A Pythagorean-carpet fractal multi-frequency antenna based on aperture-coupled feeding

Abstract

The present invention discloses a Pythagorean-carpet fractal multi-frequency antenna based on aperture-coupled feeding. The antenna comprises a Pythagorean-Sierpinski carpet fractal radiator 1, a dielectric substrate 2, a slotted conductor ground plane 3, a dielectric substrate 4, and a microstrip feeder 5. The antenna employs a layered structure, with the Pythagorean-Sierpinski carpet fractal radiator 1 being a thin patch attached to the dielectric substrate 2. The slotted conductor ground plane 3 is sandwiched between the dielectric substrates 2 and 4, which are of similar size. The dielectric substrate 4 separates the microstrip feeder 5 from the slotted conductor ground plane 3, while the dielectric substrate 2 separates the slotted conductor ground plane 3 from the Pythagorean-Sierpinski carpet fractal radiator 1. The antenna has the advantages of miniaturization, thin profile, light weight, and ease of integration of microstrip antennas. It overcomes the shortcomings of microstrip antennas, such as narrow bandwidth and single frequency band, by presenting multiple operating frequency bands within a limited scale, with good isolation between the frequency bands, thus meeting the requirements of current wireless communication systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave and radio frequency antenna design, and in particular relates to a Pythagorean tree-carpet fractal multi-frequency antenna based on aperture coupling feeding. Background Art

[0002] Antennas, as energy conversion devices in radio systems, require excellent performance. With the advancement of antenna technology, demands for increasingly high performance are being placed on antennas, including directivity, bandwidth, input impedance, and polarization. To develop more high-performance antennas, researchers are continuously optimizing antenna feeding methods and structures, and categorizing antennas with similar characteristics.

[0003] Fractal structures are special geometric shapes with self-similar structures, first proposed by French mathematicians in 1975. In 1995, Cohen first applied fractal geometry to phantom antennas, bending the wire in a fractal manner to maintain a constant total arc length. Each iteration introduced new bends, allowing more complex antennas to be integrated into smaller wireless communication systems. The space-filling properties of fractal structures also enabled antenna miniaturization. Fractal geometry holds enormous potential in various fields, and numerous universities and research institutes both domestically and internationally have already conducted research on fractal antennas.

[0004] Existing microstrip antennas offer many advantages, such as low profile, low cost, flexible electrical parameter adjustments, and ease of integration into miniaturized devices. However, they suffer from a inherent disadvantage: a narrow frequency band. Microwave theory has proven that a microstrip antenna is equivalent to a leaky-wave cavity, with resonance characteristics similar to an RLC parallel resonant circuit. Its bandwidth (B) is inversely proportional to its quality factor (Q), which often depends on the antenna's inherent electrical dimensions. Traditional rectangular patch antennas are often used to achieve dual-band or multi-band operation by stimulating multimode or layered structures. Fractal antennas, on the other hand, often leverage self-similar properties to achieve multiple frequency bands within a certain range, simplifying circuit design and reducing costs. Multi-band operation directly increases the antenna's communication capacity by a factor of 1-n.

[0005] Many current satellite and LiDAR wireless communication systems, particularly in LiDAR ranging, often require simultaneous laser ranging systems with multiple modulation frequencies to achieve high-precision, dynamic distance and velocity measurements. These systems utilize multi-path parallel measurement and use receivers to collect multiple incoming reference and received signals. Electromagnetic wave receivers must be easily integrated, capable of parallel reception, and exhibit strong anti-interference performance across all received frequency bands, placing high demands on the antenna's absolute bandwidth. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention combines antenna technology and fractal geometry to propose a Pythagorean tree-carpet fractal multi-frequency antenna based on aperture coupling feeding.

