EP4070129A1

EP4070129A1 - Scanning antenna

Info

Publication number: EP4070129A1
Application number: EP20820130.1A
Authority: EP
Inventors: Iman VAKILI
Original assignee: Sencept AB
Current assignee: Sencept AB
Priority date: 2019-12-04
Filing date: 2020-12-04
Publication date: 2022-10-12
Also published as: SE543769C2; SE1951395A1; WO2021110947A1

Abstract

A scanning antenna (1) comprising several stacked microwave lenses (2), each microwave lens comprising a first lens contour (7) and a second lens contour (8) arranged opposite to the first lens contour. The first lens contour comprises input ports (3) and the second lens contour comprises output ports (5), and each microwave lens is sandwiched between ground layers (4). The output ports of each microwave lens are located at the same position along the respective second lens contour, with respect to the other stacked microwave lenses, the input ports of each microwave lens are located at different positions along the respective first lens contour, with respect to the other stacked microwave lenses, and the output ports of the microwave lenses are coupled to a common antenna output. This provides a compact scanning antenna with high resolution.

Description

SCANNING ANTENNA

FIELD OF THE INVENTION

The present invention relates to a scanning antenna and to a radar system and a scanning device comprising such a scanning antenna.

BACKGROUND OF THE INVENTION

Radar systems are extensively used for detecting location, velocity and range of a target, for example in automotive sensing, mining, robotics and drones, by emitting electromagnetic waves and measuring the reflected signals. Common automotive radars on the market use a frequency modulated continuous wave (FMCW) scheme to find the range and velocity of targets. These radars have multiple transmitting and receiving antennas. The transmitting antennas propagate the radar signal in the radar field-of-view (FOV) and the receiving antennas collect the reflected signals from targets. By comparing the signal phase at different receiving antennas and performing spatial Fourier transform or similar techniques, the angle of the target is estimated. These methods, in which signal processing is used to estimate the direction of arrival, are called digital beam forming (DBF).

The combined need for more low-level processing, on the one hand, and high amount of data, on the other hand, demand complex and costly processing units. Radars in the past made use of mechanical scanning using pencil beam or fan beam antennas and a rotational stage to control the scan angle. These radars are usually bulky, cost inefficient, and suffer from vibrations in extreme conditions. Another known type of radar system is electronically steering radars. These radars use phase shifters to scan the radar beam. The use of phase shifters is not appropriate in wide-band applications due to their narrow-band nature.

Microwave lenses have been studied for radar applications, mainly due to the wide-band and true time-delay (TTD) nature of these structures, making them an ideal choice for scanning applications. These lenses are realizable at millimeter-waves. However, it would be advantageous to improve the resolution of radar systems using such lenses without compromising the overall scanning performance of the lens due to e.g. an increased side lobe level, nor its compactness.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome, or at least lessen the above-mentioned problems. A particular object is to provide a compact scanning antenna with an improved resolution.

To better address this concern, in a first aspect of the invention there is presented a scanning antenna comprising several stacked microwave lenses, each microwave lens comprising a first lens contour and a second lens contour arranged opposite to the first lens contour. The first lens contour comprises input ports and the second lens contour comprises output ports, and each microwave lens is sandwiched between ground layers. The output ports of each microwave lens are located at the same position along the respective second lens contour, with respect to the other stacked microwave lenses, the input ports of each microwave lens are located at different positions along the respective first lens contour, with respect to the other stacked microwave lenses, and the output ports of the microwave lenses are coupled to a common antenna output.

The input ports can be connected to a control system consisting of multiple high-speed switches. By exciting a specific input port, or several input ports, the propagated wave inside the lens cavity, i.e. between the first and the second lens contours, reaches the output ports at different time instants, resulting in a linear progressive phase shift across the output ports. A flat microwave lens used for radar applications is generally capable of providing the same number of beams as the number of input ports on the first contour.

