antenna-theory.com

[emcengineer]

I have questions related to slot antennas and slot apertures.

I work as an electromagnetic compatibility (EMC) engineer. My company is considering adopting a patented shielded chassis design which is advertised to reduce the effective length of a slot aperture and provide better shielding and less radiation. It is done without adding contact points across the slot aperture. But I am very skeptical about the theory behind this.

My understanding is that a slot aperture will radiate just like a slot antenna, and the shape of the slot doesn't matter, it's all about the length of the slot.

I have reviewed the presentation and the actual patent, and I don't see a valid explaination. It seems to imply that an RF E-field will "leak" through a slot aperture, much like a coin will pass through a coin slot, and if you change the shape of the coin slot, then the coin won't fit through. Am I missing something? Please see the presentation:

http://www.tomcoughlin.com/Techpapers/Tortured%20Path.pdf

[Schubert]

Slot apertures will radiate similarly to slot antennas.

As to meandering the slot, it depends on how the boundary is wrapped. If you think about a dipole antenna, the effect of a meandering the dipole will cause the radiation to not add up in phase. As long as the currents are not adding in destructive phase, then the overall radiation efficiency will not be affected.

However, if the meander snakes back and forth, there will be some loss in radiation efficiency in bandwidth. It is similar in the case of the slot antenna - except it is the aperture fields that give rise to the radiation.

As for reading the patents - they are of no use. They are written to be general and confusing and contain little actual information - i.e. what lawyers use for job security.

As for your coin analogy - yeah that doesn't make sense. If you bend the aperture by 90 degrees, you'll still have about the same radiation.

Your application is not clear to me though. You want to reduce radiation and increase shielding but you can't short out the slot at a few places?

[emcengineer]

Schubert,

Thanks for your reply. For our chassis applications, we can certainly short out the slots by adding contact points, or even place an EMI gasket in the slot to completely seal it. That is normally what we do.

However, in the attached presentation, they claim that they can accomplish the same thing by changing the shape of the slot. The whole idea is that EMI gaskets and contact points are not required, resulting in a cost savings.

If you look at the first page of the presentation, they say that the new effective wavelength is reduced to the length of just one of the tiny sinusoidal segments. That is what I don't understand. That appears to make no sense what so ever.

Remember, the attached presentation is from a vendor who is trying to "sell" their patented technology to our company. There would be a royalty for each chassis that uses this technology. People can file a patent for any idea, regardless of whether it works or if it makes sense. There are patents for valid technologies, and there are "April Fools" patents. My concern is that this is an April Fools patent.

Any thoughts?

[Schubert]

Well I'd say it doesn't make a ton of sense. I would ask them for a sample or equivalent mockup to evaluate the effectiveness relative to nothing and with EMI gaskets.

I'd be interested in hearing if it works. I would guess no - if the slot is still there the radiation will make it out one way or the other.

[emcengineer]

So the patent claim is that the "effective wavelength" is reduced to a straight line segment that would fit in the transition segment of a sinusoid. This would mean that any signal with a frequency lower than 1/2 of this effective wevelength would not pass through.

But my understanding is that the opposite may happen. Changing a straight slot to a sinusoid will increase the perimeter around the slot. And in doing that, it would lower the primary radiation frequency.

And as Schubert mentioned, the meandering section of the slot would phase cancel a higher frequency signal where the wavelength would match a segment of the sinusiod.

Does that make sense? Can anyone else chime in or at least give a quick vote on there thoughts about this technology? Valid or Bogus?