Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
  • G01S3/02—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using radio waves
  • G01S3/14—Systems for determining direction or deviation from predetermined direction
  • G01S3/143—Systems for determining direction or deviation from predetermined direction by vectorial combination of signals derived from differently oriented antennae
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
  • G01S3/02—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using radio waves
  • G01S3/14—Systems for determining direction or deviation from predetermined direction
  • G01S3/146—Systems for determining direction or deviation from predetermined direction by comparing linear polarisation components

Definitions

• This invention involves antennas and relates to measurements of electromagnetic wave field characterizations. Specifically, it relates to a method and a system dealing with determination of wave polarization and direction of wave propagation for arbitrary frequencies.
• the present invention utilizes the polarization properties of electromagnetic fields to determine the direction to the source. Furthermore the measurements need not be from more than one point in space. In this respect a one-point measurement is considered to be such that all antennas are well within a sphere of a wavelength scale.
• the present invention also makes it possible to distinguish between several sources and register their separate polarization simultaneously.
• At least three electric antennas, or three magnetic antennas are used to measure the wave field.
• the antennas are arranged such that three spatial components of the wave field can be registered.
• the registered field components need not be a p ⁇ o ⁇ orthogonal to each other.
• the measured wave field is processed in accordance to predetermined formulae so that the propagation direction and other polarization characteristics, such as the spectral intensity and the spectral degree of circular polarization, are derived.
• FIG. 1 shows a preferred embodiment for a radio receiver, which implements the direction finding method explained in the text
• FIG. 2 illustrates the method for obtaining the spectral intensity in a preferred embodiment
• FIG. 3 describes how the degree of circular polarization is obtained in a preferred embodiment
• FIG. 4 shows an example of an antenna arrangement and a casing for a preferred embodiment.
• Theoretical analysis utilizes the polarization properties of electromagnetic radiation to determine propagation direction. Three orthogonal components of the electric or the magnetic field, are required in the analysis.
• antenna arrangements One of the simplest types of antenna arrangements is three mutually perpendicular dipole antennas for measuring the electric field or three mutually perpendicular coils for measuring the magnetic field.
• Other antenna arrangements can be used, which is obvious for persons skilled in the art of antenna engineering.
• the registered spatial components of the time-dependent field f(t) are not orthogonal to each other, they need first be orthogonalized.
• the spatially orthogonalized components of the wave field f(t), by fx(t), f y (t), and fz(t).
• the field vector f(t) sweeps out an ellipse, which describes the state of polarization. This ellipse is called the polarization ellipse. Since we wish to distinguish between different frequencies, a temporal transform of the field will be used.
• the transform is of the Cohen class of transformations [L.Cohen, "Generalized phase-space distribution functions", Jour. Math.
• WFT Windowed Fourier Transform
• Wavelet transform the transform of the field by F( ⁇ ), with components Fx( ⁇ ), F y ( ⁇ ), and Fz( ⁇ ), or simply Fx, Fy, and Fz, respectively.
• the field vector F for a transverse electromagnetic wave lies in the plane transverse to the direction of propagation.
• the vector _F f lies also in the transverse plane, but ahead of F in phase. Together these two vectors form a plane, which is perpendicular to the direction of propagation.
• a vector which is always parallel to the direction of propagation is therefore given by ⁇ F x F f .
• V which we define by
• the direction in which the polarization ellipse is traced out determines if the helicity of the field is positive or negative.
• positive helicity means that the vector V points in the same direction as the propagation direction
• negative helicity means that the vector V points in the opposite direction to the direction of propagation.
• the helicity cannot be determined a prio ⁇ without simultaneously measuring both the electric and magnetic fields, indicating two possible propagation directions. In many cases, some additional information is known about the wave field so that one of the two possible propagation directions can be excluded.
• the existence of a signal at the receiver input is marked by an intensity at a certain frequency band. Therefore we also need to measure the spectral intensity of the wave field. Also the spectral degree of circular polarization can be determined.
• the spectral intensity, I, of the wave field is given by
• the spectral degree of circular polarization does, according to this definition, vary between zero and one.
• the two other polarization parameters can be interpreted as the two angles which determine the direction of the semi major axis of the polarization ellipse (for instance see R. Karlsson, "Three- dimensional spectral Stokes parameters", Master thesis, UPTEC 97 069E, 1998).
