Passive Radar, an overview

Lars Ulander, Prof.1Radar Systems Unit, Division of C4ISRSwedish Defence Research Agency (FOI)

1Part-time at Chalmers University of Technology

Contents

• Principles and Terminology• What’s on the market?• Some research results• International cooperation• Conclusions

Bistatic vs. Monostatic radar

• Monostatic radar: Self-contained but sensitive to ECM• Bistatic radar: Receiver is silent, but relies on suitable transmitters

Different types of Passive Radar

• Passive Coherent Location (PCL)• Passive Covert Radar (PCR)• Parasitic Radar• Hitchhiking Radar

Taxonomy

RadarMonostatic Bistatic

Cooperativetransmitter

Non-cooperativetransmitter

Taxonomy

RadarMonostatic Bistatic

Cooperativetransmitter

Non-cooperativetransmitter

Passive Radar

Taxonomy

RadarMonostatic Bistatic

Cooperativetransmitter

Non-cooperativetransmitter

Radar signal

Broadcast com signal

Taxonomy

RadarMonostatic Bistatic

Cooperativetransmitter

Non-cooperativetransmitter

Radar signal

Broadcast com signal

Passive Coherent Location (PCL) orPassive Covert Radar (PCR)

Taxonomy

RadarMonostatic Bistatic

Cooperativetransmitter

Non-cooperativetransmitter

Radar signal

Broadcast com signal

Parasitic Radar or Hitchhiking Radar

WWII Parasitic Radar

German Kleine Heidelberg(parasitic radar)

British Chain Home Radar(radar transmitter of opportunity)

f = 20-30 MHz, P = 750 kW

Passive radar: How does it work?

When direct signal is not available, Doppler-onlytracking from multiple receiving stations can be used

Correlationprocessing

DVB-T signal: Range-Doppler processing

(from Christiansen, thesis, NTNU)

Passive radar: Positioning

Positioning based on multiple receiving sites or receiver antenna array

Ambiguous position

Transmitters

• FM Radio 87.5-108 MHz– High power; Wide elevation antenna beam– Disadvantage: Bandwidth depends on program content

• Digital TV 170-230 MHz, 470-694 (790) MHz– High power; Narrower elevation antenna beam– DVB-T standard (OFDM) provides a good signal since

bandwidth is independent on program content• Other possibilities

– Satellite broadcasting, communication signals

Industrial developments

Silent Sentry (1999)

Other examples: AULOS (2011), Airbus Defence and Space (2012)

ERA Silent Guard (2014)

THALES HA-100 (2007)

Typical performance: 100-300 km range

A

FOI research: Passive radar ground imaging

Imaged ground area

High-resolution passive radar imaging of ground by synthetic-aperture radar (SAR) processing

FOI research: Passive SAR trials 2012

• Airborne receiver with digital TV as transmitter• Gotland island, the Baltic Sea (Follingbo TV mast)

FOI research: Passive SAR images of ships

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Size 99m x 14m

Size 190m x 32m

Ships located on eastern side of Gotland (Slite harbour) at 40 km and identified by AIS logs

FOI research: Passive SAR image of Gotland

Resolution: ca 5 m x 20 m (limited by a single DVB-T channel)

Artifacts due to TV transmitter tower at Follingbo

FOI research: International cooperation

• NATO SET-186 (closed 2014)– APRA - Airborne Passive Radar Applications– Poland is lead nation

• NATO SET-207 (on-going since 2014)– Advanced situation-specific modeling, sensing and

vulnerability mitigation using passive radar technology– Germany is lead nation

Conclusions

• Passive radar is emerging technology, withsome production and prototype systems

• The main advantage is that system is passive (silent) and does not transmit signals

• The main disadvantage is that system dependson the availability of suitable transmitters

• Passive SAR for ground surveillance is a new research area, with first successful flight trials in 2012 by FOI. New flights conducted in 2016.