A dual-passband filtering balun

Abstract

This invention discloses a dual-passband filtering balun, relating to the field of radio frequency wireless technology. It includes: a single-passband filtering balun comprising: a top microstrip, ground metal I, ground metal II, a bottom microstrip, and multiple metal vias; a first interlayer dielectric is disposed between the top microstrip and ground metal I, a second interlayer dielectric is disposed between ground metal I and ground metal II, and a third interlayer dielectric is disposed between ground metal II and the bottom microstrip; the multiple metal vias penetrate from top to bottom through the top microstrip, the first interlayer dielectric, ground metal I, the second interlayer dielectric, ground metal II, the third interlayer dielectric, and the bottom microstrip; windows of the same size are drilled at the center of ground metal I and ground metal II; both the top microstrip and the bottom microstrip have two single-passband resonant cavities; a coupling resonant cavity is added below each of the single-passband resonant cavities to obtain the dual-passband filtering balun. This invention provides greater coupling strength and greater design freedom.

Description

Technical Field

[0001] This invention relates to the field of radio frequency wireless technology, and in particular to a dual-passband filtering balun. Background Technology

[0002] A balun is the English transliteration of a balanced-to-unbalanced converter. In radio frequency systems, baluns are mainly used for the conversion between single-ended and differential signals. Differential signals have a strong ability to suppress common-mode noise. External electromagnetic interference often appears in the form of common-mode noise, and differential structures can effectively reduce the impact of this common-mode noise, thereby improving signal integrity and accuracy. At the same time, the swing of differential signals is relatively large, which means that it has a higher noise margin and can transmit information more reliably in noisy environments.

[0003] Most existing microstrip baluns are microstrip Marchand structures, primarily composed of four quarter-wavelength (λ / 4) microstrip transmission lines. These transmission lines are coupled together in a specific manner, forming a symmetrical four-port network. One port serves as the unbalanced port, used to receive or transmit unbalanced signals; the other two ports serve as balanced ports, outputting or inputting balanced signals with the same amplitude but a 180° phase difference. Based on this coupled microstrip transmission line structure, a relatively wide bandwidth of balanced-to-unbalanced conversion can be achieved.

[0004] In existing RF systems, selection between multiple frequency bands is often required, necessitating the cascading of filters. However, this often leads to increased losses and system overhead, necessitating the combination of balun and filtering functions. However, the inter-line coupling strength between microstrip transmission lines is limited, resulting in a planar network with relatively low design freedom, making it difficult to meet complex design requirements. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide a dual-passband filter balun that can solve the problems of insufficient coupling strength of planar microstrip lines and insufficient freedom of planar design of microstrip lines.

[0006] This invention provides a dual-passband filter balun, comprising: a single-passband filter balun, coupled resonant cavity R3, coupled resonant cavity R4, coupled resonant cavity R3' and coupled resonant cavity R4'. The single-passband filter balun comprises, from top to bottom: a top microstrip, ground metal I, ground metal II, a bottom microstrip and multiple metal vias.

[0007] A first interlayer dielectric is placed between the top microstrip and ground metal I; a second interlayer dielectric is placed between ground metal I and ground metal II; and a third interlayer dielectric is placed between ground metal II and the bottom microstrip. Multiple metal vias penetrate from top to bottom through the top microstrip, the first interlayer dielectric, ground metal I, the second interlayer dielectric, ground metal II, the third interlayer dielectric, and the bottom microstrip. Window of the same size is drilled at the center of ground metal I and ground metal II for coupling between the top and bottom microstrips. Both the top and bottom microstrips have two single-passband resonant cavities.

[0008] A coupled resonant cavity R3 is set on the ground metal I below the single passband resonant cavity R1 in the top microstrip, and a coupled resonant cavity R4 is set on the ground metal I below the single passband resonant cavity R2 in the top microstrip; a coupled resonant cavity R3' is set on the ground metal II above the single passband resonant cavity R1' in the bottom microstrip, and a coupled resonant cavity R4' is set on the ground metal II above the single passband resonant cavity R2' in the bottom microstrip, thus obtaining a dual passband filter balun.

[0009] Optionally, both the first and third interlayer media are RT / duroid 5880 interlayer media materials made of polytetrafluoroethylene glass fiber reinforced material with a thickness of 0.203 mm.

[0010] The second interlayer medium is specifically a prepreg material RO 4450F with a thickness of 0.101mm.

