Compact broadband balance band-pass filter based on strip line
By adopting a band-shaped line and multi-layer dielectric substrate structure in a broadband balance filter, combined with the centerline short-circuit coupled three-wire and half-wavelength resonator design, it is solved that the broadband balance filter is difficult to balance among multiple performance indicators in the prior art. The problem of this method realizes efficient broadband filtering response and common mode rejection, which is suitable for modern wireless communication systems.
Patent Information
- Application Number
- CN202411444885.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-16
- Publication Date
- 2024-12-10
AI Technical Summary
The existing broadband balance filter cannot achieve balance between the characteristics of simple structure, large working bandwidth, good matching performance of differential mode ports, high common mode rejection level in the broadband range, compact size and low production cost, which hinders its modernity. Application and promotion in wireless communication systems.
A compact broadband balanced bandpass filter based on band-shaped lines is designed, adopting a top-down multi-layer dielectric substrate structure, combining a coupling three-wire structure with a center line short circuit and a half-wavelength resonator to achieve wide-side coupling and Differential feed network, which improves coupling strength through dielectric board stacking and ground plate structure, uses short-circuit quarter-wavelength resonators to design differential feed networks to achieve high common mode rejection.
It has achieved low production cost, simple structure, large working bandwidth, good matching performance of differential mode ports, high common mode suppression level in the broadband range, and compact size. The relative bandwidth of 3-dB reaches 115%, and the common mode suppression reaches 30.9dB. The occupied area is only 0.21λg×0.36λg.
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Figure CN119108779A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of microwave passive devices, and in particular relates to a compact broadband balanced bandpass filter based on strip lines. Background Art
[0002] In recent years, the rapid development of modern wireless communication technology has led to an increasing demand for high-performance, low-cost, and miniaturized microwave devices. The electromagnetic environment of electronic equipment has also become increasingly complex, requiring more and more high-performance microwave filters to suppress frequency band interference and use balanced circuits to reduce environmental noise interference. In this context, balanced filters have shown significant advantages in environmental noise control, electromagnetic interference reduction, and crosstalk prevention between channels due to their efficient differential mode transmission and good common mode suppression characteristics, and have therefore become a hot topic in industry research. At the same time, in order to increase the data transmission rate, the bandwidth requirements of passive devices have also gradually increased. How to achieve broadband and high-performance balanced filters has become the current research goal.
[0003] Reference 1 (L. Yang and R. Gómez-García, “High-Order Quasi-Elliptic-Type Single-Ended and Balanced Wideband Bandpass Filters Using Microstrip-to-Microstrip Vertical Transitions,” IEEE Transactions on Circuits and Systems II: Express Briefs, vol. 70, no. 4, pp. 1425-1429, April 2023) proposes to design a ninth-order quasi-elliptic balanced broadband filter using a vertical transition structure. Since the vertical transition structure adopts a microstrip-slotline-microstrip structure, the balanced filter has an inherent common-mode suppression capability. Although the balanced filter achieves differential-mode transmission and common-mode suppression of a certain bandwidth, the final circuit layout is not compact and occupies a large area.
[0004] Reference 2 (Z.-A.Ouyang, L.Zhu and L.-L.Qiu, "Wideband Balanced Filters With Intrinsic Common-Mode Suppression on Coplanar Stripline-Based Multimode Resonators," IEEE Transactions on Circuits and Systems I: Regular Papers, vol.69, no.6, pp.2263-2275, June 2022) introduces two multimode resonators based on coplanar striplines, and designs a balanced broadband bandpass filter with multimode differential mode resonance and inherent common mode suppression. The circuit model is constructed by dualizing the open-circuit end and the short-circuit end. Although the in-band common mode suppression level of the designed balanced filter reaches more than 40dB, its excessive circuit size cannot be ignored.
[0005] Reference 3 (K.Aliqab and J.Hong, “UWB Balanced BPF Using a Low-Cost LCPBonded Multilayer PCB Technology,” IEEE Transactions on Microwave Theory and Techniques, vol.67, no.3, pp.1023-1029, March 2019) designed a miniaturized broadband balanced filter based on liquid crystal polymer technology, and adopted the concept of lateral signal interference to design the differential mode passband and common mode stopband. Although the circuit has the advantages of large operating bandwidth and small size, its differential mode impedance matching performance needs to be further improved, and the circuit processing technology is special and the cost is relatively high.
[0006] In summary, the core problem of current technology is that the broadband balanced filter cannot achieve a balance between the characteristics of simple structure, large operating bandwidth, good differential mode port matching performance, high common mode suppression level in the broadband range, compact size and low manufacturing cost, which hinders its application and promotion in modern wireless communication systems. Summary of the invention
[0007] In view of the deficiencies in the prior art, the present invention provides a stripline-based compact broadband balanced bandpass filter with simple structure, large operating bandwidth, good differential mode port matching performance, high common mode suppression level within a broadband range, compact size and low manufacturing cost.
