EP2962123A2 - Apparatus and method for assisting vertical takeoff vehicles - Google Patents
Apparatus and method for assisting vertical takeoff vehiclesInfo
- Publication number
- EP2962123A2 EP2962123A2 EP13876483.2A EP13876483A EP2962123A2 EP 2962123 A2 EP2962123 A2 EP 2962123A2 EP 13876483 A EP13876483 A EP 13876483A EP 2962123 A2 EP2962123 A2 EP 2962123A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- ranging system
- receiver
- transmitter
- radar ranging
- beams
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/003—Bistatic radar systems; Multistatic radar systems
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/08—Systems for measuring distance only
- G01S13/32—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
- G01S13/325—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of coded signals, e.g. P.S.K. signals
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/882—Radar or analogous systems specially adapted for specific applications for altimeters
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/93—Radar or analogous systems specially adapted for specific applications for anti-collision purposes
- G01S13/933—Radar or analogous systems specially adapted for specific applications for anti-collision purposes of aircraft or spacecraft
- G01S13/935—Radar or analogous systems specially adapted for specific applications for anti-collision purposes of aircraft or spacecraft for terrain-avoidance
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S2013/0236—Special technical features
- G01S2013/0245—Radar with phased array antenna
- G01S2013/0254—Active array antenna
Definitions
- the present application relates to apparatus and methods for assisting operators of vertical takeoff vehicles in landing operations within environments of low visual acuity.
- the present application relates to a radar altimeter for assisting in landing operations of vertical takeoff vehicles.
- the basic radar altimeter utilizes a radar ranging system which measures the time delay of the signal reflected from the nearest object within a single wide beam illuminating the ground. This wide -beam is intended to monitor aircraft height even when in a bank or flying near steep slopes.
- US Patent No. 5,047,779 to Hager which is capable of tracking at least two targets.
- the altimeter of Hager information relating to the first target is captured via a first set of radar antennas and stored before the altimeter switches to a track and store information of the second target via a second set of radar antennas.
- US Patent No. 6,750,807 also to Hager et al., describes a similar scheme, but with a forward-looking scanning beam for obstacle warning. Both arrangements proposed in Hager patents simply provide range information to both targets and as such are generally useful in assisting a pilot with obstacle avoidance in flight. Neither of the altimeter Hager patents is capable of providing the pilot of any useful information regarding the tomography of the desired landing surface.
- a radar ranging system for imaging the topography of an area of interest; said system comprising at least one linear arrays of, for instance, 32 transmitter elements that transmit transmitter beams comprising a sequence of ranging signals phased to form a beam pattern covering part of the area of interest, the sequence phased to scan the beam pattern over an entire area of interest, at least one linear array of, for instance, 32 receiver elements arranged orthogonally to the transmitter linear arrays, e.g., as shown in FIG.
- each receiver element receives a time sequence of the ranging signals reflected from variations on the ground as illuminated by the sequence of the ranging signals, the receiver elements each producing a receiver signal; and at least one processor adapted to process each receiver signal, wherein the at least one processor forms a multiplicity of receiver beams complementary to the transmitter beams such that the combination of the transmitter beams and the receiver beams form pencil beams which cover the entire area of interest in time sequence, wherein the at least one processor measures a time delay of a first reflection received in each of the formed pencil beams and converts the time delay into a range measure at each beam angle to form a topographic profile of the area of interest in range and beam angle coordinates.
- the at least one transmitter array may comprise two parallel transmitter sub-arrays of, for instance, 16 elements each operating at about 35 GHz and the at least one linear array of receiver elements may comprise two parallel receiver sub-arrays of 16 elements each.
- the spacing between the two parallel receiver sub-arrays should be equal to the length of each transmitter sub-array; likewise the spacing between the two parallel transmitter sub-arrays should be equal to the length of each receiver sub-array.
- the two pairs can be separated, such as shown, e.g., in FIG. 2E, or they can be in the form of a perimeter array, such as shown, e.g., in FIG. 2C, for a more compact arrangement.
- a time delay on the first return in each beam may be captured and scaled to a range measurement.
- the shortest range measured by all the beams may be displayed numerically as radar altitude.
