CN115425375B - Band-pass filter and miniaturized CQ topological structure thereof - Google Patents

Abstract

The invention discloses a bandpass filter and its miniaturized CQ topological structure. The bandpass filter includes a miniaturized CQ topological structure, an input feed unit, an output feed unit, a first microstrip line and a second microstrip The input feed unit and the output feed unit are non-contact coupled with the miniaturized CQ topology; the miniaturized CQ topology includes the first double resonator unit, the second double resonator unit and the In the cross-coupling unit, the first double-resonator unit includes a first resonator and a second resonator, and the second double-resonator unit includes a third resonator and a fourth resonator, and each resonator is open-circuited at one end and short-circuited at the other end A quarter-wavelength resonator, and the short-circuit end is connected to the metal ground on the back of the dielectric substrate through a metallized ground via hole, and the open-circuit end points to the short-circuit end after being bent at 180 degrees. The invention realizes a 4-pole 4-zero band-pass filter with miniaturization, high flatness and high out-of-band rejection.

Description

A Bandpass Filter and Its Miniaturized CQ Topology

technical field

The invention relates to the field of microwave circuits, in particular to a band-pass filter and its miniaturized CQ topological structure.

Background technique

Band-pass filters play an important role in signal filtering in microwave integrated circuits. Common band-pass filters include cavity filters, SIW (Substrate Integrated Waveguide, substrate integrated waveguide) filters, silicon-based MEMS (Micro-electromechanical Systems, microelectromechanical systems) filters and microstrip filters. The cavity filter has a high Q value, small insertion loss, and flat in-band, which has advantages in narrow-band applications. The disadvantage is that it is large in size, cannot effectively realize miniaturization, and is limited in high-density integration applications. The SIW filter realizes a flat waveguide filter structure on the dielectric substrate, and uses metallized vias to realize the waveguide side wall, thereby realizing a miniaturized SIW filter. Its Q value is moderate, but it is still too large in high-density integration applications to meet SIP (System in Package, system-in-package) requirements for integrated applications. Due to the advantages of small size, easy integration, and self-shielding, silicon-based MEMS filters are widely used in microwave integrated circuits. The disadvantage is that the cost is high, and the thickness of 0.82mm in high-density applications makes the device characteristics vulnerable to the grounding performance of the shielding cover. Influence, it is often necessary to increase the grounding characteristics of the shield cover to achieve high suppression requirements. Microstrip filters are widely used in microwave components, common types such as parallel coupled lines, interdigitated lines, hairpin lines, and split resonators. Large insertion loss, poor in-band flatness, but its advantages are also very prominent, that is, it is suitable for broadband high-density integration applications, and the cost is low.

Bandpass filters used in microwave systems usually have strict requirements on in-band flatness, near-end out-of-band rejection, broadband rejection, and volume. Taking a bandpass filter with a center frequency of 22GHz and an absolute bandwidth of 1GHz as an example, it is generally required that the in-band flatness of 1GHz is less than 1dB, the low-end deviation from the lower sideband 1GHz out-of-band suppression is greater than 35dBc, the high-end suppression within 40GHz is greater than 40dBc, and the volume is less than 4mm ×2.5mm×1mm and the smaller the better. However, the in-band flatness and out-of-band rejection, out-of-band rejection and volume of the filter are often contradictory indicators. Generally speaking, the lower the filter order, the better the in-band flatness, but the worse the out-of-band rejection, and increasing the order can improve the out-of-band rejection, but the in-band flatness will deteriorate and the volume will increase. In order to solve this contradiction, superconducting filter technology, lossy filter and other technologies can be used in the design to achieve high flatness and high out-of-band rejection characteristics, but they also face their own shortcomings: for superconducting filters, they are faced with small problems of integration, integration, and harsh working conditions; for lossy filters, non-uniform Q value technology is often used, and high-Q and low-Q transmission paths need to be designed, which are generally larger in size and more complex in structural design. Density-integrated applications still have a certain distance. Relatively speaking, it is more engineering achievable to adopt the cross-coupling structure to reduce the filter order to achieve high flatness and high rejection index.