[0008] The present invention provides the following technical solutions:
[0009] Provided is a stripline-based compact broadband balanced bandpass filter, comprising a first two-notch dielectric substrate, a first four-notch dielectric substrate, a second four-notch dielectric substrate, a third four-notch dielectric substrate, a fourth four-notch dielectric substrate, and a second two-notch dielectric substrate stacked from top to bottom;
[0010] The upper surface of the first two-notch dielectric substrate is provided with a first ground plate, and the lower surface is provided with a first differential input feed line and a second differential input feed line; the first differential input feed line includes a first 50Ω microstrip line guide strip, a first 50Ω stripline guide strip, a first quarter-wavelength coupled connecting line and a first quarter-wavelength open line connected in sequence; the second differential input feed line includes a second 50Ω microstrip line guide strip, a second 50Ω stripline guide strip, a first quarter-wavelength delay line and a first quarter-wavelength coupled open line connected in sequence;
[0011] A second grounding plate is provided between the second four-notch dielectric substrate and the third four-notch dielectric substrate; the second four-notch dielectric substrate is provided with a first quarter-wavelength short-circuit resonator, and the third four-notch dielectric substrate is provided with a second quarter-wavelength short-circuit resonator, and one end of the first quarter-wavelength short-circuit resonator and the second quarter-wavelength short-circuit resonator are respectively connected to the second grounding plate, and the other ends are connected through a metallized via passing through the second grounding plate;
[0012] The upper surface of the second two-notch dielectric substrate is provided with a first differential output feed line and a second differential output feed line, and the lower surface is provided with a third grounding plate.
[0013] Optionally, the first differential output feed line comprises a third 50Ω microstrip line guide strip, a third 50Ω stripline guide strip, a second quarter-wavelength coupled connection line, and a second quarter-wavelength open line connected in sequence;
[0014] The second differential output feed line includes a fourth 50Ω microstrip line guide strip, a fourth 50Ω stripline guide strip, a second quarter-wavelength delay line, and a second quarter-wavelength coupled open-ended line which are connected in sequence.
[0015] Optionally, the first 50Ω microstrip line guide strip, the first 50Ω stripline guide strip and the first quarter-wavelength coupled connecting line are arranged in an L-shaped bending layout; the first quarter-wavelength coupled connecting line and the first quarter-wavelength open line are arranged in an S-shaped bending layout;
[0016] Therefore, the first quarter-wavelength delay line and the first quarter-wavelength coupled open line are arranged in an S-shaped bending pattern;
[0017] The second quarter-wavelength coupled connecting line and the second quarter-wavelength open line are arranged in an S-shaped bending pattern;
[0018] The second quarter-wavelength delay line and the second quarter-wavelength coupled open line are arranged in a U-shaped bend.
[0019] Optionally, the first quarter-wavelength short-circuit resonator comprises a first quarter-wavelength transmission line, and a first grounded short-circuit post and a first metallized via respectively located at two ends thereof;
[0020] The second quarter-wavelength short-circuit resonator comprises a second quarter-wavelength transmission line, and a second ground short-circuit post and a second metallized via respectively located at two ends thereof; the first metallized via and the second metallized via are opposite to each other; the second ground plate is provided with a square groove facing the first metallized via and the second metallized via;
[0021] The first quarter-wavelength transmission line and the second quarter-wavelength transmission line are both L-shaped and parallel to each other.
[0022] Optionally, the first quarter-wavelength coupled connecting line and the first quarter-wavelength coupled open-circuit line are spaced and parallel to each other; the first quarter-wavelength coupled connecting line and the first quarter-wavelength coupled open-circuit line are symmetrical with respect to the central axis of the L-shaped long side of the first quarter-wavelength transmission line; the signal input end of the first quarter-wavelength coupled connecting line, the open-circuit end of the first quarter-wavelength coupled open-circuit line, and the short-circuit end of the first quarter-wavelength short-circuit resonator are aligned vertically;
[0023] The second quarter-wavelength coupled connecting line and the second quarter-wavelength coupled open-circuit line are spaced apart and parallel to each other; the second quarter-wavelength coupled connecting line and the second quarter-wavelength coupled open-circuit line are symmetrical with respect to the central axis of the L-shaped long side of the second quarter-wavelength transmission line; the signal input end of the second quarter-wavelength coupled connecting line, the open end of the second quarter-wavelength coupled open-circuit line and the short-circuit end of the second quarter-wavelength short-circuit resonator are aligned vertically.