- the processor may be configured to process the topographic profile to display an image of the terrain topography in the area of interest and/or the processor may be configured to process the topographic profile in the area of interest to determine if the area of interest is safe for landing an aircraft.
- the processor may be configured to provide a warning signal if a hazard is present and configured to show a hazard and/or a safe area on a display.
- the display of the topographic profile may include a color display, a contour display, or a mesh plot display.
- the display may be referenced to a vertical coordinate system and/or may be referenced to a coordinate system of a platform employing the imaging system. Moreover, the display may be presented as an artificial perspective of the ground as viewed looking forward from an aircraft platform.
- the topographic profile may be compared with a threshold value denoting the slope, a level clearance, and a flatness according to pre-specified data to safely land an airborne vehicle within the area of interest and display suitable and unsuitable areas to an operator of the airborne vehicle.
- the processor may be adapted to compare the topographic profile with pre-specified profiles needed for safe rotor and tail rotor clearance on approach to the area of interest and display suitable and unsuitable areas for landing.
- the signal processor may form a guard channel to mitigate the effect of sidelobe leakage. This sets a detection threshold for all beams to ensure the signal detected in any beam has not entered through the sidelobes of its directional pattern. For this, for any one beam, the signal processor may weight the signals from all other beams according to the sidelobe pattern of the one beam and set the detection threshold above this by a suitable margin.
- the processor may perform the Clean Algorithm on the data streams from all the beams to mitigate any effects caused by sidelobe leakage.
- This algorithm may sequentially subtract small proportions of the currently strongest beam signal from the signals in other beams, until the cross correlation, and hence the leakage, between signals from all the beams is minimized.
- the radar ranging system may be mounted to look down, to assist operators make a vertical landing.
- the radar ranging system may be mounted to include a suitable forward look in the area of interest, to assist operators making a forward approach to the landing zone.
- FIG. 1 is a schematic diagram of a radar system according to principles of the invention
- FIG. 2A is a schematic diagram of an open array arrangement antenna which may be used in a radar altimeter, according to principles of the invention
- FIG. 2B is a schematic diagram of a T-shaped open antenna array which may be used in a radar altimeter, configured according to principles of the invention
- FIG. 2C is a schematic diagram of a perimeter antenna array which may be used in a radar altimeter, configured according to principles of the invention
- FIG. 2D is a schematic diagram of a spaced-apart T-shaped open antenna array which may be used in a radar altimeter, configured according to principles of the invention
- FIG. 2E is a schematic diagram of an antenna array showing sub-arrays arranged to form a generally parallel Tx and Rx pairs, with one pair adjacent to and spaced apart from the other pair, to form displaced pairs, configured according to principles of the invention;
- FIG. 3 is a schematic diagram depicting landing area surveying operation performed by a radar altimeter, according to principles of the invention.
- FIG. 4 is a schematic diagram of an alternative arrangement of the at least one transmitter array and at least one receiver array forming a compact two dimensional array, according to principles of the invention.
- a "processor”, as used in this disclosure, means any machine, device, circuit, component, or module, or any system of machines, devices, circuits, components, modules, or the like, which are capable of manipulating data according to one or more instructions, such as, for example, without limitation, a computer, a
- microprocessor a central processing unit, a general purpose computer, a super computer, a personal computer, a laptop computer, a palmtop computer, a notebook computer, a desktop computer, a workstation computer, a server, or the like, or an array of processors, microprocessors, central processing units, general purpose computers, super computers, personal computers, laptop computers, palmtop computers, notebook computers, desktop computers, workstation computers, servers, or the like.
- Devices that are in communication with each other need not be in continuous communication with each other, unless expressly specified otherwise.
- devices that are in communication with each other may communicate directly or indirectly through one or more intermediaries.
- a "computer-readable medium”, as used in this disclosure, means any medium that participates in providing data (for example, instructions) which may be read by a computer. Such a medium may take many forms, including non-volatile media, volatile media, and transmission media. Non-volatile media may include, for example, optical or magnetic disks and other persistent memory. Volatile media may include dynamic random access memory (DRAM). Transmission media may include coaxial cables, copper wire and fiber optics, including the wires that comprise a system bus coupled to the processor. Transmission media may include or convey acoustic waves, light waves and electromagnetic emissions, such as those generated during radio frequency (RF) and infrared (IR) data communications.
