A differential MIMO microstrip antenna with high port isolation

Abstract

The application discloses a high-port-isolation differential MIMO microstrip antenna and belongs to the technical field of wireless communication antennas. The antenna comprises a single-layer dielectric substrate, a metal grounding plate, a 1*2 differential MIMO microstrip radiation unit array and a port-isolation optimization structure. The radiation unit adopts a rectangular microstrip patch design. The port-isolation optimization structure inhibits electromagnetic coupling between units by etching DGS bandgap units on the grounding plate. The antenna is differentially fed through a coaxial line. The antenna spacing is only 0.06. The port-isolation degree reaches-42dB at a 5.36GHz center frequency, is improved by 32dB, the relative bandwidth is 2.22%, the E-plane cross polarization is lower than-30dB within an angle range of-60°<<60°, the in-band gain stability is greater than 6.8dB, and the radiation pattern is stable.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication antenna technology, specifically a differential MIMO microstrip antenna with high port isolation, which is mainly used in 5G / 6G mobile communication base stations or terminal equipment. Background Technology

[0002] MIMO technology improves spectral efficiency and system capacity through parallel transmission via multiple antennas, and is a core technology for 5G / 6G, millimeter-wave communication, and satellite communication. Microstrip antennas have become the preferred carrier for MIMO systems due to their advantages such as low profile, ease of fabrication, and integrability. However, in MIMO systems, coupling interference between antennas can seriously affect communication performance, so improving antenna isolation has become a key technical requirement.

[0003] Currently, the industry has developed various decoupling technologies, including electromagnetic bandgap (EBG) structures, defective grounding (DGS) structures, antenna decoupling surfaces (ADS), and decoupling networks (DN). For example, Lee used EBG structures to suppress surface wave propagation, achieving 30dB isolation within a 110MHz bandwidth; the application of fractal DGS can reduce coupling between microstrip antennas by 30dB; and DN, composed of directional couplers and transmission lines, can achieve 50dB isolation at the center frequency. These methods have all played an important role in mitigating the coupling effects of antenna arrays.

[0004] However, existing decoupling techniques have significant drawbacks: First, most designs are only suitable for single-port microstrip antennas, making it difficult to meet the decoupling requirements of differentially fed antennas. Second, for 1-differential-fed MIMO microstrip antennas, existing decoupling methods mostly rely on symmetrical decoupling networks. While these networks offer advantages such as minimal radiation pattern impact and good decoupling performance, they suffer from design complexity, and the decoupling effect and antenna matching performance interfere with each other, requiring cumbersome collaborative optimization to balance both. Furthermore, while improving isolation, existing technologies often struggle to simultaneously achieve bandwidth expansion, low cross-polarization, and stable radiation patterns, limiting their application in high-performance wireless communication scenarios. Summary of the Invention

[0005] This invention addresses the port coupling problem between MIMO microstrip antennas by combining differential feeding with a DGS decoupling structure to propose a differential MIMO microstrip antenna with high port isolation. While achieving high port isolation and low cross-polarization, the antenna matching performance is further optimized and the bandwidth is expanded, which is of great research significance in the field of MIMO antenna technology.

[0006] This invention is achieved through the following technical solution: A differential MIMO microstrip antenna with high port isolation includes a single-layer dielectric substrate; the upper surface of the single-layer dielectric substrate is provided with two rectangular radiating patches, and the lower surface is provided with a metal ground plane; each rectangular radiating patch is connected to the metal ground plane through two differential feed metal vias. Two rectangular radiating patches are symmetrically arranged and parallel to each other on the upper surface of a single-layer dielectric substrate; a defect structure is provided on the metal ground plane; the defect structure is located between the two projections of the two rectangular radiating patches on the metal ground plane.

[0007] Furthermore, the defect structure includes rectangular longitudinal gap a, rectangular longitudinal gap b and rectangular longitudinal gap c connected in sequence, wherein rectangular longitudinal gap a and rectangular longitudinal gap b are each provided with a rectangular transverse gap group perpendicularly connected to them, the rectangular transverse gap group including rectangular transverse gap a, rectangular transverse gap b and rectangular transverse gap c. Rectangular horizontal gaps a, b, and c asymptotically approximate rectangular vertical gap b.

