WO2024119437A1

WO2024119437A1 - Low pass filter and method for manufacturing the same

Info

Publication number: WO2024119437A1
Application number: PCT/CN2022/137575
Authority: WO
Inventors: Dong Wang; Hongjun Zhao; Shouli JIA; Min Zhang
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy
Priority date: 2022-12-08
Filing date: 2022-12-08
Publication date: 2024-06-13

Abstract

Example embodiments of the present disclosure relate to a low-pass filter and a method manufacturing the same. The low pass filter may comprise a conductive beam extending to provide a signal flow path, and a plurality of conductive stubs provided along the signal flow path, the conductive stubs including a stub rod connected to the conductive beam and a coupling-enhancing structure supported by the stub rod.

Description

LOW PASS FILTER AND METHOD FOR MANUFACTURING THE SAME

TECHNICAL FIELD

Various exemplary embodiments of the present disclosure pertain to low pass filters and methods for manufacturing the low pass filters.

BACKGROUND

Low pass filters (LPFs) are widely adopted to select desirable frequency and to suppress harmonic and spurious signals in telecommunication systems especially in the 5G communication system. With continuous development of the 5G communication system, considerable performance improvements of LPF such as lower insertion loss, higher rejection and wider spurious-free frequency ranges are required. Meanwhile, LPFs with compact size are always required to minimize overall system size and reduce production cost.

SUMMARY

In general, some example embodiments of the present disclosure provide a low pass filter (LPF) with compact size and improved performance, and a method of manufacturing the LPF.

According to a first aspect, an example embodiment of a low pass filter is provided. The low pass filter may comprise a conductive beam extending to provide a signal flow path, and a plurality of conductive stubs provided along the signal flow path. The plurality of conductive stubs may include a stub rod connected to the conductive beam and a coupling-enhancing structure supported by the stub rod.

In some example embodiments, the conductive beam may have one or more bending parts so that the conductive beam extends in a two dimensional plane or a three dimensional space.

In some example embodiments, the coupling-enhancing structure may comprise at least one protrusion projecting from a distal end of the stub rod.

In some example embodiments, the at least one protrusion may extend in a direction substantially parallel to the signal flow path.

In some example embodiments, at least two adjacent conductive stubs may have the coupling-enhancing structures, and the stub rods of the at least two adjacent conductive stubs may have different heights so that the coupling-enhancing structures of the at least two adjacent conductive stubs may be separated from each other in the height direction and overlaps with each other in the direction substantially parallel to the signal flow path.

In some example embodiments, a distance between the coupling-enhancing structures of two adjacent conductive stubs may be less than or equal to one eighth of a wavelength of the resonant frequency of at least one of the two adjacent conductive stubs.

In some example embodiments, at least two conductive stubs having the coupling-enhancing structures may be provided opposite to each other at both sides of the conductive beam.

In some example embodiments, the plurality of conductive stubs may have a “T” shape or an “L” shape.

In some example embodiments, one of the plurality of conductive stubs may be connected to a bending part of the conductive beam and bent conformal with the bending part.

In some example embodiments, the conductive beam and the plurality of conductive stubs may have a flat plate shape, and the plurality of conductive stubs may be oriented coplanar with or perpendicular to the conductive beam.

In some example embodiments, the plurality of conductive stubs may be integrally formed with the conductive beam.

In some example embodiments, the low pass filter may further comprise a conductive housing enclosing a cavity for accommodating the conductive beam and the plurality of conductive stubs, at least one of the plurality of conductive stubs being oriented parallel to a wall of the cavity.

According to a second aspect, an example embodiment of a method for manufacturing a low pass filter is provided. The method may comprise providing a conductive plate, and removing portions of the conductive plate to form a conductive beam and a plurality of conductive stubs connected to the conductive beam. The plurality of conductive stubs may include a stub rod connected at a proximal end to the conductive beam and a coupling-enhancing structure supported at a distal end of the stub rod.

In some example embodiments, removing portions of the conductive plate may be performed by a punching process or a cutting process.

In some example embodiments, the method may further comprise bending the conductive beam at one or more parts such that the conductive beam may extend in a two dimensional plane or a three dimensional space.

In some example embodiments, one of the plurality of conductive stubs connected to the bending part of the conductive beam may be bent conformal with the bending part.

In some example embodiments, the method may further comprise bending one or more conductive stubs at the proximal end of the stub rod such that the one or more conductive stubs are oriented perpendicular to the conductive beam.

In some example embodiments, the method may further comprise mounting the conductive beam into a cavity enclosed by a conductive housing, at least one of the plurality of conductive stubs being oriented substantially parallel to a wall of the cavity.

It should be appreciated that the summary section is neither used to limit the present disclosure, nor is it intended to identify the prime technical features. For being easily comprehended by the persons skilled in the art, the above and further objects, features and advantages of the present disclosure will be more fully apparent from the following detailed description of the embodiments with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described, by way of non-limiting examples, with reference to the accompanying drawings, where:

FIG. 1A illustrates a perspective view of a stepped impedance LPF.

