From: roucaries bastien <roucaries.bastien+<qucs@gm...>  20110328 09:13:18

On Mon, Mar 28, 2011 at 10:07 AM, Julien Hillairet <julien.hillairet@...> wrote: > 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...) They are two rectangular waveguide implementation:  one in linecalc (transmission line calculator)  one used internally for simulation of rectangular waveguide. Bastien > > Best regards, > > Julien > > 