Miniaturized double-passband micro-strip differential filter based on double-layer structure

Abstract

The invention belongs to the technical field of differential filters with double-layer structures, and discloses a miniaturized double-passband microstrip differential filter based on a double-layer structure, which is mainly composed of half-wavelength stepped impedance resonators and open-circuit branch microstrip lines on an upper metal coating and a lower metal coating, wherein the two symmetrical resonator structures are symmetrically arranged about the center of the metal grounding plate, the two open-circuit branch microstrip lines are connected at the center of the half-wavelength stepped impedance resonator, and a stepped gap and a square gap which are symmetrically arranged about the center of the metal grounding plate are etched on the grounding plate; the input ports 1 and 2 and the output ports 1 and 2 are respectively arranged at two sides of the centers of the two half-wavelength stepped impedance resonators, the center frequency is controlled by adopting the double-layer symmetrical half-wavelength stepped impedance resonators loaded by the open-circuit branches, and a control coupling structure of an etching step type and a square gap is adopted, so that the selectivity of a passband is improved, and the frequency of the passband is reduced; the size of the filter is reduced; and the common-mode gain in a passband is inhibited.

Description

Technical Field

[0001] The present invention belongs to the technical field of double-layer structured differential filters, and in particular relates to a miniaturized dual-passband microstrip differential filter based on a double-layer structure. Background Art

[0002] As modern wireless communication systems mature, high-speed differential signal processing standards and the need for common-mode interference mitigation continue to rise. The demand for differential filters in millimeter-wave radar, multi-standard base stations, and other applications is increasing. Currently, various types of resonator structures are used to design differential filters, but due to size limitations, their performance often fails to meet engineering requirements.

[0003] With the development of multimode resonators, it is becoming increasingly important to balance dual-band design with limited volume. Not only must the synergy between differential-mode response and common-mode suppression be achieved, but also miniaturization requirements often require a double-layer structure.

[0004] Although the topological structure based on the hybrid electromagnetic coupling mechanism in the existing differential filter can generate transmission zero points, it often makes it difficult to coordinately optimize the differential mode response and common mode rejection characteristics in the dual-passband scenario. In particular, it is easily affected by parasitic parameters in the millimeter wave band, causing mode splitting.

[0005] There are also methods that can construct a dual-passband response by cascading single-passband differential units, but this will introduce additional return loss and deteriorate the group delay characteristics.

[0006] In order to improve the insertion loss of the differential filter, existing literature attempts to combine a defective ground structure with a slotline resonator to suppress common-mode signals. However, this method results in insufficient isolation between the dual passbands and greatly increases the insertion loss of the signal.

[0007] With the advent of the 6G era, the versatility of frequency bands has also been greatly improved. How to design a differential filter that can meet the requirements of multiple frequency bands and has high passband selectivity, low insertion loss, high common-mode rejection and small size is an issue to be solved.

[0008] Through the above analysis, the problems and defects of the existing technology are as follows:

[0009] Although the topological structure based on the hybrid electromagnetic coupling mechanism in the existing differential filter can generate transmission zero points, it often makes it difficult to coordinately optimize the differential mode response and common mode rejection characteristics in the dual-passband scenario. In particular, it is easily affected by parasitic parameters in the millimeter wave band, causing mode splitting. Summary of the Invention

[0010] In view of the problems existing in the prior art, the present invention provides a miniaturized dual-passband microstrip differential filter based on a double-layer structure.

[0011] The present invention is implemented as follows: a miniaturized dual-passband microstrip differential filter based on a double-layer structure includes:

[0012] It is mainly composed of a half-wavelength step impedance resonator and an open-circuit branch microstrip line on a symmetrical metal coating. Its characteristics are that the resonator structure of the metal coating is arranged symmetrically about the center of the metal ground plate, the open-circuit branch microstrip line is connected and arranged at the center of the half-wavelength step impedance resonator, and the metal ground plate in the two-layer dielectric substrate is etched with stepped gaps and square gaps symmetrical about the center of the plate; the entire filter is arranged symmetrically with the central symmetric point of the metal ground plate; input ports 1 and 2, and output ports 1 and 2 are respectively arranged on both sides of the center of the main microstrip line of the two-layer half-wavelength step impedance resonator.

