Broadband low-profile full-wavelength loop antenna

Abstract

The invention discloses a broadband low-profile full-wavelength loop antenna which comprises a full-wavelength loop antenna body, an annular matching structure, a dielectric plate, a feed port, a metal reflecting plate and a supporting column. The full-wavelength loop antenna and the annular matching structure are printed on the upper surface of the dielectric plate, and the feed port is used for realizing signal feed-in; the annular matching structure and the full-wavelength loop antenna are coaxially connected in a coplanar manner; the metal reflecting plate is arranged below the dielectric plate in parallel through supporting columns, and the supporting columns are used for fixing the dielectric plate and the metal reflecting plate and maintaining a preset distance; according to the antenna, through the cooperative design of matching structure optimization and metal reflecting plate loading, resonance point splitting and broadband coverage are achieved, meanwhile, the profile of the antenna is reduced to one eighth of the wavelength, the problems that a traditional full-wavelength loop antenna is narrow in bandwidth, poor in impedance matching and high in profile are solved, and good engineering application prospects are achieved.

Description

Technical Field

[0001] This invention relates to the field of antenna technology, and more specifically to a broadband low-profile full-wavelength loop antenna. Background Technology

[0002] Loop antennas, as a compact and stable antenna type, are widely used in wireless communication, radar detection and other fields. According to the relationship between the ring circumference and the operating wavelength, loop antennas can be divided into small loop antennas (circumference ≤ λ / 10) and large loop antennas (circumference ≥ λ). Among them, the full-wavelength loop antenna (circumference ≈ λ) is a typical large loop structure. It has low cross-polarization characteristics and stable radiation pattern at a specific resonant frequency, making it one of the ideal candidate antennas for communication systems.

[0003] With the development of next-generation wireless communication technologies, communication systems are placing increasingly stringent demands on antennas for broadband, miniaturization, low profile, and high integration. Traditional full-wavelength loop antennas suffer from narrow bandwidth and poor resonant point matching performance, while existing bandwidth extension technologies often increase structural complexity. Furthermore, in conventional directional antenna designs, the distance between the antenna and the metal reflector needs to be at least a quarter wavelength to achieve both high gain and good matching, resulting in a relatively high overall antenna profile that is difficult to meet miniaturization and integration requirements. Therefore, there is an urgent need for a technical solution that can achieve broadband and low-profile design for full-wavelength loop antennas without significantly increasing structural complexity. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems by providing a broadband low-profile full-wavelength loop antenna. Through the synergistic design of matching structure optimization and metal reflector loading, it achieves bandwidth expansion, low-profile layout, and good impedance matching and radiation performance, thus solving the problems of narrow bandwidth, poor impedance matching, and high profile in existing full-wavelength loop antennas.

[0005] The technical solution adopted in this invention is as follows: A broadband low-profile full-wavelength loop antenna, the antenna comprising a full-wavelength loop antenna, a loop matching structure, a dielectric substrate, a feed port, and a metal reflector; The full-wavelength loop antenna and the matching structure are coplanar and coaxially laid on the upper surface of the dielectric substrate, and the full-wavelength loop antenna is electrically connected to the ring matching structure; the feed port is located on the full-wavelength loop antenna; the metal reflector is opposite to the lower surface of the dielectric substrate and is parallel to and separate from the dielectric substrate.

[0006] Furthermore, the full-wavelength loop antenna is a ring-shaped metal strip structure with an outer radius of 20mm, an inner radius of 18mm, and a width of 2mm.

[0007] Furthermore, the ring matching structure includes an inner ring and two rectangular stubs. The inner ring is located inside the full-wavelength ring antenna and is coaxial and coplanar with the full-wavelength ring antenna. The two rectangular stubs are symmetrically distributed on both sides of the central axis of the full-wavelength ring antenna and extend in the horizontal direction. The inner ring is electrically connected to the full-wavelength ring antenna through the rectangular stubs.

[0008] Furthermore, the inner radius of the inner ring is 14mm, the width of the inner ring is the same as that of the full-wavelength ring antenna, and the rectangular stub has a length of 2.3mm and a width of 2mm.

