Radar stations as a means of ensuring the security of critical information infrastructure

Critical infrastructure is commonly understood as a set of enterprises, networks, systems, the failure or disruption of which can cause loss of control or cause significant damage at the national, regional, local or facility level. [1]. Critical infrastructure (CI) management is carried out through information systems, information and telecommunication networks, automated control systems, as well as telecommunication networks that are used to organize their interaction. The totality of these systems and networks is defined as a critical information infrastructure (CII) [2; 3]. СI and CII are protected objects. There are special physical observation units that also solve a number of specific tasks for their security protection.

The first of these tasks is to illuminate the situation in close proximity to the protected perimeter of the object and on the approaches to it. [4–10]. To solve this problem, the physical protection units of the facility use optical and infrared means, contact and acoustic systems, and radar stations. The use of the latter is increasingly being used, especially in conditions of precipitation (snow and rain) and limited visibility (fog and drizzle). The quality of solving the problems of illuminating the situation directly depends on the effectiveness of the use of radar stations. Proper use of radar for solving various problems is determined by the knowledge and use of the basic properties of radar stations.

The aim of the work is to systematize the main characteristics of radar stations (RS) as a means of ensuring the security of critical information infrastructure [11 –15]. To achieve this goal, it is necessary to consistently solve the following tasks. Firstly, to analyze the main types of radar stations and determine the dominant type of radar. Secondly, to give the concept of tactical and technical characteristics of radar stations. Thirdly, to consider the feature of the main tactical characteristic - the range of the radar station.

The main types of radar stations and the dominant type of radar

Radar station, radar is a system for detecting air, sea and ground objects, as well as for determining their range, speed and geometric parameters [4; 12; 16–19]. Currently, they are usually distinguished by purpose: detection radar, control and tracking radar, target designation radar etc. Depending on the wavelength range used, they are divided into meter, decimeter, centimeter and millimeter ones. Primary radar mainly serves to detect targets by illuminating them with an electromagnetic wave and then receiving its reflection (echo) from the target. Since the speed of electromagnetic waves is constant (equal to the speed of light), it becomes possible to determine the distance to the target based on the measurement of various signal propagation parameters. The radar device is based on three components: a transmitter, an antenna and a receiver. [8; 20–23].

The transmitter is a source of high power electromagnetic signal and is a powerful pulse generator. For centimeter and millimeter range radars, a magnetron is usually used as a generator.

Depending on the design, the transmitter can either operate in a pulsed mode, generating repetitive short powerful electromagnetic pulses, or emit a continuous electromagnetic signal.

The antenna performs focusing of the emitted signal and the formation of a radiation pattern, as well as receiving the signal reflected from the target and broadcasting it to the receiver. So that a powerful signal does not leak from the transmitter to the receiver and does not blind it when receiving a weak echo, a special device (antenna switch) is placed in front of the receiver, which closes the receiver input at the moment the probing signal is emitted.

The receiver performs amplification and processing of the received signal. In the simplest case, the resulting signal is applied to a cathode ray tube (radar screen), which displays an image synchronized with the movement of the antenna.

Modern radars are based, as a rule, on frequency, phase and pulse methods for measuring the reflected signal [24–29]. Among surveillance radars, pulse radars are the dominant type. Pulse radar transmits an emitting signal with a short pulse (usually from fractions to units of a microsecond), after which it switches to receive mode, while the emitted pulse propagates in space. Since the pulse propagates from the radar at a constant speed, the distance to the target is determined by the time elapsed from the moment the pulse was emitted to the moment the echo response was received. The time interval between the emissions of pulses is called the pulse repetition frequency, which determines the working range scale of the station. The use of the pulse method allows you to create radar with one antenna and a fairly simple and ergonomic indicator device.

Thus, among the many types of radar stations, the most numerous are detection radars, which are designed to illuminate the situation around their location. The dominant type among these radars are centimeter and millimeter wave impulse radar stations, which use a single antenna, are quite simple and ergonomic when used for their intended purpose.

Tactical and technical characteristics of radar stations

The tactical characteristics of the radar are the key properties of the combat use of radar stations for their intended purpose, primarily to identify dangerous targets approaching the protected perimeter, and to ensure the use of technical and other means available to the security systems of critical information infrastructure to neutralize them or to reduce risk [5; 30].

The tactical characteristics of the surveillance radar include eight combat properties, expressed in certain numerical units of measurement. The first is range.

The range is the greatest detection range of the main target of the radar search, for example, a specific type of intruder (an armed saboteur equipped with special technical equipment and uniforms) or an aircraft (with a given radius of an equivalent reflective surface) located at a certain height, or a rubber watercraft (with a given equivalent reflecting surface radius).

The following parameters are view areas (and dead zone), angle and distance resolution, alert time, continuous operation time, noise immunity, antenna installation height.

