Band-pass filter and multiplexer

Abstract

The invention discloses a band-pass filter and a multiplexer. The band-pass filter comprises a first port, a second port, a third port, at least one first filtering unit and at least one second filtering unit, each of the first filtering unit and the second filtering unit comprises at least one T-shaped network structure, a cross coupling network structure and a notch network structure; the cross coupling network structure is connected in parallel with the series structure of the at least one T-shaped network structure; the cross coupling network structure is used for forming cross coupling with a series structure of the T-shaped network structure, and the notch network structure is used for forming a notch point with a parallel structure of the T-shaped network structure; wherein the frequency corresponding to the notch point of the first filtering unit and the frequency corresponding to the notch point of the second filtering unit are located on the two sides of a pass band of the band-pass filter respectively. On the basis of ensuring the insertion loss of band-pass signals, the roll-off characteristic and the stop-band suppression characteristic of the band-pass filter can be improved, and the number of devices required by the band-pass filter can be reduced.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of signal processing, and in particular to a bandpass filter and a multiplexer. Background Art

[0002] In communication systems, signal interference can significantly reduce signal transmission efficiency. Filters can effectively suppress out-of-band signal interference to improve signal transmission efficiency. In modern communications, improving the filter's stopband suppression characteristics while ensuring the filter's passband signal insertion loss is one of the design challenges for filters. Summary of the invention

[0003] The present invention provides a bandpass filter and a multiplexer to improve the stopband suppression characteristics of the bandpass filter and improve the filtering performance of the bandpass filter.

[0004] In a first aspect, an embodiment of the present invention provides a bandpass filter, comprising a first port, a second port, a third port, and at least one first filtering unit and at least one second filtering unit;

[0005] The first filtering unit and the second filtering unit each include at least one T-type network structure, a cross-coupling network structure and a notch network structure;

[0006] The two series structures of the T-type network structure are connected in series between the first port and the second port, the first end of the parallel structure of the T-type network structure is connected to the middle node of the series structure, the second end of the parallel structure is connected to the third port through the notch network structure, and the cross-coupling network structure is connected in parallel to at least one series structure of the T-type network structure; the cross-coupling network structure is used to form a cross coupling with the series structure of the T-type network structure, and the notch network structure is used to form a notch point with the parallel structure of the T-type network structure; wherein the frequency corresponding to the notch point of the first filtering unit and the frequency corresponding to the notch point of the second filtering unit are respectively located on both sides of the passband of the bandpass filter.

[0007] Optionally, the cross-coupling network structure includes a cross-over capacitor and / or a cross-over inductor; the cross-over capacitor and the cross-over inductor are connected in parallel with at least one series structure of the T-type network structure.

[0008] Optionally, each of the series structures of the T-type network structure comprises a first inductive element and a first capacitive element connected in series;

[0009] In the first filtering unit, a first inductive element of a series structure is connected to a first inductive element of another series structure; the parallel structure of the T-type network structure includes a second capacitive element; a first pole of the second capacitive element is connected to a node between the two first inductive elements, and a second pole of the second capacitive element is connected to the notch network structure;

[0010] In the second filtering unit, the first capacitive element of one of the series structures is connected to the first capacitive element of another series structure; the parallel structure of the T-type network structure includes a second inductive element; the first pole of the second inductive element is connected to the node between the two first capacitive elements, and the second pole of the second inductive element is connected to the notch network structure.

[0011] Optionally, the trap network structure includes a first trap inductor; a first end of the first trap inductor is connected to a second end of the parallel structure of the T-type network structure, and a second end of the first trap inductor is connected to the third port.

[0012] Optionally, at least one of the first filtering unit and the second filtering unit further comprises at least one parallel resonant network structure;

[0013] The first end of the parallel resonant network structure is connected to the series port of the T-type network structure, and the second end of the parallel resonant network structure is connected to the third port.

[0014] Optionally, the parallel resonant network includes a third inductive element and a third capacitive element;

[0015] The first end of the third inductive element and the first pole of the third capacitive element are connected to the series port of the T-type network structure, and the second end of the third inductive element and the second pole of the third capacitive element are connected to the third port.

[0016] Optionally, the bandpass filter further comprises at least one electromagnetic filtering network, wherein the electromagnetic filtering network is connected in series between the first port and the second port.