- RF radio frequency
- IR infrared
- Computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EEPROM, any other memory chip or cartridge, or any other medium from which a computer can read.
- a computer program product may be provided that stores software configured to, when read and executed by a processor, perform one or more steps of the processes described herein.
- sequences of instruction may be delivered from a RAM to a processor, (ii) may be carried over a wireless transmission medium, and/or (iii) may be formatted according to numerous formats, standards or protocols, including, for example, WiFi, WiMAX, IEEE 802.1 1, DECT, 0G, 1G, 2G, 3G or 4G cellular standards, Bluetooth, or the like.
- MIMO Multiple Input Multiple Output
- the MIMO technique makes use of the fact that the signal received from the far field with a bi-static transmitter receiver pair is identical to the signal which would be received by a single mono-static transmit/receive element placed at the mid point between the bi-static pair.
- the image computation can be based on the geometry arising from a notional plurality of transient elements.
- the technique can also be used for signals from the nearer field, but additional processing by, e.g., a computer or processor, is required to account for an ellipsoidal co-phase surface with the bi-static elements at the foci. In the far field this ellipsoid tends to a spherical surface centered on a synthetic element at the mid-point.
- each receiver element is able to separate the return signals in order to match them to the corresponding signals transmitted from each transmitter element (i.e. a form of multi-static processing within the array itself).
- a number of beams equal to the product of the transmitter and receiver element numbers NxM.
- this may be achieved by transmitting from each element in turn (time division multiplexing), or by simultaneously transmitting separable code sequences from each element (code division
- FIG. 1 illustrates the concept of synthesizing multiple beams under the MIMO technique.
- the coding scheme is modulated onto a carrier 101 by encoders 102a, 102b,..., 102M via mixers 103a, 103b,..., 103M to produce a set of M discrete coded signal, before being transmitted toward the area of interest 105 from transmitting elements 104a, 104b,..., 104M.
- a set of reflected encoded signals is received by each receiver element 106a, 106b,..., 106N, i.e., each receiver element captures reflected signals corresponding to the transmitted signals from each of the transmitter elements Txl, Tx2,..., TxM.
- the received encoded signals are then decoded by applying a decode signal 107a, 107b,..., 107M to each of the received signals captured ([Rxl l, Rxl2,..., RxlM], [Rx21, Rx22,..., Rx2M], [RxNl, RxN2,..., RxNM]) by each of the receiver 106a, 106b,..., 106N via banks of mixers 108a, 108b,..., 108N.
- the proposed radar altimeter utilizes a downward looking MIMO phased array to form multiple beams, covering a relatively wide sector, +/- 60 degrees or thereabouts. The distance to the ground is then measured in each beam allowing the ground profile to be formed. The beams may be tilted forward to cover from +90 degrees forward (horizontal) to 30 degrees behind nadir. The provision of such a forward tilt gives a greater degree of coverage in the direction of approach vector to the ground. This additional cover enables the altimeter to more accurately detect other vehicles in the proximity to the current approach vector of the vehicle to the desired landing zone.
- a downward looking MIMO phased array to form multiple beams, covering a relatively wide sector, +/- 60 degrees or thereabouts.
- the distance to the ground is then measured in each beam allowing the ground profile to be formed.
- the beams may be tilted forward to cover from +90 degrees forward (horizontal) to 30 degrees behind nadir.
- the provision of such a forward tilt gives a greater degree of coverage in the direction of
- FIG. 2A depicts an open array 200 arrangement which is formed from two sub-arrays 201a, 201b, one a transmitter array and one receiver array arranged substantially orthogonal to one another such that they form an L shape.
- An alternative open array construction 200 is shown in FIG. 2B in this case the sub- arrays 201a, 201b have been arranged to form a T shape. Again, the sub-arrays 201a, 201b are aligned substantially orthogonal to one another.
- FIG. 2D is similar to FIG. 2B in this case the sub-arrays 201a, 201b have been arranged to form a generally T shape.