[0007] The present invention employs a Pythagorean-carpet fractal multi-frequency antenna based on aperture-coupled feeding, comprising a Pythagorean-Sierpinski carpet fractal radiator 1, a dielectric substrate 2, a slotted conductor ground plane 3, a dielectric substrate 4, and a microstrip feeder 5. The antenna employs a layered structure, with the Pythagorean-Sierpinski carpet fractal radiator 1 consisting of a thin patch attached to the dielectric substrate 2. The slotted conductor ground plane 3 is sandwiched between the dielectric substrates 2 and 4, which are of similar size. The dielectric substrate 4 separates the microstrip feeder 5 from the slotted conductor ground plane 3, while the dielectric substrate 2 separates the slotted conductor ground plane 3 from the Pythagorean-Sierpinski carpet fractal radiator 1.

[0008] Furthermore, the antenna introduces an adjustable combined fractal structure, which refers to an antenna radiation patch, namely a Pythagorean tree-Sierpinski carpet combined fractal radiator 1, the main structure of which is a third-order or higher Pythagorean tree fractal structure of the outer layer, and the internal structure is a Sierpinski carpet fractal structure, and the whole serves as a patch antenna.

[0009] Among them, in the combined fractal, both the external (Pythagorean tree fractal) and internal (Sierpinski carpet) fractal structures are at least two orders, and the Pythagorean tree fractal shape is composed of square patches.

[0010] Furthermore, the Pythagorean tree-Sierpinski carpet combined fractal radiator 1 is a metal sheet, which is made of fractal primitives tightly attached to the dielectric substrate 2, and based on this, it is translated, rotated and scaled to form a high-order Pythagorean tree fractal, and is electrically connected to the fractal primitives to form a whole.

[0011] Furthermore, the inner Sierpinski carpet is based on squares, requiring that the side length of each row of square holes is 1 / 3 of the side length of the square holes in the previous level, and that squares at the same level are the same size and spaced apart by the side length of the square. The same requirements apply to squares in the same column. A higher-order Sierpinski carpet can be obtained by dividing a solid square into nine small squares, removing the middle small square, and repeating this operation for the remaining small squares.

[0012] Furthermore, the dielectric substrate is rectangular in shape, and the substrate plate is required to be a radio frequency plate with a small loss angle, and the material is selected from FR-4 plate or a dielectric constant ε r=2.2 RogersRT Droide / 5880(tm), and the RF substrate is rectangular with a length of 24mm, a width of 18mm, and a thickness of 1.6mm.

[0013] Furthermore, the microstrip feed line 5 includes an input wave port and a central signal line. The central signal line is in the shape of a narrow strip as a whole, with one end close to the feeding edge of the entire device and the other end guiding the electromagnetic wave to pass through the slotted conductor ground plane 3. The central signal line and the Pythagorean-Sierpinski carpet combination fractal radiator 1 both take the central axis of the slotted aperture of the slotted conductor ground plane 3 as the axis of symmetry.

[0014] The microstrip feeding line 5 is attached to the bottom of the dielectric substrate 4 and a microstrip line with a resonant branch can be added.

[0015] Furthermore, the antenna operates in a frequency band ranging from 1 to 12 GHz.

[0016] Furthermore, in the antenna, fractal geometry is combined with a radio frequency antenna, and an aperture-coupled feeding method is used, that is, a rectangular band gap is slotted on a ground plane to form electromagnetic coupling between the feed line and the radiator.

[0017] Beneficial effects of the present invention: The antenna of the present invention includes: a Pythagorean-Sierpinski carpet combination fractal radiator 1, a dielectric substrate 2, a slotted conductor ground plane 3, a dielectric substrate 4, and a microstrip feed line 5; the antenna adopts a layered structure, wherein the overall structure is a very thin patch of the Pythagorean-Sierpinski carpet combination fractal radiator 1 attached to the dielectric substrate 2, the slotted conductor ground plane 3 is sandwiched between the dielectric substrate 2 and the dielectric substrate 4 of the same size, the dielectric substrate 4 separates the microstrip feed line 5 from the slotted conductor ground plane 3, and the dielectric substrate 2 separates the slotted conductor ground plane 3 from the Pythagorean-Sierpinski carpet combination fractal radiator 1. The antenna described in the present invention combines fractal geometry with radio frequency antennas. Taking into account the shortcomings of the narrow bandwidth of microstrip antennas, a rarely used combined structure fractal geometry radiation patch is designed, which further expands the antenna operating bandwidth and presents multi-band characteristics in the operating frequency band. It not only has the advantages of miniaturization, thin profile, light weight and easy integration of microstrip antennas, but also solves the shortcomings of narrow bandwidth and single frequency band of microstrip antennas. It presents multiple operating frequency bands within a limited scale, and the isolation between each frequency band is good, meeting the needs of today's wireless communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural front view of a Pythagorean tree-carpet fractal multi-frequency antenna based on aperture coupling feeding according to the present invention.

