METHOD AND APPARATUS FOR ESTABLISHING LOW FREQUENCY/ULTRA LOW FREQUENCY AND VERY LOW FREQUENCY COMMUNICATIONS

• US 20100164747A1
• Filed: 12/15/2009
• Published: 07/01/2010
• Est. Priority Date: 12/18/2008
• Status: Active Grant

• Current Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Original Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Inventors: PAPADOPOULOS, Konstantinos
• Granted Patent: US 8,299,936 B2
• Time in Patent Office: Days
• US Class Current: 340/850
• CPC Class Codes: H01Q 1/04 Adaptation for subterranean or subaqueous use
• CPC Class Codes: H01Q 11/12 Resonant antennas
• CPC Class Codes: H01Q 9/16 with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole H01Q9/44 takes precedence

Abstract

A method for generating electromagnetic waves in the ELF/ULF comprising the steps of using a ground-based Horizontal Electric Dipole (HED) antenna to send electromagnetic pulses upwardly in the E-region of the ionosphere to form an oscillatory or pulsed electric field; allowing said pulsed electric field to interact with magnetized plasma of the lower ionosphere to generate a pulsed horizontal and vertical current which have associated Horizontal and Vertical Electric Dipole moment; and allowing them to radiate.

Claims

1. A method for generating electromagnetic waves in the ELF/ULF comprising the step of:

using a ground-based horizontal electric dipole antenna to send electromagnetic pulses upwardly in the E-region of the ionosphere to form an oscillatory or pulsed electric field, the oscillatory or pulsed electric field interacting with magnetized plasma of the lower ionosphere to generate oscillatory or pulsed horizontal and vertical currents which have an associated electric dipole moment, the oscillatory or pulsed horizontal and vertical currents radiating in the earth-ionosphere waveguide.

2. The method of claim 1, wherein the ground-based dipole is located at a location close to the magnetic equator to take advantage of the large ionospheric conductance.

3. The method of claim 1, wherein the electromagnetic pulses sent by the dipole have millisecond to second durations.

4. The method of claim 3, wherein the electromagnetic pulses have electric field amplitudes larger than 0.1m V/m at a 100 km height.

5. The method of claim 1, wherein the horizontal and vertical currents have electric moments that exceed 1×

10⁷ A-m.

6. The method of claim 1, wherein the vertical electric dipole in the earth-ionosphere that is generated as a result of the ground-based pulses radiates isotropically with a magnetic field amplitude on the order of nano-Tesla at a distance of 1000 km from a source.

7. Apparatus for communicating from a ground-based transmitter at extra low frequencies to a receiver, comprising;

a ground-based transmitter having an antenna located near the magnetic dipole of the earth, said transmitter transmitting extremely low frequency signals to said receiver, whereby the signal strength at said receiver is stronger than that associated with signals from an identical ground-based transmitter at upper latitudes.

8. The apparatus of claim 7, wherein said receiver is a subsurface receiver, whereby the received extra low frequency signals are detected at a significant distance from the surface due to the magnitude of said received extra low frequency signals.

9. The apparatus of claim 8, wherein said subsurface receiver is located in a sub-sea location.

10. The apparatus of claim 8, wherein said subsurface receiver is located in a subterranean location.

11. The apparatus of claim 8, and further including a submarine, said sub-sea receiver located on said submarine.

12. The apparatus of claim 7, and further including a detector for detecting signals returned from subsurface objects.

13. The apparatus of claim 12, wherein said detector is located above the surface of the earth.

14. The apparatus of claim 13, and further including a unit coupled to said detector for imaging said subsurface objects.

15. The apparatus of claim 7, and further including a module for modulating said signals from said ground-based transmitter to provide pulses, the length of said pulses being less than the delay associated with a ground return pulse, whereby said ground return pulse is not effective in reducing corresponding signals from the ionosphere, whereby signals received at said receiver are between 15 to 20 dB stronger than signals that are not pulsed.

16. The apparatus of claim 15, wherein the length of said pulses depends on the length of said antenna and the ground conductivity at said antenna.

17. The apparatus of claim 7, wherein signals received at said receiver are 25 to 30 dB higher than those associated with an identical ground-based transmitter at higher altitudes.

18. Apparatus for reliable extra low frequency communication with submarines that does not require the existence of an electrojet in the ionosphere, comprising:

a ground-based transmitter for transmitting extra low frequency signals from a location near the magnetic equator, whereby signals received at a receiver at said submarine are robustly detected regardless of the non-existence of said electrojet.