Miniaturized ultra-wideband conformal monopole antenna

Abstract

The invention discloses a miniaturized ultra-wideband conformal monopole antenna, and belongs to the technical field of wireless communication antennas. The antenna aims at solving the technical problems that an existing circular polarization conformal antenna is narrow in bandwidth, limited in application scene and poor in structural adaptability. The antenna adopts the design of a monopole + polymorphic radiation structure and comprises a dielectric substrate, a coplanar waveguide feed structure, a rectangular monopole radiator, an asymmetric floor and a parasitic metal square ring with an opening in the bottom, the asymmetric metal grounds with unequal left and right heights are arranged, the monopole radiator and the metal grounds are subjected to grooving and corner cutting treatment, a parasitic metal square ring with an opening in the bottom is introduced, two adjacent circular polarization modes are coupled, and bandwidth expansion and circular polarization are achieved. The antenna disclosed by the invention is small in overall size, simple in structure, 2.85 GHz-11. 06 GHz in-band bandwidth coverage and stable in-band peak gain, and can meet the application requirements of a WiMAX (Worldwide Interoperability for Microwave Access) system at the frequency bands of 3.3 GHz-3. 8 GHz and 5.5 GHz.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication antenna technology, specifically relating to miniaturized ultra-wideband conformal monopole antennas and their design methods. Background Technology

[0002] With the rapid development of wireless communication technology, satellite communication, mobile communication, wireless local area networks (WLANs) and other fields have placed higher demands on antenna performance. Circularly polarized antennas, due to their advantages such as resistance to multipath effects, resistance to rain and fog interference, and immunity to Faraday rotation, can ensure signal transmission stability in complex electromagnetic environments and have become one of the core components of communication systems.

[0003] The increasing demand for data transmission rates and communication capacity in current communication systems has made broadband a key development trend in antenna technology. Simultaneously, the widespread adoption of portable electronic devices necessitates antenna miniaturization, and circular polarization is a crucial indicator for ensuring communication quality in scenarios such as satellite navigation and precision communication. However, existing circularly polarized antennas face numerous technical bottlenecks in achieving compatibility between miniaturization, broadband, and circular polarization.

[0004] While traditional microstrip-fed circularly polarized antennas are compact, they have narrow bandwidths. The axial ratio bandwidth of single-fed structures is typically less than 20%, making it difficult to meet the demands of broadband communication. Multi-fed structures can extend the bandwidth, but they require complex power-dividing and phase-shifting networks, leading to increased antenna profile, reduced radiation efficiency, and hindering miniaturization integration. Although dipole-type circularly polarized antennas have high gain, they often require metal reflectors or cavity structures to enhance directional radiation, resulting in larger antenna size and higher profiles, limiting their application in small devices.

[0005] Monopole antennas, requiring only a quarter-wavelength electrical dimension, possess a natural advantage in miniaturization and are easily made suitable for ultra-wideband characteristics, thus becoming a research hotspot. Existing circularly polarized monopole antennas often achieve circular polarization by modifying the ground plane structure or introducing parasitic stubs, but these generally suffer from insufficient circular polarization bandwidth. Furthermore, while some designs can achieve wide bandwidth, their complex structures, high fabrication difficulty, or low impedance-axis ratio bandwidth overlap rates negatively impact practical application performance.

[0006] Coplanar waveguide feeding technology has advantages such as simple structure, easy conformal feeding, low radiation loss, and high isolation, and has been widely used in broadband antenna design. However, existing coplanar waveguide-fed monopole antennas still have shortcomings in balancing miniaturization, broadband, and circular polarization: some designs have a wide bandwidth but low circular polarization bandwidth and unstable axial ratio performance; some designs can guarantee circular polarization, but have a narrow bandwidth or are too large, which cannot meet the multi-performance compatibility requirements of modern communication equipment.

