WO2019003194A1

WO2019003194A1 - 3d scanning radar and method for determining altitude of a present object

Info

Publication number: WO2019003194A1
Application number: PCT/IB2018/054840
Authority: WO
Inventors: Saulius RUDYS
Original assignee: Vilnius University
Priority date: 2017-06-30
Filing date: 2018-06-29
Publication date: 2019-01-03
Also published as: LT6622B; LT2017517A

Abstract

Purpose of the invention is to obtain distance and altitude data of an object position in 3D space by using conventional radar hardware including at least an antenna, a transmitter, a receiver and other devices and equipment required for operation of conventional radars, as well as an additional device for processing and presenting information obtained by the radar.

Description

3D SCANNING RADAR AND METHOD FOR DETERMINING ALTITUDE OF A PRESENT

OBJECT

Field of the invention

The invention relates to scanning radars and operation method, in particular to a 3D scanning radar and method for determining presence and position of an object in horizontal and vertical planes by scanning around a unidirectional axis.

Background

A scanning radar, equipped with a transmitter, a receiver, an antenna and other necessary equipment, transmit electromagnetic waves and then receive them reflected from objects. Such radar rotates around a vertical axis and has directional antenna with a narrow radiation pattern in horizontal plane and a wide radiation pattern in vertical plane (fan-beam).

In order to determine altitude of an object in relation to a radar, the height-finding radar (radar with an antenna swinging on a horizontal axis) is used in conjunction with the object-detection and range-detection radar (search radar). Radar antenna, swinging on the horizontal axis, can scan only a narrow area, so the operating speed of such system is essentially limited only to the direction of the present objects detected at that time. A radar system also may comprise two or more independent radars, which makes it difficult to operate and expensive to install. In order to reduce the price of the antenna, antennas with frequency-dependent beam elevation may be used as described in US Patent Application No. US 13 / 299.986. By changing frequency of the signal it is possible to determine the altitude, but the radar system becomes more complex due to the antenna and signal processing specifics.

To determine the direction, mono-pulse antennas may be used as described in U.S. Patent Application No. US 13 / 976.550. They can be interpreted as a phased-array marginal case. Their accuracy of direction determination is limited and they are suitable in case of only one target. Antenna systems having 2 beams one above the other as described in US Patent Application No. US 13 / 976.550 can be used. The altitude is determined according to amplitudes or phases of signals that travel through different beams. The accuracy of this method for determining the altitude is limited.

The closest prior art is described in US patent application No. US 14/125.358. A three- dimensional observation radar system that includes conventional radar equipment is disclosed. At least two radars having different azimuth scanning angles and rotatable around a common axis are used to determine the azimuth. A separate radar, which is rotatable around a vertical axis, is used to determine the altitude. Upon detecting an object with one of the azimuth radars, the altitude radar is positioned so that it scans the azimuth radar coverage area and determines the altitude of the object. The main disadvantages of this system and method are the use of several separate radars, a narrow altitude detection area, slow operation, and limited object altitude detection area; this system requires a rotation mechanism for two axes.

The invention does not have some of the usual three-dimensional scanning radar-specific flaws, and can be used in radars, sonars, or lidars for reception of reflected from objects waves using wave radiation sources with different radiation spreading (with different orientation diagrams) in different planes, using different orientation of radiation sources on two perpendicular axes with different inclination angles.

Short Description of the Invention

The invention discloses a radar comprising at least one longitudinal antenna with one aperture dimension larger than the other dimension, transmitter, receiver and other hardware. The antenna's radiation pattern is narrow a first plane and wide in a second plane that is perpendicular to the first plane. The plane in which the antenna's aperture dimensions are larger, the directional diagram is narrower.

One antenna, or the at least one antenna that is in first position, is rotated at an angle around longitudinal axis (or roll). During scanning, where scanning includes sending signals and receiving responses each time in different directions, the antenna or antennas are rotated around the vertical axis (or yaw). At least one other antenna or the at least one antenna in second position of the at least one antenna is rotated at second angle around longitudinal (roll) axis that coincides with the main signal spreading direction. During the scanning process the antenna is rotated about the vertical (yaw) axis. The space is scanned at least once at least at two different roll angles of the antenna.