[0024] Optionally, the two notches of the first two-notch dielectric substrate are located at two adjacent sides, respectively, and expose the third 50Ω microstrip line guide strip and the fourth 50Ω microstrip line guide strip, respectively;
[0025] The two notches of the second two-notch dielectric substrate are located at two opposite sides, respectively, and expose the first 50Ω microstrip line guide strip and the second 50Ω microstrip line guide strip, respectively;
[0026] The four notches of the first four-notch dielectric substrate, the second four-notch dielectric substrate, the third four-notch dielectric substrate and the fourth four-notch dielectric substrate are aligned vertically, and the four notches respectively expose the first 50Ω microstrip line guide strip, the second 50Ω microstrip line guide strip, the third 50Ω microstrip line guide strip and the fourth 50Ω microstrip line guide strip.
[0027] Optionally, the widths of the first quarter-wavelength coupled connection line, the second quarter-wavelength coupled connection line, the first quarter-wavelength coupled open line, and the second quarter-wavelength coupled open line are all the same.
[0028] Optionally, the distance between the first quarter-wavelength coupled connection line and the first quarter-wavelength coupled open line is the same as the distance between the second quarter-wavelength coupled connection line and the second quarter-wavelength coupled open line.
[0029] Optionally, the first quarter-wavelength open line and the second quarter-wavelength open line have the same size and a length of one quarter-wavelength at the center frequency; the first quarter-wavelength delay line and the second quarter-wavelength delay line have a length of one quarter-wavelength at the center frequency.
[0030] Optionally, the first two-notch dielectric substrate, the first four-notch dielectric substrate, the second four-notch dielectric substrate, the third four-notch dielectric substrate, the fourth four-notch dielectric substrate and the second two-notch dielectric substrate are all rectangular; the first grounding plate has the same shape as the first two-notch dielectric substrate, the second grounding plate has the same shape as the second four-notch dielectric substrate, and the third grounding plate has the same shape as the second two-notch dielectric substrate.
[0031] Compared with the prior art, the present invention has the following beneficial effects:
[0032] (1) Low production cost and simple structure: The present invention uses PCB boards to make each layer of circuits and uses screw packaging to facilitate processing and integration;
[0033] (2) Large working bandwidth: The present invention adopts a coupled three-wire structure with a short-circuited center line, and utilizes a dielectric plate stack and a ground plate structure to realize a wide-side coupling structure in the form of a stripline, thereby improving the coupling strength and achieving a broadband filtering response. The 3-dB relative bandwidth of the example simulation can reach 115%.
[0034] (3) Good differential mode port matching characteristics: The present invention adopts a stripline form to realize the wide side coupling of the coupled three-wire structure, and realizes an in-band return loss of less than -17dB.
[0035] (4) High common-mode suppression level within a broadband range: The present invention designs a differential feeding network by feeding a short-circuited quarter-wavelength resonator with a half-wavelength resonator. By minimizing the coupling electric field of the short-circuited quarter-wavelength resonator during common-mode excitation, a common-mode suppression of 30.9 dB is achieved, and the relative bandwidth reaches 180%.
[0036] (5) Compact size: The present invention adopts a 6-layer dielectric design, and the main structure adopts a wide-side coupled stripline, which is compact in size, and the main circuit occupies an area of only 0.21λ g ×0.36λg . BRIEF DESCRIPTION OF THE DRAWINGS
[0037] Figure 1 It is a schematic diagram of the overall structure of a compact wideband balanced bandpass filter based on striplines of the present invention.
[0038] Figure 2 is a plan view of each layer of the circuit of the present invention, wherein Figure 2 (a) is the plane diagram of the input feeder circuit layer. Figure 2 (b) is the plan view of the first coupling port feeder layer. Figure 2 (c) is the second ground plane diagram, Figure 2 (d) is the plan view of the second coupling port feeder layer. Figure 2 (e) in the figure is the plan view of the output feeder circuit layer.
[0039] Figure 3 It is a schematic diagram of the structure size of each layer of circuits of the present invention, Figure 3 (a) is the input feeder circuit layer structure dimension diagram. Figure 3 (b) is the structural dimension diagram of the first coupling port feeder layer. Figure 3 (c) is the structural dimension diagram of the second grounding plate. Figure 3 (d) is the structural dimension diagram of the second coupling port feeder layer. Figure 3 (e) in the figure is the structural dimension diagram of the output feeder circuit layer.
[0040] Figure 4 It is a mixed mode S parameter simulation diagram of the broadband balanced bandpass filter in a specific example of the present invention.
