High-selectivity broadband three-mode filtering microstrip patch antenna based on snakelike slot

Abstract

The invention discloses a high-selectivity broadband three-mode filtering microstrip patch antenna based on a snakelike slot. The antenna comprises a single-layer dielectric substrate, a square microstrip patch arranged on the upper surface of the substrate, and a grounding plate arranged on the lower surface of the substrate. The microstrip patch is fed through the coaxial probe; two snakelike slots with identical sizes are respectively etched on radiation edges on two sides of the patch, the two slots on the same side are symmetrically distributed on two sides of a feed axis, and the slots on the radiation edges on the two sides are mutually symmetrical in position and opposite in bending direction. Three resonance modes with similar radiation characteristics are excited in a passband by loading the symmetrical snakelike slots, and a radiation zero point is generated on each of the two sides of the passband, so that broadband response, stable radiation, high frequency selectivity and high out-of-band rejection are realized. Compared with a traditional square microstrip patch antenna, the square microstrip patch antenna has wider bandwidth and better frequency selectivity and out-of-band rejection capability under similar sizes, and has structural and performance advantages.

Description

Technical Field

[0001] This invention belongs to the field of microwave antenna technology, specifically relating to a highly selective broadband tri-mode filtered microstrip patch antenna based on a serpentine slot. Background Technology

[0002] Microstrip patch antennas are widely used in modern wireless communication systems due to their advantages such as low profile, light weight, ease of fabrication and integration. However, traditional microstrip patch antennas have two inherent drawbacks: first, their impedance bandwidth is usually narrow (typically only 1%-5%), making it difficult to meet the requirements of broadband communication systems; second, their frequency selectivity is poor, with slow passband roll-off and limited out-of-band rejection capability.

[0003] To extend bandwidth, the industry has proposed various technical solutions, such as using thick substrates with low dielectric constants, adding parasitic patches, loading U-shaped slots, or using L-shaped probes for feeding. While these methods can effectively broaden bandwidth, they often come at the cost of sacrificing antenna size, gain, or radiation stability, and rarely improve the antenna's frequency selectivity at the same time.

[0004] On the other hand, to achieve excellent frequency selectivity and out-of-band rejection in the RF front-end, antennas typically need to be cascaded with independent filters. While this "antenna + filter" solution offers good electrical performance, it introduces additional insertion loss, increases circuit size and complexity, and hinders system miniaturization and integration. Therefore, designing an integrated antenna that combines good radiation characteristics with inherent filtering capabilities—i.e., a filtered antenna—has become a current research hotspot.

[0005] Existing design approaches for filtered antennas largely focus on introducing radiated nulls through additional resonant structures (such as stubs, slots, and parasitic elements) to achieve out-of-band suppression. However, these methods often face the following challenges: 1) the number of introduced radiated nulls is limited or poorly controllable; 2) while improving selectivity, they may disrupt the radiation pattern or gain stability of the main radiating patch; 3) the structure is complex, increasing design difficulty and manufacturing costs; and 4) the reduction in antenna size is not significant.

[0006] Specifically, in designing multimode resonant broadband filter antennas using slot loading, existing techniques typically perturb the current path by etching simple linear or regular slots on the patch. For example, slots are etched at the center of the patch or at the non-radiating edge. However, these methods result in limited mode coupling strength and resonant frequency tuning freedom, making it difficult to achieve a wide bandwidth while precisely generating radiation nulls with high suppression ratios on both sides of the passband. Furthermore, how to introduce new resonant modes through refined slot design while ensuring that all modes have similar and good radiation characteristics is also a technical challenge. It is particularly noteworthy that traditional slot-loaded multimode designs usually require a certain thickness of the dielectric substrate, relying on a certain profile height to support and match multiple resonant modes, thereby expanding the bandwidth. This makes it difficult for the antenna to achieve sufficient excitation and good matching of multiple resonant modes under extremely low profile conditions, thus making it difficult to "support" a sufficiently wide and flat passband while maintaining a compact physical size.

