A planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure

Abstract

The present invention discloses a planar spiral antenna based on fractal dielectric loading and metamaterial absorbing structure, comprising a radome, a fractal dielectric loading structure, a composite planar spiral structure, a metamaterial absorbing structure, a metal back cavity, and a feeding structure. The present invention achieves low-frequency expansion by using hybrid spirals to extend the electrical dimensions of the radiating spirals on a limited area and utilizing annular fractal dielectric loading. Furthermore, the present invention enhances absorption and adjusts the back-reflection phase by embedding a hybrid metamaterial absorbing structure with a resistive frequency selective surface, solving the gain sag problem with the help of dual control of absorption and reflection, and making the antenna gain flat within the frequency band. Based on this technology, the operating bandwidth of a planar spiral antenna of the same caliber can be increased from 9 octaves to more than 12 octaves.

Description

Technical Field

[0001] The present invention belongs to the field of antenna technology, and in particular relates to a planar spiral antenna based on fractal dielectric loading and metamaterial absorbing structure. Background Art

[0002] Antennas, as sensors for transmitting and receiving signals, are essential components of radio systems. Many applications, particularly radar detection, communications, electronic countermeasures, and precision guidance systems, require antennas to operate over a wide frequency band. Therefore, ultra-wideband (UWB) technology has been a research hotspot in the radio frequency field. Currently, common UWB antennas include log-periodic antennas, ridged horn antennas, Vivaldi antennas, tightly coupled antennas, Eleven antennas, and spiral antennas. However, these types of antennas are large and have high profiles, making them difficult to manufacture and integrate. In contrast, planar spiral antennas offer advantages such as wide bandwidth, circular polarization, a low profile, and ease of fabrication. Planar spiral antennas are a type of UWB antenna. Common examples include Archimedean spiral antennas, equiangular spiral antennas, and hybrid spiral antennas. Due to their inherent frequency similarity, these antennas can maintain excellent circular polarization characteristics over a wide range.

[0003] The trend toward integration and miniaturization of radio frequency systems places stringent, sometimes even demanding, size requirements on planar helical antennas. Antenna aperture miniaturization has become a hot topic in current antenna design research. Planar helical antenna miniaturization techniques include aperture miniaturization and low-profile design.

[0004] Research on aperture miniaturization focuses on modifying the radiation structure. This is because the radiation of a planar spiral antenna occurs within a circular radiation band with a circumference approximately 1.25 times the wavelength of the operating frequency. Therefore, while maintaining the radius of the radiation band, extending the electrical length of the spiral within the band can reduce the operating frequency of the radiation band and simultaneously achieve miniaturization. Common methods include: using thinner spiral wires at the antenna arm terminals, loading radiation resistors at the ends, loading absorption rings in the terminal radiation zone, and loading the spiral's zigzag arms with structures. Currently, the above methods have almost reached their limits, but advanced engineering applications, such as aircraft platforms, require further solutions to expand the low-frequency band within a limited aperture or to minimize the aperture within a given low-frequency limit. This problem has become a major difficulty in the current design of planar spiral antennas.

[0005] A simple planar spiral radiates bidirectionally, so to achieve unidirectional radiation, a back cavity needs to be added. There are two types of back cavities: absorptive and reflective. The reflective back cavity has a depth of λ / 4 and achieves unidirectional radiation by virtue of the phase alignment of reflection and radiation. However, since the depth is related to the wavelength, it is a narrowband structure and cannot achieve a broadband design. The absorptive back cavity is to add absorbing material to the cavity to absorb the back radiation, thereby obtaining broadband radiation at the expense of gain. Even so, traditional absorbing materials are thicker in the low-frequency band and their absorption performance fluctuates with frequency, making it difficult to significantly reduce the antenna profile. In addition, the broadband performance is unstable, and the gain band is uneven or even concave.