[0008] Furthermore, the length and width of rectangular longitudinal slits a and c are the same, and both are larger than the length and width of rectangular longitudinal slit b; the inner wide side of rectangular longitudinal slit a and the inner wide side of rectangular longitudinal slit c are respectively connected to the two wide sides of rectangular longitudinal slit b.

[0009] Furthermore, the rectangular transverse slit a is connected to the outer wide side of the corresponding rectangular longitudinal slit, and the outer wide side of the rectangular longitudinal slit is located at the center of the inner long side of the rectangular transverse slit a. The length of the three transverse gaps a, b, and c gradually decreases.

[0010] Furthermore, the differential-fed metal via penetrates through a single-layer dielectric substrate.

[0011] Furthermore, the single-layer dielectric substrate uses Rogers RT / duroid 5880 substrates with dielectric constant 2.2 and loss factor 0.0009.

[0012] Compared with the prior art, the beneficial effects of the present invention are: a) The present invention adopts a differential feeding method. On the one hand, differential feeding makes the antenna surface current more directional, and the decoupling effect is better when combined with the DGS decoupling structure. On the other hand, the differential microstrip antenna itself has a certain surface wave coupling suppression effect.

[0013] b) The DGS decoupling structure designed in this invention significantly improves port isolation by changing the direction of the ground current and blocking the coupling path, and optimizes antenna matching performance and expands bandwidth.

[0014] c) It has a simple structure, is easy to manufacture, and can be produced using printed circuit board technology. The materials used in its production are only a dielectric substrate and copper foil. Attached Figure Description

[0015] Figure 1 This is a top view of the overall structure of the present invention.

[0016] Figure 2 This is the main view of the overall structure of the present invention.

[0017] Figure 3 This is a bottom view of the overall structure of the present invention.

[0018] Figure 4 This is a diagram of the DGS decoupling structure of the present invention.

[0019] Figure 5 This is a graph showing the antenna impedance matching (SDD11) and port isolation (SDD21).

[0020] Figure 6 This is the impedance matching SDD11 curve diagram for antennas with and without DGS structure.

[0021] Figure 7 This is a curve showing the port isolation (sdd21) of the antenna with and without a DGS structure.

[0022] Figure 8 It shows the E-plane main polarization and cross-polarization pattern of the antenna at 5.36 GHz with and without DGS structure.

[0023] Figure 9 It shows the H-plane main polarization and cross-polarization patterns of the antenna at 5.36 GHz with and without DGS structure.

[0024] In the figure: 1. Rectangular radiating patch a, 2. Rectangular radiating patch b, 3. Differential feed metal via aa, 4. Differential feed metal via bb, 5. Differential feed metal via ba, 6. Differential feed metal via bb, 7. Single-layer dielectric substrate, 8. Defect structure, 9. Metal ground plane, 10. Rectangular longitudinal slot b, 11. Rectangular transverse slot aI, 12. Rectangular longitudinal slot a, 13. Rectangular transverse slot bI, 14. Rectangular transverse slot cI, 15. Rectangular transverse slot aII, 16. Rectangular longitudinal slot c, 17. Rectangular transverse slot bII, 18. Rectangular transverse slot cII. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] This invention proposes a high-port isolation differential MIMO microstrip antenna design that combines differential feeding with a DGS decoupling structure. Utilizing the characteristics of differential excitation suppressing surface waves and the directional nature of surface current in differential microstrip patch antennas, a special DGS bandgap is designed in the ground plane to change the direction of the ground current and block the coupling path. This achieves high isolation while simultaneously optimizing antenna matching performance and expanding bandwidth, ensuring a stable radiation pattern and low cross-polarization characteristics throughout the entire frequency band. This design provides an effective solution for self-interference cancellation technology for differentially fed full-duplex antennas, further enhancing the antenna's anti-interference capability and having significant implications for the development of future wireless communication networks.

[0027] I. Overall Structural Composition See Figures 1 to 3 This embodiment provides a differential MIMO microstrip antenna with high port isolation. Its overall structure, from top to bottom, includes: two rectangular radiating patches (including rectangular radiating patch a1 and rectangular radiating patch b2), a single-layer dielectric substrate 7, and a metal ground plane 9.

[0028] 1. Single-layer dielectric substrate 7: serving as the support carrier for the antenna, its lower surface is covered with a complete metal ground plane 9, and its upper surface is covered with two rectangular radiating patches as radiating units, namely rectangular radiating patch a1 and rectangular radiating patch b2.

