Frequency agile radar system

Claim 3

A skin-tracking radar system which comprises transmitter means for generating illuminating pulses having different frequencies, receiver means for producing video signals representing echo returns from said illuminating pulses having different frequencies, antenna means for scanning a space stabilized volume at a large number of fixed points, said transmitter means and said receiver means being connected to said antenna means, beam sterring means connected to said antenna means for causing said antenna means to illuminate said fixed volume by steering a beam stepwise to said large number of beam positions, computer means for simultaneously controlling said transmitter means, said receiver means and said beam steering means for causing said transmitter means to generate said illuminating pulses at each of said beam positions before said steering means steers the beam to the next stepwise beam position, for periodically causing a small number of said beam positions which cover a target to be scanned by said illuminating pulses having different frequencies, for summing the amplitudes of all the echo returns at each of said small number of beam position and computing the location of a centralized point of the target cross section based upon the sums of said amplitudes.

Claim 4

A skin-tracking radar system which comprises transmitter means for generating illuminating pulses having different frequencies, receiver means for producing video signals representing echo returns from said illuminating pulses having different frequencies, antenna means for scanning a space stabilized volume at a large number of fixed points, said transmitter means and said receiver means being connected to said antenna means, beam sterring means connected to said antenna means for causing said antenna means to illuminate said fixed volume by steering a beam stepwise to said large number of beam positions, computer means for simultaneously controlling said transmitter means, said receiver means and said beam steering means for causing said transmitter means to generate said illuminating pulses at each of said beam positions before said steering means steers the beam to the next stepwise beam position, for periodically causing a small number of said beam positions which cover a target to be scanned by said illuminating pulses having different frequencies, for summing the amplitudes of all the echo returns at each of said small number of beam position and computing the location of a centralized point of the target cross section based upon the sums of said amplitudes.

Claim 5

A skin-tracking radar system as defined in claim 2 wherein the location of said centralized point is computed by equal area distribution of the area defined by the amplitude scans versus angle in both the azimuth and elevation planes.

Claim 6

A skin-tracking radar system which comprises transmitter means for generating illuminating pulses having different frequencies, receiver means for producing video signals representing echo returns from said illuminating pulses having different frequencies, antenna means for scanning a space stabilized volume at a large number of fixed points, said transmitter means and said receiver means being connected to said antenna means, beam steering means connected to said antenna means for causing said antenna means to illuminate said fixed volume by steering a beam stepwise to said large number of beam positions, computer means for simultaneously controlling said transmitter means, said receiver means and said beam steering means for periodically causing a small number of said beam positions which cover a target to be scanned by said illuminating pulses having different frequencies, for summing the amplitudes of all the echo returns at each of said small number of beam position and computing the location of a centralized point of the target cross section based upon the sums of said amplitudes, the location of said centralized point being computed by summing the products of the sums of columns of raster points and their corresponding azimuth angles referenced to a point within the raster and dividing the sums of such products by the sum of the column amplitudes to determine azimuth angular displacement of the centralized point from said point in the raster, and by summing the products of the sums of rows of raster points and their corresponding elevation angles referenced to said point within the raster and dividing the sums of such products by the sum of the row amplitude to determine angular displacement of the centralized point from said point in the raster.

Claim 7

A skin-tracking radar system which comprises transmitter means for generating illuminating pulses having different frequencies, receiver means for producing video signals representing echo returns from said illuminating pulses having different frequencies, antenna means for scanning a space stabilized volume at a large number of fixed points, said transmitter means and said receiver means being connected to said antenna means, beam steering means connected to said antenna means for causing said antenna means to illuminate said fixed volume by steering a beam stepwise to said large number of beam positions, computer means for simultaneously controlling said transmitter means, said receiver means and said beam steering means for periodically causing a small number of said beam positions which cover a target to be scanned by said illuminating pulses having different frequencies, for summing the amplitudes of all the echo returns at each of said small number of beam position and computing the location of a centralized point of the target cross section based upon the sums of said amplitudes, the location of said centralized point being computed by summing the products of the sums of columns of raster points and their corresponding azimuth angles referenced to a point within the raster and dividing the sums of such products by the sum of the column amplitudes to determine azimuth angular displacement of the centralized point from said point in the raster, and by summing the products of the sums of rows of raster points and their corresponding elevation angles referenced to said point within the raster and dividing the sums of such products by the sum of the row amplitude to determine angular displacement of the centralized point from said point in the raster.

