Ultra-wideband composite planar helical antenna for underground target detection system

Abstract

The invention provides an ultra-wideband composite planar helical antenna for an underground target detection system, which comprises an FR-4 dielectric substrate, an inner-ring equiangular helical antenna, an outer-ring square Archimedes helical antenna, an absorption resistor and an outer metal ring, and is characterized in that the inner-ring equiangular helical antenna and the outer-ring square Archimedes helical antenna are arranged on the FR-4 dielectric substrate; the inner-ring equiangular helical antenna is located on the inner side of the outer-ring square Archimedes helical antenna, the intersection positions of the inner-ring equiangular helical antenna and the outer-ring square Archimedes helical antenna are connected through the absorption resistor, and the outer-side metal ring is located on the outer side of the outer-ring square Archimedes helical antenna. According to the technical scheme, the problems that in the prior art, a spiral antenna for an underground target detection system is narrow in bandwidth and large in physical size are solved.

Description

Technical Field

[0001] The present invention relates to the field of underground target detection, and in particular to an ultra-wideband composite planar spiral antenna for an underground target detection system. Background Art

[0002] Underground target detection technology uses the propagation characteristics of high-frequency electromagnetic waves in underground media to image underground structures. It analyzes and determines the spatial location, structure, morphology, and burial depth of underground media through changes in electromagnetic signals emitted and captured by antennas.

[0003] Antennas are a crucial component of underground target detection systems, and their performance directly impacts the system's detection range, resolution, and anti-interference capabilities. Therefore, antenna research is crucial to the design of underground target detection systems. Currently, antennas widely used in such systems include TEM horn antennas, butterfly antennas, Vivaldi antennas, and planar spiral antennas. However, in certain scenarios, users demand higher antenna specifications, aiming to capture weak signals from deeper strata. Planar spiral antennas, as a type of frequency-invariant antenna, have a structure determined entirely by angle. This makes their directional and impedance characteristics independent of frequency, enabling them to achieve a very wide relative bandwidth. Various loading techniques can further reduce the minimum operating frequency of the antenna. This allows the design of antennas with very low minimum operating frequencies and wide relative bandwidths for underground target detection systems.

[0004] The planar helical antenna in the prior art has the following problems:

[0005] First, the radius of the equiangular spiral antenna increases too quickly, occupying too much area, while the radius of the Archimedean spiral antenna increases too slowly and has too many turns.

[0006] Second, the radial sinusoidal loading space of the planar helical antenna arm is still limited, and the low-frequency characteristics cannot be significantly improved;

[0007] Third: The current reflection caused by truncation of the end of the planar spiral antenna will destroy the impedance matching and radiation characteristics.

[0008] Therefore, there is a need for an ultra-wideband composite planar helical antenna with a wide bandwidth, small physical size, and the ability to improve the theoretical resolution of an underground target detection system. Summary of the Invention

[0009] The main purpose of the present invention is to provide an ultra-wideband composite planar helical antenna for an underground target detection system, so as to solve the problems of narrow bandwidth and large physical size of the helical antenna used in the underground target detection system in the prior art.

[0010] To achieve the above objectives, the present invention provides an ultra-wideband composite planar helical antenna for an underground target detection system, comprising: an FR-4 dielectric substrate, an inner equiangular helical antenna, an outer square Archimedean spiral antenna, an absorption resistor, and an outer metal ring. The inner equiangular helical antenna and the outer square Archimedean spiral antenna are arranged on the FR-4 dielectric substrate, the inner equiangular helical antenna is located inside the outer square Archimedean spiral antenna, the inner equiangular helical antenna and the outer square Archimedean spiral antenna are connected at their intersection via an absorption resistor, and the outer metal ring is located outside the outer square Archimedean spiral antenna.

[0011] Furthermore, the outer circle square Archimedean spiral antenna is a square spiral with equal width, and the inner circle equiangular spiral antenna is a spiral with exponentially increasing width.

