Method for secure communications using spiral antennas

• US 6,448,941 B1
• Filed: 04/21/1999
• Issued: 09/10/2002
• Est. Priority Date: 04/21/1999
• Status: Expired due to Term

• Current Assignee: United States Department Of Health And Human Services (Government of the United States of America), the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Adams, Richard C., Rast, Howard E.
• Primary Examiner(s): Ho, Tan
• Application Number:
  US09/295,950
• Time in Patent Office: 1,238 Days
• Field of Search: 343/700.MS, 343/792.5, 343/895, 455/7, 455/39
• US Class Current: 343/895
• CPC Class Codes: H01Q 1/36 Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewithH01Q1/08, H01Q1/14 take precedence
• CPC Class Codes: H01Q 9/27 Spiral antennas

Abstract

A method for communicating with a decreased probability of detection by an unintended listening party uses frequency hopping and two substantially identical linearly polarized antennas whose polarization vector is synchronized to frequency. Synchronization of polarization with frequency is accomplished through specifically designed conductor-backed spiral antennas. For these conductor-backed spiral antennas, a change in frequency is synchronized to a change in the polarization vector of the communication signal. Since the receiving station will be programmed to alter its reception frequencies in accordance with those being transmitted, the second spiral antenna will automatically change its polarization upon making these frequency changes. A rapid change of polarization increases the difficulty in detecting and intercepting the communication by parties for whom the message was not intended.

Claims

1. A communication method comprising:

transmitting a frequency-hopped communications signal from an antenna radiator that changes polarization with a change in frequency;

receiving said frequency-hopped communications signal on an antenna receiver that has frequency-polarization characteristics matched to said antenna radiator and that is synchronized with said frequency-hopped communications signal as transmitted;

wherein said antenna radiator and receiver are conductor-backed spiral antennas each comprising;

a substrate with first and second substantially flat, opposite sides;

at least one pair of spiral antenna elements disposed on said first side of said substrate; and

a conducting ground plane disposed on said second side of said substrate.

2. The method of claim 1 wherein the performance of each of said antennas is described by an axial ratio defined as the difference between vertical gain and horizontal gain at a particular frequency and wherein said axial ratio varies by no less than plus or minus 5 dB.

3. The method of claim 2 wherein said spiral antenna elements makes at least three 360 degree turns.

4. The method of claim 3 wherein said substrate separates said spiral antenna elements from said conducting ground plane by a distance that is no greater than 6 inches.

5. The method according to claim 4 wherein said antennas operate between 225 megaHertz and 400 megaHertz.

6. The method of claim 3 wherein said substrate separates said spiral antenna elements and said conducting ground plane by a distance that is no greater than 3 inches.

7. The method of claim 6 wherein said antennas operate between 225 megaHertz and 400 megahertz.

8. The method of claim 3 wherein said substrate separates said spiral antenna elements and said conducting ground plane by a distance that is no greater than 1 inch.

9. The method according to claim 8 wherein said antennas operate between 225 megaHertz and 400 megaHertz.

10. The method of claim 2 wherein said antenna elements comprise metal foil.

11. The method of claim 10 wherein said antenna elements are arranged in an Archimedean spiral pattern.

12. The method of claim 10 wherein said substrate has a dielectric constant of approximately 1.

13. A communication method comprising:

transmitting a frequency-hopped communications signal from an antenna radiator that changes polarization with a change in frequency;

receiving said frequency-hopped communications signal on an antenna receiver that has frequency-polarization characteristics matched to said antenna radiator and that is synchronized with said frequency-hopped communications signal as transmitted;

wherein said antenna radiator and receiver are conductor-backed spiral antennas each comprising;

a substrate with first and second substantially flat, opposite sides;

at least one pair of Archimedean spiral-shaped antenna elements disposed on said first side of said substrate, said spiral elements making at least three 360 degree turns; and

a conducting ground plane disposed on said second side of said substrate, wherein said substrate separates said spiral antenna elements from said conducting ground plane by a distance that is no greater than 6 inches.

14. The method of claim 13 wherein the performance of each of said antennas is described by an axial ratio defined as the difference between vertical gain and horizontal gain at a particular frequency and wherein said axial ratio varies by no less than plus or minus 5 dB.

15. The method of claim 14 wherein said antenna elements comprise metal foil.

16. The method of claim 15 wherein said substrate has a dielectric constant of approximately 1.

17. The method according to claim 16 wherein said antennas operate between 225 megaHertz and 400 megaHertz.