Patent EA-002451-B1 (EA)
Title: Radar plant and measurement technique for determination of the orientation and the depth of buried objects
Inventor: GREGERSEN OLE
IPC: G01S13/32
Filed: 1998-07-01
Abstract: 1. Plant for generation of information indicative of the depth and the orientation of an object positioned below the surface of the ground which plant is adapted to use electromagnetic radiation emitted from and received by an antenna system associated with the plant and having a transmitter and a receiver for generation of the electromagnetic radiation in cooperation with the antenna system and for reception of an electromagnetic radiation reflected from the object in cooperation with the antenna system, respectively, characterized in that the antenna system comprises a plurality of individual antenna elements having substantially linear polarization, especially dipole antennas, which are positioned in relation to the geometrical center of the antenna system with each of the centers of the antenna elements displaced in relation to the geometrical center of the antenna system and that the plant has means for rotation, either mechanically or electrically, of the antenna system and thus polarization of the electromagnetic field around or in relation to the geometric center of the antenna system. 2. Plant according to claim 1, characterized in that the individual antenna elements of the antenna system, especially dipole antennas, are positioned radially relative to the geometric center of the antenna system. 3. Plant according to claim 1 or 2, characterized in that the individual antenna elements of the antenna system form polygonal structures symmetrically or alternatively asymmetrically around the geometric center of the antenna system. 4. Plant according to any of the claims 1-3, characterized in that the individual antenna elements, especially dipole antennas, form orthogonally oriented, alternatively in parallel oriented, sets of transmitter and receiver antennas. 5. Plant according to any of the claims 1-4, characterized in that the transmitter and receiver antennas of the antenna system are co-polar or alternatively cross-polar. 6. Plant according to any of the claims 1-5, characterized in that the means for providing rotation of the antenna system are arranged to provide the rotation of the antenna system mechanically or electrically and thus provide polarization of the electromagnetic field around the geometric center in angular increments, typically in the order of 22.5 degree , 30 degree , 36 degree  or divisions of or multiples of such angles. 7. Plant according to any of the claims 1-6, characterized in that the transmitter and the receiver of the plant are arranged to perform generation and reception, respectively, of electromagnetic radiation at several individual frequencies, typically within the range 100MHz to 1GHz in steps of 5MHz. 8. Plant according to any of the claims 1-7, characterized in that the plant comprises signal processing means for measuring a transfer function, for example a voltage transfer function, a current transfer function or combinations thereof or a power transfer function between signals between the emitted and the received radiation. 9. Plant according to any of the claims 1-8, characterized in that the signal processing means are arranged for measuring the transfer function for associated values of angular rotation and frequency. 10. Plant according to claim 9, characterized in that the signal processing means are arranged to perform a transformation from frequency to time by Fourier transformation or by using a mathematical exponential model with corresponding rational transfer function on the transfer function associated with that angle, for generation of a time dependent function continuous in time for each angle, calculated at a predetermined number of discrete times using identical calculation times for all the angles. 11. Plant according to claim 10, characterized in that the signal processing means are adapted to perform a signal analysis by Fourier transformation for each of the times in the time dependent function continuous in time associated with each angle, with the time as a constant and the angle as independent variable, for generation of a representation in the angle domain. 12. Plant according to claim 9, characterized in that the signal processing means are adapted to perform a signal analysis by Fourier transformation for each frequency ha ving the frequency as a constant and the angle as an independent variable, for generation of a set of numbers having the angle harmonic and the measuring frequency as independent variables. 13. Plant according to claim 12, characterized in that the signal processing means furthermore are adapted to perform a transformation from frequency to time by Fourier transformation or by applying a mathematical exponential model with corresponding rational transfer function deriving for each angle harmonic a time dependent, in time continuous function at a predetermined number of discrete times, using identical calculation times for every angle harmonic, generating a set of numbers corresponding to a mathematical function having the angle harmonic in discrete form and the time in discrete form as independent variables. 14. Plant according to any of the claims 11-13, characterized in that the signal processing means furthermore are adapted to perform a scanning for local and global maxima indicating angle periodical reflections from objects, in the representation in the angle domain, and where the peak value indicates the time delays of associated reflections from an object. 15. Plant according to any of the claims 10-14, characterized in that the signal processing means furthermore are adapted to perform a calculation of angle position relative to the antenna system for the angle periodical reflections. 16. Plant according to any of the claims 10-15, characterized in that the plant comprises signal processing means for utilizing, during horizontal movement above the ground, collocated measurements for the suppression of clutter. 17. Method for generation of information indicative of the depth and the orientation of an object positioned below the surface of the ground which method comprises the use of electromagnetic radiation emitted from and received by an antenna system by means of a transmitter and a receiver for the generation of the electromagnetic radiation in cooperation with the antenna system and for reception of an electromagnetic radiation reflected from the object in cooperation with the antenna system, respectively, characterized in that for transmission and reception of the electromagnetic radiation a plurality of individual antenna elements is used having substantially linear polarization, especially dipole antennas, which are positioned in relation to the geometrical center of the antenna system with each of the centers of the antenna elements displaced in relation to the geometrical center of the antenna system and that the antenna system is rotated, either mechanically or electrically, around or in relation to the geometric center of the antenna system. 18. Method according to claim 17, characterized in that for transmission and reception of the electromagnetic radiation said antenna system is used having the individual antenna elements, especially the dipole antenna, positioned radially from the geometric center of the antenna system. 19. Method according to claim 17 or 18, characterized in that for transmission and reception of the electromagnetic radiation said antenna system is used having the individual antenna elements, especially the dipole antenna, forming polygonal structures positioned symmetrically or alternatively asymmetrically around the geometric center of the antenna system. 20. Method according to any of the claims 17-19, characterized in that for transmission and reception of the electromagnetic radiation the individual antenna elements of said antenna system mentioned are used, especially the dipole antennas, forming orthogonally oriented, alternatively in parallel oriented sets of transmitter and receiver. 21. Method according to any of the claims 17-20, characterized in that for transmission and reception of the electromagnetic radiation transmitter and receiver antennas are used, which are co-polar or alternatively cross-polar. 22. Method according to any of the claims 17-21, characterized in that the rotation of the antenna system is produced by rotating, mechanically or electrically, the antenna system and thus achieving polarization of the electromagnetic field around the geometric center in angular increments, typically in the order of 22.5 degree , 300 degree  36 degree  or divisions of or multiples of such angles. 23. Method according to any of the claims 17-22, characterized in that the generation and the reception of electromagnetic radiation are performed at several individual frequencies, typically within the range 100 MHz to 1 GHz in steps of 5 MHz. 24. Method according to any of the claims 17-23, characterized in that, in said method, signal processing is performed for measurement of a transfer function, for example a voltage transfer function, a current transfer function or combinations thereof or a power transfer function between signals between the emitted and the received radiation. 25. Method according to any of the claims 17-24, characterized in that, in said signal processing, a measurement of the transfer function for associated values of angular change and frequency is performed. 26. Method according to claim 25, characterized in that, in said signal processing, a transformation from frequency to time is performed by Fourier transformation or by the use of a mathematical exponential model with corresponding rational transfer function of said transfer function associated with that angle, for generation of a time dependent function, continuous in time for each angle, calculated at a predetermined number of discrete times using identical calculation times for all the angles. 27. Method according to claim 26, characterized in that, in said signal processing, a signal ana