[0012] Furthermore, it also includes: an antenna feed port located in the center of the FR-4 dielectric substrate, an inner circle equiangular spiral antenna with the antenna feed port as the starting point, and is spirally distributed on the FR-4 dielectric substrate. After the spiral radius reaches a set value, the spiral line converges, and the antenna arm of the inner circle equiangular spiral antenna begins to be sharpened, and finally intersects with the outer circle square Archimedean spiral antenna.

[0013] Furthermore, absorption resistors are provided at two intersections formed by the antenna arms of the inner circle equiangular spiral antenna and the outer circle square Archimedean spiral antenna, and the inner circle equiangular spiral antenna and the outer circle square Archimedean spiral antenna are connected via the absorption resistors.

[0014] Furthermore, each group of absorption resistors has two absorption resistors, and the two absorption resistors are connected to each other.

[0015] Furthermore, each absorption resistor is 50Ω, and the total resistance of each group of absorption resistors is 100Ω.

[0016] Furthermore, the antenna arm on each side of the outer square Archimedean spiral antenna is sinusoidally loaded, the shape of the edge of the FR-4 dielectric substrate is adapted to the sinusoidal loading of the antenna arm, and the shape of the outer metal ring is adapted to the sinusoidal loading of the antenna arm.

[0017] Furthermore, the FR-4 dielectric substrate is a substrate of uniform thickness, the four corners and non-edge portions of the FR-4 dielectric substrate are flat, the edges of the FR-4 dielectric substrate present sinusoidal loading, and the shapes of the antenna arm and the outer metal ring of the outer ring square Archimedean spiral antenna are adapted to the shape of the FR-4 dielectric substrate.

[0018] Furthermore, the width of the outer metal ring is smaller than the width of the antenna arm of the outer square Archimedean spiral antenna.

[0019] Furthermore, the ultra-wideband composite planar spiral antenna covers a frequency range of 100 MHz to 3 GHz, and the side length of the outer square Archimedean spiral antenna is no more than 490 mm.

[0020] The present invention has the following beneficial effects:

[0021] To address the problems of equiangular spiral antennas with too large an area occupied by their radius growing too quickly and Archimedean spiral antennas with too many turns growing too slowly, the present invention combines the two. An equiangular spiral antenna is used in the high-frequency region of the inner circle and a square Archimedean spiral antenna is used in the outer circle. This increases the electrical length while maintaining the same area, thereby achieving the goal of miniaturization of the antenna.

[0022] In order to solve the problem that the radial sinusoidal loading space of the antenna arm of the planar spiral antenna is still limited and cannot significantly improve the low-frequency characteristics, the present invention adopts axial loading of the antenna arm, which greatly expands the loading space of the antenna arm. At the same time, axial loading is only performed on the outer ring square Archimedean spiral antenna, which also provides certain convenience for subsequent processing and production, enabling the antenna to be further miniaturized.

[0023] To address the problem that the truncation of the end of a planar spiral antenna will cause current reflection and destroy the impedance matching and radiation characteristics, this solution adopts an outer metal ring loading solution. In this solution, the outer metal ring couples with the current at the end of the antenna, compensating for the interference of the original reflected wave on the far-field circular polarization, thereby improving the low-frequency characteristics of the antenna, reducing the minimum operating frequency of the antenna, and optimizing the radiation characteristics, improving the axial ratio and gain flatness in the low-frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0025] Figure 1 A top view of an ultra-wideband composite planar helical antenna for an underground target detection system according to the present invention is shown.

[0026] Figure 2 Shown Figure 1 A magnified detail of point A.

[0027] Figure 3 Shown Figure 1 A magnified view of the detail at point B.

[0028] Figure 4 Shown Figure 1A partial axonometric view of the ultra-wideband composite planar helical antenna, with detail enlarged at point C.

[0029] Figure 5 A schematic diagram of an outer square Archimedean spiral antenna is shown.

