GB2569620A

GB2569620A - Optimization of the performances of an antenna array

Info

Publication number: GB2569620A
Application number: GB1721622.7A
Authority: GB
Inventors: Thoumy Francois; Le Bars Philippe; Achir Mounir
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2017-12-21
Filing date: 2017-12-21
Publication date: 2019-06-26
Anticipated expiration: 2037-12-21
Also published as: GB201721622D0; GB2569620B

Abstract

The invention relates to a method of selecting an antenna array configuration to be used by a radar apparatus, the configuration comprising a plurality K of active antenna elements out of a total T of antenna elements, each antenna element being configured to receive a signal based on reflection of an emitted radar wave on at least one target. The method comprising the steps of determining an angular interval to be used; and selecting, from a correspondence table comprising a number of active antenna elements and corresponding image quality parameters with respect to the determined angular interval, the configuration to be used in order to provide an image quality greater than or equal to a predetermined image quality threshold.

Description

OPTIMIZATION OF THE PERFORMANCES OF AN ANTENNA ARRAY

FIELD OF THE INVENTION

The invention relates to the field of radar apparatuses, in particular radars able to provide improved image quality and energy consumption.

BACKGROUND OF THE INVENTION

Pulsed radar (“RAdio Detection And Ranging”) systems may have antenna arrays comprising a plurality of antenna elements and work by emitting a signal composed of regular pulses at a given frequency. When the signal is reflected by a target, an echo is received by the radar and processed so as to obtain a compressed signal exhibiting a main lobe whose position on the distance axis corresponds to the distance of the target (hereafter termed “range”), as well as secondary lobes of lower amplitude, known as side lobes, on either side of the main lobe on the distance axis.

If a total T of transmitting antenna elements are available and a number K of transmitting antenna elements are active at a given time, K is less than or equal to T. A “full” antenna array uses all antenna elements, K = T. In contrast, a “sparse” antenna array only uses a portion of all the available antenna elements, for example K = 10 out of T = 30. A sparse antenna array offers the advantage of conserving system energy as fewer antenna elements are needed to transmit and fewer received echoes are needed to be processed. Furthermore, a sparse antenna array can achieve at least the same resolution as a full antenna array, but may have an increased number and/or amplitude of side lobes.

However, when selecting a sparse antenna array, many combinations are possible with respect to the number K of active antenna elements and their positions. For example, if K = 1 then 30 combinations are possible, if K = 2 then 435 combinations are possible, and so forth, each combination providing a different radiation pattern.

An example distribution of eighteen active antenna elements (K = 18) out of thirty total antenna elements (T = 30) may be represented by the following onedimension vector G1 (positions P1 to P30 from left to right):

G1= [1 0100110011100111010101101001 1] [vector 1] wherein all the positions occupied by an active antenna element are indicated by a 1, and the positions not occupied by an active antenna element are indicated by a 0.

Another example distribution of eighteen active antenna elements out of a total of thirty antenna elements would be for example:

G2 = [1 0101010011100111010101101011 1] [vector2]

Both vectors G1, G2 provide similar resolutions but their radiation patterns are different since the positions and levels of the side lobes vary.

The radiation pattern of the array can be computed by considering the vector elements as coefficients of a digital filter. In case of digital filters, the frequency response of the filters provides a power variation as a function of the input signal frequency. In the case of an antenna array, computing the frequency response Η(ζ(θ)) of the equivalent digital filter provides the radiation pattern of the array, which means the variation of the received power as a function of the angle of view, according to the principle of reciprocity in electromagnetism.

In the case of the above sparse antenna array examples G1, G2, the corresponding frequency responses Η1(ζ(θ)), Η2(ζ(θ)) are computed as follows:

Hi(z(0)) = Σ^Τ _ρ=19Κρ) * e [equation 1] wherein p is an index of the antenna element from 1 to T (here T = 30), gi(p) is equal to 0 or 1 depending on whether the corresponding antenna element (index p) of the vector G is inactive (providing a 0) or active (providing a 1), Θ (Greek letter theta) is the angle from 0 to a maximum angle, z(0)=1*k*sin(0), k is equal to 2*π/λ, π (Greek letter pi) and λ (Greek letter lambda is the wavelength).

