KR19980025395A - Vehicle location tracking method and system - Google Patents

Abstract

A method and system 50 for tracking the position of a mobile transmitter using angle of arrival measurements from the direction finding antenna arrays 60, 70 is disclosed. Each array includes a number of devices 60A-60N, 70A-70N, which devices form a group to provide subarrays with different device spacings that are multiples of one half of the transmitter wavelength. Doing. Ambiguity is eliminated by processing each data received from this subarray. The signals from the array are processed to convert electrical phase delays into spatial angles, and the spatial angle data is processed to provide the transmitter's x, y position, velocity, and acceleration. When the system is used for a transmitter mounted on a mobile vehicle, the system further processes x and y data, applies a quality weighting factor, filters and removes multipath factors, and estimates vehicle profile information.

Description

Vehicle location tracking method and system

The present invention relates to a system for accurately measuring the position of a vehicle using angle-of-arrival measurements.

Current vehicle detection systems use antenna patterns to determine the position of the transmitter in the highway network. The positional accuracy of these systems is very poor and many large antennas are required to improve their performance. The reception amplitude measurement technique can improve this performance to some extent, but it has been measured that the variation in signal strength between different vehicles is 10 dB or more, and there is a problem that the antenna pattern of these vehicles is not uniform. These problems have limited the use of open road toll systems, resulting in the use of barrier toll systems that establish vehicle separation for the purpose of location identification.

U. S. Patent No. 5,307, 349, assigned to the same person as the present invention, discloses a technology relating to a vehicle that can communicate with the infrastructure of a highway. The system disclosed in US Pat. No. 5,307,349 can be used to collect tolls electronically on open roads. U. S. Patent No. 5,227, 803, assigned to the same person as above, discloses a method of measuring the position of a transmitter mounted on a vehicle.

The present invention is directed to providing a set of closed form position calculation equations effective for combining multiple position measurements, filtering out error measurements, and providing a tracking algorithm.

1 illustrates a transmitter position detection system using a direction finding antenna.

2 is a functional block diagram of the system of FIG.

3A illustrates an embodiment of the geometry of an antenna array of the system of FIG.

3B illustrates another embodiment of the geometry of the antenna array of the system of FIG.

4A and 4B show (dx / d when β ₁ and β ₂ are 45 ⁰ ; )-(x, y) and (dy / d diagram showing each plot of (x, y). 4A shows the X (range) error value and FIG. 4B shows the Y (lane) error value.

5 is a schematic block diagram illustrating an exemplary receiver used in the system of FIG.

6 is a simplified processing flow diagram illustrating the sequence of functions executed by a processor including the system of FIG.

Explanation of symbols on the main parts of the drawings

60: antenna array

70: antenna array

42: transmitter

100: processor

The system according to the invention comprises two or more antenna arrays for measuring the signal phase difference, a phase unwrapping process for determining the spatial angle of arrival (AOA), a positioning process for determining the transmitter position and the Vehicle tracking processing for estimating speed, acceleration and position. The system also includes quality factor analysis to filter out samples that are distorted due to the multipath.

The method for tracking a moving transmitter that transmits an RF signal includes the following steps:

A plurality of antenna elements arranged to be spaced apart from each other, the antenna elements being grouped into a plurality of sub-arrays, the spacing between the elements within the sub-arrays being a different multiple of half the transmitter wavelength used Disposing the arranged first and second antenna arrays so as to be spaced apart from an area to which the transmitter moves;

Receiving RF signals from a transmitter using the first and second antenna arrays to convert the sub-array signals from each array signal into digital data;

Processing the digital data to provide phase data indicative of the electrical phase of a signal received at different sub arrays of the first and second antenna arrays;

Converting the phase data into spatial angle data representing an angle of arrival of an RF signal incident on a sub array of first and second antenna arrays; And

Processing the spatial angular data together with the shape data of the antenna representing the position and geometry of the first and second antenna arrays to provide information specifying the estimated position of the transmitter.

Other features and advantages of the invention can be more clearly understood from the following detailed description of embodiments of the invention as shown in the drawings.

The position of the moving transmitter can be detected by a Direction Finding (DF) antenna system. 1 shows a transmitter position detection system 50 for tracking the position of a moving vehicle 40 equipped with a transmitter 42. The symbols used in this figure are as follows: x1 and y1 represent the coordinates of the antenna array 60. x2 and y2 represent the coordinates of the antenna array 70. β1 and β2 represent the angles of rotation of the two antennas 60 and 70, respectively. ah represents the height of the antenna array on the gantry. x, y represents the position of the transmitter. v _h represents the height of the transmitter. 1 and 2 represents the angle of arrival measured from each antenna array 60 and 70.

