CN111864321A - A Balanced Dual-pass Band Filter Based on Branch Loaded Slotline Resonator - Google Patents

Abstract

The invention discloses a balanced dual-passband filter based on a stub-loaded slot line resonator, and belongs to the technical field of balanced bandpass filters. The dielectric resonator comprises a single-layer dielectric substrate, an upper-layer microstrip line structure and a lower-layer slot line resonator structure; the upper microstrip line structure comprises a first differential signal port pair and a second differential signal port pair which are symmetrical, the lower slot line resonator structure comprises a first slot line resonator and a second slot line resonator which are symmetrical, and the first slot line resonator and the second slot line resonator are both three-branch loading slot line structures; the first slot line resonator center loading stub is coupled to the first differential signal port pair, and the second slot line resonator center stub is coupled to the second differential signal port pair. The invention has good differential mode dual-band filtering characteristic, higher common mode signal rejection characteristic in the full frequency range, simple structure, easy processing and greater practicability.

Description

A Balanced Dual-pass Band Filter Based on Branch Loaded Slotline Resonator

technical field

The invention relates to the technical field of balanced bandpass filters in microwave frequency bands, in particular to a balanced dual-passband filter based on branch-loaded slot-line resonators.

Background technique

With the increasing amount of information transmission in modern communication systems, higher and higher requirements have been placed on signal margins and transmission rates. Compared with a single-ended signal transmission system, a differential communication system can effectively receive differential signals (useful signals) and effectively suppress common-mode signals (noise signals). Therefore, as a key component in a differential communication system, the dual-passband balanced filter has received extensive attention from industry and academia. This type of device requires good dual-band filtering characteristics under differential signal excitation, and can achieve high common-mode signal rejection in the widest possible frequency range.

A dual-passband balanced filter is proposed in the prior art. Based on a symmetrical SIR resonator, an open-circuit branch is loaded at the center position, so that the common mode resonance of each resonator is shifted, and a passband cannot be formed. In addition, a dual-passband balanced filter with high common-mode rejection is also proposed in the prior art based on an impedance resonator with a centrally loaded lumped element. However, this kind of dual-passband balanced filter has the disadvantages of complex circuit structure, numerous design parameters and low common mode rejection.

The Chinese Patent Application No. 201210278024.4 and the Chinese Patent Application No. 201510198401.7 adopt a multilayer dielectric substrate structure and propose a dual-passband balanced filter based on a microstrip resonator and a slot line resonator. However, since this type of dual-pass-band balanced filter adopts a multi-layer dielectric substrate structure, it generally has the disadvantages of complex circuit structure and high cost.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to provide a balanced dual-passband filter based on a branch-loaded slotline resonator, whose passband frequency is flexible and controllable, has excellent common-mode rejection characteristics in a wide frequency range, and It can be realized based on a single-layer dielectric substrate, and has the characteristics of simple structure and low cost.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A balanced dual-pass band filter based on a branch-loaded slotline resonator, comprising a dielectric substrate 1, and the bottom surface of the dielectric substrate 1 has a metal ground layer 10; the metal ground layer 10 has a first slot line formed by an etched structure The resonator 4 and the second slot line resonator 5, the upper surface of the dielectric substrate 1 also has first and second microstrip line structures 2 and 3 corresponding to the first and second slot line resonators one-to-one;

The two slot line resonators and the two microstrip line structures are both mirror-symmetrical with respect to the first reference plane, and each slot line resonator and each microstrip line structure are mirror-symmetrical structures with respect to the second reference plane. The reference plane and the second reference plane are perpendicular to each other, and both the first reference plane and the second reference plane are perpendicular to the dielectric substrate;

