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technospheramag
technospheramag
ТЕХНОСФЕРА_РИЦ
Issue #1/2024
M. E. Belkin, E. V. Kuznetsov
Promising Microwave-Photonics Facilities of Group and Individual Electronic Countermeasures
Promising Microwave-Photonics Facilities of Group and Individual Electronic Countermeasures
DOI: 10.22184/1993-7296.FRos.2024.18.1.48.62
Based on the globally and rapidly developing microwave-photonics approach that has already found its application in the promising radio-electronic means of telecommunications, radars, electronic countermeasures, security, computing and measurement equipment, this article proposes a new development principle for the group and individual radio-electronic protection facilities against the remote effect of unauthorized radio channels for various purposes. Its key advantages include simplicity and insensitivity to electronic interference, including intentional ones, as well as ultra-fast ultra-wideband processing of any radio-frequency signal received in an optoelectronic processor that depending on its purpose, either increases the group or individual protection area up to several kilometers, or reduces the response time for individual protection to a hundred of nanoseconds , while ensuring operation over the entire operating frequency band. The diagrams of optoelectronic processors, description of developed radio-frequency electronic protection samples with the spoofing or blocking functions for unauthorized radio channels, and the results of laboratory and preliminary field tests are provided.
Based on the globally and rapidly developing microwave-photonics approach that has already found its application in the promising radio-electronic means of telecommunications, radars, electronic countermeasures, security, computing and measurement equipment, this article proposes a new development principle for the group and individual radio-electronic protection facilities against the remote effect of unauthorized radio channels for various purposes. Its key advantages include simplicity and insensitivity to electronic interference, including intentional ones, as well as ultra-fast ultra-wideband processing of any radio-frequency signal received in an optoelectronic processor that depending on its purpose, either increases the group or individual protection area up to several kilometers, or reduces the response time for individual protection to a hundred of nanoseconds , while ensuring operation over the entire operating frequency band. The diagrams of optoelectronic processors, description of developed radio-frequency electronic protection samples with the spoofing or blocking functions for unauthorized radio channels, and the results of laboratory and preliminary field tests are provided.
Теги: blocking electronic countermeasures microwave-photonics approach optoelectronic processor spoofing unauthorized radio channel блокирование несанкционированный радиоканал оптоэлектронный процессор радиофотонный подход радиоэлектронная защита спуфинг
Promising Microwave-Photonics Facilities of Group and Individual Electronic Countermeasures
M. E. Belkin
MIREA – Russian Technological University, Moscow, Russia
E. V. Kuznetsov
Polyus Scientific Research Institute JSC, Moscow, Russia
Based on the globally and rapidly developing microwave-photonics approach that has already found its application in the promising radio-electronic means of telecommunications, radars, electronic countermeasures, security, computing and measurement equipment, this article proposes a new development principle for the group and individual radio-electronic protection facilities against the remote effect of unauthorized radio channels for various purposes. Its key advantages include simplicity and insensitivity to electronic interference, including intentional ones, as well as ultra-fast ultra-wideband processing of any radio-frequency signal received in an optoelectronic processor that depending on its purpose, either increases the group or individual protection area up to several kilometers, or reduces the response time for individual protection to a hundred of nanoseconds , while ensuring operation over the entire operating frequency band. The diagrams of optoelectronic processors, description of developed radio-frequency electronic protection samples with the spoofing or blocking functions for unauthorized radio channels, and the results of laboratory and preliminary field tests are provided.
Keywords: microwave-photonics approach, unauthorized radio channel, electronic countermeasures, optoelectronic processor, spoofing, blocking
Article received: 12.01. 2024
Article accepted: 08.02. 2024
Introduction
An analysis of the modern world development of radio-electronic systems (RES) in the microwave range demonstrates that the most efficient way to solve a strategically crucial problem, namely improvement of the throughput, weight, size and cost performances, energy consumption, and reliability of the modern microwave-band RESs for civil and military purposes, is an application of microwave-photonics (MWP) methods and approaches for the signal generation and processing [1−5], namely a new interdisciplinary field developed at the intersection of radio-frequency (RF) electronics and photonics. In addition to a significant improvement in the above technical and economic indicators, implementation of this approach in the microwave RESs will also lead to an improvement in such important specifications of dual-use RESs as electromagnetic compatibility, environmental durability (including hostile exposure), and ecological friendliness.
The devices and units of microwave-photonics equipment based on the photonics and MWP technologies, including any RF signals’ processing devices, as well as the dual-use RESs with the applied MWP principles, are widely researched and developed at the universities and scientific departments of large companies in the highly developed foreign countries. However, this area being very important for the country’s defense potential, is developing very poorly in Russia, and there is already a significant lag. To find the ways of negotiation and provide the relevant conditions, in recent years, a special working group on MWP has been established under the Scientific and Technical Council of the Defense Industrial Complex. This group has developed a Program for the Development of Domestic Microwave-photonics for 2016-2025. In addition, the Advanced Research Foundation of the Defense Industrial Complex has developed a Roadmap for Photonics and Microwave-photonics. Implementation of the shaped plans is currently being performed by a number of universities, institutions of the Russian Academy of Sciences and enterprises of the radio-electronic industry.