[0041] In the figure, the symbols are: 1 is the first differential input feed line, 11 is the first 50Ω microstrip line guide strip, 12 is the first 50Ω stripline guide strip, 13 is the first quarter-wavelength coupled connection line, and 14 is the first quarter-wavelength open line;
[0042] 2 is a second differential input feed line, 21 is a second 50Ω microstrip line guide strip, 22 is a second 50Ω stripline guide strip, 23 is a first quarter-wavelength delay line, and 24 is a first quarter-wavelength coupled open-ended line;
[0043] 3 is a first quarter-wavelength short-circuit resonator, 31 is a first grounded short-circuit post, 32 is a first quarter-wavelength transmission line, and 33 is a first metallized via hole;
[0044] 4 is a second quarter-wavelength short-circuit resonator, 41 is a second grounded short-circuit post, 42 is a second quarter-wavelength transmission line, and 43 is a second metallized via hole;
[0045] 5 is a first differential output feed line, 51 is a third 50Ω microstrip line guide strip, 52 is a third 50Ω stripline guide strip, 53 is a second quarter-wavelength coupled connection line, and 54 is a second quarter-wavelength open line;
[0046] 6 is a second differential output feed line, 61 is a fourth 50Ω microstrip line guide strip, 62 is a fourth 50Ω stripline guide strip, 63 is a second quarter-wavelength delay line, and 64 is a second quarter-wavelength coupled open-ended line;
[0047] 7 is a first grounding plate, 8 is a second grounding plate, 80 is a square groove, and 9 is a third grounding plate;
[0048] 71 is a first two-notch dielectric substrate, 72 is a first four-notch dielectric substrate, 73 is a second four-notch dielectric substrate, 81 is a third four-notch dielectric substrate, 82 is a fourth four-notch dielectric substrate, and 83 is a second two-notch dielectric substrate. DETAILED DESCRIPTION
[0049] The present invention will now be described in further detail with reference to the accompanying drawings.
[0050] It should be noted that the terms such as "upper", "lower", "left", "right", "front", "back", etc. cited in the invention are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.
[0051] like Figure 1 and 2 As shown, a compact broadband balanced bandpass filter based on striplines is provided, comprising a first differential input feedline 1, a second differential input feedline 2, a first quarter-wavelength short-circuit resonator 3, a second quarter-wavelength short-circuit resonator 4, a first differential output feedline 5, a second differential output feedline 6, a first grounding plate 7, a second grounding plate 8, a third grounding plate 9, a first two-notch dielectric substrate 71, a first four-notch dielectric substrate 72, a second four-notch dielectric substrate 73, a third four-notch dielectric substrate 81, a fourth four-notch dielectric substrate 82 and a second two-notch dielectric substrate 83.
[0052] The first two-notch dielectric substrate 71 , the first four-notch dielectric substrate 72 , the second four-notch dielectric substrate 73 , the third four-notch dielectric substrate 81 , the fourth four-notch dielectric substrate 82 and the second two-notch dielectric substrate 83 are all rectangular and are stacked from top to bottom to form a six-layer PCB board.
[0053] The first differential input feed line 1 and the second differential input feed line 2 are arranged on the lower surface of the first two-notch dielectric substrate 71 , and the first grounding plate 7 is arranged on the upper surface of the first two-notch dielectric substrate 71 .
[0054] The first differential input feed line 1 comprises a first 50Ω microstrip line guide strip 11 , a first 50Ω stripline guide strip 12 , a first quarter-wavelength coupled connection line 13 and a first quarter-wavelength open line 14 which are connected in sequence.
[0055] Specifically, one end of the first 50Ω microstrip line guide strip 11 is located at the edge of the long side of the first two-notch dielectric substrate 71 as the first input end, and the other end is connected to one end of the first 50Ω stripline guide strip 12. The other end of the first 50Ω stripline guide strip 12 is connected to the first quarter-wavelength coupling connection line 13. The first 50Ω microstrip line guide strip 11 and the first 50Ω stripline guide strip 12 are arranged in a straight line, and the first 50Ω microstrip line guide strip 11, the first 50Ω stripline guide strip 12 and the first quarter-wavelength coupling connection line 13 are arranged in an L-shaped bend; the end of the first quarter-wavelength coupling connection line 13 is connected to the signal input end of the first quarter-wavelength open line 14, and the layout of the first quarter-wavelength coupling connection line 13 and the first quarter-wavelength open line 14 is S-shaped bend to reduce the area.
[0056] The second differential input feed line 2 comprises a second 50Ω microstrip line guide strip 21 , a second 50Ω stripline guide strip 22 , a first quarter-wavelength delay line 23 and a first quarter-wavelength coupled open line 24 which are connected in sequence.
[0057] Specifically, one end of the second 50Ω microstrip line guide strip 21 is located as the second input end at the edge of the other long side of the first two-notch dielectric substrate 71, and the long side has a rectangular notch. The other end of the second 50Ω microstrip line guide strip 21 is connected to one end of the second 50Ω stripline guide strip 22. The other end of the second 50Ω stripline guide strip 22 is connected to the first quarter-wavelength delay line 23. The end of the first quarter-wavelength delay line 23 is connected to the input end of the first quarter-wavelength coupled open line 24. The first quarter-wavelength coupled open line 24 is a straight line. The layout of the first quarter-wavelength delay line 23 and the first quarter-wavelength coupled open line 24 is S-shaped to reduce the area.
