guide wavelength in a rectangular waveguide

[julie3575]

Hi,

I'm trying to simulate a waveguide fed slot antenna with only the TE01 mode using HFSS.

Is the guide wavelength only dependent on the wider waveguide dimension a? Because the narrower dimension b also seems to affect the guide wavelength when it's too narrow.

Also, would the guide wavelength change if the waveguide is terminated vs. unterminated, or if slots are made on the waveguide vs. no slots?

Thanks.

 

[biff44]

From the classical equations TE10, guide wavelength should only be dependent on a and frequency.

If you put transverse slots in the waveguild broad wall, those will look like series inductors, and should change the guide wavelength from their reactance.

As far as making the b dimension very small, well, I guess you might be violating one of the boundary conditions used in determining the (simple) classical equation (i.e. there might have been higher order terms left off for when a/b=0.5, etc).

 

[Higgler]

If the thin direction is too thick, the guide wavelength would change alot. If you shrunk the height and saw HFSS change S21 phase, that's probably more of a capacitive delay with shortened height and not wavelength in the guide change. capacitance is related to 1/d and you shortened d.

The energy really bounces side to side on the way down the waveguide. Lowest frequency is the longest path, highest frequency is a shorter path. Remember light waves goes straight down the middle. Near cutoff, the energy is virtually going all sideways. The sidewalls are then 1/4 wave shorts or open circuits on 3 of 4 sides.

Wavelength will probably change a bit by adding an antenna slot aperture. Since the energy moving around the slot goes a longer distance.

Terminated or unterminated won't matter, but the standing waves of course will change and your antenna gain will change.