The position of the transmitter 42 is determined by intercepting the transmission signal using the DF antenna. At each antenna, two or more DF antennas are used to measure the electrical phase of the signal, and this information is converted into spatial arrival angles (AOA). Based on the two AOA values, two half hyperbolas H1, H2 are identified on the surface of the roadway. These two AOA values are determined on the same signal or on separate signal segments at small time intervals to ensure that the position does not fluctuate significantly. These hyperbolas are used to find their intersection and find the position (X, Y) of the vehicle 40. This computation is repeated at different times to determine the multiple vehicle positions. These positions are combined with weights based on inspection baseline measurements to determine characteristics such as transmitter position profile and acceleration, velocity and time to reach a particular position.

2 shows a functional block diagram of the target positioning system 50. The system includes two array antennas 60, 70, two array antenna receivers 70, 80 and a processor 100 for measuring the received phase. The processor includes phase spread calculation functions 110A and 110B for determining spatial AOA, transmitter position calculation function 120 for determining the position of the transmitter, and vehicle profile calculation function 130 for estimating vehicle movement characteristics. Perform a variety of computational functions. The processor also performs qualitative parameter analysis functions 140A and 140B to identify which samples are reliable and which samples are unreliable and weight each sample to minimize the effects of multipath interference.

In the communication processor, the vehicle transmitter 42 transmits a bundle of RFs. U.S. Patent 5,307,349 describes an exemplary protocol that can be used to coordinate the transmission of an RF bundle. These signal bundles are received by at least two DF antenna arrays, that is, antenna arrays 60 and 70, which allow electrical phase difference measurements between signals received at array elements 60A-60N and 70A-70N. . The arrays have N devices and provide N-1 phase difference measurements. These N-1 measurements are unwrapped to form the spatial angle of arrival of the received signal for each array. That is, these measurements are processed to find the only AOA solution. This unwrapping technique is A Technique to Detect Angle of Arrival with Low Ambiguity. V. K. V. Cai, pending, and disclosed in a patent application assigned to the same person as the present invention (Agent Dacket No. PD-94527), the entire contents of which are incorporated herein by reference. As an alternative, Robert L., published in NRL REPORT 8005, dated September 9, 1976. The technique disclosed in Robert L. Goodwin's article Ambiguity-Resistant Three-and Four-Channel Interferometers can also be used to transform spatial angular data.

The antenna elements of each array are arranged so that the spatial AOA can be determined accurately, without ambiguity. In addition, redundant baseline measurements are used as a check baseline to establish a quality baseline used to estimate the vehicle profile.

3A and 3B show two embodiments of DF antenna arrangements each having the same base of 2.5λ, ie the maximum distance between a pair of elements is 2.5Aλ. The DF antenna 150 includes four elements 152, 154, 156, and 158 symmetrically disposed around the eri centerline 160. Adjacent elements 154 and 156 are separated by [lambda] / 2. Elements 152 and 156 are separated by 1.5λ. Elements 154 and 158 are separated by 1.5λ. Elements 152 and 158 are separated by 2.5λ. The transmitter RF wavelength is λ.

The elements of the array 150 can be thought of as a group of plural subarrays or baselines, each of which includes a pair of antenna elements with distances between elements that are multiples of [lambda] / 2. Thus, the array 150 forms elements 154 and 156 that form the first baseline by λ / 2 apart, elements 152 and 154 that form the second baseline by λ, and forms a third baseline by 1.5λ. Elements 154 and 158, wherein the elements 152 and 156 form a fourth baseline by 1.5λ apart, and the elements 152 and 158 form a fifth baseline by 2.5λ apart. The third and fourth base lines have the same distance between the elements and can be used as inspection base lines because the same phase shift value must be determined at these two base lines.

Array 150 has k = (1/2, 1, 2.5), where phase = unwrap baseline factor (defined as the ratio of distance between elements to signal wavelength, for a given baseline), and 2 Two test line baseline factors c ₁ = c ₂ = 1.5, which can be used for the quality indication function. In this example, the phase-evolution baselines are the first, second and fifth baselines, and the inspection baselines are the third and fourth baselines.