[0058] The first quarter-wavelength short-circuit resonator 3 is arranged on the upper surface of the second four-notch dielectric substrate 73, and the second grounding plate 8 is arranged on the lower surface of the second four-notch dielectric substrate 73; the second quarter-wavelength short-circuit resonator 4 is arranged on the lower surface of the third four-notch dielectric substrate 81; one end of the first quarter-wavelength short-circuit resonator 3 and the second quarter-wavelength short-circuit resonator 4 are both connected to the second grounding plate 8, and the other end is connected through a metallized via passing through the second grounding plate 8.
[0059] Specifically, the first quarter-wavelength short-circuit resonator 3 includes a first grounded short-circuit column 31 , a quarter-wavelength transmission line 32 and a first metallized via 33 ; the first quarter-wavelength short-circuit resonator 4 includes a second grounded short-circuit column 41 , a quarter-wavelength transmission line 42 and a second metallized via 43 .
[0060] The first quarter-wavelength short-circuit resonator 3 and the second quarter-wavelength short-circuit resonator 4 are connected through the first metallized via 33 and the second metallized via 43; the first metallized via 33 and the second metallized via 43 are connected through the square groove 80 in the second grounding plate 8 to avoid contact with the second grounding plate 8; the square groove 80 is a through hole, and the connection method of the first metallized via 33 and the second metallized via 43 refers to the prior art.
[0061] Furthermore, the first quarter-wavelength transmission line 32 and the second quarter-wavelength transmission line 42 are both L-shaped and parallel to each other. The L-shaped long side terminal of the first quarter-wavelength short-circuit resonator 3 is connected to the second ground plate 8 through the first ground short-circuit column 31, and the L-shaped short side terminal is connected to the first metallized via 33. The L-shaped long side terminal of the second quarter-wavelength short-circuit resonator 4 is connected to the second ground plate 8 through the second ground short-circuit column 41, and the L-shaped short side terminal is connected to the second metallized via 43.
[0062] The first differential output feeder 5 and the second differential output feeder 6 are arranged on the upper surface of the second two-notch dielectric substrate 83, and the third grounding plate 9 is arranged on the lower surface of the second two-notch dielectric substrate 83. The connection method of the grounding plate and the dielectric substrate of the present invention refers to the prior art.
[0063] The first differential output feed line 5 comprises a third 50Ω microstrip line guide strip 51 , a third 50Ω stripline guide strip 52 , a second quarter-wavelength coupled connection line 53 and a second quarter-wavelength open line 54 which are connected in sequence.
[0064] Specifically, one end of the third 50Ω microstrip line guide strip 51 is located at the edge of the short side of the second two-notch dielectric substrate 83 as the first output end, and the other end is connected to the third 50Ω stripline guide strip 52. The other end of the third 50Ω stripline guide strip 52 is connected to the second quarter-wavelength coupled connecting line 53. The end of the second quarter-wavelength coupled connecting line 53 is connected to the signal input end of the second quarter-wavelength open line 54. The third 50Ω microstrip line guide strip 51, the third 50Ω stripline guide strip 52 and the second quarter-wavelength coupled connecting line 53 are arranged in a straight line, and the second quarter-wavelength coupled connecting line 53 and the second quarter-wavelength open line 54 are arranged in an S-shaped bend to reduce the area.
[0065] The second differential output feed line 6 includes a fourth 50Ω microstrip line guide strip 61 , a fourth 50Ω stripline guide strip 62 , a second quarter-wavelength delay line 63 and a second quarter-wavelength coupled open line 64 which are connected in sequence.
[0066] Specifically, one end of the fourth 50Ω microstrip line guide strip 61 is located as the second output end at the edge of the long side of the second two-notch dielectric substrate 83, and the long side has a rectangular notch. The other end of the fourth 50Ω microstrip line guide strip 61 is connected to the fourth 50Ω stripline guide strip 62, and the other end of the fourth 50Ω stripline guide strip 62 is connected to the second quarter-wavelength delay line 63. The end of the second quarter-wavelength delay line 63 is connected to the input end of the second quarter-wavelength coupled open line 64. The fourth 50Ω microstrip line guide strip 61 and the fourth 50Ω stripline guide strip 62 are arranged in a straight line, the second quarter-wavelength coupled open line 64 is a straight line, and the second quarter-wavelength delay line 63 and the second quarter-wavelength coupled open line 64 are arranged in a U-shaped bend to reduce the area.
[0067] During operation, a pair of differential signals are inputted by the first differential input feeder 1 and the second differential input feeder 2 respectively, and are coupled through the upper and lower layer wide sides to excite the first quarter-wavelength short-circuit resonator 3 to generate resonance, and are then coupled to the second quarter-wavelength short-circuit resonator 4 through the first metallized via 33 and the second metallized via 43, and are then transmitted to the first differential output feeder 5 and the second differential output feeder 6 for output through the upper and lower layer wide sides. When a common-mode signal is inputted, equal-amplitude and anti-phase signals are transmitted on the first quarter-wavelength coupled connecting line 13 and the first quarter-wavelength coupled open line 24, so that the superposition of the signals on the first quarter-wavelength resonator 3 is ideally zero, thereby obtaining a high level of common-mode suppression.