• the main application of the present invention is to give a complete description of measured three dimensional (3D) time-dependent electromagnetic fields, in terms of their polarization characteristics.
• V and I which are defined by Equations (1) and (10) respectively.
• the vector V indicates two possible wave propagation directions. This means that there exists a 180 degrees ambiguity in the determination of direction to a radiating source. However, in most practical applications this ambiguity can be resolved without simultaneously measuring both the electric and magnetic wave fields.
• the 180 degrees ambiguity can be resolved by means of conventional Doppler techniques. This is often the case when space- or airborne measurements are considered, where the source often can be assumed to be stationary relative to the moving receiver.
• ground based measurements When ground based measurements are considered, there are two contributions to the registered wave field at the antenna input. One contribution is from the direct wave field and the other is from the wave field reflected from the ground.
• the influence caused by ground reflection can, for a person skilled in the arts of electrodynamics, complex analysis and linear algebra, be resolved analytically if the ground is assumed to be a good conductor, i.e. ⁇ / ⁇ >> 1, where ⁇ is the conductivity and ⁇ is the permittivity of the ground and ⁇ is the angular frequency of the wave.
• F( ⁇ ) a radio receiver which implements the methods described in the theory, has the possibility to simultaneously distinguish between multiple, non-identical, sources.
• a radio receiver for microwaves which are of the order of 1 cm, is in the field of digital mobile telephony.
• a subscriber i.e., a mobile telephone
• attempts to make a connection it is assigned a unique frequency from the corresponding base station in its cell.
• each telephone acts as a unique radio source in its cell.
• the client is moving to a neighboring cell during a connection it will be 5 assigned a new frequency from the new, corresponding, base station.
• the change of base stations is determined by a threshold level of the signal- strength. If the cells have small overlapings or if the traffic is low there are usually no problems using this strategy. If on the other hand, the cells have large overlapings and the traffic is high, severe problems such as drop-outs
• a radio receiver for mobile telephony which implements the direction finding method described in the theory according to the present invention will be able to determine the direction to, and thus the approximate location, of multiple subscribers in a cell.
• radio interferometry techniques it is obvious for a person skilled in the art of radio interferometry techniques, that several radio receivers, which implements the methods described in the present application, may be combined. If the distances between the radio receivers is much larger than one wavelength, conventional triangulation techniques (R.C. Johnson and H. Jasik, "Antenna Engineering Handbook",
• the employed algorithm can be inverted for the implementation of a radio transmitter, i.e., by specification of the various polarization parameters, a radio wave with certain polarization characteristics, such as the degree of circular polarization in a predetermined direction, could be transmitted.
• the antennas would then act as an electronically steerable crossed dipole.
• the present invention can be used to implement a monostatic radar. If the transmitter and the receiver are synchronized, but use different but equivalent antenna arrangements, the radar is bistatic.
• the radio receiver can also be combined with a conventional, external, radio transmitter, to form a bistatic radar.
• GPR ground penetrating radar
• an antenna array of radio transmitters which utilizes the inverted algorithm, can be formed.
• the over-all performance of the transmitting antenna array would be enhanced compared to conventional systems.
• implementations of monostatic as well as bistatic radar systems are possible.
• FIG. 1 A preferred embodiment of a radio receiver is shown in FIG. 1.
• the antenna devices 5 register the three spatial components of a time-dependent electric or magnetic vector field, f(t).
• the components of the field are denoted by f ⁇ (t), f2(t), and f_(t).
• Each component of the field is digitized by a respective Analog-to-Digital Converter (ADC) 10.
• ADC Analog-to-Digital Converter
• the signal is usually down-converted to a baseband frequency.
• each field component is down-converted digitally by the Down Converters (DC) 15.
• DC Down Converters
• analog down-conversion has to be used. In that case, the order of the ADC and the DC is interchanged. For low frequency measurements, the DC stage can be left out.
• a spatial ortogonalization 20 is required.
• the orthogonalization 20 is performed after the digital down-conversion 15 but can in principle be performed directly after the ADC which anyhow is the case when analog or no down-conversion is used.
• the three spatially orthogonalized components of the field f(t) are denoted by fx(t), f y (t), and fz(t).
• a discrete transformation algorithm is then applied to the wave-form data to obtain the spectrum field data, F( ⁇ ).
• F( ⁇ ) spectrum field data
• WFT Windowed Fourier Transform
• the three spatial components of the spectrum field data are denoted by Fx( ⁇ ), F y ( ⁇ ), and Fz( ⁇ ), or simply by Fx, F y , and Fz, respectively.