[0007] Therefore, there is a lack of microstrip patch antenna solutions in the existing technology that have a relatively simple structure and can achieve broadband, high frequency selectivity and stable radiation performance under extremely low profile conditions. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention proposes a highly selective broadband tri-mode filtered microstrip patch antenna based on a serpentine slot. Through a specific symmetrical serpentine slot design, it is possible to simultaneously achieve tri-mode resonant broadband response, controllable radiation nulls on both sides of the passband, and compact design on a low-profile single-layer dielectric substrate. This makes it suitable for modern wireless communication systems with high requirements for miniaturization, integration, and performance.

[0009] To achieve the above objectives, this invention designs a highly selective broadband tri-mode filtered microstrip patch antenna based on a serpentine slot, the antenna comprising: Dielectric substrate; A square microstrip patch disposed on the upper surface of the dielectric substrate; A metal ground plane disposed on the lower surface of the dielectric substrate; A coaxial feed structure, in which the feed probe passes through the dielectric substrate and connects to the microstrip patch; Two serpentine slots are etched inward along the two oppositely arranged radiating edges of the square microstrip patch, so that the antenna excites three resonant modes within the passband; Two serpentine slots located on the same radial edge are symmetrically distributed about the centerline of the microstrip patch perpendicular to that radial edge; The serpentine slots located on different radial edges are symmetrical about the centerline of the microstrip patch parallel to that radial edge, but the bending directions of the serpentine slots are opposite.

[0010] The etching of the four serpentine slots excites three resonant modes within the passband of the antenna. These three resonant modes include the TM inherent in microstrip patch antennas. 10 The three resonant modes include two new modes introduced by a symmetrical serpentine slot. By independently adjusting the side length of the microstrip patch and the size of the serpentine slot, the frequency and coupling strength of the three resonant modes can be tuned, thereby adapting to specific requirements for passband bandwidth, center frequency, and radiation null position.

[0011] The side length (L), the size of the serpentine slot, and the position of the feed point of the microstrip patch are configured to be scaled according to the target operating frequency band using the principle of electromagnetic similarity, so that the antenna can be used for different communication frequency bands from ultra-high frequency (UHF) to millimeter wave.

[0012] Compared with the prior art, the technical solution provided by the present invention has the following significant advantages: 1. Achieved high-performance integrated design of filtering and radiation: This invention organically integrates the frequency selection function of the filter and the radiation function of the antenna into a single patch structure, eliminating the need for cascaded filters and reducing insertion loss, circuit size and complexity.

[0013] 2. Excellent broadband characteristics were achieved under extremely low profile conditions: On a single-layer thin substrate, three resonant modes were successfully excited and matched through a unique symmetrical anti-phase serpentine slot design, enabling broadband operation from 3.375 GHz to 3.635 GHz (relative bandwidth of about 7.6%), overcoming the dependence of traditional multimode antennas on thick substrates.

[0014] 3. Extremely high frequency selectivity: The naturally generated radiation nulls on both sides of the passband (such as those located at 3.3 GHz and 3.68 GHz) make the passband edge very steep. The measured out-of-band rejection slope reaches 425 dB / GHz (low frequency side) and 850 dB / GHz (high frequency side), achieving out-of-band rejection performance comparable to independent filters.

[0015] 4. Stable radiation performance: The antenna gain remains stable between 6.5 dBi and 7.3 dBi throughout the entire passband, and the radiation pattern is stable, ensuring communication quality.

[0016] 5. Compact structure and easy to manufacture: All structures are realized on the same planar layer, without the need for multi-layer stacking or complex three-dimensional structures. The manufacturing process is simple and low-cost, achieving miniaturization. Attached Figure Description

[0017] Figure 1 This is a three-dimensional structural diagram of the antenna; where 1: dielectric substrate; 2: ground plane; 3: square microstrip patch; 4-1, 4-2, 4-3, 4-4: serpentine slots; 5: coaxial feed.