[0007] Therefore, developing a coplanar waveguide-fed monopole antenna that is simple in structure, small in size, has sufficient bandwidth, and is circularly polarized is of great practical significance for promoting the development of wireless communication technology. Summary of the Invention

[0008] To address the technical bottleneck of achieving both miniaturization and broadband in existing circularly polarized antennas, this invention proposes a miniaturized broadband circularly polarized monopole antenna. This invention excites orthogonal polarization modes through an asymmetric structure and expands the bandwidth by combining parasitic coupling and meandering effects, achieving an overlap between the impedance bandwidth and the circular polarization bandwidth. This effectively solves the problems of narrow bandwidth, narrow circular polarization bandwidth, or excessive size associated with traditional antennas.

[0009] The specific technical solution of the present invention is as follows:

[0010] A miniaturized broadband circularly polarized monopole antenna includes a dielectric substrate, a rectangular monopole radiator, a coplanar waveguide feed structure, an asymmetric metallic ground, and a parasitic metallic square ring; the coplanar waveguide feed structure, the rectangular monopole radiator, the asymmetric metallic ground, and the parasitic metallic square ring are all metallic structures and are fixed to the same upper surface of the dielectric substrate.

[0011] The coplanar waveguide feed structure is located at the center of the lower edge of the dielectric substrate; the asymmetric metal ground is fixedly distributed on the left and right sides of the coplanar waveguide feed structure; the bottom end of the rectangular monopole radiator is fixedly connected to the top end of the coplanar waveguide feed structure; the parasitic metal square ring is fixedly located on the left side of the rectangular monopole radiator and directly above the left asymmetric metal ground.

[0012] Furthermore, the coplanar waveguide feeding structure includes a central feed line and two side gaps, with the bottom end of the central feed line extending to the bottom edge of the dielectric substrate and the other end seamlessly connected to a rectangular monopole radiator.

[0013] The rectangular monopole radiator adopts a rectangular integrated structure, with a horizontally inward rectangular cutout in the middle of its right edge;

[0014] The asymmetric metal ground includes a left metal ground and a right metal ground, and adopts a left-right asymmetric structure. The height of the left metal ground is lower than that of the right metal ground, and a rectangular slot and chamfer treatment are provided on the right metal ground.

[0015] The parasitic metal square ring adopts a ring structure with an opening at the bottom, with the opening facing the bottom edge of the dielectric substrate. A gap is left between the right edge of the parasitic metal square ring and the left edge of the rectangular monopole radiator.

[0016] Furthermore, a coaxial connector is welded to the bottom of the center feeder to enable external power supply.

[0017] Furthermore, the antenna has conformal characteristics and can be bent conformally.

[0018] Furthermore, the dielectric substrate 1 is selected from FR4 epoxy resin glass cloth substrate, and the metal structure is specifically a copper-clad metal structure.

[0019] Furthermore, the rectangular slot of the right-side metal ground is located inside its left center, and the upper right corner is chamfered.

[0020] The beneficial effects of this invention are:

[0021] 1. Excellent circular polarization characteristics: Through the synergistic design of asymmetric structure and parasitic square ring, it achieves 3dB axial ratio bandwidth coverage in multiple frequency bands. The circular polarization bandwidth is significantly better than that of existing similar antennas. It has stronger signal reception stability in complex electromagnetic environments and outstanding anti-interference ability.

[0022] 2. Ultra-wideband transmission characteristics: -10dB impedance bandwidth covers a wide frequency range, fully meeting the application requirements of relevant frequency bands in WiMAX systems. Its bandwidth performance is superior to most existing monopole antennas, making it suitable for wireless communication transmission in multiple scenarios.

[0023] 3. Miniaturization and high integration: The antenna adopts a single-layer substrate integrated design, with a small overall size. It does not require an additional reflector or back cavity structure, and its simple structure and easy processing meet the installation requirements of portable devices and small communication terminals.

[0024] 4. Stable radiation performance: Excellent in-band peak gain, symmetrical radiation pattern, good bidirectional radiation characteristics, stable impedance matching and small gain fluctuation within the operating bandwidth, adaptable to communication transmission needs over a wide frequency range.

