Stealth Technology: The Quest for Reduced RCS

Exercise 2-3 Stealth Technology: The Quest for Reduced RCS EXERCISE OBJECTIVE To introduce the basic material and design principles associated with radar stealth technology. To use these principles to substantially reduce the number and amplitude of spike echoes in the RCS pattern of the Radar Jamming Pod Trainer. DISCUSSION Introduction to Stealth Design When applied to weapons, aircraft, ships, submarines, and ground installations, stealth technology encompasses the material and design principles used to make objects stealthy. A stealth object does not become invisible, it blends into its background. Stealth provides a platform with delayed detection, identification, and target acquisition by hostile forces. It effectively enhances a platform s first strike capability and its battlefield survivability. When designing a stealth platform, significant efforts are made toward signature control. A signature is a visual, acoustic, radar, infrared (IR) or other type of emission that can be used by the enemy to identify and locate an object or platform. The detection ranges for each of a stealth object s signatures must be balanced as closely as possible. Therefore, a platform that is undetectable by radar at a range of 10 km, yet that can be detected through its IR signature at a range of 20 km is not a tactically useful stealth platform. In stealth design, the most important observable aspect to be reduced is a platform s radar signature. Radar is the most prevalent sensor, particularly for operation at long ranges under a wide variety of environmental conditions. Though, as stated, the reduction of all observable aspects of a platform is important in stealth, the present discussion will focus on radar related stealth techniques. Stealth provides a platform with a shorter detection range by enemy radar, and a shorter burn-through range when in a jammed environment. A platform s radar signature strength is directly proportional to the platform's radar cross section (RCS). To reduce the RCS of a platform to background levels, as is required by stealth, implies reducing it to the RCS level of its environment. That is, in the case of an aircraft, to the returned radar signal power level of birds and insects. This will often require a 1000-fold (30-dB) reduction in the RCS of the platform! 2-33

Stealth levels of reduction are accomplished by scattering, absorbing, and/or canceling the radar energy incident on the platform. Of the possible techniques that can be used to reduce the radar echo of an object, the following are those that have been of the greatest tactical use: 1. Hard body shaping, that is, selecting the shape of a platform with the intention of controlling the direction and amplitude of reflected incident radar energy. 2. Use of radar absorbent, reflective, and transparent materials. These are materials used to reduce the radar return from difficult to conceal areas on a platform. Stealth platform design involves many phases of computer modeling, as well as judicious considerations about the placement of engines, electronic systems, and weapons. Incorporating stealth technology principles into a platform often gives the platform an untraditional appearance. Testimony to this statement are the most widely known examples of stealth platforms: The United States F-117 and F-22 fighter aircraft as well as the B-2 bomber aircraft, which are illustrated in Figure 2-10. Figure 2-10. The F-117 and F-22 stealth fighters, and the B-2 stealth bomber. Other examples of stealth technology exist that are perhaps even more interesting because of the huge RCS reductions involved. These objects are stealth ships such as the Swedish Navy s Visby Class Corvette and the US Navy s Sea Shadow. 2-34

Threat Sectors and Hard Body Shaping Geometric shaping is the most useful technique used to reduce the RCS of an object s surface. The objective of shaping is to orient platform surfaces so that they reflect (scatter) incident radar signals in directions away from threat sectors (see Figure 2-11). Figure 2-11. Threat sectors of a fighter aircraft. A threat sector is the viewing region from which a platform has a very high probability of being detected by a radar. Every type of platform has threat sectors. Depending on their specific missions, the threat sectors of one platform are located in different viewing regions than the threat sectors of another platform. For example, consider the types of missions performed by military interceptor aircraft. These platforms fly toward enemy radar systems that can either be airborne, ground, or sea based. This implies that the aircraft have a primary threat sector located in their front viewing region. The radar will not be positioned to view the aircraft from its top or bottom, and there is only a low probability of viewing the aircraft from its sides. The aircraft s rear viewing region is a lesser threat sector because a tail attack is more difficult. Consequently, a stealth aircraft must be designed to reflect all incident radar energy toward its top and bottom viewing regions, i.e., regions away from the aircraft s threat sectors. Therefore, the selection of a suitable overall shape for a platform is the first and primary step in stealth design. The geometric shape of a stealth platform s body lines should be oriented in as few directions as possible, and these orientation directions must be swept away from the platform s threat sectors. The geometric shaping used in stealth design produces higher echo return signals over discrete aspect angles in order to gain lower echo signals over the critical threat sectors, as shown in Figure 2-12. This occurs because the maximum reflection from a planar surface (analogous to a platform s surface) occurs when the radar signal is perpendicularly incident to the reflecting surface. This reflection is highly directive, and is known as a specular flash, or a spike echo. A target that has many specular flashes that occur at various aspect angles is easily detectable by a radar. Thus, geometric shaping 2-35