The frequency response H(z(0)) of an antenna array varies as a function of the angle 0. The angle 0 is thus varied, for example from 0 to 60°, and the frequency response H(z(0)) is measured.

For example:

H(z(0)) = g(1)*exp[-(1-1)*z(0)] + g(2)*exp[-(2-1)j*z(0)]... + g(3O)*exp[-(3O-1)*j*z(0)]

The integrated side lobe ratio (ISLR) may be defined as the ratio between total power (energy) of all the side lobes and the power of the main lobe. The ISLR characterizes the ability of the radar to detect “weak” targets (those that are weakly or poorly reflective) near “strong” targets (those that are strongly or highly reflective), and is a measurement of the relative significance of the side lobes with respect to the main lobe.

The ISLR is normally used in imaging radars as a measurement of the contrast achievable in an image between the weak and strong targets, and is an indicator of image quality. The lower the ISLR, the better the contrast and thus the better the quality of the radar image on a rendering system such as a screen.

The ISLR may be calculated in different manners, but in the following has been computed using the following formula:

ISLR = fe-^angle |Η(ζ(β)Ι² \ l Ηζ(0)^Λ2 I [equation 2] wherein H(z) is the frequency response of the digital filter equivalent to the sparse antenna array as shown above.

The performance of a radar apparatus thus varies depending on many factors, including the number of active antenna elements.

It may therefore be desired to provide a method of determining an antenna array configuration to meet certain criteria.

SUMMARY OF THE INVENTION

Embodiments of the invention thus aim to provide a method of determining a configuration of antenna elements of an antenna array.

Embodiments of the invention relate to a method of selecting an antenna array configuration to be used by a radar apparatus, the configuration comprising a plurality K of active antenna elements out of a total T of antenna elements, each antenna element being configured to receive a signal based on reflection of an emitted radar wave on at least one target.

The method comprises the steps of:

determining an angular interval to be used; and selecting, from a correspondence table comprising a number of active antenna elements and corresponding image quality parameters with respect to the determined angular interval, the configuration to be used in order to provide an image quality greater than or equal to a predetermined image quality threshold.

According to one embodiment, the method further comprises a step of determining the range to the target, in order to determine the angular interval.

According to one embodiment, the method further comprises the steps of: selecting a default antenna array configuration; and performing a first detection of the target using the default antenna array configuration, in order to determine the range to the target.

According to one embodiment, the method further comprises the steps of: selecting the antenna array configuration from the correspondence table providing the best image quality; and performing a second detection of the target using the selected antenna array configuration.

According to one embodiment, the method further comprises the steps of: selecting the antenna array configuration from the correspondence table providing the lowest energy consumption while meeting an image quality threshold; and performing a second detection of the target using the selected antenna array configuration.

According to one embodiment, the method further comprises a step of establishing the correspondence table by performing the steps of:

determining at least two spatial arrangements of the antenna elements;

determining at least two angular intervals for operation of the radar apparatus; computing a side lobe ratio for each angular interval and for each spatial arrangement, and selecting the spatial arrangement having the best side lobe ratio for each angular interval.

According to one embodiment, the method further comprises the step of displaying a radar image.

According to one embodiment, the method further comprises the steps of: defining at least two angular detection areas; and establishing a correspondence table for each angular detection area.

According to one embodiment, the step of selecting the angular interval comprises the steps of:

detecting a plurality of targets; and selecting the angular interval related to the range of the target that is closest to the radar.

Embodiments of the invention also relate to a computing device configured to select an antenna array configuration to be used by a radar apparatus, the configuration comprising a plurality K of active antenna elements out of a total T of antenna elements, each antenna element being configured to receive a signal based on reflection of an emitted radar wave on at least one target.

The computing device is configured to:

determine an angular interval to be used; and select, from a correspondence table comprising a number of active antenna elements and corresponding image quality parameters with respect to the determined angular interval, the configuration to be used in order to provide an image quality greater than or equal to a predetermined image quality threshold.

According to one embodiment, the device is further configured to determine the range to the target, in order to determine the angular interval.

According to one embodiment, the device is further configured to:

select a default antenna array configuration; and perform a first detection of the target using the default antenna array configuration, in order to determine the range to the target.

According to one embodiment, the device is further configured to:

select the antenna array configuration from the correspondence table providing the best image quality; and perform a second detection of the target using the selected antenna array configuration.