Following this procedure, the MWP approach is considered in this article as a new principle for generating means of group and individual electronic countermeasures against the remote effect of unauthorized radio channels for various purposes. Its key advantages include simplicity and insensitivity to electronic interference, including intentional ones, as well as ultra-fast ultra-wideband processing of any radio signal received in an optoelectronic processor that either increases the group or individual protection area length to several kilometers, or reduces the response time for individual protection to a hundred of nanoseconds depending on its purpose, while ensuring operation over the entire operating frequency band up to several octaves. The diagrams of ultra-wideband optoelectronic processors with the memory from hundreds of picoseconds to tens of microseconds, description of developed RF electronic protection samples, and the results of laboratory and preliminary field tests are provided.
Modern facilities of electronic countermeasures
In general, the modern development of telecommunications, radars and other electronic means is increasingly specified by the use of equipment remotely controlled via the wireless RF channels. The currently applied RF remote control and influence (RCI) devices, from which the group or individual protection of objects may be required, are distributed by its purpose into the civil, military and dual-use devices, by its application environment – into the air, water, or space devices, by the type of operation - into the fixed or mobile devices. Moreover, there are classifications by the operating frequency range, length of coverage area, weight and size, cost and other performances. The military and dual-use devices are usually controlled via the wireless RF channels with various security levels [6] that can be classified as authorized or unauthorized ones depending on the affiliation of parties to the conflict (“insiders” or “outsiders”).
A review of the world literature has shown that the most critical example of group protection against the effects of unauthorized RF channels is a swarm of aircrafts for any purpose. In addition, the most important objects of individual protection are currently considered to be the RF channels of fixed remotely controlled improvised explosive devices (RC-IEDs) in the field of counterterrorism [7, 8] and unmanned aerial vehicles (UAV) in the military or criminal area [9−11]. To efficiently solve the problem in this field, several years ago we have developed and preliminary studied a reactive radio-photonic blocker (RPB) with a response time to a detonation signal of less than 1 μs, operating in the entire frequency band of existing and future RC-IEDs from 20 MHz to 6 GHz [12−14]. In support of development of the proposed approach, this article describes the results of our research on the application of a MWP approach that blocking RF channels for remote control and navigation of modern UAVs [15−17] and other remote controlled attack instruments.
Principles of developing the electronic countermeasure systems based on the microwave-photonics approach
As it has been noted earlier, the MWP approach has already found application in such important areas of the modern electronic industry as telecommunications, where the protected items can be the access networks of fiber-wireless architecture for 5G cellular networks, as well as the interconnect lines of wireless data processing centers, and, in addition, radars, electronic countermeasures, security, computing and measurement equipment. The general principle of equipment generation, component baseline, reasons for its occurrence, history of development and the current state of MWP are discussed in [5]. The specific application examples of the MWP technology for the development of electronic defense systems are given below.
The ultra-wideband MWP technology makes it possible to develop efficient means of electronic countermeasures based on both well-known approaches [18]: spoofing (i.e., imitating interference with signal reception) and blocking (i.e., unacceptable deterioration in the reception quality) of RCI radio channels. In this case, the optimal option for a protection device is determined by the distance between the source and the object of radio-electronic influence. Namely, at the relatively large distances, when the total delay time of the probing and reflected RF beams exceeds several microseconds, the most efficient option for both group and individual protection against the unauthorized RF electronic influence is spoofing. In this case, the protection device must be located within the affected object. On the other part, when protecting against an unauthorized radio channel, the source of which is located in relative proximity to the RCI facility, the most efficient method of individual protection is to block the wireless channel using a separately located device. Typical examples of spoofing application include the group or individual protection of aircraft against its detection by a probing radio signal of a hostile radar. The typical example of blocking is individual protection against a RC-IED installed on an object or against a remotely controlled attacking UAV.
The general flowchart of the proposed MWP-based protective device (MWP-PD) is given in Fig. 1. The flowchart contains the input and output antennas, as well as the input and output RF amplifiers, between which an optoelectronic processor (OEP) unit is inserted. The main requirements for the input and output antennas and RF amplifiers include efficient operation over the entire operating RF range and a sufficient overall gain for reliable spoofing or blocking of all radio channels with due regard to the OEP losses within 30–35 dB.
