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    Waveguide slot antenna confusion about radiating and non-radiating slots.

    Hello all!
    Assume we have TE10 waveguide with slots.
    I have some confusion, which comes from here:

    1) http://www.radartutorial.eu/06.anten...ntenna.en.html

    it is written that (slot A) will radiate,
    and (slot B) will NOT radiate

    2) http://www.antenna-theory.com/antenn...dWaveguide.php

    Figure 2. Waveguide with a thin slot centered about its width.
    it is written that slot similar to (slot A case 1) will NOT radiate (opposite statement to case 1)

    Figure 3. Horizontal slot in a waveguide.
    it is written that slot similar to (slot B case 1) will radiate (opposite statement to case 1)

    3) http://www.qsl.net/n1bwt/ch7_part1.pdf
    explains things a little on page 4:
    Therefore, a slot in the exact
    center of the broad wall of the waveguide will not radiate at all, since the electric field is symmetrical
    around the center of the guide and thus is identical at both edges of the slot. As the slot is positioned
    away from the centerline, the difference in field intensity between the edges of the slot is larger, so
    that more current is interrupted and more energy is coupled to the slot, increasing radiated power.
    it seems that radartutorial.eu website waveguide image current distributions are somehow wrongly placed (wide wall current distribution is shown on narrow wall)?

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    What is the purpose of "U" shaped slots in this slot antenna?

    I found an image of slot antenna here: http://cn.comsol.com/model/substrate...-antenna-16021
    What is the purpose of small short 90 degree angled slot extensions at both ends of each slot? What is the idea behind this? I did not found such slot configuration in slotted waveguide papers.



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    Re: Waveguide slot antenna confusion about radiating and non-radiating slots.

    as far as the 90 degree ends of the slots in the Comsol example. I would guess the total length of the slot, including the two tabs at the end, is approximately half wavelength, so that it resonates. Then the two 90 degree tabs are coupling energy from the waveguide (near those top edges of the waveguide are maximum current flow points).


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    Re: Waveguide slot antenna confusion about radiating and non-radiating slots.

    It think that you are right about total slot length (including 90 degree parts) and excitation frequency.

    Still not sure about current distribution here (te10 waveguide):
    Click image for larger version. 

Name:	current-distribution.png 
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    (fig.3 from http://www.radartutorial.eu/06.anten...ntenna.en.html)

    and here:
    Click image for larger version. 

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ID:	125031
    (at the bottom of page http://nptel.ac.in/courses/117101057/Slides-6/7.4.html)

    The second image seems to be correct.
    Last edited by Terminator3; 13th January 2016 at 02:54.



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    Re: Waveguide slot antenna confusion about radiating and non-radiating slots.

    I have a new question about SIW (substrate integrated waveguide) to microstrip line taper transition.
    There are different formulas to calculate such taper. One approach is to calculate waveguide impedance.
    I was given few formulas:
    ZTE=Sqrt(MU/E0)*LG/LAMBDA
    ZPI=ZTE*Pi^2*B/(8*AS)
    where AS is SIW dielectric filled waveguide (DFW) width
    (AS formula from http://www.microwaves101.com/encyclo...ated-waveguide)
    As i understand, waveguide impedance ZPI then can be used to calculate microstrip line width (connected to SIW). Is it correct?

    To clarify:
    50 ohm microstrip - > quarterwave transformet to ZPI -> ZPI of SIW waveguide
    50 ohm microstrip - > taper from 50 Ohm to ZPI -> ZPI of SIW waveguide
    or ZPI can't be used in such way?



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    Re: Waveguide slot antenna confusion about radiating and non-radiating slots.

    How one can measure conductance of slot, and what equipment is required?
    Also, how to measure conductance of slot in simulation?
    Formulas exists to calculate slot conductance, how we can practically measure it?

    I think we can use two identical waveguides. One with slot, and one without slot.
    Measuring S11 and S21 of waveguide we can find variation and be sure that loss in s21 power is not due to reflection (s11). I mean if S11 not changed alot, or become better, and s s21 becomed smaller, then difference is radiated, but also maybe dissipated in heat.



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