[0006] The difficulty in solving these problems lies in the fact that miniaturizing the radiating helix requires simultaneous consideration of circular polarization characteristics, impedance matching, gain, and pattern beamwidth. With these constraints, the previously mentioned methods have been pushed to their limits, and without new mechanisms, miniaturization of the radiator is impossible. Furthermore, in the low-profile design of the back cavity, reducing the thickness of the absorbing material significantly affects absorption efficiency and results in a decrease in in-band gain. These two constraints make miniaturization and lightweighting of antennas for flight platforms challenging. Summary of the Invention

[0007] To address the aforementioned problems in the prior art, the present invention provides a planar helical antenna based on fractal dielectric loading and a metamaterial absorbing structure. The technical problems to be solved by the present invention are achieved through the following technical solutions:

[0008] A planar helical antenna based on a fractal dielectric loading and metamaterial absorbing structure comprises a fractal dielectric loading structure, a composite planar helical structure, and a metamaterial absorbing structure arranged in sequence from top to bottom, wherein:

[0009] The fractal medium loading structure is a ring structure;

[0010] The composite planar spiral structure includes a dielectric substrate and a planar spiral antenna radiator disposed on the dielectric substrate. The planar spiral antenna radiator includes an outer ring portion and an inner ring portion. The annular portion outside the fractal dielectric loading structure is disposed above at least a portion of the outer ring portion, and the inner ring portion is located below the hollow portion of the fractal dielectric loading structure. The radiation section corresponding to the outer ring portion is smaller than that of the inner ring portion. The outer ring portion includes a sinusoidally loaded Archimedean spiral, and the inner ring portion includes an improved Archimedean spiral. The radiator formed by the improved Archimedean spiral has a partial line width, duty cycle, and single-turn gain that are not constant.

[0011] In one embodiment of the present invention, the annular portion of the fractal medium loading structure is provided with multiple layers of circular hole structures with decreasing diameters from the inside to the outside, each layer of the circular hole structure includes multiple circular holes with the same diameter, and the innermost circular hole structure is a partial circular hole structure.

[0012] In one embodiment of the present invention, the outer ring part includes a first outer ring arm and a second outer ring arm, and the inner ring part includes a first inner ring arm and a second inner ring arm, the first outer ring arm and the first inner ring arm constitute a first spiral arm, the second outer ring arm and the second inner ring arm constitute a second spiral arm, and loading resistors are provided at the ends of the first spiral arm and the second spiral arm, and the first spiral arm and the second spiral arm are spirally arranged at an angle of 180 degrees.

[0013] In one embodiment of the present invention, the equation of the outer edge of the improved Archimedean spiral is:

[0014]

[0015] The equation of the inner edge of the improved Archimedean spiral is:

[0016]

[0017] Among them, r1 is the outer edge of the improved Archimedean spiral, r1' is the inner edge of the improved Archimedean spiral, W' is the starting spiral arm width, r0' is the starting radius, α1 is the coefficient for controlling the starting single-turn amplification and duty cycle, k1 is the coefficient for controlling the overall change of the single-turn amplification, k2 is the coefficient for controlling the overall change of the duty cycle, θ is the angle between the radial direction and the polar axis, and n1 and n2 are coefficients for controlling the change speed of the single-turn amplification and the duty cycle.

[0018] In one embodiment of the present invention, the equation of the outer edge of the sinusoidally loaded Archimedean spiral is:

[0019]

[0020] The equation for the inner edge of the sinusoidally loaded Archimedean spiral is:

[0021]

[0022] Wherein, r2 is the outer edge of the sinusoidally loaded Archimedean spiral, r2' is the inner edge of the sinusoidally loaded Archimedean spiral, a is the starting radius of the outer edge of the sinusoidally loaded Archimedean spiral, and a1 is the starting radius of the inner edge of the sinusoidally loaded Archimedean spiral. θ0=2πm, m is the number of turns of the inner circle, α1 is the coefficient for controlling the initial single-turn increase and duty cycle, k1 is the coefficient for controlling the overall change of the single-turn increase, k2 is the coefficient for controlling the overall change of the duty cycle, α s To control the coefficient of the initial single-turn amplification and duty cycle of the sinusoidally loaded Archimedean spiral, k s is the coefficient for controlling the overall change of the single-turn amplification, C is the amplitude of the controlled sine line, θ is the angle between the radial direction and the polar axis, and θ max is the maximum angle between the radial direction and the polar axis, n1 and n2 are the coefficients for controlling the single-turn increase and the duty cycle change speed, n s To control the growth rate of the sine line amplitude, D is the period of the controlled sine line.

