Method and apparatus for implementing automatic tilt control of a radar antenna on an aircraft

• US 6,236,351 B1
• Filed: 07/06/1999
• Issued: 05/22/2001
• Est. Priority Date: 07/06/1998
• Status: Expired due to Term

• Current Assignee: Alliedsignal Inc. (Honeywell International Inc.)
• Original Assignee: Alliedsignal Inc. (Honeywell International Inc.)
• Inventors: Joyce, Jim, Hammack, Stephen D., Conner, Kevin J, Kuntman, Daryal, Morici, Martin M.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US09/348,648
• Time in Patent Office: 686 Days
• Field of Search: 342/26, 342/73, 342/74, 342/75, 342/76, 342/77, 342/78, 342/79, 342/80, 342/159, 342/160, 342/161, 342/162
• US Class Current: 342/26.00B
• CPC Class Codes: G01S 13/882 for altimeters measuring height using barometric means G01C5/06
• CPC Class Codes: G01S 13/933 of aircraft or spacecraft
• CPC Class Codes: G01S 13/953 mounted on aircraft
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00
• CPC Class Codes: H01Q 1/28 Adaptation for use in or on aircraft, missiles, satellites, or balloons
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A method and apparatus for automatically controlling the tilt of a radar antenna to avoid ground clutter returns while scanning the weather formations of most interest. In one embodiment a terrain database is utilized to determine tilt angles for different terrain cells. The tilt angle is determined starting at the aircraft position and working out to the radar range. If a tilt angle for a more distant cell is less than for a nearer cell it is ignored taking shadowing into account. In another embodiment the weighted tilt angle frequencies are entered into a histogram and the histogram is scanned to obtain a tilt angle resulting in an acceptable amount of ground clutter.

Claims

1. A method, performed on an aircraft, for automatically adjusting the tilt angle of a radar antenna to limit ground clutter to acceptable levels, with the radar antenna scanning a forward field of view within a specified range, said method comprising the steps of:

storing a terrain database including terrain cells identified by latitude and longitude intersections indexed by ilat and ilng values, with each terrain cell including a terrain elevation value;

determining current location co-ordinate indices of the aircraft;

for co-ordinates within the field of view and range, and based on the current location co-ordinate indices, determine minimum and maximum latitude and longitude index values;

setting ilat equal to the minimum latitude index and

setting ilng equal to the minimum longitude index;

(a) retrieving the terrain elevation at the co-ordinates specified by ilat and ilng from the terrain database;

(b) based on the terrain elevation and distance between the current location co-ordinates and the point (ilat, ilng) calculating an elevation angle between a horizontal along the flight path of the aircraft and the terrain elevation point;

(c) storing the calculated elevation angle;

if ilng is less than the maximum longitude co-ordinate incrementing ilng else;

if ilng is equal to the maximum longitude co-ordinate and ilat is less than the maximum latitude co-ordinate incrementing ilat and repeating steps (a), (b), and (c) else;

adjusting the antenna to have a tilt angle equal to the elevation angle.

2. A method, performed on an aircraft, for automatically adjusting the tilt angle of a radar antenna to limit ground clutter to acceptable percentage level, with the radar antenna scanning a forward field of view within a specified range, said method comprising the steps of:

storing a terrain database including terrain cells located at latitude and longitude intersections indexed by co-ordinate index values, with each terrain cell including a terrain elevation value;

determining current location co-ordinate indices of the aircraft;

breaking the field of view into segments of constant angular width;

for each segment, breaking the segment into spokes of constant angular width;

for co-ordinates within the spoke and range, and based on the current location co-ordinate indices, set cell co-ordinate index values to minimum co-ordinate index values;

(a) obtain terrain cell height from a terrain cell located at the cell co-ordinate index values;

(b) based on the terrain elevation and distance between the current location co-ordinates and cell co-ordinates calculating a calculated tilt angle between a horizontal along the flight path of the aircraft and the terrain cell;

(c) increase a frequency count of an index, with the index equal to the calculated tilt angle, in a histogram storing frequencies at indexes of tilt angles over a predetermined range;

(d) calculating new cell co-ordinates of a next cell stepped radially along the spoke and repeat steps (a), (b), and (c) out to a terrain cell at the specified range;

(e) scanning the histogram to determine a maximum tilt angle resulting in an acceptable percentage of ground clutter.

