Electronic Order of Battle Records of Unfriendly Radar Systems using Certain Advanced Techniques as Electronic Support Measures

Transcription

1 Electronic Order of Battle Records of Unfriendly Radar Systems using Certain Advanced Techniques as Electronic Support Measures 1 Ch. Raja, 2 D. Anand and 3 E.G. Rajan 1 Associate Professor, Electronics & Communication Dept. Associate Professor, ECE Department, MGIT, Hyderabad, India rajachaluvadi@yahoo.com 2 Scientific officer-d, Tata Institute of Fundamental Research Balloon facility, ECIL post, Hyderabad , India anandd24@yahoo.co.in 3 Founder President, Pentagram Research Centre Pvt. Ltd. #201, Venkat Homes, MIGH-59, Mehdipatnam, Hyderabad, India rajaneg@yahoo.co.in Abstract Radar is the key sensor of any modern weapon system. Its capability to function in all weather environments at long ranges is unmatched with any other available sensor. Land based radars are used for variety of tasks ranging upward in size and complexity from man portable radars for detection of vehicle and personnel to ballistic missile tracking phased arrays. Increased reliance on radars, communication systems, speed of missile and weapon system and high speed detection and tracking has increased the importance of Electronic Warfare (EW). Electronic warfare is subdivided into Electronic Support Measure (ESM), Electronic Counter Measure (ECM) and Electronic Counter Counter Measure (ECCM) systems. This paper deals with the ESM which is the division of electronic warfare involving action taken to search for intercept, identify and locate sources of radiated electromagnetic energy from radar for the purpose of threat recognition. Introduction Electronic Support Systems fingerprints the electromagnetic sources with the help of sensitive receivers and direction finding (DF) systems. This provides information in the timely fashion that are readily usable by the activities in support. The prime consumers of ESM information are the operations personnel engaged in other EW activities that is ECM and ECCM. ESM provides essential to the success of operations in the air combat environment. ESM includes signal interception and detection, measurement of signal parameters, signal identification and threat signal evaluation. Signal parameters include frequency, emission type, PRF, Pulse-width, antenna scan and characteristics, polarization and angle of arrival. Special mission flights are generally taken to intercept EM radiations for ON line and OFF line signal analysis. These recorded signals are processed for estimating radar signal parameters (offline radar signal processing) to prepare Electronic Order of Battle (EOB). This paper discusses the state-of-the-art Electronic Support Measures undertaken by almost all developed countries. Electronic Support Measures (ESM) The prime objectives of ESM are (i) To acquire technical information about various radars deployed in the enemy territory, (ii) To monitor enemy radar stations round the clock and supply information to defense forces for strategic planning. The objects that are incidental to the main objectives are (i) To undertake special mission flights and special operations for intercepting Electro Magnetic (EM) radiations for ON line and OFF line signal analysis, (ii) To process recorded signals for estimating signal parameters(off Line Radar Signal Processing), (iii) To prepare Electronic Order of Battle (EOB) records of various enemy radar regiments for measuring war time, (iv) T o have joint action with Air Force, Army and Navy in the process of acquiring technical information about radars, and (v) To support Defense Laboratories by extending first hand technical information about special equipment. This can be achieved by either air surveillance or monitoring station situated at suitable geographic heights. Special flights are arranged to operate along the border in order to intercept signals from hostile radars. Tuners and wide band receivers are used for this purpose. Intercepted signals are recorded on magnetic media for OFF line analysis. Detected signals with down translated IF are stored by high speed recorders. Post detected signals are stored as stretched pulses by low speed recorders. Signal bearing is determined for each emitter from the aircraft itself using direction finding systems like rotating dipole or Bellini Tosi Antenna. Monitoring stations situated at suitable geographic height are ideal sources of acquiring radar signals. Round the clock watch is generally carried out. Very useful information about ON time, OFF time, Mean Time Between Failure (MTBF), types of ECMs and ECCMs incorporated in radar under watch could be obtained. Tuners and wide band receivers are used for the intercept. [Page No. 99]