[0068] Furthermore, in this embodiment, the two notches of the first two-notch dielectric substrate 71 are located at two adjacent sides, respectively, and the third 50Ω microstrip line conductive strip 51 and the fourth 50Ω microstrip line conductive strip 61 are exposed respectively; the two notches of the second two-notch dielectric substrate 83 are located at two opposite sides, respectively, and the first 50Ω microstrip line conductive strip 11 and the second 50Ω microstrip line conductive strip 21 are exposed respectively.
[0069] The four notches of the first four-notch dielectric substrate 72, the second four-notch dielectric substrate 73, the third four-notch dielectric substrate 81, and the fourth four-notch dielectric substrate 82 are aligned vertically, and the four notches respectively expose the first 50Ω microstrip line guide strip 11, the second 50Ω microstrip line guide strip 21, the third 50Ω microstrip line guide strip 51, and the fourth 50Ω microstrip line guide strip 61.
[0070] As an embodiment, the first quarter-wavelength coupled connecting line 13 and the first quarter-wavelength coupled open line 24 are spaced apart and parallel to each other; the first quarter-wavelength coupled connecting line 13 and the first quarter-wavelength coupled open line 24 are symmetrical with respect to the central axis of the L-shaped long side of the first quarter-wavelength transmission line 32; the signal input end of the first quarter-wavelength coupled connecting line 13, the open end of the first quarter-wavelength coupled open line 24 and the short-circuit end of the first quarter-wavelength short-circuit resonator 3 are aligned up and down.
[0071] The second quarter-wavelength coupling connection line 53 and the second quarter-wavelength coupling open line 64 are arranged at intervals and parallel to each other; the second quarter-wavelength coupling connection line 53 and the second quarter-wavelength coupling open line 64 are symmetrical with respect to the central axis of the L-shaped long side of the second quarter-wavelength transmission line 42; the signal input end of the second quarter-wavelength coupling connection line 53, the open end of the second quarter-wavelength coupling open line 64 and the short-circuit end of the second quarter-wavelength short-circuit resonator 4 are aligned up and down.
[0072] Furthermore, in this embodiment, the widths of the first quarter-wavelength coupled connecting line 13, the second quarter-wavelength coupled connecting line 53, the first quarter-wavelength coupled open line 24 and the second quarter-wavelength coupled open line 64 are all the same; changing the width can change the strength of the feeding, thereby controlling the bandwidth and impedance matching of the passband; the widths of the first quarter-wavelength short-circuit resonator 3 and the second quarter-wavelength short-circuit resonator 4 determine the coupling strength, and changing the width can also adjust the impedance matching of the differential mode response.
[0073] Further in this embodiment, the distance between the first quarter-wavelength coupling connection line 13 and the first quarter-wavelength coupling open line 24 is the same as the distance between the second quarter-wavelength coupling connection line 53 and the second quarter-wavelength coupling open line 64, which affects the coupling area of the broadside coupling line.
[0074] Furthermore, in the present embodiment, the first quarter-wavelength open line 14 and the second quarter-wavelength open line 54 have the same size, and the width affects the impedance matching at the passband edge, and the length is approximately one quarter wavelength at the center frequency, which can be used to fine-tune the common mode suppression level within the passband; the width of the first quarter-wavelength delay line 23 and the second quarter-wavelength delay line 63 affects the impedance matching level of the entire passband, and the length is approximately one quarter wavelength at the center frequency, which can also be used to fine-tune the common mode suppression level within the passband.
[0075] The present invention processes and corrodes the metal surface on the front of the circuit substrate through the printed circuit board manufacturing process to form the required metal pattern, and realizes metallized vias through the copper plating process. The structure is compact, and the six-layer PCB board can be assembled by screws, and the production cost is low. At the same time, the wide-side coupled three-wire structure is used as the main structure, so that this broadband balanced bandpass filter has broadband frequency selection characteristics, broadband high-level common-mode suppression, high-level signal transmission effect and compact design size. The present invention has a simple structure, a large working bandwidth, good differential mode port matching performance, a high common-mode suppression level in a broadband range, a compact size, and a low manufacturing cost, and is suitable for modern wireless communication systems.
