Conventional radar systems comprise a colocated transmitter and receiver, which usually share a common antenna to transmit and receive. A pulsed signal is transmitted and the time taken for the pulse to travel to the object and back allows the range of the object to be determined.
In a passive radar system, there is no dedicated transmitter, Instead, the receiver uses third-party transmitters in the environment and measures the time difference of arrival between the signal arriving directly from the transmitter and the signal arriving via reflection from the object.
Passive radar systems (also referred to as passive coherent location, passive surveillance systems, and passive covert radar) 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.
This allows the bistatic range of the object to be determined. In addition to bistatic range, a passive radar will typically also measure the bistatic Doppler shift of the echo and also its direction of arrival. These allow the location, heading and speed of the object to be calculated. In some cases, multiple transmitters and/or receivers can be employed to make several independent measurements of bistatic range, Doppler and bearing and hence significantly improve the final track accuracy. It is a specific case of bistatic radar, the latter also including the exploitation of cooperative and non-cooperative radar transmitters.
The rise of cheap computing power and digital receiver technology has led to a resurgence of interest in passive radar technology. For the first time, these allowed designers to apply digital signal processing techniques to exploit a variety of broadcast signals and to use cross-correlation techniques to achieve sufficient signal processing gain to detect targets and estimate their bistatic range and Doppler shift.
Passive multistatic radars for Counter stealth
Another types of multistatic radars are Passive multistatic radar (PMR) that makes use of transmission from opportunistic radars and communication transmitters to detect targets. Any radar which does not send active electronic magnetic pulse is known as passive radar. “Passive coherent location” also known as PCL is a special type of passive radar, which exploits the transmitters of opportunity especially the commercial signals in the environment. Potential transmissions utilized include FM and AM radio, HF radio, TV (VHF / UHF), digital audio/video broadcast, cellular phone networks and communications and navigation satellite.
Passive radar systems offer several key benefits. They are hard to detect by conventional means: Electronic sensors cannot pick them up because they do not transmit their own signals. They have no transmitters generating heat, so they cannot be detected thermal signatures, and they are small and quite difficult to spot.
The key processing step in a passive radar is cross-correlation. The principal limitation in detection range for most passive radar systems is the signal-to-interference ratio, due to the large and constant direct signal received from the transmitter. Passive radar performance is comparable to conventional short and medium range radar systems. However, as a rule of thumb it is reasonable to expect a passive radar using FM radio stations to achieve detection ranges of up to 150 km, for high-power analogue TV and US HDTV stations to achieve detection ranges of over 300 km and for lower power digital signals (such as cell phone and DAB or DVB-T) to achieve detection ranges of a few tens of kilometers.
Passive radar accuracy is a strong function of the deployment geometry and the number of receivers and transmitters being used. Most passive radars are two-dimensional, but height measurements are possible when the deployment is such there is significant variation in the altitudes of the transmitters, receiver and target, reducing the effects of geometrical dilution of precision (GDOP).
Research on passive radar systems is of growing interest throughout the world, with various open source publications showing active research and development in the United States (including work at the Air Force Research Labs, Lockheed-Martin Mission Systems, Raytheon, University of Washington, Georgia Tech/Georgia Tech Research Institute and the University of Illinois), in the NATO C3 Agency in The Netherlands, in the United Kingdom (at Roke Manor Research, QinetiQ, University of Birmingham, University College London and BAE Systems, France (including the government labs of ONERA), Germany (including the labs at Fraunhofer-FHR), Poland (including Warsaw University of Technology).
Equally, however, the additional complexity of having a number of separated transmitters and receivers brings about new challenges before these systems can be put into operational use. The most important is time and frequency synchronization for coherent operation. The distributed nature of system requires a distributed approach to data fusion and associated signal processing becomes complex. It also requires more complex sensor/resource management system. There is also need for reliable high capacity communication links in the system.
“Saab’s work on its new Giraffe 4A/8A S-band radars points to ways in which AESA technology and advanced processing improve high-band performance against small targets. Module technology is important, maximizing the AESA’s advantages in terms of signal-to-noise ratio. The goal is signal “purity” where most of the energy is concentrated close to the nominal design frequency, which makes it possible to detect very small Doppler shifts in returns from moving targets. New processing technologies include “multiple hypothesis” tracking in which weak returns are analyzed over time and either declared as tracks or discarded based on their behavior,” write Bill Sweetman in Aviation Week & Space Technology.
Passive radar market
According to Visiongain rtesearch firm, the global passive radar market is projected to grow from US$ 2,324 million in 2020 to US$ 4,313 million by 2030, at a CAGR of 6.38% between 2020 and 2030.
Passive radar is distinct from traditional forms of the radar in that it does not emit any electromagnetic radiation. Instead, it depends on reflections from other electromagnetic signals in the atmosphere in order to provide a radar picture.
Passive radar offers several distinct advantages that will allow it to corner a significant portion of defense, civilian radar, and homeland security markets. The defense sector is expected to be the major market for the adoption of passive radar systems, to detect low flying aircraft and shape-dependent stealth aircraft, during the forecast period. The response speed of radar for the detected target and classifying it as a threat are likely to be the crucial factors, while the effects of noise and clutter can affect detection adversely.
The overall effect of the COVID-19 outbreak is impacting the production process of several industries of passive radar market. The COVID-19 pandemic is impacting the society and overall economy across the global. The impact of this outbreak is growing day-by-day as well as affecting the supply chain. The crisis is creating uncertainty in the stock market, falling business confidence, massive slowing of supply chain, and increasing panic among the customer segments. As government of different provinces have already announced total lockdown and temporarily shutdown of industries, the overall production process being adversely affected; thus, hinder the overall passive radar market globally.