[0011] Optionally, the top microstrip also includes a first microstrip line, and the bottom microstrip also includes a second microstrip line and a third microstrip line; the single-passband resonator R1 and single-passband resonator R2 in the top microstrip are connected to the unbalanced port of the first microstrip line, and the single-passband resonator R1' and single-passband resonator R2' in the bottom microstrip are connected to the balanced port of the second microstrip line and the balanced port of the third microstrip line, respectively, and the width of the three microstrip lines is 0.7mm.

[0012] Optionally, the radius of each of the multiple metal vias is 0.1 mm, and they are evenly distributed.

[0013] Optionally, the single-passband resonator R1, the single-passband resonator R2, the single-passband resonator R1', and the single-passband resonator R2' in the top microstrip are dumbbell-shaped, and the coupled resonators R3, R4, R3', and R4' are C-shaped.

[0014] Optionally, the single-passband filtered balun operates at a center frequency of 2.9 GHz and a bandwidth of 400 MHz.

[0015] Optionally, the center frequency of the first operating frequency band of the dual-passband filtered balun is 2.1 GHz, and the bandwidth is 490 MHz; the center frequency of the second operating frequency band of the dual-passband filtered balun is 3.05 GHz, and the bandwidth is 310 MHz.

[0016] The dual-passband filtering balun provided in this embodiment of the invention has the following advantages compared with the prior art:

[0017] This invention proposes a spatial coupling structure. By creating a window at the center of ground metal I and ground metal II, the top microstrip and the bottom microstrip are coupled through the window. Compared with the traditional planar coupling structure, this structure can achieve a larger coupling coefficient and provide a greater coupling strength without the need for cascaded filters. It solves the shortcomings of insufficient coupling strength of planar microstrip lines and insufficient design freedom of microstrip lines. Attached Figure Description

[0018] Figure 1 This is a dual-passband filtering balun layout provided in one embodiment. Figure 1 (a) in the image is a top-down view from a 3D perspective. Figure 1 (b) is a bottom view from a 3D perspective. Figure 1 (c) in the figure represents the cross-sectional view.

[0019] Figure 2 Here is a resonant cavity coupling topology diagram of a dual-passband filtered balun provided in one embodiment. Figure 2 (a) in the diagram is the resonant cavity coupling topology of a single-passband filtered balun. Figure 2 (b) in the diagram is the resonant cavity coupling topology of the dual-passband filtered balun;

[0020] Figure 3 This is a graph showing the fitting result of the coupling matrix of a dual-passband filtering balun provided in one embodiment. Figure 3 (a) shows the coupling topology of the dual-passband filter resonant cavity and the coupling parameter settings. Figure 3 (b) in the figure represents the S-parameter response calculated from the coupling matrix;

[0021] Figure 4 A schematic diagram of a four-port network balun design for a dual-passband filtering balun provided in one embodiment;

[0022] Figure 5 This is a single-passband filter balun layout of a dual-passband filter balun provided in one embodiment. Figure 5 (a) in the image represents a 3D perspective. Figure 5 (b) in the figure represents the cross-sectional view. Figure 5 (c) in the figure shows the shape details of each metal layer;

[0023] Figure 6 This is a simulation performance diagram of a single-passband filtering balun for a dual-passband filtering balun provided in one embodiment. Figure 6 (a) in the figure represents the S-parameter response. Figure 6 (b) in the figure represents the response to phase difference and amplitude imbalance;

[0024] Figure 7 The image shows the simulation performance of a dual-passband filtering balun provided in one embodiment. Figure 7 (a) in the figure represents the S-parameter response. Figure 7 (b) in the figure represents the phase difference and amplitude imbalance response of the first passband. Figure 7 In the diagram, (c) represents the phase difference and amplitude imbalance response of the second passband. 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 the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] In one embodiment, a dual-passband filtering balun is provided. The design concept and layout drawing method of the dual-passband filtering balun are proposed and electromagnetic simulation function verification is completed. Based on the coupling topology and coupling strength calculated by the coupling matrix, it supports single-passband and dual-passband filtering responses. Furthermore, through the balun design method of a four-port network, one port of the symmetrical four-port network is opened, and the transfer function and reflection coefficient of the other ports are reasonably adjusted to support the balun response. Figure 1 and Figure 5 The diagrams illustrate dual-passband filtered baluns and single-passband filtered baluns according to exemplary embodiments. Figure 1 (a) in the image is a top view of the dual-passband filtered balun layout in 3D. Figure 1 (b) in the figure is a bottom view of the dual-passband filtered balun layout in 3D perspective. Figure 1 (c) in the figure represents the cross-sectional view of the dual-passband filtered balun pattern. Figure 5 (a) in the image represents the 3D view of a single-passband filtered balun pattern. Figure 5 (b) in the figure represents the cross-sectional view of a single-passband filtered balun pattern. Figure 5 Image (c) shows the shape details of each metal layer in the single-passband filter balun layout. The implementation scheme is described in detail below:

[0027] The dual-passband filter balun includes: a single-passband filter balun, coupled resonant cavity R3, coupled resonant cavity R4, coupled resonant cavity R3', and coupled resonant cavity R4'.