[0029] The preferred material for the single-layer dielectric substrate 7 is Rogers RT / duroid 5880, with a dielectric constant of 2.2 and a loss factor of 0.0009, to achieve low loss and high frequency stability. Example dimensions: 85mm x 65mm (length x width), thickness H of 0.787mm.

[0030] 2. Rectangular radiating patches: As radiating elements of the antenna, rectangular radiating patches a1 and b2 are symmetrically printed on the upper surface of the single-layer dielectric substrate 7.

[0031] Setup: Rectangular radiating patches a1 and b2 are parallel to each other and symmetrically arranged about the central axis of the single-layer dielectric substrate 7.

[0032] Example size: Each rectangular radiating patch measures 20.25mm in length and 17.9mm in width.

[0033] Spacing example: The edge distance between two rectangular radiating patches (1, 2) is 3.36 mm. Two rectangular radiating patches can be shifted and expanded to form 1x4, 1x8, or other elements. Regarding the radiating antenna size, the theoretical dimensions of the differential microstrip patch antenna are calculated similarly to those of a traditional single-port microstrip patch antenna. The difference lies in that, given a fixed patch shape and feed characteristics, the input impedance is a function of the distance between the two feed points; adjusting the feed distance alters the resonance effect. The edge distance between the two rectangular radiating patches (1, 2) is chosen to satisfy an antenna spacing of 0.06. This is a highly compact condition.

[0034] 3. Differential feed structure: Each rectangular radiating patch is excited through a pair of differential feed metal vias.

[0035] The first pair of differential feed metal vias: a rectangular radiating patch a1 connects the top of differential feed metal via aa3 and the top of differential feed metal via ab4.

[0036] The second pair of differential feed metal vias: rectangular radiating patch b2 connects the top of differential feed metal via ba5 and the top of differential feed metal via bb6.

[0037] Structural details: The differential feed metal via extends through the entire single-layer dielectric substrate 7, with its bottom end located in a clearance hole in the metal ground plane 9. The clearance hole has an example diameter of 2.07 mm to ensure insulation between the feed port and the ground plane.

[0038] Example dimensions: The diameter of the differential feed metal via is 0.9 mm, and the center distance between two differential feed metal vias on the same rectangular radiating patch is 4.8 mm.

[0039] The size of the differential feed metal vias has a negligible impact; the reflection loss performance is mainly affected by the position of the feed points. Differential feeding requires a perfectly symmetrical circuit structure to achieve ideal results; therefore, the feed points are symmetrical at the center of the radiating patch. From the principles and formulas of antennas and transmission lines, it is known that the antenna's input impedance is a function of the distance between the two feed points. Adjusting the distance between the two feed points can change the resonance effect. After frequency sweeping, the center distance between the two differential feed metal vias at the center frequency of 5.36 GHz is 4.8 mm. The resonance of the differential microstrip patch antenna depends on the distance d between the two feed points and the free space wavelength. The ratio. When the feed points are far apart (d / When the input resistance is greater than 0.1, the antenna will resonate, and the input resistance at resonance is very high. However, when the feed points are close to each other (d / With a resonant frequency <0.1, resonance will not occur, the input resistance is very small, and the input impedance is inductive. The antenna resonant frequency is the same as that of a single-port microstrip patch antenna, and is mainly affected by the shape, size, and structure of the patch.

[0040] 4. Defect structure 8: This is the core of achieving high port isolation, etched on the metal ground plane 9.

[0041] Location: Between the projection areas of the two rectangular radiating patches on the metal ground plane 9.

[0042] Blocking Coupling Paths: Etching defects on the ground plane interfere with the shielding current distribution within the ground plane. The overall I-shaped defect ground can be equivalent to an LC resonant circuit, producing a filtering effect at the center frequency. The size of the lateral rectangular lattice affects the effective series inductance; increasing the size increases the effective series inductance. The distance between the vertical rectangular gaps affects the parallel capacitance; increasing the gap distance decreases the parallel capacitance. Overall, the size of the lateral rectangular lattice affects the resonant and cutoff frequencies, while the distance between the vertical rectangular gaps affects the resonant frequency.

[0043] Improved impedance matching: The introduction of the DGS bandgap structure generates resonance at the center frequency of 5.36 GHz, thereby extending the antenna's operating bandwidth.