[0017] Optionally, the bandpass filter includes at least two groups of filtering units, each group of filtering units includes the first filtering unit and the second filtering unit connected in series; the filtering units are connected in series between the first port and the second port, and the bandpass filter also includes a fourth port, which is arranged between the filtering units.

[0018] In a second aspect, an embodiment of the present invention further provides a multiplexer, comprising the bandpass filter described in the first aspect.

[0019] The technical solution of the embodiment of the present invention is to set a cross-coupling network structure and at least one T-type network structure in parallel connection, so that a notch point is formed when the cross-coupling network structure and the T-type network structure are cross-coupled. At the same time, the notch network structure is connected in series with the parallel structure of the T-type network structure, so that the notch network structure and the parallel structure of the T-type network structure form a notch point. Thereby, the number of notch points on both sides of the passband of the bandpass filter can be increased without additionally increasing the order of the bandpass filter, and the stopband suppression characteristics of the bandpass filter can be improved on the basis of ensuring the insertion loss of the bandpass signal. When the notch point is set in the adjacent band, the roll-off characteristics of the bandpass filter can be improved, and the adjacent band suppression of the bandpass filter is improved. At the same time, it is beneficial to reduce the number of devices required for the bandpass filter, which is beneficial to reduce the volume of the bandpass filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic structural diagram of a bandpass filter provided by an embodiment of the present invention;

[0021] Figure 2 A schematic diagram of the structure of another bandpass filter provided by an embodiment of the present invention;

[0022] Figure 3 A schematic diagram of the structure of another bandpass filter provided by an embodiment of the present invention;

[0023] Figure 4 A schematic diagram of the structure of another bandpass filter provided by an embodiment of the present invention;

[0024] Figure 5 A schematic diagram of the structure of a bandpass filter provided for related technology;

[0025] Figure 6 A schematic diagram for comparing the performance of different bandpass filters provided by an embodiment of the present invention;

[0026] Figure 7 A schematic diagram of the structure of another bandpass filter provided by an embodiment of the present invention;

[0027] Figure 8 A schematic diagram of the structure of another bandpass filter provided by an embodiment of the present invention;

[0028] Fig. 9 A schematic diagram of the structure of another bandpass filter provided by an embodiment of the present invention;

[0029] Fig.10 A schematic diagram of the structure of another bandpass filter provided by an embodiment of the present invention;

[0030] Fig.11 A schematic diagram of the structure of a multiplexer provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0032] Figure 1 A schematic diagram of the structure of a bandpass filter provided by an embodiment of the present invention. Figure 1 As shown, the bandpass filter includes a first port A, a second port B, a third port C and at least one first filtering unit 10 and at least one second filtering unit 20; the first filtering unit 10 and the second filtering unit 20 each include at least one T-type network structure 110, a cross-coupling network structure 120 and a notch network structure 130; two series structures 111 of the T-type network structure 110 are connected in series between the first port A and the second port B, a first end of a parallel structure 112 of the T-type network structure 110 is connected to an intermediate node M of the series structure 111, and the parallel structure The second end of 112 is connected to the third port C through the notch network structure 130, and the cross-coupling network structure 120 is connected in parallel with the series structure 111 of at least one T-type network structure 110; the cross-coupling network structure 120 is used to form a cross coupling with the series structure 111 of the T-type network structure 110, and the notch network structure 130 is used to form a notch point with the parallel structure 112 of the T-type network structure 110; wherein the frequency corresponding to the notch point of the first filtering unit 10 and the frequency corresponding to the notch point of the second filtering unit 20 are respectively located on both sides of the passband of the bandpass filter.

[0033] Specifically, Figure 1 exemplarily shows that the bandpass filter includes a first filter unit 10 and a second filter unit 20. The first filter unit 10 includes a T-type network structure 110, and the second filter unit 20 also includes a T-type network structure 110. Each T-type network structure 110 includes two series structures 111 and a parallel structure 112. The series structure 111 is connected in series between the first port A and the second port B, and the connection node between the two series structures 111 serves as the middle node M of the series structure 111, and the endpoints on both sides of the two series structures 111 serve as the series ports of the T-type network structure 110. Exemplarily, as Figure 1As shown, along the direction from the first port A to the second port B, in a T-type network structure 110, the port of the first series structure 111 away from the second series structure 111 serves as the first series port A1 of the T-type network structure 110, and the port of the second series structure 111 away from the first series structure 111 serves as the second series port A2 of the T-type network structure 110. One end of the parallel structure 112 is connected to the connection node M between the two series structures 111, so that the series structure 111 and the parallel structure 112 form the T-type network structure 110.