used in stealth design, reorients the platform s surfaces in order to move the specular flashes away from the threat sectors. Figure 2-12. Different geometric platform shapes with their respective RCS patterns. After applying the above principles there can, nonetheless, be a significant level of radar radiation that is reflected back toward the threat sectors. This is the reason that special radar absorbent, reflective, and transparent materials must be used to attenuate, to redirect, or to make insignificant the stealth platform s echo as seen from its threat sectors. Radar Absorbent Materials During World War II, one of the first applications of radar absorbers was for the purpose of achieving radar camouflage of submarine snorkels and periscopes. Since then, due to military secrecy, the uses in stealth technology of absorbent materials have been quietly developed. Absorbent materials are used to complement shaping, or when shaping is not a design option. Radar absorbent materials (RAMs) may take several forms and can be used in varied ways. RAM can be classified as either specular or nonspecular, and as narrowband RAM or wideband RAM. Specular absorbers are intended to reduce specular reflections from metallic surfaces. Necessary discontinuities in the body shape of a platform may be difficult to conceal and may form a corner reflector for incident radar energy. An example of such a discontinuity is the air intakes of jet engines on a fighter aircraft. The engine face can be concealed with a serpentine inlet duct. By lining the walls with specular absorbent material, the radar echo can be significantly reduced because of the multiple bounce reflections that any incident radar energy has upon entering the inlet duct. Nonspecular absorbers are intended primarily for suppression of surface currents caused by specular reflections. Stealth technology devotes much attention to reducing the surface wave effect. This is when surface currents formed by radar energy incident on a surface, give rise to reflections when surface discontinuities, such as gaps, cracks, drain holes, bolt heads, or surface edges are encountered. 2-36

Nonspecular absorbers act as a waveguide (conduit) for surface currents, attenuating them as they propagate through the absorber and before they encounter a surface discontinuity. Materials capable of absorbing electromagnetic (EM) radiation work on varying principles, however, their end effect is the dissipation of incident EM energy into heat. Current absorbing materials used on stealth platforms are capable of reducing the radar echo power of a surface by a factor of 10 to 100 (10 to 20 db). Remember, however, that a 1000-fold (30-dB) reduction in the RCS of a platform is often required to make it completely stealthy. This is the reason that hard body shaping is the primary approach to stealth design, and that RAMs are not used alone but in conjunction with hard body shaping. Countermeasures to Stealth Various counter-stealth concepts have been studied. However to date, an effective system capable of detecting and tracking a stealth platform, as well as directing and guiding a weapon toward the platform does not exist. Table 2-4 lists various counterstealth concepts that have been proposed and considered. COUNTER-STEALTH CONCEPTS Balloon Radar Radar Shadow Detection Magnetic Disturbance Bistatic Radar Space-Based Radar Impulse Radar Over-the-Horizon Radar Ultra Wideband Radar Table 2-4. Counter-stealth concepts. No matter what the potential success of the application of these concepts, stealth will always give a wartime advantage to those who use it. Procedure Summary During the first two parts of this exercise, the tracking radar system is set up and calibrated. The Radar Jamming Pod Trainer positioning stand is correctly positioned with respect to the radar antenna. The Radar Jamming Pod Trainer is installed on the positioning stand. The height of the Radar Jamming Pod Trainer is adjusted so that it is approximately at the same level as the radar antenna. During the third part of the exercise, you will rotate the Radar Jamming Pod Trainer and measure the amplitude and angular position of the spike echoes produced by surfaces of high reflectivity on its body. You will then plot on a polar graph the RCS pattern of the Radar Jamming Pod Trainer. 2-37