Claim 8

A skin-tracking radar system as defined in claim 4 wherein said point in the raster is chosen closed to the predicted location of said centralized point.

Claim 9

A skin tracking radar system as defined in claim 2 wherein said antenna means illuminates said volume with a symmetrical pencil beam at each raster point.

Claim 10

A skin-tracking radar system as defined in claim 6 wherein said pencil beam is of 1° 3 dB beamwidth and said beam steering means steps said pencil beam in 1/2° steps.

Claim 11

A skin-tracking radar system as defined in claim 2 wherein said computer means controls said beam steering means to cover rasters of different sizes dependent upon predicted range of the target.

Claim 12

A skin-tracking radar system as defined in claim 8 wherein the raster size is four beam positions for predicted ranges greater than a predetermined range and is stepwise increased in size at predicted ranges less than said predetermined range.

Claim 13

A skin-tracking radar system as defined in claim 9 wherein each target scan is effected in a fixed time which is sufficiently short to assure that the target is essentially frozen in position during each scan.

Claim 14

A skin-tracking radar system as defined in claim 10 wherein each target scan time is about ten milliseconds.

Claim 15

A skin-tracking radar system as defined in claim 2 wherein said antenna means is fixed to an aircraft carrier and including means for sensing motions of the carrier in six degrees of freedom, said computer means being connected to said means for sensing for controlling said beam steering means to maintain the space stabilization of said beam positions.

Claim 16

A skin-tracking radar system as defined in claim 1 including data transmitter means for controlling an aircraft autopilot to fly an aircraft to and along a selected landing path onto the aircraft carrier.

Claim 17

A skin-tracking radar system as defined in claim 12 wherein the location of said centralized point is computed by equal area distribution of the area defined by the amplitude scans versus angle in both the azimuth and elevation planes.

Claim 18

A skin-tracking radar system as defined in claim 13 wherein the location of said centralized point is computed by equal area distribution of the area defined by the amplitude scans versus angle in both the azimuth and elevation planes.

Claim 19

A skin-tracking radar system which comprises transmitter means for generating illuminating pulses having different frequencies, receiver means for producing video signals representing echo returns from said illuminating pulses having different frequencies, antenna means for scanning a space stabilized volume at a large number of fixed points, said transmitter means and said receiver means being connected to said antenna means, beam steering means connected to said antenna means for causing said antenna means to illuminate said fixed volume by steering a beam stepwise to said large number of beam positions, computer means for simultaneously controlling said transmitter means, said receiver means and said beam steering means for periodically causing a small number of said beam positions which cover a target to be scanned by said illuminating pulses having different frequencies, for summing the amplitudes of all the echo returns at each of said small number of beam position and computing the location of a centralized point of the target cross section based upon the sums of said amplitudes, said antenna means being fixed to an aircraft carrier and including means for sensing motions of the carrier in six degrees of freedom, said computer means being connected to said means for sensing for controlling said beam steering means to maintain the space stabilization of said beam positions the location of said centralized point being computed by summing the products of the sums of columns of raster points and their corresponding azimuth angles references to a point within the raster and dividing the sums of such products by the sum of the column amplitudes to determine azimuth angular displacement of the centralized point from said point in the raster, and by summing the products of the sums of rows of raster points and their corresponding elevation angles referenced to said point within the raster and dividing the sums of such products by the sum of the row amplitude to determine angular displacement of the centralized point from said point within the raster.

