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Introduction
After 70 years of development, radar is a mature system
Radar provides unique sensing capabilities No other sensor can search volumes of comparable size
continuously New sensing requirements demand new radars
Radar requirements are becoming more demanding
Coupled with the rapid development of electronic technology, radar is still evolving rapidly Radar architectures that designers could only dream about a
mere 15 years ago have become implementable
Introduction
In the 1950's, the appearance of the ICBM spurred the development of completely new radars. User requirements changed: 1945: Locate a fighter aircraft at 100 km to 1955: Locate the equivalent of a metal grapfruit at 1000 nm
In the 2000's, piracy on the high seas may again spur the development of completely new radars Locate small craft approaching large ships in rough seas
within an area of 360000 nm2 Radar is the only single sensor that can provide the
information Francois Anderson has the answer!
Introduction
Radar remains a dynamic and challenging system, not fully understood yet, offering many opportunities for research In the signal path, processing and structural hardware In new and improved processing algorithms to extract useful
information from data In designing algorithms to match specific hardware platforms
manage peak loads optimise throughput
In this talk I will outline topics from the necessarily biased and limited perspective of someone involved mainly with hardware in the analogue domain which I think can provide useful research opportunities for academics, in radar hardware radar information problems
Antennas The antenna is a critical radar component The ability of a radar to locate a target in 3D space
is ultimately dependent upon the radiation pattern, bandwidth, impulse response and stability of the antenna
Radar has a unique combination of requirements for antennas, including Stringent electrical performance requirements for the
radiation pattern and losses Exceptional mechanical stability in unfriendly environments High mobility and spatial re-orientation Long life expectancy
Antennas (ctd)
Antennas are undergoing rapid evolution on two fronts Our ability to meet increased performance requirements
made possible by powerful computer-based design tools The appearance of new (and not so new!) materials and
manufacturing processes challenging the designer to apply these creatively to reduce manufacturing cost and mass metallized plastics as opposed to metal bonding as opposed to welding
The radar antenna is an interdisciplinary challenge to electronic and mechanical engineers requiring teamwork to an extraordinary degree
Antennas (ctd)
There are research opportunities in "rediscovering" known antenna configurations Using modern tools to investigate the
performance limits to which these can be pushed, including parameters such as Bandwidth Size Beamshape Mass
Using non traditional materials in their construction
Antenna wishlist
An antenna "plank" Bandwidth 20% Azimuth Beamwidth 1° non-squinting Elevation beamwidth 70° Gain > 26 dB
at the price of a travelling-wave antenna
Can one perhaps make a centre-fed pill-box with f/D=0.2 do this? or do it with left-handed materials in a travelling wave array?
Passive components
Our ability to design and produce complex filters has increased in leaps and bounds with new EM analysis software
There are also interesting developments in materials and manufacturing technology Can you use rapid prototyping techniques to
produce components in small quantities? What are the limitations on component
performance with these techniques? How far can you go with metal plated plastics?
The Powertrain
Monostatic radar requires large average transmit power. This creates ongoing opportunities for research
Solid state power technology is advancing rapidly, currently with LDMOS and HVVFET, and GaN in the near future. Per device: Last week: 350 W output power @ 10% duty in L band This week: 500 W output power @ 25% duty in L-band
17 dB gain per stage 80 W output power reported in X band Equally important is DC power conditioning for the amplifier
Pulsed loads of 20 A @ 50 V Voltage must be stable to mV level from pulse to pulse Must meet stringent EMC requirements
The Powertrain
Control devices Eg solid state electronic duplexers and limiters
X band 8 kW peak 500W average 20% bandwidth 60 dB isolation
Isolated combiners L band
10 – 20 kW peak 1 – 2 kW average
Low noise sources
With the increasing extraction of information from radar returns, there is a growing need for sources with low close-in noise
FMCW search radars require sources with very low far-out noise e.g. -150 dBc/Hz @ 1 MHz offset in X-band
Research topics phase noise mechanisms in non-linear circuits architectures for low phase noise synthesizers low phase noise power amplifiers
Receivers
Modern MMIC's and new pcb materials are revolutionising the way we build receiver and transmit chains They include niceties such as high IP3 diode
mixers with on-chip LO amplifiers, requiring less than 0 dBm of LO drive power
Gain stable and cascadable wide band amplifiers High performance downconverters Power detectors
Receivers (ctd)
A single conversion radar receiver with electronic image rejection better than 50 dB is now possible for frequencies in L-band A receive chain can consist of a low noise amplifier and RF
filter, a demodulator, an IF filter, amplifier and an analogue to digital converter
It is possible to build multi-channel radar receivers in academic laboratories on academic budgets opening up a world of research possibilities into modern
and experimental radar system approaches bonus: an inexhaustible supply of signal processing
problems! Can these architectures migrate to practical systems in
the field?
Future receivers
Still over the horizon because of bandwidth requirements: the software defined radar receiver
One sampler several simultaneous receive channels formed digitally Bandwidth > 500 MHz
Mechanical & Mechatronic Technology Radar presents the mechanical engineer with
demanding structural requirements Radar also requires tight integration of computerized
control in mechanical systems This is a problem that industry must manage
There is room for academic research on a sub system level, including characterisation and evaluation of materialsconstruction
technology cooling technology for electronics corrosion control measures
System architectures Radar architecture is driven by requirements and
constrained by available technology Often leading to compromises
The action is moving to the digital domain, where detection sensitivity is achieved by increasing processing gain rather than transmit power
Staring radars are interesting options for low-cost systems Transmitter illuminates large search volume with a possibly
stationary antenna Multiple receivers are used for digital beamforming Long integration times deliver processing gain
Staring Radars
Questions: How can radar help to change the cost equation in asymmetrical
warfare? with staring radar? with passive radar? with bistatic radar?
Once hardware problems are solved, you can start working on THE radar problem How do you extract information from data? e.g. how do you distinguish between small targets and sea clutter?
How long can you stare at a target? What are the limits to processing gain?
We think there are interesting processing approaches out there still waiting to be discovered
These are problems for multidisciplinary teams, including engineers, computer scientists and mathematicians
"Super Resolution"
Usually super-resolution refers to means to increase effective bandwidth special processing algorithms that do better than
the discrete Fourier transform to measure the frequency of a sine wave, such as the MUSIC algorithm
This is not what I have in mind I'm referring to resolution that is out of proportion
to the volume of data Often because of sub-Nyquist sampling
Sub-Nyquist Sampling
The best-known example is Doppler/MTI radar In X-band, the Doppler shift for a target with a
radial velocity of 300 m/s is about 20 kHz An observation time of 16 ms will give a velocity
resolution of about 1 m/s At the Nyquist rate we require 640 samples @ 40
kHz In MTI radar we would perhaps take only 32
samples at 2 kHz
The Prize and the Price
Our prize is that we still have a Doppler resolution of 1 m/s
The price we pay for this is Ambiguity
blind speeds, where we cannot see targets measurements lost in clutter, where we cannot see
targets
A countermeasure to reduce the price is stagger the PRF and/or use multiple frequencies
"Super Resolution" and cost
We can apply the same principle to whenever we sample e.g. by increasing spacing between radiators in an antenna
array Prize: large hardware savings Price: spatial ambiguity Countermeasure: stagger electrical spacing
e.g. sampling IF in FMCW system at sub-Nyquist rate Prize: Increased range resolution Price: range ambiguity Countermeasure: staggered chirps or filtering
Questions for Research
Subsampling schemes: Quantify the Prize and the Price Devise effective countermeasures Quantify the final system performance
There are many more questions! Polarization – what to use, multiple, how to
switch? Behaviour of clutter RCS