[0076] A specific example of a compact broadband balanced bandpass filter based on striplines is provided, wherein the dielectric plate model of the first two-notch dielectric substrate 71, the second four-notch dielectric substrate 73, the third four-notch dielectric substrate 81, and the second two-notch dielectric substrate 83 is Rogers 5880, with a relative dielectric constant of 2.2, a loss tangent value of 0.0009, and a thickness of 0.508 mm; the dielectric plate model of the first four-notch dielectric substrate 72 and the fourth four-notch dielectric substrate 82 is Rogers 5880, with a relative dielectric constant of 2.2, a loss tangent value of 0.0009, and a thickness of 0.13 mm.
[0077] Combination Figure 3 , the size parameters of the broadband balanced bandpass filter are as follows: W 11 =1.42mm, L 11 =4.5mm, W 12 =0.9mm, L 12 =4.5mm, W 13 =0.4mm, L 13 =20.5mm, W 14 =3mm, L 14 =26.5mm, W 24 =0.4mm,W 23 =1mm, L 23 =25.95mm, W 21 =0.9mm, L 21 =4mm, W3=1.2mm, L 32 =25.1mm, L 33 =2.5mm, W4=1.2mm, L 42 =25.1mm, L 43 =2.5mm, S1 = 0.3mm, the radius of all metallized vias is R1 = 0.15mm, and the width of the notch of all dielectric substrates is W slot =5mm, length is L slot=4.5mm, the total area of the broadband balanced bandpass filter excluding the 50Ω microstrip line guide is 16.6×29.1mm 2 , the final circuit layout occupies an area of about 0.21λ g ×0.36λ g , where λ g is the guided wavelength corresponding to the passband center frequency.
[0078] The broadband balanced bandpass filter in this example is modeled and simulated in the electromagnetic simulation software ANSYS EM Suite 21.1. Figure 4 This is the S parameter simulation diagram of the broadband balanced bandpass filter in this example. Figure 4 It can be seen that the passband center frequency of the broadband balanced bandpass filter is 2.52 GHz, the in-band common mode suppression level is higher than 32.5 dB, the in-band return loss is less than -16.9 dB, the 3-dB relative bandwidth is 115%, the insertion loss is lower than 0.6 dB, and there are four resonant poles in the passband, which makes the broadband balanced bandpass filter in this example have good flatness characteristics in the passband.
[0079] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.
Claims
1. A compact broadband balanced bandpass filter based on stripline, characterized in that: It comprises a first two-notch dielectric substrate (71), a first four-notch dielectric substrate (72), a second four-notch dielectric substrate (73), a third four-notch dielectric substrate (81), a fourth four-notch dielectric substrate (82) and a second two-notch dielectric substrate (83) which are stacked from top to bottom; The first two-notch dielectric substrate (71) is provided with a first grounding plate (7) on its upper surface, and a first differential input feeder (1) and a second differential input feeder (2) on its lower surface; the first differential input feeder (1) comprises a first 50Ω microstrip line guide strip (11), a first 50Ω stripline guide strip (12), a first quarter-wavelength coupled connecting line (13), and a first quarter-wavelength open line (14) connected in sequence; the second differential input feeder (2) comprises a second 50Ω microstrip line guide strip (21), a second 50Ω stripline guide strip (22), a first quarter-wavelength delay line (23), and a first quarter-wavelength coupled open line (24) connected in sequence; A second grounding plate (8) is arranged between the second four-notch dielectric substrate (73) and the third four-notch dielectric substrate (81); the second four-notch dielectric substrate (73) is provided with a first quarter-wavelength short-circuit resonator (3), and the third four-notch dielectric substrate (81) is provided with a second quarter-wavelength short-circuit resonator (4); one end of the first quarter-wavelength short-circuit resonator (3) and the second quarter-wavelength short-circuit resonator (4) are respectively connected to the second grounding plate (8), and the other ends are connected through a metallized via that passes through the second grounding plate (8); The upper surface of the second two-notch dielectric substrate (83) is provided with a first differential output feeder line (5) and a second differential output feeder line (6), and the lower surface is provided with a third grounding plate (9).
2. The stripline-based compact broadband balanced bandpass filter according to claim 1, characterized in that: The first differential output feed line (5) comprises a third 50Ω microstrip line guide strip (51), a third 50Ω stripline guide strip (52), a second quarter-wavelength coupled connection line (53) and a second quarter-wavelength open line (54) which are connected in sequence; The second differential output feed line (6) comprises a fourth 50Ω microstrip line guide strip (61), a fourth 50Ω stripline guide strip (62), a second quarter-wavelength delay line (63) and a second quarter-wavelength coupled open line (64) which are connected in sequence.
3. The stripline-based compact broadband balanced bandpass filter according to claim 2, characterized in that: The first 50Ω microstrip line guide strip (11), the first 50Ω stripline guide strip (12) and the first quarter-wavelength coupling connection line (13) are arranged in an L-shaped bending pattern; the first quarter-wavelength coupling connection line (13) and the first quarter-wavelength open line (14) are arranged in an S-shaped bending pattern; Therefore, the first quarter-wavelength delay line (23) and the first quarter-wavelength coupling open line (24) are arranged in an S-shaped bending pattern; The second quarter-wavelength coupling connection line (53) and the second quarter-wavelength open line (54) are arranged in an S-shaped bending pattern; The second quarter-wavelength delay line (63) and the second quarter-wavelength coupling open line (64) are arranged in a U-shaped bending pattern.