[0023] In one embodiment of the present invention, the metamaterial absorbing structure is disposed in a cavity of the back cavity, and the metamaterial absorbing structure includes an absorbing structure and a resistive frequency selective surface embedded in the absorbing structure.

[0024] In one embodiment of the present invention, the planar helical antenna further includes a feeding structure, and the starting end of the inner loop portion is connected to the feeding structure.

[0025] In one embodiment of the present invention, the feeding structure includes a coaxial tapered balun structure.

[0026] In one embodiment of the present invention, the planar helical antenna further comprises a radome, wherein the radome covers the fractal dielectric loading structure and the composite planar helical structure.

[0027] In one embodiment of the present invention, the material of the radome includes polytetrafluoroethylene material.

[0028] Beneficial effects of the present invention:

[0029] The present invention adopts the fractal dielectric loading technology on the top of the antenna to ensure a smooth transition between the loaded area and the non-loaded area, realizes the purpose of reducing the frequency band by dielectric loading, and achieves a low-frequency miniaturized design effect.

[0030] The double-arm spiral radiator of the present invention combines impedance loading and wave absorption to simultaneously optimize the radiation spiral structure, that is, it is formed by smoothly connecting the inner circle improved Archimedean spiral and the outer sinusoidally loaded Archimedean spiral to form an overall broadband effect.

[0031] The present invention adopts an absorbing material based on a mixture of a resistive frequency selective surface and an absorbing material. It can optimize the impact of back radiation by using both absorption and reflection strategies within a limited cavity depth, solving the gain depression caused by the modulation of the relationship between the absorptivity and reflection path length of traditional simple absorbing materials and the wavelength, making the antenna gain flat within the frequency band, and effectively solving the gain depression problem.

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of a planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure provided by an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of a fractal medium loading structure and a composite planar spiral structure provided by an embodiment of the present invention;

[0035] Figure 3 A schematic diagram of a metamaterial absorbing structure provided by an embodiment of the present invention;

[0036] Figure 4 A frequency-standing wave simulation result diagram of the present invention;

[0037] Figure 5 This is a frequency-axis ratio simulation result diagram of the present invention;

[0038] Figure 6 This is a comparison chart of the frequency-right-hand circularly polarized gain simulation results of the present invention and the resistance-free frequency selective surface hybrid absorbing material. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0040] Example 1

[0041] See Figure 1 , Figure 1 An embodiment of the present invention provides a planar spiral antenna based on a fractal dielectric loading and a metamaterial absorbing structure. The embodiment of the present invention provides a planar spiral antenna based on a fractal dielectric loading and a metamaterial absorbing structure. The miniaturized ultra-wideband planar spiral antenna includes a fractal dielectric loading structure, a composite planar spiral structure, and a metamaterial absorbing structure arranged in sequence from top to bottom, wherein:

[0042] The fractal medium loading structure is a ring structure;

[0043] The composite planar spiral structure includes a dielectric substrate and a planar spiral antenna radiator arranged on the dielectric substrate. The planar spiral antenna radiator includes an outer ring portion and an inner ring portion. The circular ring portion outside the fractal dielectric loading structure is arranged above at least a portion of the outer ring portion, and the inner ring portion is located below the hollow portion of the fractal dielectric loading structure. The radiation section corresponding to the outer ring portion is smaller than that of the inner ring portion. The outer ring portion includes a sinusoidally loaded Archimedean spiral, and the inner ring portion includes an improved Archimedean spiral. The line width, duty cycle and single-turn gain of the improved Archimedean spiral are not constant.

