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Stealth Based Ship Design on Academic Level and Role of Naval Architects in Radar Stealth for Ships
Conference Paper · June 2012
Abstract: Stealth technologies are under immense focus due to their increasing use/demand in defense sector worldwide. The stealth ship technologies are underexplored and underutilized compared to stealth aircraft. This study investigates the need of exploring stealth based ship design on academic level and role of naval architect(s) in radar stealth for ships. The paper will present a study of existing ships with one are more stealth technologies, and make a case for stealth ship exploration and setup on academic level due to frequent use of stealth technologies on ships today. Naval Architect(s)’s role in radar stealth for ships is discussed.
Keywords: stealth ships; radar cross section (RCS); shaping; radar absorbing materials (RAM)
1 Introduction
Stealth technologies are under immense focus due to their increasing use and demand in defense sector worldwide. Stealth technologies make military platforms less visible to radar, infrared and sonar sensors. The low visibility implies late detection which is vital to capitalize on the elements of surprise, initiative and covertness. This study deals with radar and infrared aspects of stealth for ships.
Fig. 3 Sea Shadow
Stealth technologies have been explored and applied extensively in stealth aircraft industry. Although most of the specific material remains classified till date due to confidential nature of research, yet enough material is available to study and explore stealth aircraft technologies on academic level. The stealth ship technologies are particularly under-explored and underutilized compared to stealth aircraft. The reasons are late start of stealth related work on ships, complexities due to presence of water-surface, dominant multiple-bounce mechanism, and complicated geometry and general arrangements compared to stealth aircraft. Consequently, there is very little, if any, stealth ship exploration and setup on academic level.
The purpose of this paper is to investigate the need of exploring stealth based ship design on academic level and role of naval architects in radar stealth for ships. The paper will present a study of existing ships with one are more stealth technologies. The results make a strong case for stealth ship exploration and setup on academic level due to frequent use of stealth technologies on ships today. The author will also comment on the advantages of such setup. Radar stealth can be acquired through passive cancellation, active cancellation, shaping and radar absorbing materials. Shaping continues to be the most effective stealth method. Shaping is implemented by manipulating above waterline geometry and general arrangements on ships. Naval Architects have most control over both geometry and general arrangements. Thus, Naval Architects are most suited to implement shaping to acquire radar stealth.
Fig. 4 Daring Class Destroyer
Fig. 5 De Zeven Provincien Class Frigate
2 Stealth Based Ship Design on Academic Level
The necessity of exploring stealth based ship design on academic level has been studied. The methodology is to study existing ships with one are more stealth technologies. The degree of unitization of stealth technologies on existing ships is expected to gauge the demand, career potential and market value of ship stealth technologies.
The ships included in this study have been listed in Table 1. Stealth techniques i.e. geometry/shaping, infrared/heat signature, materials and paints have been plotted against no of ships these technologies were used on. The chart in Fig. 6 illustrates that stealth technologies are being used rather frequently on ships. Thus an academic setup to explore stealth ship technologies is vital to facilitate defense industry in stealth applications. The advantages are availability of professionals, faster development of stealth ship applications and reduction in monetary cost. The classified nature of these technologies is an issue which can be managed along practices of stealth aircraft academia whereby specifics remain classified, yet necessary academic setup exists.
Naval Platforms Included in Stealth Based Ship Design Study
1 Sea Shadow
2 M80 Stiletto
3 Triton Trimaran Ship
4 Zumwalt Class Destroyer
5 Daring Class Destroyer
6 Project 21956 Destroyer
7 Luyang II Class Destroyer
8 Kolkata Class Destroyer
9 Formidable Class Frigate
10 La Fayette Class Frigate
11 Brandenburg Class Frigate
12 De Zeven Provincien Class Frigate
13 Sachsen Class Frigate
14 Baden-Württemberg Class Frigate
15 Jiangkai I Class Frigate
16 Jiangkai II Class Frigate
17 Admiral Grigorovich Class Frigate
18 Sergey Gorshkov Class Frigate
19 Al-Riyadh Class Frigate
20 Shivalik P17 Class Frigate
21 Shivalik P17A Class Frigate
22 Visby Class Corvette
23 Baynunah Class Corvette
24 Eilat Class Corvette
25 Gowind Class Corvette
26 Braunschweig Class Corvette
27 MEKO A Class Corvette
28 Qahir Class Corvette
29 Buyan Class Corvette
30 Tigr Steregushchy Class Corvette
31 Littoral Combat Ship
32 Absalon Class Ship
33 Skjold Class Missile Boat
34 Holland Class Patrol Vessel
35 Hamina Class Missile Boat
36 Houbei Class Missile Boat
3 Role of Naval Architect(s) in Radar Stealth for Ships
The other aspect of this study is to examine the role of naval architect(s) in radar stealth for ships. Radar stealth is achieved by reducing radar cross section (RCS) of a ship. RCS reduction options and role of naval architects in radar stealth for ships have been discussed in following sections.
