back to article Better mobe antennas a stretch goal for radiocomm boffins

Antennas can be tuned by changing their shape, and a group of University of Texas Austin researchers wants to use that simple phenomenon to help get rid of noise in silicon-scale antennas. The idea is to get rid of the magnetic isolation between transmit and receive antennas, which among other things would help shrink the RF …

  1. Christian Berger

    Yeah you can do that...

    ... at least in principle. Radio hams often have a device called a "tuner" which loads the antenna in a way to change it's resonant frequency. However to make use of this you also need to change the frequency you are transmitting at... and the antenna can always just have one resonant frequency... so I don't quite see how that could be something practically.

    1. Steve Davies 3 Silver badge

      Re: Yeah you can do that...

      the issue you raise is something that has (probably) been solved years and years ago. There was a UK Army Radio System back in the 1970/80's called Ptarmigan. Didn't that use frequency hopping techniques to help disquise the position of the transmitter.

      I expect things have moved on considerably since those days.

      1. Trigonoceps occipitalis

        Re: Yeah you can do that...

        An antenna will be resonant at more than one frequency - λ, ½λ etc.

        Ptarmigan was more than just a radio system and used many techniques, frequency hopping per se was not one of them.

  2. Paul Kinsler

    Re: I don't quite see how

    I think you need to read the article more carefully, you appear not to have understood what was done.

    1. Commswonk

      Re: I don't quite see how

      Yes; I would agree with that. Aerial "tuning" is a misnomer in any case; the correct term is "matching" because the requirement is to match the impedance of the aerial (which may have real and imaginary components) to that impedance for which a transmitter output stage is designed.

      What is being described in the article isn't frequency hopping either; frequency hopping is a means of (a) concealing the fact that a transmission is taking place, (b) making it harder to jam any such transmission, and (c) making it harder to intercept and perhaps decrypt what is being sent.

      However I would argue that it is very hard to determine the exact purpose behind this research from both the El Reg article and the "Eureka Alert" reference . At least Eureka Alert takes the trouble to add Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! at the bottom of its piece. Wise move, adding that.

      I have read and reread both articles and have been unable to avoid concluding that both may be a little "confused", but to be fair I have to admit to not being a "Marvin" with a brain the size of a planet.

  3. Gideon 1

    I read 'magnetic isolation' as in a which was used in first generation mobile phones to help prevent the transmit signal jamming the receiver. 2G phones and WIFI use Time Domain Multiple Access so don't transmit and receive at the same time.

    The article isn't very clear about the mechanism, but is it changing the antenna shape by heating?

    1. Anonymous Coward
      Anonymous Coward

      I read it as the actual physical shape of the antenna remains the same, but the low frequency modulation is causing a change in the effective shape of the antenna as far as its RF properties are concerned.

      If there was a physical change in the antenna it couldn't be fabricated into an IC like the second to last paragraph claims - it would cause fractures in the silicon substrate which would be rather a problem for the overall functionality of the IC!

  4. JohnLH

    This is warmed over news. What the authors describe is a way to implement in effect the combination of a circulator and an antenna. The previous paper (referenced in the Reg article) described just a circulator.

    Circulators are non-reciprocal and usually use lumps of magnetised ferrite. They were used in early mobile phones (and in a host of other systems to this day) to allow a single antenna to be used for both Tx and Rx, but methods were developed of making duplexers that didn't need circulators (and indeed worked better). GSM didn't need a duplexer anyway as it is in effect TDD (like Wi-Fi), but 3G and 4G phones do. (Actually there is a new generation of sub-miniature ferrite circulators now available that are finding their way back into phones to help solve the multi-band nightmare.)

    Another way to make a circulator is to use an active device such as an amplifier (which amplify one way but normally not the other). Another type of active device is a parametric amplifier which works by "pumping" a variable capacitor at a different frequency from the one you're trying to amplify - it needs input RF power just as a conventional amplifier needs input DC power. Since a major design criterion for a duplexer is power loss (attenuation), having to put additional power *into* a device to make it work is not very attractive.

    Parametric amplifiers were quite popular in the 60s when RF transistors were poor but you could use things like klystrons to generate RF power as a pump, but generally are now an engineering footnote. I remember doing a whole exam course on "non-linear and parametric circuits" in my degree, just in timefor them to go out of fashion.

    As power consumption is a major issue for mobile devices, I think this technology will remain a curiosity at least for mainstream systems.

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