Each slot line resonator includes a vertical slot line and five horizontal slot lines extending from the vertical slot line to the same side, wherein the first horizontal slot line and the fifth horizontal slot line are respectively located on the vertical slot line At the two end points, the third horizontal groove lines 42, 52 are located at the midpoint of the vertical groove lines, the second horizontal groove lines 43, 53 are located between the first and third horizontal groove lines, and the fourth horizontal groove line 44 , 54 are located between the fifth and third horizontal slot lines; the vertical line of the vertical slot line is located in the second reference plane, the vertical slot lines of the two slot line resonators are parallel to each other, and the vertical slot lines of the two vertical slot lines are parallel to each other. The middle parallel line is located in the first reference plane, and the horizontal slot lines of the two slot line resonators are opposite to each other; the first horizontal slot line, the vertical slot line and the fifth horizontal slot line constitute U-shaped slot line branches 41 and 51, The second horizontal slot line, the third horizontal slot line and the fourth horizontal slot line are loading slot lines;

The two microstrip line structures are located on both sides of the first reference plane respectively, and the two ends of the microstrip line structure are located at the edge of the dielectric substrate on this side and form a differential signal port pair. The lines are located in the second reference plane, and each microstrip line passes over the third horizontal slot line corresponding to the slot line resonator, thereby forming a microstrip-slot line coupling structure.

Further, the widths of each loading slot line are equal, each segment of the slot line of the branch of the U-shaped slot line is the same width, and the width of the loading slot line is twice the width of the slot line of the branch of the U-shaped slot line.

Further, the slot line resonator satisfies the following dimensional relationship:

L ₁ +L ₂ =L ₃ ,

Wherein, L ₁ is the length of the third horizontal slot line, L ₂ is the opposite side distance between the second horizontal slot line and the third horizontal slot line, and L ₃ is the opposite side distance between the first horizontal slot line and the second horizontal slot line The sum of the length of the first horizontal groove line.

Further, the dielectric substrate is a single-layer dielectric substrate with a dielectric constant of 2-16 and a thickness of 0.1-4 mm.

Further, the microstrip line structure is a broken line structure, and the middle section of the microstrip line structure is perpendicular to the third horizontal slot line of the corresponding slot line resonator.

The present invention has the following beneficial effects with respect to the prior art:

1. The dual-pass-band balanced filter of the present invention is based on a single-layer dielectric structure, and adopts a dual-mode three-node loaded slot-line resonator as the resonant unit of the circuit, which has the characteristics of simple structure and low cost, and overcomes the traditional dual-pass-band balanced filter. The disadvantage of the complex structure of the device.

2. The dual-pass-band balanced filter of the present invention can realize independent control of the high-frequency pass-band frequency by adjusting the length of the branch of the central loading slot line, and has greater design flexibility.

3. The dual-pass-band balanced filter of the present invention has excellent dual-band pass performance in the case of differential signal excitation, and has excellent common-mode rejection performance in a wide frequency range, which can well meet the requirements of modern communication systems. Require.

Description of drawings

1 is a schematic structural diagram of a dual-passband balanced filter in an embodiment of the present invention;

Fig. 2 is the plane perspective structure schematic diagram of Fig. 1;

Fig. 3 is the equivalent circuit diagram of Fig. 1 in the case of differential signal excitation;

Figure 4(a) and Figure 4(b) are even-mode equivalent circuit diagrams of E-slot line resonators;

Figure 5(a) and Figure 5(b) are odd-mode equivalent circuit diagrams of E-slot line resonators;

Fig. 6 is the frequency response diagram of the differential signal of the dual-passband balanced filter shown in Fig. 1 along with the slot line branch length L ₄ changes;

FIG. 7 is a schematic diagram of the results of the differential mode and common mode responses of the dual passband balanced filter shown in FIG. 1 .

Detailed ways

The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in Figures 1 and 2, a balanced dual-pass band filter based on branch-loaded slotline resonators consists of a single-layer dielectric substrate 1, a microstrip line structure on the upper layer of the dielectric substrate, and a metal structure 10 on the lower layer. The dielectric constant of the dielectric substrate can be selected from 2 to 16, and the thickness is from 0.1 to 4 mm.

In this example, the upper-layer microstrip line structure forms four signal ports of the object: port 21 , port 22 , port 31 and port 32 . The underlying metal structure forms the first slot line resonator 4 and the second slot line resonator 5 .