Microwave-photonics device for the group and individual electronic countermeasures based on spoofing
Design Principle
The flowchart of the OEP for MWP-PD based on spoofing (MWP-PD/S) is shown in Fig. 2. According to the general design principle of a MWP unit [5], the required circuit elements are as follows: a semiconductor laser emitter (SLE), laser performing electro-optical conversion functions of the received RF signal, a photodetector (PD) used to perform the reverse optical-electric conversion to the same RF carrier, and an optical recirculation loop (ORL) located between them, through which the SLE output signal is processed in the optical range. Its mandatory elements include a standard X-type passive beam splitter (BS) with two inputs 1, 3 and two outputs 2, 4, and an optical delay line (ODL) connected between the output 4 and the input 3. The operating principle of this type of BS is that the optical signal sent to the practically isolated inputs 1 and 3 is evenly distributed between the outputs 2 and 4, and the ODL is implemented using a single-mode optical fiber with a certain length, the signal delay of which is about 4.7 μs/km. In addition, the flowchart given in Fig. 2 introduces the optional elements, including optical and RF amplifiers (OA and RFA), the purpose of which is to compensate for losses, respectively, in the optical and/or RF paths of the MWP-PD/S OEP.
It should be noted that in the case of group protection, for example, the ODL can be multitapped with unequal arm lengths [19] so as to arrange an uneven sequence of false copies transmitted by the MWP-PD/S.
Description of the Experimental Sample
To confirm the correctness and efficiency of the approach proposed and conduct confirmatory tests, an experimental sample has been designed and manufactured on the basis of flowcharts given in Fig. 1 and 2, the appearance of which is shown in Fig. 3.
The developed experimental sample has the following key parameters: weight – 3.6 kg, size – 220 × 168 × 70 mm, power consumption – no more than 20 W, operating frequency band – 0.25–18 GHz, minimum delay time – 0.4 μs, maximum number of copies – 128.
Experimental Study
The overall response of the MWP-PD/S OEP (i. e. without input and output RF amplifiers, see Fig. 1) in the 0.1-26 GHz RF band is shown in Fig. 4. As it follows from the figure, due to the well-known losses during the electro-optical and optical-electrical conversions, as well as in the ORL that are compensated in the amplification paths of the MWP-PD, the intrinsic transmission coefficient of the OEP at the average operating frequency is −37 dB, and the OEP band at the level of 3 dB is 0.25 - 18 GHz, that is, it meets the specified requirements.
The measured specifications of the signal-to-noise ratio (SNR) at the output of the experimental sample, an example of which at the carrier frequency of the input RF signal of 10 GHz with a RF impulse duration from 5 to 10 μs is shown in Fig. 5, have shown that the SNR in the 25 MHz band is more than 45 dB with the ORL disabled and more than 25 dB with the ORL activated that confirms performance of the developed MWP-PD/S.
Microwave-photonics device for the individual electronic countermeasures based on blocking
Design Principle
The flowchart of the OEP for MWP-PD based on blocking (MWP-PD/B) is shown in Fig. 6. As it follows from the figure, similar to Fig. 2, it contains the SLE and PD with an RF pre-amplifier. A processing unit in the optical range is also introduced between them [5]. In this case it is implemented on the basis of a two-armed optical fiber Mach-Zehnder interferometer (FMZI), containing two passive optical splitters 1 × 2 and two standard single-mode optical fibers (OF) of different lengths (L and L0). In the FMZI, due to the difference in OF lengths in each of the arms (that is, various delay times), the false copies of the processed optical signal are generated at the output of the MWP-PD/B. The main requirements for OEP are efficient blocking of the RF channel for remote control in the entire RF operating band.
Description of the Experimental Sample
To confirm the correctness and efficiency of the approach proposed and conduct confirmatory tests, an experimental sample of MPPD-B RFB‑1 was designed and manufactured based on the flowcharts given in Fig. 1 and 6, the appearance of which with the radio-transparent cap removed is shown in Fig. 7. As it follows from the figure, it consists of a rectangular body where the circuit elements of Fig. 1 are combined with a power supply unit and an operating mode indication of the built-in battery, and an antenna unit containing the receiving (left) and transmitting (right) Vivaldi antennas (the directional pattern width is about 60°, the gain is ≈7 dBi). To increase isolation between the transmitting and receiving RF paths, the antennas are located at an angle of 90° and separated by a metal shield. The front RFB‑1 panel contains a battery charge terminal, a battery charge level indicator, a toggle switch for indicator activation, and a power toggle switch. The operating time using the built-in battery is at least 1.5 hours. The front panel also has two optical connectors designed for quick selection of the optimal MZAI arm length L (see Fig. 6) by introducing an external optical fiber of a certain length. The external dimensions of the sample case are 330 × 300 × 80 mm, its weight is 2.8 kg, the operating frequency band is equal to 0.8–6 GHz. It should be noted that the selected operating band completely corresponds to the operating frequency range of a modern remotely controlled UAVs, for example, Autel EVO Max 4T, controlled by an operator console at switchable four frequencies 0.9; 2.4; 5.2 and 5.8 GHz. It is also located within the main part of the RC–IED receiver band activated by a 4G and 5G cell phone command.