[0018] Figure 2 The results are the antenna frequency response calculated using HFSS software; where (a) represents the reflection coefficient and radiation gain, and (b) represents the radiation efficiency.

[0019] Figure 3 The antenna radiation patterns are calculated using HFSS software; (a) is the radiation pattern at 3.39 GHz in the E and H planes, (b) is the radiation pattern at 3.51 GHz in the E and H planes, and (c) is the radiation pattern at 3.62 GHz in the E and H planes. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0021] The present invention provides a high-selectivity broadband tri-mode filtered microstrip patch antenna based on a serpentine slot, the core of which lies in an innovative slot loading structure to achieve synergistic performance of broadband, high selectivity and stable radiation under low profile conditions.

[0022] Please see Figure 1 This is a three-dimensional structural schematic diagram of a preferred embodiment of the present invention. As shown in the figure, the antenna is constructed entirely on a single-layer dielectric substrate 1. The dielectric substrate 1 is preferably made of F4B material with low-loss characteristics, a relative permittivity of 2.2, and a thickness of 2 mm (0.023). λ 0). This thickness is typical of a low-profile design, intended to meet the requirements of modern communication equipment for ultra-thin antennas. The lower surface of the dielectric substrate 1 is covered with a complete metal layer as a ground plane 2 to shield back radiation. The upper surface of the dielectric substrate 1 is etched with a square microstrip patch 3, which serves as the main radiator. In this embodiment, the side length L of the square microstrip patch 3 is 26.7 mm.

[0023] The key feature of this invention lies in the slot design on the square microstrip patch 3. On each radial edge of the square microstrip patch 3, two identical serpentine slots are etched. Specifically, Figure 1 The two serpentine slots marked 4-1 and 4-2 are located on the left side of the patch's radiation edge, and the two serpentine slots marked 4-3 and 4-4 are located on the right side of the patch's radiation edge. The introduction of these four serpentine slots is the basis for realizing trimode resonance and radiation zero point.

[0024] Specifically, the arrangement of the four serpentine slits follows a strict principle of symmetry and reversal: 1. Symmetrical on the same side: Two serpentine slits (such as 4-1 and 4-2) located on the same radial edge are perfectly mirror-symmetrical about the patch centerline perpendicular to that radial edge.

[0025] 2. Reverse Symmetry: The slot groups (4-1, 4-2) on the left radial side and the slot groups (4-3, 4-4) on the right radial side are symmetrical about the patch centerline parallel to the radial side. However, their serpentine bends are exactly opposite. For example, if the left slot bends in a "first up, then down" serpentine pattern, the corresponding right slot bends in a "first down, then up" serpentine pattern. This "symmetrical position, opposite bends" design is key to generating the radiation zeros on both sides of the passband and ensuring mode radiation consistency.

[0026] Specifically, the antenna is fed using a bottom-fed coaxial probe 5. The inner conductor of the coaxial probe 5 passes through small holes on the dielectric substrate 1 and the ground plane 2, and connects to the square microstrip patch 3 on the upper surface. The feed point is located on the center line of the patch perpendicular to the radiating edge, with an offset distance Df of 10.15 mm from the closest radiating edge. This position is beneficial for simultaneously exciting multiple modes and achieving good impedance matching.

[0027] In a preferred embodiment, the specific dimensions of the serpentine slots are optimized. The edge spacing Wg between two serpentine slots located on the same radiating edge is 6.45 mm. The total extension length Ls of each serpentine slot is approximately 10.2 mm, and the total width Ws is approximately 2.55 mm. The linewidth G of the slots and the interval between the serpentine bends are both 0.6 mm. These precise dimensions collectively determine the frequency, coupling strength, and location of the radiation null point of the introduced new resonant mode.

