Dielectric antennae

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  • #2
Baluncore
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But I cannot figure out where does the energy feed-in or take-out from the antenna?
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.
 
  • #3
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The dielectric antenna must be supplied with RF energy by a transmission line or waveguide.


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?
 
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  • #4
berkeman
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The problem is WHERE is the opening?
It sounds like a traditional metal microwave horn or metal waveguide is used to inject the microwaves into the ceramic resonator:
Radio waves are introduced into the inside of the resonator material from the transmitter circuit
 
  • #5
berkeman
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This looks like a useful web page:

http://www.ijser.org/paper/Design-o...hed-Characteristics-for-UWB-applications.html
Image_002.png
 
  • #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,
 
  • #7
sophiecentaur
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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?
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.
 
  • #8
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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.


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?
 
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  • #9
sophiecentaur
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Since the antenna is made of dielectric, why is there still need for a metallic plate?
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?
 
  • #10
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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?

Yes.
At present,
I am looking for analytic solution of a ring (shell) shape (center feed?) DRA. Do you have one? Any reference?
 
  • #11
sophiecentaur
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Yes.
At present,
I am looking for analytic solution of a ring (shell) shape (center feed?) DRA. Do you have one? Any reference?
Sorry. I have only read about them in the past.
 
  • #12
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Sorry. I have only read about them in the past.
Is it true that dielectric antenna works more or less like acoustic resonator?
It is a resonator to my understanding, different from metallic antenna.
 
  • #13
Baluncore
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I am looking for analytic solution of a ring (shell) shape (center feed?) DRA.
Please link to or post a sketch of the shape you want. Rings and shells come in many shapes.

Is it true that dielectric antenna works more or less like acoustic resonator?
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.
 
  • #14
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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.

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.
 
  • #15
sophiecentaur
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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.
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?
 
  • #16
Baluncore
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Please link to or post a sketch of the shape you want. Rings and shells come in many shapes.
 
  • #17
Baluncore
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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....
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.
 
  • #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.
 
  • #19
tech99
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The purpose of a resonator in any antenna is to provide matching between the transmitter and the radiating structure.
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.
 
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  • #20
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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?
So,...what is wrong (your very first sentence)?
 
  • #21
sophiecentaur
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So,...what is wrong (your very first sentence)?
Actually, I think it's me that's got it wrong, sorry. (fools rush in) But is the "resonance" the relevant thing or just the standing wave?
There are a number of wire antenna designs that use high order modes on a wire that's several wavelengths long, to increase directivity. The standing waves are there, whatever the length of the wire but the input matching can improve efficiency.
The 5/8 wavelength vertical monopole, beloved of radio amateurs, has significantly higher vertical gain than a simple 1/4 wavelength whip. It's the equivalent of a 5/4 wavelength dipole. I can see that there is a lot to be said for using standing waves in a dielectric dome / ring because it has circular symmetry. The metallic equivalent would presumably be a disc or dish reflector where there are images of the drive over the area of the reflector. I like the 2/3 size advantage for the dielectric system.
I think there must be a limit to the achievable aperture with such antennae due to losses over several wavelengths of path in the dielectric. I remember the problems with flat plate printed circuit slot arrays limited the useable aperture.
 
  • #22
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Actually, I think it's me that's got it wrong, sorry. (fools rush in) But is the "resonance" the relevant thing or just the standing wave?
There are a number of wire antenna designs that use high order modes on a wire that's several wavelengths long, to increase directivity. The standing waves are there, whatever the length of the wire but the input matching can improve efficiency.
The 5/8 wavelength vertical monopole, beloved of radio amateurs, has significantly higher vertical gain than a simple 1/4 wavelength whip. It's the equivalent of a 5/4 wavelength dipole. I can see that there is a lot to be said for using standing waves in a dielectric dome / ring because it has circular symmetry. The metallic equivalent would presumably be a disc or dish reflector where there are images of the drive over the area of the reflector. I like the 2/3 size advantage for the dielectric system.
I think there must be a limit to the achievable aperture with such antennae due to losses over several wavelengths of path in the dielectric. I remember the problems with flat plate printed circuit slot arrays limited the useable aperture.

You seems to write this paragraph with some books? What is that? Wow,5/8 wavelength vertical monopole....
 
  • #23
tech99
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Actually, I think it's me that's got it wrong, sorry. (fools rush in) But is the "resonance" the relevant thing or just the standing wave?
There are a number of wire antenna designs that use high order modes on a wire that's several wavelengths long, to increase directivity. The standing waves are there, whatever the length of the wire but the input matching can improve efficiency.
The 5/8 wavelength vertical monopole, beloved of radio amateurs, has significantly higher vertical gain than a simple 1/4 wavelength whip. It's the equivalent of a 5/4 wavelength dipole. I can see that there is a lot to be said for using standing waves in a dielectric dome / ring because it has circular symmetry. The metallic equivalent would presumably be a disc or dish reflector where there are images of the drive over the area of the reflector. I like the 2/3 size advantage for the dielectric system.
I think there must be a limit to the achievable aperture with such antennae due to losses over several wavelengths of path in the dielectric. I remember the problems with flat plate printed circuit slot arrays limited the useable aperture.
I think you were right in the first place. If you consider a wire with a certain current flowing, then the radiation will be the same however you produce that current. For instance, you can either use transmission line resonance in the wire or terminate it with a resistor. The latter method is wasteful but radiates a very similar field for each Amp-metre.
 
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  • #24
sophiecentaur
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You seems to write this paragraph with some books? What is that? Wow,5/8 wavelength vertical monopole....
IT's the sort of antenna that suits 2m comms bands. You put it on a ground plane and mount it up on a chimney. I have even made one which worked well. It also happens to be fairly non-critical to match to a 50Ω feeder. Just google it. There is plenty of stuff written about practical applications.
But your application is for a very different wavelength.
 
  • #25
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Is it possible to have an antenna of such shape?
The left is the top view the right is the side view.
Why is such design?
 

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