[0013] Furthermore, the upper metal plating structure is composed of microstrip line 1, microstrip line 2, microstrip line 3, microstrip line 4, microstrip line 3-1, and microstrip line 4-1 connected in sequence; the lower metal plating structure symmetrical about the center of the metal ground plate is composed of microstrip line 10, microstrip line 11, microstrip line 12, microstrip line 10-1, microstrip line 11-1, and microstrip line 14 connected in sequence; the center frequency of the half-wavelength step resonator can be adjusted by adjusting the microstrip line width.

[0014] Furthermore, the square gap etched in the metal ground plane in the two-layer dielectric substrate is composed of microstrip line 6, microstrip line 7, microstrip line 6-1, and microstrip line 7-1; and the stepped gap etched in the metal ground plane is composed of microstrip line 8, microstrip line 9, microstrip line 8-1, and microstrip line 9-1; adjusting the width of the square gap and the width of the stepped gap can adjust the coupling strength of the resonator on the double-layer substrate to adjust its matching performance.

[0015] Furthermore, adjusting the open-circuit branch microstrip line loaded in the metal plating layer can suppress the common-mode signal in the differential filter and generate a transmission zero in the common-mode signal.

[0016] In combination with the above technical solutions and the technical problems solved, please analyze the advantages and positive effects of the technical solutions to be protected by the present invention from the following aspects:

[0017] First, the present invention discloses a miniaturized dual-passband microstrip differential filter based on a double-layer structure. The filter is mainly composed of half-wavelength step impedance resonators and open-circuit branch microstrip lines on the upper and lower metal plating layers. Two symmetrical resonator structures are arranged symmetrically about the center of the metal ground plate. Two open-circuit branch microstrip lines are connected and arranged at the center of the half-wavelength step impedance resonator. The ground plate in the two-layer dielectric substrate is etched with stepped slots and square slots symmetrical about the center of the metal ground plate. Input ports 1 and 2, and output ports 1 and 2 are respectively arranged on either side of the center of the two half-wavelength step impedance resonators. The present invention uses a double-layer symmetrical half-wavelength step impedance resonator loaded with open stubs to control the center frequency and adopts a control coupling structure with etched stepped and square slots. This improves the passband selectivity, reduces the filter volume, and suppresses the common-mode gain within the passband. The filter has a simple design, compact structure, convenient processing and debugging, low cost, adjustable passband, and good performance.

[0018] The present invention proposes a design method for a miniaturized dual-passband microstrip differential filter based on a double-layer structure. By adopting a half-wavelength step impedance resonator loaded by an open-circuit stub and a coupling structure of etched stepped slots and square slots, a common-mode transmission zero is introduced, thereby improving the common-mode gain and reducing the size of the filter.

[0019] The present invention not only maintains high selectivity of the center frequency and low insertion loss, but also has the advantages of small size and convenient design and debugging.

[0020] The filter has a compact structure, and the HFSS simulation results effectively verify the accuracy of this method. It is easy to process, low-cost, and has wide engineering application significance.

[0021] second,

[0022] The expected benefits of the present invention include technical benefits and market benefits. In terms of technical benefits, the present invention achieves insertion loss ≤ 0.5dB, out-of-band suppression ≥ 28dB, and common-mode suppression ≥ 22dB; the size is reduced by more than 50% compared with the traditional solution through multi-layer PCB board layout, which helps to miniaturize the equipment; the frequency range supports multi-band coverage of the 5GNR downlink range of Sub-6GHz, realizing hybrid networking of N5 and N77, and meeting the 5G spectrum allocation needs of different regions in the world; in terms of market benefits, the present invention can replace imported filters and seize the market share of base station RF front-end modules; at the same time, it is suitable for various smartphones, Internet of Things modules, etc., to meet consumers' demand for multi-band and high-speed network; and in scenarios where high-precision vehicle networking, industrial Internet of Things, etc. require high-reliability filters, the present invention is sufficiently competitive. The present invention has a cost advantage. The cost of multi-layer PCB filters is significantly lower than that of cavity filters. The cost will be further reduced after large-scale production. As a 5G RF core component, its unit price can be 3 to 5 times that of ordinary traditional filters. During the production process, the present invention can promote the development of domestic high-frequency PCB substrates such as Rogers 4003C and semiconductor processing technology. At the same time, it can cooperate with communication equipment manufacturers such as Huawei, ZTE, and China Mobile to be embedded in their 5G base station and terminal supply chains.

