Advanced Mobile Robotics
Conventional Detection Platforms
Conventional Detection Limitations
Limited Scanning Frequency
What is a Phased Array Antenna?
• In wave theory, a phased array is a group
of antennas in which the relative phases of
the respective signals feeding the
antennas are varied in such a way that the
effective radiation pattern of the array is
reinforced in a desired direction and
suppressed in undesired directions.
Passive vs. Active
• PESA: In a passive electronically scanned array (PESA),
the microwave feed network in the back of the antenna is
powered by a single RF source (magnetron, klystron,
TWT, etc.), sending its waves into phase shift modules
(usually digitally-controlled), which, in turn, feed the
numerous emitting elements
• AESA: An AESA, instead, has an individual RF source
for each of its many transmit/receive elements, making
• This provides for a graceful degradation, so that many
T/R modules may fail and the radar would not stop
An antenna array is a plurality
of active antennas coupled to a
common source or load to
produce a directive radiation
Usually the spatial relationship
also contributes to the
directivity of the antenna
Use of the term "active
antennas" is intended to
describe elements whose
energy output is modified due
to the presence of a source of
energy in the individual
Short to instantaneous (millisecond) scanning rates
Much higher range
Multiple agile beams: tremendous number of targets being tracked Desirable low probability of intercept.
Solid state devices with vastly simpler mechanical designs
No complex hydraulics for antenna movement nor hinge
appendages that are prone to failure
Occupies less space than typical radar
Distributed transmit function eliminates most common single-point failure seen in a conventional radar
Low maintenance, much more reliable.
Ability to function as a radio/jammer
High electronic counter-measure (ECM) resistance
Less susceptible to voltage failures: very low voltage in individual elements
Did you Know?
• Phased arrays are required to be used by many
AM broadcast stations to enhance signal
coverage in the city of license, while minimizing
interference to other areas.
• Due to the differences between daytime and
nighttime ionospheric propagation, it is common
for AM broadcast stations to change between
day and night radiation patterns by switching the
phase and power levels supplied to the
individual antenna elements daily at sunrise and
• Phased array radars allow a warship to use one
radar system for surface detection and tracking
(finding ships), air detection and tracking (finding
aircraft and missiles) and missile uplink
• Prior to using these systems, each surface-to-air
missile in flight required a dedicated fire-control
radar, which meant that ships could only engage
a small number of simultaneous targets.
• A phased array may be used to point a fixed radiation
pattern, or to scan rapidly in azimuth or elevation.
• Because the radar beam is electronically steered,
phased array systems can direct radar beams fast
enough to maintain a fire control quality track on many
targets simultaneously while also controlling several inflight missiles. • The AN/SPY-1 phased array radar, part of the Aegis
combat system, is able to perform search, track and
missile guidance functions simultaneously with a
capability of over 100 targets.
• A phased array is an example of N-slit diffraction
• It may also be viewed as the coherent addition
of N line sources.
• Since each individual antenna acts as a...