The DF antenna 200 also includes four antenna elements 202, 204, 206 and 208. These elements are separated from the elements of the array 150. Elements 202 and 204 are λ / 2 apart from the first baseline, elements 202 and 206 are 1.5λ apart from the second baseline, and elements 202 and 208 are 2.5λ apart from the third baseline And elements 204, 206 and 208 are λ apart from the fourth baseline. Array 200 has a phase development baseline factor k = (1/2, 1.5, 2.5) and two test baseline factors c ₁ = c ₂ = 1.

The baseline of array 150 is superior to the baseline of array 200, which has a baseline of 1.0 and a baseline of array 200 has a factor of 1.5, thereby preventing ambiguity and The accuracy of the test is improved. Moreover, the array 150 is characterized in that only one element is not included in each base line. Thus, even if any element fails, some of the base lines still operate.

The received electrical phase is processed by phase evolution processing functions 110A and 110B to determine the AOA. This phase development process in the preferred embodiment is a trellis search, which utilizes the structure of phase ambiguity and maximizes detection performance. This technique finds the shortest path from the shortest baseline to the middle baseline and finally the longest baseline. From the shortest baseline, the processor determines the developed phase with the least ambiguity. Based on this phase, the next shortest phase is examined and the developed phase closest to the last developed phase is determined. This process proceeds to the longest baseline to determine the deployment phase used to determine the AOA. The phase evolution function is a technique for detecting the angle of a received signal with a low ambiguity of the invention, and the inventors have to explain it. V. K. V. Cai, pending, and more fully disclosed in a patent application assigned to the same person as the present invention. The shortest baseline (λ / 2) has only one AOA solution, but does not provide the accuracy required. The longest baseline (5λ / 2) is as accurate as necessary but has multiple spatial angles that produce the same electrical Δφ (phase shift) values. The technique is to select the long baseline to achieve the required accuracy and the shortest baseline to resolve the ambiguity.

As a result of the AOA detection, the transmitter 42 is located on the surface of the cone. Knowing the height of the transmitter 42 (ie z = v _h ), the tag should be located on one branch of the hyperbola. The equation for the two hyperbolas is

Therefore, the transmitter difference (x, y) can be determined by finding the intersection of the two hyperbolas H ₁ and H ₂ . The solution (x, y) of the above equation can be obtained by searching starting from the intersection of two asymptotes of hyperbola H ₁ and H ₂ . This technique is time consuming and impractical for use in toll collectors. A new technique has been developed to obtain a closed form solution for transmitter tag location. First, the two hyperbolic equations are simplified as follows.

H ₁ : a ₁ x ² + a ₂ y ² + a ₃ xy + a ₄ x + a ₅ y + a ₆ = 0 (3)

H ₂ : b ₁ x ² + b ₂ y ² + b ₃ xy + b ₄ x + b ₅ y + b ₆ = 0 (4)

Next, we create a one-variable quadratic equation by substituting for x,

c ₁ y ⁴ + c ₂ y ³ + c ₃ y ² + c ₄ y + c ₅ = 0 (5)

Solve for y and find x using (H ₁ ) and (H ₂ ). There are a maximum of eight real solutions for (x, y). Equations (3) and (4) are again examined to find the correct pair of (x, y). In solving the equation, we can determine the non-solution values for equations (1) and (2). These are eliminated by substituting all values back into equations (1) and (2).

The position of the DF antennas 60 and 70 affects the accuracy of the transmitter position measurement. If the axes of the two DF antenna arrays are on the y axis, the accuracy on the x axis is maximum (minimum dx / d ), the accuracy on the y position is minimal (large dy / d ). Thus, the antennas must be rotated to focus on the region of interest. The rotation of the two antennas is chosen by β ₁ and β ₂ so that these two factors are within expectations.

These are obtained from equations (3) and (4). If the vehicle is confined within the area (x≥0, y ₁ ≤ y≤ y ₂ ), the two angles are selected between 45 ° and 60 ° to balance the range (dx) and lane (dy) errors. Should be. 4A and 4B show that when β ₁ and β ₂ are 45 ° (dx / d ) (x, y) and (dy / d ) (x, y) is shown. 4A shows the X (range) error value, and FIG. 4B shows the Y (lane) error value.