The main RFB-1 parameters have been selected based on the following considerations. According to the well-known formula and with due regard to the antenna gains, the radio signal losses in free space at a distance of 1 km are about 90 dB at the upper operating frequency of 6 GHz. Therefore, with an RF signal output power of 1 W, the input power level should be −60 dBm. In addition, according to the datasheet of the SLE applied, the modulating RF signal level must be within the range of −5...3 dBm. Moreover, calculation of the OEP transmission coefficient in Fig. 6 with due regard to the losses in two optical splitters and sensitivity of the photodetector is about −35....−40 dB. Having considered the above data, the transmission gain of the input amplifier should be about 55 dB that is implemented on two tandem amplifiers manufactured by Microwave Systems JSC, Moscow. In addition, an RF pre-amplifier with a gain of 40 dB included in the OEP in Fig. 6 was prepared in-house, and a RFLUPA02M06GA power amplifier manufactured by RF- Lambda, USA was used as the output amplifier.
Laboratory Studies
First of all, in order to confirm the blocking effect at all carrier frequencies of an up-to-date UAV and determine the requirements for optimal delay difference in the FMZI arms, the laboratory studies of RFB-1 were performed. To prevent the influence of local CNSS and WiFi channels operating at close frequencies, the tests were carried out without any release-to-air, i.e. without antennas. Their influence was simulated by introducing appropriate coaxial attenuators into the measuring equipment. First, the overall amplitude and frequency response of the sample was measured by a vector network analyzer. The measurement result is given in Fig. 8. As it follows from the figure, the ripple turned out to be no more than 5 dB over the entire operating band.
Further tests were performed in the time domain using a real-time oscilloscope when applying a pulsed RF signal to the tested device input with filling the RF carrier, the frequency of which corresponded to each of the four channels of the Autel EVO Max 4T UAV controller. The examples of input and output test signals at a frequency of 0.9 GHz are shown in Fig. 9. As it follows from a comparison of oscillograms when directly connecting the UAV controller and through the RFB-1 under test, the relevant signal processing in the MWP-PD/B led to a chaotic distortion of their shape with various noise levels during the impulse and pause processing thus indicating the availability of a blocking effect of the transmitted signal due to the pulse shape distortion and a sharp deterioration in the signal-to-noise ratio. The similar patterns were observed at other operating frequencies of the UAV’s control channel.
As it is known, the transmission quality of digitally modulated RF signals commonly used in the up-to-date transmitting devices is routinely determined by measuring the error vector magnitude (EVM) value. This key parameter was measured during the laboratory studies using a real-time digital oscilloscope when a relevant RF signal from a vector signal generator was applied to the input of the MWP-PD/B sample. As a result, Figure 10 shows the dependency diagrams of EVM values on the time delay difference (TDD) in the FMZI arms L and L0 (see Fig. 6) for the binary phase shift keying (BPSK) format widely used in the modern transmitting RF devices at the transmission rates from 10 kbit/s up to 2 Mbit/s and all operating RF carriers of the UAV under test. The horizontal dotted lines in the diagrams show the standard EVM threshold of the RFB-1 relayed digital RF signal, equal to 17.5%.
As it follows from the diagrams, at all rates and all RF carriers, the same dependence of the transmitted signal quality on TDD is observed, namely, the acceptable transmission quality for almost identical TDD arms of the FMZI and its deterioration to the unacceptably high values when their difference exceeds a certain threshold. Thus, it is possible to draw an unambiguous conclusion based on the experimental results obtained that the proposed MWP-PD/B makes it possible to reliably and efficiently block any radio frequency signals from the UAV’s operator controller (OC) with a minimum delay difference in the FMZI arms of 270 ps that corresponds to the difference in their lengths of only 5.5 cm.
Preliminary Field Tests
The above-described laboratory results were qualitatively verified during two field tests using the UAVs Autel EVO Max 4T and DJI Mavic Pro 2 and their standard remote controllers (RC). The test results are shown in the table. As it follows, the preliminary field tests have shown the general workability of the developed design principle for blocking all RF operating channels of up-to-date UAVs. The deterioration in blocking reliability with an increase of the distance from the UAV to the RFB-1 sample is due to its insufficient output power and non-optimal nature of the Vivaldi antennas applied.
Conclusion
A new design principle for the means of group and individual electronic countermeasures against the remote effect of unauthorized radio-frequency wireless channels for various purposes is developed in this article based on the microwave-photonics approach. Its key advantages include simplicity and insensitivity to electronic interference, including intentional ones, as well as ultra-fast ultra-wideband processing of any radio-frequency signal received in an optoelectronic processor that either increases the group or individual protection area length to several kilometers, or reduces the response time for individual protection to hundreds of nanoseconds depending on its purpose, while ensuring operation over the entire operating frequency band up to several octaves. The descriptions and diagrams of two optoelectronic processors are provided for the protective devices based on the spoofing principle with the memory of up to tens of microseconds and for the protective devices based on the blocking principle with a response time of up to only a hundred of nanoseconds. Moreover, there is a description of the developed experimental samples of group and individual protection and the results of laboratory and preliminary field tests. The laboratory studies of both options of protective devices and preliminary field tests using the actual UAVs have showed its fundamental suitability for simultaneous spoofing of a remote influence channel in the case of group protection, as well as blocking of all radio channels of the up-to-date UAV remote controller, the carrier radio frequency of which is switched according to the random law within the range of 0,9–6 GHz, in the case of individual protection. Moreover, the above mention high response speed makes it possible to efficiently block radio channels operating in the carrier hopping mode.
