From: Stefan Jahn <stefan@gr...>  20110328 10:12:31

Am Fr, 25.03.2011, 18:10 schrieb Julien Hillairet: > Dear Qucs staff, Hello! > 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 ?) Thanks for reporting the discrepances. Indeed in the TransCalc program it shows Z0=430.4 Ohm, but in the Qucs schamtic simulation you will get the expected 455.72 Ohm... I am going to check, what is wrong in the Transcalc calculation... Best regards, Stefan. 