• Equation (1) the spectrum field components are in pairs multiplied 40 and then summed 45 according to Equation (2).
• the three components of the obtained vector V is then transferred to an interface 50 indicated in FIG. 1.
• FIG. 2 it is shown, according to the present method, how the spectral intensity, I, of the vector field f(t), is determined. From FIG. 1 the real parts 30 and imaginary parts 35 of the spectrum field F( ⁇ ), are given. Each of the six parameters 55 are squared 60 and then summed 65 according to Equation (10) and the spectral intensity is obtained. The spectral intensity is then transferred to the interface 50 indicated in FIG. 1.
• FIG. 3 it is shown, according to the present method, how the spectral degree of circular polarization, re, of the vector field f(t) is determined.
• the components of the vector V are given from FIG. 1 and in accordance with FIG. 2 is given the spectral intensity 770.
• the components of V are first squared 75 and summed 80.
• the square root of the sum 80 is then taken 85 so that the absolute value,
• , of V is obtained.
• l/I, 90 is then multiplied by the absolute value
• the product of this multiplication is the spectral degree of circular polarization, re, which is then transferred to the interface 50 indicated in FIG. 1.
• V In practical applications, it is convenient to express the direction of V, in terms of the polar angle ⁇ and the azimuth angle ⁇ of a spherical coordinate system.
• the vector V then has the same meaning as the radius vector.
• the components of V are then given by
• V I V
• V, cos _? (6) . 2 + v v 2 + V *
• the antennas used in the preferred embodiment can be either electric or magnetic. At least three electric or three magnetic antenna devices are required for registering three spatial components of the wave field.
• the antenna devices 5 are in the preferred embodiment equivalent.
• An antenna device may consist of different antenna configurations.
• a dipole antenna can be formed by connecting two monopole elements, thereby registering the signal by measuring the voltage between the two elements.
• the simplest type of such a dipole antenna is the straight dipole antenna, meaning that the two monopole elements are parallel and point in opposite direction and that the signal is registered by measuring the voltage at a common origin.
• Another type is the V- shaped dipole antenna, which is a generalization of the straight dipole antenna with the only extension that the two monopole elements need not be parallel.
• One way is to form an arrangement consisting of three mutually perpendicular straight dipole antennas.
• An advantage of such an arrangement is that the spatial orthogonalization process 20 in the preferred embodiment can be left out.
• Another advantage is that each antenna device 5 is directly connected to the corresponding physical antenna meaning that any process for antenna selection or antenna switching is not necessary.
• Another arrangement is to use four monopole elements forming six possible V-shaped dipole antennas. This arrangement is used in the preferred embodiment where the four monopole elements 100 are mounted on the sides of the casing 110, which in the preferred embodiment is of the form of a regular tetrahedron according to FIG. 4.
• An advantage of this arrangement is that the number of needed monopole elements is minimized.
• the drawbacks are the need for a process to select or switch between the six possible V-shaped dipole antennas and the need for a spatial orthogonalization process 20.
• dipole antennas which are short compared to the wavelength.
• Short dipole antennas have both a flat frequency response curve and a flat frequency-to-phase dependence. If resonant antennas are used the usable bandwidth narrows considerably due to the steep phase- shift occurring close to the antenna resonance frequency. In this case it is in principle possible, which is obvious for a person skilled in the art of signal analysis, to calibrate the antenna devices. In practice though, this is not feasible due to the strong dependence of the many unknown variables involved.
• a magnetic dipole antenna is a small current loop in the form of a coil, registering the signal by measuring the current in the coil.
• the simplest, but not the only type of antenna arrangement, is three mutually perpendicular coils.
• impedance matching and amplification are performed by utilizing high impedance pre-amplifiers in a conventional manner. This is well known by a person skilled in the art and need not be further discussed in this context.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Variable-Direction Aerials And Aerial Arrays (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20411709

Family Applications (1)

Country Status (6)

Cited By (1)

Families Citing this family (17)

Citations (2)

Family Cites Families (1)

• 1998
  • 1998-06-15 SE SE9802126A patent/SE512219C2/sv not_active IP Right Cessation
• 1999
  • 1999-06-11 US US09/719,749 patent/US6407702B1/en not_active Expired - Fee Related
  • 1999-06-11 EP EP99931686A patent/EP1095291A1/en not_active Withdrawn
  • 1999-06-11 JP JP2000555107A patent/JP2002518683A/ja active Pending
  • 1999-06-11 AU AU48123/99A patent/AU4812399A/en not_active Abandoned
  • 1999-06-11 WO PCT/SE1999/001036 patent/WO1999066341A1/en not_active Application Discontinuation

Patent Citations (2)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events