Claim 20

A skin-tracking radar system which comprises transmitter means for generating illuminating pulses having different frequencies, receiver means for producing video signals representing echo returns from said illuminating pulses having different frequencies, antenna means for scanning a space stabilized volume at a large number of fixed points, said transmitter means and said receiver means being connected to said antenna means, beam steering means connected to said antenna means for causing said antenna means to illuminate said fixed volume by steering a beam stepwise to said large number of beam positions, computer means for simultaneously controlling said transmitter means, said receiver means and said beam steering means for periodically causing a small number of said beam positions which cover a target to be scanned by said illuminating pulses having different frequencies, for summing the amplitudes of all the echo returns at each of said small number of beam position and computing the location of a centralized point of the target cross section based upon the sums of said amplitudes, said antenna means being fixed to an aircraft carrier and including means for sensing motions of the carrier in six degrees of freedom, said computer means being connected to said means for sensing for controlling said beam steering means to maintain the space stabilization of said beam positions the location of said centralized point being computed by summing the products of the sums of columns of raster points and their corresponding azimuth angles references to a point within the raster and dividing the sums of such products by the sum of the column amplitudes to determine azimuth angular displacement of the centralized point from said point in the raster, and by summing the products of the sums of rows of raster points and their corresponding elevation angles referenced to said point within the raster and dividing the sums of such products by the sum of the row amplitude to determine angular displacement of the centralized point from said point within the raster.

Claim 21

A skin-tracking radar system which comprises transmitter means for generating illuminating pulses having different frequencies, receiver means for producing video signals representing echo returns from said illuminating pulses having different frequencies, antenna means for scanning a space stabilized volume at a large number of fixed points, said transmitter means and said receiver means being connected to said antenna means, beam steering means connected to said antenna means for causing said antenna means to illuminate said fixed volume by steering a beam stepwise to said large number of beam positions, computer means for simultaneously controlling said transmitter means, said receiver means and said beam steering means for periodically causing a small number of said beam positions which cover a target to be scanned by said illuminating pulses having different frequencies, for summing the amplitudes of all the echo returns at each of said small number of beam position and computing the location of a centralized point of the target cross section based upon the sums of said amplitudes, data transmitter means for controlling an aircraft autopilot to fly an aircraft to and along a selected landing path onto the aircraft carrier, the location of said centralized point being computed by summing the products of the sums of columns of raster points and their corresponding azimuth angles referenced to a point within the raster and dividing the sums of such products by the sum of the column amplitudes to determine azimuth angular displacement of the centralized point from said point in the raster, and by summing the products of the sums of rows of raster points and their corresponding elevation angles referenced to said point within the raster and dividing the sums of such products by the sum of the row amplitude to determine angular displacement of the centralized point from said point in the raster.

Claim 22

A skin-tracking radar system which comprises transmitter means for generating illuminating pulses having different frequencies, receiver means for producing video signals representing echo returns from said illuminating pulses having different frequencies, antenna means for scanning a space stabilized volume at a large number of fixed points, said transmitter means and said receiver means being connected to said antenna means, beam steering means connected to said antenna means for causing said antenna means to illuminate said fixed volume by steering a beam stepwise to said large number of beam positions, computer means for simultaneously controlling said transmitter means, said receiver means and said beam steering means for periodically causing a small number of said beam positions which cover a target to be scanned by said illuminating pulses having different frequencies, for summing the amplitudes of all the echo returns at each of said small number of beam position and computing the location of a centralized point of the target cross section based upon the sums of said amplitudes, data transmitter means for controlling an aircraft autopilot to fly an aircraft to and along a selected landing path onto the aircraft carrier, the location of said centralized point being computed by summing the products of the sums of columns of raster points and their corresponding azimuth angles referenced to a point within the raster and dividing the sums of such products by the sum of the column amplitudes to determine azimuth angular displacement of the centralized point from said point in the raster, and by summing the products of the sums of rows of raster points and their corresponding elevation angles referenced to said point within the raster and dividing the sums of such products by the sum of the row amplitude to determine angular displacement of the centralized point from said point in the raster.

