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Dielectric antennae

  1. Feb 15, 2017 #1
  2. jcsd
  3. Feb 15, 2017 #2

    Baluncore

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    The dielectric antenna must be supplied with RF energy by a transmission line or waveguide.
    The RF energy may be generated within the dielectric material by an RF amplifier on the ground-plane.
     
  4. Feb 15, 2017 #3

    I think this is the same as other antenna. Normal antenna also need to be supplied with electric wire.
    The problem is WHERE is the opening?

    For a linear antenna, we normally cut in the middle to feed the energy.
    For a circular antenna, we cut anywhere.
    But the only shape of dielectric antenna I have ever seen is cylindrical shell (why?) so...
    where should I cut?
     
    Last edited: Feb 15, 2017
  5. Feb 15, 2017 #4

    berkeman

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    It sounds like a traditional metal microwave horn or metal waveguide is used to inject the microwaves into the ceramic resonator:
     
  6. Feb 15, 2017 #5

    berkeman

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  7. Feb 15, 2017 #6

    tech99

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    The dielectric antenna is often a resonator having high Q. The induction fields extend outside the material to some extent and energy is coupled into it by a probe. Due to the high Q, the reactive fields are very strong, so very little coupling will be required.
    Another class of dielectric antenna may consist of a tapered rod, obtaining directivity by travelling wave action. In this case the Q is low and energy will be coupled by a structure which is larger than for the high Q variety, resembling a conventional metallic antenna located at one end.
    Notice that a dielectric contains charges which can be made to accelerate, and hence it will radiate. By contrast, a capacitor having wide spacing but filled with a vacuum will not.

    conventional ante,
     
  8. Feb 18, 2017 #7

    sophiecentaur

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    One way to describe how an antenna works is that the Feed point (where the power is connected) launches a wave onto the radiating structure. In the case of a straight wire antenna, the wave passes along the wire and is reflected at the ends to form a standing wave along the wire. A directional wire antenna uses several wires to produce a wave in a preferred direction. A dish (parabolic) antenna focusses a broad beam from the drive point (waveguide or dipole) to point in the wanted direction.
    In a dielectric antenna, the wave is launched using a capacitative coupling and directivity is achieved in a similar way to how a lens works - by refraction at a curved surface. I only know of dielectric antennae being used at high radio frequencies (microwave wavelengths).
    Have you googled "dielectric antennae' Images? Pictures are useful for this sort of subject.
     
  9. Feb 18, 2017 #8

    Yes, I googled and find some useful picture, such as
    http://file.scirp.org/Html/2-9801252/34094843-70a9-4b80-8de7-9f897d1ebfc0.jpg

    Perhaps, I never seen one, the description sounds strange for me....
    That picture is strange too. They usually said it had a ground metal plate? But the cylinder had no opening?

    Since the antenna is made of dielectric, why is there still need for a metallic plate?
     
    Last edited: Feb 18, 2017
  10. Feb 23, 2017 #9

    sophiecentaur

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    There has to be some way of applying an EM field to the dielectric so that the waves through the antenna are directed or focussed in some way. The "plate" will possibly be inside the dielectric itself and launches the wave into the shaped dielectric.
    There are many designs for dielectric antennae so, as with 'metal' antennae, it is not possible to specify much about the feeding arrangement. Some dielectric antennae behave just like an optical lens - in the same way that a reflecting dish (e.g. Newtonian Telescope) does effectively the same thing as the lens in a refracting telescope.
    Did you look in Google Images yet?
     
  11. Feb 23, 2017 #10
    Yes.
    At present,
    I am looking for analytic solution of a ring (shell) shape (center feed?) DRA. Do you have one? Any reference?
     
  12. Feb 23, 2017 #11

    sophiecentaur

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    Sorry. I have only read about them in the past.
     
  13. Feb 26, 2017 #12
    Is it true that dielectric antenna works more or less like acoustic resonator?
    It is a resonator to my understanding, different from metallic antenna.
     
  14. Feb 26, 2017 #13

    Baluncore

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    Please link to or post a sketch of the shape you want. Rings and shells come in many shapes.

    Yes, you can think of it that way, but I doubt that it will make it easier to understand. You might do better thinking of a DRA as a glass bead or lens with dimensions of only a few optical wavelengths.
     
  15. Feb 26, 2017 #14
    For a man has background in acoustics and played music instrument an acoustic resonator is indeed much easier.
    However, I think the physics inside is indeed a resonator, quite different from lens, other metallic antenna, and glass beeds....
    You put a fork on a box then it is louder.....I guess that is the way it is woking.
     
  16. Feb 26, 2017 #15

    sophiecentaur

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    You seem to have got this all wrong (which is what can happen when people jump into a very complex subject without the basics). The purpose of a resonator in any antenna is to provide matching between the transmitter and the radiating structure. Most acoustic radiators are also matched to the source and it is common to use a resonator to achieve this (A Wooffer for instance, uses a Helmholz type resonator). But there are still non-resonators in acoustics - think of the Horn structure; that has no resonance.
    Most (but not all) metallic antennae use resonance. Take the humble dipole, for instance, which is usually (but not always) chosen to have a length that resonates. A dielectric antenna is used to achieve directivity and requires an interface between the metal circuitry and the dielectric medium and that can be resonant. Can any members think of a dielectric antenna that's used for a wide / omni pattern?
     
  17. Feb 26, 2017 #16

    Baluncore

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  18. Feb 26, 2017 #17

    Baluncore

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    A glass bead or lens has a reflection coefficient at the surface that results in radiation of the transmitted component from over the entire dielectric surface, while the internally reflected component provides the internal low-loss resonance.

    An acoustic resonator behaves more like holes cut in a waveguide stub. Radiation is only released from discrete ports in the resonator wall. If you want to study perforated waveguide arrays, then you can model them as acoustic resonators. But that will not help you understand dielectric resonator antennas.
     
  19. Feb 27, 2017 #18

    tech99

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    Can any members think of a dielectric antenna that's used for a wide / omni pattern?[/QUOTE]
    In the case of some microstrip antennas, there may be radiation from the dielectric layer.
     
  20. Feb 27, 2017 #19

    tech99

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    Further, when the transmitter is switched on, the resonant structure takes some time to fill with energy. During normal operation it is not doing any radiating. Then, after switch-off, it continues to supply energy to the radiating structure for another short period of time. The stored energy provides the induction fields that are seen around an antenna. The same happens with acoustic instruments such as a guitar. The "box" does not amplify the sound, it is just the radiating structure. Energy is put into the string by plucking and then it slowly empties again into the wooden radiating structure.
     
  21. Feb 27, 2017 #20
    So,...what is wrong (your very first sentence)?
     
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