In order to improve the resolution and reduce the step size between the beams, the distance between the input ports needs to be reduced. This results in a significant increase in mutual coupling between the input ports, which, as a consequence, deteriorates the overall scanning performance and increases the side lobe level. Alternatively, the lens size can be increased and input ports added. This is however inappropriate when compactness of the antenna is desirable.

Using several stacked microwave lenses with input ports of each first lens contour at different positions with respect to the other stacked microwave lenses, i.e. having the input ports slightly shifted in position with respect to the adjacent microwave lens or lenses, and coupling the output ports of each microwave lens to a common antenna output, allows reducing the step size between the beams while keeping the overall lens size constant. That is, angles that are not covered by one of the several stacked microwave lenses can be covered by another one of the several stacked microwave lenses, such that each microwave lens covers different scan angles. This results in an improved resolution of the scanning antenna. Further, by exciting either one or several of the input ports of the scanning antenna, an arbitrary shaped antenna pattern can be produced to adaptively scan the environment.

In accordance with an embodiment of the scanning antenna the microwave lenses are Rotman lenses. The Rotman lens is a type of microwave beamforming network which is robust, simple to fabricate and is a low-cost antenna. It is further a planar lens that has the advantage of scanning wide angles over a wide frequency bandwidth by passively shifting the input phase. Its geometry is specially designed to produce true time delays for the output ports to provide multiple beams in certain directions. Thereby, this provides a robust low-cost scanning antenna with high resolution for one-dimensional scanning.

In accordance with an embodiment of the scanning antenna, the ground layers comprise a bottom ground layer, a top ground layer, and at least one intermediate ground layer. Further, the top ground layer and the at least one intermediate ground layer each comprises apertures for coupling each of the output ports to the common antenna output. One aperture is provided for each output port of each of the stacked microwave lenses. This allows transmitting the signal from each microwave lens to the common antenna output without interfering with the signal from the other stacked microwave lenses. In accordance with an embodiment of the scanning antenna, the top ground layer comprises the common antenna output. The output ports of each microwave lens are coupled to apertures of the ground layer directly adjacent thereto in the direction towards the top ground layer. The apertures extend through the subsequent layers up to the top ground layer. This provides a flat antenna in which the top ground layer comprises the antenna output. The scanning antenna may be produced in any suitable way, for example by additive manufacturing, milling, substrate integrated waveguide technology or printed circuit board techniques.

In accordance with an embodiment of the scanning antenna, the common antenna array comprises rows of apertures, the number of rows corresponding to the number of stacked microwave lenses of the scanning antenna.

According to a second aspect of the invention, there is presented a radar system comprising a scanning antenna as disclosed herein. In accordance with an embodiment of the radar system, the scanning antenna is a transmitting antenna. This allows increasing the resolution in one plane, e.g. elevation or azimuth, of the radar image obtainable by the radar system.

In accordance with an embodiment of the radar system, a receiving antenna of the radar system comprises a scanning antenna as disclosed herein. In accordance with an embodiment of the radar system, a receiving antenna and a transmitting antenna of the radar system each comprises a scanning antenna as disclosed herein. This allows lens scanning to be applied in two planes, e.g. azimuth and elevation, thereby further improving the resolution of the radar system. This also allows reducing the number of receiving channels and transmitting channels required on the radar transceiver of the radar system, providing a reduced system complexity.

In accordance with an embodiment, the radar system further comprises second and third transmitting antennas, different from the scanning antenna disclosed herein, configured to generate a complementary common antenna output. In an embodiment, the second and third transmitting antennas are arranged with a half-wavelength spacing in the same plane as the scanning of the scanning antenna is performed. These transmitting antennas can be activated sequentially or adaptively at each lens scan angle to improve the angular estimation accuracy. This allows detecting the exact angle of a target within a scanning direction of the scanning antenna. In an embodiment, the angular estimation accuracy may be less than half a degree.

In accordance with an embodiment of the radar system, the second and third transmitting antennas are single antenna elements. The single antenna elements may for example be patch antennas, slot antennas, or slotted waveguides.

In accordance with an embodiment, the radar system further comprises second and third receiving antennas, different from the scanning antennas.