FIG. 1B illustrates an equivalent circuit diagram of the stepped impedance LPF.

FIG. 1C illustrates an attenuation characteristic of the stepped impedance LPF.

FIG. 2A illustrate a perspective view of a notch LPF.

FIG. 2B illustrates an equivalent circuit diagram of the notch LPF.

FIG. 2C illustrates an attenuation characteristic of the notch LPF.

FIG. 3A illustrates a perspective view of a LPF according to an example embodiment of the present disclosure.

FIG. 3B illustrates an equivalent circuit diagram of a LPF according to an example embodiment of the present disclosure.

FIG. 3C illustrates an attenuation characteristic of a LPF according to an example embodiment of the present disclosure.

FIG. 3D illustrates comparison of attenuation characteristics between the stepped impedance LPF, the notch LPF and the LPF according to an example embodiment of the present disclosure.

FIG. 4A illustrates a perspective view of a LPF according to another example embodiment of the present disclosure.

FIG. 4B illustrates a perspective view of a conductive beam of the LPF according to the another example embodiment of the present disclosure.

FIG. 4C illustrates a bottom perspective view of coupling-enhancing structures according to the another example embodiment of the present disclosure.

FIG. 4D illustrates a perspective view of a LPF with a conductive housing according to the another example embodiment of the present disclosure.

FIG. 4E illustrates a perspective view of a LPF according to one more example embodiment of the present disclosure.

FIG. 4F illustrates an equivalent circuit diagram of a LPF with a coupling feature by non-adjacent stubs according to the another example embodiment of the present disclosure.

FIG. 4G illustrates an attenuation characteristic of a LPF according to example embodiments of the present disclosure.

FIG. 5 illustrates a flow chart of a method for manufacturing a LPF according to an example embodiment of the present disclosure.

Throughout the drawings, same or similar reference numbers indicate same or similar elements except the requirement of describing an embodiment. A repetitive description on the same elements would be omitted.

DETAILED DESCRIPTION

Herein below, some example embodiments are described in detail with reference to the accompanying drawings. The following description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. It is to be understood that, except in the example embodiments described therein, the structures and materials as generally depicted and shown in the drawings can be arranged and designed in various manners. Accordingly, the example embodiments illustrated with reference to the drawings and the detailed description made below are merely provided as examples, rather than suggesting any limitations to the scope of protection.

In addition, the features, structures or characteristics as described herein may be combined in one or more embodiments in any appropriate manner. More details will be provided below for thorough understanding on the embodiments. Nevertheless, those skilled in the art would realize that various embodiments can be implemented when one or more details are missing, or other methods, components, materials and the like are utilized. In other cases, some or all the known structures, materials or operations may not be demonstrated or described in detail for the sake of clarity. As used herein, the singular form “a” or “one” is to be read as “one or more” unless the context clearly indicates otherwise.

Reference will now be made to the drawings to describe example embodiments of the present disclosure. FIG. 1A is a perspective view of a stepped impedance low-pass filter 100. As shown in FIG. 1A, a conductive housing 102 enclosing a cavity may be formed as a shape of cylinder, and deemed as the ground potential. A conductive rod 104 is a signal conductor disposed within the cavity defined by the conductive housing 102, extending along the axis of the conductive housing 102 and separated from the conductive housing 102. An input terminal 106 is physically and electrically connected to one end of the conductive rod 104, and an output terminal 108 is physically and electrically connected to the other end of the conductive rod 104. A plurality of

capacitive conductors

110, 112, 114, 116 and 118, with identical or non-identical capacitance values, are concentrically mounted on the conductive rod 104 at predetermined intervals in such a manner that the conductive rod 104 extends through the

capacitive conductors

110, 112, 114, 116 and 118 at the center thereof. The capacitive conductors 110-118 serve as the low-impedance line sections, and portions of the conductive rod 104 sandwiched in-between the adjacent capacitive conductors 110-118 serve as the high-impedance line sections. In such a stepped impedance low-pass filter, the coupling field intensity generated by the conductive rod 104 disposed in the cavity defined by the conductive housing 102 increases with a decrease in the distance between the conductive rod 104 and the interior periphery surface of the conductive housing 102. This coupling field intensity determines the impedance characteristic of each section of the conductive rod 104.

FIG. 1B illustrates an equivalent circuit diagram of the stepped impedance low-pass filter 100. The equivalent capacitors C ₁₁₀, C ₁₁₂, C ₁₁₄, C ₁₁₆ and C ₁₁₈ denote the corresponding low-impedance line sections, i.e., the coupling effect among the conductive housing 102 and the

capacitive conductors

110, 112, 114, 116 and 118 shown in FIG. 1A, and the equivalent inductors L _a, L _b, L _c and L _d denote the high-impedance line sections sandwiched in-between the respective pairs of adjacent

capacitive conductors

110 and 112, 112 and 114, 114 and 116, 116 and 118. Thus, the stepped impedance low-pass filter 100 shown in FIG. 1A operates as a circuit equivalent to a multi-stage LC ladder-type circuit.

