An ultra-wideband array focusing radar system

Abstract

The present invention relates to the field of ground penetrating radar technology, and in particular to an ultra-wideband array focusing radar system, which comprises: a transmitter and a receiver, a power divider, a transmitting antenna array and a receiving antenna, wherein the transmitting antenna array comprises a plurality of transmitting array elements arranged in parallel and at equal intervals, wherein the transmitting array element and the receiving antenna are both exponential Vivaldi antennas, and the transmitter and the receiver are connected to each transmitting array element through a power divider. The problem of unfocused radiation direction, poor resolution and shallow detection depth of traditional commercial ground penetrating radar is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of ground penetrating radar, and in particular to an ultra-wideband array focusing radar system. Background Art

[0002] Ground Penetrating Radar (GPR) is a highly efficient, high-resolution, non-destructive electromagnetic detection method that has been widely used in road detection, pipeline detection, mine and unexploded ordnance detection, archaeology, soil assessment and many other geophysical and engineering fields. Ground penetrating radar transmits electromagnetic wave pulses through one antenna, which penetrate the ground and propagate underground. During the propagation process, the electromagnetic wave pulses are reflected by abnormal bodies, and the reflected signals are received by another antenna. The two antennas are translated again with the same offset distance until the detection of the entire survey line is completed, realizing high-resolution detection of underground space structures.

[0003] How to achieve high-precision detection of complex targets in urban underground spaces, such as dense pipelines, has always been a hot topic in the field. Bowtie antennas, which are often used in traditional commercial ground-penetrating radars, have the advantages of simple structure, low manufacturing cost, and good time-frequency comprehensive performance. However, the wide radiation lobe of the antenna leads to unfocused radiation direction, poor resolution, and shallow detection depth, which makes it difficult to meet the high-resolution detection requirements for complex targets in urban underground spaces. Summary of the invention

[0004] The purpose of the present invention is to provide an ultra-wideband array focused radar system to address the deficiencies of the above-mentioned prior art, so as to solve the problems of traditional commercial ground penetrating radar such as unfocused radiation direction, poor resolution and shallow detection depth.

[0005] The present invention is achieved in this way.

[0006] An ultra-wideband array focused radar system, the system comprising:

[0007] A transmitter and receiver, a power divider, a transmitting antenna array and a receiving antenna, wherein the transmitting antenna array includes a plurality of transmitting array elements arranged in parallel and at equal intervals, the transmitting array element and the receiving antenna are both exponential Vivaldi antennas, and the transmitter and receiver are connected to each transmitting array element via a power divider.

[0008] Furthermore, the number of the transmitting array elements is 4, the spacing between the transmitting array elements is 0.1 m, and the total length of the array is 0.4 m.

[0009] Furthermore, the exponential Vivaldi antenna has a slot line structure whose opening size follows the e exponential law from narrow to wide, and the structural parameters are: the antenna width Width is 151mm, the antenna length Length is 233mm, and the radius R of the circular open cavity at the narrow end is 12.3mm; the starting width W1 of the feeder is 3mm, the end width W2 of the feeder is 2mm, and the feeder length Feed_L is 78mm.

[0010] Furthermore, the slotted structure satisfies:

[0011] y=C1·e α·x +C2,

[0012] Among them, a rectangular coordinate system is established with the center of the circular open cavity as the coordinate origin, (x1, y1) and (x2, y2) are the starting point and end point coordinates of the gradient groove line, respectively, and α is the e-exponential groove line gradient factor.

[0013] Furthermore, the design method of the transmitting antenna array includes:

[0014] Assume the current of the i-th array element is: I Mi =I M1 ·e j·(i-1)·ψ , that is, the current amplitudes of adjacent array elements are equal and the phase difference is ψ=0; from the directional pattern product theorem, we know that: F=f1·f a , that is, the radiation pattern F of the array is composed of the array element pattern f1 and the array factor pattern f a The array factor pattern has nothing to do with the antenna type but only with the array structure, which can be expressed as:

[0015]

[0016] Where u = k·Δr+ψ = k·d·cosθ+ψ; k refers to the kth array element; N is the number of array elements; d is the array element spacing; θ is the angle between the radiation direction and the array axis, then the half-power angle θ 0.5 for:

[0017]

[0018] Perform weighted averaging on the lattice factor patterns of each frequency within the frequency band:

[0019]

[0020] Among them, u=k·Δr+ψ=k·d·cosθ+ψ, N fre is the number of frequency steps, is the pattern weight factor of the ith frequency;

[0021] The normalized overall array factor radiation pattern with different array element spacings in the frequency band of 0.6 GHz to 4 GHz is simulated. According to the changes in the main lobe and side lobe in the simulation results, the array element spacing and the number of array elements corresponding to the lowest side lobe of the overall array factor in the working frequency band are obtained.