[0030] Figure 6 The graph shows the variation of the standing wave ratio of the ultra-wideband composite planar spiral antenna of the present invention with the operating frequency.

[0031] The reference numerals of the above drawings are:

[0032] 1. Outer circle square Archimedean spiral antenna; 2. Antenna feed port; 3. Inner circle equiangular spiral antenna; 4. Outer metal ring; 5. Absorption resistor; 6. FR-4 dielectric substrate. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] like Figure 1 An ultra-wideband composite planar helical antenna for an underground target detection system is shown to solve the problems of narrow bandwidth and large physical size of helical antennas for underground target detection systems in the prior art.

[0035] To achieve the above objectives, the present invention provides an ultra-wideband composite planar helical antenna for an underground target detection system, comprising: an FR-4 dielectric substrate 6, an inner equiangular helical antenna 3, an outer square Archimedean spiral antenna 1, an absorption resistor 5, and an outer metal ring 4. The inner equiangular helical antenna and the outer square Archimedean spiral antenna are arranged on the FR-4 dielectric substrate, the inner equiangular helical antenna is located inside the outer square Archimedean spiral antenna, the inner equiangular helical antenna and the outer square Archimedean spiral antenna are connected at their intersection via an absorption resistor, and the outer metal ring is located outside the outer square Archimedean spiral antenna.

[0036] Specifically, if Figure 1 and Figure 5 As shown, the outer circle square Archimedean spiral antenna is a square spiral with equal width, and the inner circle equiangular spiral antenna is a spiral with an exponentially increasing width.

[0037] Specifically, it also includes: an antenna feed port 2 located in the center of the FR-4 dielectric substrate, an inner circle equiangular spiral antenna with the antenna feed port as the starting point, and is distributed in a spiral shape on the FR-4 dielectric substrate. After the spiral radius reaches a set value, the spiral line converges, and the antenna arm of the inner circle equiangular spiral antenna begins to be sharpened, and finally intersects with the outer circle square Archimedean spiral antenna.

[0038] Specifically, if Figure 2 As shown in the figure, absorption resistors are placed at the two intersections of the antenna arms of the inner equiangular spiral antenna and the outer square Archimedean spiral antenna, connecting the inner equiangular spiral antenna and the outer square Archimedean spiral antenna via the absorption resistors. The absorption resistors can reduce current reflection caused by structural changes, thereby improving low-frequency performance.

[0039] Specifically, each group of absorption resistors has two, and the two absorption resistors are connected to each other. Since the connection between the inner circle equiangular spiral antenna and the outer circle square Archimedean spiral antenna is not completely smooth, a large reflected current will appear at the connection, resulting in impedance mismatch. In addition to structural optimization, the present invention also adds four groups of absorption resistors to absorb the reflection of the current and further improve the low-frequency performance of the antenna. Each group can use a 100Ω resistor, which is located at the connection between the two spiral antennas and on the other antenna arm adjacent to it. Taking into account the difficulty of processing, thin film resistors can be directly used and processed together with the antenna arms to reduce the impact of welding operations on electrical performance.

[0040] Specifically, each absorption resistor is 50Ω, each group is composed of two absorption resistors, and the total resistance of each group is 100Ω.

[0041] Specifically, if Figure 4 As shown, the antenna arms on each side of the outer square Archimedean spiral antenna are sinusoidally loaded. The shape of the FR-4 dielectric substrate edge is adapted to the sinusoidal loading of the antenna arms, and the shape of the outer metal ring is also adapted to the sinusoidal loading of the antenna arms. Sinusoidal loading is a sinusoidal wave shape.