In accordance with an embodiment, the second and third receiving antennas are single antenna elements. As an example only, the single antenna element may be patch antennas, slot antennas, or slotted waveguides.

According to a third aspect of the invention, there is provided a scanning device comprising a scanning antenna as disclosed herein. In accordance with an embodiment, the scanning device is at least one of a telecommunication transceiver, an electromagnetic transmitter and an electromagnetic receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail and with reference to the appended drawings in which:

Fig. 1 is a schematic view of an embodiment of a scanning antenna according to a first aspect of the present invention;

Fig. 2 is a block diagram of an embodiment of a radar system according to a second aspect of the present invention; and

Fig. 3 is a block diagram of an embodiment of a radar system according to a second aspect of the present invention. DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments of the invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and to fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout.

With reference to Fig. 1 , there is provided an embodiment of a scanning antenna 1 comprising several stacked microwave lenses 2. Each microwave lens 2 comprises a lens substrate 12 and a conductive pattern arranged in the lens substrate 12. In this exemplifying embodiment, the microwave lenses 2 are Rotman lenses. However, providing other flat microwave lenses suitable for scanning applications is also possible within the concept of the present invention. Further, in the embodiment shown in Fig. 1 , the number of stacked microwave lenses 2 is three. These may herein be referred to as first, second and third microwave lens 2’, 2”, 2’”. However, providing a scanning antenna 1 comprising more than three stacked microwave lenses 2 is also possible and may be advantageous for further increasing the resolution provided by the scanning antenna 1.

Each Rotman lens 2 comprises a lens substrate 12 and a conductive pattern arranged therein. The conductive pattern comprises a first lens contour 7 and a second lens contour 8, arranged opposite to the first lens contour 7. The space between the first lens contour 7 and the second lens contour 8 is hereinafter referred to as a lens cavity 9. The first lens contour 7 comprises input ports 3, for the Rotman lens commonly also referred to as beam ports. The second lens contour 8 comprises output ports 5, commonly also referred to as array ports. When used in a radar system, the input ports 3 are connected to a control system through transmission lines, which control system comprises multiple high-speed switches for selecting one or several of the lines at a time for sending a signal and thereby directing the beam towards a specific direction. By exciting a specific input port 3, the propagated wave inside the lens cavity 9 reaches the output ports 5 at different time instants. This results in a linear progressive phase shift across the output ports 5. A correction of phases can be implemented at the output ports 5 of the Rotman lens 2 to improve the phase steering accuracy.

The number of discrete beams that can be provided by the Rotman lens 2 is generally limited by its number of input ports 3. In the exemplifying embodiment of Fig. 1, the number of input ports 3 provided at each Rotman lens 2 is five. However, providing a microwave lens 2 comprising a different number of input ports 3, such as for example four or more than five, is also possible within the concept of the present invention.

The input ports 3 are positioned along the first lens contour 7. Further, the position of each input port 3 along the first lens contour 7 of e.g. the second Rotman lens 2” is different from the position of the corresponding input port 3 at the first lens contour 7 of the first Rotman lens 2’. The position of each input port 3 of the third Rotman 2’” lens is further different from the position of the corresponding input port 3 of the first and second Rotman lenses 2’, 2”. That is, the input ports 3 of each Rotman lens 2 is shifted in position along the first lens contour 7 with respect to the other stacked Rotman lenses 2. This provides a constant phase shift at each of the output ports 5 of the scanning antenna 1.

The output ports 5 of each of the stacked Rotman lenses 2 are coupled to a common antenna output 10. More particularly, each of the output ports 5 of each Rotman lens 2 is connected via a respective transmission line to a respective antenna element 11. The antenna elements 11 may for example be microstrip patches, dipoles, slotted waveguides and/or Vivaldi antennas.