A classic topology in the cross-coupled topology is the CQ structure, as shown in Figure 1, where a black origin represents a resonator, a line segment represents electromagnetic coupling, a solid black line represents the main coupling, and a dotted line represents the cross-coupling. Generally speaking, the two are coupled With opposite polarity, a pair of CQ structures can introduce a pair of transmission zeros (one at the high end and one at the low end) at both ends of the passband to improve the near-end out-of-band rejection of the passband, as shown in Figure 2. By setting this type of unit structure in the filter topology, transmission zeros can be quickly and flexibly introduced at limited frequency points to improve the out-of-band rejection of the filter. The filter topology composed of the CQ structure is shown in Figure 3. Although this method is very effective and flexible for improving the out-of-band rejection of the filter, the disadvantage is that it often requires the use of complex topological structures. For example, two pairs of CQ structures are generally required to generate two pairs of transmission zeros, and the Q of the microstrip resonator above the X-band The value drops seriously, and the increase of the order will greatly increase the in-band insertion loss and in-band flatness. In terms of miniaturization, the CQ topology composed of split resonant rings is usually arranged in a "field" shape. The resonators are not in a straight line and occupy a large width, which is not conducive to miniaturization, as shown in Figure 4. In some other technologies, high-impedance lines are also used to realize the miniaturization of filters. The cost of this technical solution above the X-band is obvious, that is, high-impedance line resonators bring miniaturization and at the same time bring more If the loss is large, the in-band flatness will also deteriorate accordingly.

Contents of the invention

In order to solve the above problems, the present invention proposes a band-pass filter and its miniaturized CQ topology, wherein the band-pass filter can realize two pairs of transmission zeros (4 poles and 4 zeros). The miniaturized CQ topology, input and output feed units, and linear arrangement of feeders in this bandpass filter can effectively solve the miniaturization problem of millimeter wave filters and the volume, out-of-band suppression, and in-band flatness faced in the miniaturization process Double contradiction with out-of-band suppression. The far-end transmission zero point introduced by the design of the feed unit effectively overcomes the suppression rebound caused by the near-end zero point of the CQ topology and the parasitic passband problem caused by the structure itself, and realizes good near-end suppression, broadband suppression, and resonance All devices use uniform impedance lines, which avoids the problems of increased loss and deterioration of in-band flatness caused by using high-impedance lines for miniaturization, and solves the contradiction between miniaturization, high in-band flatness, and high out-of-band suppression in one fell swoop question.

The technical scheme that the present invention adopts is as follows:

A miniaturized CQ topology, including a first double resonator unit, a second double resonator unit and a cross-coupling unit arranged on the surface of a dielectric substrate, the first double resonator unit includes a first resonator and a second resonator The second double resonator unit includes a third resonator and a fourth resonator, each resonator is a quarter-wavelength resonator with one end open and the other end short-circuited, and the short-circuit end passes through a metallized ground via hole Connected to the metal ground on the back of the dielectric substrate, the open-circuit end is bent at 180 degrees and then points to the short-circuit end; the open-circuit parts of the first resonator and the second resonator are adjacent to each other, and the second resonator and the third resonator The open-circuit parts of the resonator are opposite to each other, and the open-circuit parts of the third resonator and the fourth resonator are adjacent to each other; the cross-coupling unit is arranged between the first resonator and the fourth resonator, and the coupling end It is opposite to the bent portion of the first resonator and the fourth resonator.

Further, the cross-coupling unit includes a first coupling end, an interconnection line, and a second coupling end connected in sequence, and the first coupling end and the second coupling end are arranged in a T-shaped structure.

Further, the horizontal portion of the first coupling end is opposite to the bent portion of the first resonator and has an equivalent length, and the horizontal portion of the second coupling end is opposite to the bent portion of the fourth resonator and has an equivalent length.

A bandpass filter comprising the miniaturized CQ topology, an input feed unit, an output feed unit, two first microstrip lines and two second microstrip lines, the input feed unit, the output The feed unit is respectively coupled with the miniaturized CQ topological structure through non-contact coupling, a first microstrip line, a second microstrip line are connected to the input feed unit in turn, another first microstrip line, another second microstrip line The strip line and the output feed unit are connected sequentially, and the impedance of the second microstrip line is greater than the impedance of the first microstrip line; the input feed unit and the output feed unit are both open-circuited at one end and short-circuited at the other end, but the length is less than a quarter A resonator with one wavelength, and the short-circuit end is located on the same side of the dielectric substrate, and the open-circuit end points to the short-circuit end after being bent at 180 degrees; the input feed unit and the open-circuit part of the first resonator are opposite to each other, and the The output feeding unit and the open-circuit part of the fourth resonator are opposite to each other in pairs.

Further, the bent parts of the input feed unit and the output feed unit are connected to the second microstrip line.

Further, the bandpass filter further includes two equivalent bonding inductance matching sections, and the equivalent bonding inductance matching sections are connected to the first microstrip line.

Further, the first microstrip line includes a 50-ohm transmission line.

Further, the second microstrip line includes a high-impedance transmission line.

Further, one or more miniaturized CQ topology structures are provided.

Further, the dielectric substrate includes a ceramic substrate, a sapphire substrate, a superconducting material substrate or a semiconductor material substrate.

The beneficial effects of the present invention are:

(1) The present invention realizes a 4-pole 4-zero (4-4) band-pass filter with miniaturization, high flatness, and high out-of-band rejection. By using a quarter-wavelength folded resonator and a miniaturized CQ topology composed of cross-coupling units, the passband flatness within 0.5dB is achieved, and the near-end transmission zero position near the passband can be adjusted by adjusting the amount of cross-coupling Realize flexible adjustment.

(2) The folded resonators of the miniaturized CQ topology of the present invention are sequentially arranged in a straight line, which can effectively reduce the width of the filter, and obtain higher low-end out-of-band suppression than the prior art.

(3) The present invention adopts a non-contact coupling feeding method with parasitic passband suppression characteristics, which not only effectively solves the problem of out-of-band suppression deterioration caused by parasitic passbands, but also introduces a pair of remote transmission zeros to realize a small Broadband, high rejection characteristics of low-order filters.

(4) the band-pass filter of the present invention is small in volume, suitable for microwave hybrid integrated circuits and SIP integrated applications, and realizes 4 transmission zeros (8 Compared with the 8-4 structure with 4 poles and 4 zeros), due to the small resonator order, it can have better in-band flatness, smaller volume and better broadband suppression characteristics (the parasitic passband is farther away), It effectively alleviates the dual contradictions between high in-band flatness and high out-of-band rejection, high out-of-band rejection and small size of the band-pass filter.

Description of drawings

Figure 1 CQ filter unit formed by CQ topology and split resonant ring.

Figure 2 CQ topology millimeter wave filter and its frequency response characteristics.

Fig. 3 Filter topology composed of CQ structure.

Figure 4 is an 8th-order microstrip filter composed of two CQ structures and its frequency response curve.

Figure 5 shows the quarter-wavelength resonator of Embodiment 1 and its improved structure.

Figure 6 shows the miniaturized filtering structure of Embodiment 1.

Fig. 7 is the frequency response characteristic of the miniaturized filtering structure of the first embodiment.

Fig. 8 is the miniaturized CQ topology structure of Embodiment 1.

FIG. 9 is the frequency response characteristic of the miniaturized CQ topology in Embodiment 1. FIG.

Fig. 10 is the non-contact coupling feeding unit of Embodiment 2.

Fig. 11 is the frequency response characteristic after the non-contact coupling feed unit is introduced in Embodiment 2.

The 4-pole and 4-zero (4-4) bandpass filter of Embodiment 2 in FIG. 12 .

Figure 13 shows the frequency response characteristics of the 4-pole and 4-zero (4-4) bandpass filter of Embodiment 3.

The 4-pole and 4-zero (4-4) bandpass filter of Embodiment 4 in FIG. 14 .

Figure 15 shows the frequency response characteristics of the 4-pole and 4-zero (4-4) bandpass filter of Embodiment 4.

Reference signs: 100-quarter waveguide wavelength resonator, 200-miniature filter structure, 300-miniature CQ topology; 11-plane metal pattern, 12-metallized ground via hole, 20-dielectric substrate; 101 - first resonator, 102 - second resonator, 103 - third resonator, 104 - fourth resonator, 105 - cross coupling unit, 1051 - first coupling end, 1052 - interconnection line, 1053 - coupling end 1053, 106-first microstrip line, 107-second microstrip line, 108-equivalent bonding inductance matching section, 109-input feeding unit, 110-output feeding unit; A-first double resonance unit, B - Second double resonant unit.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific implementations of the present invention are now described. It should be understood that the specific embodiments described here are only used to explain the present invention, and are not intended to limit the present invention, that is, the described embodiments are only some of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the present invention.

Example 1

This embodiment provides a miniaturized CQ topology, including a first dual-resonator unit A, a second dual-resonator unit B, and a cross-coupling unit 105 disposed on the surface of a dielectric substrate 20. The first dual-resonator unit A includes The first resonator 101 and the second resonator 102 , the second double resonator unit B includes a third resonator 103 and a fourth resonator 104 , and each resonator is made by folding the quarter-wavelength resonator 100 .

As shown in Figure 5, the quarter waveguide wavelength resonator 100 is composed of a planar metal pattern 11 and a metallized ground via hole 12, and is located on the upper surface of the dielectric substrate 20 (the back is the entire metal ground), one end of which is open and the other end is short-circuited , the short-circuit end is connected to the metal ground on the back of the dielectric substrate 20 through the metallized ground via hole 12 . In order to reduce the size in the width direction, the quarter-waveguide wavelength resonator 100 is folded so that the open end points to the short end, and the size in the width direction is reduced by about 50%. The bent part is used as a cross-coupling energy extraction part. Preferably, the metallized ground via hole 12 can be set as a circular ground via hole of 50um-200um.

As shown in FIG. 6 , it is a miniaturized filter structure 200 arranged in a straight line. This structure is composed of four folded resonators described above. Two of the four resonators form a group, and the open-circuit ends are adjacent to each other. That is, the first resonator 101 and the second resonator 102 form a group of double resonator units, that is, the first double resonator unit A. It should be emphasized that the resonant lengths of the first resonator 101 and the second resonator 102 are different. Similarly, the third resonator 103 and the fourth resonator 104 form another group of double resonator units, that is, the second double resonator unit B. The open-circuit ends of the second resonator 102 and the third resonator 103 are opposite to each other, and the first double resonator unit A and the second double resonator unit B are symmetrical about the vertical center line. Before cross-coupling is introduced, the structure can obtain a cut ratio Schiff response (even number of double resonator elements); generalized Chebyshev response is obtained when the number of double resonator elements is odd.

FIG. 7 shows the frequency response characteristics of the miniaturized filter structure 200 , where the number of double resonator units in the left figure is an even number, and the number of double resonator units in the right figure is an odd number.

As shown in FIG. 8 is a miniaturized CQ topology 300, a cross-coupling unit 105 is provided between the first resonator 101 and the fourth resonator 104, which includes a first coupling end 1051, an interconnection line 1052 and The second coupling end 1053, the first coupling end 1051 and the second coupling end 1053 are arranged as a T-shaped structure, the horizontal part of the first coupling end 1051 is opposite to the bent part of the first resonator 101 and has the same length, and the second coupling end The horizontal part of 1053 is opposite to the bent part of the fourth resonator 104 and has the same length.

Preferably, the cross-coupling is realized from the bending position of the resonator, and different coupling strengths can be realized by adjusting the distance between the cross-coupling unit 105 and the first resonator 101 and the fourth resonator 104 to adjust the near-end zero point position. In addition, the first microstrip line 106 can be set to realize the electromagnetic characteristic simulation of the CQ unit, the first microstrip line is connected with the first resonator 101 and the fourth resonator 104 through the second microstrip line 107, fed into point close to the side of the short-circuit end. The impedance of the second microstrip line 107 is greater than the impedance of the first microstrip line 106, so as to achieve a larger adjustment range and adapt to different bandwidth requirements. Preferably, the first microstrip line 106 may use a 50-ohm transmission line, and the second microstrip line 107 may use a high-impedance transmission line.

It should be emphasized that the miniaturized CQ topology 300 can obtain two beneficial effects different from the prior art. The first is that the folded resonators of the miniaturized CQ topology 300 are arranged in a straight line, which can effectively reduce the size of the filter The second is that the four resonators can obtain three transmission zero points (two at the low end and one at the high end), which can obtain higher low-end out-of-band rejection than the prior art. FIG. 9 shows the frequency response characteristics of the miniaturized CQ topology 300 .

Example 2

This embodiment is on the basis of embodiment 1:

This embodiment provides a bandpass filter, including a miniaturized CQ topology 300, an input feed unit 109, an output feed unit 110, two first microstrip lines 106 and two second microstrip lines 107, The input feed unit 109 and the output feed unit 110 are respectively connected to the miniaturized CQ topological structure through non-contact coupling. A first microstrip line 106, a second microstrip line 107 are connected to the input feed unit 109 in turn, and the other The first microstrip line 106, another second microstrip line 107 and the output feed unit 110 are connected in sequence.

The miniaturized CQ topology 300 provided in Embodiment 1 brings the advantages of realizing two transmission zeros at the low end of the passband to improve the low-end out-of-band suppression, but also brings about the spurious passband at the high-end of the passband that makes the high-end out-of-band suppression worsening situation. Investigating the frequency of the spurious passband (near 31.5 GHz in the ellipse in FIG. 9 ), it can be found that the characteristic frequency of the cross-coupling unit 105 is in good agreement with the spurious frequency point, and it can be determined that the spurious passband is caused by the cross-coupling unit 105 .

To solve the above problems, this embodiment introduces a non-contact coupling input feed unit 109 and output feed unit 110 , as shown in FIG. 10 . The design of the input feed unit 109 and the output feed unit 110 needs to satisfy two conditions that no resonance can occur at the eigenfrequency corresponding to the cross-coupling unit 105 and that input and output coupling can be effectively performed. Since neither the input feed unit 109 nor the first resonator 101 can resonate at the frequency corresponding to the cross-coupling unit 105, the input feed unit 109 and the first resonator 101 are magnetically coupled (the output feed unit 110 The same as between the fourth resonator 104 ), so the spurious passband introduced by the cross-coupling unit 105 can be suppressed well.

FIG. 11 shows the frequency response characteristics after introducing the input feed unit 109 and the output feed unit 110. It can be seen that this structure effectively suppresses the parasitic passband existing near 31 GHz in FIG. 9 . Not only that, the structure also produces a pair of transmission zeros (near 14GHz and 30GHz) at the low end and high end of the passband frequency 22GHz, which can well solve the problem of far-end rejection of the filter.

As shown in Figure 12, it is a kind of miniaturization, high flatness, high selectivity 4 zeros 4 poles (4-4) bandpass filter of the present embodiment, and this structure comprises the first microstrip that is made on the surface of dielectric substrate 20 Line 106 (including input and output microstrip lines), at the extreme ends of the first microstrip line 106, an equivalent bonding inductance matching section 108 is provided, which is used to match the equivalent bonding of 0.1 to 0.2nH Inductors to achieve excellent matching with millimeter wave chips and transmission lines. The first microstrip line 106 is connected to the bent part of the feed unit through the second microstrip line 107, so that a wider range of tap adjustment can be realized. Between the input feed unit 109 and the output feed unit 110, a miniaturized CQ topological structure 300 is arranged, which is used to realize the band-pass transmission characteristic with a pair of near-end zeros, and through the input feed unit 109, the output feed The unit 110 implements a pair of far-end transmission zeros, which can effectively solve the suppression bounce problem caused by the miniaturized CQ topology 300 near-end zeros, thereby realizing miniaturization, near-end and far-end broadband high suppression characteristics. Due to the use of fewer orders, the bandpass filter can achieve smaller insertion loss and better in-band flatness.

Example 3

This embodiment is on the basis of embodiment 2:

Taking a K-band bandpass filter with a center frequency of 22GHz and an absolute bandwidth of 1GHz in a radio frequency system as an example, it is usually required that its 1GHz in-band flatness be less than 1dB, and its 1GHz out-of-band rejection from the sideband be greater than 35dBc. In this embodiment, the band-pass filter of Embodiment 2 is implemented on a 0.127 mm thick Al ₂ O ₃ ceramic substrate. Its structure is shown in FIG. 12 , and the layout area is only 2.8 mm×1.4 mm. Through the full-wave simulation analysis, the frequency response curve can be obtained as shown in Figure 13. From the figure, it can be seen that the minimum insertion loss in the passband of the filter is 2.083dB, and the insertion loss away from the center frequency of 500MHz is 2.518dB and 2.470dB respectively. The in-band flatness is 0.435dB, which effectively satisfies the requirement that the in-band flatness is less than 1dB, and is better than the achievable index in the prior art, and the realization of this index benefits from the use of fewer resonators.

In terms of out-of-band suppression, due to the small number of filter orders, the out-of-band suppression achieved by conventional technologies is generally poor. In this embodiment, a miniaturized CQ topology and a non-contact coupling feed design are used to achieve a pair of near-end zeros and a pair of remote zeros. In this embodiment, a pair of near-end zeros are located around 20 GHz and 25 GHz, respectively, and a pair of far-end zeros are located around 15 GHz and 31 GHz, respectively, which effectively solves the parasitic passband problem introduced by the cross-coupling unit 105 in the proposed miniaturized CQ structure And the near-end out-of-band suppression large rebound problem, while realizing the near-end and far-end high out-of-band suppression characteristics of the low-order filter, this structure can achieve a broadband suppression characteristic of more than 40dBc within 40GHz.