Due to different antennas or different inclination (roll) angles of the one antenna, the same object will be detected at different yaw angles. Knowing difference between said yaw angles, distance to a detected object, and the roll angle of the antenna, it is possible to calculate the altitude of the target object.

Short Description of Drawings

Other features and advantages of the invention are described in the detailed description of the invention with reference to the following drawings:

Fig. 1 represents a radiation pattern of a radar with a single antenna.

Fig. 2 represents a radiation pattern of a radar with two antennas being inclined with respect to ground surface.

Fig. 3 represents an aircraft movement axis during flight.

Fig. 4 represents arrangement of angles used to calculate altitude in relation to the roll angles of the at least one antenna.

Fig. 5 represents arrangement of angles used to calculate altitude with respect to roll angles of two antennas.

Fig. 6 represents target detection azimuth angles at different roll angles.

Fig. 7 represents arrangement of antennas in aircrafts.

Fig. 8 represents application of radar in aircrafts.

Before submitting a detailed description of the invention with reference to embodiment example drawings, we note that identical elements are indicated by the same numerals in all the drawings. Detailed description of the invention

According to embodiment of the invention a radar comprises at least one side-tiltable antenna (1 ) producing a scanning beam (S) having radiation pattern, for example as shown in Fig. 1 . Such radiation pattern has different widths in orthogonal planes. The radar may comprise two such antennas (V, 1 ") that are arranged in one plane or in parallel planes but are not parallel in relation to each other, and whose scanning beams (S\ S") having radiation pattern, for example as shown in Fig. 2, have different widths in the orthogonal planes. The radar in both cases also comprises radar equipment (not shown in the drawings), such as, for example, at least one transmitter and at least one receiver, the equipment for sending, receiving, processing, and outputting of radar signals, as well as special equipment for the processing of radar data and mapping targets and parameters.

A method for determining altitude of an object that is at a certain distance R from a radar, as shown in Fig. 4 and Fig. 5, at a certain angle of azimuth a and at a certain altitude H by using a radar comprising at least one side-tiltable antenna (1 ) producing a scanning beam (S) of different widths in orthogonal planes, or two such antennas (^"Γ, 1 ") which are arranged in one plane or in parallel planes, but are not parallel in relation to each other, and whose scanning beams (S\ S ") in orthogonal planes are of different width; also comprising standard radar equipment such as at least one transmitter and at least one receiver, equipment for transmitting, receiving, processing and outputting radar signals, as well as special equipment for handling radar data, calculating and mapping targets and parameters, including the scanning of space in which the object is sought, including the scanning with an asymmetrical scanning beam (S, S', S") having height greater than width or the width greater than the height when antenna (1 , 1 ') is tilted at first roll angle φ' relative to the ground surface plane (P) and when the antenna (1 , 1 ") is tilted at second roll angle φ" relative to the ground surface plane (P). The first roll angle φ' and the second roll angle φ" are angles between the normal of the antenna and the ground surface plane as shown in Fig. 6.

When the first roll angle φ' and the second roll angle φ" are equal in numerical value but inclined at different directions, then value of a equals to half of the angle between directions of targets with respect to azimuth determined by using the antennas' radiation patterns angled at the first roll angle φ' and at the second roll angle φ" (|φ" |= | φ' |= φ) . In this case, the altitude of the detected object H is calculated as follows:

R tan φ sin a . .

" — *J ; , = 1 )

( tan q> sin a)² +1

If one of the roll angles φ' and φ" is 90°, then the second roll angle φ may be any other angle, not equal to 0 degrees. In this case, the altitude of the detected object H is also calculated by the formula 1 ). a is an angle between the directions of targets with respect to azimuth, obtained by using radiation patterns of the non-inclined (at roll angle of 90°) antenna and the antenna that is inclined at the second roll angle cp.

Variation range of the second roll angle φ is +/- 90 degrees.

