[Antennas] Fractenna in the news...

Thu Nov 25 13:22:43 EST 2010

This probably isn't far from the mark. I haven't studied the antenna 
closely, but I suspect that the arrangement of conductors on the sleeve 
creates a more uniform current distribution than you normally get with a 
1/4-wave long conductor. Hence, the pattern is "squished" in the 
vertical plane so that more power is directed to the horizon and less to 
the zenith. This is similar to what happens when a capacity hat is added 
to a 1/4-wave monopole or if a radiator is longer than 1/4 wave.
The bandwidth improvement is not surprising given that the addition of 
the sleeve vastly increases the effective thickness of the radiator. If 
one were to increase the thickness of the wire radiator so that it was 
on the order of the sleeve's diameter, a similar bandwidth improvement 
would be observed. Think biconical antennas. The copper sleeve that was 
used in the demo was not electrically connected to the radiator, so the 
bandwidth improvement was not observed in that case. Indeed, the copper 
sleeve would act more like a shield. Of course, Fractenna's sleeve is 
not connected either, but its design must allow it to couple to the 
primary radiator in such a way that the benefits of a thick radiator are 
obtained.
The mental model I use to explain why thick radiators lead to broader 
bandwidths is to note that using a thicker conductor increases the 
capacitance to ground (and therefore decreases the capacitive reactance) 
and decreases the effective inductance of the radiator (which decreases 
the inductive reactance that complements the capacitive reactance). 
Imagine a parallel or series resonant circuit with a little resistance 
present as well. Resonance occurs when the inductive reactance exactly 
cancels the capacitive reactance. However, cancellation can occur with 
large reactance magnitudes (e.g., +/- 1000 ohms) or with small 
magnitudes (e.g., +/- 25 ohms). If the reactances are small relative to 
the resistance, the Q of the circuit will be low, and the bandwidth of 
the resonator will be broad. Thus, "fat" antennas have broad bandwidths. 
Fractenna's sleeve lower the Q of the monopole as well, but it uses an 
intricate pattern of copper traces to do it.
The effects the video shows are real, and similar designs have been 
getting a lot of attention lately in the professional antenna research 
world. In my opinion, some of these ideas seem like overkill. That is, 
similar performance improvements can be achieved with simpler designs. 
However, I am not sure if most people would describe Fractenna's sleeve 
as a "metamaterial." That term is usually reserved for a new class of 
engineered materials that exhibit propagation effects that at first 
glance seem impossible or science fiction-like, but with the right 
constraints turn out to be physically realizable.
73 and Happy Thanksgiving,
Dave ND3K
>> Since the gain has to come from a change in pattern, and they make some
> reference to not showing the vertical pattern, I would assume that the
> diameter of the sleeve is somehow related to the frequency and causes
> cancellation in the vertical plane... while this is good as long as you can
> stand having a fatter monopole, it probably wouldn't scale well to HF.
>>> David Robbins K1TTT
> e-mail: mailto:k1ttt at arrl.net
> web: http://www.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
>>>> -----Original Message-----
>> From: D.J.J. Ring, Jr. [mailto:n1ea at arrl.net]
>> Sent: Wednesday, November 24, 2010 19:03
>> To: farson at shaw.ca
>> Cc: Dave AA6YQ; antennas at mailman.qth.net
>> Subject: Re: [Antennas] Fractenna in the news...
>>>> It certainly sounds like voo-doo science - like the short high efficiency
>> radiator which was developed by an Egyptian engineer.
>>>> Something like the E-H radiator. When I drove from Port Said, Egypt to
>> Cairo to visit the Cairo Museum, I listened to that station and the
>> coverage
>> was amazing. But Egypt is flat but all sand. I was impressed that I
>> could
>> hear the signal all the way across the desert from Port Said to Cairo on
>> the
>> AM Medium Wave band.
>>>> 73
>>>> DR
>>>> David J. Ring, Jr., N1EA<http://www.qsl.net/n1ea/>
>> SOWP<http://www.sowp.org/>, VWOA<http://www.vwoa.org/>,
>> OOTC<http://www.ootc.us/>,
>> FISTS<http://www.fists.co.uk/>, CW-Ops<http://www.cwops.org/>,
>> JARL-A1<http://a1club.net/>,
>> A1-OP<http://www.arrl.org/a-1-op>, ex-FOC 1271 ARRL-
>> LM<http://www.arrl.org/>
>> Chat Skype: djringjr MSN: djringjr at msn.com AIM: N1EA icq: 27380609
>> Radio-Officers Google
>> Group<http://groups.google.com/group/radio-officers?hl=en>-- Marine
>> Morse Historic Recordings Page<http://www.qsl.net/n1ea/>
>>>>>>>> On Wed, Nov 24, 2010 at 1:52 PM, Adam Farson<farson at shaw.ca> wrote:
>>>>> Yeah, and it'll make witches' brooms fly straight and level too...
>>>>>> Cheers for now, 73,
>>> Adam VA7OJ/AB4OJ
>>>>>>>>> -----Original Message-----
>>> From: antennas-bounces at mailman.qth.net
>>> [mailto:antennas-bounces at mailman.qth.net] On Behalf Of Dave AA6YQ
>>> Sent: 24-Nov-10 06:09
>>> To: antennas at mailman.qth.net
>>> Subject: [Antennas] Fractenna in the news...
>>>>>>>>> http://www.engadget.com/2010/11/24/scientists-finally-find-a-practical-
>> use-f
>>> or-metamaterials-boost/
>>>>>> 73,
>>>>>> Dave, AA6YQ
>>>>>> ______________________________________________________________