In the fourth part of the exercise, you will apply stealth technology to the Radar Jamming Pod Trainer by modifying its shape and using radar absorbent material. For each hard body shape, you will rotate the Radar Jamming Pod Trainer and measure the amplitude and angular position of the spike echoes produced by surfaces of high reflectivity on its body. You will then plot the RCS pattern associated with each body shape on a polar graph. In the fifth part of the exercise, the effectiveness of the hard body shapes and radar absorbent material used to make the Radar Jamming Pod Trainer "as stealthy as possible" will be analyzed. This will highlight the essential points of stealth design. PROCEDURE Setting Up the Tracking Radar G 1. Before beginning this exercise, the main elements of the Tracking Radar Training System (i.e., the antenna and its pedestal, the target table, the RTM and its power supply, the training modules, and the host computer) must be set up as shown in Appendix A. On the Radar Transmitter, make sure that the RF POWER switch is set to the STANDBY position. On the Antenna Controller, make sure that the MANual ANTENNA ROTATION MODE push button is depressed and the SPEED control is set to the 0 position. Turn on all modules and make sure the POWER ON LED's are lit. G 2. Turn on the host computer, start the LVRTS software, select Tracking Radar, and click OK. This begins a new session with all settings set to their default values and with all faults deactivated. If the software is already running, click Exit in the File menu and then restart the LVRTS software to begin a new session. G 3. Connect the modules as shown on the Tracking Radar tab of the LVRTS software. For details of connections to the Reconfigurable Training Module, refer to the RTM Connections tab of the software. Note: Make the connections to the Analog/Digital Output Interface (plug-in module 9632) only if you wish to connect a conventional radar PPI display to the system or obtain an O-scope display on a conventional oscilloscope. Note: The SYNC. TRIGGER INPUT of the Dual-Channel Sampler and the PULSE GENERATOR TRIGGER INPUT of the Radar Transmitter must be connected directly to OUTPUT B of the Radar Synchronizer without passing through BNC T-connectors. Connect the hand control to a USB port of the host computer. 2-38

G 4. Make the following settings: On the Radar Transmitter RF OSCILLATOR FREQUENCY....... CAL. PULSE GENERATOR PULSE WIDTH... 1 ns On the Radar Synchronizer / Antenna Controller PRF............................ 288 Hz PRF MODE..................... SINGLE ANTENNA ROTATION MODE... PRF LOCK. DISPLAY MODE............... POSITION On the Dual-Channel Sampler RANGE SPAN.................... 3.6 m In the LVRTS software System Settings: Log./Lin. Mode.................... Lin. Gain...................... as required Radar Display Settings: Range......................... 3.6 m G 5. Connect the cable of the target table to the connector located on the rear panel of the Target Controller. Make sure that the surface of the target table is free of any objects and then set its POWER switch to the I (on) position. Place the target table so that its grid is located approximately 1.2 m from the Rotating-Antenna Pedestal, as shown in Figure 2-13. Make sure that the metal rail of the target table is correctly aligned with the shaft of the Rotating-Antenna Pedestal. 2-39

Figure 2-13. Position of the Rotating-Antenna Pedestal and target table. G 6. Calibrate the Tracking Radar Training System according to the instructions in Appendix B. Set the RF POWER switch on the Radar Transmitter to the STANDBY position. Make sure that the Tracking Radar is adjusted as follows: Operating Frequency............................. 10.0 GHz Pulse-Repetition Frequency.................... single, 288 Hz Pulse Width........................................ 1 ns Observation Range................................. 3.6 m Stealth Exercise Setup G 7. On the Rotating-Antenna Pedestal, replace the dual-feed parabolic antenna with the single-feed parabolic antenna. G 8. In LVRTS, disconnect Oscilloscope probes 1 and 2 from TP1 and TP2 of the MTI Processor. Connect Oscilloscope probe 1 to TP14 of the MTI Processor. The signal at TP14 corresponds to the video output signal of the MTI Processor. In LVRTS, disconnect Oscilloscope probe E from TP8 of the Radar Target Tracker. Connect Oscilloscope probe E to TP3 (PRF signal) of the Display Processor. 2-40