- Sub-array 201a is shown as 16 transmitters and sub-array 201b is shown as 16 receivers, with the arrays spaced apart.
- FIG. 2E shows a broken-square format. In the case of FIG. 2E, the sub-arrays 201a, 201b have been arranged to form a generally parallel Tx and Rx pairs, with one pair adjacent to and spaced apart from the other pair, to form displaced pairs.
- FIG. 2C depicts one possible configuration of a closed array 200 which is referred to as perimeter array.
- the array includes 32 transmitter elements and 32 receiver elements arranged into four sub-arrays.
- Two transmitter sub-arrays 201a, 201a' disposed on opposing sides of the array and orthogonal to the two receiver sub-arrays 201b, 201b'.
- Each of the transmitter sub-arrays 201a, 201a' includes 16 antenna elements arranged in banks 203 of four antennas 205.
- Each transmission bank 203 is coupled to a switching network 207. The selection of which transmission elements 205 are active during the transmission cycle is determined by the switching network 207 which opens and closes the appropriate switches to activate the appropriate antenna element 203 based on the chosen multiplexing scheme.
- the receiver sub-arrays 202b, 202b' are arranged into banks 204 of four antenna elements 206.
- Each receiver bank 204 is coupled to a switching network 208 which passes the signals received by the active receiver elements 206 to the back-end processing section.
- each of the antenna elements in the sub-arrays 201a, 201a' and 202b, 202b' have the same polarization.
- the antenna elements should also be selected to provide sufficient beam width (element directional pattern) to illuminate a sufficient area directly beneath and beyond the extremities of the vehicle e.g. +/- 60 degrees in a long track and cross track.
- the spacing between the elements would need to be slightly greater than a half wavelength sufficient to synthesize 32 beams within the +/- 60 degree element beam.
- the array shown in FIG. 2C is a square parameter array, it will be appreciated by those skilled in the art that the array may be in the form of any suitable shape where multiple combinations of
- transmitter/receiver pairs allow the formation of a filled aperture.
- configurations might include a rectangle, a T or L shape, a circle, octagon or the like.
- a parallel pair of transmitters displaced from an orthogonal pair of parallel receiver arrays i.e., formed as
- can be used where it is desirable to minimize transmitter to receiver leakage.
- FIG. 3 depicts the use of a MIMO array in a ground profiling operation in a radar altimeter according to one embodiment of the present invention.
- the aircraft 301 scans the desired landing zone 302.
- the synthesized beams each form a narrow cone.
- the illuminated patch 302 is wide at higher altitudes.
- the aircraft 301 descends smaller features of the ground profile can be resolved.
- Each of the transmitter elements 203 in the array 200 radiate a sequence of M differing signals, the ground reflections from which are captured by each of the N receiver element 206 of the array. Each of the N receiver elements then separates out the M received ground reflections from the M transmitters to produce MxN differing received channels.
- the channels are formed into MxN beams by co-phasing the data channels to remove the phase shifts associated with a particular angle of arrival and then summing. Then by suitably filtering the data in each beam, a set of range profiles is formed, thereby allowing the time delay of the return signal via the nearest point in each beam be measured and converted to a distance. These distance measures are then converted into a profile showing the ground and any obstacles 303 on the ground, allowing the suitability of a selected landing zone to be assessed.
- separate transmitter and receiver elements may be formed where the transmitter array is electrically scanned and the receiver array forms a multiplicity of receiver channels such that the combined transmitter and receiver patterns form a set of pencil beams.
- These arrays may be mounted to, e.g., a helicopter, so that the scanning beams cover the sector below and forward of the helicopter.
- This has an advantage over conventional scanned phased array radar in that the set of scanning beams can complete a full scan of a sector much faster than a single scanning beam of a conventional phased array.
- the transmitter antenna 201a may be a linear array of elements, such as shown in, e.g., FIGs. 2A, 2B or 2D, forming a fan beam which is electronically scanned in the plane of the array.
- the receiver array 201b is also a linear array mounted orthogonally to the transmitter array 201a.