[0042] Specifically, if Figure 3 and Figure 4 As shown, the FR-4 dielectric substrate is a substrate of uniform thickness. The four corners and non-edge portions of the FR-4 dielectric substrate are flat. The edges of the FR-4 dielectric substrate are sinusoidally loaded. The antenna arm and the outer metal ring of the outer square Archimedean spiral antenna are adapted to the shape of the FR-4 dielectric substrate. The inner ring of the FR-4 dielectric plate is a flat plate, and the outer ring is axially aligned with the antenna arm (i.e. perpendicular to the Figure 2 Therefore, an ultra-wideband and miniaturized composite planar helical antenna is designed.

[0043] The dielectric substrate of the present invention is made of common FR-4 material. The dielectric substrate located in the inner circle is a substrate of equal thickness. The substrate located in the outer circle and the outer circle square Archimedean spiral antenna are sinusoidally loaded. The antenna arm of the loaded outer circle square Archimedean spiral antenna has a longer antenna path per circle than the outer circle square Archimedean spiral antenna on the plane, and the projection is a straight line, which is less difficult to process. Therefore, only loading the outer circle (i.e., the shape is sinusoidal) can achieve the purpose of lowering the minimum operating frequency. The amplitude of the sinusoidal loading will also affect the low-frequency characteristics of the antenna. The higher the amplitude, the longer the current path, and the lower the operating frequency. At the four vertex corners of the outer circle square Archimedean spiral antenna, the antenna arm, the outer metal ring and the FR-4 dielectric plate are all planar.

[0044] Specifically, the width of the outer metal ring is smaller than the width of the antenna arm of the outer square Archimedean spiral antenna. The present invention adds two outer metal rings to the outermost edge of the outer square Archimedean spiral antenna. The width of the outer metal rings is slightly smaller than the antenna arm of the outer square Archimedean spiral antenna. This structure couples with the current at the end of the outer square Archimedean spiral antenna, reducing reflected current at the end and improving the low-frequency performance of the outer square Archimedean spiral antenna. Furthermore, the outer metal rings further extend the length of the equivalent circuit, increasing the electrical length of the outer square Archimedean spiral antenna and also reducing the operating frequency of the outer square Archimedean spiral antenna.

[0045] Specifically, the ultra-wideband composite planar spiral antenna covers a frequency range of 100 MHz to 3 GHz, and the side length of the outer square Archimedean spiral antenna is no more than 490 mm.

[0046] The inner equiangular spiral antenna of the present invention is a two-arm equiangular planar spiral antenna, a typical non-frequency-variable antenna. However, an antenna cannot be infinitely long in engineering, so it must be truncated at an appropriate length. The ends of the antenna arms of the inner equiangular spiral antenna are gradually tapered to reduce current reflection on the antenna arms and minimize the truncation effect. The antenna is then connected to the subsequent narrower outer square Archimedean spiral antenna.

[0047] The outer ring square Archimedean spiral antenna of the present invention is a double-arm square Archimedean spiral antenna planar spiral antenna. Since the operating frequency and electrical size of the antenna jointly affect the physical size of the antenna, when the physical size remains unchanged and the electrical size increases, the operating frequency of the antenna will naturally decrease. Under the same diameter, if Figure 5 As shown, the length of the square helical antenna is longer than that of the circular helical antenna in the prior art, and the axial sinusoidal loading will further increase the length of the antenna arm, thereby extending the current path, so that a lower minimum operating frequency can be obtained with the same area.

[0048] The simulation results of the ultra-wideband composite planar helical antenna for underground target detection system proposed by the present invention are as follows: Figure 6 As shown, when connected to a matching feed, the standing wave ratio is less than 2 from 100 MHz to 3 GHz, demonstrating that the antenna has excellent broadband characteristics. This proves that the design proposed by the present invention is effective and can significantly reduce the area of ​​the planar helical antenna, achieving the goals of antenna miniaturization and ultra-wideband design.