[0009] Furthermore, the dielectric substrate is an FR4 dielectric substrate with a relative permittivity of 4.4 and a thickness of 1.6 mm.

[0010] Furthermore, the feed port is a simulated port configured for simulation, used to feed signals and provide energy input for the operation of the full-wavelength loop antenna.

[0011] Furthermore, multiple insulating support columns are uniformly and vertically connected between the metal reflector and the dielectric plate.

[0012] Furthermore, the metal reflector has a square structure with a side length of 150mm and a thickness of 1mm; the support column is used to maintain a vertical distance of 15mm between the metal reflector and the dielectric plate, which corresponds to one-eighth of the 2.43GHz free space wavelength.

[0013] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. Significant bandwidth expansion effect: Through the synergistic effect of the matching structure and the metal reflector, the first-order wavelength resonant point of the full-wavelength loop antenna is split into two independent frequency points of 2.2GHz and 2.55GHz, realizing broadband coverage of the 2.1-2.6GHz communication frequency band and meeting the wide-band usage requirements of wireless communication.

[0014] 2. Low profile design: By utilizing the inherent medium-to-high impedance characteristics of the full-wavelength loop antenna and the precise control of the matching structure, the distance between the antenna and the metal reflector is reduced to one-eighth of the wavelength, i.e., 15mm, through the support column. Compared with the traditional quarter-wavelength spacing design, the profile height is reduced by 51.6%, which significantly improves the antenna's miniaturization and integration capabilities.

[0015] 3. Excellent impedance matching performance: The matching structure uses the mutual inductance cancellation effect between the inner ring and the full-wavelength ring antenna and the distributed capacitance formed by the ring gap to adjust the equivalent RLC parameters of the antenna, so that |S11| ≤ -10dB at the first-order wavelength resonant point. After optimization, the input impedance is close to the 50Ω standard impedance, and the matching performance is good.

[0016] 4. Stable radiation performance: Within the operating frequency band, the antenna main lobe direction is clear, and the half-power beamwidths of the XOZ and YOZ planes are 53.5±2.5° and 69±2°, respectively, with a front-to-back ratio of over 20dB. The cross-polarization discrimination in the 0° direction is 29dB, effectively suppressing cross-polarization interference. At the same time, the peak gain can reach 9.4dBi, demonstrating excellent radiation performance.

[0017] 5. Simple structure and easy to process: The antenna adopts PCB technology, without complex structural design, low processing cost, and is suitable for large-scale production applications. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a broadband low-profile full-wavelength loop antenna according to the present invention; Figure 2 is a comparison of the |S11| curves of different antenna structures in this invention, where (a) is the |S11| curve and input impedance curve of the full-wavelength loop antenna, (b) is the |S11| curve of the antenna with matching structure, (c) is the |S11| curve of the "full-wavelength loop antenna + metal reflector" antenna, and (d) is the |S11| curve of the "full-wavelength loop antenna + matching structure + metal reflector" antenna. Figure 3 shows the current distribution of the antenna of the present invention, where (a) is the current distribution at 2.2 GHz and (b) is the current distribution at 2.55 GHz. Figure 4 This is a graph showing the |S11| curves corresponding to different inner ring radii in the antenna of this invention; Figure 5 shows the radiation patterns of the antenna of the present invention at two resonant points, where (a) is the XOZ plane radiation pattern at 2.2 GHz, (b) is the YOZ plane radiation pattern at 2.2 GHz, (c) is the XOZ plane radiation pattern at 2.55 GHz, and (d) is the YOZ plane radiation pattern at 2.55 GHz. Figure 6 This is the gain curve of the antenna of the present invention in the operating frequency band.

[0019] In the figure, 1. Full-wavelength loop antenna, 2. Ring matching structure, 21. Inner ring, 22. Rectangular stub, 3. Dielectric substrate, 4. Feed port, 5. Metal reflector, 6. Support column. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings.