- Data from the elements of this receiver array 201b may be processed with, for example, the Discrete Fourier Transform (DFT) to form a set of receiver fan beams. These are orthogonal to the scanning transmitter beam and intersect with it to form a set of scanning pencil beams. This is because the two way radar pattern is the product of the one way transmitter pattern and the one way receiver patterns.
- DFT Discrete Fourier Transform
- the two transmitter sub-arrays 201a, 201a' may form two fan beams with separate phase centers, the waveforms from the two transmitter fan beams is separately coded such that the two receiver sub-arrays 201b, 201b' can decode and apply phase correction for beam-forming.
- This is an adaption of a scanning fan beam technique but using MIMO techniques, and has the advantage of a smaller aperture for the same number of beams and the same beam-width.
- the transmitter array 201a may comprise four transmitters located at the corners of a compact two dimensional array of, for example, 32 receiver elements.
- the four transmitters each illuminates the whole scene of interest, with their well separate phase centers forming directional patterns which, when combined with the patterns of the receiver array in the processor, will form four times the number of beams, each half the width the receiver beam.
- These two-way radar beams can be formed in parallel by the processor using a two dimensional Fast Fourier Transform. Hence the range profiles from the whole scene can be collected from the returns from just four transmissions.
- the four transmitter waveforms can be in time sequence, in which case this is a form of MIMO radar with Time Division Multiplexing, alternatively the four transmissions can be orthogonal code sequences, giving a form of MIMO with for instance PCM or OFDM coding.
- four simultaneous in-phase transmissions will first illuminate the scene to form a fine grain interference pattern. This sharpens the resolving power of receiver beams phased to be coincident with the grating lobes of the transmitter interference pattern.
- Second, third and fourth transmissions then illuminate the scene, with pairs in opposite phase, to scan the grating lobes in four increments over the scene. For each transmission the receiver beams are formed to be on the peaks of the grating lobes. In this way the 32 range profiles from the sequence of four
- transmissions can be interleaved to give 128 higher resolution range profiles, and the first return in each located to form a 32 by 32 sample of the terrain profile.
- a signal detector with a short sampling widow may be utilized.
- the signal detector measures the range to the nearest point in each beam with leading edge trackers which search out from zero range to detect the first return.
- the first return in each beam is then tracked with a suitable early-late gate or similar. If the signal fades the tracker stays locked for a short interval and if the signal has not returned in this interval the tracker repeatedly searches out from zero again until it can lock onto the return signal.
- the resultant ground profile may be displayed to the pilot for assessment as a contour plot or as a mesh plot. This would allow the pilot to independently judge which regions within a surveyed area may be suitable landing sites.
- the altimeter may employ an algorithm to automatically determine the suitability of a surveyed area for landing.
- the algorithm may incorporate such considerations as whether there is adequate rotor/wing clearance, whether the ground slope is sufficiently parallel to the landing gear and determining the height at which any obstacles on the landing zone project above the landing surface, in order to decide which regions within a surveyed area are suitable for landing. Areas identified as suitable and unsuitable could then be displayed to the pilot via display unit to further assist the pilot in the selection of a landing zone.
- An audible warning may also be provided if the ground in view has a profile falling outside the specification for a safe landing. If a vertical reference is available the display could be referenced to this, otherwise the terrain display would be referenced to the pitch and roll of the vehicle. In this case the image of the ground profile would tilt according to the vehicle's angle with respect to the ground.
- a short pulse of wavelength in the order of a few millimeters e.g., 16.3GHz or 35 GHz
- the altimeter can readily image the terrain beneath the vehicle during a brownout, or similar events.
- the MIMO technique described above for the formation of multiple beams typically requires the transmission of long orthogonal transmitter code sequences from each transmitter element and the need for the ground returns to stay coherent during the sequence may limit the use of radar at speeds above a few knots.
- the MIMO technique may require heavy signal processing burden with consequential high power consumption and a limited update rate.
- An alternative technique to the MIMO technique may use similar antenna structures as was used for the MIMO radar but with differing transmitter waveforms and signal processing. This technique takes advantage of the fact that:
- Receiver arrays can form multiple beams at once by, for instance, applying the Discrete Fourier Transform to the data stream from the receiver elements. This enables very efficient beam-forming.
