Unclassified Air Systems Division Modern Architectures for Radiolocation Radars Abraham van den Berg...

Unclassified

Air Systems Division

Modern Architectures for Radiolocation Radars

Abraham van den Berg

Geneva, September 24th 2005

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Frequency sharing in Radiolocation bands

Operational System Requirements

Radar Modes and Architectures

Agenda

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Frequency sharing in Radiolocation bands

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Frequency Sharing in Radiolocation Bands

L-band: (1215 – 1400 MHz) RNSS: GPS, Glonass, Galileo

S-band: (2700 – 3600 MHz) MS: ENG/OB, Future IMT-2000

Aeronautical Telemetry

C-band: (5250 – 5850 MHz) MS: WAS, RLANs

GPS

IMT-2000

WAS ENG/OB

TELEMETRY RLANs

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Mission statements and requirements for a clear environment

Requirements for an EM polluted environment

Future radar requirements.

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L-band Requirements (1)

Mission: Long Range Air Defence

Long range detection of conventional aircraft (RCS > 2 m2)

Medium range detection of latest generation ‘stealth’ air

targets, i.e. missiles (RCS < 0.1 m2)

High performance w.r.t. Electronic Counter-Counter Measures

Guidance support for patrol aircraft

Surface surveillance up to the radar horizon.

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Mission: Volume Search by means of Multibeam Surveillance

Fast 3D scanning with gapless elevation coverage up to 70º

Excellent angular accuracy in elevation (< 1º)

Improved detection at low elevation (reduction of multipath effect)

Increased resistance against jamming and other interferences

Jamming detection

Improved operation in bad weather conditions

Suppression of sea and land clutter

Improved surface surveillance.

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An example of a naval Volume Search Radar

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L-band Requirements, highlights

Increasing number of spot frequencies in agile mode

(Interoperability, Multipath)

Increasing system bandwidth

(Detection of stealth targets, Multipath, ECM)

Digital beamforming for 3D scanning radars

Frequency diversity for ATC.

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S-band Requirements (1)

Mission: Military Air Traffic Control

Civil ATC Radar modified for military application, i.e. with additional environmental constraints

Capability of countering chaff, deception and noise jamming.

Mission: Battlefield and Border Surveillance

2D Detection and tracking of moving targets over a local area

Required to rapidly alert a co-located tracking sensor

Detection in land and weather clutter

Air and surface targets.

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Mission: Naval Surveillance

Two-dimensional

2D primary surveillance and target indication

Air as well as surface targets

Suppression of sea clutter.

Three-dimensional (3D Single Beam)

Additional facility of measuring target altitude.

Three-dimensional (3D Multi-beam)

Multiple simultaneous beams to shorten reaction time.

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Mission: Naval Multifunction Radar

Surveillance and tracking in angle, range and velocity of multiple targets

Phased array technology (Active as well as passive)

Own missile guidance

Kill assessment.

Mission: Airborne Early Warning

Long range and very long range (BTH) surveillance

Target altitude determination

All weather operation.

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An example of a naval Multifunction Radar

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S-band Requirements, highlights

Increasing pulse bandwidth

(Higher range resolution, NCTR)

Trend toward higher duty cycles

Increasing number of spot frequencies in agile mode

(Interoperability, Multipath)

Increasing system bandwidth

(Detection of stealth targets, Multipath, ECM)

Frequency diversity, up to 4 frequencies (ATC).

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C-band Requirements (1)

Mission: Naval Surveillance (2D and 3D)

Same as in S-band, but with shorter range, 30 km - 120 km.

Mission: Instrumentation Tracking

On test ranges: Very accurate tracking of space and

aeronautic

vehicles undergoing developmental and operational testing

Large parabolic reflector antennas and high EIRP

Autotracking antennas, either on the skin echo or on a beacon.

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Mission: Battlefield Weapon Locator

Required to locate position of enemy fire and impact location

Rapid horizontal scan in search mode

Rapid horizontal and vertical scan in tracking mode

Very agile, both in frequency and beam position

Extremely sensitive, due to targets with very small RCS.

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C-band Requirements, highlights

Frequency agility over a wide system bandwidth

Pulse bandwidth increases for high range resolution needs

More and more 3D radars with fast beam agility

Commonalitie with S-band radars, usually with shorter range

Specificity: Very sensitive long range instrumentation radar.

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Requirements in an EM Polluted Environment

Inter-system electromagnetic compatibility

Essentially compatibility with other radars in the same band

No known requirements to share with communication systems

Most of the time radars are protected by a primary status

When co-primary, other systems are required to avoid harmful interference to radars.

Electronic protection (or ECCM) requirements

Chaff, noise jamming, false target generation, deception

These requirements include:

Frequency hopping and automatic tuning

Advanced antenna design, combined with advanced signal and data processing.

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Future Requirements (1)

Tactical Ballistic Missile Defence (TBMD)

Detection and tracking of ballistic missiles

Cueing of other sensors

Will require a mix of sensors at different frequencies.