Ports 21 and 22 are located on the left side of the symmetry plane BB', forming a first differential signal port pair 2; ports 31 and 32 are located on the right side of the symmetry plane BB', forming a second differential signal port pair 3. The four signal ports are composed of microstrip transmission lines, wherein the port 21 and the port 22 are mirror-symmetrical and connected about the symmetry plane AA', and the port 31 and the port 32 are mirror-symmetrical and connected about the symmetry plane AA'.

The first and second line resonators 4 and 5 are three-stub loading slot-line structures, including four slot-line branches: the slot-line branch 41 is mirror-symmetrical about the symmetry plane AA', and its end portion is bent at 90° and extends away from the axis 1 ; The central axis of the slot line branch 42 coincides with the symmetry plane AA', one end of which is connected with the main road slot line branch, and extends away from the symmetry plane BB' direction, and intersects with the first differential signal port to form a microstrip-slot line coupling Structure; the slot line branches 43 and 44 are parallel to each other, mirror symmetry with respect to the symmetry plane AA', one end is connected to the slot line branch 41, and the other end extends away from the symmetry plane BB'.

As shown in FIG. 2 , in the first slot line resonator 4, the length of the slot line branches 42 and 43 is L ₄ , the width W ₂ is equal to the width W ₃ of the slot line branch 44 , and is equal to the width W ₁ of the slot line branch 41 . 2 times. The length of the slot line stub 42 is L ₁ , the distance between the slot line stub 44 and the slot line stub 44 is L ₂ , the distance between the connection between the slot line stub 44 and the slot line 41 and the end of the closer side of the slot line stub 41 is L ₃ , and the distance of the slot line resonator is L 3 . The dimensional relationship is: L ₁ +L ₂ =L ₃ .

The second slotline resonator 5 comprises slotline branches 51, 52, 53 and 54, which are mirror-symmetrical with respect to the symmetry plane BB' with the slotline branches 41, 42, 43 and 44, respectively.

The working principle of the balanced dual-passband filter is described in detail below:

When the differential signal port pair 2 and 3 of the object are excited by the common mode signal, the balanced circuit is an ideal magnetic wall at the symmetry plane AA', which is equivalent to an open circuit structure. In this case, the input/output feeder is open-ended and cannot be connected to the trench line structure in the formation. In addition, the closed structure of the slot-line structure is completely destroyed when the symmetry plane is open, so that the signal cannot be transmitted, so that high common mode noise suppression performance can be achieved in a wide frequency range.

When the differential signal port pair 2 and 3 of the object are excited by the differential signal, the balanced circuit is an ideal electric wall at the symmetry plane AA', which is equivalent to a short-circuit structure. Figure 3 shows the differential mode equivalent circuit of the balanced double-pass band filter. At this time, the input/output feed is short-circuited with the slotline structure of the E-slotline resonator, which is the classic microstrip-slotline transition structure. There is strong mutual coupling between the belt feeder and the slot line structure, which can ensure the smooth transmission of differential signals in the working frequency band.

In order to facilitate the circuit design analysis, the design parameters are specified as L ₁ +L ₂ =L ₃ , and W ₂ =W ₃ =2W ₁ , it can be seen that the E-shaped slot line resonator is a symmetrical structure, so the odd-even mode method can be used to its analysis. Under even-mode excitation, the symmetry plane CC' of the E-slotline resonator behaves as an ideal magnetic wall, which is an open surface. Under odd-mode excitation, the symmetry plane behaves as an ideal electric wall and is a short-circuit plane. Based on the above analysis, the even-mode equivalent circuit of the E-slot line resonator is shown in Figure 4(a). is a quarter-wavelength resonator, set its resonant frequency as f ₁ , the physical parameters L ₁ and L ₂ of the resonator can be obtained as follows:

Among them, c is the propagation speed of light in free space, and _εre is equivalent to the dielectric constant.