Claim 23

A skin-tracking radar system as defined in claim 16 wherein said point in the raster is chosen close to the predicted location of said centralized point.

Claim 24

A skin-tracking radar system as defined in claim 17 wherein said point in the raster is chosen close to the predicted location of said centralized point.

Claim 25

A skin-tracking radar system as defined in claim 12 wherein said antenna means illuminates said volume with a symmetrical pencil beam at each raster point.

Claim 26

A skin-tracking radar system as defined in claim 13 wherein said antenna means illuminates said volume with a symmetrical pencil beam at each raster point.

Claim 27

A skin-tracking radar system as defined in claim 20 wherein said pencil beam is of 1° 3 dB beamwidth and said beam steering means steps said pencil beam in 1/2° steps.

Claim 28

A skin-tracking radar system as defined in claim 21 wherein said pencil beam is of 1° 3 dB beamwidth and said beam steering means steps said pencil beam in 1/2° steps.

Claim 29

A skin-tracking radar system as defined in claim 12 wherein said computer means controls said beam steering means to cover rasters of different sizes dependent upon predicted range of the target.

Claim 30

A skin-tracking radar system as defined in claim 13 wherein said computer means controls said beam steering means to cover rasters of different sizes dependent upon predicted range of the target.

Claim 31

A skin-tracking radar system as defined in claim 24 wherein the raster size is four beam positions for predicted ranges greater than a predetermined range and is stepwise increased in size at predicted ranges less than said predetermined range.

Claim 32

A skin-tracking radar system as defined in claim 25 wherein the raster size is four beam positions for predicted ranges greater than a predetermined range and is stepwise increased in size at predicted ranges less than said predetermined range.

Claim 33

A skin-tracking radar system as defined in claim 26 wherein each target scan is effected in a fixed time which is sufficiently short to assure that the target is essentially frozen in position during each scan.

Claim 34

A skin-tracking radar system as defined in claim 27 wherein each target scan is effected in a fixed time which is sufficiently short to assure that the target is essentially frozen in position during each scan.

Claim 35

A skin-tracking radar system as defined in claim 28 wherein each target scan time is about ten milliseconds.

Claim 36

A skin-tracking radar system as defined in claim 29 wherein each target scan time is about ten millisecond.

Claim 37

A skin-tracking radar system as defined in claim 2 wherein said antenna means is an electronically steered planar phased array.

Claim 38

A skin-tracking radar system as defined in claim 32 wherein said planar phased array comprises a plurality of side-by-side vertical columns of subarrays.

Claim 39

A skin-tracking radar system as defined in claim 33 wherein each subarray comprises an integrated module comprising groups of E plane sectoral horns, each group having a body mounting its horns and containing a 4-bit phase shifter for each horn and a power divider for feeding the plane shifters of all of its horns, and each module including a power divider joining the bodies of the groups of horns and coaxially feeding the power dividers in such bodies.

Claim 42

The method as defined in claim 35 wherein said small number of beam positions is four.

Claim 45

having a finite number of overlapping interrogating areas, the area covered by the interrogating beam at each interrogating area being greater than the radar cross-sectional area of a potential target entering the window; b. interrogating each interrogating area with a number of pulses of diverse frequencies to minimize target scintillation and at a transmission prf of such number of pulses sufficient to freeze a potential target; c. detecting a target; d. interrogating a plurality of adjacent interrogating areas which bracket the detected target at said transmission prf during subsequent scans, and in superimposed relation thereto, until the range of the detected target has decreased so that the plurality of adjacent interrogating areas are insufficient to encompass the radar cross-sectional area of the detected target; and then e. increasing the number of interrogating areas to encompass the radar cross-sectional area of the detected target and interrogating each such increased number of interrogating areas during subsequent scans, and in superimposed relation thereto, with a small number of frequency diversity pulses, less than the number of pulses of step b, at a transmission prf sufficient to freeze the detected target but decreased relative to the transmission prf of step d by said small number; the interrogations during steps d and e including computation of the actual position of the detected target from the frequency diverse echo returns from the detected target at each of the target interrogating areas.

