IEEE - Aerospace and Electronic Systems - April 2022 - 16

Multifunction Maritime Radar and RF Systems-Technology Challenges and Areas of Development
in small batches can produce very quick " scan rates " for
tracking maneuvering targets. Using a broad transmit
beam and then multiple beamforming on receive in elevation
is a mature technology but can be applied to azimuth
in exactly the same way. Dedicated tracking tasks could
still use narrow beams formed on transmit and potentially
multiple narrow beams could be transmitted at the same
time, e.g., in the opposite side or tangential directions.
BALLISTICMISSILEDEFENSE
The use of the current in-service radar to support BMD
has been the subject of significant study. The concept of
concentrating time and energy to a specific area or on a
specific target is a fundamental in MFR design. Ideally, an
MFR is able to concurrently engage in BMD surveillance
strategies, e.g., a dedicated search fence and tracking with
BMD waveforms whilst undertaking typical AAW surveillance.
The ability to do this is improved with flexibility
in waveform design and allowing adaptation. That
flexibility may be enabled by novel technology, e.g., multiple
beamforming, or a different concept in the tactical
use of the ship's or fleet's surveillance capability. For
example, for a fleet with multiple MFRs, tasks could be
shared between radar systems.
IMAGINGANDDISCRIMINATION
In order to allow target discrimination, the radar needs to
examine an object in sufficient detail so that unique features
can be recognized. Discrimination can be undertaken
on a variety of target characteristics.
For fast targets, it can be assumed that any rapidly
(i.e., 100 s of m/s) inbound contact will be man-made and,
if on course for a ship, then hostile. Measuring this characteristic
can be achieved by forming tracks that can be done
quickly by the use of instant look-backs or exploiting plot
Doppler. This is a current baseline method.
Slower moving targets (boats, helicopters, UAVs, etc.)
are more difficult as they may include objects of no interest
such as birds. The Doppler profile of such targets is a
good measure for discrimination due to the unique features
from target classes such as helicopters and UAVs
with rotor blades but also birds with wing motion. Size
and shape of the target is another useful discriminator to
remove less threatening targets. The ability to accurately
track changes in Doppler as well as the kinematics such as
height, range, and azimuth is potentially a key for target
discrimination.
Radar can be used to create high-resolution 3-D
images from various methods. High range resolution is
achieved by high bandwidth waveforms, high Doppler by
long dwells, and high spatial resolution, i.e., azimuth and
elevation can be achieved by increasing the effective
antenna aperture size.
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Methods for achieving these exist for current systems
by the use of long dwells with stepped bandwidth waveforms
and synthetic or inverse synthetic aperture processing.
However, whilst possible, they are expensive in terms
of the energy/time budget and do not fit in well with the
MFR's task scheduling. Ideally, images should be
achieved " instantaneously " with all characteristics range,
Doppler and angle at the same time.
Instantaneously high bandwidth across a radar band is
now achievable with advances in current technology. It
would require the relevant front-end filtering to be configurable
for both broad and narrow-band reception and
needs sufficient sampling in the ADCs to cover the bandwidth.
A higher carrier frequency would improve resolution
so a multiband system could exploit a higher
frequency for discrimination. MIMO radar and multiple
beamforming could allow waveform strategies to be
employed where long dwells are possible without
compromising the required surveillance update rates.
COMMUNICATIONS
Communications is another area that could potentially
benefit from using the high gain from a radar antenna.
Radars typically operate with low duty cycles (in comparison
to typical communication systems) but have a high
bandwidth meaning a lot of data can be transmitted in a
short pulse. Messages could potentially be encoded using
random binary sequences to allow the low range sidelobes
of current chirp designs albeit with poor Doppler
tolerance.
Current radar systems are capable of communications
to support missile guidance but could potently support
low probability of intercept (LPI) communications or
ship-to-ship tactical data links. As the antenna gain from
the primary array is potentially much larger than existing
communications antennas, the power needed to communicate
is less. So long as the direction of the communications
is known remote transmitters communicating with
the ship may need less power and thus are harder to detect.
For general communications, the antenna would benefit
from being simultaneously omnidirectional but could
also use high gain directional communications for times
when longer range or covert transmission is known to be
required. Communications would also benefit from high
bandwidth digitization and on the fly waveform design.
ELECTRONICSUPPORTMEASURES
ESM systems are, by their nature, are very wide band covering
radar ESM 0.5-40 GHz and communication ESM
0-0.5 GHz. The technology best suited to covering such
wide band reception may not be best suited to a search
and track radar, however, banded ESM (i.e., looking for
signals within the radar bands) could be very well
matched.
IEEE A&E SYSTEMS MAGAZINE
APRIL 2022

IEEE - Aerospace and Electronic Systems - April 2022

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