The odd-mode equivalent circuit of the E-type slot line resonator is shown in Figure 5(a). The circuit can analyze its resonance characteristics according to the microstrip branch with double-ended short circuit in Figure 5(b). The resonator is half A wavelength resonator, set its resonant frequency as f ₂ , the physical parameter L ₄ of the resonator can be obtained as follows:

In this embodiment, the low-frequency pass-band resonance point of the balanced double-pass-band filter is generated by the even-mode equivalent circuit of the E-shaped slot line resonator, and is determined by the length of (L ₁ +L ₂ ); the high-frequency pass-band resonance The point is generated by the odd-mode equivalent circuit of the E-slotline resonator and is determined by the (L ₁ +L ₂ +L ₄ ) length.

According to the above analysis, the initial physical parameters of the slot line resonator can be obtained. This circuit uses the dielectric substrate RogersRT/duroid 6010/6010LM(tm), the electric constant is 10.2, the dielectric thickness is 0.635mm, and the loss cut angle is tanδ=0.0023. As shown in Figure 6, using the HFSS three-dimensional full-wave field simulation software, the balanced double-pass band filter is obtained, and the transmission response changes with the length of the slot line branch length L ₄ .

本发明提供的双频带平衡滤波器通过控制槽线谐振器的中心加载槽线枝节长度L₄，其高频通带中心频率f₂明显向下偏移，而低频通带中心频率，f₁，几乎保持不变，说明本发明具有较大的设计灵活性。It can be seen that in the case of common-mode signal excitation, the balanced filter achieves suppression greater than 40dB in the broadband range. In the case of differential signal excitation, this embodiment has a good dual-pass band filter response

In the dual-band balanced filter provided by the present invention, by controlling the center load slot line branch length L ₄ of the slot line resonator, the high frequency pass band center frequency f ₂ is obviously shifted downward, while the low frequency pass band center frequency, f ₁ , It remains almost unchanged, indicating that the present invention has greater design flexibility.

The low frequency passband center frequency of the balanced double passband filter in this embodiment is designed to be 3.5GHz, the relative bandwidth is 5%, and the in-band ripple is 0.0432dB; the high frequency passband center frequency is 5.3GHz, the relative bandwidth is 3%, the band The internal ripple is 0.0432dB. According to the classical filter theory, the external quality factor of the low-frequency passband is 22.16, and the coupling coefficient is 0.05; the external quality factor of the low-frequency passband is 13.3, and the coupling coefficient is 0.083. The external quality factor is adjusted by adjusting the coupling length between the central loading branch and the differential signal port, and the resonator coupling coefficient in the two passbands is controlled by adjusting the bending length L ₅ and the coupling gap W ₄ of the slot line resonator. The physical dimension parameters in the final example are shown in the following table.

L₁ L₂ L₃ L₄ L₅ L₆ 8.8mm 2.475mm 11.275mm 3.3mm 6.1mm 14.4mm L₇ W₁ W₂ W₃ W₄ W₅ 2.15mm 0.2mm 0.4mm 0.4mm 0.24mm 0.59mm

和

分别指差分信号传输特性曲线响应和回波响应曲线，

指共模信号传输特性曲线。差分信号传输特性曲线中，两个通带的中心频率分别为3.5GHz和5.3GHz，对应的插入损耗分别为0.5dB和0.8dB，回波损耗

小于-15dB；共模信号抑制水平在宽频带范围均大于47dB。FIG. 7 is a frequency response characteristic curve of the filter according to the embodiment of the present invention, the abscissa represents the frequency of the signal, the unit is GHz, and the ordinate is the response amplitude of the signal, the unit is dB.

and

refer to the differential signal transmission characteristic curve response and echo response curve respectively,

Refers to the common mode signal transmission characteristic curve. In the differential signal transmission characteristic curve, the center frequencies of the two passbands are 3.5GHz and 5.3GHz, respectively, the corresponding insertion losses are 0.5dB and 0.8dB, and the return loss is

Less than -15dB; common mode signal rejection level is greater than 47dB in a wide frequency range.

In conclusion, the present invention achieves good dual-band filtering characteristics under the condition of differential signal excitation by adopting a novel three-branched slot-line resonator, and has high common-mode signal suppression capability in a wide frequency range. By adjusting the stub length of the center loading slot line, the frequency of the high-frequency passband can be flexibly controlled without affecting the low-frequency passband.