[0034] One of the first port A and the second port B can be the input end of the bandpass filter, and the other is the output end of the bandpass filter. When the series structure 111 of the T-type network structure 110 is connected in series between the first port A and the second port B, and the cross-coupling network structure 120 is connected in parallel with the series structure 111 of at least one T-type network structure 110, when the transmission signal passes through the T-type network structure 110, the transmission signal can be transmitted from the first series port A1 of the T-type network structure 110 to the second series port A2 of the T-type network structure 110 through two transmission paths. One transmission path is the two series structures 111 of the T-type network structure 110, and the other transmission path is the cross-coupling network structure 120 connected in parallel at both ends of the T-type network structure 110. When the cross-coupling network structure 120 forms a cross-coupling with the series structure 111 of the T-type network structure 110, a notch point can be formed after the transmission signal passes through the T-type network structure 110. In addition, the parallel structure 112 of the T-type network structure 110 is connected in series with the notch network structure 130. When the notch network structure 130 and the parallel structure 112 of the T-type network structure 110 form a notch point, the number of notch points formed after the transmission signal passes through the T-type network structure 110 can be further increased. When the frequency corresponding to the notch point of the first filter unit 10 and the frequency corresponding to the notch point of the second filter unit 20 are mainly located on both sides of the passband of the bandpass filter, the number of notch points on both sides of the passband of the bandpass filter can be increased synchronously, so that the stopband suppression characteristics of the bandpass filter can be improved on the basis of ensuring the insertion loss of the bandpass signal. When the notch point is set in the adjacent band, the roll-off characteristics of the bandpass filter can be improved, and the adjacent band suppression of the bandpass filter is improved. In addition, the order of the bandpass filter can be avoided to be increased additionally, which is beneficial to reducing the number of components required for the bandpass filter, thereby helping to reduce the volume of the bandpass filter.

[0035] It should be noted that Figure 1 exemplarily shows that the first filter unit 10 and the second filter unit 20 each include a T-type network structure 110. In other embodiments, at least one of the first filter unit 10 and the second filter unit 20 may also include two or more T-type network structures 110. Exemplarily, Figure 2FIG. 1 is a schematic diagram of another structure of a bandpass filter provided by an embodiment of the present invention. Figure 2 As shown, the first filtering unit 10 and the second filtering unit 20 both include two T-type network structures 110. Then in the first filtering unit 10 and / or the second filtering unit 20, as Figure 2 As shown, the cross-coupling network structure 120 can be connected in parallel with the series structures 111 of the two T-type network structures 110 at the same time, that is, the cross-coupling network structure 120 is connected in parallel with the four series structures 111 in the two T-type network structures 110. In other embodiments, the cross-coupling network structure 120 can also be connected in parallel with the two series structures 111 in one of the T-type network structures 110, which is not limited here.

[0036] The technical solution of this embodiment is to set a cross-coupling network structure and at least one T-type network structure in parallel connection, so that a notch point is formed when the cross-coupling network structure and the T-type network structure are cross-coupled. At the same time, the notch network structure is connected in series with the parallel structure of the T-type network structure, so that the notch network structure and the parallel structure of the T-type network structure form a notch point. Thereby, the number of notch points on both sides of the passband of the bandpass filter can be increased without additionally increasing the order of the bandpass filter, and the stopband suppression characteristics of the bandpass filter can be improved on the basis of ensuring the insertion loss of the bandpass signal. When the notch point is set in the adjacent band, the roll-off characteristics of the bandpass filter can be improved, and the adjacent band suppression of the bandpass filter is improved. At the same time, it is beneficial to reduce the number of devices required for the bandpass filter, which is beneficial to reduce the volume of the bandpass filter.

[0037] Figure 3 FIG. 1 is a schematic diagram of another structure of a bandpass filter provided by an embodiment of the present invention. Figure 3 As shown, the cross-coupling network structure 120 includes a cross-over capacitor Ck1 and / or a cross-over inductor Lk1 ; the cross-over capacitor Ck1 and the cross-over inductor Lk1 are connected in parallel with the series structure 111 of at least one T-type network structure 110 .