3.1 RCS Reduction Options
Following four methods can be used for reducing RCS
a. Passive cancellation
b. Active cancellation
c. Shaping
d. Radar absorbing materials (RAMs)
Passive cancellation, also known as impedance loading, proposes introducing an echo source whose amplitude and phase can be adjusted to cancel another echo source. This can be achieved for simple objects, provided that a loading point can be identified on the body (Schindler et al., 1965; Lin and Chen, 1968; Yu and Liang, 1971). Subsequently, a port is designed in the body with size and shape of the interior cavity to present optimum impedance at aperture. However, it is difficult to generate the required frequency dependence for this built-in impedance, and the reduction obtained for one frequency disappears as frequency changes. This technique is generally used to control the RCS of antennas (Popovic, 1971; Champagne et al., 1992). Large and complex geometry of a naval ship results in hundreds of reflecting sources, it is not practical to devise a passive cancellation treatment for each of these sources. In addition, the cancellation can revert to reinforcement with change in frequency or viewing angle. As a result, passive cancellation is generally discarded as a practical RCS reduction technique for naval ships.
Active cancellation, also known as active loading, suggests that the target must emit radiation in time coincidence with the incoming pulse whose amplitude and phase cancel the reflected energy. This implies that the target must be smart enough to sense the angle of arrival, intensity, frequency, and waveform of the incident wave. It must also be fast enough to know its own echo characteristics for that particular wave to rapidly generate the proper wave. Such a system must also be versatile enough to adjust and radiate the proper wave with change in frequency. The relative difficulty of active cancellation increases with increase in frequency (Knott et al., 2004; Skolnik, 2008). Active cancellation can only be considered for reducing RCS at low frequencies where radar absorbing materials and shaping are not very effective, so research on this technique is likely to continue (Xiang et al., 2010). However, this technique is not practical to implement on naval ships with the existing technologies.
Shaping is the most suitable and extensively used technique for reducing RCS. The concept of shaping is to orient the target surfaces and edges to deflect the scattered energy in directions away from the radar. It is accomplished by maximizing scattering into directions of space where threat receivers are not present (Knott et al., 2004; Skolnik, 2008; Jenn, 2005). Shaping techniques have been very on military platforms such as stealth aircraft, tanks and trucks etc. The aspect of shaping is very complex in case of ships due to complicated geometry and dominant multiple bounce mechanism. While applying shaping, ship RCS is reduced by controlling geometry and general arrangements of above waterline structure. Shaping has more potential in ships than aircraft due to presence of dominant multiple bounce scattering effects.
Radar absorbing materials (RAMs) reduce the energy reflected back to the radar by means of absorption, converting electromagnetic energy into heat. It is customary to gather the effects of all loss mechanisms into permittivity and permeability of the material because the designer is usually interested in the cumulative effect (Strifors and Gaunaurd, 1998; Swarner and Peters, 1963). Specifically, the RAM characteristics depend on its dielectric properties (material permittivity) and its magnetic properties (material permeability). Therefore, RAM can be classified into two broad categories, either dielectric or magnetic absorbers. The foundation of RAMs is the fact that substances either exist or can be fabricated whose indices of refraction are complex numbers. In the index of refraction, the imaginary part accounts for both electrical and magnetic losses. Dielectric radar absorbers are used for experimental and diagnostic work such as indoor microwave anechoic chambers. However, these absorbers are not flexible for applications on operational platforms due to their bulky and fragile nature. Instead, magnetic absorbers are used on operational systems. The basic ingredients of magnetic absorbers are compounds of iron, such as carbonyl iron and ferrites. Magnetic absorbers offer the advantage of compactness since they are typically a fraction of the thickness of dielectric absorbers. However, magnetic absorbers are inherently narrowband than their dielectric counterparts. The basic absorbing material is usually embedded in a matrix or binder such that the composite structure has the appropriate electromagnetic characteristics for a given range of frequencies.