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] Example This embodiment provides a broadband low-profile full-wavelength loop antenna, such as... Figure 1 As shown, it includes a full-wavelength loop antenna 1, a matching structure 2, a dielectric substrate 3, a feed port 4, a metal reflector 5, and a support column 6.

[0023] The full-wavelength loop antenna 1 is printed on the upper surface of the dielectric substrate 3. The full-wavelength loop antenna 1 is a ring-shaped metal strip structure with an outer radius of... r out =20mm, inner radius r in =18mm, width w =2mm, serving as the core radiating element of the antenna, responsible for the radiation and reception of electromagnetic waves.

[0024] The ring matching structure 2 includes an inner ring 21 and two rectangular stubs 22, which are coplanar and coaxially arranged with the full-wavelength ring antenna 1; wherein, the inner radius of the inner ring 21 is... r 0 = 14mm, width is the same as the full-wavelength loop antenna 1 at 2mm; two rectangular stubs 22 are symmetrically distributed on both sides of the antenna's central axis, extending horizontally, stub length l stub =2.3mm, width w stub =2mm, the inner ring 21 and the full-wavelength ring antenna 1 are electrically connected through the rectangular stub 22. The ring matching structure 2 adjusts the real and imaginary parts of the antenna input impedance to make the impedance of the target resonant point closer to the 50Ω standard impedance, and at the same time adjusts the frequency spacing of the dual resonant points through the coupling and tuning effect of the inner ring 21.

[0025] Dielectric substrate 3 is made of FR4 material, with a relative permittivity of 1000 kJ / m². ε r =4.4, thickness h =1.6mm, providing a bearing foundation for the full-wavelength loop antenna 1 and the ring matching structure 2.

[0026] Feed port 4 is an analog port set in the simulation software, used to feed signals and provide energy support for the antenna's radiation and reception functions.

[0027] The metal reflector 5 has a square structure with a side length of... S =150mm, thickness t =1mm, parallel to the bottom of dielectric substrate 3; the metal reflector 5, on the one hand, generates a mirror antenna to form a coupling effect, splitting the original single resonant point into two adjacent resonant points, thus widening the working bandwidth; on the other hand, it concentrates radiated energy, reduces back radiation loss, and improves antenna gain.

[0028] The support columns 6 are made of insulating material. In this embodiment, four support columns are used, evenly distributed at the four corners between the dielectric plate 3 and the metal reflector 5, to fix the dielectric plate 3 and the metal reflector 5 and maintain the vertical distance between them. d =15mm, which corresponds to one-eighth of the 2.43GHz free space wavelength λ≈123.5mm. Compared with the λ / 4 spacing of the traditional half-wave dipole of about 31mm, the profile height is reduced by 51.6%, which significantly improves the miniaturization capability of the antenna.

[0029] The principle of this embodiment is as follows: In free space, the full-wavelength loop antenna 1 n The first resonant frequency satisfies the formula in r avg This represents the average of the inner and outer radii of the loop antenna. c The speed of light in free space; when a loop antenna is printed on a dielectric substrate, the medium affects the propagation speed of electromagnetic waves. Drawing on microstrip antenna theory, a full-wavelength loop antenna 1 printed on a dielectric substrate... n The formula for the first resonant frequency can be expressed as: ,in The effective dielectric constant of the substrate is given by the formula; however, simulation results show that the calculation error of this formula is relatively large.

[0030] The error arises because energy diffuses more easily into the air during radiation from a loop antenna, and the wavelength shortening effect of the medium is weaker than that of a microstrip antenna; therefore, a wavelength shortening factor is introduced. k Make corrections, the correction formula is as follows ,in f 1 represents the simulated value of 2.15 GHz for the first resonant point, calculated... k =0.855.

