth) * (Xlm/(PI*(2+r))) where
r is the ratio of diameter to length Xlm is the mth root of Jl(x)
= 0 For higher modes the expression is more complicated (!!) b)
rectangular cavity, of width a height b length c, the TE10n mode expression
is Q = (lambda0/skin depth)*(0.5*a*b*c)*(p^(2)+r^(2))^(1.5)/(p^(2)*c*(a+2*b)+r^(2)*a*(c+2*b))
where p = 1/a r = n/c Again, other modes, other expressions.
I have the formulas for resonant wavelengths lambda0, as well if
you need them. Skin depth is on the encyclopedia on the home page.
The formulas can be found in "The Microwave Engineers Handbook and Buyers
Guide" 1966 where there are also graphs for the cavity modes.
If there is a text book, I regret I do not know of one.
Top Jeanalmira Post subject: Posted: Thu Feb 08, 2007
12:12 am General Joined: Tue Mar 15, 2005 11:43 pm
Posts: 65 Location: Singapore Hi nubbage : Thank you for
your advice. I will try to find the handbook. By the way, am
I right to say that the mode numbers, which is the eigen numbers actually
represent the number of waves? I am not sure about this. Please
enlighten me. Thanks and Regards, Jean Top
nubbage Post subject: Posted: Thu Feb 08, 2007 7:40 am
General Joined: Fri Feb 17, 2006 12:07 pm Posts: 218
Location: London UK Hi Jean Yes, the mode number is the number
of cycles the field goes through. If it varies from zero through
a peak and down to zero it is mode 1. If there is no variation, so
the field value is constant, it is mode number 0. I will try to upload
a scan of the Handbook pages in the next couple of days. The 1966 "Handbook
and Buyers Guide" is very difficult to obtain these days. I am not sure
when Microwave Journal stopped issuing this, but it was a very valuable
source of design data. Top Jeanalmira Post subject:
Posted: Thu Feb 08, 2007 9:02 pm General Joined:
Tue Mar 15, 2005 11:43 pm Posts: 65 Location: Singapore Hello
Nubbage : Thank you for your advice. It is very helpful.
I am very new to this waveguide issues. I found that eigen numbers
(mode numbers) are represent by 3 variables, e.g. n,m,p. So the resonant
frequency is given as fmnp. But I am not sure what this n,m,p exactly
represents? You are right, I can't find the handbook.
Thanks again, and looking forward to your uploaded articles
Best Regards, Jean Top Jeanalmira Post
subject: Posted: Thu Feb 08, 2007 9:07 pm General
Joined: Tue Mar 15, 2005 11:43 pm Posts: 65 Location: Singapore
Hi : I have another question, what does it mean by mode spacing?
and how to calculate that? Thanks again. Cheers, Jean
Top nubbage Post subject: Posted: Fri Feb 09, 2007
6:32 am General Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218 Location: London UK I have uploaded (I hope) the 3
images for the design graphs I hope
those work OK[/url] Top nubbage Post subject:
Posted: Fri Feb 09, 2007 6:34 am General Joined:
Fri Feb 17, 2006 12:07 pm Posts: 218 Location: London UK One
did not load Here is another try Top Jeanalmira
Post subject: Posted: Sun Feb 11, 2007 9:46 pm General
Joined: Tue Mar 15, 2005 11:43 pm Posts: 65 Location:
Singapore Hello Nubbage : Thank you for your help. However,
there is only one graph that can be viewed. If you do not mind,
please send me the article/ link to j_almira@yahoo.com Thanks
in advanced. By the way, I have another question related to resonant
cavity waveguide combiner : why as the modes increase, the combining
efficiency decreases? Thank you. Best Regards, Jean
Top Jeanalmira Post subject: Posted: Sun Feb 11,
2007 9:48 pm General Joined: Tue Mar 15, 2005 11:43
pm Posts: 65 Location: Singapore Hello Nubbage : I
managed to view all graphs. Thanks a lot Top
Jeanalmira Post subject: Posted: Sun Feb 11, 2007 10:05 pm
General Joined: Tue Mar 15, 2005 11:43 pm Posts:
65 Location: Singapore Hi : regarding the number of modes
and combining efficiency, am I right to say : as dimension increases-->
lambda increases--> Q decreases and therefore, combining efficiency
decreases. and as dimension increases, the number of modes increases
and therefore, by relating both cases: as the number of modes increase,
the combining efficiency decrease? I am not sure about this,
I feel rather confused Please enlighten me. Thanks and Regards,
Jean Top nubbage Post subject: Posted: Mon Feb
12, 2007 5:07 am General Joined: Fri Feb 17, 2006
12:07 pm Posts: 218 Location: London UK Hi Jean Broadly
you are right, except the Q does not fall as the wavelength and size
increases. I think, intuitively, that with larger dimensions (for example
in a microwave oven) the number of supportable modes increases, whereas
coupling is usually designed for peak efficiency into only one of the
modes (or a few anyway). Consequently some energy in the cavity is
not coupled, and either gets reflected to the sources or dissipated
as metal resistive losses. Top Jeanalmira Post
subject: Posted: Tue Feb 13, 2007 12:06 am General
Joined: Tue Mar 15, 2005 11:43 pm Posts: 65 Location: Singapore
Thank you for your advice! Best Regards, Jean
Top tjunqueira Post subject: Posted: Thu Mar 08, 2007
11:24 am Lieutenant Joined: Thu Mar 08, 2007 11:07 am
Posts: 1 Hi Jeanalmira and nubbage! I read your messages about
designing resonant cavity combiner. It was really useful for me. I need
to design a combiner with 10 inputs of 2,5 KW each one, the frequency
is 476 MHz. For now I have no idea how to do this, but I have two months
for this. I've been studying transmission lines and wave guides,
but it too far from developing a combiner. As you shown on your discussion,
both of you are advanced on designing. Could you give me some tips about
where to study, where to look for more information, basic projects you
did. Everything is well come. Another thing, do you use anything
to simulate this combiners? HFSS, CST, or any else thing? Thanks!
Posted 11/12/2012
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