2 5 th IEEE International Conference on Advanced Computing & Communication Technologies [ICACCT-2011] ISBN Radar Intercept System and Recording A typical airborne intercept system is shown in figure 1. bearings are taken and the plot drawn to estimate the position of the emitter. Three bearings would generally yield a triangle as shown in figure 4 and in such a case the centroid of the triangle is considered to be the estimate position of the emitter. Figure 1: Airborne intercept system. A typical ground based intercept system is shown in figure 2. Figure 2: Ground based intercept system. Recorded signals are sent to BASE station for further analysis. A traditional technique which is used to fix the position of an emitter is shown in figure 3. (a) (b) Figure 3: Position fixing of an emitter using direction finding (a) Block diagram of receiver and display (b) Typical mission flight Signal bearings are obtained at various positions of a surveillance aircraft and the emitter position is estimated at the meeting point of the signal bearings. In practice, three signal Figure 4: Position fixing of an emitter Signal Intelligence (SIGINT) Standard Radar Frequency Letter-Band Nomenclature Table 1 shows the standard radar frequency bands and their nomenclature. RAVEN 1 and RAVEN 2 operators tune the frequencies band by band as per supervisor s instructions and record the pulse stretched signals. Note that the wide band receivers of all the bands are kept on throughout the mission flight and the pulse stretched signals recorded continuously. Table 1: Band of radar frequencies Band Frequency Specific Designation Range Frequency allocation Bands HF 3 30 MHz VHF MHz MHz MHz UHF MHz MHz MHz L MHz MHz S MHz MHz MHz C MHz MHz X MHz MHz Ku GHz GHz GHz K GHz GHz Ka GHz GHz mm GHz [Page No. 100]

3 Electronic Order of Battle Records of Unfriendly Radar Systems using Certain Advanced Techniques as Electronic Support Measures Recording of Intercepted Signals on a Magnetic Tape Figure 5 shows an ideal pulse train output of the receiver. But the actual pulse train recorded on the tape would not be ideal. In fact, the pulse is stretched and low pass filtered. Because of the pulse stretch, the bandwidth would be considerably reduced. The recording format of various bands of intercepted and pulse stretched radar signals on a one inch 14 track tape is shown in figure 7. Figure 5: Ideal shape of a pulse train. A 1400 feet long tape of width of one inch having 14 tracks is used for recording purposes. Recording is done using a compact airborne recording system. Band 1, 2, 3, 4 and 6 receiver outputs are recorded in the tracks 1, 2, 3, 4 and 5 respectively. The tuner output which covers all the five bands is recorded in the track 6. RAVEN #1 operator comments are recorded in track 7. Band 7, 8 and 9 receiver outputs are recorded in the tracks 8, 9 and 10 respectively. The time code signal with 8421 BCD modulated on 1 KHz carrier is recorded in track 11. A 100 KHz reference signal is recorded in the 12 th track. RAVEN #2 tuner output which covers all the three bands is recorded in the track 13. RAVEN #2 operator comments are recorded in track 14. A typical ground based 14 channel recording system is shown in figure 6. Figure 7: Recording format on a multi track tape Signal Intelligence From Low Speed Tape (Tape Speed: 3-3/4 and 7-1/2 Inches Per Second) Pulse Repetition Frequency (PRF) The recorded tape is run at the appropriate speed and the tuner signal record is fed to the first vertical input of a dual beam oscilloscope. The corresponding wide band signal output is fed to the second vertical input of the scope. Internal signal is used to stabilize both the waveforms. When tuner signal is stabilized the corresponding wide band signal will also be locked with it. The corresponding ramp output of the oscilloscope is fed to the input of a frequency counter. The frequency counter shows the PRF of the tuned signal. Scan Type and Scan Time Run the tape at the appropriate speed. Lock the tuner signal with the corresponding wide band signal. Use a stop watch. Put on the watch when the wide band signal strength is maximum and put off the watch when the next immediate maximally strong signal is heard. Note the time duration. Repeat this many times. Take the average of these trials. This is the scan period of the radar. Similar procedure can be used to find the vertical scan of the height finding radar. The beam is intercepted four times, twice for each nod. The period between two successive nods is the scan period of height finder. Refer to figure 8 which is self explanatory. First maximum Second maximum Figure 6: One inch 14-channel Instrumentation recorder 900_at_LOIRP.jpg (Courtesy) reproducer system used for signal analysis Figure 8: Successivee maxima in one nod Time Code Sinusoidal oscillations at a predetermined constant frequency are rectangularly amplitude modulated according to a binary [Page No. 101]