The developed devices can also find application in any other remote-controlled equipment used in the military, industrial and security sectors. To make a final decision on the suitability, operability, technical and economic feasibility of the proposed design principle, it is necessary to optimize the circuits and designs of MWP-PD/S and MWP-PD/B and conduct full-scale field tests under the conditions as close as possible to the actual ones.
Acknowledgments
The authors are grateful for the support of the Ministry of Education and Science of the Russian Federation (grant in the form of a subsidy, the code of the topic FSFZ‑2022-0005).
AUTHORs
Mikhail Yevseevich Belkin, Doctor of Technical Sciences, Director of the Scientific and Technology Laboratory «Microwave Photonics and Electronics», MIREA, Moscow, Russia.
Kuznetsov Evgeny Viktorovich, Doctor of Technical Sciences, General Director of JSC M.F.Stelmakh Research Institute Polyus, Moscow, Russia.
M. E. Belkin
MIREA – Russian Technological University, Moscow, Russia
E. V. Kuznetsov
Polyus Scientific Research Institute JSC, Moscow, Russia
Based on the globally and rapidly developing microwave-photonics approach that has already found its application in the promising radio-electronic means of telecommunications, radars, electronic countermeasures, security, computing and measurement equipment, this article proposes a new development principle for the group and individual radio-electronic protection facilities against the remote effect of unauthorized radio channels for various purposes. Its key advantages include simplicity and insensitivity to electronic interference, including intentional ones, as well as ultra-fast ultra-wideband processing of any radio-frequency signal received in an optoelectronic processor that depending on its purpose, either increases the group or individual protection area up to several kilometers, or reduces the response time for individual protection to a hundred of nanoseconds , while ensuring operation over the entire operating frequency band. The diagrams of optoelectronic processors, description of developed radio-frequency electronic protection samples with the spoofing or blocking functions for unauthorized radio channels, and the results of laboratory and preliminary field tests are provided.
Keywords: microwave-photonics approach, unauthorized radio channel, electronic countermeasures, optoelectronic processor, spoofing, blocking
Article received: 12.01. 2024
Article accepted: 08.02. 2024
Introduction
An analysis of the modern world development of radio-electronic systems (RES) in the microwave range demonstrates that the most efficient way to solve a strategically crucial problem, namely improvement of the throughput, weight, size and cost performances, energy consumption, and reliability of the modern microwave-band RESs for civil and military purposes, is an application of microwave-photonics (MWP) methods and approaches for the signal generation and processing [1−5], namely a new interdisciplinary field developed at the intersection of radio-frequency (RF) electronics and photonics. In addition to a significant improvement in the above technical and economic indicators, implementation of this approach in the microwave RESs will also lead to an improvement in such important specifications of dual-use RESs as electromagnetic compatibility, environmental durability (including hostile exposure), and ecological friendliness.
The devices and units of microwave-photonics equipment based on the photonics and MWP technologies, including any RF signals’ processing devices, as well as the dual-use RESs with the applied MWP principles, are widely researched and developed at the universities and scientific departments of large companies in the highly developed foreign countries. However, this area being very important for the country’s defense potential, is developing very poorly in Russia, and there is already a significant lag. To find the ways of negotiation and provide the relevant conditions, in recent years, a special working group on MWP has been established under the Scientific and Technical Council of the Defense Industrial Complex. This group has developed a Program for the Development of Domestic Microwave-photonics for 2016-2025. In addition, the Advanced Research Foundation of the Defense Industrial Complex has developed a Roadmap for Photonics and Microwave-photonics. Implementation of the shaped plans is currently being performed by a number of universities, institutions of the Russian Academy of Sciences and enterprises of the radio-electronic industry.
Following this procedure, the MWP approach is considered in this article as a new principle for generating means of group and individual electronic countermeasures against the remote effect of unauthorized radio channels for various purposes. Its key advantages include simplicity and insensitivity to electronic interference, including intentional ones, as well as ultra-fast ultra-wideband processing of any radio signal received in an optoelectronic processor that either increases the group or individual protection area length to several kilometers, or reduces the response time for individual protection to a hundred of nanoseconds depending on its purpose, while ensuring operation over the entire operating frequency band up to several octaves. The diagrams of ultra-wideband optoelectronic processors with the memory from hundreds of picoseconds to tens of microseconds, description of developed RF electronic protection samples, and the results of laboratory and preliminary field tests are provided.
