A planar compact dual-mode dual-passband balun filter

Abstract

This application discloses a planar compact dual-mode dual-passband balun filter, belonging to the field of radio frequency filtering circuit technology. It includes: a rectangular dielectric substrate with a metal ground plane on its lower surface and an input feed line, two stub-loaded dual-even-mode resonators, and two differential output feed lines on its upper surface; the non-short-circuited ends of the first short-circuited resonator and the second short-circuited resonator of the first stub-loaded dual-even-mode resonator are connected to the input terminal of the first open-circuited resonator; the non-short-circuited ends of the third short-circuited resonator and the fourth short-circuited resonator of the second stub-loaded dual-even-mode resonator are connected to the input terminal of the second open-circuited resonator; the first short-circuited resonator is parallel coupled to the input feed line; the second short-circuited resonator is parallel coupled to the fourth short-circuited resonator; and the third short-circuited resonator is three-wire parallel coupled to the two differential output feed lines. This application is based on a single-layer planar circuit design, resulting in a compact size, low manufacturing cost, wide dual-passband frequency spacing, and good selectivity.

Description

Technical Field

[0001] This utility model belongs to the field of radio frequency filter circuit design technology, specifically relating to a planar compact dual-mode dual-passband balun filter. Background Technology

[0002] A balun filter is a radio frequency (RF) device that integrates filtering and balanced-to-unbalanced signal conversion functions, and is widely used in wireless communication, radar, satellite communication, and other fields. As modern communication systems increasingly demand high performance and high integration, traditional discrete filters and balun devices often struggle to meet both space and performance requirements. Furthermore, to enhance wireless signal coverage and increase communication data capacity, dual-band communication has become an economical and effective means. Therefore, functionally integrated dual-passband balun filters with frequency selectivity and good balance characteristics have become one of the urgent needs of RF front-end systems in the communication field.

[0003] Currently, dual-mode dual-passband balun filters designed using suspended stripline structures to excite dielectric resonators achieve independent control of internal and external coupling, thus allowing for flexible control of the dual-passband filter response. However, the three-dimensional dielectric resonator structure employed in this design is not conducive to integration into planar circuit systems. While existing dual-passband balun filters designed using co-directional split-ring resonators achieve good frequency selectivity and a relatively compact size, the narrow stopband width between the two passbands makes them unsuitable for wide-ratio dual-passband systems. Utility Model Content

[0004] This invention addresses the shortcomings of existing technologies by providing a planar compact dual-mode dual-passband balun filter. Based on a single-layer planar circuit design, it features a compact size, low manufacturing cost, wide dual-passband frequency spacing, good selectivity, good amplitude and phase deviation, and good input port matching characteristics.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A planar compact dual-mode dual-passband balun filter includes: a rectangular dielectric substrate with a complete metal ground plane on its lower surface and an input feed line, a first stub-loaded dual-even-mode resonator, a second stub-loaded dual-even-mode resonator, a first differential output feed line, and a second differential output feed line on its upper surface; The first stub-loaded dual-even-mode resonator includes a first short-circuit resonator, a second short-circuit resonator, and a first open-circuit resonator; wherein, one end of the first short-circuit resonator is short-circuited through a first metallized via, one end of the second short-circuit resonator is short-circuited through a second metallized via, and the other ends of the first short-circuit resonator and the second short-circuit resonator are connected to the input terminal of the first open-circuit resonator. The second stub-loaded dual-mode resonator includes a third short-circuit resonator, a fourth short-circuit resonator, and a second open-circuit resonator; wherein, one end of the third short-circuit resonator is short-circuited through a third metallized via, and one end of the third short-circuit resonator is short-circuited through a fourth metallized via, and the other ends of the third short-circuit resonator and the fourth short-circuit resonator are connected to the input terminal of the second open-circuit resonator. The first short-circuit resonator is placed parallel to the input feed line, forming parallel coupling; the second short-circuit resonator and the fourth short-circuit resonator are placed parallel to each other, forming parallel coupling; the third short-circuit resonator is located in the middle of the first differential output feed line and the second differential output feed line in a parallel manner, forming three-line parallel coupling.