[0031] Based on the corrected wavelength shortening factor, the full-wavelength loop antenna 1 n The formula for the first resonant frequency is: Substitute the parameters to calculate the main order resonant frequencies and compare them with the |S11| curve of the full-wavelength loop antenna 1 printed on the dielectric substrate in Figure 2(a): 1st order (first resonant point): n =1, f 1 = 1 × (3 × 10) 8 ×0.855) / 0.119≈2.15GHz (consistent with the simulation value of 2.15GHz); 2nd order: n =2, f 2 = 2 × 2.15 GHz = 4.3 GHz (coinciding with the 4.08 GHz resonant point in the |S11| curve); 3rd order: n =3, f3 = 3 × 2.15 GHz = 6.45 GHz (consistent with the trend of the 5.72 GHz resonant point in the |S11| curve); This calculation model, through wavelength shortening coefficient correction, accurately reproduces the result of the first resonant point of the full-wavelength loop antenna 1, verifies the rationality of the derivation, and provides theoretical support for subsequent optimization design.

[0032] The input impedance of the full-wavelength loop antenna 1 is higher than that of a conventional half-wave dipole, an inherent characteristic that provides an important basis for low-profile design and subsequent impedance tuning; the full-wavelength loop antenna 1 operates at 2.15 GHz (… n =1), 4.08GHz ( n =2), 5.72GHz ( n =3), 7.4GHz ( n =4) Resonant peaks appear at integer multiple wavelength positions, but the |S11| value of each resonant point is greater than -10dB. Among them, the first-order wavelength resonant point |S11|=-7.62dB, which has poor matching performance and needs to be further optimized by ring matching structure 2.

[0033] The electrical characteristics of the full-wavelength loop antenna 1 can be obtained through... RLC Equivalent circuit description. Resistors R The inductance is the sum of the radiation resistance and the loss resistance. L The capacitance is the sum of the distributed inductance and parasitic inductance of the loop antenna. C The sum of the distributed capacitance and parasitic capacitance of the loop antenna; resonant frequency. f 0 by L and C Together they determine that the formula is satisfied: .

[0034] Without the ring matching structure 2, the first-order wavelength resonant point of the full-wavelength ring antenna 1 is 2.15 GHz, and the antenna input impedance is... Z =105.5- j 36Ω, equivalent RLC circuit C =2pF, L =2.7nH; After adding the inner ring 21 and the rectangular stub 22, the first-order wavelength resonant point of the antenna is 2.43GHz, and the antenna input impedance is Z =34.3- j 3Ω, its equivalent RLC circuit C =21.8pF, L =0.197nH.

[0035] After loading ring matching structure 2, the equivalent inductance LThe equivalent inductance decreased from 2.7nH to 0.197nH because the current phase of the inner ring 21 is opposite to that of the full-wavelength loop antenna 1. The mutual inductance generated by the opposing current cancels out part of the original self-inductance of the loop antenna, ultimately adjusting the overall equivalent inductance to 0.197nH. Equivalent capacitance C The increase from 2pF to 21.8pF is mainly due to the annular gap formed between the inner ring 21 and the full-wavelength ring antenna 1, which constitutes a "ring parallel plate capacitor" and generates significant distributed capacitance. Overall, without the ring matching structure 2, the antenna's resonant points at each order exhibit large capacitive reactance, and the resistance component differs significantly from the 50Ω transmission line, resulting in poor matching. After loading the ring matching structure 2, the synergistic adjustment of the equivalent inductance and capacitance at each resonant point of the antenna significantly cancels out the capacitive reactance, the resistance component is closer to the characteristic impedance of the transmission line, and the |S11| parameter is optimized to ≤-10dB, resulting in a significant improvement in matching performance.

[0036] The |S11| curve after adding the ring matching structure 2 is shown in Figure 2(b). The first-order wavelength resonant point shifts to 2.43 GHz, and the |S11| value is optimized to -14.1 dB, meeting the impedance matching requirement of |S11| ≤ -10 dB. Simultaneously, the matching performance of the second-order wavelength resonant point (4.86 GHz) and the third-order wavelength resonant point (7.01 GHz) is also improved, with |S11| decreasing to -17.6 dB and -17.9 dB, respectively. The full-wavelength ring antenna 1 only has a low cross-polarization level at the first-order wavelength resonant point; subsequent optimization work will focus on this resonant point.