FIG. 1C illustrates an attenuation characteristic comparison between a 5-stepped impedance low-pass filter and a 9-stepped impedance low-pass filter. According to the mechanism of the stepped impedance low-pass filter, it may require more capacitive conductors and longer extension of the conductive rod 104 to achieve a broader stopband bandwidth. It may lead that the stepped impedance low-pass filter is hardly to satisfy the requirement of compact size.

FIG. 2A illustrate a perspective view of a notch low-pass filter 200. The notch low-pass filter 200 includes a conductive housing 202 which defines an interior space and a signal conductor 208 is arranged therein. The conductive housing 202 may be formed as a cube, and deemed as the ground potential. An input terminal 204 is physically and electrically connected to one end of the signal conductor 208, and an output terminal 206 is physically and electrically connected to the other end of the signal conductor 208. A plurality of substantially

rectangular conductors

210, 212, 214, 216 and 218 are physically and electrically connected to the signal conductor 208, and positioned in the same plane as the signal conductor 208. The substantially

rectangular conductors

210, 212, 214, 216 and 218 are arranged at predetermined intervals along the same side of the signal conductor 208, and deemed as equivalent capacitive conductors, respectively. The substantially

rectangular conductors

210, 212, 214, 216 and 218 serve as low-impedance line sections, and those portions of the signal conductor 208 sandwiched in-between the respective pairs of

capacitive conductors

210 and 212, 212 and 214, 214 and 216, 216 and 218 serve as high-impedance line sections.

FIG. 2B illustrates an equivalent circuit diagram of the notch low-pass filter 200. As shown in FIG. 2B, the high-impedance line sections of the signal conductor 208 form inductors L _A, L _B, L _C and L _D, and the

capacitive conductors

210, 212, 214, 216 and 218 form inductors L ₂₁₀, L ₂₁₂, L ₂₁₄, L ₂₁₆ and L ₂₁₈, which inductors are connected in a ladder-type arrangement. A plurality of equivalent capacitors C ₂₁₀, C ₂₁₂, C ₂₁₄, C ₂₁₆ and C ₂₁₈ may be formed between the

capacitive conductors

210, 212, 214, 216, 218 and the ground potential i.e., the conductive housing 202, respectively.

FIG. 2C illustrates an attenuation characteristic comparison between a 3-stepped notch low-pass filter and a 5-stepped notch low-pass filter. As shown in FIG. 2C, the 5-stepped notch low-pass filter produces the same single transmission zero point as the 3-stepped notch low-pass filter does. It means that the stopbands produced by the plurality of notches (i.e., the plurality of capacitive conductors) overlap with each other, and therefore the notch low-pass filter has a narrow stopband even when the number of notches included in the notch low-pass filter increases.

Reference will now be made to the drawings to describe example embodiments of the present disclosure. In some example embodiments, alow-pass filter with a plurality of coupling-enhancing structures is provided. The low-pass filter may have a broader stopband bandwidth and better stopband rejection performance than both the stepped impedance low-pass filters shown in FIG. 1A and the notch low-pass filter shown in FIG. 2A. The low pass filter may comprise a conductive beam extending to provide a signal flow path, and a plurality of conductive stubs provided along the signal flow path. At least one conductive stub may include a stub rod connected to the conductive beam and a coupling-enhancing structure supported by the stub rod. In actual scenario such as 5G communication devices, the low-pass filter may generally be enclosed by a conductive housing, and the components thereof may be accommodated in the cavity defined by the conductive housing. The coupling-enhancing structures may be capacitively coupled with the conductive housing, and two adjacent coupling-enhancing structures may be coupled with each other, as well. Though the coupling effect field is unlimited in physical theory, the distance of two adjacent coupling-enhancing structures is less than or equal to one eighth of a wavelength of the resonant frequency of at least one of the two corresponding conductive stubs, so as to achieve a broader stopband bandwidth and higher rejection. In particular, the coupling effect by two adjacent coupling-enhancing structures may contribute two transmission zeros to the filter response. In an example embodiment, the coupling-enhancing structures may comprise at least one protrusion projecting from a distal end of the stub rod; thereby the distance between two adjacent conductive stubs is decreased to achieve better coupling effect. The quantity and the position of protrusions generating coupling effect are not limited in any way, as long as the protrusions can enhance coupling between the conductive stubs. In some example embodiments, the coupling-enhancing structure may have two protrusions disposed at the two sides of the distal end of the stub rod, and the two protrusions may extend substantially perpendicular to the stub rod. In some example embodiments, the coupling-enhancing structure may have only one protrusion disposed at the one side of the distal end of the stub rod.

