Digital receiving system for dense environment of aircraft

• US 6,792,058 B1
• Filed: 07/12/2000
• Issued: 09/14/2004
• Est. Priority Date: 07/12/2000
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Hershey, John Erik, Hoctor, Ralph Thomas, Puckette, Charles McDonald IV, Korkosz, Richard August
• Primary Examiner(s): Fan, Chieh M.
• Application Number:
  US09/614,776
• Time in Patent Office: 1,525 Days
• Field of Search: 375/260, 375/267, 375/285, 375/346, 375/347, 375/349, 375/350, 375/316, 342/357-1-3, 455/65, 455/132, 455/303
• US Class Current: 375/347
• CPC Class Codes: G01S 13/782 using multimoding or selective addressing

Abstract

The capacity of a Mode-S ADS-B surveillance radar system is increased by sectorizing the radar system by the use of a directional array of Mode-S, quarter wavelength, single element, stub antennas. The ensemble of signals from the array of Mode-S antenna elements is processed electronically. The signal processing/receiver architecture increases the capacity of the Mode-S ADS-B system to be capable of effectively functioning within a highly congested airspace.

Claims

1. A Mode-S digital receiving system for receiving and processing Mode-S signals in an aircraft operating in a dense environment of aircraft comprising:

a. a spatial array of Mode-S antenna elements mounted on the aircraft;

b. a signal processing receiver for producing and processing a separate signal for each separate antenna element;

c. at least one analog to digital (A/D) converter for converting the signals for the separate antenna elements to corresponding digital signals;

d. a multiplexer for sequentially and periodically coupling at least one signal or digital signal from the separate antenna elements;

e. a squitter filter for determining the presence of a squitter preamble in a Mode-S signal received by the receiving system;

f. a digital signal processing unit, responsive to the determined presence of the Mode-S signal, for processing and adjusting complex weights of the digital signals for the separate antenna element to maximize the signal-to-noise ratio of the received Mode-S signal;

g. a Mode-S receiver, coupled to the output of the digital signal processing unit, for processing and identifying technical data conveyed by the Mode-S signal.

2. The Mode-S digital receiving system of claim 1, further comprising:

a. a memory/buffer stores the digital signals in sequence therein;

b. a controller unit is coupled to the output of the squitter filter and controls the memory/buffer and the digital signal processing unit, wherein the controller unit, upon being notified by the squitter filter that a squitter preamble is present,

isolates the Mode-S signal in the memory/buffer wherein the Mode-S signal is retained until processing is completed,

directs the digital signal processing unit to adjust complex weights of all antenna element digital signals to maximize the signal-to-noise ratio of the isolated Mode-S signal, and

after the signal-to-noise ratio has been maximized, the controller unit directs the digital signal processing unit to output the Mode-S signal to the Mode-S receiver, and directs the memory/buffer to resume sequenced operation.

3. The Mode-S digital receiving system of claim 2, wherein:

a. the analog to digital (A/D) converter produces a pair of time offset digital signals for each signal;

b. a Hilbert Transform filter Hilbert transforms one of the pair of time offset digital signals to produce a quadrature I and Q sample pair which is directed as an input to the memory/ buffer.

4. The Mode-S digital receiving system of claim 1, wherein each Mode-S antenna element comprises a quarter wavelength, single element, stub antenna.

5. The Mode-S digital receiving system of claim 1, wherein in the signal processing receiver, each antenna element has associated therewith:

a. a preamplifier for amplifying an output of the antenna element;

b. a frequency down converter for frequency down converting an output of the preamplifier; and

c. a filter for filtering an output of the down converter to remove out of band signal energy, to produce a signal output.

6. The Mode-S digital receiving system of claim 2, wherein the memory/buffer comprises first and second cascaded memory/buffer units.

7. The Mode-S digital receiving system of claim 6, wherein the controller unit, upon being notified that the squitter preamble is present, isolates the Mode-S signal in the second memory/buffer unit.

8. The Mode-S digital receiving system of claim 1, wherein the squitter filter comprises a surface acoustic wave filter which constantly convolves a filtered output of an antenna element with a squitter preamble signature to determine the presence of the squitter preamble.

9. A method for receiving and processing Mode-S signals in an aircraft operating in a dense environment of aircraft comprising:

a. mounting a spatial array of Mode-S antenna elements on the aircraft;

b. producing and processing a separate signal for each separate antenna element;

c. converting the signals for the separate antenna elements to corresponding digital signals;

d. sequentially and periodically coupling at least one signals or digital signals from the separate antenna elements;

e. determining the presence of a squitter preamble in a Mode-S signal received by a receiving system;

f. in response to the determined presence of the Mode-S signal, processing and adjusting complex weights of the digital signals for the separate antenna element to maximize the signal-to-noise ratio of the received Mode-S signal;

g. processing and identifying technical data conveyed by the maximized signal-to-noise ratio Mode-S signal.

10. The method of claim 9, comprising:

a. storing the digital signals in sequence in a memory/buffer;

b. upon determining that presence of the squitter preamble,

isolating the Mode-S signal in the memory/buffer wherein the Mode-S signal is retained until processing is completed,

adjusting complex weights of all antenna element digital signals to maximize the signal-to-noise ratio of the isolated Mode-S signal, and

after the signal-to-noise ratio has been maximized, outputting the Mode-S signal, and resuming sequenced operation of the memory/buffer.

11. The method of claim 10, comprising:

a. producing a pair of time offset digital signals for each signal;

b. transforming one of the pair of time offset digital signals to produce a quadrature I and Q sample pair which is directed as an input to the memory/buffer.

12. The method of claim 9, comprising mounting a spatial array of quarter wavelength, single element, stub antennas.

13. The method of claim 9, comprising:

a. preamplifying an output of each antenna element;

b. frequency down converting an output of each preamplifier; and

c. filtering an output of each down converted output to remove out of band signal energy, to produce a signal output.

14. The method of claim 10, comprising providing first and second cascaded memory/buffer units, and upon being notified of the presence of the squitter preamble, isolating the Mode-S signal in the second memory/buffer unit.

15. The method of claim 9, comprising employing a surface acoustic wave filter which constantly convolves a filtered output of an antenna element with the squitter preamble signature to determine the presence of the squitter preamble.