4 5 th IEEE International Conference on Advanced Computing & Communication Technologies [ICACCT-2011] ISBN code (IRIG Standard Time Code). The modulated signal is recorded on the magnetic tape. This code provides the actual time information like time of intercept. Figure 9 shows a typical time code generator / reader used for this purpose. Figure 10 shows the IRIG serial time code format. Signal Intelligence From High Speed Tape (Tape Speed: 60 and 120 Inches Per Second) Pulse Width Tektronix 565 dual beam dual trace 10 MHz oscilloscope is traditionally used to measure pulse width of a radar signal recorded in the high speed tape. Generally the tape is run at 60 or 120 inches per second speed during recording and reproducing. Figure 12 shows the front panel view of the Tektronix 565 oscilloscope. Figure 9: Front end panel of a TCG Figure 12: Tektronix 565 oscilloscope Figure 10: IRIG serial time code format The high speed recorder output is fed to one of the channels of the oscilloscope. The time base vernier control knob is kept at calibrated position. Internal trigger is used to display a single pulse. The measurement technique is shown in figure 13. Reference signal A reference signal of 100 KHz is recorded along with other signals in track #12. This is done with the idea of running the tape with the same speed at which the recording was done, during off-line signal analysis. The recorded reference signal of 100 KHz is fed to the digital phase lock loop circuit of the recorder / reproducer used for off-line signal analysis and the speed of the take up reel motor is controlled in order to match with the speed with which the tape was run during recording. Figure 11 shows a part of the DPLL circuit of the recorder / reproducer system. Figure 13: Pulse width measurement Figure 11: DPLL circuit of the recorder / reproducer system Pulse Jitter or Stagger Ratio Staggering of PRIs is used to avoid blind speed effect in moving target indicator (MTI) radars. A suitable delay line is used to delay the PRI and delayed signal is added to the original signal to produce staggered variations. Some times two different PRIs are added to form staggered waveforms. Stagger is the delay time between two leading edges and it is visualized and measured in an oscilloscope as shown in figure 14. [Page No. 102]