[0006] Optionally, the input feed line includes a first 50Ω microstrip line conductor, a dual-line coupled feed line, and an input open-circuit loading line connected in sequence. The first differential output feed line includes a second 50Ω microstrip line conductor, a phase delay line, and a three-wire coupled open-circuit feed line connected in sequence; The second differential output feed line includes a third 50Ω microstrip line conductor, a three-wire coupling feed line, and an output open-circuit loading line connected in sequence.

[0007] Optionally, the dual-wire coupled feeder is placed parallel to the first short-circuit resonator; the third short-circuit resonator is located between the three-wire coupled open-circuit feeder and the three-wire coupled feeder, and they are parallel to each other.

[0008] Optionally, the first metallized via is located near the connection surface between the dual-wire coupled feed line and the first 50Ω microstrip line conductor, and the second metallized via is located near the input end of the second open-circuit resonator. The third metallized via is close to the open end face of the three-wire coupled open-circuit feeder; the fourth metallized via is close to the input end of the first terminal open-circuit resonator; The open end face of the three-wire coupled open-circuit feeder is close to the connection surface between the third 50Ω microstrip line conductor and the three-wire coupled feeder.

[0009] Optionally, the first open-circuit resonator has an L-shaped bend, the second short-circuit resonator has a U-shaped bend, and the fourth short-circuit resonator has a U-shaped bend. Optionally, the first 50Ω microstrip line conductor and the dual-line coupled feed line are arranged in an L-shaped bend; the L-shaped input open-circuit loading line and the dual-line coupled feed line are arranged in a U-shaped bend. The phase delay line has an L-shaped bend, with one arm of the bend perpendicular to the second 50Ω microstrip line conductor and the other arm connected to the input end of the three-wire coupled open-circuit feeder; the phase delay line and the three-wire coupled open-circuit feeder have a U-shaped bend. The third 50Ω microstrip line conductor is connected to the three-wire coupled feed line in a straight line, and the L-shaped output open-circuit loading line forms a U-shaped bend layout with the third 50Ω microstrip line conductor and the three-wire coupled feed line.

[0010] Optionally, the length and width of the first short-circuit resonator and the third short-circuit resonator are the same; the length and width of the second short-circuit resonator and the fourth short-circuit resonator are the same. The length and width of the first and second open-circuit resonators are the same.

[0011] Optionally, the length of the input open-circuit loading line is one-quarter wavelength or three-quarter wavelength at the center frequency of the dual passband; the phase delay line has the same dimensions as the output open-circuit loading line; and the length and width of the three-wire coupled open-circuit feed line are the same as those of the three-wire coupled feed line.

[0012] The beneficial effects of this utility model are: This application utilizes a single-layer PCB board for easy fabrication and integration. It employs a stub-loaded dual-mode resonator to form two passbands. By altering the impedance ratio of the open-circuit loaded stub to the short-circuit resonator, the distance between the center frequencies of the two passbands can be changed, thereby increasing the stopband width between the two passbands and resulting in a large frequency spacing and good selectivity. The dual-mode resonator is coupled and fed; by changing the coupling line width and coupling spacing, the feed strength can be controlled, achieving impedance matching at the ports. This application uses a short-circuited center-line coupled three-wire structure to achieve equal-amplitude, inverted-phase output from the balun, resulting in good amplitude and phase differences between the two passbands. This application employs a single-layer microstrip transmission line design, with the filtering response achieved through a pair of dual-mode resonators. The structural design is easily bendable, and the circuit area occupied by the 50Ω port feed line is only 0.22 square meters. λ g ×0.29 λ g , λ g The wavelength of the guided wave corresponds to the center frequency of the first passband. Attached Figure Description Figure 1 This is a schematic diagram of the overall structure of the planar compact dual-mode dual-passband balun filter of this utility model; Figure 2 This is a schematic diagram of the structural dimensions of the planar compact dual-mode dual-passband balun filter according to Embodiment 2 of this utility model; Figure 3 This is a simulation diagram of the S-parameters of the planar compact dual-mode dual-passband balun filter of Embodiment 2 of this utility model; Figure 4 This is a simulation diagram of the amplitude difference and phase difference at the output end of the planar compact dual-mode dual-passband balun filter of Embodiment 2 of this utility model.

