Multistatic radar
Encyclopedia
A multistatic radar system contains multiple spatially diverse monostatic radar
or bistatic radar
components with a shared area of coverage. An important distinction systems based on these individual radar
geometries is the added requirement for some level of data fusion
to take place between component parts.
The spatial diversity afforded by multistatic systems allows for different aspects of a target to be viewed simultaneously. The potential for information gain can give rise to a number of advantages over conventional systems.
Multistatic radar is often referred to as ‘multisite’ or ‘netted’ radar, and is comparable with the idea of macrodiversity
in communications. A further subset of multistatic radar with roots in communications is that of MIMO
radar.
transmitters and 
receivers will contain 
of these component pairs, each of which may involve a differing bistatic angle
and target radar cross section
. The following characteristics are unique to the multistatic arrangement, where multiple transmitter-receiver pairs are present:
.
Spatial diversity may also be beneficial when combining information from multiple transmitter-receiver pairs which have a shared coverage. By weighting and integrating individual returns (such as through likelihood ratio based detectors), detection can be optimised to place more emphasis on stronger returns obtained from certain monostatic or bistatic radar cross section
values, or from favourable propagation paths, when making a decision as to whether a target is present. This is analogous to the use of antenna diversity
in an attempt to improve links in wireless communications.
This is useful where multipath or shadowing effects might otherwise lead to the potential for poor detection performance if only a single radar is used. One notable area of interest is in sea clutter, and how diversity in reflectivity and Doppler shift might prove beneficial for detection in a maritime environment.
ellipses.
This involves a process of associating individual target detections to form a joint detection. Due to the un-cooperative nature of the targets there is potential, if a number of targets are present, for ambiguities or ‘ghost targets’ to be formed. These can be reduced through an increase in information (e.g. use of Doppler information, increase in down-range resolution or addition of further spatially diverse radars to the multistatic system).
through radio signal fusion. Dependent on this, a wide communications bandwidth may be required to pass the relevant data to a point where it can be fused.
Several passive radar
systems make use of multiple spatially diverse transmitters and hence may be considered to operate multistatically.
Monostatic radar
Monostatic radar is the term given to a radar in which the transmitter and receiver are collocated. This is the conventional configuration for a radar, but the term is used to distinguish it from a bistatic radar or multistatic radar....
or bistatic radar
Bistatic radar
Bistatic radar is the name given to a radar system which comprises a transmitter and receiver which are separated by a distance that is comparable to the expected target distance. Conversely, a radar in which the transmitter and receiver are collocated is called a monostatic radar...
components with a shared area of coverage. An important distinction systems based on these individual radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
geometries is the added requirement for some level of data fusion
Data fusion
Data fusion, is generally defined as the use of techniques that combine data from multiple sources and gather that information into discrete, actionable items in order to achieve inferences, which will be more efficient and narrowly tailored than if they were achieved by means of disparate...
to take place between component parts.
The spatial diversity afforded by multistatic systems allows for different aspects of a target to be viewed simultaneously. The potential for information gain can give rise to a number of advantages over conventional systems.
Multistatic radar is often referred to as ‘multisite’ or ‘netted’ radar, and is comparable with the idea of macrodiversity
Macrodiversity
In the field of wireless communication, Macrodiversity is a kind of space diversity scheme using several receiver antennas and/or transmitter antennas for transferring the same signal...
in communications. A further subset of multistatic radar with roots in communications is that of MIMO
MIMO
In radio, multiple-input and multiple-output, or MIMO , is the use of multiple antennas at both the transmitter and receiver to improve communication performance. It is one of several forms of smart antenna technology...
radar.
Characteristics
Since multistatic radar may contain both monostatic and bistatic components, the advantages and disadvantages of each radar arrangement will also apply to multistatic systems. A system with transmitters and receivers will contain of these component pairs, each of which may involve a differing bistatic angleBistatic angle
The bistatic angle is the angle subtended between the transmitter, target and receiver in a bistatic radar. When it is exactly zero the radar is a monostatic radar, when it is close to zero the radar is pseudo-monostatic, and when it is close to 180 degrees the radar is a forward scatter radar. ...
and target radar cross section
Radar cross section
Radar cross section is a measure of how detectable an object is with a radar. A larger RCS indicates that an object is more easily detected.An object reflects a limited amount of radar energy...
. The following characteristics are unique to the multistatic arrangement, where multiple transmitter-receiver pairs are present:
Detection
Increased coverage in multistatic radar may be obtained via the spreading of the radar geometry throughout the surveillance area - such that targets might be more likely to be physically closer to transmitter receiver-pairs and thus attain a higher signal-to-noise ratioSignal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
.