FIG. 3A is a perspective view illustrating a low-pass filter according to an example embodiment of the present disclosure. The shown low-pass filter may be a passive component, generally designated 300. The low-pass filter 300 comprises a conductive beam 302 with an input terminal 308 and an output terminal 310, a plurality of conductive stubs 304 connected to the conductive beam 302, and a conductive housing 306 accommodating the conductive beam 302 and the conductive stubs 304. The plurality of conductive stubs 304 each may include a stub rod 3042 physically and electrically connected to the conductive beam 302 and a coupling-enhancing structure 3044 supported by the stub rod 3042. The input terminal 308 is physically and electrically connected to one end of the conductive beam 302, and the output terminal 310 is physically and electrically connected to the other end of the conductive beam 302. The input terminal 308 and the output terminal 310 may be formed with a connecting structure for example a hole or a U-shaped notch for connecting the conductive beam 302 to upstream and downstream components. The low-pass filter 300 comprising the conductive beam 302 with the input terminal 308 and the output terminal 310 and the plurality of conductive stubs 304, may be integrally formed as a single piece.

The conductive beam 302 may be formed into a stripline shape extending to provide a signal flow path, and the plurality of the conductive stubs 304 may be disposed at the same side of the conductive beam 302. The stub rod 3042 of the conductive stub 304 may be physically and electrically connected at a proximity end to the conductive beam 302, and the stub rod 3042 may be substantially perpendicular to the conductive beam 302. In the embodiment shown in FIG. 3A, the conductive beam 302 extends in a straight line, while it may extend in a two dimensional plane or a three dimensional space in some other example embodiments discussed below. For example, the conductive beam 302 may have one or more bending parts so that the signal flow path defined by the conductive beam 302 extends in a two dimensional plane or a three dimensional space.

The coupling-enhancing structure 3044 is supported at the distal end of the stub rod 3042 and it may comprise two protrusions projecting from the distal end of the stub rod 3042. The two protrusions may extend in a direction substantially parallel to the conductive beam 302 (i.e., the signal flow path) . The conductive stub 304, with the stub rod 3042 and the coupling-enhancing structure 3044, may have a "T" shape substantially. In some example embodiments, the coupling-enhancing structure 3044 may comprise one protrusion extending parallel to the conductive beam 302 and thus the conductive stub 304 may have a "L" shape.

As shown in FIG. 3A, an equivalent capacitor is formed between the conductive stub 304 and the conductive housing 306. The coupling-enhancing structure 3044 provides a larger coupling area with the conductive housing 306 than the stub rod 3042 alone does, and therefore the equivalent capacitance between the conductive stub 304 and the conductive housing 306 is increased. In addition, an equivalent capacitor is formed between two adjacent coupling-enhancing structures 3044. As the coupling-enhancing structure 3044 extends parallel to the conductive beam 302, a distance between two adjacent coupling-enhancing structures 3044 is much smaller than a distance between two adjacent stub rods 3042, and the two adjacent coupling-enhancing structures 3044 can form an equivalent capacitor. In some example embodiments, the distance between two adjacent coupling-enhancing structures 3044 may be less than or equal to a half of a wavelength of the resonant frequency of the corresponding conductive stubs, or preferably less than or equal to one eighth of the wavelength to the resonant frequency of at least one of the corresponding conductive stubs. In this way, the two adjacent coupling-enhancing structures 3044 may be capacitively coupled with each other, and the two conductive stubs 304 can contribute two different transmission zeros points to the filter response, which will be discussed below with respect to FIG. 3C. Consequently, the low-pass filter 300 can achieve a broader stopband bandwidth and better rejection performance.

The resonant frequency f of a single conductive stub 304, i.e., the transmission zero point produced by the conductive stub 304, may be approximately estimated as follows:

wherein, L is the distributed inductance of the conductive stub 304, and C is the coupling capacitance of the conductive stub 304. As discussed above, the coupling-enhancing structure 3044 of the conductive stub 304 can greatly increase the coupling capacitance C. The coupling capacitance C may be approximately estimated as follows:

wherein, ε ₀ denotes the dielectric constant, ε _r denotes the permittivity of the material (e.g., air or other filling materials) between two adjacent coupling-enhancing structures 3044 which form two electrode plates of the equivalent capacitor, d denotes the distance between the two adjacent coupling-enhancing structures 3044, w1 denotes the width of the coupling-enhancing structure 3044, and t denotes the thickness of the conductive stub 304. And the distributed inductance L may be approximately estimated as follows:

wherein, Z ₀ denotes the characteristic impedance, h denotes the height of the conductive stub, and λ denotes the wavelength of the resonate frequency of conductive stub 304.

