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NEC2 cage experiment

The DB

Sr. Member
Aug 14, 2011
1,988
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St. Louis, MO
Did an experiment with NEC2 and out of phase elements in the form of a cage. To create the cage I used elements surrounding a central element, and driven 180 degrees out of phase.

I created these models in freespace, not that that will affect anything here as what we are interested in is the far field difference between the models.

First I created a dipole reference, its gain is 2.16 dBi.

I then created a cage reference. This model contains only the cage elements. I intentionally fed each of them out of phase and 25% of the magnitude of the dipole above. I get 2.15 dBi gain from this model, essentially the same as the dipole reference.

Next I put the two reference models together and adjusted the magnitude of power going to each element, 1/2 to the middle and 1/8 to each of the cage elements.

The result of combining the models is 1.99 dBi gain. That is a very significant amount of radiation. If cancellation were happening as many people theorize then we would have essentially no radiation in the far field from the test model, yet there it is.

Applying this to the Vector design, I don't know what, specifically NEC2 is doing with the cage area to get the results it is, but it appears it is not cancellation.


The DB
 

Shockwave

Sr. Member
Sep 19, 2009
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DB, I think you're saying the 1/4 wave cone by itself has close to unity gain? While I never tried this, it is not what I was expecting. Do you know what the impedance of the 1/4 wave cone by itself is? If I can match it close to 50 ohms it would be easy for me to field test the cone against a dipole.
 

Marconi

Usually if I can hear em' I can talk to em'.
Oct 23, 2005
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Houston
Db, you have me guessing again as to what you are trying to describe.

I did a model of the Vector cone without the radiator...and the model shows a terrible match, and worse pattern.

Show us what you have bud and then I'll post my model or eat crow.

I have confidence you can do that.
 

The DB

Sr. Member
Aug 14, 2011
1,988
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193
St. Louis, MO
OK first off, as I said above, I didn't make an actual basket, I used separate antennas instead.

Model 1, a single half wavelength center fed dipole, gain 2.16 dBi.

Model 2, four center fed dipoles, fed 180 degrees out of phase of the single dipole in Model 1, and each one 0.04 wavelengths from the center point. Also, the magnitude of the power going to each was 1/4 of the single dipole in Model 1. NOTE, this model does NOT include the dipole from Model 1. Gain 2.15 dBi.

Model 3, I put the elements from Model 1 and Model 2 together, so I now have a center fed dipole in the middle, and four center fed dipoles surrounding it. The outer dipoles are fed 180 degrees out of phase with the dipole in the middle and the same amount of power the the middle dipole gets is split between all four of them. From this model, where I expected, based on the models above, to see a gain of essentially 0, I got 1.99 dBi in gain.


The DB
 

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