Each Rotman lens 2 of the scanning antenna 1 is sandwiched by ground layers 4. In the embodiment shown in Fig. 1, the scanning antenna comprises three stacked Rotman lenses 2 and four ground layers 4. The ground layers comprise a bottom ground layer 4’, at least one intermediate ground layer 4”, and a top ground layer 4’”. The scanning antenna shown in the exemplifying embodiment of Fig. 1 comprises two intermediate ground layers 4”. The stacked Rotman lenses 2 of the exemplifying embodiment shown are hereinafter referred to as first, second and third Rotman lenses 2’, 2”, 2’” where the first Rotman lens 2’ is arranged adjacent to the bottom ground layer 4’, the third Rotman lens 2’” is arranged adjacent to the top ground layer 4’”, and the second Rotman lens 2” is arranged therebetween, between the two intermediate ground layers 4”. Between each ground layer 4 and Rotman lens 2, a dielectric substrate is further provided, not shown in Fig. 1 for reasons of clarity.

The first Rotman lens 2’ is configured to support the transverse electromagnetic (TEM) mode between the first lens 2’ and the bottom ground layer 4’.

The intermediate ground layers 4” and the top ground layer 4’” each comprises apertures 6. The lowermost intermediate ground layer 4” comprises a row of apertures 6, the number of apertures 6 corresponding to the number of output ports 5 of the first Rotman lens 2’. Thereby, each of the output ports 5 of the first Rotman lens 2’ is coupled to one of the apertures 6 of the lowermost intermediate ground layer 4”. The apertures 6 of the lowermost intermediate ground layer 4” are aligned with corresponding apertures through all the subsequent ground layers 4, lens substrates 12 and dielectric substrates up to the top ground layer 4’” and therethrough. Correspondingly, output ports 5 of the second Rotman lens 2” are coupled to apertures 6 of the uppermost intermediate ground layer 4”. The uppermost intermediate ground layer 4” comprises a first row of apertures 6, coupled to the output ports 5 of the first Rotman lens 2’, and a second row of apertures 6, coupled to the output ports of the second Rotman lens 2”. As with the lowermost intermediate ground layer 4”, the second row of apertures 6 of the uppermost intermediate ground layer 4” extend through the lens substrate 12 of the third Rotman lens 2’”, the subsequent dielectric substrate and the top ground layer 4’”, and therethrough.

Finally, the top ground layer 4’” comprises a first row of apertures 6 coupled to the output ports 5 of the first Rotman lens 2’, a second row of apertures 6 coupled to the output ports 5 of the second Rotman lens 2”, and a third row of apertures 6 coupled to the output ports 5 of the third Rotman lens 2’”. The apertures 6 form open ended waveguides through the different layers of the scanning antenna 1. The first, second and third rows of apertures 6 of the top ground layer 4’” thereby form a common antenna output 10 of the scanning antenna 1. The top ground layer 4’” thus comprises the common antenna output 10.

Although not shown, the conductive pattern of the Rotman lenses 2, or other type of microwave lenses of the scanning antenna 1 , may comprise several dummy ports positioned along each side of the lens substrate 12 that can absorb lens spillover and thus reduce multiple reflections and/or standing waves that can deteriorate the performance of the scanning antenna 1.

The scanning antenna 1 can be used in a radar system as a transmitting antenna. Radar systems generally comprises a transceiver for generating a radar signal. The transceiver sends the signal to a control unit which is in communication with the conductive pattern of the scanning antenna 1. A switch system is used to direct the beam towards a specific direction. More particularly, the switch system of the control unit connects the radar signal to one or several of the input ports 3 of the scanning antenna 1. The signal is propagated through the lens cavity 9 and reaches the output ports 5 at different time instants. The output ports 5 are connected to respective antenna elements 11 which can transmit the radio signal, generally a radio frequency signal, to a particular direction. Due to the signal reaching the output port 5 at different time instants, it also reaches the individual antenna elements 11 at different instances of time. This can result in phase shifts between the different received signals, generating a phase front across the antenna elements 11 to radiate a beam from the common antenna output 10 in a certain direction associated with the beam originating at the input port 3. By switching input port or ports 3, the beam radiating from the common antenna output 10 can be steered in different directions. Either one or several of the input ports 3 can thus be chosen to produce an arbitrary shaped antenna pattern to adaptively scan the environment in one plane.