The characteristic impedance Z ₀ may be approximately estimated as follows:

wherein w0 denotes the width of the conductive stub rod 3042, t denotes the thickness of the conductive stub 304, and s denotes the width of the cavity defined by the conductive housing 306. As shown in the above equations, the distributed inductance L of the conductive stub 304 depends on the width w0 of the conductive stub rod 3042, the height h of the conductive stub 304, the thickness t of the conductive stub 304 and the cavity width s of the conductive housing 306.

Though in the above example embodiments the coupling-enhancing structure 3044 may include one or two protrusions extending parallel to the conductive beam 302 so that the conductive stub 304 has a “T” or “L” shape, it would be appreciated that quantity and position of the protrusions forming the coupling-enhancing structure 3044 are not limited to the above example embodiments. In some other example embodiments, the coupling-enhancing structure 3044 may have two or more protrusions disposed at the same side of the distal end of the stub rod 3042, forming a comb electrode structure. In yet some example embodiments, the comb electrode structures of two adjacent coupling-enhancing structures 3044 may form an interdigital electrode capacitor.

As shown in FIG. 3A, the stub rods 3042 may have substantially identical height. In some other example embodiments, two adjacent stub rods 3042 may have different height so that the coupling-enhancing structures 3044supported on the two adjacent stub rods 3042 may be separated from each other in the height direction and overlaps with each other in the direction substantially parallel to the signal flow path. In this case, the coupling between the two coupling-enhancing structures 3044 is increased because the two coupling-enhancing structures 3044 may have an increased overlapping area. In addition, the lower coupling-enhancing structure may extend below the higher coupling-enhancing structure to vicinity of the adjacent stub rod supporting the higher coupling-enhancing structure, which also increases the coupling capacitance of the coupling-enhancing structure. The distance between the two adjacent coupling-enhancing structures in the height direction and the distance between the lower coupling-enhancing structure and the adjacent stub rod in the signal flow path direction each may be less than or equal to a half of the wavelength of the resonant frequency of the corresponding conductive stub, or preferably less than or equal to one eighth of the wavelength of the resonant frequency of at least one of the corresponding conductive stubs, for the purpose of achieving broader stopband bandwidth and higher rejection performance. The stopband bandwidth BW produced by two adjacent conductive stubs may be estimated as follows:

wherein, c denotes the capacitance between two coupling-enhancing structures, and the indexes 1, 2 denotes the two conductive stubs, respectively.

In the example embodiment shown in FIG. 3A, the conductive beam 302 and the plurality of conductive stubs 304 have a flat plate shape and they are positioned co-planar with each other. The plurality of conductive stubs 304 are positioned at the same side of the conductive beam 302. In some other example embodiments, the conductive stubs 304 may be positioned at both sides of the conductive beam 302, and one or more of the conductive stubs 304 may be bent at the proximal end of the stub rod 3042 so that the conductive stubs 304 are oriented to be substantially perpendicular to the conductive beam 302. In an example, two conductive stubs 304 positioned at both sides of the conductive beam 302 perpendicular to the conductive beam 302 may be opposite to each other, which can also induce capacitive coupling between the two conductive stubs 304.

Each of the conductive stubs 302 may be referred to as a "resonant element" in the low-pass filter 300 shown in FIG. 3A, and the plurality of conductive stubs 302 may be collectively referred to as "multi-stepped resonant element array" or "N-stepped resonant element array" where N denotes the number of conductive stubs and it may be an integer larger than or equal to 2. For example, the low-pass filter 300 shown in FIG. 3A have 5 conductive stubs 302, and the 5 conductive stubs 302 may be collectively referred to as a 5-stepped resonant element array.

One pair of I/O terminals, i.e., the input terminal 308 and the output terminal 310, are connected at both ends of the conductive beam 302 for conducting signal flowing through the conductive beam 302. The input terminal 308 and the output terminal 310 may be formed with a connecting structure for example a hole or a U-shaped notch for connecting the conductive beam 302 to upstream and downstream components. The input terminal 308 and the output terminal 310 also support the conductive beam 302 and the conductive stubs 304 within the cavity of the conductive housing 306 in such a way that they are separated from the conductive housing 306.

FIG. 3B illustrates an equivalent circuit diagram of the low-pass filter 300 according to the example embodiment shown in FIG. 3A. Referring to FIGs 3A and 3B, the conductive beam 302 forms four inductors L ₁, L ₂, L ₃ and L ₄ connected in series, and the five stub rods 3042 form five inductors L ₁₁, L ₂₂, L ₃₃, L ₄₄ and L ₅₅ connected in parallel, which inductors form a ladder-type arrangement. Five capacitors C ₁, C ₂, C ₃, C ₄ and C ₅ are formed between the five coupling-enhancing structures 3044 and the ground potential (i.e., the conductive housing 306) , respectively. In addition, coupling capacitors C ₁₂, C ₂₃, C ₃₄ and C ₄₅ are formed between every two adjacent coupling-enhancing structures 3044.