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Low Probability of Intercept (LPI)

No detection from ESM, jammer receivers, ARM receivers (even with a sensitity better than –80 dBm

LPI can only be realized by diluting emissions (Low EIRP)

In time: Increased duty cycle, CW

In space: Wide transmitted beam and digital beamforming

In frequency: Multi channel concepts.

Stealth Targets

Improved detection and tracking performance for targets with low RCS

Will require high EIRP and large bandwidth

Might require multi static modes

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Multifunction

Surveillance radar, Fire control radar, Terrestrial comms, Satellite comms, ESM, ECM

Benefits claimed for functional integration:

Common antenna system at optimum location

Increased flexibility in hardware allocation

Increased electromagnetic compatibility

Reduced radar signature

Reduced number of antennas

Reduction / elimination of electromagnetic blockage

Reduced handover time between functions.

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Non Cooperative Target Recognition (NCTR)

High resolution range profiling (< 1 m resolution)

Short pulses and thus large bandwidth wave forms

Jet Engine Modulation (JEM)

Emissions at shorter wavelength

High sample rate / high PRF for unambiguous spectrum

Good close in phase noise performance

Other techniques

Polarimetry

Multi static radar

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Radar Modes and Architectures

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Radar Modes and Architectures (1)

Classical

Main design issues for the selection of waveforms

Range resolution, accuracy and ambiguity

Doppler resolution, accuracy and ambiguity

Clutter cancelling

Multi target performance

Narrow band pulse Doppler waveforms

Variety of parameters in frequency, pulse width and PRI

Major Choices on Waveforms

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Non classical

FM-CW waveforms

Passive radar

Use of transmission of opportunity to perform radar functions

High range resolution

Target separation, isolation of target points for NCTR purposes, improved detectability in clutter

Short pulse, pulse compression, deramp or stretched waveform, step frequency

Major Choices on Waveforms

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Compromise between peak power and duty cycle

Influenced by transmitter technology.

Major Choices on Transmitted Power

Transmitted RF pulses have to contain sufficient energy to:

Detect a target with specified RCS at a specified range

Overcome environmental noise effects

Overcome path losses

Overcome system losses

Overcome man made noise sources

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RF filtering on multi frequency radars offers no rejection of in band interference

Major Choices on Receiver Selectivity

Traditionally filters have been designed to meet radar requirements and are thus not optimized for the rejection of communication signals

Digital techniques may give the compensation for some IF filter limitations

IF filters, though effective, are not ideal and therefore offer only limited protection to interferers on nearby frequencies

IF filter design has to balance in band performance against out of band rejection

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Major Choices on Beamwidth

Radar antennas are designed to concentrate RF energy in the wanted direction and suppress radiation in other directions

Choice of beamwidth is related to:

Requirements on detection range (power aperture product)

Compromise between average power and antenna gain

Requirements on angular resolution and accuracy

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Techniques Facilitating Sharing (1/4)

Receivers with high dynamic range

Minimize the chance of unwanted intermodulation products being generated by interfering signals

Reduce the risk of receiver saturation

Analogue-Digital converters currently set the limits of achievable dynamic range, regardless of the receiver

There is no advantage in the detection of small targets in the presence of low level interference

Main beam sector blanking

Protect other RF receivers in specific direction

When applied in networked radars, complete volume coverage can be conserved

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Narrowing of the beam

Minimize the width of the transmitted beam of an array antenna

Improves the received signal level

Drawback is an increase in update time

Long pulses

Longer pulses allows a reduction in peak power

Range resolution requirements dictate the use of pulse coding to maintain bandwidth

Short range performance requirements often dictate the use of additional short pulses, thus increasing spectrum usage

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Look back

Reduction of false detections due to interference

Can only be applied with phased arrays

Coverage may degrade when the number of interference sources increases.

Spread spectrum techniques

Application of conventional DSSS techniques are equivalent to phase coded pulse compression techniques.

Multi-user CDMA detection techniques could possibly be applied to improve interference suppression

Drawback of multi-user detection is as a minimum an increase in the processing load and the complexity of the required hardware.

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Frequency planning

Possible when the interference exhibits a certain regularity

Consultation between users of the frequency band can lead to frequency coordination

FMCW mode

Improved selectivity in comparison with pulse radars

CW interference in the instantaneous radar band will cause desensitization

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Radar Modes toward full Mitigation

Radar modes for frequency division

Determine bandwidth of sub-bands required for different users

Divide sub-bands with sufficient frequency separation

Allocation of a set of sub-bands spread over the available frequency range will be required

Radar modes for spatial division

Determine spatial sections to radiate

Separate spatial areas by a safety margin

To achieve optimised mitigation, it is required that cooperative arrangements aremade between users of the band. Two modes can be used:

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Burn through mode: Improved S/(N+I) at the expense of update rate

Radar Modes toward partial Mitigation

Sidelobe control mode: Complex technique that can only be applied for a limited number of interference sources

Interference suppression mode: Improve resistance against interference at the expense of an increased system complexity and reduction in performance

Frequency control mode: Does not work for unstable spectrum (frequency hopping transmitters) or when the whole band is occupied

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Thank you for your attention !

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Unclassified Air Systems Division Modern Architectures for Radiolocation Radars Abraham van den Berg...

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