[0019] Figure 2Detailed structural diagram of the internal fractal (third-order Sierpinski carpet fractal) of the antenna according to an embodiment of the present invention.

[0020] Figure 3 2 is a detailed structural diagram (top view) of the antenna according to an embodiment of the present invention.

[0021] Figure 4 Schematic diagram of return loss within the working frequency band in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0023] like Figure 1 The figure shows a front view of a Pythagorean-carpet fractal multi-frequency antenna structure based on aperture coupling feed, comprising a Pythagorean-Sierpinski carpet fractal radiator 1, a dielectric substrate 2, a slotted conductor ground plane 3, a dielectric substrate 4, and a microstrip feed line 5. The structure is layered, with the Pythagorean-Sierpinski carpet fractal radiator 1 being a thin patch attached to the dielectric substrate 2. The slotted conductor ground plane 3 is sandwiched between the dielectric substrates 2 and 4, which are of the same size and shape, and is aligned with the dielectric substrates. The dielectric substrate 4 separates the microstrip feed line 5 from the slotted conductor ground plane 3, while the dielectric substrate 2 separates the slotted conductor ground plane 3 from the Pythagorean-Sierpinski carpet fractal radiator 1.

[0024] In this embodiment, the antenna introduces an adjustable combined fractal structure, which refers to an antenna radiation patch, namely a Pythagorean tree-Sierpinski carpet combined fractal radiator 1. The main structure is a third-order or higher Pythagorean tree fractal structure on the outer layer, and the internal structure is a Sierpinski carpet fractal structure, and the whole serves as a patch antenna.

[0025] Among them, in the combined fractal, both the external (Pythagorean tree fractal) and internal (Sierpinski carpet) fractal structures are at least two orders, and the Pythagorean tree fractal shape is composed of square patches.

[0026] In this embodiment, the Pythagorean tree-Sierpinski carpet combined fractal radiator 1 is a metal sheet, which is made of fractal primitives tightly attached to a dielectric substrate 2, and based on this, it is translated, rotated, and scaled to form a high-order Pythagorean tree fractal, and is electrically connected to the fractal primitives to form a whole.

[0027] In this embodiment, the inner Sierpinski carpet is based on squares. The requirement is that the side length of each row of square holes is 1 / 3 of the side length of the square holes in the previous level. Squares of the same level are the same size, and the spacing between squares of the same level is the same square side length. The same requirements apply to squares in the same column. A higher-level Sierpinski carpet can be obtained by dividing a solid square into nine smaller squares, removing the middle small square, and repeating this process for the remaining small squares.

[0028] like Figure 2 As shown, the fractal feeding primitive is a third-order Sierpinski carpet, and its fractal dimension is 1.892. The construction method is: a square substrate 6 with a side length of a, a square 8 of a / 3 is hollowed out at its center, the centers of the lines connecting the four vertices of the square 6 and the four vertices corresponding to the square 8 are in the hollowed-out four squares 9 with a side length of a / 9, and the centers of the lines connecting the centers of the four sides of the square 6 and the four sides corresponding to the square 8 are in the hollowed-out four squares 9 with a side length of a / 9. At this time, the square 6 has a total of eight small units 7 of the "U" structure. Repeating the above operation for each "U" unit 7 can obtain the following Figure 2 The Sierpinski carpet basic feeding unit shown in FIG. In this embodiment, a Sierpinski carpet with a=2.5 mm is used.