[0013] The diagram is labeled as follows: 1 is the input feed line, 11 is the first 50Ω microstrip line conductor, 12 is the dual-line coupled feed line, and 13 is the input open-circuit loading line. 2 is a first stub-loaded dual-mode resonator, 21 is a first short-circuit resonator, 22 is a second short-circuit resonator, 23 is a first open-circuit resonator, 24 is a first metallized via, and 25 is a second metallized via. 3 is the second branch-loaded dual-mode resonator, 31 is the third short-circuit resonator, 32 is the fourth short-circuit resonator, 33 is the second terminal open-circuit resonator, 34 is the third metallized via, and 35 is the fourth metallized via. 4 is the first differential output feed line, 41 is the second 50Ω microstrip line conductor, 42 is the phase delay line, and 43 is the three-wire coupled open-circuit feed line. 5 is the second differential output feed line, 51 is the third 50Ω microstrip line conductor, 52 is the three-wire coupled feed line, and 53 is the output open-circuit loading line. 6 is a complete metal grounding plate; 7 is a rectangular dielectric substrate. Detailed Implementation

[0014] The present invention will now be described in detail with reference to the accompanying drawings. The terms "first," "second," etc., in this specification, claims, and the aforementioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such usage can be interchanged where appropriate, and furthermore, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusion.

[0015] Example 1 like Figure 1 As shown, a planar compact dual-mode dual-passband balun filter includes a rectangular dielectric substrate 7 with a complete metal ground plane 6 on its lower surface, an input feed line 1 on the upper surface of the rectangular dielectric substrate 7, a first stub-loaded dual-even-mode resonator 2, a second stub-loaded dual-even-mode resonator 3, a first differential output feed line 4, and a second differential output feed line 5.

[0016] The input feed line 1 includes a first 50Ω microstrip line conductor 11, a dual-line coupling feed line 12, and an input open-circuit loading line 13 connected in sequence.

[0017] The first stub-loaded dual-even-mode resonator 2 includes a first short-circuit resonator 21, a second short-circuit resonator 22, and a first open-circuit resonator 23. The short-circuit end of the first short-circuit resonator 21 is short-circuited through a first metallized via 24, and the short-circuit end of the second short-circuit resonator 22 is short-circuited through a second metallized via 25. The two non-short-circuit ends of the first short-circuit resonator 21 and the second short-circuit resonator 22 are connected to the input end of the first open-circuit resonator 23.

[0018] The second branch-loaded dual-even-mode resonator 3 includes a third short-circuit resonator 31, a fourth short-circuit resonator 32, and a second open-circuit resonator 33. The short-circuit end of the third short-circuit resonator 31 is short-circuited through a third metallized via 34, and the short-circuit end of the third short-circuit resonator 31 is short-circuited through a fourth metallized via 35. The two non-short-circuit ends of the third short-circuit resonator 31 and the fourth short-circuit resonator 32 are connected to the input end of the second open-circuit resonator 33.

[0019] The first differential output feed line 4 includes a second 50Ω microstrip line conductor 41, a phase delay line 42, and a three-wire coupled open-circuit feed line 43 connected in sequence.

[0020] The second differential output feed line 5 includes a third 50Ω microstrip line conductor 51, a three-wire coupling feed line 52, and an output open-circuit loading line 53 connected in sequence.

[0021] In this embodiment, the dual-wire coupled feed line 12 in the input feed line 1 and the first short-circuit resonator 21 of the first stub-loaded dual-even-mode resonator 2 are placed parallel to each other at a preset distance, forming parallel coupling; the third short-circuit resonator 31 is located parallel to the three-wire coupled open-circuit feed line 43 and the three-wire coupled feed line 52 at a preset distance, forming parallel coupling; the second short-circuit resonator 22 and the fourth short-circuit resonator 32 are placed parallel to each other at a preset distance, forming parallel coupling; the first metallized via 24 is close to the connection surface between the dual-wire coupled feed line 12 and the first 50Ω microstrip line conductor 11, and the second metallized via 25 is close to the input end of the second terminal open-circuit resonator 33. The third metallized via 34 is close to the open end face of the three-wire coupled open-circuit feed line 43; the fourth metallized via 35 is close to the input end of the first terminal open-circuit resonator 23; the open end face of the three-wire coupled open-circuit feed line 43 is close to the connection surface between the third 50Ω microstrip line conductor 51 and the three-wire coupled feed line 52.