3.2 Radar Stealth for Ships and Naval Architect(s)
Passive cancellation and active cancellation are generally discarded as useful RCSR techniques on warships due to practical limitations. Practically used ship RCS reduction methods are shaping and radar absorbing materials. In current stealth ship design, shaping techniques are first applied to create a design shape with low RCS in primary threat sectors. Radar absorbing materials are then used to treat remaining problem areas whose shape could not be optimized to reduce RCS (Peixoto et al., 2005).
Radar stealth techniques for ships can be implemented by hiring a Naval Architect who is conversant with RCS principles or including an RCS expert in the design team.
However, Naval Architect conversant with RCS techniques is best suited since he is most flexible in optimizing shaping for reducing RCS.
4 Conclusions
The academic setup to explore stealth ship technologies is vital to facilitate defense industry in stealth applications. The advantages are availability of professionals, faster development of stealth ship applications and reduction monetary cost. The classified nature of these technologies is an issue which can be managed along practices of stealth aircraft academia whereby specifics remain classified, yet necessary academic setup exists. The practical ship RCS reduction options are shaping and radar absorbing materials. In current stealth ship design, shaping techniques are first applied to create a design shape with low RCS in primary threat sectors. Radar absorbing materials are then used to treat remaining problem areas whose shape could not be optimized to reduce RCS. Radar stealth techniques for ships can be implemented by hiring a Naval Architect who is conversant with RCS principles or including an RCS expert in the design team. However, Naval Architect conversant with RCS techniques is best suited since he is most flexible in optimizing shaping for reducing RCS.
Acknowledgement
This work is financially supported by Program for New Century Excellent Talents in University under Grant No.NCET-07-0230 and the “111” Project under Grant No.B07019 at Harbin Engineering University.
References
Champagne NJ II, Williams JT, Sharpe RM, Hwu SU, Wilton DR (1992). Numerical modeling of impedance loaded multi-arm Archimedean spiral antennas. IEEE Transactions on Antennas and Propagation, 40(1), 102-108.
Jenn DC (2005). Radar and Laser Cross Section Engineering. American Institute Aeronautics and Astronautics, Reston, VA, USA, 1-96 and 257-388.
Knott EF, Shaeffer JF, Tuley MT (2004). Radar Cross Section, Second Edition. SciTech Publishing, Raleigh, NC, USA, 1-21 and 115-223.
Lin JL, Chen KM (1968). Minimization of backscattering of a loop by impedance loading - Theory and experiment. IEEE Transactions on Antennas and Propagation, 16(3), 299- 304.
Peixoto GG, De Paula AL, Andrade LA, Lopes CMA and Rezende MC (2005). Radar absorbing material (RAM) and shaping on radar cross section reduction of dihedral corners. International Conference on Microwave and Optoelectronics, 460- 463.
Popovic BD (1971). Erratum: Theory of cylindrical antennas with arbitrary impedance loading. Proceedings of the IEEE, 119(2), 1327-1332.
Schindler JK, Mack RB and Blacksmith P Jr. (1965). The control of electromagnetic scattering by impedance loading. Proceedings of the IEEE, 53(8), 993- 1004.
Skolnik MI (2008). Radar Handbook, Third Edition. McGraw-Hill Companies, New York, USA, 1.1-1.24 and 14.1-14.46.
Strifors HC, Gaunaurd GC (1998). Scattering of electromagnetic pulses by simple-shaped targets with radar cross section modified by a dielectric coating. IEEE Transactions on Antennas and Propagation, 46(9), 1252-1262.
Swarner W, Peters L Jr. (1963). Radar cross sections of dielectric or plasma coated conducting spheres and circular cylinders. IEEE Transactions on Antennas and Propagation, 11(5), 558- 569.
Yu IP, Liang S (1971). Modification of scattered field of long wire by multiple impedance loading. IEEE Transactions on Antennas and Propagation, 19(4), 554- 557.
Xiang YC, Qu CW, Su F, Yang MJ (2010). Active cancellation stealth analysis of warship for LFM radar. IEEE 10th International Conference on Signal Processing, Beijing, China, 2109-2112.