[0038] Specifically, Figure 3 The cross-coupling network structure 120 in the first filter unit 10 is exemplarily shown to include both the cross-over capacitor Ck1 and the cross-over inductor Lk1, and the cross-coupling network structure 120 in the second filter unit 20 includes the cross-over capacitor Ck1. The cross-over capacitor Ck1 and the cross-over inductor Lk1 are both connected in parallel with the series structure 111 of the T-type network structure 110, which can add an additional transmission path when the transmission signal passes through the T-type network structure 110, so that additional notch points can be added on the basis of the T-type network structure 110, increasing the number of notch points of the bandpass filter, and further improving the stopband suppression characteristics of the bandpass filter.

[0039] It should be noted that Figure 3 exemplarily shows that the cross-coupling network structure 120 in the first filter unit 10 includes both the cross-over capacitor Ck1 and the cross-over inductor Lk1, and the cross-coupling network structure 120 in the second filter unit 20 includes the cross-over capacitor Ck1. In other embodiments, the cross-coupling network structure 120 in the first filter unit 10 may also include only the cross-over capacitor Ck1 or the cross-over inductor Lk1. Alternatively, the cross-coupling network structure 120 in the second filter unit 20 may include only the cross-over inductor Lk1, or include both the cross-over capacitor Ck1 and the cross-over inductor Lk1, which is not limited here.

[0040] Figure 4 FIG. 1 is a schematic diagram of another structure of a bandpass filter provided by an embodiment of the present invention. Figure 4 As shown, each series structure 111 of the T-type network structure 110 includes a first inductive element L1 and a first capacitive element C1 connected in series; in the first filtering unit 10, the first inductive element L1 of a series structure 111 is connected to the first inductive element L1 of another series structure 111; the parallel structure 112 of the T-type network structure 110 includes a second capacitive element C2; the first pole of the second capacitive element C2 is connected to the node M between the two first inductive elements L1, and the second pole of the second capacitive element C2 is connected to the notch network structure 130; in the second filtering unit 20, the first capacitive element C1 of a series structure 111 is connected to the first capacitive element C1 of another series structure 111; the parallel structure 112 of the T-type network structure 110 includes a second inductive element L2; the first pole of the second inductive element L2 is connected to the node M between the two first capacitive elements C1, and the second pole of the second inductive element L2 is connected to the notch network structure 130.

[0041] Specifically, the two series structures 111 of the T-type network structure 110 each include a first inductive element L1 and a first capacitive element C1 connected in series. In the first filtering unit 10, a series structure 111 may be set at this time, wherein the first pole of the first capacitive element C1 serves as the series port of the series structure 111, the second pole of the first capacitive element C1 is connected to the first end of the first inductive element L1, the second end of the first inductive element L1 is connected to the second end of the first inductive element L1 of another series structure 111, and the connection point may serve as the middle node M between the two series structures 111. At this time, the parallel structure 112 may include a second capacitive element C2, the first pole of the second capacitive element C2 is connected to the middle node M of the two first inductive elements L1, and the second pole of the second capacitive element C2 is connected to the notch network structure 130, so that the T-type network structure 110 can suppress the stop band on the high frequency side of the passband. When the cross-coupling network structure 120 in the first filtering unit 10 is connected in parallel with the series structure 111 of the T-type network structure 110, the cross-coupling network structure 120 can be cross-coupled with the series structure 111 of the T-type network structure 110 to form a notch point on the high-frequency side of the passband. At the same time, the parallel structure 112 of the notch network structure 130 and the T-type network structure 110 can also form a notch point on the high-frequency side of the passband, thereby increasing the number of notch points on the high-frequency side of the passband of the bandpass filter and improving the stopband suppression characteristics of the high-frequency side of the passband of the bandpass filter.