3. The method of claim 2 where said step of scanning further comprises the steps of:

weighting a frequency entry the area of a cell from which the tilt angle is measure;

summing all frequency values in the histogram to obtain a total weight;

sum frequencies for increasing elevation angles to obtain a running sum;

determining the maximum tilt angle where the running sum has a value equal to the acceptable percentage level of the total weight.

4. The method of claim 2 further comprising the steps of:

calculating a maximum tilt angle for a first sector of the display;

clearing the histogram prior to breaking up a second sector into angular spokes;

for angular spokes in the second sector, repeating steps (a)-(e).

5. The method of claim 2 where said step (b) of calculating a calculated tilt angle further comprises the step of:

setting the calculated tilt angle equal to an immediate previous calculated tilt angle if the calculated tilt angle points more downward than the immediate previous calculated tilt angle to take into account that nearer high terrain points shadow further low terrain points.

6. The method of claim 2 where said step (d) of calculating new co-ordinates further comprises the steps of:

selecting either a long range or short range, with the magnitude of the short range being less than the magnitude of the long range and with the magnitude of both the long and short range being less than or equal to the specified range;

for the selected range, terminating calculating calculated co-ordinates when a cell located at the calculated co-ordinates is outside a selected range.

7. A system, located on an aircraft, for adjusting the tilt angle of a weather radar antenna located on the aircraft, said system comprising:

a terrain awareness system storing a terrain database including terrain cells at latitude and longitude intersections indexed by co-ordinate index values, with each terrain cell including a terrain elevation value;

an antenna tilt control mechanism for controlling the tilt of the antenna;

a tilt control computer, including storage for storing program code and data;

a bus system coupling the tilt control computer, antenna tilt control mechanism, and tilt control computer;

with the tilt control computer executing program code to;

determine current location co-ordinate indices of the aircraft;

for co-ordinates within the field of view and range, and based on the current location co-ordinate indices, determine minimum and maximum latitude and longitude index values;

set ilat equal to the minimum latitude index and

set ilng equal to the minimum longitude index;

(a) retrieve the terrain elevation at the co-ordinates specified by ilat and ilng from the terrain database;

(b) based on the terrain elevation and distance between the current location co-ordinates and the point (ilat, ilng) calculate an elevation angle between a horizontal along the flight path of the aircraft and the terrain elevation point;

(c) store the calculated elevation angle;

if ilng is less than the maximum longitude co-ordinate increment ilng else;

if ilng is equal to the maximum longitude co-ordinate and ilat is less than the maximum latitude co-ordinate increment ilat and repeat steps (a), (b), and (c) else;

adjust the antenna to have a tilt angle equal to the elevation angle.

8. A method, performed on an aircraft, for automatically adjusting the tilt angle of a radar antenna to limit ground clutter to acceptable percentage level, with the radar antenna scanning a forward field of view within a specified range, said method comprising the steps of:

storing a terrain database including terrain cells located at latitude and longitude intersections indexed by co-ordinate index values, with each terrain cell including a terrain elevation value;

determining current location co-ordinate indices of the aircraft;

scanning the field of view and range, based on the current location, to determine frequencies of calculated tilt angles;

based on the frequencies and acceptable amount of clutter, determine a control tilt angle.

9. A method, performed on an aircraft, for automatically adjusting the tilt angle of a radar antenna to limit ground clutter to acceptable levels, with the radar antenna scanning a forward field of view within a specified range, said method comprising the steps of:

storing a terrain database including terrain cells identified by latitude and longitude intersections indexed by ilat and ilng values, with each terrain cell storing including a terrain elevation value;

determining current location co-ordinate indices of the aircraft;

for co-ordinates within the field of view and range, and based on the current location co-ordinate indices, determine minimum and maximum first and second co-ordinate index values;

setting the first co-ordinate index equal to the minimum first co-ordinate index and

setting the second co-ordinate index equal to the minimum second co-ordinate index;

(a) retrieving the terrain elevation at the co-ordinates specified by first and second co-ordinate indices from the terrain database;

(b) based on the terrain elevation and distance between the current location co-ordinates and the point specified by the co-ordinate indices calculating an elevation angle between a horizontal along the flight path of the aircraft and the terrain elevation point;

(c) storing the calculated elevation angle;

if ilng is less than the maximum longitude co-ordinate incrementing ilng else;

if the second co-ordinate index is less than the maximum second co-ordinate index increment the second co-ordinate index and else;

adjusting the antenna to have a tilt angle equal to the elevation angle.