Claim 46

having a finite number of overlapping interrogating areas, the area covered by the interrogating beam at each interrogating area being greater than the radar cross-sectional area of a potential target entering the window; b. interrogating each interrogating area with a number of pulses of diverse frequencies to minimize target scintillation and at a transmission prf of such number of pulses sufficient to freeze a potential target; c. detecting a target; d. interrogating a plurality of adjacent interrogating areas which bracket the detected target at said transmission prf during subsequent scans, and in superimposed relation thereto, until the range of the detected target has decreased so that the plurality of adjacent interrogating areas are insufficient to encompass the radar cross-sectional area of the detected target; and then e. increasing the number of interrogating areas to encompass the radar cross-sectional area of the detected target and interrogating each such increased number of interrogating areas during subsequent scans, and in superimposed relation thereto, with a small number of frequency diversity pulses, less than the number of pulses of step b, at a transmission prf sufficient to freeze the detected target but decreased relative to the transmission prf of step d by said small number; the interrogations during steps d and e including computation of the actual position of the detected target from the frequency diverse echo returns from the detected target at each of the target interrogating areas.

Claim 47

The method as defined in claim 37 wherein the plurality of bracketing interrogating pulses of step d is at least three.

Claim 48

The method as defined in claim 38 wherein the increased number of interrogating areas of step e is six.

Claim 49

The method as defined in claim 39 wherein the number of interrogating areas of step e is progressively increased as an inverse function of range.

Claim 50

The method as defined in claim 37 wherein the number of interrogating areas of step e is progressively increased as an inverse function of range.

Claim 51

In a method of skin tracking a radar target, the steps of: a. repetitively scanning a large raster of beam positions by steering an illuminating beam stepwise to point the beam successively through a fixed sequence cf the large raster of beam positions; b. transmitting rf energy at a number of different frequencies at each beam position to cover a large band of frequencies before steering the beam stepwise to the next position in the fixed sequence of the large raster of beam positions; and c. acquiring a target and then altering the scanning of step a s1teer the beam positions successively through a small raster of beam positions comprising at least three overlapping beam positions which bracket the acquired target before steering the beam stepwise to said next position while continuing transmission as in step b to cover a large band of frequencies at each beam position of the small raster of beam positions.

Claim 52

In a method of skin tracking a radar target, the steps of: a. repetitively scanning a large raster of beam positions by steering an illuminating beam stepwise to point the beam successively through a fixed sequence cf the large raster of beam positions; b. transmitting rf energy at a number of different frequencies at each beam position to cover a large band of frequencies before steering the beam stepwise to the next position in the fixed sequence of the large raster of beam positions; and c. acquiring a target and then altering the scanning of step a s1teer the beam positions successively through a small raster of beam positions comprising at least three overlapping beam positions which bracket the acquired target before steering the beam stepwise to said next position while continuing transmission as in step b to cover a large band of frequencies at each beam position of the small raster of beam positions.

Claim 53

In the method defined in claim 42 wherein said three adjacent, overlapping beam positions encompass two beam positions separated one half beamwidth in azimuth and one beam position separated one half beamwidth in elevation from the two beam positions.

Claim 54

In the method defined in claim 42 including the step of stepwise increasing the number of overlapping beam positions of step c as a function of inverse range to the acquired target.

Claim 55

In the method as defined in claim 44 wherein the stepwise increase in the number of beam positions of step c is accompanied by transmitting the rf energy as a number of chirps cumulatively covering the large band of frequencies.

Claim 56

In the method as defined in claim 45 wherein the transmissions of steps b and c are at a large number of discrete frequencies prior to the stepwise increase in the number of beam positions.