According to one embodiment, the device is further configured to:

select the antenna array configuration from the correspondence table providing the lowest energy consumption while meeting an image quality threshold; and perform a second detection of the target using the selected antenna array configuration.

According to one embodiment, the device is further configured to:

determine at least two spatial arrangements of the antenna elements;

determine at least two angular intervals for operation of the radar apparatus;

compute a side lobe ratio for each angular interval and for each spatial arrangement; and select the spatial arrangement having the best side lobe ratio for each angular interval in order to establish the correspondence table.

According to one embodiment, the device is further configured to display a radar image.

According to one embodiment, the device is further configured to:

define at least two angular detection areas; and establish a correspondence table for each angular detection area.

According to one embodiment, the device is further configured to:

detect a plurality of targets; and select the angular interval related to the range of the target that is closest to the radar;

in order to select the angular interval.

Embodiments of the invention also relate to a radar apparatus comprising a computing device according to an embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Other particularities and advantages of the invention will also emerge from the following description, illustrated by the accompanying drawings, in which:

Figures 1A, 1B provide different target detection scenarios;

Figure 2 is a radiation pattern (received power) (dB) with respect to angle (degrees) for a sparse antenna configuration and a full antenna configuration;

Figures 3A, 3B respectively illustrate the variation of the image quality with respect to the number of active antenna elements for a narrower angular interval and a wider angular interval;

Figure 4 is a flowchart of a method of selecting an antenna array configuration according to one embodiment;

Figure 5 is a flowchart of a method of selecting an antenna array configuration according to another embodiment;

Figure 6 is a schematic block diagram of a computing device for implementing one or more embodiments of the invention; and

Figure 7 illustrates the implementation of a radar, according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention relate to methods of selecting an antenna array configuration, wherein the configuration comprises a number K of total T antenna elements, K being less than or equal to T. The aim is to obtain the best image quality possible.

Figures 1A, 1B provide different target detection scenarios.

In these scenarios, the target T is a human being, assumed to have a height H of 2 meters. Figure 1A shows the target T at a long range R1 (5 meters) from a radar apparatus RA1, and Figure 1B shows the same target T at a short range R2 (1 meter) from a radar apparatus RA2.

The radar appartuses RA1, RA2 may be separate apparatus with different configurations or may be a single same apparatus with different antenna elements activated/deactivated, depending on the scenario. Generally, the detection angle to be used is not determined by the antenna configuration but by the scenario and the signal processing.

In order to fully detect the target (from top to bottom), an angular interval Al, here AH or AI2, is required, the angular interval being the angle from the top to the bottom of the target with respect to the radar. When trying to track the target T with Angle of Arrival (AoA) algorithms, the angular interval Al varies inversely with the range. That is to say, for a longer range R1, a smaller angular interval is required, for example AH = 22° (degrees) in the case of Figure 1A, but for a shorter range, a larger angular interval is required, for example AI2 = 90° in the case of Figure 1B.

As previously indicated, using a sparse antenna array does not modify the system resolution but the side lobes are increased for the result supplied by the AoA algorithm. If the level of side lobes increase, it may be difficult to differentiate main lobes (due to targets being set at different angles) from side lobes coming from a unique target. Thus, the side lobes should be minimized as much as possible.

Figure 2 is a radiation pattern (received power) (dB) with respect to angle (degrees) for two antenna array configurations - a sparse antenna array, and a full antenna array.

Curve 201 (solid line) relates to a sparse antenna array of eighteen active antenna elements out of thirty total antenna elements as follows:

G3 = [1 0100110101011011100111010011 1] [vector3]

Curve 202 (dotted line) relates to a full antenna array (K = T = 30), that is to say:

G4 = [1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1] [vector 4]

Curves 201, 202 provide the power variation (y-axis) of the received signals versus the angle (x-axis) for the antenna array configuration. Each curve 201, 202 has a respective main lobe ML1, ML2. The main lobes ML1, ML2 are similar in terms of width (indicating that they have similar angular resolutions). However, the full antenna array (curve 202) has a gain of 30 dB whereas the sparse antenna array (curve 201) has a gain of only 25 dB, as there are fewer active antenna elements in the sparse antenna array.