[0028] The antenna of this invention works in concert through the following design: 1. Three-mode resonance mechanism: The etched serpentine slots are positioned along the strong current path of the microstrip patch master mode (TM10 mode), thus having minimal impact on the master mode's resonant frequency. Simultaneously, these specific shapes and symmetrically distributed slots strongly perturb and redistribute the current on the patch surface, thereby exciting two new resonant modes. This can be achieved by independently adjusting the patch size (master control TM...). 10 The dimensions, position, and bending shape of the serpentine slots (controlling the two new modes) allow the three resonant modes to be reasonably close together and merged in the frequency domain, forming a wide bandwidth. Furthermore, the symmetrical but oppositely bent serpentine slot design gives the two new modes characteristics similar to TM. 10 Similar radiation characteristics.

[0029] 2. Radiation Null Generation Mechanism: The serpentine slot causes the equivalent magnetic current distributed along the patch edge at a specific frequency (both sides of the passband) to no longer be uniformly oriented in the same direction, but instead exhibits components in opposite directions. These opposing magnetic current components generate a radiation cancellation effect in the far field, thereby generating a transmission null (i.e., a radiation null) on each side of the passband, endowing the antenna with inherent high frequency selectivity and out-of-band suppression capability.

[0030] 3. Low-profile broadband implementation mechanism: The serpentine slot has a high electrical length, enabling strong inductive loading and complex current perturbations within a limited physical area of ​​the patch. This design allows for effective modulation of new resonant modes even when using a thin dielectric substrate, thereby further optimizing impedance matching between modes and successfully fusing the three modes into a wide and flat impedance bandwidth under low-profile conditions.

[0031] The working principle and performance of this invention were verified using the electromagnetic simulation software HFSS.

[0032] Please see Figure 2 This refers to the simulated frequency response characteristics of the antenna. Figure 2 Figure (a) shows the curves of the antenna's reflection coefficient |S11| versus gain in the main radiation direction as a function of frequency. It can be seen that in the frequency range of 3.375 GHz to 3.635 GHz, |S11| is consistently below -10 dB, forming a wide and flat passband with a relative bandwidth of approximately 7.6%. The gain within the passband remains stable between 6.5 dBi and 7.3 dBi. Simultaneously, two very deep zeros in the reflection coefficient appear on either side of the passband (approximately 3.3 GHz and 3.68 GHz), corresponding to the antenna's radiation nulls, making the passband edges extremely steep. Calculations show that the out-of-band rejection roll-off rate reaches 425 dB / GHz on the low-frequency side and as high as 850 dB / GHz on the high-frequency side, demonstrating excellent frequency selectivity. Figure 2 (b) shows that the antenna’s radiation efficiency is higher than 87% throughout the entire passband.

[0033] Please see Figure 3 It is a simulated radiation pattern of the antenna at three characteristic frequency points (3.39 GHz, 3.51 GHz, 3.62 GHz) within the passband. Figure 3 Images (a), (b), and (c) show the normalized radiation patterns of these three frequencies in the E-plane (yoz plane) and H-plane (xoz plane), respectively. It can be seen that the antenna's radiation characteristics are stable throughout the passband. The highly similar radiation patterns of the three resonant modes demonstrate that the symmetrical anti-phase serpentine slot design successfully aligns the introduced new modes with the radiation characteristics of the original TM10 mode, avoiding radiation pattern distortion caused by multimode resonance.

[0034] In summary, this embodiment successfully realizes a compact and easily fabricated high-performance filter antenna by etching specific symmetrical and reverse-distributed serpentine slots on the aforementioned low-profile single-layer dielectric substrate. It effectively solves the problems of narrow bandwidth and poor selectivity in traditional microstrip antennas, and in particular, overcomes the dependence of traditional multimode slot antennas on thick substrates, achieving broadband, high selectivity, and stable radiation on a thin substrate, thus possessing high engineering application value.

[0035] It should be noted that the above embodiments and specific dimensional parameters are preferred designs for a center frequency of approximately 3.5 GHz, used to clearly demonstrate the technical effects of the present invention. However, the core design concept proposed in this invention, which involves "etching symmetrically positioned, oppositely bent serpentine slots on both sides of the radiating edge of a square patch to generate tri-mode resonance and radiation nulls," has universal applicability and is not limited to a specific frequency band.

