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I'm used to seeing log-periodic antennas, the classic "TV antenna" that one can still see on the tops of houses or older buildings. There is a long row of transversely-mounted elements, connected in some way along the center axis, whose length and spacing vary in a log-periodic fashion.

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From: https://www.scannermaster.com/CLP_5130_1N_Log_Periodic_Antenna_p/40-541274.htm

But when I was doing research before writing this question I came across this log-periodic antenna.

Does this design have a name? It's one continuous conductor, and serpentine with each successive element connected in the opposite direction than the previous. Why? is the serpentine nature important for the way that it functions?

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above: Cropped detail of "Log-periodic shortwave antenna besides the old Varberg Radio Station, Sweden" From here. Right click and open in a new window for larger view.

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above: "Log-periodic shortwave antenna besides the old Varberg Radio Station, Sweden" From here.

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    \$\begingroup\$ From what I understand, a Yagi-Uda antenna and a log antenna are two different things. A Yagi-uda has a single driving element (half-wavelength dipole) with parallel (passive) resonators added to significantly boost the directivity , a log-periodic is multiple half-wavelength dipoles tuned to slightly different frequencies to get much higher BW (but by nature of them all radiating, this also often get you an increase in directivity, just not as significant as a yagi) \$\endgroup\$ – Joren Vaes May 20 '17 at 12:59
  • \$\begingroup\$ @JorenVaes That sounds like something I knew once, yes. In a a Yagi-Uda adjacent elements only differ by maybe 4 or 5% in length and usually only one is driven. The log-periodic is a different animal altogether. I'm going to edit the beginning a bit to clear that up, thanks! \$\endgroup\$ – uhoh May 20 '17 at 13:10
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    \$\begingroup\$ Interesting configuration. Most Log periodic antennas I have seen are phased from the centre somehow with alternating elements I think for this reason. Below is news link describing a very neat cryogenically cooled SETI antenna and a technical PDF about it as used on the Allen Telescope Array. - archive.redding.com/news/… - seti.org/sites/default/files/ATA-memo-series/memo95.pdf \$\endgroup\$ – KalleMP May 20 '17 at 20:04
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    \$\begingroup\$ @KalleMP I see what you mean, there's at least something alternating in this case. Oh the ATA feed antenna is such a complicated critter! I hadn't thought about how they receive the power, from the reflectors, but ya for such a wide passband a simple dipole inside a horn/waveguide would not work. \$\endgroup\$ – uhoh May 20 '17 at 21:41
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A interesting structure for sure and one can learn a lot by researching SE answers.

The antenna type you illustrate is called a Tapered Ladder Log-Periodic wedge antenna. A patent by RH du Hamel et al from 1963 shows the structure you seek in figure 7 it is similar to the Zig-Zag Log-Periodic antenna. The patents are mostly from the 1940's to 1960's and the benefits of the ladder/zig-zag style have been described as having structural and phasing benefits. A patent from 2003 still shows the general configuration as prior art so it is not forgotten.prior art

Some of the patents and literature show a additional tapered feed-line that is used to drive the ladder style elements at a points away from the centreline at some suitable matching impedance, the desired configurations seem to use the structure or the inter element connections for excitation and phasing.

Here is a forum thread with a lot of collected data by someone investigating indoor antennas and a 1960's magazine article is mentioned. Simulation, calculation and construction ideas are discussed.

What looks very similar to your sample is illustrated on a general Log-Periodic description page.

A vertical element earth reflected monopole type is mentioned in a patent showing alternative top-hat and trapezoidal geometries.

The geometries of Log-Periodic antennas are many. From long wave to micro-scale they do however share much in common.

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    \$\begingroup\$ Wow! This reflects quite a research effort, thank you for taking the time to put this together! There is a lot to read hear and it will keep me busy for a while. The wide variety of implementations from wires to solid slabs to screws shown in the first link is really interesting, and remind me of the microwave spiral antennas on satellites and some satellite-receiving antenna designs. \$\endgroup\$ – uhoh May 23 '17 at 1:36
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It appears to me that the features at the ends of the elements are non-conducting and are there simply for mechanical support.

On the other hand, it could be a method of phasing the successive elements since there is no other feedpoint on each element visible. The alternating pattern of the interconnecting pieces and the shortened element spacing for the shorter elements would give credence to this analysis.

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  • \$\begingroup\$ Any thoughts on why not do it the simpler way - one non-conducting line up one side, instead of flip-flopping back and forth? I've added some additional cropped details from the same photo. It looks like welded aluminum, darked in places from hight temperature oxidation. Note also the tuning tap on the right side of the longest elements. \$\endgroup\$ – uhoh May 20 '17 at 14:32
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    \$\begingroup\$ Weight, wind resistance, or snow/ice loading. Notice that there are also (monofilament?) lines supporting the antenna. \$\endgroup\$ – Glenn W9IQ May 20 '17 at 14:32
  • \$\begingroup\$ The picture doesn't have enough resolution to say for sure, unfortunately. \$\endgroup\$ – Glenn W9IQ May 20 '17 at 14:38
  • \$\begingroup\$ OK that's something to think about. Then I'd also wonder why even for the tiniest elements at the top they still keep connecting them. If it's mechanical, that doesn't make sense. If you click the From here in the question, or here, you have access to the original 5 MB image. \$\endgroup\$ – uhoh May 20 '17 at 14:41
  • \$\begingroup\$ That's a really good point - I never thought to look at the feedpoints, or lack thereof I should say. That does seem to be a central point now that I think more about it. Also this comment. \$\endgroup\$ – uhoh May 21 '17 at 6:17

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