[0023] The technical solution of the present invention fills the gap in the domestic and foreign industry's requirements for high-precision communications, which not only meet the miniaturization of RF devices but also meet the performance requirements of multiple frequency bands and high network speeds in current mobile communications. Currently, the domestic and foreign industries usually adopt a single-layer PCB board design when implementing RF differential filters, but this will make the surface volume too large, and the volume will be further enlarged when integrated with other RF devices. The technical solution of the present invention not only achieves multi-band coverage of the Sub-6GHz 5GNR downlink range, but also achieves the requirement of further miniaturization, successfully filling the gap in the realization of miniaturized multi-band differential filters in 5G communications.

[0024] The present invention overcomes the technical bias that common-mode rejection and passband performance of differential filters conflict. Traditionally, enhancing common-mode rejection can sacrifice differential-mode gain. The present invention employs a metal ground plane with etched slots as a common-mode resonant structure. Common-mode rejection is achieved in specific frequency bands by adjusting the slot size. The resonant structures on the two metal plating layers are symmetrically designed to reduce common-mode gain, and open-circuit branches are added to the resonator to create common-mode resonant zeros, broadening the common-mode rejection bandwidth. The present invention overcomes the technical bias that multi-layer structures typically increase device size. Traditionally, stacking multiple dielectric plates results in excessive volume, thus impacting filter performance. The present invention utilizes a double-layer Rogers 4003C dielectric substrate, employing a single plate with double-sided copper cladding and an etched intermediate metal ground layer, rather than stacking multiple dielectric plates. Compared to a single-plate structure, the length and width of the dielectric plate are reduced by 50%. Furthermore, vertical coupling is achieved by etching slots in the intermediate metal ground layer, significantly reducing lateral dimensions while maintaining filter performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a structural diagram of a miniaturized dual-passband microstrip differential filter based on a double-layer structure provided by an embodiment of the present invention.

[0026] Figure 2 The figure is a schematic structural diagram of a metal ground layer of a miniaturized dual-passband microstrip differential filter based on a double-layer structure provided by an embodiment of the present invention.

[0027] Figure 3 The figure is a schematic structural diagram of the lower metal plating layer of a miniaturized dual-passband microstrip differential filter based on a double-layer structure provided by an embodiment of the present invention.

[0028] Figure 4 The figure is a schematic top view of the upper resonator structure of the miniaturized dual-passband microstrip differential filter based on a double-layer structure provided by an embodiment of the present invention.

[0029] Figure 5 The figure is a schematic top view of the metal ground layer structure of a miniaturized dual-passband microstrip differential filter based on a double-layer structure provided by an embodiment of the present invention.

[0030] Figure 6 This is a schematic diagram of the bottom-up structure of the resonator structure of the lower layer of the miniaturized dual-passband microstrip differential filter based on the double-layer structure provided by an embodiment of the present invention.

[0031] Figure 7 It is a schematic diagram of S parameters of the physical structure of the initial structure of the present invention simulated in HFSS according to an embodiment of the present invention.

[0032] Figure 8It is a schematic diagram of S parameters of the physical structure of the optimized structure of the present invention provided by an embodiment of the present invention simulated in HFSS.

[0033] Figure 9 It is a schematic diagram of S parameters of the physical structure of the final structure of the present invention simulated in HFSS according to an embodiment of the present invention.

[0034] Figure 10 This is a diagram of adjusting the center frequency of the first passband by adjusting the width of the wide microstrip line provided by an embodiment of the present invention.

[0035] Figure 11 This is a diagram of adjusting the width of the wide microstrip line to adjust the center frequency of the second passband provided by an embodiment of the present invention.