For the full antenna array (curve 202), the power of the side lobe levels decreases as the angle value increases, whereas for the sparse antenna array (curve 201) the power of the side lobe levels varies irregularly.

For the case of the entire span of angles [x-axis : 0 to +/- 60°], the computation of the ISLR values for both cases provides a lower value for the full antenna array than for the sparse antenna array, which means that the full antenna array provides images of higher/better radar image quality.

However, for a narrower angular interval, for instance for the interval 0° to +/15°, the computation of the ISLR values provides a lower value for the sparse antenna array than for the full antenna array, which means that the sparse antenna array provides images of higher/better radar image quality for narrower angular intervals in some cases, for example in the case of Fig. 1A.

In other words, the antenna array configuration providing higher image quality depends on the considered angular interval Al and may depend on the range of the target.

To this end, an angular interval to be used is determined, and a configuration is selected from a correspondence table linking the determined angular interval, an image quality, and a number of active antenna elements as will now be described.

Figures 3A, 3B respectively illustrate the variation of the image quality (ISLR values) with respect to the number of active antenna elements for a narrower angular interval and a wider angular interval. Specifically, Figure 3A shows the variation of the ISLR with respect to the number of active antenna elements for an angular interval equal to 30° (+/- 15°), while Figure 3B shows the variation of the ISLR with respect to the number of active antenna elements for an angular interval equal to 90° (+/- 45°).

As explained previously, there are many possible configurations for a same number K of active antenna elements. Each configuration provides a radiation pattern with different positions and levels of the side lobes.

The curves of Figures 3A, 3B have been plotted considering the best configuration for each number of active antenna elements.

That is to say, for each angular interval (here +/-15 or +/- 45) and number K of active antenna elements, each possible configuration (30 configurations for one active antenna element, and so forth) provides an ISLR value. However, only the lowest (best) ISLR value is shown in the figure. A similar process is performed for all values of active antenna elements, providing the curve ISLR= f(active antenna elements).

Table 1 below summarizes Figures 3A, 3B - the first column indicates the number K of active antenna elements (x-axes of the figures), the second column indicates the angular interval Al (divided into values +/- 15° for Figure 3A, and values +/- 45° for Figure 3B), and the third column indicates the ISLR values (y-axes of the 5 figures).

Number of Active Antenna Elements	Angular Interval Al	ISLR
9	+/- 15	43.1
+/-45	122.9
10	+/- 15	37.7
+/-45	97.7
11	+/- 15	34.4
+/-45	85.8
12	+/- 15	32.2
+/-45	77.4
13	+/- 15	31.0
+/-45	69.2
14	+/- 15	29.9
+/-45	65.4
15	+/- 15	29.1
+/-45	62.7
16	+/- 15	28.4
+/-45	60.6
17	+/- 15	28.0
+/-45	60.8
18	+/- 15	27.7
+/-45	59.1
19	+/- 15	27.6
+/-45	58.0
20	+/- 15	27.7
+/-45	55.6
21	+/- 15	27.6
+/-45	53.4
22	+/- 15	27.9

	+/-45	51.7
23	+/- 15	28.9
+/-45	51.0
24	+/- 15	29.3
+/-45	50.2
25	+/- 15	32.3
+/-45	49.2
30	+/- 15	30.2
+/-45	38.6

Table 1: Example Correspondence Table between the number of active antenna elements, the chosen angular intervals, and the image quality

It may be noted that not all numbers (K) of active antenna elements are included in the table above. It may be assumed that some values, for example K from 1 to 8 are too few active antenna elements and do not provide sufficient image quality, and that other values, for example K from 26 to 29, do not provide enough of a difference of image quality and energy consumption with respect to the full array to be worth considering.

In Figure 3A and Table 1 (values +/-15°), it may be noted that the numbers of active antenna elements providing the lowest ISLR values are K = 18, 19, 20, and 21, respectively providing the ISLR values of 27.7, 27.6, 27.7, 27.6.

Since the ISLR values are similar (the difference being less than a predetermined threshold), it may be desired to select the lowest number K of active antenna elements (in this case, K = 18) as the energy consumed by the system will be decreased due to there being fewer active antenna elements.