Conference Paper · June 2012
Abstract: Stealth technologies are under immense focus due to their increasing use/demand in defense sector worldwide. The stealth ship technologies are underexplored and underutilized compared to stealth aircraft. This study investigates the need of exploring stealth based ship design on academic level and role of naval architect(s) in radar stealth for ships. The paper will present a study of existing ships with one are more stealth technologies, and make a case for stealth ship exploration and setup on academic level due to frequent use of stealth technologies on ships today. Naval Architect(s)’s role in radar stealth for ships is discussed.
Keywords: stealth ships; radar cross section (RCS); shaping; radar absorbing materials (RAM)
1 Introduction
Stealth technologies are under immense focus due to their increasing use and demand in defense sector worldwide. Stealth technologies make military platforms less visible to radar, infrared and sonar sensors. The low visibility implies late detection which is vital to capitalize on the elements of surprise, initiative and covertness. This study deals with radar and infrared aspects of stealth for ships.
Fig. 3 Sea Shadow
Stealth technologies have been explored and applied extensively in stealth aircraft industry. Although most of the specific material remains classified till date due to confidential nature of research, yet enough material is available to study and explore stealth aircraft technologies on academic level. The stealth ship technologies are particularly under-explored and underutilized compared to stealth aircraft. The reasons are late start of stealth related work on ships, complexities due to presence of water-surface, dominant multiple-bounce mechanism, and complicated geometry and general arrangements compared to stealth aircraft. Consequently, there is very little, if any, stealth ship exploration and setup on academic level.
The purpose of this paper is to investigate the need of exploring stealth based ship design on academic level and role of naval architects in radar stealth for ships. The paper will present a study of existing ships with one are more stealth technologies. The results make a strong case for stealth ship exploration and setup on academic level due to frequent use of stealth technologies on ships today. The author will also comment on the advantages of such setup. Radar stealth can be acquired through passive cancellation, active cancellation, shaping and radar absorbing materials. Shaping continues to be the most effective stealth method. Shaping is implemented by manipulating above waterline geometry and general arrangements on ships. Naval Architects have most control over both geometry and general arrangements. Thus, Naval Architects are most suited to implement shaping to acquire radar stealth.
Fig. 4 Daring Class Destroyer
Fig. 5 De Zeven Provincien Class Frigate
2 Stealth Based Ship Design on Academic Level
The necessity of exploring stealth based ship design on academic level has been studied. The methodology is to study existing ships with one are more stealth technologies. The degree of unitization of stealth technologies on existing ships is expected to gauge the demand, career potential and market value of ship stealth technologies.
The ships included in this study have been listed in Table 1. Stealth techniques i.e. geometry/shaping, infrared/heat signature, materials and paints have been plotted against no of ships these technologies were used on. The chart in Fig. 6 illustrates that stealth technologies are being used rather frequently on ships. Thus an academic setup to explore stealth ship technologies is vital to facilitate defense industry in stealth applications. The advantages are availability of professionals, faster development of stealth ship applications and reduction in monetary cost. The classified nature of these technologies is an issue which can be managed along practices of stealth aircraft academia whereby specifics remain classified, yet necessary academic setup exists.
Naval Platforms Included in Stealth Based Ship Design Study
1 Sea Shadow
2 M80 Stiletto
3 Triton Trimaran Ship
4 Zumwalt Class Destroyer
5 Daring Class Destroyer
6 Project 21956 Destroyer
7 Luyang II Class Destroyer
8 Kolkata Class Destroyer
9 Formidable Class Frigate
10 La Fayette Class Frigate
11 Brandenburg Class Frigate
12 De Zeven Provincien Class Frigate
13 Sachsen Class Frigate
14 Baden-Württemberg Class Frigate
15 Jiangkai I Class Frigate
16 Jiangkai II Class Frigate
17 Admiral Grigorovich Class Frigate
18 Sergey Gorshkov Class Frigate
19 Al-Riyadh Class Frigate
20 Shivalik P17 Class Frigate
21 Shivalik P17A Class Frigate
22 Visby Class Corvette
23 Baynunah Class Corvette
24 Eilat Class Corvette
25 Gowind Class Corvette
26 Braunschweig Class Corvette
27 MEKO A Class Corvette
28 Qahir Class Corvette
29 Buyan Class Corvette
30 Tigr Steregushchy Class Corvette
31 Littoral Combat Ship
32 Absalon Class Ship
33 Skjold Class Missile Boat
34 Holland Class Patrol Vessel
35 Hamina Class Missile Boat
36 Houbei Class Missile Boat
3 Role of Naval Architect(s) in Radar Stealth for Ships
The other aspect of this study is to examine the role of naval architect(s) in radar stealth for ships. Radar stealth is achieved by reducing radar cross section (RCS) of a ship. RCS reduction options and role of naval architects in radar stealth for ships have been discussed in following sections.