[0044] Specifically, the circular ring portion on the outside of the fractal medium loading structure is the loading area, the hollow portion in the middle is the non-loading area, part of the outer ring portion is located under the circular ring portion on the outside of the fractal medium loading structure, and the remaining outer ring portion and inner ring portion are located under the hollow portion of the fractal medium loading structure. The radiation segment corresponding to the outer ring portion is the low frequency segment, and the radiation segment corresponding to the inner ring portion is the high frequency segment. The circular ring portion covers the outer ring portion of the antenna radiating the low frequency segment to achieve the purpose of dielectric loading to reduce the frequency segment. The top of the antenna of the present invention adopts fractal dielectric loading technology to ensure a smooth transition between the loading area and the non-loading area, achieve the purpose of dielectric loading to reduce the frequency segment, and achieve a low-frequency miniaturized design effect. The composite planar spiral structure of the present invention combines impedance loading and wave absorption as a radiator, optimizes the radiation spiral structure, that is, the inner ring portion adopts an improved Archimedean spiral and the outer ring portion adopts a sinusoidal loading Archimedean spiral to be smoothly connected, forming an overall broadband effect.

[0045] In a specific embodiment, the annular portion of the fractal medium loading structure is provided with multiple layers of circular hole structures with decreasing diameters from the inside to the outside, each layer of the circular hole structure includes multiple circular holes with the same diameter, and the innermost circular hole structure is a partial circular hole structure, and all the circular holes in each layer of the circular hole structure are arranged at equal intervals.

[0046] Specifically, the fractal dielectric loading structure is composed of an annular dielectric substrate, and the annular portion covers the outer ring portion of the antenna radiating low frequency to achieve the purpose of dielectric loading to reduce the frequency band, thereby achieving a low-frequency miniaturization design effect. Furthermore, in order to achieve a smooth transition between the high-frequency unloaded area and the low-frequency loaded area, the present invention utilizes dielectric fractal punching technology to punch holes layer by layer from the inside to the outside in the annular dielectric substrate. The diameters of the multiple circles of circular holes adopt a self-similar strategy, gradually becoming smaller from the inside to the outside, which is equivalent to gradually changing the equivalent dielectric constant of the fractal dielectric loading structure at the top. Based on this, the loading area and the non-loading area are matched with a gradual transition, forming a broadband matching effect. Simultaneously, the purpose of dielectric loading to reduce the frequency band is achieved with the help of loading, thereby achieving a low-frequency miniaturization design effect.

[0047] Optionally, the fractal dielectric loading structure has a dielectric constant of 3, a loss tangent of 0.0015, and a thickness of 0.762 mm.

[0048] In one specific embodiment, the outer ring portion includes a first outer ring arm and a second outer ring arm, and the inner ring portion includes a first inner ring arm and a second inner ring arm. The first outer ring arm and the first inner ring arm form a first spiral arm, and the second outer ring arm and the second inner ring arm form a second spiral arm. Loading resistors are provided at the ends of the first and second spiral arms. The first and second spiral arms are arranged in a spiral configuration staggered 180 degrees, i.e., the first and second spiral arms spiral about the same center and are staggered 180 degrees. The first and second outer ring arms are sinusoidally loaded Archimedean spirals, while the first and second inner ring arms are improved Archimedean spirals.

[0049] Specifically, the composite planar spiral structure is the antenna's radiator, using a combination of an improved Archimedean spiral and a sinusoidally loaded Archimedean spiral. Specifically, the improved Archimedean spiral is used in the center, while the sinusoidally loaded Archimedean spiral is used at the outer ends. This effectively extends the electrical length of the radiation band, lowering the operating frequency corresponding to the outer radiation band, resulting in better low-frequency characteristics. The line width, duty cycle, and single-turn amplification of the traditional Archimedean spiral are all constant, and the entire structure has good low-frequency and high-frequency characteristics, creating an overall broadband effect. The center of this composite planar spiral structure is an improved Archimedean spiral, while the outer ends use end-resistance-loaded sinusoidally loaded Archimedean spirals to zigzag the spiral antenna arms, thereby extending the electrical dimensions of the radiating spiral within a limited area and achieving a miniaturized aperture.