The ISLR for the full antenna array (30) is equal to 30.2, and it may thus be noted that the configurations K = 14 to 24 provide ISLR values that are lower than that of the full antenna array, thus any one of these would provide improved image quality with respect to that of the full antenna array, but the configurations K = 18 to 21 would provide the best image quality, and the configuration K = 18 would provide the best image quality (difference with the others being less than a predetermined threshold) and the lowest energy consumption.

In Figure 3B and Table 1 (values +/- 45°), it may be noted that the number of active antenna elements providing the lowest ISLR value is that of the full antenna array K = 30.

Consequently, from Figures 3A, 3B and Table 1, it may be confirmed that the antenna array arrangement providing the best image quality depends on the angular interval of interest, which may in turn depend on the range.

It may be noted that the image quality is thus highly dependent on the angular interval considered or of interest (here +/- 15° or +/- 45°) and the number of active antenna elements.

Figure 4 is a flowchart of a method 400 of selecting an antenna array configuration according to one embodiment, wherein the best image quality for a given angular interval is obtained. The method 400 comprises the steps 401 to 407.

In step 401, a default antenna array configuration is selected, for example by a processing module of the radar, such as the full antenna array configuration. Other radar parameters enabling detection of a target T are also selected, such as the pulse width, the pulse repetition frequency, the algorithm used to calculate the Angle of Arrival, and so forth.

In step 402, a first detection of the target T is done using the default configuration.

In step 403, the radar apparatus performs processing and supplies range R information related to the target T. The range R information can be determined by any known method, such as by measuring the round trip time of emitted/received signals.

In step 404, depending on the range R information and on the expected use of the radar (for instance the scan of a human body as shown in Figures 1A, 1B as opposed to the scan of vehicles) an angular interval Al is determined. For instance, if the range R is 5 meters, the angular interval may be +/- 15°, whereas if the range R is 1 meter, the angular interval may be +/- 45°. If several targets T are detected, the range related to the target T that is the closest to the radar may be used to determine the angular interval.

In step 405, depending on the determined angular interval Al and a correspondence table (such as Table 1 above) linking the number of active antenna elements, the determined angular interval, and an image quality parameter (such as the ISLR) the antenna array configuration providing the best image quality (here the lowest ISLR) is selected. The correspondence table to use may be pre-set by the manufacturer, selected by the operator, determined based on preliminary characteristics, and so forth.

In step 406, the radar apparatus performs a second detection using the selected antenna array configuration.

In step 407, the signals are processed and a radar image is displayed. The method 400 may then either stop or return to step 403, for example to find a new configuration or to detect a new target.

In the method 400, it may be considered that the “best image quality” is an image quality greater than or equal to a predetermined image quality threshold, that is to say, the best image quality.

The method 400 thus allows the optimum number of active antenna elements to be implemented, depending on an angular interval determined based on characteristics (range, size, etc.) of the target(s) to detect, to provide the best image quality.

Figure 5 is a flowchart of a method 500 of selecting an antenna array configuration according to another embodiment, wherein the lowest possible energy consumption is obtained while conserving a predetermined radar image quality. The method 500 comprises the steps 501 to 507.

In step 501, a default antenna array configuration is selected, such as the full antenna array arrangement. Other radar parameters enabling detection of a target T are also selected.

In step 502, a first detection of the target T is done using the default configuration.

In step 503, the radar apparatus performs processing and supplies range R information related to the target T. The range R information can be determined by any known method as previously indicated.

In step 504, depending on the range R information and on the expected use of the radar (for instance the scan of a human body as shown in Figures 1A, 1B) an angular interval Al is determined. As previously, if several targets T are detected, the range related to the target T that is the closest to the radar may be used to determine the angular interval.

In step 505, depending on the determined angular interval Al and a correspondence table (such as Table 1 above) linking the number of active antenna elements, the determined angular interval, and an image quality parameter (such as the ISLR) the antenna array configuration providing the lowest energy consumption by using the fewest number of active antenna elements, while still meeting an image quality threshold, is selected. To this end, the radar is provided with the image quality threshold (minimum acceptable image quality). The image quality threshold may be determined by the type of application, the type of targets expected to be detected, predefined by the manufacturer, entered by the operator, and so forth.

In step 506, the radar performs a second detection using the selected antenna array configuration.

