Method and system for obtaining direction of an electromagnetic wave

• US 6,407,702 B1
• Filed: 02/26/2001
• Issued: 06/18/2002
• Est. Priority Date: 06/15/1998
• Status: Expired due to Fees

• Current Assignee: Jan Bergman, Roger Karlsson, Tobia Carozzi
• Original Assignee: Red Snake Radio Technology AB
• Inventors: Karlsson, Roger, Bergman, Jan, Carozzi, Tobia
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Mull, Fred H
• Application Number:
  US09/719,749
• Time in Patent Office: 477 Days
• Field of Search: 342/188, 342/361-366, 342/417, 342/445
• US Class Current: 342/364
• CPC Class Codes: G01S 3/143 by vectorial combination of signals derived from differently oriented antennae
• CPC Class Codes: G01S 3/146 by comparing linear polarisation components

Abstract

A method and a system are disclosed which utilize the polarization properties of electromagnetic fields for a determination of the direction to the source of the electromagnetic radiation. The method and system primarily use a particular antenna device with is associated receiver means for obtaining a wave field measurement Assuming separate frequencies, the present method and system also make it possible to distinguish between several sources and register their separate polarizations simultaneously. At least three electric antennas, or three magnetic antennas, are used to measure the wave field. The registered field components need not be 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 I and the spectral degree of circular polarization rc, are derived. 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.

Claims

1. A method for obtaining a direction of elliptically polarized electromagnetic wave propagation by measuring electromagnetic wave field quantities, characterized by the steps of

(a) arranging a group of receiver means for receiving the electromagnetic wave;

(b) arranging at least three antenna devices (5) for measurement of spatial components of a time-dependent electromagnetic vector field (f(t)), each antenna device connected to an individual receiver means forming a received spatial signal;

(c) digitizing the spatial signal formed by the receiver means;

(d) utilizing a discrete transformation algorithm which is applied to the wave-form data for obtaining spectrum field data, whereby each spatial component of a spectrum field (F(ω

)) is separated into a real part (25) and an imaginary part (30) thereby forming an entity F(t) having six quantities;

(e) determining a vector (V) being parallel to the direction of wave propagation, by taking the cross product of said spectrum field (F(ω

)) with its Hermite conjugate F^t(ω

)) times the imaginary unit i, whereby, in a Cartesian base, the three components of the vector (V) are given by in pairs multiplying (40) said six quantities and summing (45) the products.

2. The method according to claim 1, characterized in that step (c) further comprises the step of analog down-conversion ahead of said step of digitizing.

3. The method according to claim 1, characterized in that step (c) further comprises the step of digital down-conversion after said step of digitizing.

4. The method according to claim 1, characterized in that step (c) further comprises the step of spatial orthogonalization after said step of digitizing.

5. The method according to claim 1, characterized in that step (e) further comprises the step of determining a spectral intensity (I) by squaring (60) each of said six quantities and summing (65) the products.

6. A system for obtaining a direction of elliptically polarized electromagnetic wave propagation by measuring electromagnetic wave field characterization, characterized by

a group of receiver means for receiving an electromagnetic wave;

at least three antenna devices (5) for measuring spatial components of a time-dependent electromagnetic vector field (f(t)) representing the electro-magnetic wave, each antenna device being connected to an individual receiver means to thereby form a received spatial signal,

analog-to-digital converters (ADC) performing a digitizing of the spatial signals formed at each receiver means,

means for performing a discrete transformation algorithm (WFT) being applied to the wave-form data for obtaining spectrum field data, whereby each component of said spectrum field (F(ω

)) is separated into a real part (25) and an imaginary part (30) thereby forming an entity having six quantities,

means determining a vector (V) parallel to the direction of wave propagation, by taking the cross product of said spectrum field (F(ω

)) with its Hermite conjugate (F^t(ω

)) times the imaginary unit i, whereby, in a Cartesian base, the three components of said vector (V) are given by multiplying (40) in pairs said six quantities and summing (45) the products.

7. The system according to claim 6, characterized by having analog down-conversion means (DC) in front of the analog-to digital converters (ADC).

8. The system according to claim 6, characterized by including a process for digital down-conversion of signals to baseband frequencies by utilizing digitized data after the analog-to digital converters (ADC).

9. The system according to claim 6, characterized by including a process for spatial orthogonalization of wave-form data after the Analogue-to-Digital Converters (ADC).

10. The system according to claim 6, characterized by means for calculating a spectral intensity (I) from said spectrum field by performing a squaring (60) and then a summing (65) of said six quantities.