W H ITE PA PE R
Aircraft Carrier Electromagnetic Compatibility
MARCH 2015
Dr. Avigdor Shechter
Senior Principal Mechanical Engineer
Alion Science and Technology
703.933.6868
[email protected]
© 2015 Alion Science and Technology Corp. All rights reserved.
04/15
Aircraft Carrier Electromagnetic Compatibility
THE INTERFERENCE between electromagnetic
emitters and sensors on ships’ topsides is a well-known
and unavoidable occurrence. This is particularly an issue
on “crowded” naval platforms such as aircraft carriers
that have many broadband emitting [e.g., radar and
electronic countermeasures (ECM) systems and aircraft]
and receiving systems whose antennas are located in
close proximity to each other. Antenna-to-antenna
coupling can cause interference effects ranging from
temporary disruption and impairment of performance,
to permanent damage of equipment. The problem is
particularly acute where multiple antennas are being
operated simultaneously while sharing a relatively small
space. Therefore, due considerations for electromagnetic
compatibility (EMC) must be given to the antenna
placement, frequency assignment, and transmitting and
receiving time-sharing.
Figure 1. Aircraft Carrier Island Top
The frequency range utilized by naval avionic systems
spans the electromagnetic (EM) spectrum from a
few kilohertz to several gigahertz. At the low end are
the navigation positioning systems which operate in
the very low frequency (VLF) range of 10 to 14 kHz.
Omnidirectional Range Finders (ORF), radio beacons
used in point to point navigation, operate in the high
VHF band from 108 to 118 MHz. Glideslope Systems
used during landings operate in the 328 to 335 MHz of
the UHF range. Voice aircraft-to-ship communication
systems operate in the VHF (30-156 MHz) and UHF
(225-400 MHz) ranges. TACAN that provides aircraft
with bearing and distance (slant-range) to the shipborne station operates at just over 1 GHz.
In the spectrum above 1 GHz are also global positioning,
collision avoidance, and cockpit weather radar systems.
An aircraft carrier is also equipped with powerful
directional radar systems for the purpose of monitoring
and controlling the operational airspace of its aircraft.
Furthermore, due to the frequent and irregular
traversing of aircraft at various altitudes above the
deck, the EM environment (EME) on aircraft carriers
is not constant nor is it repeatable. As an aircraft enters
the deck space, EM energy is bounced around in an
uncontrollable fashion, which can result in disruption of
operations or in radiation hazards (RADHAZ) to crew
and/or equipment. This is why awareness of the EM
environment is critical when establishing requirements
to support early stage design. It is only through early
consideration of these critical design drivers that the
topside design efforts can proceed with any degree
of viability. While there will always be changes to the
Aircraft carriers are characterized by significant physical
limitations in regards to the placement of topside
antennas, sensors, and equipment of mission systems.
Typically, aircraft carriers incorporate electromagnetic
(EM) systems comprising in excess of 150 powerful
topside transmitters and a similar number of sensitive
receivers. Due to aircraft launch, recovery, and handling
operations occupying much of the topside real estate,
most of the antennas and sensors of aircraft carriers’
mission systems are mounted on the compact space
available on the island, aft tower, and mast (Figure 1),
or along the flight-deck edge, and many of these
systems must be operated concurrently. Hence, due
to thephysical limitations of such a platform and the
operational mission requirements, the shipboard EM
environment is congested and intense.
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Aircraft Carrier Electromagnetic Compatibility
design as new systems are considered; by working for a
full understanding of the baseline EMC condition, the
designer will be assured that the topside arrangement
will be electromagnetically compatible as the overall
design develops.
and its appendages) intercept and redirect the high
intensity EM energy that is transmitted by the topside
transmitters in the direction of the topside sensors and
receiver antennas, interruption of aviation and nonaviation communications and operations receivers is
produced. Therefore, the impact of such conditions
should be considered in the design of the topsides of
aircraft carriers (Figure 3).
Accordingly, the topside of aircraft carriers constitute
complex EM environments that require meticulous
investigation of EME corresponding to antenna
and topside equipment placement for the purpose
of reducing to a minimum the direct (Figure 2) and
indirect interactions among pairs of antennas of culprits
(emitters), and victims (receivers and other sensitive
devices) that are mounted on the scarcely available
topside spaces.
The collocations of large numbers of powerful
transmitters in a limited area of aircraft carriers
produce intense EME on the deck. This may cause
adverse health effects to personnel, the inadvertent
initiation of Electro-Explosive Devices (EEDs),
or the ignition of fuel vapors. Therefore, careful
scrutiny of carrier topside RADHAZ environments
is required and should be addressed by EM emission
control (EMCON) bills (operational procedures).
These subject areas should be incorporated in the Ship
Requirement document in order to ensure that the
intricacies of aircraft carrier topside EME are enforced
on the design and integration of the ship. Due to the
fact that the numerous engineering tradeoffs and design
decisions taken during the evolution of the ship design
affect the topside design; quantification of the EM
viability of the aircraft carrier design should be assessed
at each stage of the design process via a timely and
efficient modeling and simulation computer toolset.
Figure 2. Direct Interactions between Transmitter and Receiver Antennas on
the Island, Aft Tower, and Mast of an Aircraft Carrier
Furthermore, the presence of a large number of moving
aircraft (EM scatterers) in proximity to the ship emitters
and receivers produces undesired and uncontrolled paths
of EM energy. As the aircraft structure (the fuselage
Figure 3. The Variable Direct and Indirect EM Interactions of a Landing Aircraft with an Aircraft Carrier Island and its Antennas
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