From: Julien Hillairet <julien.hillairet@gm...>  20110328 08:07:12

2011/3/28 roucaries bastien <roucaries.bastien+qucs@...> > On Fri, Mar 25, 2011 at 5:10 PM, Julien Hillairet > <julien.hillairet@...> wrote: > > Dear Qucs staff, > > > > First of all, thank you for providing the world this very nice tool ! It > is > > of great interest, especially for education but also for research (not > > everyone can afford ADS or Ansoft Designer...) > > > > My question is related to the rectangular waveguide line transmission > > calculator. If the attached picture, I've calculated the properties of a > > WR284 waveguide (72mm x 34mm) @ 3.7GHz. Qucs gives a characteristic > > impedance of Z0=430.4 Ohm. > > > > However, taking the analytical equations, I obtain (this is matlab code) > > > > % TE characteristic impedance of a rectangular waveguide > > a = 72e3; % [m] height > > b = 34e3; % [m] width > > c = 299792458; % [m/s] light velocity > > m = 1; > > n = 0; % for mode TEmn = TE10 > > f = 3.7e9; % [Hz] > > > > lambda = c / f; > > k = 2 * pi / lambda; > > nabla = 119.9169832 * pi; > > beta = sqrt( k^2  (m*pi/a)^2  (n*pi/b)^2 ); > > Z_TEmn = k * nabla / beta > > > > > > > Z_TEmn = 455.7152 Ohm > > > > Could you explain we what is calculated in Qucs ? (and how ?) > > Could you try the simulation of TE10 waveguide ? Or it is only linecalc ? > > Bastien > > Hello, Well, I'm not sure to understand the question (is linecalc the transmission line calculator?). What I've done is launching the rectangular waveguide transmission line calculator, put in the waveguide dimensions and frequency, then launching the "analyse". The simulator gave me the impedance value (see attached picture on first mail) of 430.4 Ohm in my case. However, using standard equations (e.g. from Pozar's book), I find an other result. I'm not saying the Qucs results is wrong, but I would like to understand what is calculated (characteristic impedance of rect waveguide is really a matter of convention...) Best regards, Julien 