[0022] Furthermore, the end of the feeding microstrip line short-circuits the microstrip line.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention adopts an exponential Vivaldi antenna radiation patch, which is a frequency-independent structure. The operating frequency of the antenna can be changed by controlling the slot line parameters. Compared with the traditional ground penetrating radar based on the bowtie antenna, it has good radiation directivity;

[0025] (2) The present invention proposes to short-circuit the microstrip line at the end of the Vivaldi antenna feeding microstrip line (near the coupling point) to ensure that the length of the extended part remains unchanged, reduce reflection at the coupling point, and broaden the antenna working bandwidth. To address the problem of insufficient resolution of complex targets 0 to 1.5 m underground, to a certain extent, the widening of the bandwidth can significantly improve the system's longitudinal resolution;

[0026] (3) The present invention utilizes the basic array theory to detect complex underground targets in cities, which can effectively compress the width of the radiation main lobe and reduce the impact of side lobes within the working frequency band. 0.1m is selected as the array element spacing, the total number of array units is 4, the total array length is 0.4m, and they are arranged horizontally along the x-axis, achieving an antenna working frequency band of 0.6GHz to 4GHz, a maximum gain of 16dBi, and a half-power angle width of 29.6°, effectively reducing the impact of side lobes, further improving the gain and directivity of the transmitting antenna, and providing technical support for improving detection resolution and enhancing detection depth. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 An overall technical schematic diagram of an array focused radar system provided by an embodiment of the present invention;

[0028] Figure 2 A structural diagram of an exponential Vivaldi antenna model provided in an embodiment of the present invention;

[0029] Figure 3 A schematic diagram of a Vivaldi four-transmitting antenna array provided in an embodiment of the present invention;

[0030] Figure 4 This is a comparison diagram of an indoor sand tank after data processing between the embodiment of the present invention and the commercial ground penetrating radar Zond-12e and T1R1 (Vivaldi antenna). DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] like Figure 1 As shown, a transmitter and receiver 1, a power divider 2, a transmitting antenna array 3 and a receiving antenna 4, the transmitting antenna array includes a plurality of transmitting array elements that are equally spaced and arranged in parallel, the transmitting array element and the receiving antenna are both exponential Vivaldi antennas, and the transmitter and receiver are connected to each transmitting array element through a power divider.

[0033] The array focused radar system uses the network analyzer Agilent N9925A as the system transmitter and receiver. The four-port Wilkinson power divider distributes the UWB excitation signal to the Tx1~Tx4 transmitting antennas to achieve simultaneous excitation; the receiving antenna Rx1 is used to capture the reflected signal. The system needs to be calibrated with a calibrator before the experiment begins to compensate for the time delay and energy loss caused by the coaxial cable and power divider. This synchronous transmission array solution breaks through the limitation of the number of equipment ports, maintains the detection efficiency while improving the focusing radiation capability of the transmitted electromagnetic waves and the forward gain of the antenna, which has the effect of suppressing the interference of the surrounding environment and electromagnetic noise, and can improve the system signal-to-noise ratio, increase the detection depth, and improve the accuracy of underground target location and contour detection.