Spatial diversity may also be beneficial when combining information from multiple transmitter-receiver pairs which have a shared coverage. By weighting and integrating individual returns (such as through likelihood ratio based detectors), detection can be optimised to place more emphasis on stronger returns obtained from certain monostatic or bistatic radar cross section
Radar cross section
Radar cross section is a measure of how detectable an object is with a radar. A larger RCS indicates that an object is more easily detected.An object reflects a limited amount of radar energy...
values, or from favourable propagation paths, when making a decision as to whether a target is present. This is analogous to the use of antenna diversity
Antenna diversity
Antenna diversity, also known as space diversity, is any one of several wireless diversity schemes that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoor environments, there is no clear line-of-sight between transmitter and...
in an attempt to improve links in wireless communications.
This is useful where multipath or shadowing effects might otherwise lead to the potential for poor detection performance if only a single radar is used. One notable area of interest is in sea clutter, and how diversity in reflectivity and Doppler shift might prove beneficial for detection in a maritime environment.
Resolution
Resolution may benefit from spatial diversity, due to the availability of multiple spatially diverse down-range profiles. Conventional radar typically has a much poorer cross-range resolution compared to down-range resolution, thus there is potential for gains through the intersection of constant bistatic rangeBistatic range
Bistatic range refers to the basic measurement of range made by a radar or sonar system with separated transmitter and receiver. The receiver measures the time difference of arrival of the signal from the transmitter directly, and via reflection from the target...
ellipses.
This involves a process of associating individual target detections to form a joint detection. Due to the un-cooperative nature of the targets there is potential, if a number of targets are present, for ambiguities or ‘ghost targets’ to be formed. These can be reduced through an increase in information (e.g. use of Doppler information, increase in down-range resolution or addition of further spatially diverse radars to the multistatic system).
Classification
Target features such as variation in the radar cross section or jet engine modulation may be observed by transmitter-receiver pairs within a multistatic system. The gain in information through observation of different aspects of a target may improve classification of the target. Most existing air defence systems utilize a series of networked monostatic radars, without making use of bistatic pairs within the system.Robustness
Increased survivability and ‘graceful degradation’ may result from the spatially distributed nature of multistatic radar. A fault in either transmitter or receiver for a monostatic or bistatic system will lead to a complete loss of radar functionality. From a tactical point of view, a single large transmitter will be easier to locate and destroy compared to several distributed transmitters. Likewise, it may be increasingly difficult to successfully focus jamming on multiple receivers compared to a single site.Spatio-temporal synchronization
To deduce the range or velocity of a target relative to a multistatic system, knowledge of the spatial location of transmitters and receivers is required. A shared time and frequency standard must be also be maintained if the receiver has no direct line of sight of the transmitter. As in bistatic radar, without this knowledge there would be inaccuracy in the information reported by the radar. For systems exploiting data fusion before detection, there is a need for accurate time and or phase synchronisation of the different receivers. For plot level fusion, time tagging using a standard GPS clock (or similar) is more than sufficient.Communications bandwidth
The increase in information from the multiple monostatic or bistatic pairs in the multistatic system must be combined for benefits to be realised. This fusion process may range from the simple case of selecting plots from the receiver closest to a target (ignoring others), increasing in complexity to effectively beamformingBeamforming
Beamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in the array in a way where signals at particular angles experience constructive interference and while others experience destructive...
through radio signal fusion. Dependent on this, a wide communications bandwidth may be required to pass the relevant data to a point where it can be fused.
Processing requirements
Data fusion will always mean an increase in processing compared to a single radar. However it may be particularly computationally expensive if significant processing is involved in data fusion, such as attempts to increase resolution.Examples of multistatic radar systems
- Massachusetts Institute of Technology’s Netted Radar System.
- Hamburg University of Technology’s Automotive Radar Network
- Jindalee Operational Radar NetworkJindalee Operational Radar NetworkThe Jindalee Operational Radar Network is an over-the-horizon radar network that can monitor air and sea movements across 37,000 km2. It has an official range of 3,000 km. It is used in the defence of Australia and can also monitor maritime operations, wave heights and wind directions...
- Norwegian Defence Research Establishment’s Experimental Bi-Multistatic CW Radar
- SAIC’s Passive, Multi-Static Radar System
- University College London’s NetRad System
- Xidian University’s Coast-ship Bi/multistatic Ground-wave Over-the-horizon Radar
Several passive radar
Passive radar
Passive radar systems encompass a class of radar systems that detect and track objects by processing reflections from non-cooperative sources of illumination in the environment, such as commercial broadcast and communications signals...
systems make use of multiple spatially diverse transmitters and hence may be considered to operate multistatically.
Further reading
- Chernyak, V.S. (1998). “Fundamentals of Multisite Radar System. Gordon and Breach Science Publishers. ISBN 9056991655.
- Li, J. Stoica, P. (ed) (2008). "MIMO Radar Signal Processing. Wiley-IEEE Press. ISBN 0470178981.