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  • 1.
    Persson, Björn
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Swedish Defence University.
    Assessment of Aircraft Radar Cross-Section for Detection Analysis2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hiding from and surprising an opponent are tactics that have been used in warfare throughout history. They were features that aircraft originally possessed when they were first used in military operations. However, development of military technology is an endless struggle between advances in technology and counter technology. During World War II this struggle led to the development of a new technology called radar, which was designed to detect sea vessels and aircraft at a distance and deny them the element of surprise. This laid the foundation for modern air defenses and simultaneously created a need for aircraft to penetrate such defenses. Central to the tactics and technological development that followed from the deployment of radar on the modern battlefield is the radar cross-section (RCS) of aircraft, which dictates the range at which aircraft can be detected by radar. In this thesis some aspects of the RCS of aircraft in radar detection are investigated. A combination of experimental measurement of aircraft and digital model development of the RCS of aircraft has been used.

    From flight experiments, the uncertainty in aspect angle to a threat sensor, due to aircraft dynamics, is quantified for various aircraft. In addition, the RCS fluctuation behavior of a military jet trainer is investigated by dynamic in-flight measurement. The monostatic and bistatic RCS of an F-117 are modeled and findings show that spline interpolation provides superior accuracy when interpolating the RCS data. Smooth and conservative RCS models are suggested and a new RCS sampling scheme is presented. A model based on experimental data is suggested for determining the range of aspect angles that an aircraft is likely to orient towards a threat sensor, and experimental RCS data is compared to the classical Swerling radar target models.

    Possible consequences for military operations and the design of military systems are discussed and considerations for modeling the interaction between air defenses and aircraft penetrating those defenses are given.  

    This thesis should be of interest to military actors and the defense industry, since the analyses of the ability to detect aircraft using radar are important for military operations and their planning.

  • 2.
    Persson, Björn
    Swedish Defence University.
    Radar Target Modeling Using In-Flight RCS MeasurementsManuscript (preprint) (Other academic)
    Abstract [en]

    A flight experiment with the Saab 105 aircraft and the radar cross-section measurement system Arken has been performed at C and Ku bands. Two types of trajectories were flown and the flight state was recorded using inertial and satellite navigation equipment.  The data was used to recreate the flight in a simulator where aspect angles and range to the measurement system could be calculated. The measured radar cross-section as a function of time is presented and compared to various statistical fluctuation models, including the distributions used in Swerling cases. Findings show that the Generalized Pareto distribution fits the measured data best and that Swerling Case 2 is also a good candidate for describing the dynamics of the radar cross-section at Ku-band when the aircraft approaches the radar head on. The measured radar cross-section data was analyzed using the Fast Fourier Transform from which fluctuation rates for different carrier frequencies and trajectories could be estimated.

  • 3.
    Persson, Björn
    et al.
    Swedish Defence University.
    Bull, Peter
    Swedish Defence University.
    Empirical Study of Flight-Dynamic Influences on Radar Cross-Section2016In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 53, no 2, p. 463-474Article in journal (Refereed)
    Abstract [en]

    In this work, measurements and a method for analyzing flight-dynamic effects on radar cross-section models for aircraft are presented. Flight-dynamic effects need to be considered when designing combat aircraft and creating target models for radar simulators. The work is based on flight data from three different types of aircraft: Piper PA-28 Archer II, Boeing 737, and Saab JAS 39 Gripen. Using inertial navigation and global-positioning systems, the motions of the three aircraft are recorded in flight. From the data, aspect angles toward a radar station located in the extension of the intended flight path are generated using a simulator. It is found that the major contribution to perturbations in aspect angles is due to the rotational degrees of freedom and that bivariate normal distributions are a good candidate for approximating the uncertainty in aspect angles for all three aircraft types. It is also found that each rotational degree of freedom is close to a normal distribution but that the parameter values of the distribution vary with altitude and aircraft type.

