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October 1968 Electronics World
 Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
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This article describes
an electronically steerable aperiodic loop antenna developed that claims
superior beam pinpointing on targets with high gain in minimal space for
high-frequency signals (2-32 MHz) via ionosphere, akin to linear arrays.
Comprising 36 untuned balanced loops, each about 1 meter in diameter with
transistorized preamplifiers, arranged on a 150-foot (50-meter) circular
perimeter, the system weighs roughly 12 pounds per element and withstands 100
mph winds. Phase shifts enable simultaneous beams every 10° through 360°, or
commutator scanning for direction finding, equating to 18 rhombic antennas at
10° intervals. The flat frequency response ensures constant effective height
over four octaves and precise phasing for end-fire arrays with bidirectional
outputs. The configuration was adopted by entities like the UK's Diplomatic
Wireless Service, Canada's Department of Transport, the U.S. Navy, and
University of Denver for communications.
Electronically Steerable Antenna
Fig. 1 - Typical aperiodic loop antenna array has 36 elements
in 50-meter circle.
An electronically steerable antenna has an important advantage over other antenna
types; it can pinpoint its beam at a single target. Steerability and high performance
are features of a truly unique antenna design developed by E.M.I.-Cossor Electronics
Ltd.
This aperiodic loop antenna is a high-gain steerable system designed to provide
the maximum directive gain in the smallest possible amount of space. The basic beam
pattern is optimized for the reception of high-frequency signals (2 MHz to 32 MHz)
propagated via the ionosphere, in the same manner as the aperiodic linear arrays.
Table 1 - Directional characteristics of aperiodic loop antennas.
The antenna consists of 36 loop elements arranged around the perimeter of a 150-foot
circle. By appropriate phase shifts, the loop outputs are combined to provide simultaneous
beams every 10 through 360 degrees. Alternatively, with a commutator switch, the
beam can be made to scan at a fixed rate. This latter capability is especially valuable
when the antenna system is used as a direction finder, while the former arrangement
provides directional gain characteristics equivalent to 18 rhombic antennas inclined
at 10° to one another.
The basic antenna element is an untuned balanced loop whose dimensions are small
compared to the wavelength. A transistorized preamplifier, fitted at the antenna
base, exactly complements the loop characteristics. This combination results in
a constant effective height over the full four-octave frequency range, that is,
the preamplifier output voltage (at a constant 50-ohm impedance) is constant over
the complete frequency range for fixed incident field strength. Because of the flat
frequency response, the antenna has a well-defined phase characteristic and is,
therefore, particularly suited for a phased antenna system. The aperiodic configuration
comprises loop/preamplifier elements in an "end fire" array with interconnecting
transmission lines coupling each element. Outputs are available at both ends so
that the array can look both ways simultaneously if required or can be switched
rapidly through 180° with a coaxial relay.
 The aperiodic loop array antenna is available
in at least three different models whose principal differences lie in the number
of loops employed. A typical 50-meter (diameter), 36-loop array would have directional
characteristics such as those listed in Table 1. The loop in a basic element assembly
is about 1 meter in diameter. Including the support tripod and preamplifier, the
element weighs about 12 pounds. When rigidly bolted to the ground, the vertically
polarized individual antenna elements are capable of withstanding winds up to 100
miles-per-hour.
Several government agencies mid institutions have begun to use aperiodic loop
antennas as part of their national and international communications systems. The
array is being used by Diplomatic Wireless Service in Buckingham, England; Department
of Transport, Ottawa, Canada; U.S. Navy; and University of Denver.
<---- Technological prescience refers to the rare ability
to accurately foresee or anticipate future technological developments, inventions,
or trends well in advance of their realization. It combines deep technical insight,
pattern recognition from historical precedents, and intuitive leaps about scientific
trajectories. In practice, it's undervalued today amid hype cycles (e.g., metaverse
flops vs. steady AI progress). True prescience demands skepticism of short-term
trends and focus on exponential laws like computing power doubling. Few possess
it; most "futurists" recycle buzzwords.
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