3.1 RCS Reduction Options
Following four methods can be used for reducing RCS
a. Passive cancellation
b. Active cancellation
c. Shaping
d. Radar absorbing materials (RAMs)
Passive cancellation, also known as impedance loading, proposes introducing an echo source whose amplitude and phase can be adjusted to cancel another echo source. This can be achieved for simple objects, provided that a loading point can be identified on the body (Schindler et al., 1965; Lin and Chen, 1968; Yu and Liang, 1971). Subsequently, a port is designed in the body with size and shape of the interior cavity to present optimum impedance at aperture. However, it is difficult to generate the required frequency dependence for this built-in impedance, and the reduction obtained for one frequency disappears as frequency changes. This technique is generally used to control the RCS of antennas (Popovic, 1971; Champagne et al., 1992). Large and complex geometry of a naval ship results in hundreds of reflecting sources, it is not practical to devise a passive cancellation treatment for each of these sources. In addition, the cancellation can revert to reinforcement with change in frequency or viewing angle. As a result, passive cancellation is generally discarded as a practical RCS reduction technique for naval ships.
Active cancellation, also known as active loading, suggests that the target must emit radiation in time coincidence with the incoming pulse whose amplitude and phase cancel the reflected energy. This implies that the target must be smart enough to sense the angle of arrival, intensity, frequency, and waveform of the incident wave. It must also be fast enough to know its own echo characteristics for that particular wave to rapidly generate the proper wave. Such a system must also be versatile enough to adjust and radiate the proper wave with change in frequency. The relative difficulty of active cancellation increases with increase in frequency (Knott et al., 2004; Skolnik, 2008). Active cancellation can only be considered for reducing RCS at low frequencies where radar absorbing materials and shaping are not very effective, so research on this technique is likely to continue (Xiang et al., 2010). However, this technique is not practical to implement on naval ships with the existing technologies.
Shaping is the most suitable and extensively used technique for reducing RCS. The concept of shaping is to orient the target surfaces and edges to deflect the scattered energy in directions away from the radar. It is accomplished by maximizing scattering into directions of space where threat receivers are not present (Knott et al., 2004; Skolnik, 2008; Jenn, 2005). Shaping techniques have been very on military platforms such as stealth aircraft, tanks and trucks etc. The aspect of shaping is very complex in case of ships due to complicated geometry and dominant multiple bounce mechanism. While applying shaping, ship RCS is reduced by controlling geometry and general arrangements of above waterline structure. Shaping has more potential in ships than aircraft due to presence of dominant multiple bounce scattering effects.
Radar absorbing materials (RAMs) reduce the energy reflected back to the radar by means of absorption, converting electromagnetic energy into heat. It is customary to gather the effects of all loss mechanisms into permittivity and permeability of the material because the designer is usually interested in the cumulative effect (Strifors and Gaunaurd, 1998; Swarner and Peters, 1963). Specifically, the RAM characteristics depend on its dielectric properties (material permittivity) and its magnetic properties (material permeability). Therefore, RAM can be classified into two broad categories, either dielectric or magnetic absorbers. The foundation of RAMs is the fact that substances either exist or can be fabricated whose indices of refraction are complex numbers. In the index of refraction, the imaginary part accounts for both electrical and magnetic losses. Dielectric radar absorbers are used for experimental and diagnostic work such as indoor microwave anechoic chambers. However, these absorbers are not flexible for applications on operational platforms due to their bulky and fragile nature. Instead, magnetic absorbers are used on operational systems. The basic ingredients of magnetic absorbers are compounds of iron, such as carbonyl iron and ferrites. Magnetic absorbers offer the advantage of compactness since they are typically a fraction of the thickness of dielectric absorbers. However, magnetic absorbers are inherently narrowband than their dielectric counterparts. The basic absorbing material is usually embedded in a matrix or binder such that the composite structure has the appropriate electromagnetic characteristics for a given range of frequencies.