Modern facilities of electronic countermeasures
In general, the modern development of telecommunications, radars and other electronic means is increasingly specified by the use of equipment remotely controlled via the wireless RF channels. The currently applied RF remote control and influence (RCI) devices, from which the group or individual protection of objects may be required, are distributed by its purpose into the civil, military and dual-use devices, by its application environment – into the air, water, or space devices, by the type of operation - into the fixed or mobile devices. Moreover, there are classifications by the operating frequency range, length of coverage area, weight and size, cost and other performances. The military and dual-use devices are usually controlled via the wireless RF channels with various security levels [6] that can be classified as authorized or unauthorized ones depending on the affiliation of parties to the conflict (“insiders” or “outsiders”).
A review of the world literature has shown that the most critical example of group protection against the effects of unauthorized RF channels is a swarm of aircrafts for any purpose. In addition, the most important objects of individual protection are currently considered to be the RF channels of fixed remotely controlled improvised explosive devices (RC-IEDs) in the field of counterterrorism [7, 8] and unmanned aerial vehicles (UAV) in the military or criminal area [9−11]. To efficiently solve the problem in this field, several years ago we have developed and preliminary studied a reactive radio-photonic blocker (RPB) with a response time to a detonation signal of less than 1 μs, operating in the entire frequency band of existing and future RC-IEDs from 20 MHz to 6 GHz [12−14]. In support of development of the proposed approach, this article describes the results of our research on the application of a MWP approach that blocking RF channels for remote control and navigation of modern UAVs [15−17] and other remote controlled attack instruments.
Principles of developing the electronic countermeasure systems based on the microwave-photonics approach
As it has been noted earlier, the MWP approach has already found application in such important areas of the modern electronic industry as telecommunications, where the protected items can be the access networks of fiber-wireless architecture for 5G cellular networks, as well as the interconnect lines of wireless data processing centers, and, in addition, radars, electronic countermeasures, security, computing and measurement equipment. The general principle of equipment generation, component baseline, reasons for its occurrence, history of development and the current state of MWP are discussed in [5]. The specific application examples of the MWP technology for the development of electronic defense systems are given below.
The ultra-wideband MWP technology makes it possible to develop efficient means of electronic countermeasures based on both well-known approaches [18]: spoofing (i.e., imitating interference with signal reception) and blocking (i.e., unacceptable deterioration in the reception quality) of RCI radio channels. In this case, the optimal option for a protection device is determined by the distance between the source and the object of radio-electronic influence. Namely, at the relatively large distances, when the total delay time of the probing and reflected RF beams exceeds several microseconds, the most efficient option for both group and individual protection against the unauthorized RF electronic influence is spoofing. In this case, the protection device must be located within the affected object. On the other part, when protecting against an unauthorized radio channel, the source of which is located in relative proximity to the RCI facility, the most efficient method of individual protection is to block the wireless channel using a separately located device. Typical examples of spoofing application include the group or individual protection of aircraft against its detection by a probing radio signal of a hostile radar. The typical example of blocking is individual protection against a RC-IED installed on an object or against a remotely controlled attacking UAV.
The general flowchart of the proposed MWP-based protective device (MWP-PD) is given in Fig. 1. The flowchart contains the input and output antennas, as well as the input and output RF amplifiers, between which an optoelectronic processor (OEP) unit is inserted. The main requirements for the input and output antennas and RF amplifiers include efficient operation over the entire operating RF range and a sufficient overall gain for reliable spoofing or blocking of all radio channels with due regard to the OEP losses within 30–35 dB.
Microwave-photonics device for the group and individual electronic countermeasures based on spoofing
Design Principle
The flowchart of the OEP for MWP-PD based on spoofing (MWP-PD/S) is shown in Fig. 2. According to the general design principle of a MWP unit [5], the required circuit elements are as follows: a semiconductor laser emitter (SLE), laser performing electro-optical conversion functions of the received RF signal, a photodetector (PD) used to perform the reverse optical-electric conversion to the same RF carrier, and an optical recirculation loop (ORL) located between them, through which the SLE output signal is processed in the optical range. Its mandatory elements include a standard X-type passive beam splitter (BS) with two inputs 1, 3 and two outputs 2, 4, and an optical delay line (ODL) connected between the output 4 and the input 3. The operating principle of this type of BS is that the optical signal sent to the practically isolated inputs 1 and 3 is evenly distributed between the outputs 2 and 4, and the ODL is implemented using a single-mode optical fiber with a certain length, the signal delay of which is about 4.7 μs/km. In addition, the flowchart given in Fig. 2 introduces the optional elements, including optical and RF amplifiers (OA and RFA), the purpose of which is to compensate for losses, respectively, in the optical and/or RF paths of the MWP-PD/S OEP.
It should be noted that in the case of group protection, for example, the ODL can be multitapped with unequal arm lengths [19] so as to arrange an uneven sequence of false copies transmitted by the MWP-PD/S.
Description of the Experimental Sample
To confirm the correctness and efficiency of the approach proposed and conduct confirmatory tests, an experimental sample has been designed and manufactured on the basis of flowcharts given in Fig. 1 and 2, the appearance of which is shown in Fig. 3.