[0036] Figure 12 This is a graph showing experimental results of adjusting the width of a narrow microstrip line to adjust the center frequency of a first passband, provided by an embodiment of the present invention.

[0037] Figure 13 This is a graph showing experimental results of adjusting the width of the narrow microstrip line to adjust the center frequency of the second passband, provided by an embodiment of the present invention.

[0038] Figure 14 This is a gain diagram of a microstrip line without adding an open-circuit stub provided by an embodiment of the present invention.

[0039] Figure 15 This is a gain diagram of the microstrip line with added open stubs provided by an embodiment of the present invention.

[0040] Figure 16 This is a gain diagram of the step-type gap added according to an embodiment of the present invention.

[0041] In the figure: 1, microstrip line; 2, microstrip line; 3, microstrip line; 4, microstrip line; 5, microstrip line; 6, microstrip line; 7, microstrip line; 8, microstrip line; 9, microstrip line; 10, microstrip line; 11, microstrip line; 12, microstrip line; 13, microstrip line; 3-1, microstrip line; 4-1, microstrip line; 5-1, microstrip line; 6-1, microstrip line; 7-1, microstrip line; 8-1, microstrip line; 9-1, microstrip line; 10-1, microstrip line; 11-1, microstrip line; 13-1, microstrip line. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0043] The present invention is achieved by: It primarily consists of half-wavelength stepped impedance resonators and open-circuit microstrip stub lines on two metal coatings. The two open-circuit stub-loaded half-wavelength stepped impedance resonators are arranged on one side of the upper and lower metal coatings, respectively, and are symmetrically distributed relative to the central axis of the metal ground plane. The two open-circuit microstrip stub lines are connected and arranged at the center of the half-wavelength stepped impedance resonators. The metal ground plane at the center of the dielectric substrate primarily consists of etched stepped slots and square slots. The entire filter is symmetrically arranged around the center of the ground plane, with input ports 1 and 2, and output ports 1 and 2, symmetrically located on either side of the center of the main stub lines of the half-wavelength stepped impedance resonators.

[0044] The present invention realizes a dual-passband differential filter by adopting a method of coupling a half-wavelength stepped impedance resonator loaded with an open stub and an etched stepped slot and a square slot. The center frequencies of the two passbands are controlled by a symmetrical half-wavelength stepped impedance resonator loaded with an open stub, and the passband frequency is changed by changing the width of its main microstrip branch line.

[0045] One end of two symmetrically arranged open-circuit microstrip branch lines is connected to the center of a half-wavelength stepped impedance resonator, so that a transmission zero point is generated in the common mode between the two passbands. This can widen the common-mode stopband without any impact on the differential mode. The transmission zero point frequency can be adjusted by adjusting the length of the microstrip line.

[0046] Etching a ground plane with square and stepped slots allows the resonator structures on the double-layer dielectric substrate to couple with each other. The coupling strength is determined by the length and width of the square slots, and these two parameters control the filter's out-of-band rejection capability. The length and width of the stepped slots, on the other hand, adjust the common-mode gain in the passband. Therefore, by properly adjusting the length and width of the stepped slots, the common-mode gain can be reduced to an appropriate level, and by adjusting the square slots, the passband bandwidth can be adjusted to meet design requirements, ensuring that the filter achieves both out-of-band rejection and common-mode rejection.

[0047] The board used to make this dual-passband microstrip differential filter is a Rogers4003C dielectric board with a relative dielectric constant of 3.55 and a thickness of 0.508mm. The copper plating thickness on the surface is 0.018mm, and the metal ground plane in the two-layer dielectric substrate is made of copper material.

[0048] from Figure 4 、 Figure 5 、 Figure 6, it can be seen that the resonator structure on the upper metal coating is mainly composed of a half-wavelength step impedance resonator and an open microstrip branch line, while the resonator structure on the lower metal coating is composed of a half-wavelength step impedance resonator and open microstrip branch lines of different lengths that are symmetrical about the center of the metal ground plate. The metal ground plates in the two layers of dielectrics are etched with stepped gaps and square gaps, which are also designed to be symmetrical about the center of the metal ground plate. The entire filter is arranged symmetrically about the center point of the ground plate, and the input ports 1 and 2, and the output ports 1 and 2 are symmetrically arranged on both sides of the center of the main branch line of the symmetry line of the half-wavelength step impedance resonator.

