Hi,
I have a rectangular waveguide(WR90) that operates at 9.6 GHz. Its guided wavelength is approximately λ_g = 42.34 mm, and the length of my waveguide is L = 950 mm.
Calculation of S21 Phase
According to my calculations, the S21 phase should be: Δφ = ((2π) / λ_g) × L = (360° / 42.34) × 950 = 8077° Since the wave cycle is 360°, I removed all multiples of 360°, so: Δφ = 157.46°
However, the CST simulator shows an S21 phase of approximately -175°. Because the phase in CST varies between -180° and 180°, -175° is equal to 355°. So they are different.
what is my mistake?
I think that -175 degrees is equal to 185 degrees. This is about 28 degrees out from 157 degrees. There are about 22 cycles along the waveguide, so you only need the guide wavelength to be about half a percent out and that would make the difference. Do you know the guide wavelength accurately enough?
Checking the numbers, CST does seem to be a little out, but only by about 0.34% in guide wavelength. Does this change if you change the mesh size or the stopping limit? (-30 dB, -40 dB, -50 dB).
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