- the two-way radar directional patterns are formed as the product of the receiver directional patterns and the transmitter directional pattern
- Transmitter directional pattern can be scanned over the scene of
- the wide transmitter footprint allows the entire area of interest to be covered with a few scans of the transmitter.
- patterns can scan a set of fine beam width directional patterns over the scene with a few transmissions.
- transmitter and receiver arrays will form fan beams
- a linear transmitter array may be mounted orthogonal to a linear receiver array configured such as shown in FIG. 2A.
- a suitably timed sequence of wide band ranging signals is applied to the elements of the transmitter array 201a with phase shifts such as to form fan beam directional patterns stepped in sequence over the area of interest.
- the timing of the transmissions must be long enough to allow all the reflections from the region of interest to die away before the transmission is repeated.
- the phase shifts must form a linear phase slope across the aperture for any one ranging signal (typically a pulse).
- a sequence of different phase slopes then scans a fan beam across the scene.
- the signals reflected from the scene are collected by the elements of the receiver array 201b and processed typically with a Discrete Fourier Transform (DFT).
- DFT Discrete Fourier Transform
- This synthesizes a set of receiver fan beam directional patterns aligned orthogonally to the transmitter fan beams.
- the intersection of the transmitter fan beam with the set of receiver fan beams forms a set of pencil beams. These are stepped over the scene as the transmitter fan beam is so stepped.
- the data streams received by these pencil beams are then processed to measure the time delay to the first return received in each pencil beam and this time delay is converted to a distance measure.
- the distance measured by each beam then defines a profile describing the topography seen by the radar in the beam angular coordinates. This ground profile may be displayed in suitable coordinates, and may be processed to determine if and where the topography is unsuitable for landing, showing such regions on the display.
- This simple first example is based on a known scanning scheme, but has been adapted for a landing aid by measuring the ground topography, displaying an image of the topography, and giving a warning of unsafe conditions, which has not been previously provided.
- a new type of scanning technique is used. This offers an advantage over the first simple example, requiring an aperture which is half the size for a given performance (number of beams and beam-width) and with the same number of antenna elements.
- two linear and parallel transmitter sub-arrays and two linear and parallel receiver sub-arrays are formed around the perimeter of a square such as shown in FIG. 2C.
- the two fan beams formed by the two transmitter sub-arrays e.g., sub-arrays 201a, 201a'
- the interference pattern so produced from the widely spaced transmitter arrays illuminates the ground with a row of narrow pencil beams within the fan beam footprint. These pencil beams will be spaced by twice their beam- width; hence the space between each beam needs to be filled. So, when the phase between the two fan beams is reversed the two fan beams will illuminate the ground again with a row of narrow pencil beams but interlaced between the co-phase pencil beams. In this way the area of interest is fully illuminated with rows of pencil beams in sequence as the fan beams are stepped over the area of interest.
- two sets of data may be received at each of the transmitter pointing angles: the set from the co-phase illumination, and the set from the anti-phase illumination. These are processed by first applying a DFT to the sum of these sets and then applying a DFT to the difference of these. This again forms two interlaced interference patterns, but orthogonal to the transmitter orthogonal patterns. A pencil beam as formed by the intersection of a transmitter and receiver fan beam now forms four pencil beams, doubling the resolving power in each dimension.
- the transmitter fan beam should be incremented in half beam-width steps across the scene and the receiver DFT should be interpolated to double the number of samples.
- the two transmitter sub arrays can be fired in sequence rather than simultaneously.
- the two interference patterns can then be formed in the receiver signal processing to complete the transmitter beam synthesis.
- This is a form of MIMO radar with simple time-division-multiplexing (TDM) providing orthogonal coding for the two transmitter sub-arrays only.
- TDM time-division-multiplexing
- both transmitter arrays fire simultaneous to provide the full available energy.
- the two transmitter sub arrays each transmit a code sequence forming an orthogonal pair, using for instance phase code modulated or orthogonal frequency code (PCM or OFDM).
- PCM phase code modulated or orthogonal frequency code
- the signal stream from the receiver array elements are then de-coded into the two channels representing the reflections from the scene as illuminated by the two transmitter fan beams with their displaced phase centers.