[0025] 5. Low cost and easy mass production: It adopts conventional dielectric substrate and metal etching process, and the structure does not have complex three-dimensional shape or special material requirements. When mass production, the processing cost is low and the yield is high, which has good industrialization prospects. Attached Figure Description

[0026] Figure 1 A structural diagram of a miniaturized ultrawideband conformal monopole antenna;

[0027] Figure 2 To achieve a miniaturized ultrawideband conformal monopole antenna, it conforms to a cylindrical surface with a radius of 100 mm;

[0028] Figure 3 S-parameter simulation diagram of a miniaturized ultrawideband conformal monopole antenna;

[0029] Figure 4 Simulation diagram of the radiation direction of a miniaturized ultrawideband conformal monopole antenna in the 3.5GHz band;

[0030] Figure 5Simulation diagram of the radiation direction of a miniaturized ultrawideband conformal monopole antenna in the 5.5 GHz band;

[0031] Figure 6 The axial ratio simulation diagram for a miniaturized ultrawideband conformal monopole antenna.

[0032] The labels in the attached figures are explained as follows:

[0033] 1. Dielectric substrate; 2. Coplanar waveguide feeding structure; 3. Asymmetric metallic ground; 4. Rectangular monopole radiator; 5. Parasitic metallic square ring. Detailed Implementation

[0034] The miniaturized ultrawideband conformal monopole antenna of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] The miniaturized ultra-wideband conformal monopole antenna of the present invention mainly comprises a dielectric substrate 1, a rectangular monopole radiator 4, a coplanar waveguide feed structure 2, an asymmetric metal ground 3, and a parasitic metal square ring 5 with an open bottom. Except for the dielectric substrate 1, the coplanar waveguide feed structure 2, the rectangular monopole radiator 4, the asymmetric metal ground 3, and the parasitic metal square ring 5 are all copper-clad structures. The relative positions of the above structures are fixed, and they are all printed or etched on the same upper surface of the dielectric substrate 1. It is manufactured using a single-layer PCB process, resulting in a compact structure that is easy to mass-produce.

[0036] like Figure 1 As shown, the specific positions of each fixed structure are as follows: the coplanar waveguide feed structure 2 is located at the center of the lower edge of the dielectric substrate; the asymmetric metal ground 3 is fixedly distributed on the left and right sides of the coplanar waveguide feed structure; the bottom end of the rectangular monopole radiator 4 is fixedly connected to the top end of the coplanar waveguide feed structure; the parasitic metal square ring is fixedly located on the left side of the rectangular monopole radiator and directly above the left asymmetric metal ground.

[0037] The performance characteristics and simulation results of this invention are further explained below in conjunction with the accompanying drawings:

[0038] The dielectric substrate 1 is a conventional FR4 epoxy resin glass cloth substrate, used as the antenna's carrier and electromagnetic transmission medium. To clarify the relative positions of each structure, this paper defines the edge of the dielectric substrate where the input port of the coplanar waveguide feed structure is located as the "bottom edge" of the antenna. The substrate has a rectangular structure, and its length and width dimensions have been optimized through simulation to achieve miniaturized integration while ensuring antenna performance, making it suitable for installation in portable devices. Its dielectric constant and loss tangent are stable, effectively reducing the impact of dielectric loss on antenna radiation efficiency within the operating frequency band.

[0039] The rectangular monopole radiator 4 adopts a rectangular integrated structure with a horizontally inward rectangular cutout (4mm long and 1mm wide) in the middle of its right edge. This structure reduces current terminal reflections and improves radiation stability and bandwidth performance. The bottom of the rectangular monopole radiator is seamlessly connected to the center feed line of the coplanar waveguide feed structure, providing stable power to the radiator. At the same time, through the optimized position of the rectangular monopole radiator, transverse current is effectively excited, providing a basis for circularly polarized radiation.