Make the following settings on the Oscilloscope: Channel 1......................... 0.1 V/div Channel 2.............................. Off Time Base........................ 0.5 ms/div Set the Oscilloscope to Continuous Refresh. G 9. Remove the target table from the radar detection range. Place the positioning stand (part number 33179) 1.75 m from the radar antenna, as shown in Figure 2-14. Figure 2-14. Placement of the positioning stand. G 10. Install the Radar Jamming Pod Trainer positioning stand adapter (part numbers 33157 and 33160) onto the top of the positioning stand. Install the Radar Jamming Pod Trainer onto the positioning stand (in the horizontal position) using the short support shaft (part number 33125). Adjust the height of the positioning stand so that the Radar Jamming Pod Trainer horn antennas are approximately at the same height as the center of the parabolic reflector of the radar antenna. Align the Radar Jamming Pod Trainer so that its horn antennas are facing the Tracking Radar antenna and aligned with the shaft of the Rotating- Antenna Pedestal. The longitudinal axis of the Radar Jamming Pod Trainer should be aligned with the shaft of the Rotating-Antenna Pedestal. Set the angular reading dial on the positioning stand so that it indicates 0 when the Radar Jamming Pod Trainer is pointing toward the shaft of the Rotating-Antenna Pedestal. Align the radar antenna axis with Radar Jamming Pod Trainer. 2-41

G 11. On the Radar Transmitter, depress the RF POWER push button. The RF POWER ON LED should start to flash on and off. This indicates that RF power is being radiated by the Dual Feed Parabolic Antenna. Using the angular reading dial on the positioning stand, rotate the Radar Jamming Pod Trainer 90. After rotation, one of the flanks of the Radar Jamming Pod Trainer should be facing the radar antenna. The Radar Jamming Pod Trainer echo signal should be displayed on the Oscilloscope. Slightly readjust the orientation of the Radar Jamming Pod Trainer to maximize the amplitude of its echo signal on the Oscilloscope. Slightly realign the radar antenna to maximize the amplitude of the Radar Jamming Pod Trainer echo signal on the Oscilloscope. G 12. Observing the Oscilloscope, set the Gain of the MTI Processor so that the amplitude of the Radar Jamming Pod Trainer flank echo signal is 0.5 V, as shown in Figure 2-15. Figure 2-15. The Radar Jamming Pod Trainer flank echo signal normalized to an amplitude of 0.5 V. Using the angular reading dial on the positioning stand, rotate the Radar Jamming Pod Trainer back to 0. The Radar Jamming Pod Trainer horn antennas should be facing the radar antenna. 2-42

Radar Jamming Pod Trainer RCS Pattern Measurement and Analysis G 13. The equipment is now ready to record data required to obtain the RCS pattern of the Radar Jamming Pod Trainer. Using Table 2-5, record the amplitude of each peak radar return (spike echo) produced by the Radar Jamming Pod Trainer (RJPT). For each spike echo, record the corresponding angular position of the Radar Jamming Pod Trainer (to a precision of ±5 ). To do so, slowly rotate the Radar Jamming Pod Trainer until a spike echo signal appears on the Oscilloscope. At this point, maximize the echo signal amplitude by slightly adjusting the angular position of the Radar Jamming Pod Trainer. Read the angular position of the Radar Jamming Pod Trainer (it is indicated on the angular reading dial of the positioning stand) and record it in Table 2-5. Then measure the echo signal amplitude on the Oscilloscope and record it in Table 2-5. Continue rotating the Radar Jamming Pod Trainer until the next spike echo appears on the Oscilloscope screen, or until a complete rotation has been made. RJPT ANGULAR POSITION SPIKE ECHO AMPLITUDE ( A SPIKE ) SPIKE ECHO RELATIVE LEVEL ( 20 LOG [A SPIKE/0.5] ) degrees V db Table 2-5. Amplitude and relative level of the spike echoes associated with the Radar Jamming Pod Trainer (RJPT). G 14. For each spike echo, calculate the spike echo level relative to the amplitude (0.5 V) of the spike echo of one of the Radar Jamming Pod Trainer flank, using the following formula: Spike Echo Relative Level = 20 log (A SPIKE /0.5) Note your results in Table 2-5. 2-43