- the sum and differences output from these two fan-beams are then processed as with the TDM approach.
- the transmitter and receiver arrays can be in a square or rectangular format, for instance the arrangement in FIG. 4, where a square array of receiver elements (201a) feeds a two dimensional Fast Fourier Transform (2D-DFT).
- 2D-DFT Two dimensional Fast Fourier Transform
- a two-dimensional interference pattern is formed illuminating the scene with an array of dark and light footprints. These bright footprints are narrower than the receiver beam footprints and the combined transmitter and receiver pattern spans a finer resolution area of the scene than the receiver beam alone.
- the gaps in the transmitter interference pattern are filled stepping the transmitter interference across the scene with suitable phase shifts applied to the transmitter elements.
- the 2D FFT outputs are interleaved to form the higher resolution image.
- This combination offers faster sector cover than is possible with a single scanning beam or with the fully coded MIMO approach requiring long code sequences.
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Abstract
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Application Number | Priority Date | Filing Date | Title |
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PCT/US2013/027831 WO2014133488A2 (en) | 2013-02-26 | 2013-02-26 | Apparatus and method for assisting vertical takeoff vehicles |
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EP2962123A2 true EP2962123A2 (en) | 2016-01-06 |
EP2962123A4 EP2962123A4 (en) | 2016-10-19 |
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EP13876483.2A Withdrawn EP2962123A4 (en) | 2013-02-26 | 2013-02-26 | Apparatus and method for assisting vertical takeoff vehicles |
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EP (1) | EP2962123A4 (en) |
AU (2) | AU2013379851B2 (en) |
IL (1) | IL240770A0 (en) |
WO (1) | WO2014133488A2 (en) |
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SE545379C2 (en) * | 2020-11-26 | 2023-07-25 | Saab Ab | A multiple-input multiple-output radar system |
Family Cites Families (8)
Publication number | Priority date | Publication date | Assignee | Title |
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US5128683A (en) * | 1991-04-16 | 1992-07-07 | General Electric Company | Radar system with active array antenna, elevation-responsive PRF control, and beam multiplex control |
US5539412A (en) * | 1994-04-29 | 1996-07-23 | Litton Systems, Inc. | Radar system with adaptive clutter suppression |
US6054947A (en) * | 1998-08-28 | 2000-04-25 | Kosowsky; Lester H. | Helicopter rotorblade radar system |
EP2153245A1 (en) * | 2007-05-04 | 2010-02-17 | Teledyne Australia Pty Ltd. | Collision avoidance system and method |
US8286477B2 (en) * | 2007-12-21 | 2012-10-16 | Bae Systems Plc | Apparatus and method for landing a rotary wing aircraft |
US8248298B2 (en) * | 2008-10-31 | 2012-08-21 | First Rf Corporation | Orthogonal linear transmit receive array radar |
EP2391906B1 (en) * | 2009-01-30 | 2016-12-07 | Teledyne Australia Pty Ltd. | Apparatus and method for assisting vertical takeoff vehicles |
CN102866401B (en) * | 2012-08-06 | 2014-03-12 | 西北工业大学 | Three-dimensional imaging method based on multiple input multiple output (MIMO) technology |
-
2013
- 2013-02-26 EP EP13876483.2A patent/EP2962123A4/en not_active Withdrawn
- 2013-02-26 AU AU2013379851A patent/AU2013379851B2/en not_active Ceased
- 2013-02-26 WO PCT/US2013/027831 patent/WO2014133488A2/en active Application Filing
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2015
- 2015-08-23 IL IL240770A patent/IL240770A0/en active IP Right Grant
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2018
- 2018-06-01 AU AU2018203898A patent/AU2018203898A1/en not_active Abandoned
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WO2014133488A3 (en) | 2015-06-25 |
IL240770A0 (en) | 2015-10-29 |
EP2962123A4 (en) | 2016-10-19 |
AU2018203898A1 (en) | 2018-06-21 |
AU2013379851A1 (en) | 2015-09-10 |
WO2014133488A2 (en) | 2014-09-04 |
AU2013379851B2 (en) | 2018-03-01 |
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