[0040] The coplanar waveguide feeding structure 2 includes a central feed line and two side slots. It employs a coplanar integrated design, eliminating the need to penetrate the dielectric substrate and reducing radiation loss and fabrication complexity. The bottom end of the central feed line extends to the bottom edge of the dielectric substrate for welding a coaxial connector to achieve external feeding, while the other end is seamlessly connected to the rectangular monopole radiator 4. The slot width between the central feed line and the asymmetric metal grounds 3 on the left and right sides is precisely designed to be 0.7mm, ensuring that the characteristic impedance of the feed line matches a 50Ω standard transmission line, guaranteeing efficient transmission of input energy and reducing reflection loss.

[0041] The asymmetric metal ground 3 comprises a left metal ground and a right metal ground, employing an asymmetric structure. This structure uses the height difference to excite orthogonal polarization currents, while simultaneously expanding bandwidth through slot and chamfer design. The left and right metal grounds have the same width, ensuring the symmetry and stability of the feeding structure. The height difference between the left and right metal grounds (e.g., the left metal ground is 13.5mm high, and the right metal ground is 24mm high) provides a structural basis for exciting vertical polarization currents, forming an orthogonal distribution with the lateral current of the radiator. Notably, the left metal ground is lower than the right metal ground, and the rectangular slot and chamfer are specifically placed on the right metal ground. This arrangement is closely related to the height difference between the left and right metal grounds, and both work synergistically within the same asymmetric structural system. Placing them on the same side metal ground further and directionally breaks the symmetry of the antenna surface current distribution, thereby better balancing the amplitude and phase of the two orthogonal polarization modes. Furthermore, the meandering effect of the slot from the left center inward and the chamfer at the upper right corner on the right metal ground extends the current path, introducing additional resonant points and significantly expanding the bandwidth.

[0042] The parasitic metal square ring 5 adopts a bottom-opening ring structure with its opening facing the bottom edge of the dielectric substrate. It expands bandwidth and optimizes circular polarization through capacitive coupling. The dimensions and opening width of the square ring are optimized through simulation to ensure sufficient current carrying capacity. A precise gap (0.1 mm) is maintained between its right edge and the left edge of the rectangular monopole radiator, forming strong capacitive coupling. This allows the square ring to generate a low-frequency resonant mode, which superimposes with the high-frequency mode of the radiator, achieving synergistic optimization of bandwidth and polarization. The precise positioning of the square ring further enhances the coupling effect and the purity of circular polarization.

[0043] like Figure 2 As shown, the miniaturized ultrawideband conformal monopole antenna of the present invention has excellent conformal characteristics and can be conformally bent onto a cylindrical surface with a radius of 100mm, thus adapting well to complex or restricted installation environments.

[0044] Figure 3 The S-parameters (S) of this antenna 11 Simulation diagram. As shown in the diagram, the antenna's -10dB impedance bandwidth covers an ultra-wideband range from 2.85GHz to 11.06GHz, demonstrating excellent broadband transmission characteristics.

[0045] Figure 4 and Figure 5 Simulated radiation patterns of the antenna in the 3.5 GHz and 5.5 GHz frequency bands are shown. The results indicate that the antenna maintains stable and symmetrical radiation performance in both typical frequency bands, exhibiting good bidirectional radiation characteristics.

[0046] Figure 6 The figure shows the simulated axial ratio of the antenna. As can be seen from the figure, the 3dB axial ratio bandwidth of the antenna mainly covers two frequency bands: 2.85GHz-3.9GHz and 4.3GHz-5.9GHz, achieving excellent multi-band circular polarization performance.

[0047] This invention is based on electromagnetic radiation theory, coplanar waveguide transmission principle, orthogonal polarization coupling mechanism, and bandwidth extension technology. Through multi-structure collaborative design, it achieves the unification of miniaturization, broadband, and circular polarization. The detailed derivation of each core principle and formula is as follows:

[0048] I. The principle of circularly polarized radiation generation: The essence of circularly polarized radiation is to excite two equal-amplitude, orthogonal radiation sources with a phase difference of π / 2. The linear polarization mode is theoretically based on the decomposition and synthesis of the electric field vector. Let the antenna radiation field in the Cartesian coordinate system be along... Directional propagation, the electric field vector can be decomposed into , Two orthogonal components:

[0049]

[0050] In the formula, E x and E y , , represent the instantaneous electric field intensity components of the electric field vector in the x-axis and y-axis directions, respectively; t is the time variable; z is the spatial position coordinates of the electromagnetic wave along the propagation direction; , They are respectively , The amplitude of the component Angular frequency, For wave number, , This is the initial phase. Circular polarization requires two core conditions to be met: equal amplitude. , The amplitude constant is and the phase difference is . ( ): (Right-handed circular polarization) or (Left-handed circular polarization)

[0051] This invention precisely generates circularly polarized radiation through an asymmetric metal floor combined with an offset radiator structure.

