Presentation on theme: "2008 Ledger Conference Research Topics in Radar for Academics PW van der Walt Reutech Radar Systems why?"— Presentation transcript:
2008 Ledger Conference Research Topics in Radar for Academics PW van der Walt Reutech Radar Systems why?
2008 Ledger Conference 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
2008 Ledger Conference 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 nm 2 Radar is the only single sensor that can provide the information Francois Anderson has the answer!
2008 Ledger Conference 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
2008 Ledger Conference 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
2008 Ledger Conference 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
2008 Ledger Conference Two antenna arrays Single stick, non squinting 2x12 stick arrays, squinting
2008 Ledger Conference 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
2008 Ledger Conference 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?
2008 Ledger Conference 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?
2008 Ledger Conference 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
2008 Ledger Conference L Band LDMOS Low Z ports
2008 Ledger Conference 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
2008 Ledger Conference 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
2008 Ledger Conference Measured phase noise Noise floor set by system architecture
2008 Ledger Conference 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
2008 Ledger Conference 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?
2008 Ledger Conference 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
2008 Ledger Conference 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
2008 Ledger Conference 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
2008 Ledger Conference 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
2008 Ledger Conference "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
2008 Ledger Conference Resolution and data TsTs TPTP 1/T P 1/T s t t f d D x u
2008 Ledger Conference 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
2008 Ledger Conference 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
2008 Ledger Conference "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
2008 Ledger Conference 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
2008 Ledger Conference Conclusions Technological advance and new user requirements continuously generate new radar questions Radar continues to offer stimulating research topics Few things in life com free We hope soon to be able to provide data to academics who want to become involved in the exciting world of radar