The altitude can also be calculated when roll angles |φ" | and |cp' | are not equal or none of them is equal to 90 degrees. Then the altitude H can be calculated according to the following formula:

^ _ R tan φ' tan φ" siny

Vtan² φ' + tan² φ" +2 tan φ' tan (p" cosy+(tan (p' tan (p" siny)²

wherein y \s the angle between the directions of targets with respect to azimuth, obtained from radiation patterns of antennas (1 , 1 ', 1 ") inclined at the first roll angle φ' and the second roll angle cp", for example as shown in Fig. 4 and Fig. 5. The angle BOC or BOD, for example as shown in Fig. 5, which is required in order to determine azimuth of the target, when H is known, can be calculated according to the Formula 1 ). Then the angle BOC would be equal to the angle a and the first roll angle cp' would be equal to the second roll angle cp, and in particular cp'=cp or the angle BOD would be equal to the angle a and cp"=cp- According to one embodiment of the invention, the radar comprises one antenna (1 ) whose beam (S) is not symmetrical in the direction of spreading of the beam, and means (2', 2") for inclining it at an angle to one side or the other side. Such means can be a rotatable stand (2') that rotates the aforementioned antenna (1 ) at the same time around the vertical axis (3) and changes the roll angle from the first roll angle φ' to the second roll angle φ". Scanning beam (S) of the antenna (1 ) is formed for scanning of the environment using the at least one first roll angle φ' of the antenna with respect to the ground surface plane (P) and the at least one second roll angle φ" of the antenna (1 ) with respect to the ground surface plane (P), for example as shown in Fig. 4 and Fig. 5.

The means for inclining the antenna (1 ) at an angle to one side or the other can be an aircraft (2"), wherein one or several antennas (1 ) have a narrow radiation pattern in one plane and a wide radiation pattern in another plane, wherein said planes are perpendicular one to another, wherein said antennas (1 ) are arranged in parallel to the wings. During flight of the aircraft (2") its inclination with respect to vertical axis (yaw) and/or longitudinal axis (roll) changes the roll angle of signals being spread by antennas (1 ) (the radiation pattern of antennas) from the first roll angle φ' to the second roll angle φ". Thus it is possible to scan using at least two roll angles φ' and cp", and to determine the distance R to the target object and its altitude H, in relation to the radar installed on the aircraft (2").

According to another embodiment of the invention the radar comprises two antennas (1 ', 1 "), each producing scanning beams (S, S') being relatively narrow in one plane and wide in another, which are perpendicular to one another and which are arranged either in the same plane or in two parallel planes and the radiation pattern's roll angle φ' of one antenna and radiation pattern's roll angle φ" OCB of another antenna with respect to the ground surface plane (P), for example as shown in Fig. 5, differs or is equal to the same numerical value. The radar also comprises means (2', 2") for rotation of antennas (1 ',1 ") around their common axis (z) in one or other direction. Such means can be controllably rotatable stand (2') that simultaneously rotates the aforementioned antennas (1 ', 1 ") around the common axis (z), as shown in Fig. 2. In this way, two scanning beams (S\ S") are formed for scanning the space using at least two roll angles φ' and φ" of antennas in relation to the ground surface plane (P), which may differ or may be of the same numerical value.

Means (2") for rotating two antennas (1 ', 1 ") forming X or V shape can be an aircraft (2"), wherein the assembly of the two antennas (V, 1 ") forming said X of V shape or combination of X an V shapes is either mounted in parallel to the wings or inside thereof, as, for example, shown in Fig. 7, wherein beams (S', S") of each antenna is relatively narrow in one plane and wide in the other plane, which beams (S\ S") of each antenna are perpendicular one to another.

During flight of the aircraft (2") or during change of flight direction in relation to axis of any orientation the present invention allows to scan the area of space, thus determining the distance R to the object and its altitude H or the azimuth and elevation angles with respect to the radar mounted in the aircraft (2").

As for the number of receivers / transmitters, if a single transmitter / receiver is used then either at least two scans or switching of antennas is required, and if more than one transmitter / receiver is used, then the switching of antennas is not required.

Also, one transmitter / receiver together with two switching antennas, arranged in the shape of X or V, can be used.

As for duration of use of transmitters, they can send signals either simultaneously or alternately.

As for direction of radiation, the antennas can be directed in the same direction or in opposite directions.

As for scanning method, the scanning is performed by changing direction of the antenna, and/or changing direction of the antenna's radiation pattern relative to the antenna by using known methods, such as signal phase shift in antenna's elements.