[0042] In the second filtering unit 20, a series structure 111 may be provided, wherein the first end of the first inductive element L1 is used as the series port of the series structure 111, the second end of the first inductive element L1 is connected to the first pole of the first capacitive element C1, the second pole of the first capacitive element C1 is connected to the second pole of the first capacitive element C1 in another series structure 111, and the connection point may be used as the middle node M between the two series structures 111. At this time, the parallel structure 112 may include a second inductive element L2, the first pole of the second inductive element L2 is connected to the node M between the two first capacitive elements C1, so that the T-type network structure 110 can suppress the stop band on the low-frequency side of the passband. When the cross-coupling network structure 120 in the second filtering unit 20 is connected in parallel with the series structure 111 of the T-type network structure 110, the cross-coupling network structure 120 can be cross-coupled with the series structure 111 of the T-type network structure 110 to form a notch point on the low-frequency side of the passband. At the same time, the parallel structure 112 of the notch network structure 130 and the T-type network structure 110 can also form a notch point on the low-frequency side of the passband, thereby increasing the number of notch points on the low-frequency side of the passband of the bandpass filter and improving the stopband suppression characteristics of the low-frequency side of the passband of the bandpass filter.

[0043] Continue to refer Figure 4The trap network structure 130 includes a first trap inductor Lk2; a first end of the first trap inductor Lk2 is connected to a second end of the parallel structure 112 of the T-type network structure 110, and a second end of the first trap inductor Lk2 is connected to the third port C.

[0044] Specifically, the parallel structure 112 has a capacitive element. At this time, the first end of the first trap inductor Lk2 is connected to the second end of the parallel structure 112, and the second end of the first trap inductor Lk2 is connected to the third port C. The capacitive element on the parallel structure 112 and the first trap inductor Lk2 form a series LC structure on the parallel branch, thereby forming a trap point, increasing the trap points of the filtering unit, and further increasing the number of trap points on the high-frequency side of the passband of the bandpass filter, thereby improving the stopband suppression characteristics of the high-frequency side of the passband of the bandpass filter.

[0045] Continue to refer Figure 4 At least one of the first filtering unit 10 and the second filtering unit 20 also includes at least one parallel resonant network structure 140; the first end of the parallel resonant network structure 140 is connected to the series port of the T-type network structure 110, and the second end of the parallel resonant network structure 140 is connected to the third port C.

[0046] Specifically, the T-type network structure 110 may include two serial ports, namely, a first serial port A1 and a second serial port A2. The first end of the parallel resonant network structure 140 may be connected to the first serial port A1 or the second serial port A2, and the second end of the parallel resonant network structure 140 may be connected to the third port C, so that the parallel resonant network structure 140 serves as a parallel branch of the bandpass filter, which may increase the passband range of the bandpass filter.

[0047] Continue to refer Figure 4 The parallel resonant network structure 140 includes a third inductive element L3 and a third capacitive element C3; the first end of the third inductive element L3 and the first pole of the third capacitive element C3 are connected to the series port of the T-type network structure 110, and the second end of the third inductive element L3 and the second pole of the third capacitive element C3 are connected to the third port C.

[0048] Specifically, the third inductive element L3 and the third capacitive element C3 are connected in parallel to form a parallel LC resonant network, and as a parallel branch of the bandpass filter unit, the passband range of the bandpass filter can be increased. Figure 4 As shown, the first filtering unit 10 may include two parallel resonant network structures 140, which are respectively connected to the first series port A1 and the second series port A2 of the T-type network structure 110, so as to increase the passband range of the bandpass filter.

[0049] Continue to refer Figure 4When the parallel resonant network structure 140 includes a third inductive element L3 and a third capacitive element C3, the parallel resonant network structure 140 and the parallel structure 112 can be equivalent to capacitive elements, and the first trap inductor Lk2 is connected in series with the parallel resonant network structure 140 and the parallel structure 112, which can be equivalent to a series LC structure on the parallel branch of the bandpass filter, thereby forming a trap point, increasing the trap points of the filter unit, and further increasing the number of trap points on the high-frequency side of the passband of the bandpass filter, thereby improving the stopband suppression characteristics of the high-frequency side of the passband of the bandpass filter.

[0050] For example, Figure 5 A structural schematic diagram of a bandpass filter provided for related technology. Figure 6 The performance comparison diagram of different bandpass filters provided by the embodiment of the present invention is shown in FIG. 1 , wherein the horizontal axis is the frequency and the vertical axis is the insertion loss. Figure 6 The frequency-insertion loss curve of the bandpass filter provided is shown in Curve 2. Figure 6 The frequency-insertion loss curve of the bandpass filter structure is provided. Figure 6 As shown, curve 1 has multiple notch points on the low-frequency side of the passband (including the phenomenon of overlapping notch points), and also has multiple notch points on the high-frequency side. Compared with curve 2, the roll-off characteristics of the bandpass filter can be improved on the basis of ensuring the insertion loss of the bandpass signal, and the adjacent band suppression of the bandpass filter can be improved. At the same time, the anti-warping of the transmission signal in the stopband is reduced, and the stopband suppression characteristics of the bandpass filter are improved.