[0028] The single-passband filter balun comprises: a top microstrip, ground metal I, ground metal II, a bottom microstrip, and multiple metal vias. A first interlayer dielectric is placed between the top microstrip and ground metal I; a second interlayer dielectric is placed between ground metal I and ground metal II; and a third interlayer dielectric is placed between ground metal II and the bottom microstrip. The multiple metal vias penetrate from top to bottom through the top microstrip, the first interlayer dielectric, ground metal I, the second interlayer dielectric, ground metal II, the third interlayer dielectric, and the bottom microstrip. A window of the same size is drilled at the center of ground metal I and ground metal II; this window is used for coupling between the top and bottom microstrips.

[0029] Both the top and bottom microstrips have two single-passband resonant cavities. A coupling resonant cavity R3 is positioned below the single-passband resonant cavity R1 in the top microstrip, and a coupling resonant cavity R4 is positioned below the single-passband resonant cavity R2 in the top microstrip. A coupling resonant cavity R3' is positioned above the single-passband resonant cavity R1' in the bottom microstrip, and a coupling resonant cavity R4' is positioned above the single-passband resonant cavity R2' in the bottom microstrip, resulting in a dual-passband filter balun.

[0030] The first and third interlayer dielectrics are both RT / duroid 5880 interlayer dielectric materials made of polytetrafluoroethylene glass fiber reinforced material, with a thickness of 0.203 mm, used in PCB fabrication. The second interlayer dielectric is specifically RO 4450F prepreg material, with a thickness of 0.101 mm, used as an adhesive layer in the laminate.

[0031] The single-passband resonators R1, R2, R1', and R2' in the top microstrip, the single-passband resonators R1' and R2' in the bottom microstrip are dumbbell-shaped, while the coupled resonators R3, R4, R3', and R4' are C-shaped.

[0032] The top microstrip also includes a first microstrip line, and the bottom microstrip includes a second and a third microstrip line. Single-passband resonators R1 and R2 in the top microstrip are connected to the unbalanced port of the first microstrip line, while single-passband resonators R1' and R2' in the bottom microstrip are connected to the balanced ports of the second and third microstrip lines, respectively. The widths of the first, second, and third microstrip lines are all 0.7 mm, used to achieve a transmission line characteristic impedance of 50 Ω.

[0033] Multiple metal vias, each with a radius of 0.1 mm, are evenly distributed to ensure that the potentials of ground metal I and ground metal II are consistent.

[0034] The window size directly affects the coupling strength, since single-passband and dual-passband filter baluns require different coupling. Therefore, the window size for a single-passband filter balun can be set to 1.2mm*1.9mm, and the window size for a dual-passband filter balun can be adjusted to 2.4mm*5.9mm.

[0035] The single-passband filtered balun operates at a center frequency of 2.9 GHz and a bandwidth of 400 MHz. The dual-passband filtered balun operates at a center frequency of 2.1 GHz and a bandwidth of 490 MHz for its first operating band; and at a center frequency of 3.05 GHz and a bandwidth of 310 MHz for its second operating band.

[0036] Step 1, Topology selection based on the resonant cavity:

[0037] To design a filter balun based on a microstrip resonator, the size and parameters of the resonator, as well as the order and number of passbands of the filter, must first be determined. The main coupling strength and coupling topology of the required resonator can be calculated using the coupling matrix. A typical second-order filter network requires two resonators, while a dual-passband filter network requires four resonators for coupling, and the coupling topology and coupling strength need to be selected in a specific way.

