Here's a more current reference, with good citations:
P. R. Winniford, et al., "New Analysis and Design Techniques for
Arbitrary Reactance Trap Dipoles," IEEE Open Journal of Antennas and
Propagation, Vol. 4, Oct. 5, 2023, doi: 10.1109/OJAP.2023.3322382,
https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10272714
This isn't as senior as the patent filed in July 1938, but has a
thorough ist of citations establishing the well-recognized meaning of
"trap dipole."
Here's another:
Y. Beers, "Designing trap antennas: a new approach," Ham Radio, August
1987, pp. 60-65, 67, 69, 173, http://www.iz5cml.it/forum/trap.pdf
This references Howard K. Morgan, "A Multifrequency Tuned Antenna
System," Electronics, August 1940, pg. 42, as noted in F. E. Terman,
Radio Engineers' Handbook, McGraw Hill, 1943, pg. 854.
Apparently, this is hard to find. Here it is:
https://www.worldradiohistory.com/Archive-Electronics/40s/Electronics-1940-08.pdf
Go to page 42, continues on pp. 44, 46 and 48. Can be downloaded.
73 de Dave, W6NL/HC8L
On 1/9/24 9:57 AM, Jim Lux wrote:
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@luxfamily.com> wrote:
Here's an interesting 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
Show affiliations
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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