In the case of partial-time interference, such as multi-path or burst noise, some AOA phase measurements may be wrong, and thus a target location sample Can also be wrong. Such false samples can be identified and processed to minimize the effects of partial-time interference. Thus, in the case of the DF antennas 60 and 70, two independent base lines of the same length should be set for inspection purposes. If the two base lines are of equal length, the detected phase shift for each base line should be the same. Otherwise, there is an error, so the measurement should be weighted as shown in the following equations (8, 9, 10). If the DF antenna does not have two independent bases of equal length, any two bases with a factor of c ₁ and c ₂ can be used to set the quality factor.

3A and 3B show two exemplary DF antenna arrays 150, 200 with four elements on a baseline of 2.5λ. The antenna array 150 has a baseline factor k = (1/2, 1, 2.5) and can provide AOA phase evolution with low ambiguity. Also based on this structure, two baselines with a factor of 1.5 (c ₁ = c ₂ = 1.5) can be obtained and used to examine the quality of the detected AOA.

Let c ₁ and c ₂ be two quality baselines. Quality indicators using Gaussian weighting are defined as:

γ = exp (-max (β ₁ ² , β ₂ ² ) / 2σ ² ) (8)

β ₁ = ((c ₂ / c ₁ ) Δø _{c (1)} -Δø _{c (2)} ) mod (-180, 180) at DF antenna 150 (9)

β ₂ = ((c ₂ / c ₁ ) Δø _{c (1)} -Δø _{c (2)} ) mod (-180, 180) at DF antenna 200 (10)

[Where σ is the selected value for the weighting method and depends on the signal-to-noise ratio at the antenna receiver.] In the absence of noise, β ₁ and β ₂ are both 0 and the quality factor γ is 1. However, in the case of strong interference, both β ₁ and β ₂ become large, the quality factor γ decreases to almost zero, and the influence of such position samples is likely to be suppressed. Alternatively, other weights may be used, which may be effective against partial-time interference.

Tracking moving targets requires collecting and processing many samples to predict acceleration, speed, or arrival time. Vehicle profile processing is performed separately for the x-axis and the y-axis. The movement of the vehicle on the x-axis can be expressed as

x (t) = (1/2) at ² + v ₀ t + x ₀ (11)

[Where x (t) is the x-position of the transmitter at time t, a is the x-acceleration constant, v ₀ is the initial x-speed, and x ₀ is the x-position of the transmitter at time zero. However, since partial time interference can cause some of the location samples to be severely wrong, it is necessary to determine the quality factor γ _i associated with each location sample and weight the sample as follows.

γ ₁ x ₁ = γ ₁ [(1/2) at ₁ ² + v ₀ t ₁ + x ₀ ]

γ ₂ x ₂ = γ ₂ [(1/2) at ₂ ² + v ₀ t ₂ + x ₀ ] (12)

γ _n x _n = γ _n [(1/2) at _n ² + v ₀ t _n + x ₀ ]

[Where t _i represents the time in sample i (i-1, 2, n).] The above formula can be expressed as follows.

The goal is to solve for D to determine the vehicle profile on the x-axis.

X = (T'T) ^-1 T'D (14)

Once a, v ₀ , and x ₀ are found, the x-coordinate of the vehicle can be found at any time. It should be noted that the equation is only harmful if the number of quality samples (of n samples) is 3 or more. However, it should be noted that for many applications where the transmitter is expected to move at a constant speed, a can be set to 0, which can be simplified to a two-parameter equation.

At least two quality samples are needed to find v ₀ and x ₀ .

This process can be repeated for the y-position, the transmitter position (x, y) is determined, and the time at which the transmitter crosses the gantry line (x = 0) can be obtained from equation (11).

FIG. 5 shows a special schematic block diagram implementing the elements of the system 50, and in particular the antenna receiver elements. The antenna array elements are connected to the RF switches 81 and 91, which provide a means for switching the receiver elements between the antenna arrays so that one set of receiver hardware is used for both antenna arrays while being temporally multiplexed. Reduce costs Thus, one antenna array is selected for the measurement.

In the embodiment of Figure 5, antennas 60 and 70 are of the type shown in Figure 3B. The array 60 includes an RF switch 61 that switches between the elements 60B- 60N corresponding to the elements 204, 206 and 208 shown in FIG. 3B, and the selected element is connected to the input of the switch 81. Connected. Similarly, array 70 includes an RF switch 71 that switches between elements 70B-70N and connects the selected element to the input of switch 81. In general, N arrays may be connected to the switch 81. The element 60A is connected to the input of the switch 91 as a reference element. This device is common to all baselines in the array in this example. Similarly, element 70A is connected as a reference element to the input of switch 91.