[0049] like Figure 1 、 Figure 2 、 Figure 3 The upper metal plating structure is composed of microstrip line 1, microstrip line 2, microstrip line 3, microstrip line 4, microstrip line 3-1, and microstrip line 4-1 connected in sequence; the lower metal plating structure symmetrical about the center of the metal ground plate is composed of microstrip line 10, microstrip line 11, microstrip line 12, microstrip line 10-1, microstrip line 11-1, and microstrip line 14 connected in sequence; the passband center frequency can be adjusted by adjusting the microstrip line width of the half-wavelength step resonator.

[0050] The square slots etched in the metal ground plane in the two-layer dielectric substrate are composed of microstrip lines 6, 7, 6-1, and 7-1; while the stepped slots etched in the ground plane are composed of microstrip lines 8, 9, 8-1, and 9-1. Adjusting the widths of the square slots and the stepped slots can adjust the coupling strength of the resonator on the double-layer substrate to adjust its matching performance.

[0051] The signal input port and output port are respectively composed of microstrip line 5, microstrip line 5-1, microstrip line 13, and microstrip line 13-1, and are used for signal transmission of the filter.

[0052] The detailed dimensions of the miniaturized dual-passband microstrip differential filter according to the embodiment of the present invention are as follows: (Unit: mm)

[0053]

[0054] Figure 7 、 Figure 8 、 Figure 9The frequency response characteristics of the filter according to the present invention are shown, including the transmission characteristics (|S21| differential-mode amplitude response and common-mode amplitude response), and the reflection response (|S11| amplitude response). As shown in the figure, the center frequencies of the filter are 0.84 GHz and 3.4 GHz, respectively. The in-band insertion loss is less than -1 dB, and the return loss is greater than -16 dB, demonstrating excellent test results. The 3 dB bandwidth of this filter is 9.2% and 23.9%, respectively. The common-mode insertion loss is less than -22 dB throughout the entire test range, demonstrating excellent common-mode rejection. The filter measures 48 mm by 48 mm.

[0055] This invention can be specifically applied in the following scenarios: 1. 5G base stations and terminal devices: This invention can be used in communication devices such as 5G macro base stations, small base stations, and smartphones to filter and enhance N5 / N77 dual-band signals, achieving multi-band and enhanced high-speed communication requirements. 2. IoT devices: This invention can be used in wireless modules for smart city sensors and industrial IoT devices, providing compatibility with both low-frequency wide-area N5 and medium- and high-speed N77 communication requirements, adapting to diverse data transmission scenarios. 3. In-vehicle communications and intelligent connected systems: This invention can be integrated into an in-vehicle T-Box or V2X module, supporting multi-band communication between vehicles, infrastructure (N77), and remote control (N5), ensuring low latency and high reliability. Specific product forms of this invention include: 1. 5G base station RF front-end module: This module integrates dual-passband filters to achieve efficient separation and low-loss transmission of N5 / N77 band signals. 2. Smartphone antenna tuning unit: This module uses a differential structure to suppress PCB-level noise, improving the efficiency of multi-band antennas. 3. Industrial IoT gateway RF board: This module achieves full Sub-6 GHz frequency band coverage within a limited space, reducing hardware complexity. 4. On-board multi-mode communication module: embedded in the vehicle system to meet the multi-band redundant communication needs in autonomous driving.

[0056] The present invention realizes a dual-passband microstrip differential filter based on a double-layer structure. The center frequency of the dual passbands can be independently controlled by adjusting the width of the microstrip line of the half-wavelength step impedance resonator. The transmission zero of the common-mode gain is increased by increasing the length of the open branch microstrip line, and the common-mode gain is suppressed by adding a stepped gap. By adjusting the width of the two microstrip lines of the half-wavelength step impedance resonator, the center frequency of the dual passbands can be adjusted separately. The experimental results of adjusting the width of the wide microstrip line to adjust the center frequency of the first passband are shown as follows. Figure 10 and Figure 11 As shown:

[0057] As shown in the figure above, adjusting the width of the wide microstrip line adjusts the center frequency of the first passband. The wider the width of the wide microstrip line, the higher the center frequency of the first passband becomes, while the center frequency of the second passband remains unchanged.