The invention has good differential-mode dual-band filtering characteristics, high common-mode signal suppression characteristics in the whole frequency range, simple structure, convenient design and production, easy processing, good performance and great practicability.

It should be understood that the above descriptions of the specific embodiments of the present patent are merely exemplary descriptions for the convenience of those of ordinary skill in the art to understand the solutions of the present patent, and do not imply that the protection scope of the present patent is only limited to these examples. Those of ordinary skill in the art can, on the premise of fully understanding the technical solution of this patent, without any creative work, combine technical features, replace some technical features, add more technical features, etc., to obtain more specific implementations, all of which are within the scope of the patent claims, therefore, these new specific implementations should also be within the protection scope of this patent .

Claims (5)

1. A balanced double-passband filter based on a branch-loaded slotline resonator, comprising a dielectric substrate (1), and the bottom surface of the dielectric substrate (1) has a metal formation (10); it is characterized in that the metal formation ( 10) There are a first slot line resonator (4) and a second slot line resonator (5) formed by an etched structure, and the upper surface of the dielectric substrate (1) also has the first and second slot line resonators. One-to-one corresponding first and second microstrip line structures (2, 3); The two slot line resonators and the two microstrip line structures are both mirror-symmetrical with respect to the first reference plane, and each slot line resonator and each microstrip line structure are mirror-symmetrical structures with respect to the second reference plane. The reference plane and the second reference plane are perpendicular to each other, and both the first reference plane and the second reference plane are perpendicular to the dielectric substrate; Each slot line resonator includes a vertical slot line and five horizontal slot lines extending from the vertical slot line to the same side, wherein the first horizontal slot line and the fifth horizontal slot line are respectively located on the vertical slot line At the two end points, the third horizontal slot line (42, 52) is located at the midpoint of the vertical slot line, the second horizontal slot line (43, 53) is located between the first and third horizontal slot lines, and the fourth The horizontal slot lines (44, 54) are located between the fifth and third horizontal slot lines; the vertical line of the vertical slot line is located in the second reference plane, the vertical slot lines of the two slot line resonators are parallel to each other, and the two The middle parallel lines of the two vertical slot lines are located in the first reference plane, and the horizontal slot lines of the two slot line resonators are opposite to each other; the first horizontal slot line, the vertical slot line and the fifth horizontal slot line constitute a U-shaped slot line Branches (41, 51), the second horizontal slot line, the third horizontal slot line and the fourth horizontal slot line are loading slot lines; The two microstrip line structures are located on both sides of the first reference plane respectively, and the two ends of the microstrip line structure are located at the edge of the dielectric substrate on this side and form a differential signal port pair. The lines are located in the second reference plane, and each microstrip line passes over the third horizontal slot line corresponding to the slot line resonator, thereby forming a microstrip-slot line coupling structure. 2. a kind of balanced double-pass band filter based on branch loading slot line resonator according to claim 1, is characterized in that, the width of each loading slot line is all equal, and each segment slot line of U-shaped slot line branch Equal width, the width of the loading groove is twice the width of the branch groove of the U-shaped groove. 3. a kind of balanced double-pass band filter based on branch loading slot line resonator according to claim 1, is characterized in that, described slot line resonator satisfies following size relation: L ₁ +L ₂ =L ₃ , Wherein, L ₁ is the length of the third horizontal slot line, L ₂ is the opposite side distance between the second horizontal slot line and the third horizontal slot line, and L ₃ is the opposite side distance between the first horizontal slot line and the second horizontal slot line The sum of the length of the first horizontal groove line. 4 . The balanced double-pass band filter based on branch-loaded slot line resonators according to claim 1 , wherein the dielectric substrate is a single-layer dielectric substrate, and its dielectric constant is 2-16, 5 . The thickness is 0.1～4mm. 5. a kind of balanced dual-pass band filter based on branch loading slot line resonator according to claim 1, is characterized in that, described microstrip line structure is broken line structure, and the middle section of microstrip line structure corresponds to The third horizontal slot line of the slot line resonator is perpendicular.

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