Due to the scanning antenna 1 comprising several stacked microwave lenses 2, and comprising a common antenna output 11, the step size between beams is reduced. Thereby, the number of scan angles is increased, improving the overall resolution of the scanning antenna 1. In a corresponding manner, the scanning antenna 1 can also be used in a radar system as a receiving antenna.

With reference now to Fig. 2, there is presented a radar system 20 comprising a scanning antenna 1 as previously described. The scanning antenna 1 is generally configured to scan horizontally or vertically, i.e. one of the azimuth and the elevation planes. The radar system 20 further comprises a second transmitting antenna 22 and a third transmitting antenna 23. The second transmitting antenna 22 and the third transmitting antenna 23 are spaced half a wavelength in the same dimension as the main extension of the lens 2 of the scanning antenna 1. Providing additional transmitting antennas is also possible within the concept of the present invention.

The radar system 20 of the exemplifying embodiment of Fig. 2 further comprises four receiving antennas 25. The receiving antennas 25 are generally spaced by half a wavelength in a direction orthogonal to that of the microwave lens 2 of the scanning antenna 1. According to another embodiment, the radar system 20 comprises more than four receiving antennas 25. The radar system 20 further comprises a radar transceiver 26. The radar transceiver 26 comprises multiple transmitting and receiving channels to generate radar signals and receive the reflections by means of multiple receivers. The radar transceiver 26 can generate signals of any of the types frequency modulation continuous wave (FMCW), fast chirp modulation, modulated square pulses, or phase modulation continuous wave (PMCW). FMCW signals can for example be generated at a carrier frequency of for example 77/79 GFIz.

The radar system 20 also comprises a control unit 24. In an embodiment, the control unit comprises pin-diode or micro-electromechanical systems (MEMS) switches with multiple input and multiple output.

In use, the radar transceiver 26 transmits the generated signals to the control unit 24 via one or more transmitting channels. The control unit 24 comprises outputs connected to the input ports 3 of the scanning antenna 1 and comprises multiple high-speed switches for connecting the transmitting channel from the radar transceiver 26 to the input ports 3 of the scanning antenna 1 sequentially. Using amplitude tapering along the common antenna output 10 of the scanning antenna 1 , sidelobe levels of the antenna output are low relative to the level of the main lobe. According to an embodiment, the detected target falls within the half-power beam width of the scanning antenna 1. An input of the control unit 24 is further connected to the second and third transmitting antennas 22, 23, which are spaced half a wavelength from each other. The second and third transmitting antennas 22, 23 are activated sequentially at each lens scan angle. The output ports 5 of the scanning antenna 1 are connected to the common antenna output 10, which scans different directions based on choosing different input ports 3 of the several stacked lenses 2. The propagated radar signal hits a target and a portion thereof is reflected back towards the radar and collected by the receiving antennas 25. The second and third transmitting antennas 22, 23 generate a detectable signal when reflected on the target and collected by the receiving antennas 25, allowing to detect the angle of the target within the illumination direction of the scanning antenna 1 with a high accuracy. In an embodiment, the angular estimation accuracy is as high as less than half a degree.