In step 507, the signals are processed and a radar image is displayed. The method 500 may then either stop or return to step 503.

The method 500 thus allows the minimum number of active antenna elements to be implemented, depending on an angular interval determined based on characteristics (range, size, etc.) of the target(s) to detect, to provide a minimum image quality.

Consequently, if it is desired to obtain the best image quality (method 400), the selected antenna array configuration is that with 19 antenna elements for an angular interval of 15° and that with 30 antenna elements (the full antenna array) for an angular interval of 45°.

However, if it is desired to consume the least amount of energy (method 500) while still meeting an image quality threshold (for example ISLR less than 45), the selected antenna array configuration it that with 9 antenna elements (ISLR = 43.1) for an angular interval equal to 15° and that with 30 antenna elements (the full antenna array) for an angular interval of 45°.

It may be noted that in some embodiments, the method 500 of Figure 5 may be integrated within the method 400 of Figure 4, such as an optional sub-routine.

The correspondence table may be constructed by performing the following steps:

- determining at least two spatial arrangements of the antenna elements;

- determining at least two angular intervals for operation of the radar apparatus;

- computing a side lobe ratio for each angular interval and for each spatial arrangement, and

- selecting the spatial arrangement having the best side lobe ratio for each angular interval.

It may be noted that the correspondence table does not necessarily comprise the values for the two or more angular intervals, as shown in Table 1 above, but may be specific for each angular interval, in which case each angular interval has a dedicated correspondence table. Furthermore, an angular interval may have two or more correspondence tables, the use of which may depend on other factors.

Figure 6 is a schematic block diagram of a computing device 600 for implementing one or more embodiments of the invention. The computing device 600 may be integrated into a radar apparatus or coupled thereto.

The computing device 600 may be a device such as a micro-computer, a workstation or a light portable device.

The computing device 600 comprises:

- a communication bus 610;

- a central processing unit 620 or CPU, such as a microprocessor;

- a random access memory 630 or RAM;

- a read only memory 640 or ROM;

- a network interface 650 or Nl;

- a user interface 660 or Ul;

- a hard disk 670 or HD; and

- an input/output module 680 or I/O.

The RAM 630 stores the executable code of the method of embodiments of the invention as well as the registers adapted to record variables and parameters necessary for implementing the method according to embodiments of the invention, the memory capacity thereof can be expanded by an optional RAM connected to an expansion port for example.

The ROM 640 stores computer programs for implementing embodiments of the invention.

The network interface 650 is typically connected to a communication network over which digital data to be processed are transmitted or received. The network interface 650 can be a single network interface, or composed of a set of different network interfaces (for instance wired and wireless interfaces, or different kinds of wired or wireless interfaces). Data packets are written to the network interface for transmission or are read from the network interface for reception under the control of the software application running in the CPU 620.

The user interface 660 may be used for receiving inputs from a user or to display information to a user, the hard disk 670 may be provided as a mass storage device, and the I/O module 680 may be used for receiving/sending data from/to external devices such as a video source or display (not shown).

The executable code may be stored either in the ROM 640, on the hard disk 670, on a removable digital medium such as a disk, or even received by means of a communication network, via the network interface 650, in order to be stored in one of the storage means, such as the hard disk 670, before being executed.

The central processing unit 620 is adapted to control and direct the execution of the instructions or portions of software code of the program or programs according to embodiments of the invention, the instructions of which are stored in one of the aforementioned storage means. After powering on, the CPU 620 is capable of executing instructions from main RAM memory 630 relating to a software application after those instructions have been loaded from the program ROM 640 or the hard disc 670 for example. Such a software application, when executed by the CPU 620, causes the steps of the flowcharts shown in Figures 4 and/or 5 to be performed.

In particular, any step of the algorithm shown in Figures 4 and/or 5 may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC (“Personal Computer”), a DSP (“Digital Signal Processor”), a microcontroller, or else implemented in hardware by a machine or a dedicated component, such as an FPGA (“Field-Programmable Gate Array”) or an ASIC (“Application-Specific Integrated Circuit”).

Figure 7 illustrates the implementation 700 of a radar apparatus, according to one embodiment. The implementation 700 comprises a radar apparatus 710, a scene 720, a target 730 present within the scene, and a human-machine interface 740.