3.2 Radar Stealth for Ships and Naval Architect(s)
Passive cancellation and active cancellation are generally discarded as useful RCSR techniques on warships due to practical limitations. Practically used ship RCS reduction methods are shaping and radar absorbing materials. In current stealth ship design, shaping techniques are first applied to create a design shape with low RCS in primary threat sectors. Radar absorbing materials are then used to treat remaining problem areas whose shape could not be optimized to reduce RCS (Peixoto et al., 2005).
Radar stealth techniques for ships can be implemented by hiring a Naval Architect who is conversant with RCS principles or including an RCS expert in the design team.
However, Naval Architect conversant with RCS techniques is best suited since he is most flexible in optimizing shaping for reducing RCS.
4 Conclusions
The academic setup to explore stealth ship technologies is vital to facilitate defense industry in stealth applications. The advantages are availability of professionals, faster development of stealth ship applications and reduction monetary cost. The classified nature of these technologies is an issue which can be managed along practices of stealth aircraft academia whereby specifics remain classified, yet necessary academic setup exists. The practical ship RCS reduction options are shaping and radar absorbing materials. In current stealth ship design, shaping techniques are first applied to create a design shape with low RCS in primary threat sectors. Radar absorbing materials are then used to treat remaining problem areas whose shape could not be optimized to reduce RCS. Radar stealth techniques for ships can be implemented by hiring a Naval Architect who is conversant with RCS principles or including an RCS expert in the design team. However, Naval Architect conversant with RCS techniques is best suited since he is most flexible in optimizing shaping for reducing RCS.
Acknowledgement
This work is financially supported by Program for New Century Excellent Talents in University under Grant No.NCET-07-0230 and the “111” Project under Grant No.B07019 at Harbin Engineering University.
References
Champagne NJ II, Williams JT, Sharpe RM, Hwu SU, Wilton DR (1992). Numerical modeling of impedance loaded multi-arm Archimedean spiral antennas. IEEE Transactions on Antennas and Propagation, 40(1), 102-108.
Jenn DC (2005). Radar and Laser Cross Section Engineering. American Institute Aeronautics and Astronautics, Reston, VA, USA, 1-96 and 257-388.
Knott EF, Shaeffer JF, Tuley MT (2004). Radar Cross Section, Second Edition. SciTech Publishing, Raleigh, NC, USA, 1-21 and 115-223.
Lin JL, Chen KM (1968). Minimization of backscattering of a loop by impedance loading - Theory and experiment. IEEE Transactions on Antennas and Propagation, 16(3), 299- 304.
Peixoto GG, De Paula AL, Andrade LA, Lopes CMA and Rezende MC (2005). Radar absorbing material (RAM) and shaping on radar cross section reduction of dihedral corners. International Conference on Microwave and Optoelectronics, 460- 463.
Popovic BD (1971). Erratum: Theory of cylindrical antennas with arbitrary impedance loading. Proceedings of the IEEE, 119(2), 1327-1332.
Schindler JK, Mack RB and Blacksmith P Jr. (1965). The control of electromagnetic scattering by impedance loading. Proceedings of the IEEE, 53(8), 993- 1004.
Skolnik MI (2008). Radar Handbook, Third Edition. McGraw-Hill Companies, New York, USA, 1.1-1.24 and 14.1-14.46.
Strifors HC, Gaunaurd GC (1998). Scattering of electromagnetic pulses by simple-shaped targets with radar cross section modified by a dielectric coating. IEEE Transactions on Antennas and Propagation, 46(9), 1252-1262.
Swarner W, Peters L Jr. (1963). Radar cross sections of dielectric or plasma coated conducting spheres and circular cylinders. IEEE Transactions on Antennas and Propagation, 11(5), 558- 569.
Yu IP, Liang S (1971). Modification of scattered field of long wire by multiple impedance loading. IEEE Transactions on Antennas and Propagation, 19(4), 554- 557.
Xiang YC, Qu CW, Su F, Yang MJ (2010). Active cancellation stealth analysis of warship for LFM radar. IEEE 10th International Conference on Signal Processing, Beijing, China, 2109-2112.