  • 4.
    Persson, Björn
    et al.
    Swedish Defence University, Sweden.
    Norsell, Martin
    Swedish Defence College, Sweden.
    Conservative RCS Models for Tactical Simulation2015In: IEEE Antennas and Propagation Magazine, ISSN 1045-9243, Vol. 57, no 1Article in journal (Refereed)
    Abstract [en]

    This paper describes a procedure for generating conservative radar cross section (RCS) models able to meet the computational requirements imposed by simulation and related applications. The key concept is to downsample calculated or measured RCS data retaining local extreme values; thus, a conservative RCS matrix is obtained. Spline approximations are used in order to obtain continuity in the RCS models. RCS models with varying resolution have been generated and analyzed, and it is shown how spatial Fourier transforms can be used when determining feasibility for certain decision making applications. Furthermore, it is found that the interpolation errors obtained from the conservative RCS models are well described by generalized extreme value theory.

  • 5.
    Persson, Björn
    et al.
    Swedish Defence University, Sweden.
    Norsell, Martin
    Swedish Defence College, Sweden.
    On Modeling RCS of Aircraft for Flight Simulation2014In: IEEE Antennas and Propagation Magazine, ISSN 1045-9243, Vol. 56, no 4, p. 34-43Article in journal (Refereed)
    Abstract [en]

    This paper investigates the implementation of the radar cross section (RCS) of aircraft in modeling and simulation (M&S). More specifically, it addresses the tradeoff between accuracy and computational cost introduced by spatial RCS fluctuations. High-resolution RCS matrices, generated using Physical Optics (PO), were used in an investigation of RCS matrix resolution, and an evaluation of different bivariate interpolation methods is presented. The spatial Fourier transform was used for resolution analysis. It was found that the smallest RCS interpolation error was obtained using splines. Furthermore, results showed that the distribution of the relative interpolation error in detection range was well approximated by a log-normal distribution.

  • 6.
    Persson, Björn
    et al.
    Swedish Defence University.
    Norsell, Martin
    Swedish Defence College.
    Reduction of RCS Samples Using the Cubed Sphere Sampling SchemeManuscript (preprint) (Other academic)
    Abstract [en]

     An alternative to the traditional method of sampling radar cross section data from measurements or electromagnetic code is presented and evaluated. The Cubed Sphere sampling scheme solves the problem of oversampling at high and low elevation angles and at equal equatorial resolution the scheme can reduce the number of samples required by approximately 25%. The analysis is made of an aircraft model with a monostatic radar cross section at C-band and a bistatic radar cross section at VHF-band, using Physical Optics and the Multilevel Fast Multipole Method, respectively. It was found that for the monostatic radar cross section, the Cubed Sphere sampling scheme required approximately 12% fewer samples compared to that required for traditional sampling while maintaining the same interpolation accuracy ever the entire domain. For the bistatic data, it was possible to reduce the number of samples by approximately 45% for high sampling resolutions. Using spline interpolation the number of samples required could be reduced even further. 

  • 7.
    Persson, Björn V.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Norsell, M.
    Reduction of RCS samples using the cubed sphere sampling scheme2016In: Progress In Electromagnetics Research M, ISSN 1937-8726, Vol. 48, p. 103-112Article in journal (Refereed)
    Abstract [en]

    An alternative to the traditional method of sampling radar cross section data from measurements or electromagnetic code is presented and evaluated. The Cubed Sphere sampling scheme solves the problem of oversampling at high and low elevation angles and at equal equatorial resolution the scheme can reduce the number of samples required by approximately 25%. The analysis is made of an aircraft model with a monostatic radar cross section at C-band and a bistatic radar cross section at VHF-band, using Physical Optics and the Multilevel Fast Multipole Method, respectively. It was found that for the monostatic radar cross section, the Cubed Sphere sampling scheme required approximately 12% fewer samples compared to that required for traditional sampling while maintaining the same interpolation accuracy over the entire domain. For the bistatic data, it was possible to reduce the number of samples by approximately 35% for high sampling resolutions. Using spline interpolation the number of samples required could be reduced even further.

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