G 15. Measure the mean amplitude of the noise spikes in the video signal displayed on the Oscilloscope. Noise Mean Amplitude (A NOISE ): V Calculate the noise level relative to the amplitude (0.5 V) of the spike echo of one of the Radar Jamming Pod Trainer flank, using the following equation: Noise Relative Level = 20 log (A NOISE /0.5) = db G 16. Using the noise relative level obtained in the previous step, and the angular positions and spike echo relative levels recorded in Table 2-5, plot the RCS pattern of the Radar Jamming Pod Trainer on the polar graph in Figure 2-16. G 17. Observe the Radar Jamming Pod Trainer RCS pattern you plotted in Figure 2-16. How many reflective surfaces does the Radar Jamming Pod Trainer have? G 18. Knowing that the role of the Radar Jamming Pod Trainer is to electronically attack the radar, what is the main threat sector of this pod? What technique was used to reduce the radar echo of the Radar Jamming Pod Trainer horn antennas? a. Active cancellation b. Stealth jamming signal c. Passive cancellation d. Radar absorbent materials (RAM) 2-44

Stealth Technology: The Quest for Reduced RCS Figure 2-16. RCS pattern (spike echo pattern) of the Radar Jamming Pod Trainer (RJPT). Applying Stealth Technology to the Radar Jamming Pod Trainer G 19. You will now modify the hard body design of the Radar Jamming Pod Trainer in four steps, as shown in Figure 2-17. For each step, you will measure and record the amplitude of the spike echoes produced by the Radar Jamming Pod Trainer as well as the angular position of the Radar 2-45

Jamming Pod Trainer. You will then use the recorded data to plot the spike echo pattern on a polar graph. Place stealth cover number 1 (SC1, part number 33150), which is provided with the EWT, over the Radar Jamming Pod Trainer as shown in Figure 2-17. G 20. Using the angular reading dial on the positioning stand, make certain that the Radar Jamming Pod Trainer has an angular position of 0. The Radar Jamming Pod Trainer horn antennas should be facing the radar antenna. Figure 2-17. Radar Jamming Pod Trainer hard body designs offered by the EWT accessories. G 21. As in procedure step 13, measure the amplitude of the spike echoes produced by the Radar Jamming Pod Trainer with stealth cover 1 (RJPT + SC1). For each spike echo, record the amplitude and the corresponding angular position of the Radar Jamming Pod Trainer (to a precision of ±5 ) in Table 2-6. 2-46

For each spike echo, calculate the spike echo level relative to the amplitude (0.5 V) of the spike echo of one of the Radar Jamming Pod Trainer flank, using the formula given in step 14. Record your results in Table 2-6. RJPT ANGULAR POSITION SPIKE ECHO AMPLITUDE ( A SPIKE ) SPIKE ECHO RELATIVE LEVEL ( 20 LOG [A SPIKE/0.5] ) degrees V db Table 2-6. Amplitude and relative level of the spike echoes associated with the Radar Jamming Pod Trainer with stealth cover 1 (RJPT + SC1). G 22. Using the noise relative level obtained in step 15, and the angular positions and spike echo relative levels recorded in Table 2-6, plot the RCS pattern of the Radar Jamming Pod Trainer with stealth cover 1 (RJPT + SC1) on the polar graph in Figure 2-18. G 23. As shown in Figure 2-17, add the tail stabilizer (TS) accessory (part number 33151 provided with the EWT) to the hard body shape of the Radar Jamming Pod Trainer. G 24. Using the angular reading dial on the positioning stand, make sure that the Radar Jamming Pod Trainer has an angular position of 0. The Radar Jamming Pod Trainer horn antennas should be facing the radar antenna. 2-47

