1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Waveguide basics, please.

  1. Aug 29, 2012 #1
    1. The problem statement, all variables and given/known data
    OK, so, a compounding of my knowledge so far.
    - A waveguide is a conduit for EM waves.
    - They can be parallel plate (infinite), circular, or as I'm looking at - rectangular.
    - Speed of propogation is limited by skin effect - the higher freq, the thinner the skin & so higher resistance . . . . .
    - they are classified in terms of mode (TE, TM, TEM)
    - the modes have different operating conditions (TE10, etc.)

    2. Relevant equations
    Stupid questions I should know regarding TE mode;
    - do the EM waves travel through the media inside the guide(i.e. air) or do they travel in the wall of the guide?
    - in TE mode what do the figures in sbbscript indicate (m & n, I understand as in TEmn)
    - EM waves travel in, say, z-direction. Electric field (transverse, i.e. at 90degrees) to EM propogation, but magnitude of E is less at sides than centre. Why? Is this the infamous boundary conditions? B 1 ⊥ -B 2 ⊥ =0

    Just basics, but I need clarification. Thanks.
  2. jcsd
  3. Aug 30, 2012 #2


    User Avatar
    Science Advisor
    Gold Member

    Resistance does not determine group velocity. At frequencies well above cutoff, the group velocity vg is determined by the dielectric constant inside the guide, while close to cutoff vg becomes frequency dependent. This is termed "dispersion."
    1. Both--they travel within the waveguide system. The wave propagates in the dielectric while the metal "guide" confines and directs the fields.
    2. The subscripts denote the particular mode. In a rectangular guide, the first refers to the x mode and the second to y.
    3. Boundary conditions impose constraints on the fields at the guide surface. You are referring to the configuration of the characteristic mode, or eigenmode, of a wave between two plates. The characteristic functions are sines, and the mode index gives the number of half cycles present between the walls.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook