A compact microstrip dual-band filter with stepped impedance

Abstract

The present application discloses a compact microstrip dual-band filter with stepped impedance, comprising: a first stepped impedance resonator arranged on a dielectric substrate; a second stepped impedance resonator forming an inner coupling connection with the first stepped impedance resonator; a first quarter impedance matching line connected to one side of the first stepped impedance resonator, the first stepped impedance resonator and the first quarter impedance matching line forming a first frequency band, which is configured to determine the first wavelength impedance based on the Q value of the load connected to the first frequency band and the characteristic impedance of the transmission cable; a second quarter impedance matching line connected to one side of the second stepped impedance resonator, the second stepped impedance resonator and the second quarter impedance matching line forming a second frequency band, which is configured to determine the second wavelength impedance based on the Q value of the load connected to the second frequency band and the characteristic impedance of the transmission cable, and also determines the resonant frequency of the second frequency band. This makes the filter structure compact and easy to mass produce.

Description

Technical Field

[0001] The present application relates to a compact microstrip dual-band filter with stepped impedance, belonging to the field of filters. Background Art

[0002] With the growing demand for wireless communications, dual-band portable phones and wireless local area networks have become widely used. Dual-band filters have become essential front-end components in communication systems. The structure and size of dual-band filters can be optimized, reducing their size to facilitate structural integration. Therefore, a new, compact microstrip dual-band filter with stepped impedance has become a pressing need for those skilled in the art. Summary of the Invention

[0003] According to one aspect of the present application, a compact microstrip dual-band filter with stepped impedance is provided. The method forms a compact dual-band filter by setting an internally coupled and externally coupled filter, and connecting two centrally symmetrically arranged stepped impedance resonators with a quarter-wavelength matching line. The filter can provide two passbands in the S band and the L band respectively.

[0004] The present invention provides a compact microstrip dual-band filter with stepped impedance, comprising:

[0005] A first ladder impedance resonator is arranged on a dielectric substrate;

[0006] a second stepped impedance resonator, forming an inner coupling connection with the first stepped impedance resonator, wherein the second stepped impedance resonator and the first stepped impedance resonator are symmetrically arranged about the center of the dielectric substrate, and the openings of the first stepped impedance resonator and the second stepped impedance resonator are arranged relative to each other;

[0007] One side of the first stepped impedance resonator is connected to a first quarter impedance matching line, the first stepped impedance resonator and the first quarter impedance matching line constitute a first frequency band, the first quarter impedance matching line is configured to determine a first wavelength impedance of the first quarter impedance matching line according to a Q value of a load connected to the first frequency band and a characteristic impedance of a transmission cable, and the first wavelength impedance also determines a resonant frequency of the first frequency band;

[0008] A second quarter impedance matching line is connected to one side of the second stepped impedance resonator. The second stepped impedance resonator and the second quarter impedance matching line constitute a second frequency band. The second quarter impedance matching line is configured to determine the second wavelength impedance of the second quarter impedance matching line based on the Q value of the connected load and the characteristic impedance of the transmission cable in the second frequency band. The second wavelength impedance also determines the resonant frequency of the second frequency band.

[0009] Optionally, the stepped resonant cavity is provided with a double-layer stepped impedance, the double-layer stepped impedance is connected to the openings on the first stepped impedance resonator and the second stepped impedance resonator, and the two double-layer stepped impedances arranged inside the first stepped impedance resonator and the second stepped impedance resonator are arranged in a centrally symmetrical manner.

[0010] Optionally, the double-layer stepped impedance includes a first step and a second step, the length of the first step is greater than the length of the second step, one end of the second step is connected to the first step, and the other end is provided with the opening;

[0011] The openings provided inside the two first stepped impedance resonators and the second stepped impedance resonator are opposite to each other and have the same height.

[0012] Optionally, the opening is located at a center position of the first step away from one end of the second step.

[0013] Optionally, a first coupling gap S1 is provided between the first stepped impedance resonator and the second stepped impedance resonator, and a distance of the first coupling gap S1 is set to 0.6 mm.

[0014] Optionally, the three bending sections provided on the first quarter impedance matching line divide the matching line into: a first microstrip line, a second microstrip line, a third microstrip line and a fourth microstrip line;

[0015] One end of the first microstrip line is connected to the first input / output port, and the first microstrip line has a stepped structure. The first microstrip line, the second microstrip line, the third microstrip line and the fourth microstrip line are connected in sequence, and the first microstrip line and the second microstrip line are bent 90° in a vertical direction, the second microstrip line and the third microstrip line are bent 90° in a horizontal direction, and the third microstrip line and the fourth microstrip line are bent 90° in a horizontal direction.

[0016] Optionally, a second coupling gap S2 is provided between the fourth microstrip line and the first stepped impedance resonator or the second stepped impedance resonator, and the second coupling gap S2 is 1 mm.

[0017] Optionally, an external coupling connection is formed between the first stepped impedance resonator, the first quarter impedance matching line and the first input / output port connected in sequence and the second stepped impedance resonator, the second quarter impedance matching line and the second input / output port connected in sequence.

[0018] The beneficial effects of this application include:

[0019] 1. This invention uses two centrosymmetrical first-step impedance resonators and a second-step impedance resonator to form an inner coupling connection, and then uses two first-quarter impedance matching lines and a second-quarter impedance matching line provided on the two resonators to form an outer coupling connection. This makes the filter structure simple and compact, easy to process, low-cost, and easy to mass-produce.

[0020] 2. The two resonators provided in this application are connected to a quarter-impedance matching line. The quarter-impedance matching line adopts a zigzag feeder structure, forming a first microstrip line, a second microstrip line, a third microstrip line, and a fourth microstrip line, effectively reducing the feeder size.

[0021] 3. The three transmission zeros improve the out-of-band suppression and frequency selectivity of the filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the filter structure distribution diagram;

[0023] Figure 2 Schematic diagram of filter structure distribution size;

[0024] Figure 3 Schematic diagram of the coupling coefficient of the dual-band resonator changing with the distance between the resonators;

[0025] Figure 4 Schematic diagram of the change between the input and output group delay curves and the second coupling gap S2;

[0026] Figure 5 for the reason Figure 1 The S parameter simulation curve of the filter structure obtained by sonnet software;

[0027] Figure 6 Schematic diagram of current density at the first resonance;

[0028] Figure 7 Schematic diagram of current density at the second resonance;

[0029] Figure 8 Schematic diagram of current density distribution at the three transmission zero points of the filter;

[0030] List of components and reference numerals: 1. dielectric substrate; 2. first ladder impedance resonator; 3. second ladder impedance resonator; 4. first quarter impedance matching line; 41. first microstrip line; 42. second microstrip line; 43. third microstrip line; 44. fourth microstrip line; 5. second quarter impedance matching line; 6. first input / output port; 7. second input / output port; 8. ladder-type resonant cavity; 9. opening. DETAILED DESCRIPTION

[0031] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0032] Please refer to Figure 1 and Figure 2 As shown, the present application provides a compact microstrip dual-band filter with stepped impedance, comprising:

[0033] The filter device provided in this application has dimensions of 52.2mm in width, 40mm in length, and 1mm in thickness. The filter has a center frequency of 1.68 / 2.99GHz, providing two passbands in the L-band and S-band, respectively. The relative bandwidths of the two bands are 3.27% and 2.85%, respectively, achieving an insertion loss of less than 1dB and a return loss of greater than 20dB in each band. A transmission zero is generated in the impedance-compact dual-passband microstrip, resulting in increased out-of-band attenuation. The passband frequency ranges from 1.96GHz to 2.59%GHz, and the isolation between the two passbands is better than 25dB. The filter was analyzed using sonnet software.

[0034] A first stepped impedance resonator 2 is arranged on the dielectric substrate 1;

[0035] The dielectric substrate 1 has a vertical axis AA and a horizontal axis BB, and the intersection of the vertical axis AA and the horizontal axis BB is the center position of the dielectric substrate 1 .

[0036] The second stepped impedance resonator 3 is internally coupled to the first stepped impedance resonator 2, and the second stepped impedance resonator 3 and the first stepped impedance resonator 2 are symmetrically arranged about the center of the dielectric substrate 1, and the openings 9 of the first stepped impedance resonator 2 and the second stepped impedance resonator 3 are relatively arranged;

[0037] One side of the first stepped impedance resonator 2 is connected to a first quarter impedance matching line 4. The first stepped impedance resonator 2 and the first quarter impedance matching line 4 constitute a first frequency band. The first quarter impedance matching line 4 is configured to determine a first wavelength impedance of the first quarter impedance matching line 4 according to a load Q value connected to the first frequency band and a characteristic impedance of a transmission cable. The first wavelength impedance also determines the resonant frequency of the first frequency band.

[0038] A second quarter impedance matching line 5 is connected to one side of the second stepped impedance resonator 3. The second stepped impedance resonator 3 and the second quarter impedance matching line 5 constitute a second frequency band, and the second quarter impedance matching line 5 is configured to determine the second wavelength impedance of the second quarter impedance matching line 5 based on the Q value of the connected load and the characteristic impedance of the transmission cable in the second frequency band. The second wavelength impedance also determines the resonant frequency of the second frequency band.

[0039] A first coupling gap S1 is defined between the first stepped impedance resonator 2 and the second stepped impedance resonator 3 , and the distance of the first coupling gap S1 is set to be 0.6 mm.

[0040] One side of the first stepped impedance resonator 2 is connected to a first quarter impedance matching line 4, and the side of the second stepped impedance resonator 3 opposite to the first quarter impedance matching line 4 is connected to a second quarter impedance matching line 5;

[0041] One end of the first quarter impedance matching line 4 away from the first stepped impedance resonator 2 is connected to a first input / output port 6;

[0042] One end of the first quarter impedance matching line 4 away from the second stepped impedance resonator 3 is connected to a second input / output port 7;

[0043] The size of the first quarter impedance matching line 4 and the second quarter impedance matching line 5 depends on the load Q value of the two frequency bands and the characteristic impedance of 50 ohms. The two quarter impedance matching lines are one quarter of the wavelength corresponding to the center frequency. When designing a single cavity of the filter, the cavity size is designed approximately according to a quarter wavelength. The loaded Q value refers to the steepness of the filter frequency turning point, and is also reflected in the degree of suppression of the filter. The larger the Q value, the better the suppression of the filter. The input and output impedance ladder lines formed by the two quarter impedance matching lines are designed to match the impedance of the cavity to the port 50Ω. The stepped impedance of a single cavity is designed to achieve miniaturization of the cavity. The quarter impedance matching line adopts a zigzag feeding structure, which effectively reduces the size of the filter.

[0044] Please continue to refer to Figure 1 and Figure 2 As shown, a stepped resonant cavity 8 is provided inside the first stepped impedance resonator 2 and the second stepped impedance resonator 3;

[0045] An inner coupling connection is formed between the first stepped impedance resonator 2 and the second stepped impedance resonator 3, and a first coupling gap S1 formed between the first stepped impedance resonator 2 and the second stepped impedance resonator 3 is 0.6 mm. The first stepped impedance resonator 2 has a stepped resonant cavity 8 inside. The length of the stepped resonant cavity 8 is as follows: Figure 2 As shown, they are: L1 = 10.5 mm, L2 = 11.5 mm, L3 = 2.5 mm. Among them, L3 is the opening distance of the first stepped impedance resonator 3, and the length of the first stepped impedance resonator 2 is L = 12 mm, the width is W = 17.5 mm, and the opening of the first stepped impedance resonator 2 is set at the center position;

[0046] The stepped resonant cavity 8 is provided with a double-layer stepped impedance, which is connected to the openings 9 on the first stepped impedance resonator 2 and the second stepped impedance resonator 3, and the two double-layer stepped impedances arranged inside the first stepped impedance resonator 2 and the second stepped impedance resonator 3 are centrally symmetrical.

[0047] The double-layer ladder impedance includes a first step and a second step, the length of the first step is greater than the length of the second step, one end of the second step is connected to the first step, and the other end is provided with the opening 9;

[0048] The openings 9 provided inside the first stepped impedance resonator 2 and the second stepped impedance resonator 3 are opposite to each other and have the same height.

[0049] The opening 9 is located at the center of the first step away from the end of the second step.

[0050] The first quarter impedance matching line 4 and the second quarter impedance matching line 5 are provided with three bending sections.

[0051] The three bending sections provided on the first quarter impedance matching line 4 divide the matching line into: a first microstrip line 41, a second microstrip line 42, a third microstrip line 43 and a fourth microstrip line 44;

[0052] One end of the first microstrip line 41 is connected to the first input / output port 6, and the first microstrip line 41 has a stepped structure. The first microstrip line 41, the second microstrip line 42, the third microstrip line 43 and the fourth microstrip line 44 are connected in sequence, and the first microstrip line 41 and the second microstrip line 42 are bent 90° in the vertical direction, the second microstrip line 42 and the third microstrip line 43 are bent 90° in the horizontal direction, and the third microstrip line 43 and the fourth microstrip line 44 are bent 90° in the horizontal direction.

[0053] A second coupling gap S2 is defined between the fourth microstrip line 44 and the first stepped impedance resonator 2 or the second stepped impedance resonator 3 . The second coupling gap S2 is 1 mm.

[0054] An external coupling connection is formed between the first ladder impedance resonator 2, the first quarter impedance matching line 4 and the first input / output port 6 connected in sequence and the second ladder impedance resonator 3, the second quarter impedance matching line 5 and the second input / output port 7 connected in sequence.

[0055] When two similar first-step impedance resonators 2 and second-step impedance resonators 3 are close to each other, electromagnetic field coupling occurs. For dual-frequency resonators, both the fundamental frequency (f1) and the second harmonic frequency (f2) should be considered. Therefore, when the two resonators are coupled, the resonant frequency (f 11 ,f 12 ,f 21 ,f 22 ) will have four peaks. Frequency f separated from f1 11 and f 12 Close to the fundamental frequency. The frequency f separated from f2 21 and f 22 Close to the second harmonic frequency. The coupling coefficients for the first and second frequency bands are listed below.

[0056]

[0057] The coupling coefficient of the dual-band resonator decreases as the coupling distance D0 between the resonators increases. Figure 3 , which can be used to determine the relative positions between resonators.

[0058] In terms of the group delay of a single resonator, the load Q value (Q e ) and input and output group delay τ s11 The relationship between (f0) is shown in the following equation 3.

[0059]

[0060] Where: f0 is the center frequency;

[0061] The relationship between the input and output group delay curves and the coupling distance D0 is as follows: Figure 4 shown.

[0062] The input and output structures used in the present invention, the S parameter simulation curve obtained by sonnet is as follows Figure 5 As shown in the figure, the return loss in the first frequency band is less than -21.97 dB. The return loss in the second frequency band is -22.23 dB. The three transmission zeros are located at 1.18 GHz, 2.36 GHz, and 3.32 GHz, with attenuations of -75.36 dB, -62.64 dB, and -49.52 dB, respectively. The transmission zeros increase the filter's rejection and frequency selectivity.

[0063] Please refer to Figure 6 、 Figure 7 and Figure 8 As shown, Figure 6 、 Figure 7 and Figure 8 The vertical axis represents the current distribution;

[0064] Figure 6 describes the current density at the first resonance. It is worth noting that the strong coupling is determined by the longer impedance lines on the left and right. The current density at the second resonance frequency is as follows Figure 7 It is obvious that the second resonant frequency is determined by the shorter impedance lines below and above.

[0065] To further understand the transmission zeros of the filter response, Figure 8 The current distribution at each transmission zero is shown.

[0066] from Figure 8 As can be seen, the first transmission zero at f = 1.18 GHz has an attenuation of -75.36 dB, and the current density distribution is determined by the input feeder and the intermediate microstrip line of the first resonant cavity. The second transmission zero at f = 2.36 GHz has an attenuation of -62.64 dB, and the current density distribution is determined by the input feeder and the upper portion of the first resonant cavity. The third transmission zero at f = 3.32 GHz has an attenuation of -49.52 dB, and the current density distribution is determined by the input feeder and the lower portion of the first resonant cavity. These three transmission zeros significantly improve the filter's out-of-band rejection and frequency selectivity, significantly enhancing the filter's performance. Therefore, adding more transmission zeros to the filter design will increase the filter's rejection and improve stopband performance.

[0067] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A compact microstrip dual-band filter with stepped impedance, characterized in that: include: A first ladder impedance resonator (2) is arranged on the dielectric substrate (1); The second stepped impedance resonator (3) forms an inner coupling connection with the first stepped impedance resonator (2), and the second stepped impedance resonator (3) and the first stepped impedance resonator (2) are symmetrically arranged about the center of the dielectric substrate (1), and the openings (9) of the first stepped impedance resonator (2) and the second stepped impedance resonator (3) are relatively arranged; One side of the first stepped impedance resonator (2) is connected to a first quarter impedance matching line (4), the first stepped impedance resonator (2) and the first quarter impedance matching line (4) constitute a first frequency band, the first quarter impedance matching line (4) is configured to determine a first wavelength impedance of the first quarter impedance matching line (4) according to a load Q value connected to the first frequency band and a characteristic impedance of a transmission cable, and the first wavelength impedance also determines a resonant frequency of the first frequency band; A second quarter impedance matching line (5) is connected to one side of the second stepped impedance resonator (3), the second stepped impedance resonator (3) and the second quarter impedance matching line (5) constitute a second frequency band, and the second quarter impedance matching line (5) is configured to determine a second wavelength impedance of the second quarter impedance matching line (5) according to the Q value of the load connected in the second frequency band and the characteristic impedance of the transmission cable, and the second wavelength impedance also determines the resonant frequency of the second frequency band; The stepped resonant cavity (8) is provided with a double-layer stepped impedance, the double-layer stepped impedance is connected to the openings (9) on the first stepped impedance resonator (2) and the second stepped impedance resonator (3), and the two double-layer stepped impedances arranged inside the first stepped impedance resonator (2) and the second stepped impedance resonator (3) are centrally symmetrically arranged.

2. The compact microstrip dual-band filter with stepped impedance according to claim 1, characterized in that: The double-layer ladder impedance comprises a first step and a second step, the length of the first step is greater than the length of the second step, one end of the second step is connected to the first step, and the other end is provided with the opening (9); The openings (9) provided inside the two first stepped impedance resonators (2) and the second stepped impedance resonator (3) are opened relative to each other at the same height.

3. The compact microstrip dual-band filter with stepped impedance according to claim 2, characterized in that: The opening (9) is located at a central position of the first step away from one end of the second step.

4. The compact microstrip dual-band filter with stepped impedance according to claim 1, characterized in that: A first coupling gap (S1) is provided between the first stepped impedance resonator (2) and the second stepped impedance resonator (3), and the distance of the first coupling gap (S1) is set to 0.6 mm.

5. The compact microstrip dual-band filter with stepped impedance according to claim 1, characterized in that: Three bending sections provided on the first quarter impedance matching line (4) divide the matching line into: a first microstrip line (41), a second microstrip line (42), a third microstrip line (43) and a fourth microstrip line (44); One end of the first microstrip line (41) is connected to the first input / output port (6), and the first microstrip line (41) has a stepped structure. The first microstrip line (41), the second microstrip line (42), the third microstrip line (43) and the fourth microstrip line (44) are connected in sequence, and the first microstrip line (41) and the second microstrip line (42) are bent 90 degrees in a vertical direction, the second microstrip line (42) and the third microstrip line (43) are bent 90 degrees in a horizontal direction, and the third microstrip line (43) and the fourth microstrip line (44) are bent 90 degrees in a horizontal direction.

6. The compact microstrip dual-band filter with stepped impedance according to claim 5, characterized in that: A second coupling gap (S2) is provided between the fourth microstrip line (44) and the first stepped impedance resonator (2) or the second stepped impedance resonator (3), and the second coupling gap (S2) is 1 mm.

7. The compact microstrip dual-band filter with stepped impedance according to claim 6, characterized in that: An external coupling connection is formed between the first ladder impedance resonator (2), the first quarter impedance matching line (4), and the first input / output port (6) connected in sequence and the second ladder impedance resonator (3), the second quarter impedance matching line (5), and the second input / output port (7) connected in sequence.

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