[0034] like Figure 2 As shown, the transmitting array element and receiving antenna of the present invention adopt an exponential Vivaldi antenna. The radiation patch of the exponential Vivaldi antenna has a slot line structure whose opening size follows the e exponential law from narrow to wide. This structure is a frequency-independent structure. The operating frequency of the antenna can be changed by controlling the slot line parameters. The slot line parameters C1, C2, and α satisfy:

[0035] y=C1·e α·x +C2,

[0036] Among them, (x1, y1) and (x2, y2) are the starting point and end point coordinates of the gradient slot line, respectively, and α is the e-exponential slot line gradient factor. The antenna width Width is 151mm, and the antenna length Length is 233mm; the circular open cavity radius R is 12.3mm; the feed line starting width W1 is 3mm, the feed line end width W2 is 2mm, and the feed line length Feed_L is 78mm. The microstrip line is short-circuited at the end of the Vivaldi antenna feeding microstrip line (near the coupling point) to ensure that the length of the extended part remains unchanged and reduce reflections at the coupling point.

[0037] To a certain extent, the widening of bandwidth can significantly improve the system longitudinal resolution, where the system longitudinal resolution R res The relationship with bandwidth B satisfies:

[0038]

[0039] Where c is the speed of light; ε r is the relative dielectric constant of the medium.

[0040] like Figure 3 As shown in the figure, in order to further improve the gain and directivity of the transmitting antenna, a transmitting antenna array is designed. From the basic array theory, it can be known that the transmitting array can effectively compress the width of the radiation main lobe. For an N-element equal-amplitude linear array, N refers to the number of antennas, and the current of the i-th array element can be set to: I Mi =I M1 ·e j·(i-1)·ψ , that is, the current amplitudes of adjacent array elements are equal and the phase difference is ψ=0; from the directional pattern product theorem, we know that: F=f1·f a , that is, the radiation pattern F of the array is composed of the array element pattern f1 and the array factor pattern f a The array factor pattern has nothing to do with the antenna type but only with the array structure, and can be expressed as:

[0041]

[0042] Among them, u=k·Δr+ψ=k·d·cosθ+ψ; k refers to the kth array element; N is the number of array elements; d is the array element spacing; θ is the angle between the radiation direction and the array axis. Then the half-power angle θ 0.5 From its definition we can know:

[0043]

[0044] In addition to the number of array elements, the spacing between array elements is another important factor in array design. Especially for UWB arrays, due to the large span of electrical dimensions of the array element spacing, the array factor pattern within the frequency band will change significantly. In order to ensure that the sidelobe effect within the working band is minimized, a method for calculating the overall array factor by weighted averaging the array factor pattern of each frequency point within the frequency band is proposed to meet the following requirements:

[0045]

[0046] Among them, u=k·Δr+ψ=k·d·cosθ+ψ, N fre is the number of frequency steps, is the pattern weight factor for the ith frequency.

[0047] According to the above overall array factor, half-power angle θ 0.5A simulation is performed, and according to the simulation, a normalized overall array factor pattern with different array element spacings in the 0.6GHz to 4GHz frequency band can be obtained. When an equal weight configuration is used for the 0.6GHz to 4GHz working frequency band, as the array element spacing increases, the overall array factor pattern main lobe width decreases rapidly, and side lobes begin to appear after the array element spacing exceeds a certain threshold (0.1m). Although the main lobe width of the array is further compressed when the array element spacing continues to increase to 0.15m, stronger side lobes begin to appear, and a large array element spacing will increase the overall size of the array. Therefore, 0.1m is selected as the array element spacing of the present invention, and the number of array elements is 4, so that the overall array factor pattern side lobes are as small as possible, a narrower main lobe width is obtained, and the lowest side lobe of the overall array factor of the working frequency band is obtained.

[0048] like Figure 4 As shown in Figure 2, in order to verify the exploration performance of the proposed UWB array antenna radar system, a comparative experiment was conducted on an indoor sand tank, including Figure 4 (a) is a single antenna transmission, Figure 4 (b) is the commercial ground penetrating radar Zond-12e (900MHz antenna), Figure 4 (c) is a comparative test of three schemes for four-array transmission.

[0049] Depend on Figure 4 (a) and 4(c), it can be seen that the four-array transmission can observe the bottom trend of the sand trough more clearly, and can also obtain obvious echo signals, improve the signal-to-noise ratio, and enhance the detection ability of shallow weak targets.

[0050] Depend on Figure 4 By comparing (b) and (c), we can see that Figure 4 (b) Due to the large radiation angle of the bow tie antenna, the diffraction wave tail of the pipe inside the frame is long. Figure 4 In (c), because the Vivaldi transmitting array structure radiates focused energy and has a narrow main lobe width, the pipe diffraction wave curve shown in the red box is shorter, making it less likely for two target signals to cross each other, revealing the differences in buried depths of densely distributed pipes and making it more suitable for accurate interpretation of complex underground targets.

[0051] The present invention provides a method for detecting underground complex targets by an ultra-wideband array focusing radar system, comprising the following steps:

[0052] a. The four-element antenna is installed in the antenna slot with a fixed spacing. The transmitting antenna array includes Tx1, Tx2, Tx3, and Tx4, with a spacing of 0.1m. The receiving antenna Rx is also spaced 0.1m apart from the transmitting antenna array.

[0053] b. Using the network analyzer Agilent N9925A as the transmitter and receiver, the four-port Wilkinson power divider evenly distributes the power of the single transmit port of the network analyzer to the transmit antenna array.

[0054] c. The system needs to be calibrated using a calibrator before the experiment begins to compensate for the time delay and energy loss caused by the coaxial cable and power divider.

[0055] d. The four elements of the transmitting antenna synchronously transmit electromagnetic waves underground. The electromagnetic waves are reflected or refracted when they encounter the interface of the material, and then a receiving antenna receives and records the reflected or refracted electromagnetic waves.

[0056] e. Considering the application scenario of high attenuation underground and the bandwidth limitation of the power divider, after experimental testing, the antenna operating frequency band is 0.6GHz~4GHz, the maximum gain is 16dBi, the half-power angle width is 29.6°, and it maintains high spatial resolution while having a certain penetration ability.

[0057] f. The detection results are processed by data processing methods such as background elimination and automatic gain control (AGC) and then analyzed.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An ultra-wideband array focused radar system, It is characterized in that The system includes: A transmitter and receiver, a power divider, a transmitting antenna array and a receiving antenna, wherein the transmitting antenna array includes a plurality of transmitting array elements that are equally spaced and arranged in parallel, the transmitting array elements and the receiving antenna are both exponential Vivaldi antennas, and the transmitter and receiver are connected to each transmitting array element through a power divider; The number of transmitting array elements is 4, the spacing between transmitting array elements is 0.1m, and the total length of the array is 0.4m; The exponential Vivaldi antenna has a slot line structure whose opening size follows the e exponential law from narrow to wide, and the structural parameters are: the antenna width Width is 151mm, the antenna length Length is 233mm, and the radius R of the circular open cavity at the narrow end is 12.3mm; the feed line starting width W1 is 3mm, the feed line end width W2 is 2mm, and the feed line length Feed_L is 78mm; The slot line structure meets the following requirements: y=C 1 ·its α·x +C 2 , In which, the center of the circular open cavity is taken as the coordinate origin to establish a rectangular coordinate system, (x 1 ,y 1 ) and (x 2 ,y 2 ) are the coordinates of the starting point and the end point of the gradient groove line, and α is the gradient factor of the e-exponential groove line; The design method of the transmitting antenna array comprises: Assume the current of the i-th array element is: I Mi =I M1 ·e j·(i-1)·ψ , that is, the current amplitudes of adjacent array elements are equal and the phase difference is ψ=0; from the directional pattern product theorem, we know that: F=f 1 ·f a , that is, the radiation pattern F of the array is given by the element pattern = f 1 and array factor pattern f a The array factor pattern has nothing to do with the antenna type but only with the array structure, which can be expressed as: Where u = k·Δr+ψ = k·d·cosθ+ψ; k refers to the kth array element; N is the number of array elements; d is the array element spacing; θ is the angle between the radiation direction and the array axis, then the half-power angle θ 0.5 for: The weighted average of the array factor patterns of each frequency point in the frequency band is used to obtain the overall array factor pattern: Among them, u=k·Δr+ψ=k·d·cosθ+ψ, N fre is the number of frequency steps, is the pattern weight factor of the ith frequency; The normalized overall array factor radiation pattern with different array element spacings in the frequency band of 0.6 GHz to 4 GHz is simulated. According to the changes in the main lobe and side lobe in the simulation results, the array element spacing and the number of array elements corresponding to the lowest side lobe of the overall array factor in the working frequency band are obtained.

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