Example 4

This embodiment is on the basis of embodiment 2:

Still taking the above-mentioned band-pass filter as an example, in this embodiment, the input feed unit 109 and the output feed unit 110 in the band-pass filter shown in FIG. A bandpass filter whose frequency response characteristics are shown in Figure 15. It can be seen from Fig. 15 that the bandpass filter still effectively realizes four transmission zero points, has good in-band flatness and out-of-band suppression characteristics, and this structure can effectively reduce the input feed unit 109 and the first resonator 101, The machining accuracy requirements for the coupling distance between the output feeding unit 110 and the fourth resonator 104 are met.

It should be noted that the orientations or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "inner" and "outer" are based on the orientations or positions shown in the drawings relationship, or the usual orientation or positional relationship when the present invention is used, is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the referred device or element must have a specific orientation or be constructed in a specific orientation. and operation, and therefore should not be construed as limiting the invention. In addition, the terms "first", "second", "third", etc. are only used for distinguishing descriptions, and should not be construed as indicating or implying relative importance.

Claims (10)

1. The miniaturized CQ topological structure is characterized by comprising a first double-resonator unit (A), a second double-resonator unit (B) and a cross coupling unit (105) which are arranged on the surface of a medium substrate (20), wherein the first double-resonator unit (A) comprises a first resonator (101) and a second resonator (102), the second double-resonator unit (B) comprises a third resonator (103) and a fourth resonator (104), each resonator is a quarter-wavelength resonator with one open end and the other short end, the short-circuited end is connected to a metal ground on the back surface of the medium substrate (20) through a metallized grounding via hole (12), and the open end is bent by 180 degrees and then points to the short-circuited end; the open circuit parts of the first resonator (101) and the second resonator (102) are two by two, the open circuit parts of the second resonator (102) and the third resonator (103) are opposite to each other, and the open circuit parts of the third resonator (103) and the fourth resonator (104) are two by two; the cross coupling unit (105) is arranged between the first resonator (101) and the fourth resonator (104), and the coupling end is opposite to the bending parts of the first resonator (101) and the fourth resonator (104).

2. The miniaturized CQ topology according to claim 1, characterized in that the cross-coupling unit (105) comprises a first coupling end (1051), an interconnect line (1052) and a second coupling end (1053) connected in sequence, the first coupling end (1051) and the second coupling end (1053) being arranged in a T-shaped structure.

3. The miniaturized CQ topology according to claim 2, characterized in that the horizontal portion of the first coupling end (1051) is opposite and of comparable length to the bent portion of the first resonator (101) and the horizontal portion of the second coupling end (1053) is opposite and of comparable length to the bent portion of the fourth resonator (104).

4. A band-pass filter comprising a miniaturized CQ topology according to any one of claims 1 to 3, characterized by further comprising an input feed unit (109), an output feed unit (110), two first microstrip lines (106) and two second microstrip lines (107), wherein the input feed unit (109), the output feed unit (110) are respectively coupled with the miniaturized CQ topology by non-contact, one first microstrip line (106), one second microstrip line (107) and the input feed unit (109) are sequentially connected, the other first microstrip line (106), the other second microstrip line (107) and the output feed unit (110) are sequentially connected, and the impedance of the second microstrip line (107) is larger than the impedance of the first microstrip line (106);

the input feed unit (109) and the output feed unit (110) are resonators with one open end and the other short circuit end and the length smaller than a quarter wavelength, the short circuit ends are positioned on the same side of the medium substrate (20), and the open circuit ends are bent by 180 degrees and then are directed to the short circuit ends; the open circuit portions of the input feed unit (109) and the first resonator (101) are opposite to each other, and the open circuit portions of the output feed unit (110) and the fourth resonator (104) are opposite to each other.

5. The band-pass filter according to claim 4, characterized in that the bent portions of the input feed unit (109) and the output feed unit (110) are connected to the second microstrip line (107).

6. The bandpass filter according to claim 4, further comprising two equivalent bonded inductance matching sections (108), the equivalent bonded inductance matching sections (108) being connected with the first microstrip line (106).

7. The band pass filter according to claim 4, characterized in that the first microstrip line (106) comprises a 50 ohm transmission line.

8. The band pass filter according to claim 4, characterized in that the second microstrip line (107) comprises a high impedance transmission line.

9. The bandpass filter according to claim 4, wherein the miniaturized CQ topology is provided with one or more than one.

10. The bandpass filter according to claim 4, characterized in that the dielectric substrate (20) comprises a ceramic substrate, a sapphire substrate, a superconducting material substrate or a semiconductor material substrate.