[0038] Figure 2 This is the coupled topology of the dual-passband filter response used in this invention. Figure 2 (a) in the diagram is the resonant cavity coupling topology of a single-passband filtered balun. Figure 2 (b) shows the resonant cavity coupling topology of the dual-passband filter balun. It can be seen that strong coupling occurs between single-passband resonant cavities R1 and R2, R1 and R3, and R2 and R4. Strong coupling also occurs between single-passband resonant cavities R1' and R2', R1' and R3', and R2' and R4'. This results in the response of the dual-passband filter. Figure 3 This invention is based on the coupling matrix calculated using MATLAB tools. Figure 3 (a) shows the coupling topology of the dual-passband filter resonant cavity and the coupling parameter settings. Figure 3 (b) in the figure represents the S-parameter response calculated from the coupling matrix. This response is generated by the dual-passband filter topology, taking into account the weak coupling between different resonant cavities and between the resonant cavity and the source load.

[0039] Step 2, Balun design method based on four-port network:

[0040] The desired filtering effect can be obtained through reasonable resonator design and topology selection. The present invention adopts a balun design method based on a four-port network. By performing odd-even mode analysis on any symmetrical four-port network, as long as its reflection coefficient meets the corresponding conditions, the four-port network can realize the function of a balun.

[0041] Figure 4 middle, It is the reflection coefficient. It is the transmission coefficient. even Representing the even model, odd This represents an odd modifier. The specific correspondence conditions mentioned here are... Figure 4 Formulas (1) and (2) in the text:

[0042] ;

[0043] ;

[0044] Satisfying formula (1) enables the reverse characteristics of 2-port and 3-port, and satisfying formula (2) enables the matching characteristics of 1-port, i.e., the return loss is 0.

[0045] Figure 4 This invention employs the design principle of a four-port network balun. The specific details of this design principle are as follows: First, in odd-mode, the symmetry plane can be considered a virtual ground. Considering only the response of one half of the circuit, the resonator is grounded, thus it is a quarter-wavelength resonator. In even-mode, the symmetry plane is considered an open circuit, therefore the resonator of one half of the circuit is open, making it a half-wavelength resonator. According to basic electromagnetic and microwave knowledge, the operating frequency of a half-wavelength resonator is twice that of a quarter-wavelength resonator. Therefore, in the single-path response of one half, the passband frequency of the odd mode is half that of the even mode. Thus, when the operating frequency is set at the passband frequency of the odd mode, the even mode can be considered not to propagate and not to transmit signals; therefore, the even-mode transmission coefficient = 0, and the reflection coefficient = -1.

[0046] To satisfy formula (2) for port matching, the propagation coefficient and reflection coefficient of the odd mode must be:

[0047] ;

[0048] This value is mainly achieved by changing the feed position and shape of the 50-ohm port in the resonant cavity. By continuously simulating and adjusting to select a suitable position and shape, a good match can be achieved. It can be seen that for any symmetrical four-port network, when one port is open-circuited, by analyzing only half of the circuit response through odd-even mode analysis, and by having the odd and even modes satisfy different transmission and reflection conditions, the differential response of ports 2 and 3, as well as the input matching of port 1, can be achieved.

[0049] The different transmission and reflection conditions mentioned here are specifically:

[0050] ;

[0051] Step 3, Design and layout of a single-passband filter balun based on a spatially coupled structure:

[0052] A four-port symmetrical layout design is used to draw the layout of a single-passband filter balun. This invention innovatively proposes a spatial coupling structure, by hollowing out a portion of the ground metal in the middle, allowing the microstrips of the upper and lower layers to couple through the central opening. Compared to the traditional planar coupling structure, this structure achieves a larger coupling coefficient, while the vertical manipulation on multi-layer PCBs provides greater design freedom. Single-passband and dual-passband filter baluns are designed using ADS (Advanced Design System) and HFSS (High Frequency Structure Simulator) tools to rationally select interlayer media and complete the layout. They exhibit excellent filtering characteristics and balun imbalance characteristics, and can be widely applied in RF wireless communication scenarios.

[0053] Figure 5 The diagram illustrates a single-passband filter balun according to an embodiment. Only the half-symmetric circuit is analyzed, and its response is a second-order filter response based on two coupled resonant cavities.

[0054] Step 4, Design and layout of a dual-passband filter balun based on a spatially coupled structure:

[0055] After verifying the function of the single-passband filter balun, a dual-passband filter balun was proposed to further verify the design applicability and freedom of this invention. The dual-passband response is achieved by adding two additional coupled resonant cavities. The additional resonant cavities are placed below the original single-passband resonant cavities, which can realize the topology of the dual-passband filter. The interlayer medium is reasonably selected and the layout is completed by using ADS and HFSS tools.