[0050] Furthermore, the equation of the outer edge of the improved Archimedean spiral is:

[0051]

[0052] The equation of the inner edge of the improved Archimedean spiral is:

[0053]

[0054] Among them, r1 is the outer edge of the improved Archimedean spiral, r1' is the inner edge of the improved Archimedean spiral, W' is the starting spiral arm width, r0' is the starting radius, α1 is the coefficient controlling the starting single-turn amplification and duty cycle, k1 is the coefficient controlling the overall change of the single-turn amplification, k2 is the coefficient controlling the overall change of the duty cycle, θ is the angle between the radial direction and the polar axis, and n1 and n2 are coefficients controlling the change speed of the single-turn amplification and the duty cycle.

[0055] Furthermore, the equation for the outer edge of a sinusoidally loaded Archimedean spiral is:

[0056]

[0057] The equation for the inner edge of a sinusoidally loaded Archimedean spiral is:

[0058]

[0059] Wherein, r2 is the outer edge of the sinusoidally loaded Archimedean spiral, r2' is the inner edge of the sinusoidally loaded Archimedean spiral, a is the starting radius of the outer edge of the sinusoidally loaded Archimedean spiral, which is consistent with the end radius of the outer circle of the improved Archimedean spiral, and a1 is the starting radius of the inner edge of the sinusoidally loaded Archimedean spiral, that is, the end radius of the inner circle of the improved Archimedean spiral. θ0=2πm, m is the number of circles in the inner circle, such as m=3, α s To control the coefficient of the initial single-turn amplification and duty cycle of the sinusoidally loaded Archimedean spiral, k s is the coefficient for controlling the overall change of the single-turn amplification, C is the amplitude of the controlled sine line, θ max is the maximum angle between the radial direction and the polar axis, n s To control the growth rate of the sine line amplitude, D is the period of the controlled sine line.

[0060] Optionally, the dielectric substrate may be Rogers RT / duroid 5880.

[0061] In a specific embodiment, the metamaterial absorbing structure is disposed in the cavity of the back cavity, and the metamaterial absorbing structure includes an absorbing structure and a resistive frequency selective surface embedded in the absorbing structure.

[0062] Specifically, helical antennas radiate bidirectionally, while metamaterial absorbing structures can achieve unidirectional radiation. The mechanism is that if the cavity height is 1 / 4 of the wavelength, the wave radiated backward from the antenna experiences half a wave loss due to total reflection from the metamaterial absorbing structure. Adding the half-wavelength path difference created by the round trip, the wave superimposes in phase with the electromagnetic wave radiated forward from the antenna, achieving maximum gain. However, as the frequency changes, the wave reflected back from the antenna does not always superimpose in phase with the forward wave; some may even superimpose in phase with it. This creates a "dip" in the direction of maximum antenna radiation. A common solution is to add absorbing materials to the cavity to absorb the energy of the reverse radiation, thereby preventing significant gain fluctuations and broadening the antenna's operating bandwidth. However, traditional single absorbing materials require a certain thickness to achieve the desired absorption rate. Furthermore, insufficient thickness modulates the relationship between the absorption rate and the reflection path length with wavelength, resulting in a gain dip. For example, a 2-18 GHz antenna filled with a single absorbing material will result in a gain dip between 7 and 9 GHz.

[0063] Resistive frequency selective surfaces (RFSSs) have properties similar to those of absorbing materials, absorbing energy within specific frequencies. Embedding the RFSS within a three-layer absorbing structure to create a hybrid material enhances absorption while also causing the overall reflection phase of the material to change depending on where the RFSS is embedded within the three-layer absorbing structure. Therefore, choosing the appropriate embedding position allows the material's absorption pits and in-phase flip positions to complement each other, ensuring full coverage across the entire frequency band through both strong absorption and in-phase reflection, resulting in stable gain for the resulting planar helical antenna.

[0064] Furthermore, the absorbing structure of this embodiment comprises three layers of absorbing material, with a resistive frequency selective surface embedded in the topmost layer. This resistive frequency selective surface simultaneously provides enhanced absorption at specific frequencies and phase adjustment capabilities. By leveraging dual absorption and reflection control, it addresses gain notch issues and ensures flat gain across the antenna frequency band.