The radar apparatus 710 comprises a transmitter 711 with a transmitting antenna 712 and a receiver 713 with a receiving antenna 714. The transmitting antenna 712 is configured to emit a coded pulse signal modulated at stepped carrier frequencies, which reaches the target 730.

The scene 720, illuminated by the radar apparatus 710, is represented as a circular sector. The signal (echoes) reflected off the target 720 are captured by the receiving antenna 714.

The human-machine interface 740, such as a screen, is coupled to the radar apparatus 710 (or may be integrated therewith), in particular to the receiver 713 and displays a relative position 745 of the detected target 730, and may also be configured to display video data.

Although the above description and appended figures relate to onedimensional antenna arrays, embodiments of the invention can also be implemented in two-dimensional 2D antenna arrays. In this case, two angular detection areas may be defined- an azimuth detection area and an elevation detection area. In this case, two correspondence tables like that of Table 1 may be defined and implemented.

In another embodiment, even though a 2D antenna array is implemented, the invention is applied in only one dimension (such as the azimuth) in order to reduce the corresponding side lobes, but not applied in the other direction (such as the elevation).

In summary, embodiments of the invention provide the best image quality achievable for a given angular interval (detection angle) and antenna array configuration.

If more than one configuration provides an image quality above a threshold value, the energy consumption may be decreased according to further embodiments.

Though reference has been made to the image quality in relation with the ISLR, any other indicator which represents image quality, in particular a ratio of sidelobes with respect to a main lobe, may be used.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications which lie within the scope of the present invention will be apparent to a person skilled in the art. In particular different features from different embodiments may be interchanged, where appropriate. Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention as determined by the appended claims.

Claims

1. A method of selecting an antenna array configuration to be used by a radar apparatus, the configuration comprising a plurality K of active antenna elements out of a total T of antenna elements, each antenna element being configured to receive a signal based on reflection of an emitted radar wave on at least one target, the method comprising the steps of:

2. The method according to claim 1, further comprising a step of determining the range to the target, in order to determine the angular interval.

3. The method according to one of claims 1 or 2, further comprising the steps of:

selecting a default antenna array configuration; and performing a first detection of the target using the default antenna array configuration, in order to determine the range to the target.

4. The method according to claim 3, further comprising the steps of:

selecting the antenna array configuration from the correspondence table providing the best image quality; and performing a second detection of the target using the selected antenna array configuration.

5. The method according to claim 3, further comprising the steps of:

selecting the antenna array configuration from the correspondence table providing the lowest energy consumption while meeting an image quality threshold; and performing a second detection of the target using the selected antenna array configuration.

6. The method according to one of claims 1 to 5, further comprising a step of establishing the correspondence table by performing the steps of:

determining at least two spatial arrangements of the antenna elements;

7. The method according to one of claims 1 to 6, further comprising the step of displaying a radar image.

8. The method according to one of claims 1 to 7, further comprising the steps of:

defining at least two angular detection areas; and establishing a correspondence table for each angular detection area.

9. The method according to one of claims 1 to 8, wherein the step of selecting the angular interval comprises the steps of:

10. A computing device configured to select an antenna array configuration to be used by a radar apparatus, the configuration comprising a plurality K of active antenna elements out of a total T of antenna elements, each antenna element being configured to receive a signal based on reflection of an emitted radar wave on at least one target, the computing device being configured to:

11. The device according to claim 10, further configured to determine the range to the target, in order to determine the angular interval.

12. The device according to one of claims 10 or 11, further configured to:

13. The device according to claim 12, further configured to:

14. The device according to claim 12, further configured to:

15. The device according to one of claims 10 to 14, further configured to: determine at least two spatial arrangements of the antenna elements; determine at least two angular intervals for operation of the radar apparatus; compute a side lobe ratio for each angular interval and for each spatial arrangement; and select the spatial arrangement having the best side lobe ratio for each angular interval in order to establish the correspondence table.

16. The device according to one of claims 10 to 15, further configured to display a radar image.

17. The device according to one of claims 10 to 16, further configured to:

18. The device according to one of claims 10 to 17, further configured to: detect a plurality of targets; and

5 select the angular interval related to the range of the target that is closest to the radar in order to select the angular interval.

19. A radar apparatus comprising a computing device according to one of

10 claims 10 to 18.