[TowerTalk] Trapped Antenna in the "formal" literature?

Tue Jan 9 12:57:48 EST 2024

More interesting stuff..

Here's what's probably the original patent (oh for the days when a patent was only 3 pages...)
https://patents.google.com/patent/US2229865A/en

On Mon, 08 Jan 2024 20:36:50 -0500, "Jim Lux" <jim at luxfamily.com> wrote:

Here's an intersting one - can't find the actual paper, but it seems to be an antenna with a bunch of traps spaced in a log periodic way. 
I also found someone who had one with 13 wires and 39 traps.

The log-periodic trapped monopole
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Smith, C. L.

Abstract

The concept is being investigated of an HF monopole constructed of short segments interspersed with antiresonant traps; the segment lengths and trap resonant frequencies follow a modified log-periodic sequence so that the hand-off from section to section through the traps is such that the VSWR does not exceed some predetermined value (3:1 was used in the studies). Two versions were investigated: (1) the 'free' monopole in which the segments and traps are chosen such that the driving point VSWR is at or below the limit and (2) a 'constrained' version in which a nearly arbitrary limit on the height has been imposed such as might be encountered in submarine antennas. In the first case an antenna of perhaps 15 or 20 meters tall results but no special matching network is required; in the second case the driving point impedance exceeds the limits and a matching network is needed.

Publication:

In: Antenna Applications Symposium, Urbana, Ill., September 20-22, 1978, Proceedings. (A79-24701 09-32) Urbana, Ill., University of Illinois, 1978. 7 p.

On Mon, 08 Jan 2024 20:28:23 -0500, "Jim Lux"  wrote:

perfect... that's exactly the kind of thing I was looking for.

https://ieeexplore.ieee.org/document/1141000
Abstract:
The trap-loaded cylindrical antenna is a cylindrical antenna having one or more traps located in its arms. The traps are either parallel inductor-capacitor circuits or short-circuited transmission line stubs that are designed to be antiresonant (having essentially an infinite input impedance) at some particular frequency. The location and the antiresonant frequency of the traps are selected to enhance the radiation pattern or input impedance of the antenna. This study is confined to the properties of trap-loaded cylindrical antennas that contain only one trap in each arm. The effect of the length of the outer section, length of the inner section, diameter of the cylinder and characteristic impedance or inductance-capacitance ratio of the trap on the input impedance, radiation pattern, and current distribution were studied both experimentally and with the aid of two numerical solutions of an integral equation for the current distribution. The conclusions drawn from this study are that the design procedure for the multiband trap antenna described by Greenberg [1], adjusting the antiresonant frequency of the trap to control the upper resonant frequency, is indeed valid. Graphs suitable for designing trap antennas using this procedure are available in this paper. Furthermore, it is shown that the characteristic impedance or inductance-capacitance ratio of the trap can also be adjusted to vary the lower resonant frequency of the antenna. Design graphs using this procedure are also available in this paper. This study also showed that a relatively wide range of upper to lower antenna resonant frequency ratios can be obtained while still maintaining radiation patterns and input impedances close to those of a half-wave dipole at both frequencies. Graphs are available showing the tradeoff in pattern shape and input impedance that must be made to obtain resonant frequency ratios other than 2 to 1. It was discovered that the trap antenna, sometimes called a Franklin array, must be operated somewhat below the nominal design f

requency or have the spacing between traps shortened somewhat, for it to have a radiation pattern similar to a collinear array of half-wave dipoles. Furthermore, the thicker the antenna, the more pronounced this effect is. While the nominal design was discovered to give an input impedance nearly resistive and near 70\Omega (for a dipole), any of the aforementioned modifications resulted in a nonresonant highly capacitive input impedance.

Pretty cool work - he actually measured the current along the antenna.
"The current distribution was measured in the 9-ft cube anechoic chamber described earlier. The probe used to measure the current was an 0.108-in OD shielded loop constructed out of 0.027-in OD coaxial cable. Care was taken to level the antenna so that the probe would neither lift off the surface of the antenna, nor bind while being moved along the antenna."

0.027" OD coax, eh?

On Mon, 8 Jan 2024 17:13:30 -0800, Michael Tope wrote:

This is the earliest reference I could find:
Morgan, H. K. A multifrequency tuned antenna system,. Electronics, 13,
pp. 42-8. August 1940

If you look at the reference list item 12 in this paper it appears that
the paper's author did his PHD thesis on trapped cylindrical antennas:
D. Smith, "The trap-loaded cylindrical antenna," in /IEEE Transactions
on Antennas and Propagation/, vol. 23, no. 1, pp. 20-27, January 1975,
doi: 10.1109/TAP.1975.1141000.
https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1141000

73, Mike W4EF.........

On 1/8/2024 3:06 PM, Jim Lux wrote:
>
>
>
> I'm looking for a paper reference to basic trapped antenna design and performance, preferably in something like an IRE or AIEE journal (I'm sure it's pre-IEEE).
>
> I'm writing a paper and I make a reference to "yeah, you could do this with traps, but here's a different way" and a reviewer (who is obviously not a ham) said "what's a trapped antenna".  And rather than write paragraphs about L/C resonant circuits and how they work in an antenna, I'd like to just say:
>
> Trapped antennas as described by [Maxwell, 1862, Rayleigh, 1903, and Pocklington, 1897] were explored, but suitable trap configurations could not be found.
>
> (Obviously, Maxwell, Rayleigh, and Pocklington didn't talk about trapped antennas)
>
>
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