Radar technical characteristics are specific technical properties (technical parameters) of radar stations that ensure the implementation of their tactical characteristics (key properties of combat use). There are ten of them. The main factors determining the range of the radar are the following three:

• –    carrier frequency f , Hz –the frequency of harmonic electromagnetic oscillations that serve as a carrier of impulse signals when they are emitted through modulation. It is measured in hertz and is related to the emitted wavelength λ with the ratio C = f· λ, where C = 3·10⁵ km/s is propagation speed of electromagnetic waves ;

• –    radiated pulsed power Р и , W is an average power over the pulse time . This power value is used to characterize rectangular, bell-shaped and other pulses;

• –    receiver sensitivity Р пр , W, characterizes the ability of the receiver to get weak signals and is defined as the minimum input signal level of the device necessary to ensure the required quality of the received information .

Other technical parameters are the antenna directivity width, antenna directivity and gain, signal recognition coefficient, space scanning speed, power consumption and overall parameters.

Thus, the tactical characteristics of radar stations in critical information infrastructure security systems include range, coverage areas, angle and distance resolution, alert time and continuous operation time, noise immunity and antenna installation height. Radar technical characteristics are specific technical properties (technical parameters) of radar stations that ensure the implementation of their tactical characteristics (key properties of combat use).

Features of the main tactical characteristic - the range of the radar station

It is customary to distinguish four types of radar range: energy, geometric, expected and actual.

Energy target detection range Д э (with equivalent reflecting surface radius R э ), measured in meters, is found from the basic equation (non-strict inequality) of radar

P u • K yc • 2 n- R Э

( 4 п Д ) 4

. 10 - 0,2 -Р- Дкм >§• Д^Р. ^K yc

where β is volume attenuation coefficient. Its value depends on the frequency of electromagnetic oscillations propagating in space, and is found empirically.

The target detection energy range Д is a calculated value and does not take into account the curvature of the earth's surface, due to its shape, terrain features in the area of the protected object.

Geometric range Д г takes into account these features. It is based on the principle of rectilinear propagation of electromagnetic waves, like a beam of light. The curvature of the earth's surface due to the fact that the Earth has a spherical shape, the presence of positive and negative relief causes the formation of zones of illumination and zones of shadow. Targets in the shadow zone are not detected.

The expected target detection range takes into account the refraction of electromagnetic waves – the curvature of a rectilinearly propagating electromagnetic beam due to a change in the state of the surface layers of the atmosphere, which traditionally depends on air temperature, its humidity and atmospheric pressure. This is taken into account by the anomaly coefficient A, which is calculated analytically using empirical methods corresponding to different ranges of electromagnetic waves – centimeter, decimeter and meter. In addition, there are methods for determining the coefficient of anomaly according to other local features.

In a number of cases to determine the expected detection range Д о , not the geometric, but the energy detection range is used. This happens in cases where Д э << Д г . In this regard, it is true that :

Д о = A

Д , если ^Д г * ^Д э , , Д_Э> если Д э <<  Д г

It should be noted that both the energy, geometric, and expected detection ranges are the result of an analytical calculation.

Actual range Д ф is the detection range , obtained as a result of using the radar for its intended purpose. It is the result of measuring the range of a newly detected standard target under certain conditions. Observed in such conditions, various standard targets – air, surface, ground – are detected in a certain range of distances each. The dialed (systematized according to the results of the combat use of the radar) set of distances obeys the normal distribution law, on the basis of which an integral pattern of detection of a specific radar target under certain conditions is built.

In other words, the actual (statistical, experimental) detection range Д ф is defined as :

^Дmin , если ^Р обн = 1, Д ф =Up , если Р обн = 0,5,

^Дmax , если P ^ <  0,5.

Depending on the probability of target detection, it is possible to build detection zones. The distance from which the target detection probability is equal to one is taken as the reliable detection range. It forms a zone of reliable detection, which is located in a circle, the radius of which is conventionally equal to one. If the distance at which the probability of target detection is 0.5, then the radius of the detection zone is from 1 to 1.5. The zone formed by this circle, which is located outside the area of reliable detection, is the zone of probable detection. The area of space located behind the zone of probable detection is usually called the zone of uncertain detection, the radius of which is from 1.5, where the actual detection range is maximum.

Conclusion

Among the many types of radar stations, the most numerous are detection radars, which are designed to illuminate the situation around their location. The dominant type among these radars are pulsed centimeter and millimeter wave radars, which use a single antenna, are quite simple and ergonomic when used for their intended purpose.

To determine the target detection range, taking into account the influence of environmental conditions and terrain (at the location of the radar station), it is necessary to use a system of equations containing dependencies of detection ranges: energy, geometric, expected and actual (statistical), the first three of which are used for analytical calculations, and the actual one to evaluate the detection results. The correspondence of analytical calculations to the actual results also makes it possible to assess the reliability of assumptions about the reflective properties of targets in various environmental conditions while ensuring the security of critical information infrastructure.

Acknowledgements . The work was carried out within the framework of the state assignment on topic No. 0555-2021-0005.