[0022] The first 50Ω microstrip line conductor 11 and the dual-wire coupled feed line 12 are arranged in an L-shaped bend; the L-shaped input open-circuit loading line 13 and the dual-wire coupled feed line 12 are arranged in a U-shaped bend; the phase delay line 42 is arranged in an L-shaped bend, with one bend perpendicular to the second 50Ω microstrip line conductor 41, and the other end face of the phase delay line 42 connected to the input end of the three-wire coupled open-circuit feed line 43. The phase delay line 42 and the three-wire coupled open-circuit feed line 43 are arranged in a U-shaped bend. The L-shaped bent layout; the third 50Ω microstrip line conductor 51 and the three-wire coupled feed line 52 are connected in a straight line, and the L-shaped output open-circuit loading line 53, the third 50Ω microstrip line conductor 51 and the three-wire coupled feed line 52 form a U-shaped bent layout; the first terminal open-circuit resonator 23 has an L-shaped bent layout, the second short-circuit resonator 22 has a U-shaped bent layout, the second terminal open-circuit resonator 33 has a U-shaped bent layout, and the fourth short-circuit resonator 32 has a U-shaped bent layout. When the length of the open-circuit loading line 13 at the input terminal is one-quarter wavelength at the center frequency of the dual passband, the transmission zero point is located outside the high-frequency band of the upper passband. When the length is three-quarter wavelength at the center frequency, the transmission zero point is located between the two passbands.

[0023] The phase delay line 42 has the same dimensions as the output open-circuit loading line 53. Its length mainly controls the phase balance of the balun filter output port, and its width is used to control the amplitude balance of the balun filter. The three-wire coupled open-circuit feed line 43 has the same length and width as the three-wire coupled feed line 52. Its width is used to control the coupling strength and can change the impedance matching of the dual-passband filter response. The first short-circuit resonator 21 has the same length and width as the third short-circuit resonator 31. The second short-circuit resonator 22 has the same length and width as the fourth short-circuit resonator 32. The first open-circuit resonator 23 and the second open-circuit resonator 33 have the same length and width.

[0024] During operation, the signal excited by the input feeder 1 is transmitted to the first stub-loaded dual-mode resonator 2 via a two-wire parallel coupling method, and then transmitted again via parallel coupling to the second stub-loaded dual-mode resonator 3. By setting a three-wire parallel coupling method, the signal is coupled out by the first differential output feeder 4 and the second differential output feeder 5 located on both sides of the second stub-loaded dual-mode resonator 3.

[0025] The input-terminal open-circuit loading line 13 in input feeder 1 is used for impedance matching and to generate a transmission zero, thereby improving the out-of-band selectivity of the filter response. When its length is one-quarter wavelength at the center frequency of the dual passband, the transmission zero is located outside the high-frequency band of the upper passband. When its length is three-quarter wavelength at the center frequency, the transmission zero is located between the two passbands. The first stub-loaded dual-even-mode resonator 2 and the second stub-loaded dual-even-mode resonator 3 form two passbands through coupling. The greater the coupling strength, the greater the distance between the two poles in the band, and the larger the achievable passband bandwidth. The first-terminal open-circuit resonator 23 and the second-terminal open-circuit resonator 33... The impedance ratio of the first short-circuit resonator 21, the second short-circuit resonator 22, the third short-circuit resonator 31, and the fourth short-circuit resonator 32 determines the frequency ratio of the two passbands. The smaller the impedance ratio, the greater the distance between the two passbands. The first differential output feed line 4 and the second differential output feed line 5 achieve phase inversion of the output signal by setting the output ports at different positions. The phase difference at the output end can be adjusted by adjusting the length and width of the phase delay line 42 and the open-circuit loading line 53 at the output end. The coupling distance between the input and output sections controls the external Q value of the filter circuit and affects the achievable filter response bandwidth. The smaller the coupling distance, the larger the achievable bandwidth.