The radar signal received at the receiving antennas 25 is down- converted and sampled in the radar transceiver 26. The signal can then be further transferred to a signal processing unit, not shown in the block diagram of Fig. 2, to perform 4D radar processing to generate a radar image and estimate the position of the target in three dimensions, and its velocity as the fourth dimension. The transmitting antennas of the radar system shown in Fig. 2, i.e. the scanning antenna 1, the second transmitting antenna 22 and the third transmitting antenna 23 provide angular estimation of a target in one plane, e.g. azimuth. The angle of the target in the other plane, e.g. elevation, is determined using classical digital beam forming by estimating the phase difference between the receiving antennas 25. The radar transceiver of the exemplifying embodiment of Fig. 2 comprises four receiving channels and two transmitting channels. Flowever, providing a radar transceiver with a different number of receiving and transmitting channels is also possible within the concept of the present invention. With reference now to Fig. 3, there is provided a radar system 30 comprising a first scanning antenna 1 as a transmitting antenna 31 and a second scanning antenna 1 as a receiving antenna 35. Providing scanning antennas 1 both for transmitting and receiving the radar signal allows scanning to be applied to two planes, i.e. elevation and azimuth. In this exemplifying embodiment, the radar transceiver 36 comprises two receiving channels and two transmitting channels. The transmitting and receiving channels are connected to two control units 34. One of the two control units 34 is further connected to second and third transmitting antennas 32, 33 and the other control unit 34 is further connected to second and third receiving antennas 37, 38. The second and third transmitting and receiving antennas 32, 33, 37, 38 are provided to improve the angular accuracy by estimating the phase difference between the channels.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. For instance, a radar system as described with respect to Figs. 2 and 3 may be provided comprising, instead of the scanning antenna 1 as transmitting antenna and/or receiving antenna, a scanning antenna comprising only one microwave lens, such as a Rotman lens. In this radar system, the second and third transmitting antennas and/or second and third receiving antennas provide improved angular accuracy of the target.

The scanning antenna 1 , although having been described mainly for use in radar systems, can also be used for other scanning applications such as for telecommunication transceivers, and any electromagnetic transmitter or receivers. Thus, according to another aspect of the present invention there is provided a scanning device comprising the scanning antenna 1.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

C L A I M S

1. A scanning antenna (1 ) comprising several stacked microwave lenses

(2), each microwave lens comprising a first lens contour (7) and a second lens contour (8) arranged opposite to the first lens contour, the first lens contour comprising input ports (3) and the second lens contour comprising output ports (5), and each microwave lens being sandwiched between ground layers (4), wherein the output ports of each microwave lens are located at the same position along the respective second lens contour with respect to the other stacked microwave lenses; the input ports of each microwave lens are located at different positions along the respective first lens contour, with respect to the other stacked microwave lenses; and the output ports of the microwave lenses are coupled to a common antenna output (10). 2. The scanning antenna (1 ) according to claim 1 , wherein the microwave lenses (2) are Rotman lenses.

3. The scanning antenna (1 ) according to claim 1 or 2, wherein the ground layers (4) comprise a bottom ground layer (4’), a top ground layer (4’”), and at least one intermediate ground layer (4”), wherein the top ground layer and the at least one intermediate ground layer comprises apertures (6) for coupling each of the output ports (5) to the common antenna output (10).

4. The scanning antenna (1 ) according to claim 3, wherein the top ground layer (4’”) comprises the common antenna output (10).

5. The scanning antenna (1 ) according to any one of the preceding claims, wherein the common antenna output (10) comprises rows of apertures (6), the number of rows corresponding to the number of stacked microwave lenses (2) of the scanning antenna.

6. A radar system comprising a scanning antenna (1 ) according to any one of the preceding claims.

7. The radar system according to claim 6, wherein the scanning antenna (1 ) is a transmitting antenna.

8. The radar system according to claim 6 or 7, wherein a receiving antenna of the radar system comprises a scanning antenna (1 ) according to any one of claims 1 -5.

9. The radar system (20) according to claim 6 or 7, further comprising second and third transmitting antennas (22, 23), different from the scanning antenna (1 ), configured to generate a complementary common antenna output.

10. The radar system (20) according to claim 9, wherein the second and third transmitting antennas (22, 23) are single antenna elements.

11 .The radar system (30) according to claims 8 and 9, further comprising second and third receiving antennas (37, 38), different from the scanning antenna.

12. The radar system (30) according to claim 11 , wherein the second and third receiving antennas (37, 38) are single antenna elements.

13. A scanning device comprising a scanning antenna (1 ) according to any one of claims 1-5.

14. The scanning device according to claim 13, wherein the scanning device is at least one of a telecommunication transceiver, an electromagnetic transmitter and an electromagnetic receiver.