[0049] The ultra-wideband composite planar helical antenna for underground target detection systems proposed in this invention utilizes multiple loading methods, achieving a compact design and expanding the antenna's relative operating bandwidth. This addresses the issues of insufficient antenna bandwidth and excessive physical size, while significantly improving the theoretical resolution of the underground target detection system. Compared to existing technologies, this invention utilizes a combination of a square Archimedean spiral antenna, an outer metal ring, axial sinusoidal loading of the spiral arms, and an absorption resistor, addressing the difficulty of achieving a 20-fold impedance bandwidth in existing technologies.

[0050] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. An ultra-wideband composite planar helical antenna for an underground target detection system, characterized in that: include: An FR-4 dielectric substrate, an inner circle equiangular spiral antenna, an outer circle square Archimedean spiral antenna, an absorption resistor and an outer metal ring are provided. The inner circle equiangular spiral antenna and the outer circle square Archimedean spiral antenna are provided on the FR-4 dielectric substrate. The inner circle equiangular spiral antenna is located inside the outer circle square Archimedean spiral antenna. The inner circle equiangular spiral antenna and the outer circle square Archimedean spiral antenna are connected at their intersection through an absorption resistor. The outer metal ring is located outside the outer circle square Archimedean spiral antenna.

2. The ultra-wideband composite planar helical antenna for an underground target detection system according to claim 1, characterized in that: The outer circle square Archimedean spiral antenna is a square spiral with equal width, and the inner circle equiangular spiral antenna is a spiral with exponentially increasing width.

3. The ultra-wideband composite planar helical antenna for an underground target detection system according to claim 1, wherein: Also includes: The antenna feed port is located at the center of the FR-4 dielectric substrate. The inner circle equiangular spiral antenna is distributed in a spiral shape on the FR-4 dielectric substrate with the antenna feed port as the starting point. After the spiral radius reaches the set value, the spiral line converges, and the antenna arm of the inner circle equiangular spiral antenna begins to be sharpened, and finally intersects with the outer circle square Archimedean spiral antenna.

4. The ultra-wideband composite planar helical antenna for an underground target detection system according to claim 1, characterized in that: Absorption resistors are set at two intersections formed by antenna arms of the inner circle equiangular spiral antenna and the outer circle square Archimedean spiral antenna, and the inner circle equiangular spiral antenna and the outer circle square Archimedean spiral antenna are connected through the absorption resistors.

5. The ultra-wideband composite planar helical antenna for an underground target detection system according to claim 4, characterized in that: Each group of absorption resistors has two absorption resistors, which are connected to each other.

6. The ultra-wideband composite planar helical antenna for an underground target detection system according to claim 5, characterized in that: Each absorption resistor is 50Ω, and the total resistance of each group of absorption resistors is 100Ω.

7. The ultra-wideband composite planar helical antenna for an underground target detection system according to claim 1, characterized in that: The antenna arm on each side of the outer square Archimedean spiral antenna is sinusoidally loaded, the shape of the edge of the FR-4 dielectric substrate is adapted to the sinusoidal loading of the antenna arm, and the shape of the outer metal ring is adapted to the sinusoidal loading of the antenna arm.

8. The ultra-wideband composite planar helical antenna for an underground target detection system according to claim 7, characterized in that: The FR-4 dielectric substrate is a substrate of uniform thickness. The four corners and non-edge portions of the FR-4 dielectric substrate are flat. The edges of the FR-4 dielectric substrate present sinusoidal loading. The shapes of the antenna arm and the outer metal ring of the outer square Archimedean spiral antenna are adapted to the shape of the FR-4 dielectric substrate.

9. The ultra-wideband composite planar helical antenna for an underground target detection system according to claim 1, characterized in that: The width of the outer metal ring is smaller than the width of the antenna arm of the outer square Archimedean spiral antenna.

10. The ultra-wideband composite planar helical antenna for an underground target detection system according to claim 1, characterized in that: The ultra-wideband composite planar spiral antenna covers a frequency range of 100 MHz to 3 GHz, and the side length of the outer circle square Archimedean spiral antenna is no more than 490 mm.

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