[0051] Figure 7 FIG. 1 is a schematic diagram of another structure of a bandpass filter provided by an embodiment of the present invention. Figure 7 As shown, the bandpass filter further includes at least one electromagnetic filter network 30, and the electromagnetic filter network 30 is connected in series between the first port A and the second port B.

[0052] Specifically, the electromagnetic filtering network 30 may include inductive elements and / or capacitive elements. When the electromagnetic filtering network 30 includes only inductive elements or capacitive elements, the electromagnetic filtering network 30 may compensate for the bandpass filter composed of the first filtering unit 10 and the second filtering unit 20, thereby reducing the insertion loss of the bandpass filter and further improving the filtering performance of the bandpass filter. When the electromagnetic filtering network 30 includes both inductive elements and capacitive elements, the electromagnetic filtering network 30 may adjust the passband range and stopband range of the bandpass filter, thereby meeting the filtering requirements of the bandpass filter.

[0053] Figure 8 FIG. 1 is a schematic diagram of another structure of a bandpass filter provided by an embodiment of the present invention. Figure 8As shown, the bandpass filter includes at least two groups of filter units 100, each group of filter units 100 includes a first filter unit 10 and a second filter unit 20 connected in series; the filter units 100 are connected in series between the first port A and the second port B.

[0054] Specifically, Figure 8 exemplarily shows that the bandpass filter includes two groups of filter units 100, and the two filter units 100 are connected in series between the first port A and the second port B. When at least two groups of filter units 100 are connected in series between the first port A and the second port B, each group of filter units 100 can generate notch points on both sides of the passband of the bandpass filter, thereby improving the degree of suppression of the stopband by the bandpass filter, and further improving the filtering performance of the bandpass filter. At the same time, the roll-off slope of the bandpass filter can be further improved, and the adjacent band suppression of the bandpass filter can be further improved.

[0055] Among them, when the bandpass filter includes two groups of filter units 100, the frequencies corresponding to the notch points of different filter units 100 can be equal, which can improve the suppression degree of the frequencies corresponding to the notch points and improve the filtering performance of the bandpass filter. In other embodiments, the frequencies corresponding to the notch points of the same filter unit 100 can be different, which can increase the number of notch points on both sides of the passband of the bandpass filter, and can also improve the suppression degree of the stopband on both sides of the passband of the bandpass filter, thereby improving the filtering performance of the bandpass filter.

[0056] It should be noted that, in other embodiments, the bandpass filter may include a plurality of filter units 100 , and the plurality of filter units 100 are connected in series between the first port A and the second port B, which is not limited here.

[0057] Fig. 9 FIG. 1 is a schematic diagram of another structure of a bandpass filter provided by an embodiment of the present invention. Fig. 9 As shown, when the bandpass filter includes at least two groups of filter units 100 , the electromagnetic filter network 30 can be disposed between the filter units 100 .

[0058] Fig.10 FIG. 1 is a schematic diagram of another structure of a bandpass filter provided by an embodiment of the present invention. Fig.10 As shown, the bandpass filter further includes a fourth port D, and the fourth port D is arranged between the filter units 100 .

[0059] Specifically, Fig.10exemplarily shows that the bandpass filter includes two filter units 100, and a fourth port D is provided between the two filter units 100. The fourth port D can be used to connect to an external circuit, so that the bandpass filter can be connected to different types of external circuits, increasing the application range of the bandpass filter. In addition, the fourth port D can also be connected to an element with equivalent large impedance, so that the fourth port D is equivalent to an open circuit, so as to meet different usage scenarios of the bandpass filter.

[0060] It should be noted that when the bandpass filter includes multiple filter units 100, the bandpass filter may include at least two fourth ports D, which are respectively arranged between different filter units 100, further increasing the application scope of the bandpass filter, which is not limited here.

[0061] The embodiment of the present invention further provides a multiplexer. Fig.11 A schematic diagram of the structure of a multiplexer provided by an embodiment of the present invention. Fig.11 As shown, the multiplexer includes the bandpass filter 1000 provided by any embodiment of the present invention.