Switches 81 and 91 select specific inputs, which pass through respective gain stages 82 and 92 to increase signal strength. The selected inputs then pass through respective band pass filters 101 and 102 that filter out potential out-of-band interference signals. Each log amplifier 83 and 93 provides two functions. First, they provide amplification and a limited output signal (constant amplitude for all received signals) that will drive the synchronous phase detector. The second function is to provide a log video output of one channel from amplifier 92. This video output is used to detect the presence of energy in the ASK modulated signal. In an embodiment, the transmitter 42 transmits using ASK modulation, where half of the bits are filled with a bundle of signals and the other half are no signals. To prevent the measurement from going wrong, it is necessary to perform AOA measurements only when there is signal energy. This function is performed by circuitry 85 receiving a log video signal from a log amplifier 93 connected to a reference element selected as input. The input signal passes through an amplifier stage 86 that is adjusted to set a threshold for the lowest level signal that should be detected. Diode 88 sets a detection threshold so that signals above this level drive amplifier 87 to a positive limit. This positive signal is used by the A / D circuits 97 and 98 to initiate the I and Q detection processes.

Of course, if you use other modulation techniques with constant signal amplitude levels such as FSK, PSK, MSK, circuit 85 would not be necessary.

Respective log amplified signals from amplifiers 83 and 93 pass through synchronous phase detection circuit 95, which provides analog to ground (A / D) gain and offset circuitry 96. ) Provide I and Q signal components. An amplifier 96 is used to alter the I and Q channel signals so that their amplitude represents a phasor with an angle used to measure the differential phase between the device signal being measured. These signals are then digitized by the A / D circuits 97 and 98 and passed to the processor 100.

Control register 89 provides control signals for actuating switches 81 and 91.

The given baseline of the selected antenna array can be observed at any point in time, and all can be observed according to the time-multiplexing scheme.

6 is a simple flow diagram illustrating the operational flow in the processor 100. In step 100 I and Q data from the receiver is read. This data is averaged to increase the signal-to-noise ratio [step 302], and an electrical phase angle is obtained from this averaged data. This electrical phase angle is converted to spatial angle data (step 306). The spatial angle data is converted into transmitter position information [step 310], and the x and y outputs are provided. Spatial angle data is also used to determine the quality factor [step 308], which is used to weight the x, y position data for vehicle profile estimation [step 312].

The present invention has made several advances in vehicle location and tracking technology.

(1) An open road gantry with multiple multi-element antenna arrays measures the phase of the transmitted signal.

(2) The antenna array can rotate to maximize the surveillance area of the antenna and to improve tracking accuracy.

(3) Redundant antenna array spacing is used on the checking baselines. This inspection baseline is used to weight the position measurements to reduce the error caused by multipath.

(4) AOA measurements are converted to position measurements using a search algorithm or a solution of quadratic equations.

(5) Vehicle movement profile estimation uses weighted minimum mean square error prediction along with inspection baseline weighting.

It will be appreciated that the above embodiments are merely specific embodiments that can explain the principles of the present invention. Those skilled in the art will be able to devise other embodiments in accordance with the principles of the invention without departing from the scope of the invention.

Claims (14)