[0058] The experimental results of adjusting the width of the narrow microstrip line to adjust the center frequency of the first passband are as follows: Figure 12 and Figure 13 As shown:

[0059] As shown in the figure above, adjusting the width of the narrow microstrip line adjusts the center frequency of the second passband. The wider the narrow microstrip line, the smaller the center frequency of the second passband becomes, while the center frequency of the first passband remains unchanged.

[0060] By increasing the length of the open branch microstrip line, the transmission zero of the common mode gain is increased. The gain diagram without increasing the length of the open branch microstrip line is as follows: Figure 14 As shown, the gain diagram of adding open branch microstrip line is as follows Figure 15 shown.

[0061] As can be seen from the above figure, by increasing the length of the open-circuit branch microstrip line, the transmission zero point of the common-mode gain is increased, and two common-mode transmission zero points are added at 1.13 GHz and 3.992 GHz respectively.

[0062] By adding stepped gaps to suppress the common-mode gain, the common-mode gain is reduced to below -20dB. The gain diagram of the open microstrip line structure without stepped gaps is shown in the figure below. Figure 15 As shown, the gain diagram of the open microstrip line structure loaded with a stepped gap is as follows Figure 16 shown.

[0063] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A miniaturized dual-passband microstrip differential filter based on a double-layer structure, comprising two dielectric substrates, a metal ground plane located between the two dielectric substrates, and a metal plating layer arranged on the outer side of the dielectric substrate, characterized in that: The metal plating layer comprises an upper metal layer and a lower metal layer respectively located on the surface of the upper and lower dielectric substrates; The upper metal layer includes a first half-wavelength stepped impedance resonator composed of sequentially connected microstrip line 1, microstrip line 2, microstrip line 3, microstrip line 4, microstrip line 3-1, and microstrip line 4-1, and a centrally connected open branch microstrip line; The lower metal layer includes a second half-wavelength stepped impedance resonator composed of sequentially connected microstrip lines 10, 11, 12, 10-1, 11-1, and 14, and an open branch microstrip line connected in the center; The metal ground plate is etched with stepped gaps and square gaps symmetrically arranged about the center of the plate. The stepped gaps are composed of microstrip lines 8, 9, 8-1, and 9-1, and the square gaps are composed of microstrip lines 6, 7, 6-1, and 7-1. Input port 1 and input port 2 are respectively connected to both sides of the center of the main microstrip line of the first half-wavelength step impedance resonator, and output port 1 and output port 2 are respectively connected to both sides of the center of the main microstrip line of the second half-wavelength step impedance resonator; The overall structure is arranged symmetrically with the central symmetry point of the metal ground plate.

2. The microstrip differential filter according to claim 1, wherein The operating center frequency of the first half-wavelength stepped impedance resonator is set by adjusting the width of microstrip line 1 to microstrip line 4 - 1 .

3. The microstrip differential filter according to claim 1, wherein The operating center frequency of the second half-wavelength stepped impedance resonator is set by adjusting the width of the microstrip line 10 to the microstrip line 14 .

4. The microstrip differential filter according to claim 1, wherein The square gaps on the metal ground plate control the coupling strength between the resonators by adjusting the widths of the microstrip lines 6, 7, 6-1 and 7-1.

5. The microstrip differential filter according to claim 1, wherein The stepped gaps on the metal ground plate control the coupling strength between the resonators by adjusting the widths of the microstrip lines 8 , 9 , 8 - 1 and 9 - 1 .

6. The microstrip differential filter according to claim 1, wherein: The open-circuit branch microstrip line is arranged at the center of the first and second half-wavelength stepped impedance resonators to introduce a differential mode transmission path.

7. The microstrip differential filter according to claim 1, wherein: The structural dimensions of the open-circuit branch microstrip line are set by adjusting length and width parameters.

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