10. A method, performed on an aircraft, for automatically adjusting the tilt angle of a radar antenna to limit ground clutter to acceptable levels, with the radar antenna scanning a forward field of view within a specified range, said method comprising the steps of:

storing a terrain database including terrain cells identified by latitude and longitude intersections indexed by ilat and ilng values, with each terrain cell storing including a terrain elevation value;

utilizing information in the terrain database to steer the radar antenna to avoid hilly terrain.

11. A device for automatically managing the tilt angle of an aircraft radar comprising:

a tilt angle controller having an input adapted to receive data indicative of a height above terrain; and

said tilt angle controller further including a signal processing device coupled to said input and to said output for outputting a radar tilt control signal according to a predetermined schedule of tilt angles as a function of said height above terrain.

17. The device of claim 11 wherein said tilt angle controller includes a second input adapted to receive signals indicative of a phase of aircraft flight and wherein said predetermined schedule further includes a schedule for defining tilt angles according to aircraft phase of flight.

12. A device for automatically managing the tilt angle of an aircraft radar comprising:

a tilt angle controller having an input adapted to receive information from a terrain data base and an output; and

said tilt angle controller further including a signal processing device coupled to said input and to said output for outputting a radar tilt control signal according to a predetermined logic defining tilt angle as a function of said information from said terrain data base.

13. The device of claim 12 wherein said tilt angle controller input is coupled to receive data from an EGPWS type terrain data base.

14. The device of claim 12 wherein said tilt angle controller includes a second input adapted to receive data indicative of an antenna parameter and wherein said predetermined logic accounts for said antenna parameter when defining tilt angle.

15. The device of claim 12 wherein said tilt angle controller further includes a second input adapted to receive data indicative of a position of the aircraft and wherein said predetermined logic defines said tilt angle as a function of the position of the aircraft relative to terrain.

16. A controller for automatically managing the tilt angle of an aircraft radar comprising:

an Enhanced Ground Proximity Warning System type device having an output adapted to assert signals useful for controlling a radar antenna and wherein said Enhanced Ground Proximity Warning System computes a radar tilt angle based upon a position of the aircraft relative to terrain.

18. A controller device for automatically managing the tilt angle of an aircraft radar comprising:

a tilt angle controller having an first input adapted to receive information from a terrain data base and a second input adapted to receive information indicative of an aircraft performance parameter, and an output; and

said tilt angle controller further including a signal processing device coupled to said first and to said second inputs and to said output for outputting a plurality of radar tilt control signals, each one of said plurality of radar tilt control signals to command a tilt angle for a given sector of radar sweep and wherein said signal processing device outputs said plurality of radar tilt control signals according to a predetermined logic defining tilt angle as a function of said information from said terrain data base and said information indicative of an aircraft performance parameter.

19. An aircraft radar apparatus comprising:

a radar receiver/transmitter unit having an input;

a terrain based ground proximity warning system having an output coupled to said input of said radar receiver/transmitter unit and wherein said warning system outputs a radar tilt value to said receiver/transmitter unit; and

said radar receiver/transmitter unite further including an output for outputting an automatic tilt control signal.

20. The radar apparatus of claim 19 further comprising:

a radar control panel coupled to said radar receiver/transmitter unit for toggling said radar receiver/transmitter between a first state wherein said automatic tilt control signal is enabled and a second state wherein said tilt control signal ins disabled.

21. The radar apparatus of claim 19 further comprising:

a radar control panel coupled to said terrain based ground proximity warning system for toggling said warning system between a first state wherein said system outputs said tilt angle and a second sate wherein said tilt angle is not output.

22. The radar apparatus of claim 19 further comprising:

a display, coupled to said receiver/transmitter unit.

23. The radar apparatus of claim 22 wherein said display is an EFIS type device.