4. The stripline-based compact broadband balanced bandpass filter according to claim 2, characterized in that: The first quarter-wavelength short-circuit resonator (3) comprises a first quarter-wavelength transmission line (32), and a first grounded short-circuit column (31) and a first metallized via (33) respectively located at two ends thereof; The second quarter-wavelength short-circuit resonator (4) comprises a second quarter-wavelength transmission line (42), and a second ground short-circuit column (41) and a second metallized via (43) respectively located at two ends thereof; the first metallized via (33) and the second metallized via (43) are opposite to each other; the second ground plate (8) is provided with a square groove (80) facing the first metallized via (33) and the second metallized via (43); The first quarter-wavelength transmission line (32) and the second quarter-wavelength transmission line (42) are both L-shaped and parallel to each other.
5. The stripline-based compact broadband balanced bandpass filter according to claim 4, characterized in that: The first quarter-wavelength coupled connecting line (13) and the first quarter-wavelength coupled open line (24) are spaced apart and parallel to each other; the first quarter-wavelength coupled connecting line (13) and the first quarter-wavelength coupled open line (24) are symmetrical with respect to the central axis of the L-shaped long side of the first quarter-wavelength transmission line (32); the signal input end of the first quarter-wavelength coupled connecting line (13), the open end of the first quarter-wavelength coupled open line (24) and the short-circuit end of the first quarter-wavelength short-circuit resonator (3) are aligned vertically; The second quarter-wavelength coupled connecting line (53) and the second quarter-wavelength coupled open line (64) are spaced apart and parallel to each other; the second quarter-wavelength coupled connecting line (53) and the second quarter-wavelength coupled open line (64) are symmetrical with respect to the central axis of the L-shaped long side of the second quarter-wavelength transmission line (42); the signal input end of the second quarter-wavelength coupled connecting line (53), the open end of the second quarter-wavelength coupled open line (64) and the short-circuit end of the second quarter-wavelength short-circuit resonator (4) are aligned vertically.
6. The stripline-based compact broadband balanced bandpass filter according to claim 2, characterized in that: The two notches of the first two-notch dielectric substrate (71) are located at two adjacent sides, respectively, and expose a third 50Ω microstrip line guide strip (51) and a fourth 50Ω microstrip line guide strip (61) respectively; The two notches of the second two-notch dielectric substrate (83) are located at two opposite sides, respectively, and expose the first 50Ω microstrip line guide strip (11) and the second 50Ω microstrip line guide strip (21) respectively; The four notches of the first four-notch dielectric substrate (72), the second four-notch dielectric substrate (73), the third four-notch dielectric substrate (81), and the fourth four-notch dielectric substrate (82) are aligned vertically, and the four notches respectively expose a first 50Ω microstrip line guide strip (11), a second 50Ω microstrip line guide strip (21), a third 50Ω microstrip line guide strip (51), and a fourth 50Ω microstrip line guide strip (61).
7. The stripline-based compact broadband balanced bandpass filter according to claim 2, characterized in that: The widths of the first quarter-wavelength coupled connection line (13), the second quarter-wavelength coupled connection line (53), the first quarter-wavelength coupled open line (24) and the second quarter-wavelength coupled open line (64) are all the same.
8. The stripline-based compact broadband balanced bandpass filter according to claim 2, characterized in that: The distance between the first quarter-wavelength coupling connection line (13) and the first quarter-wavelength coupling open line (24) is the same as the distance between the second quarter-wavelength coupling connection line (53) and the second quarter-wavelength coupling open line (64).
9. The stripline-based compact broadband balanced bandpass filter according to claim 2, characterized in that: The first quarter-wavelength open line (14) and the second quarter-wavelength open line (54) have the same size and both have a length of one quarter of a wavelength at the center frequency; the first quarter-wavelength delay line (23) and the second quarter-wavelength delay line (63) both have a length of one quarter of a wavelength at the center frequency.
10. The stripline-based compact broadband balanced bandpass filter according to claim 1, characterized in that: The first two-notch dielectric substrate (71), the first four-notch dielectric substrate (72), the second four-notch dielectric substrate (73), the third four-notch dielectric substrate (81), the fourth four-notch dielectric substrate (82) and the second two-notch dielectric substrate (83) are all rectangular; the first grounding plate (7) has the same shape as the first two-notch dielectric substrate (71); the second grounding plate (8) has the same shape as the second four-notch dielectric substrate (73); and the third grounding plate (9) has the same shape as the second two-notch dielectric substrate (83).