EMRFD Message Archive 10989

Message Date From Subject
10989 2015-04-20 12:31:41 Ashhar Farhan antennas out of dielectric materials?
an old marconi patent seems to have arisen from the dead. anybody else has a clue as to how this works?

sorry to treat emrfd as a radio designer's shrink couch....

- f
10990 2015-04-20 13:00:23 Jim Strohm Re: antennas out of dielectric materials?

It's the multiple discontinuities between the metallic conductor from the transmitter, the dielectric attached to it, and the air that make this work.  It's very similar to light diffracting as it passes through an optical lens, and it was a popular antenna design in the 1990s as we were learning the nuances of cellular networking.

At the time, I filed the effect under "if they sell a working product, then it must be good enough."

I'm sure that you've already seen how stuff behaves differently at microwave frequencies than at HF.  My best simplistic explanation is that molecules of everything are many orders of magnitude larger, as a relative percentage of wavelength, at microwave than at HF.  So you'd expect quantum differences -- or else be foolish NOT to expect them.


11005 2015-04-25 18:42:00 kb1gmx Re: antennas out of dielectric materials?
Yes, this is not new by any means.

It was an early not quite expressed recognition that light and EM waves appeared 
to obey the same rules of physics.

Lets see there is a dielectric antenna in an older issue of the antenna compendium.
The first ones I played with were at X band and later K.

The reason they are used more at millimeter wavelengths is the same relationship of light and color(wavelength) when applied to diffraction gratings, Fresnel lenses, and prisms.
The RF obeys the same physics.  

Light travels in optical waveguides and can be focused to a spot or a diffuse area.
Same for RF flowing down a wave guide, or coax to an emitter(radiating element).

You can build, an impractical antenna at HF using the same techniques but long wavelengths would mean large antennas just like reflectors.  Dish antennas can be made for say 10M but what value is a 30M dish that performs only slightly better than a 
more practical yagi?

At about 3-6 ghz the effect is useful, at 10 its very effective and at 78ghz its small.

After all the accelerated charges from an antenna are just photons.  Directional antennas
of all forms are just various type of lenses.  Its fun stuff to play with and it does behave like light  save for at a few GHz its easier to visulize the origin and focus where at 10mhz we are talking about things that have appreciable size so the focal point is measured using 
meter sized or maybe scales.