[0044] II. Detailed Composition and Principle of Defect Structure See Figure 4 The defect grounding structure 8 is formed by etching a series of interconnected rectangular slots, and the whole structure is centrally symmetrical.

[0045] The rectangular longitudinal gap b10 is located on the centerline of the structure. Example dimensions: 9mm (length) × 2.75mm (width).

[0046] On both sides of the long side of the rectangular longitudinal slit b10, there are symmetrically connected rectangular longitudinal slits a12 and c16. The connection relationship is as follows: the inner wide side of rectangular longitudinal slit a12 connects to one wide side of rectangular longitudinal slit b10; the inner wide side of rectangular longitudinal slit c16 connects to the other wide side of rectangular longitudinal slit b10. The dimensional relationship is as follows: the length and width of rectangular longitudinal slits a12 and c16 are the same, and both are larger than the width of rectangular longitudinal slit b10. Example dimensions of rectangular longitudinal slits a12 and c16 are length × width 2mm × 0.8mm.

[0047] A set of rectangular transverse gaps are perpendicularly connected to the rectangular longitudinal gaps a12 and c16, respectively.

[0048] The first group of transverse gaps consists of a rectangular transverse gap aI11 connected to the outer wide side of the rectangular longitudinal gap a12, with the outer wide side of the rectangular longitudinal gap a12 located at the center of the inner long side of the rectangular transverse gap aI11. Rectangular transverse gaps bI13 and cI14 are connected to the long side of the rectangular longitudinal gap a12, and both rectangular transverse gaps bI13 and cI14 are symmetrical about the rectangular longitudinal gap a12.

[0049] The second group of transverse gaps consists of a rectangular transverse gap aII15 connected to the outer wide side of the rectangular longitudinal gap c16, with the outer wide side of the rectangular longitudinal gap c16 located at the center of the inner long side of the rectangular transverse gap aII15. Rectangular transverse gaps bII17 and cII18 are connected to the long side of the rectangular longitudinal gap c16, and both rectangular transverse gaps bII17 and cII18 are symmetrical about the rectangular longitudinal gap c16.

[0050] Dimensions and Layout: Rectangular horizontal gaps aI11 and aII15 have the same dimensions, with an example length × width of 5.2mm × 0.8mm. Rectangular horizontal gaps bI13 and bII17 have the same dimensions, with an example length × width of 13.25mm × 1.65mm. Rectangular horizontal gaps cI14 and cII18 have the same dimensions, with an example length × width of 5mm × 1.25mm.

[0051] The lengths of these three transverse slits gradually decrease from the outside in (i.e. towards the central axis), forming a layout that "approaches" the central area (rectangular longitudinal slit b).

[0052] The I-shaped defect can be equivalent to an LC resonant circuit, producing a filtering effect at the center frequency. The size of the horizontal rectangular lattice affects the effective series inductance; increasing the size increases the effective series inductance. The distance between the vertical rectangular gaps affects the parallel capacitance; increasing the gap distance decreases the parallel capacitance. Overall, the size of the horizontal rectangular lattice affects the resonant and cutoff frequencies, while the distance between the vertical rectangular gaps affects the resonant frequency. This patent's multiple I-shaped defect structures can be equivalent to cascaded LC resonators, allowing for more precise control of the isolation effect at the center frequency. Size optimization: Adjusting the size of the horizontal rectangular lattice and the distance between the vertical rectangular gaps can achieve a specific filtering effect at the center frequency.

[0053] III. Working Principle and Synergistic Effect This invention achieves high port isolation through the synergistic design of differential feeding and a specific DGS structure: Differential excitation exhibits surface wave coupling suppression. Qualitative comparative verification was performed on a single-port fed microstrip patch antenna and a differentially fed microstrip patch antenna with the same center frequency. Qualitative verification was also conducted by loading a vertically polarized monopole probe antenna on the other side of the dielectric substrate. The vertical electric field generated by the antenna exhibits a strong coupling effect with the vertical electric field component of the TM0 mode surface wave. HFSS simulation results comparing coupling power show that differential excitation can significantly suppress surface wave coupling.

