HEc11 to TEM mode?
I've learned that it is common to use elliptical waveguide in microwave backhaul connections which are HEc11 mode dominant. If the TEM mode is used in coaxial transmission lines why do we use elliptical waveguide if it does not allow the TEM mode to propagate. I understand that the elliptical waveguide handles much higher frequencies but I'm trying to understand why the HEc11 mode is still ok for transmission of a signal. Forgive me if this is a silly question. Also, is there a way when using a waveguide to coax adapter to "covert modes"?
I know for high frequencies, it’s a loss issue. It order to stay TEM for coax, you have too keep reducing the diameter, then the loss increases substantially. Using coax past 26 GHz for more than a few meters length is problematic.
Waveguide has much lower loss per unit length than the equivalent TEM coax, but now dispersion becomes the issue.
So back in school, my Microwave professor said Bell had manufactured miles of circular waveguide for use in telecom, which was obsolete overnight by fiber. There was a certain circular mode that has very low dispersion, compared to rectangular.
This looks like a good discussion of the elliptical waveguide.
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