[0065] Furthermore, the resistive frequency selective surface is formed by thin film printing, and the loading medium is based on a thin layer of medium, which is embedded in the original antenna design and hardly brings any additional thickness and weight burden.

[0066] In a specific embodiment, the ultra-wideband planar helical antenna further includes a feeding structure, and the starting end of the inner loop portion is connected to the feeding structure.

[0067] Furthermore, the feeding structure includes a coaxial tapered balun structure, that is, the starting end of the inner ring part is connected to the feeding needle.

[0068] In a specific embodiment, the ultra-wideband planar helical antenna further includes a radome, which covers the fractal dielectric loading structure and the composite planar helical structure.

[0069] Furthermore, the material of the radome includes polytetrafluoroethylene material.

[0070] To overcome the shortcomings of the prior art, the present invention primarily proposes a design method for miniaturizing and achieving high in-band gain flatness in planar spiral antennas based on a fractal dielectric loading structure and a metamaterial absorbing structure. This design employs a hybrid helix to extend the electrical dimensions of the radiating spiral within a limited area and utilizes a ring-shaped fractal dielectric loading structure to achieve low-frequency extension. Specifically, a top fractal dielectric loading structure is provided in conjunction with the optimization of the hybrid planar helix to address the difficulty of reducing the aperture size of existing ultra-wideband planar spiral antennas at a given frequency limit. Furthermore, a metamaterial absorbing structure filled in the back cavity based on a resistive frequency selective surface is provided to address the uneven gain band dip caused by reflection from the planar metal cavity and the limitations of the absorbing material within the cavity. By embedding a hybrid metamaterial absorbing structure with a resistive frequency selective surface, absorption is enhanced and the back-reflection phase is adjusted. This dual absorption and reflection control addresses the gain dip and achieves in-band gain flatness. This technology can increase the operating bandwidth of a planar spiral antenna of the same aperture from 9 octaves to over 12 octaves.

[0071] The technical effects of the present invention are further described through the following simulation results.

[0072] The electromagnetic simulation software HFSS is used to perform simulation calculations in the range of 1 to 18 GHz.

[0073] Figure 4 This is a frequency-standing wave simulation result diagram of the present invention. As shown in the figure, under the cavity aperture constraint size of 59mm, the embodiment of the present invention has a standing wave ratio of less than 2 within the bandwidth range of 1.43 to 18GHz, compared with the original standing wave bandwidth of 2 to 18GHz, verifying the standing wave band widening or low-frequency miniaturization design effect.

[0074] Figure 5 This is a frequency-axial ratio simulation result diagram of the present invention. As shown in the figure, within the bandwidth range of 1.07 to 18 GHz, the axial ratio is less than 3, indicating that the circular polarization performance of the antenna is good.

[0075] Figure 6 This graph shows the frequency-to-right-hand circularly polarized gain results for the present invention. As shown, within the 4.34-18 GHz bandwidth, the right-hand circularly polarized gain exceeds 4.4 dB, demonstrating high overall antenna gain stability and flatness. Simultaneously presented are simulation results for a non-resistance frequency selective surface hybrid absorber, demonstrating that the proposed loading technique effectively improves gain flatness and avoids gain pits.

[0076] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0077] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0078] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0079] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0080] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0081] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure, characterized in that: It includes a fractal medium loading structure, a composite planar spiral structure and a metamaterial absorbing structure arranged in sequence from top to bottom, wherein: The fractal medium loading structure is a ring structure; The composite planar spiral structure includes a dielectric substrate and a planar spiral antenna radiator disposed on the dielectric substrate. The planar spiral antenna radiator includes an outer ring portion and an inner ring portion. The annular portion outside the fractal dielectric loading structure is disposed above at least a portion of the outer ring portion, and the inner ring portion is located below a hollow portion of the fractal dielectric loading structure. The radiation section corresponding to the outer ring portion is smaller than that of the inner ring portion. The outer ring portion includes a sinusoidally loaded Archimedean spiral, and the inner ring portion includes an improved Archimedean spiral. The radiator formed by the improved Archimedean spiral has a non-constant line width, duty cycle, and single-turn gain. The fractal dielectric loading structure is composed of an annular dielectric substrate, the annular portion of which covers the outer portion of the antenna radiating low frequencies; holes are punched layer by layer from the inside to the outside of the annular dielectric substrate, and the diameters of the multiple circles of holes adopt a self-similar strategy, gradually decreasing from the inside to the outside.