[0029] like Figure 3 As shown, the Pythagorean tree fractal is constructed using a fractal feed element as the reference, starting with an initial square patch as the main radiating element of the aperture slot. Two secondary square patches 11 and 12 are typically set at 0.707 or slightly larger than the side length of the primary square patch. The edges of the two secondary square patches are angled 45 degrees clockwise and counterclockwise with the edges of the primary square patch, respectively. The two secondary square patches are symmetrical about the central axis of the primary square patch. Side lengths slightly larger than those specified in the instructions facilitate soldering and avoid process issues caused by small intersections. Based on the edges of the second-order square patch, third-order square patches 13, 14, 15, and 16, each with a side length of approximately 0.707 of the second-order square patch, are rotated 45 degrees clockwise and counterclockwise, respectively, to form a symmetrical pattern around the axis of the second-order square patch. Four patches are then bonded together. This process continues in this manner, ultimately forming a high-order Pythagorean tree fractal antenna.

[0030] It can be seen that Pythagorean fractals 11, 13, 14 or 12, 15, 16 are similar to 10, 11, and 12. For the third-order Sierpinski carpet, 7 is similar to 6, satisfying both local and overall similarity, fulfilling the basic elements of a fractal structure. The Sierpinski carpet structure can also be replaced with other hollow fractal structures as needed. The Pythagorean fractals and Sierpinski carpet fractals used in this embodiment are both third-order, but can also be replaced with other orders. This will affect the generation and offset of the antenna resonance point.

[0031] In this embodiment, the dielectric substrate is rectangular in shape, and the substrate material is required to be a radio frequency material with a small loss angle, and the material is selected from FR-4 material or a dielectric constant ε r = 2.2 RogersRT Droide / 5880 (tm), the loss tangent value is 0.0009, and the RF substrate is rectangular with a length of 24 mm, a width of 18 mm, and a thickness of 1.6 mm.

[0032] The two dielectric substrates sandwich a very thin slotted conductor grounding plate 3, which is consistent in shape and size with the dielectric substrate. There is a rectangular slot on the slotted conductor grounding plate 3, which is 0.155mm*1.4mm in size and is located 8mm away from the lower end of the dielectric substrate and in the center of the left and right ends.

[0033] In this embodiment, the microstrip feed line 5 includes an input wave port and a central signal line. The central signal line is in the shape of a narrow strip, one end of which is close to the feeding edge of the entire device, and the other end guides electromagnetic waves to pass through the slotted conductor ground plate 3. The central signal line and the Pythagorean-Sierpinski carpet combination fractal radiator 1 both take the central axis of the slotted diameter of the slotted conductor ground plate 3 as the symmetry axis.

[0034] Among them, the microstrip feed line 5 is attached to the bottom of the dielectric substrate 4, which can increase the microstrip line of the resonant branch, and the length of the microstrip feed line 5 can be freely adjusted, with a size of 9mm*0.55mm. The end of the microstrip feed line 5 and the diameter of the slotted conductor ground plane 3 are separated by the thickness of the dielectric substrate 4, and the diameter of the slotted conductor ground plane 3 and the Pythagorean-Sierpinski carpet combination fractal radiator 1 are separated by the thickness of the dielectric substrate 2.

[0035] like Figure 3 As shown, in this embodiment, the Pythagorean fractal structure adopts a third-order fractal, and the embedded substrate constituting the Pythagorean fractal adopts a third-order Sierpinski carpet. The antenna operates in a frequency band of 1-12 GHz. When operating in the operating frequency band, the input port is connected to the Figure 1The electromagnetic energy of the microstrip feed line 5 passes through the dielectric substrates 2 and 4 and the slotted conductor ground plane 3, exciting a radio frequency electromagnetic field between the conductor patch and the ground plane. The field radiates outward through the gaps around the patch, ultimately inducing an induced current in the Sierpinski carpet. The current in the fractal elements within the Sierpinski carpet is consistent with that of the entire carpet and is guided by the Pythagorean fractal structure, thereby enhancing directivity and generating multi-frequency characteristics within the entire operating frequency band. Each frequency point has a certain regularity, which depends on the fractal structure.

