[AMPS] More Relevant SWR FINAL EXAM

[Jon Ogden]

measures wrote:

>�  I used isolators when I worked in a calibration lab.  They had two 
>waveguide connections, and they had no characteristic Z.  

No characteristic Z huh, Rich?  Or perhaps you just didn't know what that characteristic Z was?

A waveguide has a characteristic impedance at a given frequency.  The math is a little too complicated to go into here.  Typically the characteristic impedance for the TE10 mode in rectangular waveguide is set equal to unity (Zo=1) ("Applied Electromagnetism" by Shen and Kong page 136).

So whatever the impedance is of the waveguide (depending on the design, etc) the termination resistance in the isolator must be set equal to that in order for proper function.

Many times the loads in microwave waveguide isolators are of a conical shape which gives them wider bandwidth and better impedance matching so that the incoming waves are properly damped and absorbed.

But more common nowdays (at least for frequencies below 2 GHz) are stripline or coaxial isolators.  Since most stripline (this term I use can also cover microstrip) circuits and most coaxial circuits are 50 Ohms, the impedance of the isolator needs to be matched to that as well.  So while I will concede that for waveguide, you might not necessarily spec or deal with a characteristic Zo for an isolator, you definitely do for other transmission line media.

73,

Jon
KE9NA


--------------------------------------------------------------------------
The Second Amendment is NOT about duck hunting!


Jon Ogden

jono@enteract.com
www.qsl.net/ke9na

"A life lived in fear is a life half lived."


--
FAQ on WWW:               http://www.contesting.com/ampsfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm