Ultra-wideband ground penetrating radar antenna based on anisotropic material

Abstract

The invention relates to the technical field of electromagnetic wave time domain antennas, in particular to an anisotropic material-based ultra-wideband ground penetrating radar antenna, which comprises a time domain butterfly antenna unit, a sponge layer, an anisotropic material, a metal back cavity and a coaxial feed part. According to the invention, a butterfly antenna is mainly selected. The antenna is made of an all-metal material, the patch is an elliptical butterfly antenna, a distributed loading resistance loading mode is selected, the characteristic impedance of the antenna is basically kept unchanged along with the frequency, and meanwhile, the bandwidth is increased; the back cavity is added to reduce the influence of the surrounding environment and all parts in the system on the antenna and suppress the omnidirectional radiation of the antenna, and the absorption layer is added in the back cavity to cover the back cavity, so that multiple reflections between the antenna and the cavity are suppressed. The designed antenna is low in working frequency band, wide in frequency band, good in time-domain characteristic, simple in feeding and capable of achieving long-distance high-resolution detection under a deep layer.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave time-domain antennas, and more specifically, to an ultra-wideband ground-penetrating radar antenna based on anisotropic materials. Background Art

[0002] With the development of technology, ground-penetrating radar has also developed rapidly. Ground-penetrating radar uses a transmitting antenna to send microwave signals to a target at a fixed transmitting period, and judges the nature of the target by sampling and analyzing the echo signals. Traditional ground-penetrating radar uses an equivalent sampling method to sample the radar echo, and dozens of transmitting pulses are required to complete the sampling of one echo. At the same time, ground-penetrating radar mainly detects and searches for underground targets, and the antenna is undoubtedly a very important part of the ground-penetrating radar. When the ground-penetrating radar works in the deep layer, the deep underground is a lossy inhomogeneous medium, which has a great influence on the ground-penetrating radar. Therefore, it is required that the antenna works in a relatively low frequency band. At the same time, the signal radiated by the ground-penetrating radar is a pulse signal. In order to obtain higher resolution, the bandwidth requirement for the antenna is also relatively strict, and the larger the bandwidth, the better.

[0003] For a ground-penetrating radar system, it is desired that the antenna has the characteristic that the input impedance hardly changes with frequency in a very wide frequency band. The size and structure of the dipole biconical antenna have the property of "scaling up proportionally", that is, the radius of the dipole antenna increases as its length increases. The dipole biconical antenna is composed of two symmetric conical conductors, which can be divided into an inner domain and an outer domain. However, in reality, there cannot be an infinitely long biconical antenna, and a finite-length biconical antenna will produce a truncation effect at the antenna end, generating a reflected wave, which affects the input impedance of the antenna port. In addition, the biconical antenna occupies a relatively large space and does not have the characteristic of antenna miniaturization.

[0004] The dipole of the bow-tie antenna has a large cross-sectional area, making the characteristic impedance of each point along the dipole constant everywhere, reducing the reflection caused by the discontinuity of the characteristic impedance, and at the same time broadening the frequency band. In the process of designing the bow-tie antenna, it is found that at the end of the antenna arm, a large amount of current accumulates and generates an echo, which returns to the antenna feed port, deteriorating the port input impedance of the antenna. Therefore, a method of resistance loading is used to weaken the influence of current reflection. The method of loading the resistor is divided into lumped loading and structural loading. Lumped loading is further divided into distributed loading and end loading. Distributed loading is to add parallel lumped elements at specific intervals on the antenna arm, which can not only improve the impedance discontinuity on the antenna arm, but also play a role in guiding the current flow, thereby radiating a stronger signal and obtaining an echo signal with less ringing.

[0005] End loading is to connect a lumped element at the end of the antenna arm, which can release a large amount of current accumulated at the end of the antenna arm, optimize the input impedance of the feed end, and obtain a wider frequency band.

[0006] In the structure of the antenna, structural loading is generally adopted. Structural loading is divided into shape loading and shielding structure loading. Shape loading mostly uses means such as rounding, truncation, and slotting to improve various performance parameters of the antenna.

[0007] Rounding is to add rounded corners at the sharp vertices of the butterfly antenna. It can not only reduce the area of the antenna, making the antenna have the characteristics of miniaturization, but also reduce the reflection of the input current at the edge of the antenna, improve the current distribution on the radiation surface of the antenna, flatten the input impedance curve of the antenna, and improve the return loss. Truncation is to truncate the antenna and use a gradually shaped edge to trim the antenna arm. It can not only reduce the size of the antenna, but also increase the flatness of the antenna impedance bandwidth and the antenna bandwidth. Slotting is to remove a specific shaped part from the antenna arm of the ultra-wideband antenna to weaken the current reflection generated by truncation mismatch at the end of the antenna arm.

[0008] Shielding structure loading is to place a shielding cavity in the direction of the antenna facing the air to suppress the clutter interference generated by the background environment.

[0009] Therefore, we propose an ultra-wideband ground penetrating radar antenna based on anisotropic materials to solve the above problems. Summary of the Invention

[0010] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide an ultra-wideband ground penetrating radar antenna based on anisotropic materials to solve the problems proposed in the above-mentioned background technology.

[0011] To achieve the above object, the present invention provides the following technical solution: An ultra-wideband ground penetrating radar antenna based on anisotropic materials, including a time-domain butterfly antenna unit, a sponge layer, an anisotropic material, a metal back cavity, and a coaxial feeding part; The time-domain butterfly antenna unit includes an upper butterfly patch, a lower butterfly patch, and a dielectric substrate; The upper butterfly patch includes an upper elliptical patch, a first loading resistor, a first long strip metal patch, and a first circular hole dug at the top; The lower butterfly patch includes a lower elliptical patch, a second loading resistor, a second long strip metal patch, and a second circular hole dug at the top; The dielectric substrate includes a metal substrate made of FR material and a first circular small hole dug in the center for coaxial feeding; The sponge layer includes a sponge and a second circular small hole dug out for coaxial feeding and cables; The anisotropic material includes an anisotropic material body and a first cable circular hole; The metal back cavity includes a metal back cavity body and a second cable round hole, and the metal back cavity covers the anisotropic material layer, with the bottom and side wall thicknesses both being 2 mm, and the second cable round hole is dug at the bottom; The coaxial feeding part penetrates through the dielectric substrate, the sponge layer, the anisotropic material and the metal back cavity for signal transmission.

[0012] In a preferred embodiment, the distance between adjacent metal strips of the upper layer butterfly patch is 10.3 mm, the length is 240 mm, and the width is 4 mm; The major axis and minor axis of the upper layer elliptical patch are 134 mm and 140 mm respectively; The size of the first loading resistor is 2 mm * 1.2 mm, and the length of the first long strip metal patch is 240 mm and the width is 6.4 mm.

[0013] In a preferred embodiment, the lower layer butterfly patch has the same size as the upper layer butterfly patch, the difference being that a set of circular rings are added to the top end of the lower layer butterfly patch to receive feeding.

[0014] In a preferred embodiment, the thickness of the dielectric substrate is 2 mm, and the length and width are 310 mm and 245 mm respectively.

[0015] In a preferred embodiment, the thickness of the sponge layer is 70 mm.

[0016] In a preferred embodiment, the thickness of the anisotropic material is 114 mm, which is used to suppress the multiple reflection signals between the antenna and the metal back cavity.

[0017] In a preferred embodiment, the bottom and side wall thicknesses of the metal back cavity are both 2 mm, forming a fully enclosed shielding structure to suppress environmental interference.

[0018] In a preferred embodiment, the operating frequency band of this antenna is from 160 MHz to 400 MHz, the return loss is lower than -10 dB, and the voltage standing wave ratio is less than 2.

[0019] In a preferred embodiment, the anisotropic material layer is a layered material with a gradually changing conductivity, which absorbs the reflected signals through the distributed resistance characteristics.

[0020] The technical effects and advantages of the present invention: 1. The butterfly antenna is generally circular. In this design, the butterfly antenna is ellipticized, that is, rounded corners are added at the sharp vertices of the butterfly antenna. This can not only reduce the area of the antenna, making the antenna have the characteristics of miniaturization, but also reduce the reflection of the input current at the edge of the antenna, improve the current distribution on the radiation surface of the antenna, flatten the input impedance curve of the antenna, improve the return loss, and at the same time increase the antenna bandwidth by adding antenna arms, that is, adding a group of metal strips on the patch.

[0021] 2. During the design of the butterfly antenna, it is found that at the end of the antenna arm, a large amount of current accumulates and generates echoes, which return to the antenna feed port and deteriorate the port input impedance of the antenna. Therefore, the method of resistance loading is used to weaken the influence brought by current reflection.

[0022] The selected resistance loading method this time is distributed loading: connecting lumped elements at the end of the antenna arm can release a large amount of current accumulated at the end of the antenna arm, optimize the input impedance of the feed end, and obtain a wider frequency band.

[0023] 3. Add a cavity of a certain size on the back of the metal substrate to suppress the radiation on the back of the antenna, and can shield the interference brought by the environment and metal devices to the antenna. A reasonable back cavity can also play a role in strengthening the radiation field of the antenna to the ground.

[0024] 4. Fill anisotropic materials between the antenna and the back cavity to suppress the multiple reflection signals formed between the antenna and the back cavity. The essence of filling anisotropic materials is to absorb unnecessary reflection signals through the distributed resistance characteristics of anisotropic materials and the gradual change of layered conductivity. Description of the Drawings

[0025] Figure 1 is the time-domain antenna diagram of a ground-penetrating radar with ultra-wideband in the low-frequency band based on anisotropic materials in the present invention; Figure 2 is the exploded view of the unit of the time-domain antenna of the ground-penetrating radar with ultra-wideband in the low-frequency band based on anisotropic materials in the present invention; Figure 3 is the exploded view of the time-domain butterfly antenna unit in the present invention; Figure 4 is the exploded view of the dielectric substrate of the time-domain antenna in the present invention; Figure 5 is the exploded view of the sponge layer of the time-domain antenna in the present invention; Figure 6 is the exploded view of the anisotropic material of the time-domain antenna in the present invention; Figure 7 is the exploded view of the metal back cavity of the time-domain antenna in the present invention; Figure 8Result graph of the return loss of the present invention; Figure 9 Result graph of the voltage standing wave ratio of the feeding port of the present invention; Figure 10 Two-dimensional radiation pattern of the time-domain antenna of the present invention operating at 160 MHz; Figure 11 Two-dimensional radiation pattern of the time-domain antenna of the present invention operating at 280 MHz; Figure 12 Two-dimensional radiation pattern of the time-domain antenna of the present invention operating at 400 MHz; Figure 13 Pulse waveform graph of the time-domain signal of the present invention; Figure 14 Result graph of the group delay of the time-domain signal of the present invention.

[0026] Reference numerals 1 Time-domain butterfly antenna element; 11 Upper butterfly patch, 111 Upper elliptical patch, 112 First loading resistor, 113 First round hole, 114 First long strip metal patch; 12 Lower butterfly patch, 121 Lower elliptical patch, 122 Second loading resistor, 123 Second round hole, 124 Second long strip metal patch; 13 Dielectric substrate, 131 Metal substrate, 132 First circular small hole; 2 Sponge layer, 21 Sponge, 22 Second circular small hole; 3 Anisotropic material, 31 Anisotropic material body, 32 First cable round hole 32; 4 Metal back cavity, 41 Metal back cavity body, 42 Second cable round hole 42; 5 Coaxial feeding part. Detailed implementation manners

[0027] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] It should be particularly noted that, as proposed below, the first long strip metal patch 114 is the long strip metal patch connecting the end of the resistor and the butterfly patch, the first round hole 113 is the coaxial feeding round hole dug at the top of the butterfly patch, the second long strip metal patch 124 is the long strip metal patch connecting the end of the resistor and the butterfly patch, the second round hole 123 is the coaxial feeding round hole dug at the top of the butterfly patch, the first circular small hole 132 is the circular small hole 132 for coaxial feeding dug in the center, the second circular small hole 22 is the round hole for coaxial feeding and the cable dug out, the first cable round hole 32 is the round hole for digging out the cable, the second cable round hole 42 is the round hole for the dug out cable, the upper layer elliptical patch 111 is the butterfly patch after elliptical loading and shape loading, and the lower layer elliptical patch 121 is the butterfly patch after elliptical loading and shape loading; The ultra-wideband ground penetrating radar antenna based on anisotropic materials includes a time-domain butterfly antenna unit 1, a sponge layer 2, an anisotropic material 3, a metal back cavity 4, and a coaxial feeding part 5; The time-domain butterfly antenna unit 1 includes an upper layer butterfly patch 11, a lower layer butterfly patch 12, and a dielectric substrate 13; The upper layer butterfly patch 11 includes an upper layer elliptical patch 111, a first loading resistor 112, a first long strip metal patch 114, and a first round hole 113 dug at the top; The adjacent metal strip spacing of the upper layer butterfly patch 11 is 10.3 mm, the length is 240 mm, and the width is 4 mm; The major axis and minor axis of the upper layer elliptical patch 111 are 134 mm and 140 mm respectively; The size of the first loading resistor 112 is 2 mm * 1.2 mm, and the length of the first long strip metal patch 114 is 240 mm and the width is 6.4 mm; The lower layer butterfly patch 12 includes a lower layer elliptical patch 121, a second loading resistor 122, a second long strip metal patch 124, and a second round hole 123 dug at the top; the lower layer butterfly patch 12 has the same size as the upper layer butterfly patch 11, and the difference is that a group of circular rings are added at the top of the lower layer butterfly patch 12 to receive feeding; The dielectric substrate 13 includes a metal substrate 131 made of FR4 material and a first circular small hole 132 for coaxial feeding dug in the center; the thickness of the dielectric substrate 13 is 2 mm, and the length and width are 310 mm and 245 mm respectively; The sponge layer 2 includes a sponge 21 and a second circular small hole 22 for coaxial feeding and the cable dug out; the thickness of the sponge layer 2 is 70 mm; The anisotropic material 3 includes an anisotropic material body 31 and a first cable round hole 32; the thickness of the anisotropic material 3 is 114 mm, which is used to suppress the multiple reflection signals between the antenna and the metal back cavity; the anisotropic material layer 3 is a layered material with a gradually changing conductivity, which absorbs the reflection signals through the distributed resistance characteristics; The metal back cavity 4 includes a metal back cavity body 41 and a second cable round hole 42, and the metal back cavity 4 covers the anisotropic material layer. The thickness of the bottom and the side walls is 2 mm each, and the second cable round hole 42 is dug at the bottom; the thickness of the bottom and the side walls of the metal back cavity 4 is 2 mm each, forming a fully enclosed shielding structure to suppress environmental interference; The coaxial feeding part 5 penetrates through the dielectric substrate 13, the sponge layer 2, the anisotropic material 3 and the metal back cavity 4 for signal transmission.

[0029] The operating frequency band of this antenna is from 160 MHz to 400 MHz, the return loss is lower than -10 dB, and the voltage standing wave ratio is less than 2.

[0030] See Figure 1 A low-frequency ultra-wideband ground penetrating radar time-domain antenna based on anisotropic materials, including a time-domain butterfly antenna unit 1, a sponge layer 2, an anisotropic material 3, a metal back cavity 4 and a coaxial feeding part 5, and the selected connector model for the coaxial feeding is SMA-KFD-20.

[0031] See Figure 2 The time-domain antenna unit is composed of an upper-layer butterfly patch 11, a lower-layer butterfly patch 12 and a dielectric substrate 13, and they are interconnected coaxially; The above antenna unit is different from the traditional butterfly antenna. The butterfly antenna in this design has been ellipticized, and metal strips are added in the oscillator direction of the antenna to increase the bandwidth. Two patches are extended at the tail of the butterfly antenna and connected to the resistor patch. The other end of the resistor patch is connected to a microstrip antenna and finally connected to the top of the metal substrate. Through this distributed resistance loading method, a large amount of current accumulated at the end of the antenna can be released limitedly, weakening the input impedance at the input end and effectively increasing a certain bandwidth.

[0032] See Figure 3 As shown in the figure, the upper-layer butterfly patch 11 and the lower-layer butterfly patch 12 are shown respectively. The major axis and minor axis of the elliptical shape of the upper-layer butterfly patch 111 are 140 mm and 134 mm respectively. The length and width of the metal strip are 240 mm and 4 mm respectively. The interval between each metal strip is 10.3 mm, and the distance from the metal strip to the end of the dielectric substrate 13 is 72.2 mm; The lengths and widths of the first loading resistor 112 and the first metal strip 114 of the dielectric substrate 13 are 240 mm and 6.4 mm respectively. The length and width of the first loading resistor 112 used are 2 mm and 1.2 mm respectively. The size of the rectangular patch at the tail of the elliptical patch for connecting the resistor is 14 mm x 7.4 mm. A group of rectangles are loaded at the top of the upper butterfly patch 11 to serve as the receiving end for feeding. Its size is 8 mm x 10 mm respectively. The lower butterfly patch 12 has the same shape as the upper butterfly patch 11. A group of circular rings are added at the top of the lower butterfly patch 12 to receive the feed. The size of the circular ring is the subtraction of two circles with widths of 2.7 mm and 1 mm respectively.

[0033] See Figure 4 , the thickness of the dielectric substrate 13 is 2 mm, and the dimensions of the length and width are 310 mm and 245 mm respectively.

[0034] Participate in Figure 5 , the thickness of the sponge layer 2 is 70 mm.

[0035] See Figure 6 , the thickness of the anisotropic material 3 is 114 mm.

[0036] See Figure 7 , the bottom thickness of the metal back cavity 4 is 2 mm, and the thickness of the metal walls around is also 2 mm.

[0037] See Figure 8 , through simulation tests, the bandwidth of the designed time-domain antenna is from 160 MHz to 400 MHz, and it can better meet the functional requirements of the design.

[0038] See Figure 9 , through simulation tests, the voltage standing wave ratio of the feed port of the designed time-domain antenna is less than 2, and it can better meet the functional requirements of the design.

[0039] See Figure 10 , through simulation tests, the radiation pattern of the designed time-domain antenna at 160 MHz is unidirectional radiation, and it can better meet the functional requirements of the design.

[0040] See Figure 11 , through simulation tests, the radiation pattern of the designed time-domain antenna at 280 MHz is unidirectional radiation, and it can better meet the functional requirements of the design.

[0041] See Figure 12 , through simulation tests, the radiation pattern of the designed time-domain antenna at 400 MHz is unidirectional radiation, and it can better meet the functional requirements of the design.

[0042] See Figure 13, after simulation design, the pulse waveform of the time-domain characteristics of the designed time-domain antenna can better meet the functional requirements of the design.

[0043] See Figure 14 , after simulation design, the group delay of the time-domain characteristics of the designed time-domain antenna is basically about 3, which is relatively stable and can better meet the functional requirements of the design.

[0044] Finally: The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An ultra-wideband ground penetrating radar antenna based on anisotropic materials, characterized by: It includes a time-domain butterfly antenna unit (1), a sponge layer (2), an anisotropic material (3), a metal back cavity (4) and a coaxial feeding part (5); The time-domain butterfly antenna unit (1) comprises an upper butterfly patch (11), a lower butterfly patch (12) and a dielectric substrate (13); The upper butterfly patch (11) comprises an upper elliptical patch (111), a first loading resistor (112), a first long metal patch (114), and a first circular hole (113) dug at the top; The lower butterfly patch (12) comprises a lower elliptical patch (121), a second loading resistor (122), a second long metal patch (124), and a second circular hole (123) dug at the top; The dielectric substrate (13) comprises a metal substrate (131) made of FR (4) material and a first circular small hole (132) dug in the center for coaxial feeding; The sponge layer (2) comprises a sponge (21) and a second circular small hole (22) cut out for coaxial feeding and cable. The anisotropic material (3) comprises an anisotropic material body (31) and a first cable circular hole (32); The metal back cavity (4) comprises a metal back cavity body (41) and a second cable circular hole (42), and the metal back cavity (4) is coated with an anisotropic material layer, the bottom and side wall thicknesses are both 2 mm, and the second cable circular hole (42) is dug at the bottom; The coaxial feeding portion (5) penetrates the dielectric substrate (13), the sponge layer (2), the anisotropic material (3) and the metal back cavity (4) for signal transmission.

2. The ultra-wideband ground penetrating radar antenna based on anisotropic materials according to claim 1, characterized in that: The distance between adjacent metal strips of the upper butterfly patch (11) is 10.3 mm, the length is 240 mm, and the width is 4 mm; The major axis and minor axis of the upper elliptical patch (111) are 134 mm and 140 mm respectively; The first loading resistor (112) has a size of 2 mm*1.2 mm, and the first long metal patch (114) has a length of 240 mm and a width of 6.4 mm.

3. The ultra-wideband ground penetrating radar antenna based on anisotropic materials according to claim 2, characterized in that: The lower butterfly patch (12) has the same size as the upper butterfly patch (11), but the difference is that a group of circular rings are added to the top of the lower butterfly patch (12) to receive power feeding.

4. The ultra-wideband ground penetrating radar antenna based on anisotropic materials according to claim 1, characterized in that: The dielectric substrate (13) has a thickness of 2 mm, and a length and width of 310 mm and 245 mm respectively.

5. The ultra-wideband ground penetrating radar antenna based on anisotropic materials according to claim 1, characterized in that: The thickness of the sponge layer (2) is 70 mm.

6. The ultra-wideband ground penetrating radar antenna based on anisotropic material according to claim 1, characterized in that: The anisotropic material (3) has a thickness of 114 mm and is used to suppress multiple reflection signals between the antenna and the metal back cavity.

7. The ultra-wideband ground penetrating radar antenna based on anisotropic material according to claim 1, characterized in that: The bottom and side walls of the metal back cavity (4) are both 2 mm thick, forming a fully enclosed shielding structure to suppress environmental interference.

8. The ultra-wideband ground penetrating radar antenna based on anisotropic material according to claim 1, characterized in that: The antenna operates in the frequency band of 160MHz to 400MHz, with a return loss lower than -10dB and a standing wave ratio less than 2.

9. The ultra-wideband ground penetrating radar antenna based on anisotropic materials according to claim 1, characterized in that: The anisotropic material layer (3) is a layered conductivity gradient material, which absorbs the reflected signal through the distributed resistance characteristics.

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