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Interesting to see this antenna here. I heard the creator speak at a local IEEE event a few years ago. Quite remarkable. Nobody would intuit an antenna design

Interesting to see this antenna here. I heard the creator speak at a local IEEE event a few years ago. Quite remarkable. Nobody would intuit an antenna design like that. Great demonstration of the power of GA. Antenna optimization software has changed antenna design completely. Before wide-spread computer simulation, there was an awful lot of antenna range cut-and-try. Antennas are much better now. Learning to drive the modeling software is still a huge amount of work, but the results are well worth it. An example from the world of amateur radio: the only popular HF tri-band beam to survive from the pre-simulation days is the KT-34 and big brother KT-34XA, originally from KLM. I was talking to Mike Stahl about it (The M in KLM, also one of the M's in M-squared) and he said he spent months going up and down towers at an antenna range. Pretty much all other hand-tuned competitors from that era have fallen by the wayside, the new simulation-verified designs being much better. Mike is a great hands-on antenna designer -- when the Stanford dish was new he designed several feed horns for it.

mrguyorama 8y ago
Another good example of this is fractal antenna design that allowed significant efficiency/space improvements in mobile phones and allowed one physical antenna to work for multiple frequencies quite well. https://en.wikipedia.org/wiki/Fractal_antenna https://en.wikipedia.org/wiki/Fractal_antenna
- chiph 8y ago
  One of my high-school science-fair projects was a fractal high voltage insulator. The idea was that since high voltage follows the surface of an object, why not give it a lot of surface to run out of energy on? I failed of course - the ceramic was too hard to work (I dulled so many saw blades). And I didn't have an oven to bake it at the required temperature profile, nor a high-voltage lab to test my designs. But a cool idea anyway.
  - namibj 8y ago
    You want a shere/distance/minimize maximum curvature.
    - chiph 8y ago
      An unanswered question was whether the voltage would just jump across the edges of the fractal or follow the surface of the ceramic. Which would likely vary with humidity. I'm sure that General Electric & Siemens test in all kinds of weather conditions - another thing I couldn't do. ;)
guelo 8y ago
Are the software radiation simulations accurate? Are they based on solving complex physics formulas?
- dbcurtis 8y ago
  Well..... for some definition of accurate. For large antennas with thin structures, the typical solver is "Method of Moments". NEC2 was developed by the government and is public domain. It is quite popular, and does some things well but it is also easy to stumble into modeling bugs/deficiencies, and isn't much use above high UHF. But is very useful if you know how not to step in the bugs, and is free. NEC4 falls under ITAR, the last I heard. So it isn't particularly hard to get a license, but you have to clear ITAR. Microwave structures are more often done with a finite-element model, as I understand it. Both rely on numerical approximations to Maxwell's equations. At least for MoM, each element cheats the boundary conditions a bit in order to make the problem tractable. With a fine enough grid, you get a good enough answer. Another friend that has started two antenna companies is an NEC4 guru. I asked him: "How can I tell if my model has a small enough grid?" Him: "Keep reducing the mesh until the answer stops changing. When it stops, you had enough elements in the previous try." Antenna modelling is a bit of an art, I'm not expert, just hack a few as a hobby.
  - jacquesm 8y ago
    That's the exact same trick you use to determine model granularity when using finite element analysis for construction purposes. It is actually quite surprising how coarse models can be and still give useful answers.
  - guelo 8y ago
    Sounds like there's some manual steps to create the simulation. I'm wondering how these genetic algorithms can automatically feed into the simulation and get back a single number to drive the GA fitness function.
    - dbcurtis 8y ago
      Well, I used a Yagi optimizer at one point. With that system, the antenna was parameterized. I specified certain fixed values, like overall boom length and nominal element diameter, and total number of elements. The element lengths and spacings were free for optimization. Fitness function was a scoring of front-to-back ratio, front-to-side ratio, and max allowable SWR over a frequency range of interest, with a goal of maximum forward gain. The optimizer tuned the free variables. For different applications the various scoring measurements would be adjusted differently. (Sometimes you care greatly about minimizing back and side lobes, other times not so much, for instance.)
caf 8y ago
...there was an awful lot of antenna range cut-and-try. My mother's beach house still has a shed full of various aluminium pieces, many of them part of a range of semi- or fully-built customised Yagi designs, the legacy of years of my father's cut-and-try attempts to optimise very marginal UHF television reception.

mrguyorama 8y ago

Another good example of this is fractal antenna design that allowed significant efficiency/space improvements in mobile phones and allowed one physical antenna to work for multiple frequencies quite well. https://en.wikipedia.org/wiki/Fractal_antenna https://en.wikipedia.org/wiki/Fractal_antenna

chiph 8y ago
One of my high-school science-fair projects was a fractal high voltage insulator. The idea was that since high voltage follows the surface of an object, why not give it a lot of surface to run out of energy on? I failed of course - the ceramic was too hard to work (I dulled so many saw blades). And I didn't have an oven to bake it at the required temperature profile, nor a high-voltage lab to test my designs. But a cool idea anyway.
- namibj 8y ago
  You want a shere/distance/minimize maximum curvature.
  - chiph 8y ago
    An unanswered question was whether the voltage would just jump across the edges of the fractal or follow the surface of the ceramic. Which would likely vary with humidity. I'm sure that General Electric & Siemens test in all kinds of weather conditions - another thing I couldn't do. ;)

guelo 8y ago

Are the software radiation simulations accurate? Are they based on solving complex physics formulas?

dbcurtis 8y ago
Well..... for some definition of accurate. For large antennas with thin structures, the typical solver is "Method of Moments". NEC2 was developed by the government and is public domain. It is quite popular, and does some things well but it is also easy to stumble into modeling bugs/deficiencies, and isn't much use above high UHF. But is very useful if you know how not to step in the bugs, and is free. NEC4 falls under ITAR, the last I heard. So it isn't particularly hard to get a license, but you have to clear ITAR. Microwave structures are more often done with a finite-element model, as I understand it. Both rely on numerical approximations to Maxwell's equations. At least for MoM, each element cheats the boundary conditions a bit in order to make the problem tractable. With a fine enough grid, you get a good enough answer. Another friend that has started two antenna companies is an NEC4 guru. I asked him: "How can I tell if my model has a small enough grid?" Him: "Keep reducing the mesh until the answer stops changing. When it stops, you had enough elements in the previous try." Antenna modelling is a bit of an art, I'm not expert, just hack a few as a hobby.
- jacquesm 8y ago
  That's the exact same trick you use to determine model granularity when using finite element analysis for construction purposes. It is actually quite surprising how coarse models can be and still give useful answers.
- guelo 8y ago
  Sounds like there's some manual steps to create the simulation. I'm wondering how these genetic algorithms can automatically feed into the simulation and get back a single number to drive the GA fitness function.
  - dbcurtis 8y ago
    Well, I used a Yagi optimizer at one point. With that system, the antenna was parameterized. I specified certain fixed values, like overall boom length and nominal element diameter, and total number of elements. The element lengths and spacings were free for optimization. Fitness function was a scoring of front-to-back ratio, front-to-side ratio, and max allowable SWR over a frequency range of interest, with a goal of maximum forward gain. The optimizer tuned the free variables. For different applications the various scoring measurements would be adjusted differently. (Sometimes you care greatly about minimizing back and side lobes, other times not so much, for instance.)

caf 8y ago

...there was an awful lot of antenna range cut-and-try. My mother's beach house still has a shed full of various aluminium pieces, many of them part of a range of semi- or fully-built customised Yagi designs, the legacy of years of my father's cut-and-try attempts to optimise very marginal UHF television reception.