Claim 57

In an automatic landing system for aircraft, the combination of: a planar, phased array antenna oapable of producing a pencil beam which may be steered; steering means for causing said antenna repetitively to point its beam stepwise successively through a fixed sequence of a raster of beam positions; transmitter means for causing the antenna to transmit rf energy at a plurality of different frequencies covering a large frequency band at each beam position before the beam is steered stepwise to a next position; means for detecting and acquiring a target and for determining its range; means responsive to target acquisition and connected to said steering means for steering the beam successively through at least three overlapping beam positions which bracket the acquired target before steering the beam stepwise to a next position in the fixed sequence of the raster of beam positions; and means for receiving target echos over said frequency band from the overlapping beam positions and for tracking the target with minimal error due to target scintillation from such echos.

Claim 58

In an automatic landing system for aircraft, the combination of: a planar, phased array antenna oapable of producing a pencil beam which may be steered; steering means for causing said antenna repetitively to point its beam stepwise successively through a fixed sequence of a raster of beam positions; transmitter means for causing the antenna to transmit rf energy at a plurality of different frequencies covering a large frequency band at each beam position before the beam is steered stepwise to a next position; means for detecting and acquiring a target and for determining its range; means responsive to target acquisition and connected to said steering means for steering the beam successively through at least three overlapping beam positions which bracket the acquired target before steering the beam stepwise to a next position in the fixed sequence of the raster of beam positions; and means for receiving target echos over said frequency band from the overlapping beam positions and for tracking the target with minimal error due to target scintillation from such echos.

Claim 59

In an automatic landing system for aircraft as defined in claim 47 wherein said means responsive to target acquisition causes the steering means to steer the beam successively through increasing numbers of overlapping beam positions as a function of target range and correspondingly to alter the prf of the transmitter means.

Claim 60

In an automatic landing system for aircraft, the combination of: a planar, phased array antenna capable of producing a pencil beam which may be steered; steering means for causing said antenna repetitively to point its beam stepwise successively through a fixed sequence of a large raster of beam positions; transmitter means for causing the antenna to transmit rf energy at a plurality of different frequencies covering a large frequency band at each of the beam positions to which the antenna means is pointed before the beam is steered stepwise to point to a next position in the large raster of beam positions; means for detecting and acquiring a plurality of targets and for determining their positions relative to the antenna means; means responsive to target acquisition and connected to said steering means for steering the beam successively through a small raster of beam positions, which may vary in size to cover an acquired target, before steering the beam stepwise to a next position in the fixed sequence of the large raster of beam positions; and means for receiving target echos from each small raster of beam target scintillation from such echos; said means responsive to target acquisition causing the steering means to adjust the size of each small raster of beam positions as an inverse function of range to the target in question and correspondingly to control the prf of the transmitter means during transmission over each small raster of beam positions.

Claim 61

In an automatic landing system for aircraft, the combination of: a planar, phased array antenna capable of producing a pencil beam which may be steered; steering means for causing said antenna repetitively to point its beam stepwise successively through a fixed sequence of a large raster of beam positions; transmitter means for causing the antenna to transmit rf energy at a plurality of different frequencies covering a large frequency band at each of the beam positions to which the antenna means is pointed before the beam is steered stepwise to point to a next position in the large raster of beam positions; means for detecting and acquiring a plurality of targets and for determining their positions relative to the antenna means; means responsive to target acquisition and connected to said steering means for steering the beam successively through a small raster of beam positions, which may vary in size to cover an acquired target, before steering the beam stepwise to a next position in the fixed sequence of the large raster of beam positions; and means for receiving target echos from each small raster of beam target scintillation from such echos; said means responsive to target acquisition causing the steering means to adjust the size of each small raster of beam positions as an inverse function of range to the target in question and correspondingly to control the prf of the transmitter means during transmission over each small raster of beam positions.

Claim 62

In an automatic landing system for aircraft as defined in claim 49 wherein said means responsive to target acquisition also controls said steering means to scan the small rasters of beam positions at different rates based upon the ranges of the acquired targets.