Compared to the equivalent circuit diagram of the notch low-pass filter 200 shown in FIG. 2B, the low-pass filter 300 can produce more coupling capacitors C ₁₂, C ₂₃, C ₃₄ and C ₄₅ by including the coupling-enhancing structures 3044. The capacitance magnitude of the coupling capacitors C ₁₂, C ₂₃, C ₃₄ and C ₄₅ may be calculated according to the above equation 2, and the resonant frequency f of each conductive stubs 304 may be calculated according to the above equations 1-5. As discussed above, with the coupling-enhancing structures 3044, the conductive stubs 304 can contribute different transmission zeros points (i.e., the resonant frequency f) to the filter response, thereby extending the stopband bandwidth of the low-pass filter 300. The stopband bandwidth obtained from two adjacent conductive stubs 304 may be calculated according to the above equation 6.

FIG. 3C illustrates an attenuation characteristic comparison between a low-pass filter with 5-stepped resonant element array and a low-pass filter with 3-stepped resonant element array. When supplied with signals, such as VHF, UHF, microwave or milli-wave band and so on, via the input terminal 308, the low-pass filter of the present disclosure attenuates signals above the cut-off frequency that may be determined by the LC ladder-type circuit, and the low-pass filter 300 permits the passage therethrough of only signals below the cut-off frequency for output via the output terminal 310. From the graph shown in FIG. 3C, the N-stepped resonant element array produces N transmission zero points, and the low pass filter with 5-stepped resonant element array has a broader stopband bandwidth and better rejection performance than the low pass filter with 3-stepped resonant element array. Therefore, it would be desirable to form more conductive stubs 304 for the low-pass filter 300.

FIG. 3D illustrates an attenuation characteristic comparison of the low-pass filter 300 with 5-stepped resonant element array, the 5-stepped impedance low-pass filter 100 and the 5-stepped notch low-pass filter 200. Also, the low-pass filter 300 with 5-stepped resonant element array has a broader stopband bandwidth and better rejection performance than the 5-stepped impedance low-pass filter 100 and the 5-stepped notch low-pass filter 200. The low-pass filter 300 also has a sharper cut-off frequency edge than the 5-stepped impedance low-pass filter 100.

In the following descriptions, those which have been described will be briefly described or omitted, and it may be appreciated that in case of no contradiction, those applied in the example embodiments regarding FIG. 3A to 3D may also be applied in the example embodiments regarding FIG. 4A to 4G. FIG. 4A illustrates a low-pass filter 400 with a three dimensional space structure according to another example embodiment of the present disclosure. The shown low-pass filter 400 may also be a passive component. The low-pass filter 400 comprises a conductive beam 402 with an input terminal 408 and an output terminal 410, a plurality of

conductive stubs

4041, 4042, 4043 and 4044 connected to the conductive beam 402 and an conductive housing 406 accommodating the conductive beam 402 and the

conductive stubs

4041, 4042, 4043 and 4044, wherein the conductive beam 402may provide a signal flow path. At least one conductive stub may include a stub rod connected physically and electrically to the conductive beam and a coupling-enhancing structure supported by the stub rod.

The input terminal 408 is physically and electrically connected to one end of the conductive beam 402, and the output terminal 410 is physically and electrically connected to the other end of the conductive beam 402. The input terminal 408 and the output terminal 410 may be formed with a connecting structure for example a hole or a U-shaped notch for connecting the conductive beam 402 to upstream and downstream components. The low-pass filter 400 comprising the conductive beam 402 with the input terminal 408 and the output terminal 410, and the plurality of

conductive stubs

4041, 4042, 4043 and 4044 may be integrally formed as a single piece.

The conductive beam 402 may be bent to form a plurality of

straight portions

4021, 4022, 4023, 4024, 4025 and 4026 extending towards a direction different from a neighboring straight portion connect to each other. As the illustration in FIG. 4A, the conductive beam 402 including the

portions

4021, 4022, 4023, 4024, 4025 and 4026 may be a structure with a three dimensional space, and a plurality of sets of conductive stubs may be provided along the one side of the

portions

4021, 4022 and 4023 respectively, and a plurality of sets of conductive stubs may be provided along both sides of the

portions

4025 and 4026 respectively. The plurality of conductive stubs may be disposed at predetermined intervals, and the size of the predetermined intervals may be identical or not identical. FIG. 4B illustrates a perspective view of a conductive beam 402 of the LPF according to the another example embodiment of the present disclosure. The conductive beam 402 with the

portions

4021, 4022, 4023, 4024, 4025 and 4026, may provide a signal flow passage. When signals are supplied to the input terminal 408, the signals may be transmitted along the bent conductive beam 402 with the plurality of

portions

4021, 4022, 4023, 4024, 4025 and 4026, as shown in FIG. 4B. Comparing with the linear structure of the low-pass filter 300 shown in FIG. 3A, the low-pass filter 400 with a three dimensional structure may have a compacter size.