[0037] The formation of the dual resonant points is the result of the synergistic effect of the "dual-ring coupling foundation" of the metal reflector 5 and the "current distribution regulation" of the ring matching structure 2. The metal reflector 5 constructs a symmetrical dual-ring system through the mirror effect, providing the physical premise for dual modes; the ring matching structure 2 makes the implicit dual modes explicit by reconstructing the current path and regulating the coupling phase, ultimately realizing the splitting of the resonant points and broadband coverage.

[0038] When only the full-wavelength loop antenna 1 and the metal reflector 5 are used, the metal reflector 5 constructs a dual-loop coupling system of "original antenna + mirror antenna" through the mirror principle. The current direction of the mirror antenna is opposite to that of the original antenna. The dual-loop system forms an overall resonant system through electromagnetic coupling. Its coupling effect will cause the antenna's equivalent electromagnetic parameters to have the potential for differentiation. However, due to the large capacitive reactance of the full-wavelength loop antenna 1 and the lack of effective current path control, the frequency difference between the two coupling modes is extremely small and is covered by the resonant bandwidth, which is manifested as a single narrow peak in Figure 2(c), i.e., "hidden dual mode".

[0039] The ring matching structure 2 is crucial for achieving dual-mode dominance. Its core function is to separate the implicit dual-mode of the dual-ring system into two independent resonant points by changing the current path and adjusting the coupling phase. As shown in Figure 2(d), after the full-wavelength ring antenna 1 with the metal reflector 5 is fitted with the ring matching structure 2, the original first-order wavelength resonant point splits into two resonant points at 2.2 GHz and 2.55 GHz, forming a continuous operating frequency band of 2.1~2.6 GHz with a bandwidth of 21.3%. At this time, the |S11| values ​​of the two split resonant points are -18 dB and -20 dB, respectively, both of which meet the impedance matching requirements.

[0040] Figure 3(a) shows the current distribution at 2.2 GHz of the full-wavelength loop antenna 1 with metal reflector 5 after adding the ring matching structure 2. The current is mainly concentrated in the full-wavelength loop antenna 1. The equivalent inductance component introduced by the inner ring 21 is much smaller than the equivalent inductance component of the full-wavelength loop antenna 1 itself. Combined with the effect of increased equivalent capacitance brought by the ring matching structure 2, a lower resonant frequency (2.2 GHz) is finally formed. Figure 3(b) shows the current distribution at 2.55 GHz of the full-wavelength loop antenna 1 with metal reflector 5 after adding the ring matching structure 2. The current is concentrated in the full-wavelength loop antenna 1 and the inner ring 21, and the current in the inner ring 21 is out of phase with the current in the full-wavelength loop antenna 1, forming a demagnetizing coupling effect. The magnetic fields generated by the out-of-phase current cancel each other out, greatly weakening the overall equivalent inductance. The cancellation effect exceeds the positive contribution of the distributed inductance, making the equivalent inductance significantly lower. Although the equivalent capacitance has increased significantly, the significant reduction in inductance still dominates the increase in resonant frequency, ultimately forming a high-frequency resonant point of 2.55 GHz.

[0041] To further clarify the modulating effect of the inner ring 21 on the resonant frequency, such as Figure 4 As shown, the inner ring with a radius of 21 was developed. r The parameter sweep simulation of 0 shows that the smaller the radius of the inner ring 21, the higher the frequency of the second resonant point. This is because the coupling strength between the inner ring 21 and the full-wavelength ring antenna 1 decreases as the radius decreases. When the coupling weakens, the inductive load constraint exerted by the inner ring 21 on the full-wavelength ring antenna 1 decreases, reducing the inductive component of the total equivalent inductance. At the same time, the coupling capacitance between the two rings also decreases as the spacing increases (which can be derived from the formula for a parallel plate capacitor), reducing the capacitive component of the total equivalent capacitance. Combined with the resonant frequency formula... The decrease in the inductive component of the equivalent inductance and the capacitive component of the equivalent capacitance directly drives the resonant frequency to shift to higher frequencies, ultimately showing the rule that the smaller the radius of the inner ring 21, the higher the frequency of the second resonant point.