5 Electronic Order of Battle Records of Unfriendly Radar Systems using Certain Advanced Techniques as Electronic Support Measures Figure 14: Staggering of pulses Intra-Pulse Modulation Parameters such as frequency profile within pulse, amplitude profile within pulse, phase profile within pulse, rise time, fall time, pulse width, amplitude variations over time and frequency and signal modulations are determined. In modern radar systems FM chirp, Barker codes, pseudorandom codes and poly-phase codes are used as an ECCM measure. A pulse to pulse frequency agile radar operates with a set of discrete RF switched in a pseudorandom fashion. To extract intelligence from intra-pulse modulation, lock wide band receiver signal with tuner signal. Trigger wide band receiver signal at its leading edge in the oscilloscope. Feed the signal to the RF section of the spectrum analyzer and tune it to obtain the spectrum of the signal. From the spectrum, one can verify intra-pulse FM, chirp and Barker codes. For example, AN/TPS-43 is a light weight transportable radar designed for use in a wide variety of tactical environments. The radar works in 16 discrete frequencies ranging from 2800 MHz to 3000 MHz. It radiates six beams stacked one over the other to form a cosec 2 radiation pattern. Each beam is switched with one of the 16 discrete frequencies following a pseudo random bit sequence. The system provides 3-D cover to 447 km on a fighter or fighter-bomber aircraft and measures heights over the full range by signal amplitude comparisons in six channels. Clutter rejection and electronic counter-countermeasures features are incorporated in the design. Figure 15 shows the spectrum of all 16 discrete frequencies. Signal Intelligence From Operator s Comments (RAVEN #1 and RAVEN #2) RAVEN #1 operator s comments are recorded in track #7 and RAVEN #2 operator s comments are recorded in track # 14 of the tape. The operators provide information about the RF of the radar with the help of tuner and Angle Of Arrival (AOA) of the signal. They also provide very valuable information about the signal strength, locking of the height finding system with early warning system, locking of the fire control radar with a target and so on. Signal Intelligence From Collateral Sources Apart from the techniques outlined in earlier sub sections, one can collect intelligence from literature and contacts. The literatures available are Janes Weapon Systems, ECM and ECCM Journals, text books, research articles, conference proceedings etc. Foreign intelligence agencies, national intelligence agencies, professionals and informers are also the sources of information through contacts. From the analysis report, it is usual practice to match a set of parameters with existing literature and estimate the presence and type of radar at a particular site. With these details, most of the intelligence is collected about various radar systems in the enemy territory. Now, one goes in for creating the Order Of Battle (EOB) record as explained below. Electronic Order of Battle Generating an Electronic Order of Battle (EOB) requires identifying SIGINT emitters in an area of interest, determining their geographic location or range of mobility, characterizing their signals, and, where ever possible, determining their role in the broader organizational order of battle. EOB covers both Communication Intelligence (COMINT) and Electronic Intelligence (ELINT), The National Defense Intelligence Agency maintains an EOB by location. Army, Nay and Air Force Intelligence Agencies involve in SIGINT and COMINT activities and the Joint Intelligence Committee (JIC) of the government consolidates the EOB reports of all such agencies. Modern ESM Network Centric Warfare (NCW) Unlike traditional ESM and warfare activities, the Network Centric Warfare (NCW) involves various domains in spite of the fact that domains do clash with one another. Figure 15: Spectrum of 16 frequencies of TPS 43 One may observe that the received signal by the tuner is not continuous where as the one received by the wide band receiver would present a scenario which is shown in figure 15. Hence, one should take care in measuring pulse width information from the recorded signal. The radio frequency of this radar is phase code modulated inside the pulse. Appropriate techniques are used to decode. [Page No. 103]

6 5 th IEEE International Conference on Advanced Computing & Communication Technologies [ICACCT-2011] ISBN Radar, Sonar and Navigation, [7] Rajan E. G., Symbolic Computing-Signal and Image Processing, Anshan Publications, United Kingdom, attee.html Figure 16: Domain conflicts in NCW. Figure 16 depicts one such possible domain conflicts scenario which clearly indicates that the nations which have spectrum superiority and technical superiority blended with national integrity would always win the future battles, Conclusions In this paper, we have just outlined a broad based and sensitive concept of Electronic Support Measures and their significance in the light of security. The material covered in this paper is due to certain basic research carried out by the first two authors and a vast practical experience of the third author. Acknowledgements The authors express their sincere thanks to the administration of Pentagram Research Centre Pvt Limited, Hyderabad, India for the technical and logistic support given to them in carrying out advanced research in allied fields. References [1] August Golden Jr., Radar Electronic Warfare AIAA Education series [2] Fred E. Nathanson, Radar Design Principle, Second Edition. [3] Dr. V K Atre, Electronic Warfare- A perspective, IETE Technical review Vol 17, No6, Nov-Dec [4] G Nagendra Rao, CVS Sastry, N Diwakar, Trends in Electronic Warfare, IETE Technical review Vol20, N02, and March-April [5] T.D. Bhatt, E.G. Rajan, P.V.D. Somasekhar Rao, Design of frequency-coded waveforms for target detection, IET Radar, Sonar and Navigation, March 2008, Vol. 2, No. 5, pp [6] T.D. Bhatt, E.G. Rajan, P.V.D. Somasekhar Rao, Design of High-Resolution Radar Waveforms for Multi-radar and Dense Target Environments, IET [Page No. 104]