As shown in FIG. 4A, a set of

conductive stubs

4041, 4042, 4043 and 4044 may be disposed at one side of the portion 4021 of the conductive beam and may be oriented coplanar with the portion 4021. Each of the

conductive stubs

4041, 4042, 4043 and 4044 may comprise a stub rod and a coupling-enhancing structure. The stub rods of the set of

conductive stubs

4041, 4042, 4043 and 4044 may be physically and electrically connected to the portion 4021 respectively, and the coupling-enhancing structure with two protrusions may project from a distal end of the stub rod. The set of

conductive stubs

4041, 4042, 4043 and 4044 may have a "T" shape substantially, and it may cause the coupling effect generated by the end of the protrusion of two adjacent conductive stubs, such as the adjacent

conductive stubs

4041 and 4043. For the purpose of achieving coupling effect, the distance between two adjacent coupling-enhancing structures of the adjacent

conductive stubs

4041 and 4043 may be less than or equal to a half of the wavelength of the resonant frequency of the corresponding conductive stub, or preferably less than or equal to one eighth of the wavelength of the resonant frequency of at least one of the corresponding conductive stub. The coupling-enhancing structures of the set of

conductive stubs

4041, 4042, 4043 and 4044 may have two protrusions projecting from a distal end of the corresponding stub rod and may be parallel to the portion 4021 of the conductive beam and perpendicular to the corresponding stub rod. The shapes of the set of

conductive stubs

4041, 4042, 4043 and 4044 may have a "T" shape substantially. The coupling-enhancing structure of the conductive stubs 4045 may have only one protrusion projecting from the distal end of the corresponding stub rod, and may be parallel to the portion 4021 of the conductive beam 402 and perpendicular to the corresponding stub rod. The shapes of the conductive stubs 4045 may have an "L" shape substantially. It would be appreciated that quantity and position of the protrusions forming the coupling-enhancing structure are not limited to the above example embodiments. In some example embodiments more conductive stubs may be disposed along the portion 4021 of the conductive beam 402 depending on size and shape.

FIG. 4C illustrates a bottom perspective view of the low-pass filter 400 of the present disclosure. The stub rod of the conductive stub 4042 may be shorter than those of both the conductive stub 4041 and the conductive stub 4043, and the conductive stub 4041 and the conductive stub 4043 have a substantially identical height. It may lead that, the coupling-enhancing structure of the conductive stub 4042 not only separates from the coupling-enhancing structures of both the conductive stub 4041 and the conductive stub 4043 in the height direction, but also overlaps the coupling-enhancing structures of both the conductive stub 4041 and the conductive stub 4043 in the direction substantially parallel to the portion 4021 of the conductive beam. Thus, the coupling-enhancing structure of the conductive stub 4042 may be coupled with both the coupling-enhancing structure and the stub rod of the conductive stub 4041and both the stub rod and the coupling-enhancing structure of the conductive stub 4043. For the purpose of achieving better coupling effect, the condition may be that the interval between the coupling objects, for example, the coupling-enhancing structure of the conductive stub 4042 and the stub rod of the conductive stub 4043, and the coupling-enhancing structure of the conductive stub 4042 and the coupling-enhancing structure of the conductive stub 4041, etc. may be less than or equal to a half of the wavelength of the resonant frequency of the corresponding conductive stub, or preferably less than or equal to one eighth of the wavelength of the resonant frequency of at least one of the corresponding conductive stubs. And the estimation rules of the resonant frequency may follow the formulas as mentioned above. For example, the resonant frequency of the

conductive stubs

4041, 4042, 4043 and 4044 that may contribute a transmission zero point to the filter response may follow the above formulas. And the distributed inductance generated by the stub rods of the

conductive stubs

4041, 4042, 4043 and 4044 may be also associated with the characteristic impedance Z ₀ as described with respect to the above equations ①～⑥.

FIG. 4D illustrates a perspective view of a LPF with a conductive housing according to the example embodiment of the present disclosure. In the FIG. 4D, the physical variants associated with impedance Z ₀ and the parameter α are shown: w denotes the width of the corresponding stub rod; h denotes the height of the corresponding conductive stub; t denotes the thickness of the corresponding conductive stub; and s denotes the width of the conductive housing. For example, the coupling-enhancing structures of the

conductive stubs

4041 and 4043 may be extended parallel to the conductive housing 406, and respectively coupled with the conductive housing 406 as shown in FIG. 4A.

FIG. 4E illustrates a perspective view of a LPF according to one more example embodiment of the present disclosure. In the example embodiment shown in FIG. 4E, two pairs of the

conductive stubs

4046a and 4046b, 4047a and 4047b may be placed opposite to each other at both sides of the conductive beam, respectively. For the purpose of achieving a broader stopband bandwidth and higher rejection, the interval distance between the

conductive stubs

4046a and 4047a and 4046b and 4047b may be less than or equal to a half of the wavelength of the resonant frequency of the corresponding conductive stub, or preferably less than or equal to one eighth of the wavelength of the resonant frequency of at least one of the corresponding conductive stubs. And the

conductive stubs

4048 and 4049 may be connected to a bending part of the conductive beam and bent conformal with the bending part.

