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Waveguide VSWR  RF Cafe Forums

The
Amplifier 
Post subject: Waveguide VSWR
Posted: Mon May 08, 2006 7:47 am



Captain 

Joined: Fri Jul 16, 2004
4:08 pm Posts: 11 
Hello, I need to desing a waveguide system
for Ku band that will have a total length of around
100' and will have a total of about 135 degrees
worth of bends between the Tx and the antenna (parabolic
dish). Throw in a coupler and a SPDT switch (redundant
paths). My question is how do I calculate
the total VSWR for the system given the loss and
VSWR of each section? I know I could do worst case,
but that's not what I excpect to really show up
when testing it. Does anyone know how to go about
it? Do you use an RSS or RMS addition from stage
to stage? Any assistance will be welcome. I hate
to go into these things blind (this is my first
WG system). Thanks guy.





RFTEJerry 
Post subject: Cascaded VSWR formula
Posted: Mon May 08, 2006 3:08 pm



Captain 

Joined: Thu Apr 13, 2006
9:53 am Posts: 18 Location: Florida

I can't figure out how to write an equation here
so I'll "write" it out in the hopes it is clear
enough to understand. The basic formula for
cascaded VSWR is: VSWR(total)= 1+gamma(total)/1gamma(total).
The trick here is to figure out what the total
gamma is. In the early nineties I had a supplier
who built for us an RF switching/conditioning WRA.
In his ATP he had the following formula to calculate
the cascaded VSWR through the many switches to the
front panel. He got it from a text book. The formula
goes like this: gamma total = the square
root of the sum of the squares of the individual
gammas minus the product of the square of the individual
gammas. gamma total = SQRT[(gamma_1^2 + gamma_2^2+...gamma_n^2)
* (gamma_1^2*gamma_2^2...gamma_n^2)] Hopes
this helps RFTEJerry





vince 
Post subject: Cascade VSWR
Posted: Thu May 18, 2006 3:38 pm


Joined: Thu May 18, 2006
1:54 pm Posts: 1 
I found a reference for calculating cascade VSWRS
using a linear combination method refer to web site
for equation
http://www.y1pwe.co.uk. I don't know how much
this differs from the one you provided. I
would like to refer to a text reference on this
subject and how does this equation differ for when
you have two components and the worst VSWR is the
multiplication of each VSWR individual VSWR.
Thanks.





nubbage 
Post subject: WAVEGUIDE VSWR
Posted: Fri May 19, 2006 7:36 am



General 

Joined: Fri Feb 17, 2006
12:07 pm Posts: 304 Location: London UK

Hi All Back on line again Jerry, I think
the formula you mention (in which you have * instead
of  ???) is actually the range of variation that
Gamma can take. The Gamma will range between
a min and max set of values as the relative phasing
of the components' gammas change (gamma is a vector).
Hence you need to calculate both halves of the
expression independently and this gives the extreme
limits of gamma. I think.


Posted 11/12/2012