[0054] The defective structure can be equivalent to an LC resonant circuit, providing precise band-stop filtering at the target center frequency and effectively suppressing unnecessary electromagnetic coupling between antenna ports. Multiple slotted structures combined are equivalent to multiple cascaded LC resonators. Compared to a single resonant structure, this cascaded design allows for more flexible and precise control of the filtering characteristics and isolation effect at the center frequency.

[0055] The introduction of the DGS bandgap structure generates resonance at the center frequency of 5.36 GHz, thereby extending the antenna's operating bandwidth.

[0056] IV. Performance Verification The simulation and test results of the antenna prototype manufactured to the specified dimensions are as follows: Figures 5 to 9 As shown: High isolation: such as Figure 5 and Figure 7 As shown, the port isolation (Sdd21) reaches -42 dB at the center frequency of 5.36 GHz. Compared with a conventional differential antenna without a DGS structure, the isolation is improved by approximately 32 dB, which is extremely significant.

[0057] Good matching and bandwidth: such as Figure 5 and Figure 6 As shown, the antenna has a reflection coefficient (Sdd11) of less than -10 dB in the frequency range of 5.306 GHz to 5.425 GHz, a relative impedance bandwidth of 2.22%, and good matching.

[0058] Excellent radiation characteristics: such as Figure 8 and Figure 9 As shown, within the operating frequency band, the antenna gain is stable (>6.8 dBi), and the front-to-back ratio of the radiation pattern is high. In the main beam range of -60° to 60°, the cross-polarization level of the E-plane is below -30 dB, indicating that the antenna has purified linear polarization characteristics.

[0059] The above embodiments and dimensional parameters are a preferred embodiment with a center frequency of 5.36 GHz. Those skilled in the art should understand that by adjusting the material and thickness of the single-layer dielectric substrate 7, the size of the rectangular radiating patch, and the geometry and proportions of the gaps in the defect structure 8, the antenna's operating frequency can be flexibly adjusted to other desired communication frequency bands (such as other 5G bands or future 6G bands) while maintaining the aforementioned high isolation, low cross-polarization, and good matching characteristics. All modifications and improvements based on the core concept of this invention fall within the scope of protection of the claims of this invention.

Claims

1. A differential MIMO microstrip antenna with high port isolation, comprising a single-layer dielectric substrate (7); characterized in that, The single-layer dielectric substrate (7) has two rectangular radiating patches on its upper surface and a metal ground plane (9) on its lower surface; each rectangular radiating patch is connected to the metal ground plane (9) through two differential power feeding metal through holes. Two rectangular radiating patches are symmetrically arranged and parallel to each other on the upper surface of a single-layer dielectric substrate (7); a defect structure (8) is provided on the metal ground plane (9); the defect structure is located between the two projections of the two rectangular radiating patches on the metal ground plane (9).

2. The differential MIMO microstrip antenna with high port isolation according to claim 1, characterized in that, The defect structure (8) includes rectangular longitudinal gap a, rectangular longitudinal gap b and rectangular longitudinal gap c connected in sequence. Each of the rectangular longitudinal gap a and the rectangular longitudinal gap b is provided with a rectangular transverse gap group that is perpendicular to it. The rectangular transverse gap group includes rectangular transverse gap a, rectangular transverse gap b and rectangular transverse gap c. Rectangular horizontal gaps a, b, and c asymptotically approximate rectangular vertical gap b.

3. A differential MIMO microstrip antenna with high port isolation according to claim 2, characterized in that, The length and width of rectangular longitudinal slits a and c are the same, and both are larger than the length and width of rectangular longitudinal slit b. The inner wide side of rectangular longitudinal slit a and the inner wide side of rectangular longitudinal slit c are respectively connected to the two wide sides of rectangular longitudinal slit b.

4. A differential MIMO microstrip antenna with high port isolation according to claim 2, characterized in that, The rectangular horizontal slit a is connected to the outer wide side of the corresponding rectangular vertical slit, and the outer wide side of the rectangular vertical slit is located at the center of the inner long side of the rectangular horizontal slit a. The length of the three transverse gaps a, b, and c gradually decreases.

5. A differential MIMO microstrip antenna with high port isolation according to claim 1, characterized in that, The differential-fed metal via penetrates the single-layer dielectric substrate (7).

6. A differential MIMO microstrip antenna with high port isolation according to claim 1, characterized in that, The single-layer dielectric substrate (7) uses Rogers RT / duroid 5880 substrates with dielectric constant 2.2 and loss factor 0.0009.

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