[0036] This embodiment fully integrates the advantages of two different fractals, utilizing the directional properties of the Pythagorean tree fractal and the self-filling properties of the Sierpinski carpet fractal. The embedded Sierpinski carpet fractal changes the direction of surface current flow within a limited space, changing the overall impedance characteristics, providing more resonant modes, and generating multi-frequency characteristics within a wide frequency band.

[0037] In this embodiment, the antenna combines fractal geometry with the radio frequency antenna, comprehensively considering the disadvantage of the narrow bandwidth of the microstrip antenna, and chooses to use the aperture-coupled feeding method, that is, by slotting a rectangular band gap on the ground plane to form electromagnetic coupling between the feed line and the radiator. It is an indirect feeding method that can effectively avoid the electromagnetic radiation interference caused by the feed line itself. However, at the process level, aperture-coupled feeding requires strict alignment between multiple layers. Compared with direct feeding, the aperture-coupled feeding method needs to consider more design parameters and is more convenient for optimizing antenna performance. The aperture will significantly change the input impedance characteristics. This method excites the radiator on the other side of the substrate through the gap. The feed element and the parasitic element are two resonant circuits. When the frequencies of the two are close, the frequency band is greatly widened.

[0038] The combined fractal structure described in this embodiment is adjustable, with both the inner and outer fractal orders adjustable to meet specific needs. When the outer Pythagorean fractal reaches third order or higher, it can often generate multiple frequency points within the operating frequency band, while the embedded Sierpinski carpet fractal structure can use second or third order. While varying the order of the inner fractal structure can broaden the operating frequency band at certain frequencies, it can also increase return loss or cause frequency shifts within a given operating frequency band.

[0039] The combined fractal antenna designed in this embodiment has fractal structures that vary in size depending on the fractal order, necessitating the appropriate feed aperture and feed line length to ensure optimal antenna performance. Because the feed line isn't directly connected to the fractal radiator, its position and size can be optimally set to ensure optimal antenna radiation performance. If necessary, the input impedance can be adjusted by adding branches to the feed line to better match the impedance of the radiating patch for optimal radiation.

[0040] like Figure 4 The following figure shows the return loss S11 simulation results for this embodiment, with each curve representing the results for different substrate sizes. Compared to the narrow bandwidth and single operating frequency of traditional microstrip patch antennas, this embodiment not only achieves better radiation performance but also features multiple resonant frequencies with a consistent relationship between them, achieving optimal performance of -38dB. This essentially achieves the antenna's radiation characteristics of miniaturization and multi-frequency operation with a good ratio of adjacent operating frequencies.

[0041] This embodiment can be applied to the field of LiDAR ranging. As a receiving device for high-precision functional safety radars, its high directivity enables it to receive electromagnetic waves of a specific resonant frequency from a specific transmission direction, making it less susceptible to interference. Furthermore, it meets current requirements for parallel reception and can serve as a receiving component for LiDAR ranging devices.

[0042] In summary, the present invention combines fractal geometry with radio frequency antennas, taking into account the narrow bandwidth shortcomings of microstrip antennas. It employs a more flexible aperture-coupled feeding method and designs a less commonly used combined structure fractal geometry radiating patch. These two methods further expand the antenna's operating bandwidth, exhibiting multi-band characteristics within the operating frequency band. The antenna described in the present invention not only possesses the advantages of microstrip antennas in miniaturization, thin profile, light weight, and ease of integration, but also overcomes the shortcomings of microstrip antennas in terms of narrow bandwidth and single frequency band. It presents multiple operating frequency bands within a limited scale, with good isolation between each band, meeting the requirements of today's wireless communication systems.