Claim 63

In an automatic landing system for aircraft, the combination of: a planar, phased array antenna capable of producing a pencil beam which may be steered; steering means for causing said antenna repetitively to point its beam stepwise successively through a fixed sequence of a large raster of beam positions; transmitter means for causing the antenna to transmit rf energy at a plurality of different frequencies covering a large frequency band at each of the beam positions to which the antenna means is pointed before the beam is steered stepwise to point to a next position in the large raster of beam positions; means for detecting and acquiring a target and for determining position relative to the antenna means; means responsive to target acquisition and connected to said steering means for steering the beam successively through a small raster of beam positions covering an acquired target before steering the beam stepwise to a next position in the fixed sequence of the large raster of beam positions; and means for receiving target echos over said frequency band from each small raster of beam positions and for tracking the acquired target from successive scans of the small raster of beam positions with minimal error due to target scintillation from such echos; said means responsive to target acquisition causing the steering means to adjust the size and the location of the small raster of beam positions within the large raster of beam positions from successive large raster scans and as an inverse function of range to the target in question and correspondingly to control the prf of the transmitter means during transmission over each small raster of beam positions.

Claim 64

In an automatic landing system for aircraft, the combination of: a planar, phased array antenna capable of producing a pencil beam which may be steered; steering means for causing said antenna repetitively to point its beam stepwise successively through a fixed sequence of a large raster of beam positions; transmitter means for causing the antenna to transmit rf energy at a plurality of different frequencies covering a large frequency band at each of the beam positions to which the antenna means is pointed before the beam is steered stepwise to point to a next position in the large raster of beam positions; means for detecting and acquiring a target and for determining position relative to the antenna means; means responsive to target acquisition and connected to said steering means for steering the beam successively through a small raster of beam positions covering an acquired target before steering the beam stepwise to a next position in the fixed sequence of the large raster of beam positions; and means for receiving target echos over said frequency band from each small raster of beam positions and for tracking the acquired target from successive scans of the small raster of beam positions with minimal error due to target scintillation from such echos; said means responsive to target acquisition causing the steering means to adjust the size and the location of the small raster of beam positions within the large raster of beam positions from successive large raster scans and as an inverse function of range to the target in question and correspondingly to control the prf of the transmitter means during transmission over each small raster of beam positions.

Claim 65

In the method of automatically landing aircraft by skin tracking aircraft targets, the steps of: a. repetitively scanning a large raster of beam positions defining an acquisition window by steering an illuminating beam stepwise to point the beam successively through a fixed sequence of the large raster of beam positions; b. transmitting rf energy at a number of different frequencies at each beam position to cover a large band of frequencies before steering the beam stepwise to the next position in the fixed sequence of the large raster of beam positions; and c. acquiring a target aircraft and, in response thereto, superimposing target scans, each covering a small number of beam positions which overpaint the target aircraft, upon the repetitive scanning of step a so as to complete a target scan before steering the beam stepwise to said next position in the fixed sequence of the large raster while continuing transmission as in step b to cover a large band of frequencies at each beam position of the target scan.

Claim 66

In the method of automatically landing aircraft by skin tracking aircraft targets, the steps of: a. repetitively scanning a large raster of beam positions defining an acquisition window by steering an illuminating beam stepwise to point the beam successively through a fixed sequence of the large raster of beam positions; b. transmitting rf energy at a number of different frequencies at each beam position to cover a large band of frequencies before steering the beam stepwise to the next position in the fixed sequence of the large raster of beam positions; and c. acquiring a target aircraft and, in response thereto, superimposing target scans, each covering a small number of beam positions which overpaint the target aircraft, upon the repetitive scanning of step a so as to complete a target scan before steering the beam stepwise to said next position in the fixed sequence of the large raster while continuing transmission as in step b to cover a large band of frequencies at each beam position of the target scan.

Claim 67

In the method as defined in claim 52 wherein the small number of beam positions of a target scan is periodically increased as an inverse function of range to the target aircraft.

Claim 68

In the method as defined in claim 53 including the step of acquiring a plurality of target aircraft and superimposing target scans for each of the acquired aircraft targets as in step c.

Claim 69

In the method as defined in claim 54 wherein the frequency of target scans for each acquired aircraft target is periodically increased as an inverse function of range to the aircraft target in question.