Stealth Technology: The Quest for Reduced RCS Figure 2-18. RCS pattern (spike echo pattern) of the Radar Jamming Pod Trainer with stealth cover 1 (RJPT + SC1). G 25. As in procedure step 13, measure the amplitude of the spike echoes produced by the Radar Jamming Pod Trainer with stealth cover 1 and the tail stabilizer (RJPT + SC1 + TS). For each spike echo, record the amplitude and the corresponding angular position of the Radar Jamming Pod Trainer (to a precision of ±5 ) in Table 2-7. 2-48

For each spike echo, calculate the spike echo level relative to the amplitude (0.5 V) of the spike echo of one of the Radar Jamming Pod Trainer flank, using the formula given in step 14. Record your results in Table 2-7. RJPT ANGULAR POSITION SPIKE ECHO AMPLITUDE ( A SPIKE ) SPIKE ECHO RELATIVE LEVEL ( 20 LOG [A SPIKE/0.5] ) degrees V db Table 2-7. Amplitude and relative level of the spike echoes associated with the Radar Jamming Pod Trainer with stealth cover 1 and the tail stabilizer (RJPT + SC1 + TS). G 26. Using the noise relative level obtained in step 15, and the angular positions and spike echo relative levels recorded in Table 2-7, plot the RCS pattern of the Radar Jamming Pod Trainer with stealth cover 1 and the tail stabilizer (RJPT + SC1 + TS) on the polar graph in Figure 2-19. G 27. As shown in Figure 2-17, add stealth cover 2 (part number 33152 provided with the EWT) to the hard body shape of the Radar Jamming Pod Trainer. G 28. Using the angular reading dial on the positioning stand, make sure that the Radar Jamming Pod Trainer has an angular position of 0. The Radar Jamming Pod Trainer horn antennas should be facing the radar antenna. 2-49

Stealth Technology: The Quest for Reduced RCS Figure 2-19. RCS pattern (spike echo pattern) of the Radar Jamming Pod Trainer with stealth cover 1 and the tail stabilizer (RJPT + SC1 + TS). G 29. As in procedure step 13, measure the amplitude of the spike echoes produced by the Radar Jamming Pod Trainer with stealth covers 1 and 2, and the tail stabilizer (RJPT + SC1 + TS + SC2). For each spike echo, record the amplitude and the corresponding angular position of the Radar Jamming Pod Trainer (to a precision of ±5 ) in Table 2-8. 2-50

For each spike echo, calculate the spike echo level relative to the amplitude (0.5 V) of the spike echo of one of the Radar Jamming Pod Trainer flank, using the formula given in step 14. Record your results to Table 2-8. RJPT ANGULAR POSITION SPIKE ECHO AMPLITUDE ( A SPIKE ) SPIKE ECHO RELATIVE LEVEL ( 20 LOG [A SPIKE/0.5] ) degrees V db Table 2-8. Amplitude and relative level of the spike echoes associated with the Radar Jamming Pod Trainer with stealth covers 1 and 2, and the tail stabilizer (RJPT + SC1 + TS + SC2). G 30. Using the noise relative level obtained in step 15, and the angular positions and spike echo relative levels recorded in Table 2-8, plot the RCS pattern of the Radar Jamming Pod Trainer with stealth covers 1 and 2, and the tail stabilizer (RJPT + SC1 + TS + SC2) on the polar graph in Figure 2-20. G 31. As shown in Figure 2-17, add the radar absorbent material (RAM) sidings (part numbers 33153, 33153-01, and 33153-02 provided with the EWT) to the hard body shape of the Radar Jamming Pod Trainer. G 32. Using the angular reading dial on the positioning stand, make sure that the Radar Jamming Pod Trainer has an angular position of 0. The Radar Jamming Pod Trainer horn antennas should be facing the radar antenna. 2-51

Stealth Technology: The Quest for Reduced RCS Figure 2-20. RCS pattern (spike echo pattern) of the Radar Jamming Pod Trainer with stealth covers 1 and 2, and the tail stabilizer (RJPT + SC1 + TS + SC2). 2-52