[0062] Continue to refer Fig.11 The multiplexer includes a first terminal IN and at least two second terminals; each bandpass filter 1000 is connected in series between the first terminal IN and any second terminal of the multiplexer.

[0063] Specifically, Fig.11 It is exemplarily shown in the figure that the multiplexer includes a first terminal IN and n second terminals, which are OUT1, OUT2, ... OUTn. Each bandpass filter 1000 is connected in series between the first terminal IN and a second terminal. For example, the first bandpass filter 1000 is connected in series between the first terminal IN and the first second terminal OUT1, the second bandpass filter 1000 is connected in series between the first terminal IN and the first second terminal OUT2, ... and so on. Since the multiplexer has the bandpass filter 1000 provided by any embodiment of the present invention, it has the same beneficial effects as the bandpass filter 1000, which will not be repeated here.

[0064] It should be noted that the multiplexer may also include other filters, which are connected in series between the first end IN and any second end. The other filters may be low-pass filters, high-pass filters or band-pass filters, which are not limited in the embodiment of the present invention.

[0065] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A bandpass filter, characterized in that: comprising a first port, a second port, a third port and at least one first filtering unit and at least one second filtering unit; The first filtering unit and the second filtering unit each include at least one T-type network structure, a cross-coupling network structure and a notch network structure; The two series structures of the T-type network structure are connected in series between the first port and the second port, the first end of the parallel structure of the T-type network structure is connected to the middle node of the series structure, the second end of the parallel structure is connected to the third port through the notch network structure, and the cross-coupling network structure is connected in parallel to at least one series structure of the T-type network structure; the cross-coupling network structure is used to form a cross coupling with the series structure of the T-type network structure, and the notch network structure is used to form a notch point with the parallel structure of the T-type network structure; wherein the frequency corresponding to the notch point of the first filtering unit and the frequency corresponding to the notch point of the second filtering unit are respectively located on both sides of the passband of the bandpass filter.

2. The bandpass filter according to claim 1, characterized in that The cross-coupling network structure includes a cross-over capacitor and / or a cross-over inductor; the cross-over capacitor and the cross-over inductor are connected in parallel with at least one series structure of the T-type network structure.

3. The bandpass filter according to claim 1 or 2, characterized in that: Each of the series structures of the T-type network structure includes a first inductive element and a first capacitive element connected in series; In the first filtering unit, a first inductive element of a series structure is connected to a first inductive element of another series structure; the parallel structure of the T-type network structure includes a second capacitive element; a first pole of the second capacitive element is connected to a node between the two first inductive elements, and a second pole of the second capacitive element is connected to the notch network structure; In the second filtering unit, the first capacitive element of one of the series structures is connected to the first capacitive element of another series structure; the parallel structure of the T-type network structure includes a second inductive element; the first pole of the second inductive element is connected to the node between the two first capacitive elements, and the second pole of the second inductive element is connected to the notch network structure.

4. The bandpass filter according to claim 3, characterized in that: The trap network structure includes a first trap inductor; a first end of the first trap inductor is connected to a second end of the parallel structure of the T-type network structure, and a second end of the first trap inductor is connected to the third port.

5. The bandpass filter according to claim 1, characterized in that: At least one of the first filtering unit and the second filtering unit further comprises at least one parallel resonant network structure; The first end of the parallel resonant network structure is connected to the series port of the T-type network structure, and the second end of the parallel resonant network structure is connected to the third port.

6. The bandpass filter according to claim 5, characterized in that: The parallel resonant network includes a third inductive element and a third capacitive element; The first end of the third inductive element and the first pole of the third capacitive element are connected to the series port of the T-type network structure, and the second end of the third inductive element and the second pole of the third capacitive element are connected to the third port.

7. The bandpass filter according to claim 1, characterized in that: It also includes at least one electromagnetic filtering network, which is connected in series between the first port and the second port.

8. The bandpass filter according to claim 1, characterized in that It comprises at least two groups of filter units, each group of the filter units comprises the first filter unit and the second filter unit connected in series; the filter units are connected in series between the first port and the second port, and the bandpass filter further comprises a fourth port, which is arranged between the filter units.

9. A multiplexer, characterized in that: The bandpass filter comprises the bandpass filter as described in any one of claims 1 to 8.

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