[0052] (1) Asymmetrical metal floor design: floor height on the left side Right side floor height height difference This height difference causes a vertical current to be generated on the floor surface. The amplitude and height difference satisfy: ,in Input voltage, The characteristic impedance of the coplanar waveguide feeder is... is the dielectric constant.

[0053] (2) Radiator offset design: The rectangular radiator is offset to the right so that the coplanar waveguide feed line is connected to the left edge of the radiator to excite the transverse current. By optimizing the radiator width Offset, making .

[0054] (3) Phase difference modulation: The asymmetric structure disrupts the symmetry of the current distribution, making and This generates a natural phase difference. Combined with a slot in the center of the rectangular radiator to reduce current reflection, this ultimately reduces the phase difference. Synthetic circularly polarized electric field:

[0055]

[0056] In the formula, This represents the total electric field vector after synthesis. and It is the unit vector in the corresponding direction in a rectangular coordinate system; = Let be the instantaneous spatial phase angle. Its trajectory satisfies the equation of a circle. To achieve pure circular polarization radiation.

[0057] II. The principle of high-efficiency transmission and impedance matching of coplanar waveguide feeding.

[0058] The transmission characteristics of a coplanar waveguide directly determine its feeding efficiency, and its core parameter is its characteristic impedance. With effective dielectric constant Ensure with Transmission line matching. Characteristic impedance formula (derived using quasi-static analysis):

[0059]

[0060] In the formula: , , The width of the gap between the feeder cable and the floor; It is a function of the first kind of complete ellipticity. , hour, Substitute have to Effective dielectric constant ( (where FR4 is the dielectric constant). Substituting into the characteristic impedance formula, we get... Perfectly matches transmission lines, reducing power supply reflection loss. Impedance broadband extension: By slotting and chamfering the right-side floor, a meandering effect is introduced to extend the current path. This extends the antenna resonant frequency to a multi-frequency coupling, where the resonant frequency satisfies:

[0061]

[0062] In the formula, This is the nth resonant frequency; The speed of light; The effective dielectric constant; , These are the equivalent current path lengths for the fundamental and harmonic waves, respectively, to achieve wide impedance broadband.

[0063] III. Coupling widening and circular polarization optimization principle of parasitic square rings.

[0064] 1. Introduce a parasitic metal square ring with an open bottom (length) ,width Opening width This achieves bandwidth expansion and polarization purity enhancement through capacitive coupling. Parasitic coupling resonant mode superposition: the distance between the square ring and the radiator. Forming a coupling capacitor Its value is:

[0065]

[0066] In the formula, This is the equivalent coupling capacitance; It is the absolute permittivity of vacuum; It is the relative permittivity; The coupling area is approximately equal to the overlapping projected area of ​​the square ring and the radiator. This is the physical gap distance. The capacitor causes the square ring to generate an additional low-frequency circular polarization mode. With respect to the inherent high-frequency mode of the radiator The coupling superposition, the total bandwidth satisfies:

[0067]

[0068] In the formula, For operating bandwidth; and These are the highest and lowest effective resonant frequencies after coupling and superposition, respectively; and These represent the longest and shortest equivalent current paths, respectively. The final result is a -10dB bandwidth covering 2.85GHz-11.06GHz, and a 3dB axial ratio bandwidth covering 2.85GHz-3.9GHz and 4.3GHz-5.9GHz.

