High Frequency Spiral Antenna

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-02820A000600030037-2
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 2
• Document Creation Date: December 9, 2016
• Document Release Date: May 9, 2000
• Sequence Number: 37
• Publication Date: February 2, 1960
• Content Type: MFR

Approved For Rel "E DP78;A282W0604b36031- Monthly
T4 7 9.11 ?- ' Report - Jan. 1960
TO TIN FILE
gUWEcT: Nigh ?requency Spiral Antenna
1. Mr. Kapitan, the Liaison Officer, notified us that a discussion
of the Nigh Frequency Spiral Antenna would be held 1400 hours, 1 Feb
--
1960 in Building T3, Roos 1515 under the auspices of the Navy.
members of the Nugineering Division attended.
. The meeting was opened by Commander Dixon of the office
25X1A9a
Chief of Naval operations. Navy bad a requirement for an antenna Which
would be transportable, that is., it could be knocked down in a kit which
could be carried in a van and could be erected within a few hours by a
seal-skilled crew. This antenna must have a frequency range above 9 mcs.,
at least equal to that of a rhombic, and have gain comparable to that of
a rhombic. The antenna should also reduce selective fading. Commander
Dixon introduced Mr. Dunlevy of All Products C .
3. Kr. DunleVy gave us a hasty background of the subject mentioned.
The Bureau of Standards had previously published a report on experiments
with polarization diversity at W. It had been found that two dipoles,
I vertical and 1 horizontal on the same support, gave equivalent perform-
ance to two horizontal dipoles 11 wave lengths & Part- Apparently signal
strength does not fade as much as it shifts in polarity. Accordingly
experimented with models of equt-augular spiral antennas. Results were
so encouraging that a full-scale model of a portable antenna was built.
It. This antenna consists of two circles,, 70 feet in diameter, built
of 3" thin-wall aluminum tubing, each section about 12 feet long. These
are held in parallel planes by 3" fiber glass tubing. The active portion
of the antenna is a spiral composed of three wires whose spacing increases
from the center to the circumference of the circle and which are supported
by fiber glass tubing. The second element is a reflector, having IS radial
elements and 9 concentric rings of aluminum tubing. The over-all height
of the antenna is 96 feet, and it weight 900 pounds. The gulps, are of
fiber glass rope, having an extruded 1linyl cover. It is rotatable.
fixed models will probably bays, steel, rather than alumin , conducting
members. APC believes that with,.."'- the limitations imposed by light
weight and portability, the fixed models may have improved operating
NAVY DECLASSIFICATION/RELEASE INSTRUCTIONS ON FILE
Approved For Relea k 78-0282OA000600030037-2
 CIA-RDP78 2OA000600030037-2
Migb frequency Spiral Antenna
characteristics. The. portable model requires a square space, 130 Zest
on, a aide. be fixed models will require a space 130 feet x 80 feet.
Each model will cost about $7,,000.00 apiece. The characteristic impedance
of the spiral is 130 ohms. This is matched to a standard transmission
line by a special coaxial conductor built into the spiral having an inner
conductor of varying diameter.
. 5. Tests of the antenna show that it receives a
signal near sun rise and sun not when propagation conditions are one
that a rhombic or other horizontally polarized antenna may be subject to very
deep fading. The Navy was so favorably impressed with the results of the
portable model that they have contracted for a fixed installation a
Cheltenham, Maryland to use an their Londonderry reland circuit.
6. The spiral antenna is said to outperforms a convential rhoa-bic
scept in periods of good promotion, such as at aid-day, but this is
not considered a drawback *Inc* the signal to noise ratio at such times
usually high and the a additional gain afforded by the rhombic is
eded, Moreover the spiral requires such less space and several units
may be placed side by side without interaction.
taacbmeent:
1. Data Sheets
Distribution t
Original - Pouting and file
e - Monthly Report
cC_j/ ; 8W je /293?
Approved For Release 2001/08/31 : CIA-RDP78-0282OA000600030037-2