[0042] As shown in Figure 5, Figure 5(a) and Figure 5(b) are the radiation patterns of the XOZ and YOZ planes at 2.2 GHz, respectively, and Figure 5(c) and Figure 5(d) are the radiation patterns of the XOZ and YOZ planes at 2.55 GHz, respectively. Both resonant points exhibit a clear main lobe direction. The half-power beamwidth of the XOZ plane is 53.5 ± 2.5°, and the half-power beamwidth of the YOZ plane is 69 ± 2°. The front-to-back ratio is ≥ 20 dB, and the cross-polarization discrimination at 0° is 29 dB. The directional radiation characteristics are excellent and can effectively suppress cross-polarization interference.

[0043] like Figure 6 As shown, the curve illustrates the gain variation trend of the antenna within the operating frequency band. The simulated gain value remains between 8.1 and 9.4 dBi, with a peak gain of 9.4 dBi. The gain level is stable and relatively high, meeting the signal transmission strength requirements of the communication system.

[0044] In summary, this invention optimizes impedance matching through the ring matching structure 2, achieves resonant point splitting and bandwidth expansion by combining the mirror effect of the metal reflector 5, realizes low profile layout through the support column 6, and adds a feed port 4 to ensure effective signal feeding. It solves the inherent defects of traditional full-wavelength ring antennas with narrow bandwidth and high profile, and provides an effective technical path for broadband and low profile design of full-wavelength ring antennas, which has good engineering application prospects.

[0045] In the description of the embodiments of the present invention, it should be noted that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. It is only for the purpose of facilitating the description of the present invention and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the present invention.

[0046] This article uses specific embodiments to illustrate the principles and implementation methods of the present invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A broadband low-profile full-wavelength loop antenna, characterized in that, The antenna includes a full-wavelength loop antenna, a loop matching structure, a dielectric substrate, a feed port, and a metal reflector. The full-wavelength loop antenna and the matching structure are coplanar and coaxially laid on the upper surface of the dielectric substrate, and the full-wavelength loop antenna is electrically connected to the ring matching structure; the feed port is located on the full-wavelength loop antenna; the metal reflector is opposite to the lower surface of the dielectric substrate and is parallel to and separate from the dielectric substrate.

2. The broadband low-profile full-wavelength loop antenna according to claim 1, characterized in that, The full-wavelength loop antenna is a ring-shaped metal strip structure with an outer radius of 20mm, an inner radius of 18mm, and a width of 2mm.

3. A broadband low-profile full-wavelength loop antenna according to claim 1, characterized in that, The ring matching structure includes an inner ring and two rectangular stubs. The inner ring is located inside the full-wavelength ring antenna and is coaxial and coplanar with the full-wavelength ring antenna. The two rectangular stubs are symmetrically distributed on both sides of the central axis of the full-wavelength ring antenna and extend in the horizontal direction. The inner ring is electrically connected to the full-wavelength ring antenna through the rectangular stubs.

4. A broadband low-profile full-wavelength loop antenna according to claim 3, characterized in that, The inner radius of the inner ring is 14mm, and the width of the inner ring is the same as that of the full-wavelength ring antenna. The rectangular stub has a length of 2.3mm and a width of 2mm.

5. A broadband low-profile full-wavelength loop antenna according to claim 1, characterized in that, The dielectric substrate is an FR4 dielectric substrate with a relative permittivity of 4.4 and a thickness of 1.6 mm.

6. A broadband low-profile full-wavelength loop antenna according to claim 1, characterized in that, The feed port is a simulated port set up in the simulation, used to feed in signals and provide energy input for the operation of the full-wavelength loop antenna.

7. A broadband low-profile full-wavelength loop antenna according to claim 1, characterized in that, Multiple insulating support columns are uniformly and vertically connected between the metal reflector and the dielectric plate.

8. A broadband low-profile full-wavelength loop antenna according to claim 7, characterized in that, The metal reflector is a square structure with a side length of 150mm and a thickness of 1mm; the support column is used to maintain a vertical distance of 15mm between the metal reflector and the dielectric plate, which corresponds to one-eighth of the 2.43GHz free space wavelength.

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