Claims

1. A Pythagorean tree-carpet fractal multi-frequency antenna based on aperture coupling feeding, comprising: A Pythagorean tree-Sierpinski carpet combined fractal radiator (1), a first dielectric substrate (2), a slotted conductor grounding plate (3), a second dielectric substrate (4), and a microstrip feeder (5); the antenna adopts a layered structure, the Pythagorean tree-Sierpinski carpet combined fractal radiator (1) is a very thin patch attached to the first dielectric substrate (2), the slotted conductor grounding plate (3) is sandwiched between the first dielectric substrate (2) and the second dielectric substrate (4) of the same size, the second dielectric substrate (4) separates the microstrip feeder (5) from the slotted conductor grounding plate (3), and the first dielectric substrate (2) separates the slotted conductor grounding plate (3) from the Pythagorean tree-Sierpinski carpet combined fractal radiator (1); The antenna introduces a combined fractal structure with adjustability, the combined fractal structure refers to an antenna radiation patch, namely, a Pythagorean tree-Sierpinski carpet combined fractal radiator (1), wherein the Sierpinski carpet fractal is used as an embedded substrate to form a Pythagorean tree fractal, that is, the main structure of the Pythagorean tree-Sierpinski carpet combined fractal radiator (1) is a third-order or higher Pythagorean tree fractal structure of the outer layer, and the internal structure is a Sierpinski carpet fractal structure, and the whole serves as a patch antenna; The combined fractal includes an outer Pythagorean tree fractal and an inner Sierpinski carpet fractal structure, both of which are at least two orders high. The outer shape of the Pythagorean tree fractal is composed of square patches.

2. The Pythagorean tree-carpet fractal multi-frequency antenna based on aperture coupling feeding according to claim 1, characterized in that: The Pythagorean tree-Sierpinski carpet combined fractal radiator (1) is a metal sheet, which is formed by fractal primitives tightly attached to a first dielectric substrate (2). Based on the first dielectric substrate (2), translation, rotation, and scaling are performed to form a high-order Pythagorean tree fractal, which is electrically connected to the fractal primitives to form a whole.

3. The Pythagorean tree-carpet fractal multi-frequency antenna based on aperture coupling feeding according to claim 1, characterized in that: The Sierpinski carpet is based on squares, requiring that the side length of each row of square holes be 1 / 3 of the side length of the square holes in the previous level, that squares on the same level be the same size, and that the spacing between squares on the same level be the same square side length. The same requirements apply to squares in the same column. A higher-order Sierpinski carpet can be obtained by dividing a solid square into nine smaller squares, removing the middle smaller square, and repeating this process for the remaining smaller squares.

4. The Pythagorean tree-carpet fractal multi-frequency antenna based on aperture coupling feeding according to claim 1, characterized in that: The dielectric substrate is rectangular in shape, and the substrate plate is required to be a radio frequency plate with a small loss angle. The material is selected from FR-4 plate or dielectric constant ε r =2.2 RogersRT Droide / 5880(tm), and the RF substrate is rectangular with a length of 24mm, a width of 18mm, and a thickness of 1.6mm.

5. The Pythagorean tree-carpet fractal multi-frequency antenna based on aperture coupling feeding according to claim 1, characterized in that: The microstrip feed line (5) includes an input wave port and a central signal line. The central signal line is in a narrow strip shape as a whole, with one end close to the feed edge of the entire device and the other end guiding electromagnetic waves to pass through the aperture of the slotted conductor grounding plate (3). The central signal line and the Pythagorean tree-Sierpinski carpet combined fractal radiator (1) both take the central axis of the slot aperture of the slotted conductor grounding plate (3) as the symmetry axis. The microstrip feeding line (5) is attached to the bottom of the second dielectric substrate (4), and a microstrip line with a resonant branch can be added.

6. The Pythagorean tree-carpet fractal multi-frequency antenna based on aperture coupling feeding according to claim 1, characterized in that: The antenna operates in a frequency range of 1-12 GHz.

7. The Pythagorean tree-carpet fractal multi-frequency antenna based on aperture coupling feeding according to claim 1, characterized in that: In the antenna, fractal geometry is combined with a radio frequency antenna, and an aperture-coupled feeding method is used, that is, a rectangular band gap is slotted on a ground plane to form electromagnetic coupling between a feed line and a radiator.

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