[0026] This invention utilizes printed circuit board (PCB) manufacturing processes to etch the metal surface of the circuit board to form the desired metal pattern. Metallized vias are then achieved through a copper plating process, resulting in a compact structure and low production cost for a single-layer PCB. Furthermore, by employing a dual-mode resonator and a three-wire coupling as the main structural components, this dual-passband balun filter exhibits a controllable passband frequency ratio, high frequency selectivity, excellent single-ended-balanced signal transmission performance, and a compact design size. This invention features a large dual-passband frequency spacing, good selectivity, good amplitude and phase deviation, good input port matching characteristics, and low manufacturing cost, making it suitable for modern wireless communication systems.

[0027] Example 2 like Figure 2 As shown, a specific example of a planar compact dual-mode dual-passband balun filter is provided. The selected dielectric substrate is Rogers 4003C, with a relative permittivity of 3.55, a loss tangent of 0.0027, and a thickness of 0.508 mm. Figure 2 The dimensions and parameters of the dual-passband balun filter are as follows: L 1 = 13mm, W 1 = 0.15mm, S 1 = 0.1 mm L 2 = 11.5mm, W 2 = 0.1mm,L 13 = 0.5mm, L 3 = 13mm, W 3 = 0.15mm, S 2 = 0.3 mm L 4 = 11.15mm, W 4 = 1.5mm, S 3 = 0.1 mm L 5 = 6.15mm L 51 =2.65mm, W 5 = 1.65mm L 6 = 6.47 mm L 61 =2mm, W 6 = 1.65mm W 7 = 0.15mm, L p=5.5mm, W p =1.18mm, the radius of all metallized vias is R = 0.15mm, the side length of the square patch on the through-hole surface is 0.4mm, and the total area of ​​the dual-passband balun filter excluding the 50Ω microstrip line conductor is 15.5 × 20.8mm. 2 The final circuit layout occupies an area of ​​approximately 0.22 square meters. λ g × 0.29 λ g ,in λ g The wavelength of the guided wave corresponds to the center frequency of the first passband.

[0028] The broadband balanced bandpass filter in this example was modeled and simulated in the electromagnetic simulation software ANSYS EM Suite 21.1. Figure 3 This is a simulation diagram of the S-parameters of the broadband balanced bandpass filter in this example. Figure 4 This is a simulation diagram of the amplitude difference and phase difference at the output port of the dual-passband balun filter in this embodiment. From Figure 3 As can be seen, the center frequencies of the two passbands of this dual-passband balun filter are 2.53 GHz and 5.4 GHz, respectively. The in-band return losses are less than -16 dB and -24 dB, respectively. The 3-dB relative bandwidths are 11.9% and 3%, respectively. The insertion losses are less than 1.3 and 2.5 dB, respectively. There are two transmission zeros between the two passbands, which gives the dual-passband balun filter in this example good isolation between the two passbands. Figure 4 It can be seen that the amplitude difference of this dual-passband balun filter is less than 0.4dB and 0.6dB, and the phase difference is less than 8°, indicating good balance characteristics.

[0029] The above are merely preferred embodiments of this utility model. The protection scope of this utility model is not limited to the above embodiments. All technical solutions falling within the scope of this utility model's concept are within its protection scope. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of this utility model should be considered within its protection scope.

Claims

1. A planar compact dual-mode dual-passband balun filter, characterized by, include: A rectangular dielectric substrate (7) has a complete metal ground plane (6) on its lower surface and an input feed line (1), a first stub-loaded dual-mode resonator (2), a second stub-loaded dual-mode resonator (3), a first differential output feed line (4), and a second differential output feed line (5) on its upper surface. The first stub-loaded dual-mode resonator (2) includes a first short-circuit resonator (21), a second short-circuit resonator (22), and a first open-circuit resonator (23); wherein, one end of the first short-circuit resonator (21) is short-circuited through a first metallized via (24), one end of the second short-circuit resonator (22) is short-circuited through a second metallized via (25), and the other ends of the first short-circuit resonator (21) and the second short-circuit resonator (22) are connected to the input terminal of the first open-circuit resonator (23); The second stub-loaded dual-mode resonator (3) includes a third short-circuit resonator (31), a fourth short-circuit resonator (32), and a second open-circuit resonator (33); wherein, one end of the third short-circuit resonator (31) is short-circuited through a third metallized via (34), and the other end of the third short-circuit resonator (31) is short-circuited through a fourth metallized via (35); the other ends of the third short-circuit resonator (31) and the fourth short-circuit resonator (32) are connected to the input terminal of the second open-circuit resonator (33); The first short-circuit resonator (21) is placed parallel to the input feed line (1) to form parallel coupling; the second short-circuit resonator (22) and the fourth short-circuit resonator (32) are placed parallel to each other to form parallel coupling; the third short-circuit resonator (31) is located in the middle of the first differential output feed line (4) and the second differential output feed line (5) in a parallel manner to each other to form three-line parallel coupling.