First example

When distance to an object to be detected is R and the altitude is H in the north direction (point A) from the radar, as shown in Figure 4. In one case, the radar antenna is a) in horizontal position (the beam energy is the largest in plane OAB), in other case b), c) is inclined at angle φ with respect to the ground surface plane OCB (P) (the beam energy is maximal in the plane OAC), where the plane OAB is perpendicular to the plane OBC, the plane OAC is inclined at a roll angle φ with respect to the plane OBC, for example as shown in Fig. 4 and Fig. 6.

After performing a scanning i.e. a signal transfer and the reception of reflection in various directions, in case a), as shown in Fig. 6, by rotation of antenna (1 ) around the vertical axis, the target will be detected in the north direction and the distance to the detected object will be determined.

In the case of scanning b) or c) the object will be detected by a scanning beam by scanning space at a different angle than in the case a) - i.e. at an angle a.

Knowing the distance to the target R obtained in the case of scanning of a), b), or c), the angle of inclination of the antenna φ, and the angle a, the altitude H and the elevation of the target (the angle between the direction of the target and the horizontal plane) β can be calculated as shown in Fig. 4.

When using two antennas (V, 1 ") that are equally inclined at longitudinal axis in opposite directions, at least one scanning is performed in relation to the center of the vertical antenna rotation axis (z) (roll) without changing roll angles with respect to the ground surface plane (P). In this case, after at least one scanning in the north direction where the target is located, the target image on the radar screen (4), obtained with respect to each of the antennas, would be symmetrical in relation to the north direction, and the angle between them would be 2a, as shown in Fig. 6.

When using two antennas (^"Γ, 1 "), one of which is inclined at a roll angle of 90° and the other one, which is inclined at any other roll angle not equal to 0° with respect to the central vertical antenna rotation (roll) axis (ζ'), at least one scanning is performed without changing the roll angles of antennas with respect to the ground surface plane (P). In this case, after performing at least one scanning, the obtained images of the target in the north in relation to the antenna which is not inclined at a roll angle, would be located at an angle a with respect to the north direction.

This method allows simultaneous detection of several target altitudes or elevation angles when the radar is continuously scanning the space by rotating antennas around the vertical axis of the radar.

If some of the target images are overlapped (this is possible when the targets are at equal distance from the radar but at different altitudes and/or in different directions from the radar), this problem can be solved by performing an additional scanning after changing the roll angle φ of the antenna with respect to longitudinal axis. Second example

The radar comprising at least one antenna (1 ) can be realized by placing the radar antenna (1 ) into front area of a wing of the plane (2"), for example as shown in Fig. 7. The antennas (1 , 1 ', 1 ") can also be distributed in different wings. This could be useful in the case of FMCW radar, where it is common to use separate antennas to send and receive signals. The scanning would be performed when the plane changes its direction (K). When making a turn during the flight, the airplane naturally inclines. When flying in a zigzag trajectory (VT) the space sector would be scanned. When turning clockwise direction, the plane is inclined in one direction and when turning counterclockwise it is inclined in another direction, for example as shown in Fig. 8. Thus, after a zigzag maneuver, the sector would be scanned twice with different inclination angles of the antenna (1 , 1 ', 1 ") relative to the horizontal plane. In this way, a radar screen (4) would receive target images (5, 5') relative to each antenna symmetrically positioned with respect to the north direction, and the angle between them would be 2a. If some target cannot be distinguished from the others, it is possible to easily change the first roll angle φ' or the second roll angle φ" of the airplane and, accordingly, that of the antenna (1 , 1 ', 1 ") with respect to longitudinal axis.

This technical solution is well-suited for unmanned aircraft, since radar weight is reduced due to antenna's integration with the wing and lack of an antenna's rotation mechanism, while the scan by twisting does not trouble the crew since there is no crew in unmanned aircraft.

The main application is in the field of ground or aircraft radars, but it can also be applied in sonars or lidars.

Although the present description includes numerous characteristics and advantages of the invention together with structural details and features, the description is given as an example of the invention embodiment. There may be changes in the details, especially in the form, size and layout of materials without departing from the principles of the invention, in accordance with the widely understood definition of terms used in claims.

