POSTED 15 NOV 2010
HERE’S A PICTURE OF THE KEY SLIDE, IN HIGH RESOLUTION (Spectrum from 600-2600 MHz; GAIN in 5dB steps; SWR in unit steps)):
“Welcome to our video. Here we show how fractal metamaterials can be used to retrofit a simple monopole antenna, dramatically increasing its bandwidth and gain.
The monopole antenna was invented by Marconi and uses a ¼ wave vertical wire and typically a ½ wave diameter plate. It is a very simple, omnidirectional in azimuth, and the most common antenna in electronics.
Using a calibrated Agilent network analyzer, we can show both the gain and SWR of an 800 MHz monopole. We used the usual cal kits for S11 and normalized to a 6 dBi log periodic for S12. There’s nothing but choked cables going to the pickup antenna and so-called antenna under test . Here’s the data.
Notice the top curve showing the gain of the monopole. Since this was calibrated with the log periodic antenna as a standard, you can see that the gain is about -5 from that, or about 1 dBi, exactly what you expect from a standard monopole . The SWR has a moderate Q, or said another way, a limited passband. There is no first harmonic. You can see the edge of the second harmonic over on the right, coming in to resonance.
The monopole works fine for a narrow band of interest, but is useless in most modern wireless apps, where multiband and wideband uses are required. Wouldn’t it be great to have a simple way to broaden that bandwidth and keep the gain about the same or better? That’s what motivated us and we show here a lab prototype of our proprietary, new technology that does this, called fractal metamaterials .
FRACTAL’s scientist(s) invented fractal antennas and fractal resonators, and reported them in the first scientific publication in August 1995. Resonators are tuned circuits. We use fractals to make the tuned circuit, without any components, just as a circuit board trace. They are partless circuits. When placed close together these fractal resonators use evanescent waves to ‘talk to one another’, effectively making a sheet of resonators acting as one unit . It has an unusual current distribution compared to a continuous sheet. Such a resonator sheet is also called a metamaterial. Fractal enhance this metamaterial property by increasing the bandedness and bandwidth, an shrink the resonator size for greater packing and performance. We will now use them to make a better monopole, using a slip-on sleeve assembly from these fractal metamaterials. Let’s do an experiment to show this.
All experiments need controls, and in this case we are introducing a copper sleeve, that is a continuous cylindrical sheet, that sits on top of the monopole but has no direct contact with it. The sleeve is interfaced with a shallow cone and uses lossless foam. Lets pop that copper sleeve on top of the monopole. We placed the network analyzer in the shot so you can see the only change is the slip on sleeve . The network analyzer is not providing noticeable reflected path, as we saw no difference when the network analyzer was much farther away. Notice that we have a long time constant on the network analyzer to make it easier to see the change.
The bandwidth looks a bit better than the monopole alone, but not by much. This a blow up of that data, compared to the monopole itself. Notice how the sleeve of copper actually suppresses the gain as you go up in frequency.
Now to replace that copper sleeve with one made of fractal metamaterials. The blue tape is used to secure the fractal cylinder and is lossless at these frequencies. There is no dielectric loading from the tape. Here’s the two side by side.
And here’s the video of the fractal metamaterial slip-on.
Slipping this fractal metamaterial sleeve on top of the monopole produces a huge difference. The bandwidth is now essentially tripled and the gain even increases as the frequency increases. That is a startling and unexpected result. All from a slip-on collar with no components, no power, and no direct electrical connection .
And here’s the data, compares as well to the monopole alone.
Not only is the bandwidth greater for the fractal metamaterial sleeve but the gain increases also. Some of that is because the SWR mismatch is reduced, but a substantial amount is overage. We can prove this. Look at the blowup of the upper section of the passband, where the second harmonic kicks in for the monopole by itself.
Here, the SWR’s are identical but the fractal metamaterials has a 3 dB increase over the monopole. So the gain increase is not from correction of a relative mismatch change. The fractal metamaterials uses the entire sheet as a current source while the dipole breaks up into 2 sinusoids separated in height.
And once again, the fractal metamaterial sleeve compared to the monopole alone.
Here’s a summary of the fractal advantage in this particular example of fractal metamaterial when applied to this monopole.
We hope you enjoyed the video and invite you to see others from Fractal Antenna Systems at www.fractenna.com.”
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