The developed experimental sample has the following key parameters: weight – 3.6 kg, size – 220 × 168 × 70 mm, power consumption – no more than 20 W, operating frequency band – 0.25–18 GHz, minimum delay time – 0.4 μs, maximum number of copies – 128.
Experimental Study
The overall response of the MWP-PD/S OEP (i. e. without input and output RF amplifiers, see Fig. 1) in the 0.1-26 GHz RF band is shown in Fig. 4. As it follows from the figure, due to the well-known losses during the electro-optical and optical-electrical conversions, as well as in the ORL that are compensated in the amplification paths of the MWP-PD, the intrinsic transmission coefficient of the OEP at the average operating frequency is −37 dB, and the OEP band at the level of 3 dB is 0.25 - 18 GHz, that is, it meets the specified requirements.
The measured specifications of the signal-to-noise ratio (SNR) at the output of the experimental sample, an example of which at the carrier frequency of the input RF signal of 10 GHz with a RF impulse duration from 5 to 10 μs is shown in Fig. 5, have shown that the SNR in the 25 MHz band is more than 45 dB with the ORL disabled and more than 25 dB with the ORL activated that confirms performance of the developed MWP-PD/S.
Microwave-photonics device for the individual electronic countermeasures based on blocking
Design Principle
The flowchart of the OEP for MWP-PD based on blocking (MWP-PD/B) is shown in Fig. 6. As it follows from the figure, similar to Fig. 2, it contains the SLE and PD with an RF pre-amplifier. A processing unit in the optical range is also introduced between them [5]. In this case it is implemented on the basis of a two-armed optical fiber Mach-Zehnder interferometer (FMZI), containing two passive optical splitters 1 × 2 and two standard single-mode optical fibers (OF) of different lengths (L and L0). In the FMZI, due to the difference in OF lengths in each of the arms (that is, various delay times), the false copies of the processed optical signal are generated at the output of the MWP-PD/B. The main requirements for OEP are efficient blocking of the RF channel for remote control in the entire RF operating band.
Description of the Experimental Sample
To confirm the correctness and efficiency of the approach proposed and conduct confirmatory tests, an experimental sample of MPPD-B RFB‑1 was designed and manufactured based on the flowcharts given in Fig. 1 and 6, the appearance of which with the radio-transparent cap removed is shown in Fig. 7. As it follows from the figure, it consists of a rectangular body where the circuit elements of Fig. 1 are combined with a power supply unit and an operating mode indication of the built-in battery, and an antenna unit containing the receiving (left) and transmitting (right) Vivaldi antennas (the directional pattern width is about 60°, the gain is ≈7 dBi). To increase isolation between the transmitting and receiving RF paths, the antennas are located at an angle of 90° and separated by a metal shield. The front RFB‑1 panel contains a battery charge terminal, a battery charge level indicator, a toggle switch for indicator activation, and a power toggle switch. The operating time using the built-in battery is at least 1.5 hours. The front panel also has two optical connectors designed for quick selection of the optimal MZAI arm length L (see Fig. 6) by introducing an external optical fiber of a certain length. The external dimensions of the sample case are 330 × 300 × 80 mm, its weight is 2.8 kg, the operating frequency band is equal to 0.8–6 GHz. It should be noted that the selected operating band completely corresponds to the operating frequency range of a modern remotely controlled UAVs, for example, Autel EVO Max 4T, controlled by an operator console at switchable four frequencies 0.9; 2.4; 5.2 and 5.8 GHz. It is also located within the main part of the RC–IED receiver band activated by a 4G and 5G cell phone command.
The main RFB-1 parameters have been selected based on the following considerations. According to the well-known formula and with due regard to the antenna gains, the radio signal losses in free space at a distance of 1 km are about 90 dB at the upper operating frequency of 6 GHz. Therefore, with an RF signal output power of 1 W, the input power level should be −60 dBm. In addition, according to the datasheet of the SLE applied, the modulating RF signal level must be within the range of −5...3 dBm. Moreover, calculation of the OEP transmission coefficient in Fig. 6 with due regard to the losses in two optical splitters and sensitivity of the photodetector is about −35....−40 dB. Having considered the above data, the transmission gain of the input amplifier should be about 55 dB that is implemented on two tandem amplifiers manufactured by Microwave Systems JSC, Moscow. In addition, an RF pre-amplifier with a gain of 40 dB included in the OEP in Fig. 6 was prepared in-house, and a RFLUPA02M06GA power amplifier manufactured by RF- Lambda, USA was used as the output amplifier.
Laboratory Studies
First of all, in order to confirm the blocking effect at all carrier frequencies of an up-to-date UAV and determine the requirements for optimal delay difference in the FMZI arms, the laboratory studies of RFB-1 were performed. To prevent the influence of local CNSS and WiFi channels operating at close frequencies, the tests were carried out without any release-to-air, i.e. without antennas. Their influence was simulated by introducing appropriate coaxial attenuators into the measuring equipment. First, the overall amplitude and frequency response of the sample was measured by a vector network analyzer. The measurement result is given in Fig. 8. As it follows from the figure, the ripple turned out to be no more than 5 dB over the entire operating band.