G 33. As in procedure step 13, measure the amplitude of the spike echoes produced by the Radar Jamming Pod Trainer with stealth covers 1 and 2, the tail stabilizer, and the RAM sidings (RJPT + SC1 + TS + SC2 + RAM). For each spike echo, record the amplitude and the corresponding angular position of the Radar Jamming Pod Trainer (to a precision of ±5 ) in Table 2-9. For each spike echo, calculate the spike echo level relative to the amplitude (0.5 V) of the spike echo of one of the Radar Jamming Pod Trainer flank, using the formula given in step 14. Record your results in Table 2-9. RJPT ANGULAR POSITION SPIKE ECHO AMPLITUDE ( A SPIKE ) SPIKE ECHO RELATIVE LEVEL ( 20 LOG [A SPIKE/0.5] ) degrees V db Table 2-9. Amplitude and relative level of the spike echoes associated with the Radar Jamming Pod Trainer with stealth covers 1 and 2, the tail stabilizer, and the RAM sidings (RJPT + SC1 + TS + SC2 + RAM). G 34. Using the noise relative level obtained in step 15, and the angular positions and spike echo relative levels recorded in Table 2-9, plot the RCS pattern of the Radar Jamming Pod Trainer with stealth covers 1 and 2, the tail stabilizer, and the RAM sidings (RJPT + SC1 + TS + SC2 + RAM) on the polar graph in Figure 2-21. 2-53

Stealth Technology: The Quest for Reduced RCS Figure 2-21. RCS pattern (spike echo pattern) of the Radar Jamming Pod Trainer with stealth covers 1 and 2, the tail stabilizer, and the RAM sidings (RJPT + SC1 + TS + SC2 + RAM). 2-54

Radar Jamming Pod Trainer Stealth Design Analysis G 35. Compare the spike echo patterns in Figures 2-16 and 2-18. Briefly explain how stealth cover 1 reduced the Radar Jamming Pod Trainer s number of spike echoes. G 36. Compare the spike echo patterns in Figures 2-18 and 2-19. Observe that adding the tail stabilizer accessory to the Radar Jamming Pod Trainer hard body shape increased the number of spike echoes. Note that platforms will often have hard body features which place constraints on their optimum stealth design. The tail stabilizer is a stealth hard body design constraint to the Radar Jamming Pod Trainer. Compare the spike echo patterns in Figures 2-19 and 2-20. How has stealth cover 2 affected the spike echoes produced by the tail stabilizer? Briefly explain how this has been achieved. G 37. Compare the spike echo patterns in Figures 2-18 and 2-20. Are they similar? Briefly comment. G 38. Compare the spike echo patterns in Figures 2-20 and 2-21. What is the effect of the RAM sidings on the spike echo pattern of the Radar Jamming Pod Trainer? 2-55

Compare the amplitude of the spike echoes coming from the rear end and flanks of the Radar Jamming Pod Trainer in the pattern of Figure 2-20, to the amplitude of the same spike echoes in the pattern of Figure 2-21. Evaluate the average attenuation level (ATT. RAM ) provided by the RAM sidings placed on the Radar Jamming Pod Trainer? ATT. RAM = db G 39. Turn off the radar. Disconnect all cables and remove all accessories. CONCLUSION During the exercise procedure, you verified that to give a stealth design to the hard body of a platform it was necessary to: 1. Reduce the number of radar visible surfaces. 2. Facet the design of hard body features with planar segments that slope away from the directions of incidence of radar energy, so that this energy is reflected in directions away from threat sectors. During the exercise procedure, you also used a radar absorbent material to further reduce the spike echo amplitudes of important radar reflector features present on the Radar Jamming Pod Trainer. REVIEW QUESTIONS 1. Why is it acceptable for a stealth platform to have spike echoes at certain viewing angles but not at others? Would not a tracking radar be able to acquire a continuous tracking lock? 2. How are radar absorbent materials used in stealth design? 2-56

3. Briefly explain what a threat sector is. 4. What does stealth provide a platform with? 5. What modification to stealth cover 1 (SC1 in Figure 2-17) would eliminate, or at least greatly attenuate, the side and back specular flashes from the RCS pattern obtained in Figure 2-18? 2-57