Claims

1 . A 3D scanning radar comprising at least one antenna, a transmitter and a receiver c h a r a c t e r i z e d in that a scanning beam (S, S\ S") of the radar is inclined at least at first roll angle φ' and then at second roll angle φ" in relation to the ground surface plane (P) by means (2\ 2") for forming such angles.

2. The radar according to claim 1 , wherein of the at least two roll angles φ' and φ" of the radar scanning beam (S, S\ S") only one roll angle φ' of the scanning beam (S, S\ S") is equal to 90° with respect to the ground surface plane (P).

3. The radar according to claim 1 , wherein two roll angles φ' and φ" of the radar scanning beam (S, S\ S") of the at least two roll angles φ' and φ" of the radar scanning beam (S, S\ S"), in relation to the ground surface plane (P) are equal in numeric value and are oriented in opposite directions.

4. The radar according to claim 1 , wherein two roll angles φ' and φ" of the radar scanning beam (S, S\ S") of the at least two roll angles φ' and φ" of radar scanning beam (S, S\ S") in relation to the ground surface plane (P) are different in numeric value.

5. The radar according to any one of the preceding claims, wherein means for forming roll angles p'and φ" of the radar scanning beam (S, S', S") in relation to the ground surface plane (P) is a controllably rotatable stand (2').

6. The radar according to any one of claims 1 to 4, wherein means for forming roll angles φ' and φ" of the radar scanning beam (S, S', S") in relation to the ground surface plane (P) is an aircraft (2").

7. The radar according to claim 6, wherein antennas (1 , 1 ', 1 ") for radar scanning beam (S, S', S ") are arranged in at least one wing of the aircraft (2").

8. A method for scanning environment in 3D format by using a scanning antenna of a 2D scanning radar . c h a r a c t e r i s e d in that the scanning is performed at least at two roll angles φ' and φ" of the scanning beam (S, S', S") with respect to a ground surface plane (P).

9. The method according to claim 8, wherein of said at least two roll angles φ' and φ" of the radar scanning beam (S, S\ S") only one roll angle φ' of the scanning beam (S, S\ S") is equal to 90° with respect to the ground surface plane (P).

10. The method according to claim 8, wherein of said at least two roll angles φ' and φ" of the radar scanning beam (S, S\ S") two roll angles φ' and φ" of radar the scanning beam (S, S\

S") in relation to the ground surface plane (P) are equal in numeric value while they are oriented in opposite directions.

1 1. The method according to claim 8, wherein of said at least two roll angles φ' and φ" of the radar scanning beam (S, S\ S") two roll angles φ' and φ" of the radar scanning beam (S, S\ S") in relation to the ground surface plane (P) are different in numeric value.

12. The method according to any of the claims 8 to 1 1 , wherein roll angles φ' and φ" of the radar scanning beam (S, S', S") in relation to the ground surface plane (P) is formed by a controllably rotatable stand (2').

13. The method according to any one of claims 8 to 1 1 , wherein roll angles φ' and φ" of the radar scanning beam (S, S', S") in relation to the ground surface plane (P) are formed by the flight trajectory of the airplane (2").

14. The method according to claim 9 or 10, wherein the altitude H of the detected object is calculated by the following formula:

R tan φ sin a

H = ,

( tan (p sin a)² +1

wherein, a is a half-angle between the target directions with respect to azimuth, obtained by using radiation patterns of antennas, wherein the first roll angle φ' and the second roll angle φ" of said radiation patterns and |φ"|=| φ'|= φ; or wherein, a is the angle between the target directions with respect to azimuth, obtained by using radiation patterns of antennas, wherein one radiation pattern of un-inclined antenna, being positioned at a first roll angle of 90°, and the another radiation pattern is of inclined antenna, being inclined at the second roll angle φ.

15. The method according to claim 1 1 , wherein the altitude H of the detected object is calculated by the following formula:

R tan φ' tan φ" siny

tan² φ' + tan² φ" +2 tan φ' tan (p" cos y+(tan (p' tan (p" siny)²

wherein γ is the angle between the directions of targets with respect to azimuth and the variation range of the first roll angle φ' and the second roll angle φ" is +/- 90 degrees.