E-field Physical Interpretations

[GFEM]

Hi,

I'm currently working on a project investigating power transfer using helical antennae, however, before I can construct an experimental verification of the designed system I need to conform to the RF legal requiremetns, seeing as the system emits EM-waves (Far-Field, not the power transfer medium).

My questions regards the physical interpretation of the E-field component emitted by antennae, specifically a normal mode helix antenna.

One gets two components 90 deg out of phase, however the one component is a complex value. What is the physical interpreation of this complex component? Is this notation merely an indication of the 90 deg phase shift or does it have a physical connotation?

Regards

 

[Noway2]

This sounds like it could be a veiled student post, but I will assume that it is not.

The two signals, one real and complex, repersent the signal with magnitude and phase. The (physical representation) of the complex signal (sinuoid?) is rotation, in time and / or space.

 

[GFEM]

We're all students

However it is not a student post.

Yes, I understand the mathematical interpretation of the complex notation, however I'm specifically concerned with this complex value, seeing as RF transmission standards limit the magnitude of emitting E-fields above which one requires licensing (which I prefer not to get for only experimental purposes).

Although not entirely the answer I was looking for, it does provide some clarification even if only reminding me of the basics.

Thanks.

 

[MacGyverS2000]

seeing as RF transmission standards limit the magnitude of emitting E-fields above which one requires licensing (which I prefer not to get for only experimental purposes).

There's a reason for that licensing... to prevent experimenters from blasting radiation out every orifice of their metal structures and screwing with those who are licensed.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[GFEM]

I have no intention of emitting fields that will interfere with bands for which one requires licensing, hence my humble attempt to clarify certain gaps in my understanding to confrom to requirements for which one would not need licensing.

This does not seem to be the right place for such endeavours.

 

[djs]

The magnitude of the EM wave is sqrt(re^2+img^2).

 

[GFEM]

Yes, basic mathematics, however, in case of the helical antenna the complex component is contributed solely by the ideal dipole component of the antenna.

This relates to a complex power component, which in real world applications may be neglected in terms of telecommunication limits.

Which brings me to my question, is the latter a correct assumption? Meaning I’m only concerned with limiting the small loop component of the helix design.

Regards

 

[VEBill]

I'm not sure if the following background information is already known to you, but it might provide pointers to further information to clarify things.


Helical antennas come in two varieties:

The normal mode (intended to radiate like a monopole) are typically built such that the diameter is a tiny fraction of the wavelength. So what you're left with is a short and relatively inefficient antenna. They're typically covered with black plastic and are called "rubber duck" antennas, as seen on walkie-talkies.

Because of the tiny dimensions of the diameter as a fraction of wavelength, there's not much talk of circular polarization.

But there is plenty of talk of how inefficient they are. Usually about 6 dB down (roughly!) from a simple 0.25-lambda whip.


The axial mode (radiating Circularly Polarized off the far end) helical antenna are built much larger. Where a VHF rubber duck antenna will slip into your pocket, an axial mode helical antenna for the same band would fill a pick-up truck. These are often used for VHF/UHF SatCom.

They can be essentially perfectly efficient. The axial mode helical antenna is equivalent to two crossed Yagis fed (or space) 90-degrees out of phase. The crossed Yagis feed system can be easily switched RHCL / LHCP.

Perhaps that's the 90-degree phase result that you're seeing in your math. But it only applies to 'big' axial mode helical antennas. If you see it for normal mode, then check the magnitude.


As far as using a small, inefficient, omni-directional, normal mode helical antenna for power transfer - good luck...

By way of example, the antennas used to 'light up' RFID tags (the type powered by the RF) are usually chosen for maximum efficiency and the gain carefully directed to the target location. The fixed antennas on our local toll bridges RFID system are large panels, and they're only trying to span an 8-foot gap.

 

[GFEM]

Hi,

Definitely gives me something to "chew" on.

The power transfer mechanism to be used does not use the power radiated in the far-field of the antennae, the main reason for my interest is to limit such radiation to conform to telecommunication regulations.

The more inefficient the antenna is in the far-field the better.

Regards