[0069] 2. Shaft Ratio Control: Shaft ratio (AR) is a core indicator for measuring circular polarization, and its theoretical formula is as follows:

[0070]

[0071] In the formula, AR is the axial ratio of the antenna; This is the imbalance factor of the orthogonal component amplitudes. The parasitic square ring compensates for this imbalance through coupling effects. and The tiny amplitude difference makes This reduces the axial ratio. hour, (Ideal circular polarization); This invention optimizes the distance from the upper end of the square ring to the top of the antenna. ,at this time Substituting into the axis ratio formula, we get To achieve circular polarization.

[0072] IV. Miniaturization Principle The miniaturization of monopole antennas stems from their quarter-wavelength electrical size characteristics and the coplanar integration design of coplanar waveguide feeding. The core formula is as follows:

[0073] Theoretical dimensions of a monopole antenna: Length of a printed monopole antenna satisfy:

[0074]

[0075] In the formula, The theoretical electric length of a rectangular monopole radiator; Wavelength in free space; (Center frequency), substituting, we get It is consistent with the length of the rectangular monopole radiator of the present invention.

[0076] Size reduction due to meandering effect: The groove and chamfer on the right floor lengthen the current path. The above is equivalent to reducing the physical size of the antenna at the same resonant frequency:

[0077]

[0078] In the formula, This represents the effective extension of the current path. Using the length of a traditional monopole, the overall size of the final antenna is much smaller, reducing the size by more than 30% compared to a traditional monopole antenna, thus achieving the design goal of an electrically small antenna. ).

[0079] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A miniaturized ultrawideband conformal monopole antenna, characterized in that, It includes a dielectric substrate (1), a rectangular monopole radiator (4), a coplanar waveguide feed structure (2), an asymmetric metal ground (3), and a parasitic metal square ring (5); the coplanar waveguide feed structure (2), the rectangular monopole radiator (4), the asymmetric metal ground (3), and the parasitic metal square ring (5) are all metal structures and are fixed to the same upper surface of the dielectric substrate (1); The coplanar waveguide feed structure (2) is located at the center of the lower edge of the dielectric substrate (1); the asymmetric metal ground (3) is fixedly distributed on the left and right sides of the coplanar waveguide feed structure; the bottom end of the rectangular monopole radiator (4) is fixedly connected to the top end of the coplanar waveguide feed structure; the parasitic metal square ring (5) is fixedly located on the left side of the rectangular monopole radiator (4) and directly above the left asymmetric metal ground.

2. The miniaturized ultra-wideband conformal monopole antenna according to claim 1, characterized in that, The coplanar waveguide feeding structure (2) includes a central feed line and two side gaps. The bottom end of the central feed line extends to the bottom edge of the dielectric substrate (1), and the other end is seamlessly connected to the rectangular monopole radiator 4. The rectangular monopole radiator (4) adopts a rectangular integrated structure, with a horizontally inward rectangular cutout in the middle of its right edge; The asymmetric metal ground (3) includes a left metal ground and a right metal ground, and adopts a left-right asymmetric structure. The height of the left metal ground is lower than that of the right metal ground, and a rectangular groove and chamfer treatment are provided on the right metal ground. The parasitic metal square ring (5) adopts a ring structure with an open bottom, and its opening direction is towards the bottom edge of the dielectric substrate. A gap is left between the right edge of the parasitic metal square ring (5) and the left edge of the rectangular monopole radiator (4).

3. A miniaturized ultra-wideband conformal monopole antenna according to claim 2, characterized in that, The coaxial connector is welded to the bottom of the center feeder to enable external power supply.

4. A miniaturized ultra-wideband conformal monopole antenna according to claim 2, characterized in that, The antenna has conformal characteristics and can be bent conformally.

5. A miniaturized ultra-wideband conformal monopole antenna according to claim 2, characterized in that, The dielectric substrate (1) is selected from FR4 epoxy resin glass cloth substrate, and the metal structure is specifically a copper-clad metal structure.

6. A miniaturized ultra-wideband conformal monopole antenna according to claim 2, characterized in that, The rectangular slot of the metal ground on the right is located inside the center on its left side, and the upper right corner is chamfered.

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