A method for tracking a mobile transmitter for transmitting an RF signal, the method comprising: Arranging the first and second antenna arrays 60, 70 in a position spaced apart from the area in which the transmitter 42 moves, wherein each antenna array is arranged with a plurality of antenna elements 60A spaced apart from each other; -60N, 70A-70N, wherein the device comprises a plurality of baseline pairs of elements, and the device-to-device spacing d of the device in the baseline pair is in each baseline pair. For different, batching steps, Receiving RF signals from the transmitter using the first and second antenna arrays and converting baseline signals from each element base pair into digital data; Processing the digital data to provide phase data indicative of electrical phases of signals received at different base pairs of the first and second antenna arrays (110A, 110B), Converting the phase data into spatial angle data representing angles of arrival of RF signals incident on baseline pairs of the first and second antenna arrays (110A, 110B), and Processing the spatial angular data with antenna structure data representing the position and geometry of the first and second antenna arrays to provide information indicating the estimated position of the transmitter (120) Method comprising a. The method of claim 1, further comprising: collecting RF signal transmission signals from the transmitter over a period of time to provide a plurality of samples, and processing the samples received over time to process the mobile transmitter. Providing (130) data indicative of velocity and acceleration. 3. The method of claim 2, comprising determining 140A and 140B sample quality weighting factors, and multipath distorted samples by weighting the transmitter position data as the factor. Compensating (130) further comprises. 4. The antenna array of claim 3, wherein each of the antenna arrays comprises first and second checking baseline pairs of elements 152, 156, 154, 158 spaced apart from each other by a distance equal to the distance d. Determining a sample quality weighting factor comprises comparing the electrical phase received at the first and second base pairs for a given set of samples, and if the electrical phases for the first and second base pairs are not the same, Assigning a quality weighting factor to a predetermined set of samples. The antenna array device as claimed in claim 1, wherein the antenna array elements are arranged along respective linear array axes, the array axes being respectively relative to a nominal direction of vehicle movement relative to the array. Arranged in an angle, wherein the angle is in the range of about 30 degrees to 60 degrees. The device of any one of claims 1 to 5, wherein the element spacing d in the baseline pair is a multiple of lambda / 2, where lambda represents the nominal wavelength of the RF signal. Wherein the first pair of baseline pairs has an interval d of λ / 2. 7. A method according to any one of the preceding claims, wherein no one antenna element comprises each of said plurality of element base pairs. 8. The method of any one of claims 1 to 7, wherein processing the spatial angle data and providing information indicative of the estimated position of the transmitter comprises determining the intersection of two hyperbolas H ₁ , H ₂ . Wherein the hyperbola H ₁ , H ₂ is H ₁ : a ₁ x ² + a ₂ y ² + a ₃ xy + a ₄ x + a ₅ y + a ₆ = 0 H ₂ : b ₁ x ² + b ₂ y ² + b ₃ xy + b ₄ x + b ₅ y + b ₆ = 0 The position of the transmitter is at x, y, the solution of the equation, and the solution of the hyperbolic equation is the fourth order single variable equation c ₁ y ⁴ + c ₂ y ³ + c by substituting the variable x. ₃ y ² + c ₄ y + c ₅ = 0 to solve for y and determine x using the equation H ₁ or H ₂ . A system (50) for tracking a mobile transmitter that transmits an RF signal, First and second directional detection antenna arrays 60, 70 disposed at positions spaced relative to the area to which the transmitter is moving, each antenna array having a plurality of antenna elements 60A- arranged to be spaced apart from each other. 60N, 70A-70N, wherein the device comprises a plurality of baseline pairs of elements, and the device-to-device spacing d of the device in the baseline pair is for each baseline pair. Different, first and second directional antenna arrays 60, 70, Receiving devices 80 and 90 for receiving RF signals from the transmitter using the first and second antenna arrays and converting baseline signals from respective element base pairs into digital data, and Processor device 100 for processing the Ditizal data Including, the apparatus 100 is Means (110A, 110B) for providing phase data indicative of the electrical phase of a signal received at different baseline pairs of said first and second antenna arrays in response to said digital data; Means (110A, 110B) for converting the phase data into spatial angle data representing a spatial angle of arrival of RF signals incident on baseline pairs of the first and second antenna arrays, and Means for processing antenna structure data representing the position and geometry of the first and second antenna arrays and the spatial angle data to provide information indicating the estimated position of the transmitter 120 System comprising a. 10. The apparatus of claim 9, wherein the receiving device collects RF signal transmission signals from the transmitter over a period of time to provide a plurality of samples, wherein the processor device collects the samples received over time. Means (130) for processing to provide data indicative of the speed and acceleration of the mobile transmitter. 11. The processor apparatus of claim 10, wherein the processor apparatus weights the means 140A, 140B for determining sample quality weighting factors, and the transmitter position data as the factor. means (130) for compensating for multipath distorted samples. 12. The antenna array element according to any one of claims 9, 10 and 11, wherein the antenna array elements are arranged along each linear array axis, the array axis being a nominal direction of vehicle movement relative to the array. Arranged at each angle relative to the angle, wherein the angle is in the range of about 30 degrees to 60 degrees. 13. The device of any one of claims 9 to 12, wherein the element spacing d in the baseline pair is a multiple of lambda / 2, where lambda represents the nominal wavelength of the RF signal. And the first pair of pairs has an interval d of λ / 2. 14. The system of any of claims 9 to 13, wherein no one antenna element comprises each of the plurality of element base pairs.