Further tests were performed in the time domain using a real-time oscilloscope when applying a pulsed RF signal to the tested device input with filling the RF carrier, the frequency of which corresponded to each of the four channels of the Autel EVO Max 4T UAV controller. The examples of input and output test signals at a frequency of 0.9 GHz are shown in Fig. 9. As it follows from a comparison of oscillograms when directly connecting the UAV controller and through the RFB-1 under test, the relevant signal processing in the MWP-PD/B led to a chaotic distortion of their shape with various noise levels during the impulse and pause processing thus indicating the availability of a blocking effect of the transmitted signal due to the pulse shape distortion and a sharp deterioration in the signal-to-noise ratio. The similar patterns were observed at other operating frequencies of the UAV’s control channel.
As it is known, the transmission quality of digitally modulated RF signals commonly used in the up-to-date transmitting devices is routinely determined by measuring the error vector magnitude (EVM) value. This key parameter was measured during the laboratory studies using a real-time digital oscilloscope when a relevant RF signal from a vector signal generator was applied to the input of the MWP-PD/B sample. As a result, Figure 10 shows the dependency diagrams of EVM values on the time delay difference (TDD) in the FMZI arms L and L0 (see Fig. 6) for the binary phase shift keying (BPSK) format widely used in the modern transmitting RF devices at the transmission rates from 10 kbit/s up to 2 Mbit/s and all operating RF carriers of the UAV under test. The horizontal dotted lines in the diagrams show the standard EVM threshold of the RFB-1 relayed digital RF signal, equal to 17.5%.
As it follows from the diagrams, at all rates and all RF carriers, the same dependence of the transmitted signal quality on TDD is observed, namely, the acceptable transmission quality for almost identical TDD arms of the FMZI and its deterioration to the unacceptably high values when their difference exceeds a certain threshold. Thus, it is possible to draw an unambiguous conclusion based on the experimental results obtained that the proposed MWP-PD/B makes it possible to reliably and efficiently block any radio frequency signals from the UAV’s operator controller (OC) with a minimum delay difference in the FMZI arms of 270 ps that corresponds to the difference in their lengths of only 5.5 cm.
Preliminary Field Tests
The above-described laboratory results were qualitatively verified during two field tests using the UAVs Autel EVO Max 4T and DJI Mavic Pro 2 and their standard remote controllers (RC). The test results are shown in the table. As it follows, the preliminary field tests have shown the general workability of the developed design principle for blocking all RF operating channels of up-to-date UAVs. The deterioration in blocking reliability with an increase of the distance from the UAV to the RFB-1 sample is due to its insufficient output power and non-optimal nature of the Vivaldi antennas applied.
Conclusion
A new design principle for the means of group and individual electronic countermeasures against the remote effect of unauthorized radio-frequency wireless channels for various purposes is developed in this article based on the microwave-photonics approach. Its key advantages include simplicity and insensitivity to electronic interference, including intentional ones, as well as ultra-fast ultra-wideband processing of any radio-frequency signal received in an optoelectronic processor that either increases the group or individual protection area length to several kilometers, or reduces the response time for individual protection to hundreds of nanoseconds depending on its purpose, while ensuring operation over the entire operating frequency band up to several octaves. The descriptions and diagrams of two optoelectronic processors are provided for the protective devices based on the spoofing principle with the memory of up to tens of microseconds and for the protective devices based on the blocking principle with a response time of up to only a hundred of nanoseconds. Moreover, there is a description of the developed experimental samples of group and individual protection and the results of laboratory and preliminary field tests. The laboratory studies of both options of protective devices and preliminary field tests using the actual UAVs have showed its fundamental suitability for simultaneous spoofing of a remote influence channel in the case of group protection, as well as blocking of all radio channels of the up-to-date UAV remote controller, the carrier radio frequency of which is switched according to the random law within the range of 0,9–6 GHz, in the case of individual protection. Moreover, the above mention high response speed makes it possible to efficiently block radio channels operating in the carrier hopping mode.
The developed devices can also find application in any other remote-controlled equipment used in the military, industrial and security sectors. To make a final decision on the suitability, operability, technical and economic feasibility of the proposed design principle, it is necessary to optimize the circuits and designs of MWP-PD/S and MWP-PD/B and conduct full-scale field tests under the conditions as close as possible to the actual ones.
Acknowledgments
The authors are grateful for the support of the Ministry of Education and Science of the Russian Federation (grant in the form of a subsidy, the code of the topic FSFZ‑2022-0005).
AUTHORs
Mikhail Yevseevich Belkin, Doctor of Technical Sciences, Director of the Scientific and Technology Laboratory «Microwave Photonics and Electronics», MIREA, Moscow, Russia.
Kuznetsov Evgeny Viktorovich, Doctor of Technical Sciences, General Director of JSC M.F.Stelmakh Research Institute Polyus, Moscow, Russia.
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