2. The planar compact dual-mode dual-passband balun filter according to claim 1, characterized in that, The input feed line (1) includes a first 50Ω microstrip line conductor (11), a dual-line coupling feed line (12), and an input open-circuit loading line (13) connected in sequence. The first differential output feed line (4) includes a second 50Ω microstrip line conductor (41), a phase delay line (42), and a three-wire coupled open-circuit feed line (43) connected in sequence. The second differential output feed line (5) includes a third 50Ω microstrip line conductor (51), a three-wire coupling feed line (52), and an output open-circuit loading line (53) connected in sequence.

3. The planar compact dual-mode dual-passband balun filter according to claim 2, characterized in that, The dual-wire coupled feed line (12) is placed parallel to the first short-circuit resonator (21); the third short-circuit resonator (31) is located between the three-wire coupled open-circuit feed line (43) and the three-wire coupled feed line (52), and they are parallel to each other.

4. The planar compact dual-mode dual-passband balun filter according to claim 2, characterized in that, The first metallized via (24) is close to the connection surface between the dual-line coupled feed line (12) and the first 50Ω microstrip line conductor (11), and the second metallized via (25) is close to the input end of the second terminal open-circuit resonator (33); The third metallized via (34) is close to the open end face of the three-wire coupled open-circuit feed line (43); the fourth metallized via (35) is close to the input end of the first terminal open-circuit resonator (23); The open end face of the three-wire coupled open feeder (43) is close to the connection surface between the third 50Ω microstrip conductor (51) and the three-wire coupled feeder (52).

5. The planar compact dual-mode dual-passband balun filter according to claim 1, characterized in that, The first open-circuit resonator (23) has an L-shaped bend, the second short-circuit resonator (22) has a U-shaped bend, the second open-circuit resonator (33) has a U-shaped bend, and the fourth short-circuit resonator (32) has a U-shaped bend.

6. The planar compact dual-mode dual-passband balun filter according to claim 2, characterized in that, The first 50Ω microstrip line conductor (11) and the dual-line coupled feed line (12) are arranged in an L-shaped bend; the L-shaped input open-circuit loading line (13) and the dual-line coupled feed line (12) are arranged in a U-shaped bend. The phase delay line (42) has an L-shaped bend, with one arm of the bend perpendicular to the second 50Ω microstrip line conductor (41) and the other arm connected to the input end of the three-wire coupled open-circuit feeder (43); the phase delay line (42) and the three-wire coupled open-circuit feeder (43) have a U-shaped bend. The third 50Ω microstrip conductor (51) is connected to the three-wire coupled feed line (52) in a straight line. The L-shaped output open-circuit loading line (53) forms a U-shaped bend layout with the third 50Ω microstrip conductor (51) and the three-wire coupled feed line (52).

7. The planar compact dual-mode dual-passband balun filter according to claim 1, characterized in that, The length and width of the first short-circuit resonator (21) and the third short-circuit resonator (31) are the same; the length and width of the second short-circuit resonator (22) and the fourth short-circuit resonator (32) are the same. The length and width of the first open-circuit resonator (23) and the second open-circuit resonator (33) are the same.

8. The planar compact dual-mode dual-passband balun filter according to claim 2, characterized in that, The length of the input open-circuit loading line (13) is one-quarter wavelength or three-quarter wavelength at the center frequency of the dual passband; The phase delay line (42) has the same dimensions as the output open-circuit loading line (53); The length and width of the three-wire coupled open-circuit feeder (43) and the three-wire coupled feeder (52) are the same.

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