The European countries under lockdowns have suffered major loss of business and revenue, due to the shutdown of manufacturing units in the region. The operations of the production and manufacturing industries have been heavily impacted by the outbreak of the COVID-19 disease; thereby, leading to slowdown in the growth of the radar market in 2020.
Cancellation of several military exercises between nations and reduction in military activities worldwide due to COVID-19, has been impacting adversely to military radars market as demand of relevant spare parts is also low. Post COVID-19, military radars market can see a significant growth as several countries have either already ordered or planning to procure military drones for their forces.
Top Impacting Factors
Currently, the defense segment has the largest market share in the passive radars market. The use of stealth technology in the design of newer generation fighter jets is widespread currently, and it plays a crucial role in military affairs. On the other hand, research on counter stealth threats has also gained considerable attention these days. Passive radar has advanced a long way over the past two decades, due to the advancements in technology and increased investment from the armed forces and research institutions.
Few companies are developing advanced air defense systems with passive sensor systems that will offer the silent power of early warning and air situation picture without the use of active radars, to the air defense system. The recent advancements made by China and Russia in stealth fighter jets has raised concern for the United States that has, over the past, invested more on stealth technology rather than counter stealth systems. China’s J-20A and Russia’s Su-57 are expected to compel the countries in the region, to opt for defensive systems, like passive radars, in the coming years.
- Lack of electromagnetic waves in the target area can render the passive radar systems useless is expected to hamper the growth of the market.
- Environment friendly can be seen as an opportunity for the market investments.
United States Currently Dominates the North American Passive RADAR Market
In 2019, the United States has the largest market share in the North American passive RADAR market. Historically, the United States has placed limited emphasis on developing passive radar systems. Nevertheless, the design and deployment of stealth aircraft by potential adversaries, like Russia and China, have encouraged investments into the development of advanced passive radar systems. The financial boost to the R&D of passive radar systems is anticipated to augment the research in passive radar technology, in the country, over the upcoming period.
Raytheon has fielded several passive radars for the US military over the years. The patriot air defense system, currently in operation with the army, includes the MPQ-65A radar, which is a passive radar. The army operates more than 60 MPQ-65 radars across 15 patriot battalions. In addition to companies like Lockheed-Martin Corporation and Raytheon Company, universities and public and private entities in the country, such as the Air Force Research Labs, are keenly investing in the persistent R&D of advanced passive radar systems in the region. For instance, the researchers at the University of Washington operate a distributed passive radar exploiting FM broadcasts, to study ionospheric turbulence at altitudes of 100 km and ranges out to 1,200 km.
Thus, the market in focus is expected to grow in the United States, fueled by the technological opportunities and the emergence of stealth-based threats from foreign adversaries. Also, the ongoing research, related to various potential applications of passive radars, is expected to foster the imminent growth in the adoption of passive radar technologies by both commercial and defense end users.
Airbus SE, Advanced Electronics Company, BAE Systems PLC, SRC Inc., ERA AS (Omnipol Group), Hensoldt Holding Germany GmbH, Indra Sistemas SA, Israel Aerospace Industries Ltd, L3Harris Technologies Inc., Leonardo SpA, Raytheon Company, Ramet AS, Thales Group, are some of the major players in the market.
Players are unveiling new advanced passive RADAR models that help them tap into new markets. For instance, in June 2019, ELTA Systems unveiled the Next Generation Multi-Sensor ELM-2084 MMR Radar that fuses additional ELTA sensors to the main MMR system thereby providing an active, passive, and combined Air Situational Picture (ASP) at the Paris Air Show. Such developments are expected to make the market more competitive in the years to come.
IAI Unveiled a Passive Radar
ELTA Systems, a subsidiary of Israel Aerospace Industries Group, unveiled in Oct 2020 a new Passive Coherent Location Radar System, enables the creation of an air situation using non-cooperative transmitters. It detects and tracks aerial threats based on target reflection from FM or Digital Audio Broadcasting (DAB) towers. The reflections are received by one or a network of antennas, providing 3D real-time tracking of multiple targets in congested airborne traffic.
The PCL system installation can include one sensor or a cluster of sensors for redundancy and improved coverage. The sites are connected to the central PCL command and control processing unit via a dedicated data link. General Manager of ELTA Intelligence, Communications and EW division, Adi Dulberg, said that the PCL system detects and classifies aerial risks, “without unveiling the locator.”
Silentium to deliver passive radar systems for Australian Army
Silentium Defence has secured a $7.4 million contract from the Department of Defence to supply its Maverick M-series passive radar system to the Australian Army for capability development and evaluation activities.
Designed in collaboration with Defence, it is the first high-performance, low-power, soldier-portable, covert radar system for air defence and maritime surveillance, providing critical sovereign capability for the ADF and its allies. The Maverick M-series also enables users to see without being seen, an obvious advantage in the air, land and in maritime domains.
A complementary or replacement technology to traditional surveillance systems, the Maverick M-series passive radars use existing energy in the environment (for example, broadcast television signals) as their transmission source. As they do not emit, they do not highlight the user’s presence or create a radiation hazard. This makes the radar system quick, safe, and easy to deploy, even in densely populated environments.
They are also more cost-effective than traditional active radar systems, which require spectrum allocation to operate.