[0036] Those skilled in the art will understand that, based on the required center frequency (f0) of the antenna, all critical dimensions of the antenna can be scaled proportionally using the principle of electromagnetic similarity. These critical dimensions include, but are not limited to: the thickness (h) of the dielectric substrate 1, the side length (L) of the square microstrip patch 3, the total length (Ls) and width (Ws) of the serpentine slots 4-1 to 4-4, the slot spacing (Wg), and the feed point location (Df). The scaling factor is essentially inversely proportional to the wavelength (λ) or frequency (f0).

[0037] Furthermore, by independently and non-proportionally fine-tuning the patch side length and the size of the serpentine slot while maintaining the basic shape, symmetry, and reverse bending characteristics of the serpentine slot, the frequency spacing, passband width, and position of the radiation null point of the three resonant modes can be flexibly controlled. This allows the invention to be applied to various wireless communication systems from the UHF band to the millimeter wave band, such as (but not limited to) satellite communication, 5G / 6G mobile communication, Wi-Fi, and the Internet of Things at different frequency bands.

[0038] Therefore, any antenna with the same structure obtained by scaling or optimizing the size based on the core design concept of this invention should fall within the spirit and scope of this invention.

[0039] It should be noted that the above embodiments use a thin substrate with a thickness of 2mm to demonstrate the outstanding effect of this invention in overcoming the limitations of low-profile design. It is understood that the symmetrical anti-phase serpentine slot structure described in this invention, as an effective multimode excitation and coupling unit, is not limited to dielectric substrates of a specific thickness. When applied to thinner or thicker dielectric substrates, those skilled in the art can perform impedance matching and performance optimization by readjusting the patch side length, slot size, and feed position (e.g., utilizing the greater design freedom offered by the thicker substrate), thereby designing antennas operating in other frequency bands or with different bandwidth characteristics. However, compared to traditional thick-substrate broadband antennas, the structure of this invention may still retain advantages in reducing the overall antenna size, improving out-of-band selectivity, or improving cross-polarization.

Claims

1. A high-selectivity broadband tri-mode filtered microstrip patch antenna based on a serpentine slot, characterized in that, The antenna includes: Dielectric substrate (1); A square microstrip patch (3) is disposed on the upper surface of the dielectric substrate (1); Metal floor (2) disposed on the lower surface of the dielectric substrate (1); The coaxial feed structure (5) has a feed probe that passes through the dielectric substrate (1) and connects to the microstrip patch (3); Two serpentine slots are etched inward along the two oppositely arranged radiating edges of the square microstrip patch (3), so that the antenna can excite three resonant modes in the passband; Two serpentine slots located on the same radial side are symmetrically distributed about the center line of the microstrip patch (3) perpendicular to the radial side; The serpentine slots located on different radial sides are symmetrical about the center line of the microstrip patch (3) parallel to the radial side, but the bending direction of the serpentine slots is opposite.

2. The antenna according to claim 1, characterized in that, The dielectric substrate (1) is made of F4B with a relative permittivity of 2.2 and a thickness of 2 mm.

3. The antenna according to claim 1, characterized in that, The microstrip patch (3) has a side length of 26.7 mm.

4. The antenna according to claim 1, characterized in that, The feed point of the coaxial feed structure (5) is located on the center line of the microstrip patch (3) perpendicular to the radiation edge.

5. The antenna according to claim 1, characterized in that, The distance between the two serpentine slits located on the same radial edge is 6.45 mm.

6. The antenna according to claim 1, characterized in that, The four serpentine slits are identical in size, with each serpentine slit having a total length of 10.2 mm, a total width of 2.55 mm, a slit line width of 0.6 mm, and a spacing of 0.6 mm between adjacent bends.

7. The antenna according to claim 1, characterized in that, The three resonant modes include the TM inherent in microstrip patch antennas. 10 The pattern and two new patterns introduced by the symmetrical serpentine slit.

8. The antenna according to claim 7, characterized in that, The serpentine slot along the microstrip patch (3) in TM 10 Surface current path etching under the mold.

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