2. The planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure according to claim 1, characterized in that: The annular portion of the fractal medium loading structure is provided with multiple layers of circular hole structures with decreasing diameters from the inside to the outside. Each layer of circular hole structure includes multiple circular holes with the same diameter, and the innermost circular hole structure is a partial circular hole structure.

3. The planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure according to claim 1, characterized in that: The outer ring part includes a first outer ring arm and a second outer ring arm, and the inner ring part includes a first inner ring arm and a second inner ring arm. The first outer ring arm and the first inner ring arm constitute a first spiral arm, and the second outer ring arm and the second inner ring arm constitute a second spiral arm. Loading resistors are provided at the ends of the first spiral arm and the second spiral arm, and the first spiral arm and the second spiral arm are spirally arranged at an angle of 180 degrees.

4. The planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure according to claim 1 or 3, characterized in that: The equation of the outer edge of the improved Archimedean spiral is: The equation of the inner edge of the improved Archimedean spiral is: Among them, r1 is the outer edge of the improved Archimedean spiral, r1' is the inner edge of the improved Archimedean spiral, W' is the starting spiral arm width, r0' is the starting radius, α1 is the coefficient for controlling the starting single-turn amplification and duty cycle, k1 is the coefficient for controlling the overall change of the single-turn amplification, k2 is the coefficient for controlling the overall change of the duty cycle, θ is the angle between the radial direction and the polar axis, and n1 and n2 are coefficients for controlling the change speed of the single-turn amplification and the duty cycle.

5. The planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure according to claim 1 or 3, characterized in that: The equation for the outer edge of the sinusoidally loaded Archimedean spiral is: The equation for the inner edge of the sinusoidally loaded Archimedean spiral is: Wherein, r2 is the outer edge of the sinusoidally loaded Archimedean spiral, r2' is the inner edge of the sinusoidally loaded Archimedean spiral, a is the starting radius of the outer edge of the sinusoidally loaded Archimedean spiral, and a1 is the starting radius of the inner edge of the sinusoidally loaded Archimedean spiral. θ0=2πm, m is the number of turns of the inner circle, α1 is the coefficient for controlling the initial single-turn increase and duty cycle, k1 is the coefficient for controlling the overall change of the single-turn increase, k2 is the coefficient for controlling the overall change of the duty cycle, α s To control the coefficient of the initial single-turn amplification and duty cycle of the sinusoidally loaded Archimedean spiral, k s is the coefficient for controlling the overall change of the single-turn amplification, C is the amplitude of the controlled sine line, θ is the angle between the radial direction and the polar axis, and θ max is the maximum angle between the radial direction and the polar axis, n1 and n2 are the coefficients for controlling the single-turn increase and the duty cycle change speed, n s To control the growth rate of the sine line amplitude, D is the period of the controlled sine line.

6. The planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure according to claim 1, characterized in that: The metamaterial wave absorbing structure is arranged in the cavity of the back cavity, and the metamaterial wave absorbing structure comprises a wave absorbing structure and a resistive frequency selective surface embedded in the wave absorbing structure.

7. The planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure according to claim 1, characterized in that: It also includes a feeding structure, and the starting end of the inner ring part is connected to the feeding structure.

8. The planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure according to claim 7, characterized in that: The feeding structure includes a coaxial tapered balun structure.

9. The planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure according to claim 1, characterized in that: The invention also includes a radome, which covers the fractal medium loading structure and the composite planar helical structure.

10. The planar helical antenna based on fractal dielectric loading and metamaterial absorbing structure according to claim 9, characterized in that: The material of the radome includes polytetrafluoroethylene material.

Images