[0056] Figure 1 The diagram illustrates a dual-passband filter balun according to an exemplary embodiment. Only half of the symmetrical circuit is analyzed. Compared with the single-passband filter response, by adding a resonant cavity below each of the original two coupled resonant cavities to generate strong coupling, a dual-passband filter response based on four coupled resonant cavities can be achieved.

[0057] Step 5, Electromagnetic simulation verification:

[0058] Design and draw the layout according to the above requirements, complete the electromagnetic simulation of the layout, and plot the S-parameter curves to obtain the performance of the corresponding balun response. The simulation response of a single-passband filter balun is shown below. Figure 6 As shown, Figure 6 (a) in the figure represents the S-parameter response. Figure 6 (b) in the figure represents the phase difference and amplitude imbalance response. It can be seen that this single-pass filter balun exhibits a good second-order filtering response and excellent amplitude and phase imbalance responses. The simulated response of the dual-passband filter balun is shown below. Figure 7 As shown, Figure 7 (a) in the figure represents the S-parameter response. Figure 7 (b) in the figure represents the phase difference and amplitude imbalance response of the first passband. Figure 7 In the diagram, (c) represents the phase difference and amplitude imbalance response of the second passband. It can be seen that this dual-passband filter balun exhibits good filtering response and excellent amplitude and phase imbalance response.

[0059] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A dual-passband filter balun, characterized in that, include: The single-passband filter balun comprises, from top to bottom: a top microstrip, ground metal I, ground metal II, bottom microstrip and multiple metal vias; A first interlayer dielectric is disposed between the top microstrip and the ground metal I; a second interlayer dielectric is disposed between ground metal I and ground metal II; and a third interlayer dielectric is disposed between ground metal II and the bottom microstrip. Multiple metal vias penetrate from top to bottom through the top microstrip, the first interlayer dielectric, the ground metal I, the second interlayer dielectric, the ground metal II, the third interlayer dielectric, and the bottom microstrip. Windows of the same size are drilled at the center of ground metal I and ground metal II, and these windows are used for coupling between the top microstrip and the bottom microstrip. Both the top microstrip and the bottom microstrip are provided with two single-passband resonant cavities. The coupled resonant cavity R3 is set on the ground metal I below the single passband resonant cavity R1 in the top microstrip, and the coupled resonant cavity R4 is set on the ground metal I below the single passband resonant cavity R2 in the top microstrip; the coupled resonant cavity R3' is set on the ground metal II above the single passband resonant cavity R1' in the bottom microstrip, and the coupled resonant cavity R4' is set on the ground metal II above the single passband resonant cavity R2' in the bottom microstrip, thus obtaining a dual passband filter balun; The top microstrip also includes a first microstrip line, and the bottom microstrip also includes a second microstrip line and a third microstrip line. The single-passband resonator R1 and single-passband resonator R2 in the top microstrip are connected to the unbalanced port of the first microstrip line. The single-passband resonator R1' in the bottom microstrip is connected to the balanced port of the second microstrip line and the balanced port of the third microstrip line, respectively. The single-passband resonator R2' in the bottom microstrip is connected to the balanced port of the second microstrip line and the balanced port of the third microstrip line, respectively.

2. The dual-passband filter balun as described in claim 1, characterized in that, Both the first and third interlayer media are RT / duroid 5880 interlayer media materials made of polytetrafluoroethylene glass fiber reinforced material, with a thickness of 0.203 mm; The second interlayer medium is specifically a prepreg material RO 4450F with a thickness of 0.101 mm.

3. The dual-passband filter balun as described in claim 1, characterized in that, The widths of the first, second, and third microstrip lines are all 0.7 mm.

4. The dual-passband filter balun as described in claim 1, characterized in that, The radius of each of the multiple metal vias is 0.1 mm, and they are evenly distributed.

5. A dual-passband filter balun as described in claim 1, characterized in that, The single-passband resonator R1, R2, R1', and R2' in the top microstrip are dumbbell-shaped, while the coupled resonator R3, R4, R3', and R4' are C-shaped.

6. A dual-passband filter balun as described in claim 1, characterized in that, The single-passband filter balun operates at a center frequency of 2.9 GHz and a bandwidth of 400 MHz.

7. A dual-passband filter balun as described in claim 1, characterized in that, The center frequency of the first operating frequency band of the dual-passband filter balun is 2.1 GHz, and the bandwidth is 490 MHz; the center frequency of the second operating frequency band of the dual-passband filter balun is 3.05 GHz, and the bandwidth is 310 MHz.

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