FIG. 4F illustrates an equivalent circuit diagram of the portion comprising the

conductive stubs

4041, 4042 and 4043 of a low-pass filter according to the example embodiment shown in FIG. 4C. The equivalent inductors L ₄₄₁, L ₄₄₂ and L ₄₄₃ may respectively correspond to the conductive stub rods of the

conductive stubs

4041, 4042 and 4043. The equivalent inductors L ₄₁₂ and L ₄₂₃ may respectively correspond to the portions of the conductive beam between the

conductive stubs

4041 and 4042, 4042 and 4043. The equivalent capacitors C ₄₄₁, C ₄₄₂ and C ₄₄₃ may respectively correspond to the coupling effects generated by the coupling-enhancing structures of the conductive stub 4041, the conductive stub 4042 and the conductive stub 4043 relative to the conductive housing (i.e., the ground potential) . The equivalent capacitors C ₄₁₂ and C ₄₂₃ may respectively correspond to the coupling effects generated by the coupling-enhancing structures of the conductive stub 4042 towards the conductive stub rods of the conductive stub 4041 and the conductive stub 4043. The equivalent capacitors C ₄₁₃ may correspond to the cross coupling effect between the conductive stub 4041 and the conductive stub 4043, as the conductive stub 4042 may be disposed between the conductive stub 4041 and the conductive stub 4043 that may cause the conductive stub 4041 and the conductive stub 4043 to be non-adjacent stubs. Also, the equivalent inductors L ₄₄₁, L ₄₄₂ and L ₄₄₃ may be connected with the equivalent inductors L ₄₁₂ and L ₄₂₃to form a ladder-type arrangement.

FIG. 4G illustrates an attenuation characteristic of example embodiments of the present disclosure. As mentioned above with reference to formulas ①～⑥, the stopband bandwidth may be direct proportional to the capacitance generated by the coupling effect, i.e., the capacitance generated by the coupling effect may be greater, the stopband bandwidth may be broader.

As embodiments described herein above, the low-pass filter according to the present disclosure may be integrally formed. The example materials for the low-pass filter may include, but not limited to, Al, Cu, Ag, Au or alloy or chemical compound thereof.

FIG. 5 illustrates a flow chart of a method 500 for manufacturing the low-pass filter 300 and/or the low-pass filter 400 according to an example embodiment of the present disclosure. As the structures and functions of the low-pass filter 300 and/or the low-pass filter 400 have been described in details herein, the following specification may focus on the process of manufacturing thereof. The method 500 may comprise a step 502 of providing a conductive plate; and a step 504 of removing portions of the conductive plate to form a conductive beam 302 and a plurality of conductive stubs 304 connected to the conductive beam 302, the plurality of conductive stubs 304 including a stub rod 3042 connected at a proximal end to the conductive beam 302 and a coupling-enhancing structure 3044 supported at a distal end of the stub rod 3042.

In specifically, the step 502 of providing a conductive plate may be punching or cutting a conductive base material including but not limited to Al, Cu, Ag, Au or alloy or chemical compound thereof. During a punching process, a mold for conductive plate work-piece may be installed in a press machine, and respective parts of the conductive base material are punched out in the mold while a coil feeding device feeds out a conductive plate formed by slitting the conductive sheet into predetermined widths. The above-mentioned punching process may be generally employed because it may be excellent in productivity. On the other hand, the conductive plate needs to be punched out one by one in a normal punching. Accordingly, when the thickness of the conductive base material may be increased, a large number of conductive sheet are required to manufacture the conductive plate. In this case, the punching process may be combined with the cutting process, so as to satisfy the various thicknesses of the conductive base materials.

Besides, the step 504 of removing portions of the conductive plate may be also performed by a punching process or a cutting process. The conductive plate is further punched into a cavity by clamping the conductive plate during the punching process. Firstly, it may be necessary to fix any periphery of the conductive plate as or part of the periphery of the conductive plate with a fixture, which depends on the forming demand of the conductive plate and the type of base material, etc., which will be described in detail below. It should be appreciated that during the conductive plate forming process, a punch head may move with a certain stroke to press the conductive plate. The working states of the punch head includes an initial position that contacts the conductive plate in the initial state but does not punch the conductive plate, and an end position that punches the conductive plate and forms the conductive plate into the final formed shape, i.e., the conductive beam 302, the input terminal 308, the output terminal 310, a plurality of conductive stubs 304 with stub rods 3042 connected physically and electrically to the conductive beam 302 and coupling-enhancing structures 3044. The distance that the punch head moves between the initial position and the end position is the total stroke of the punch head. In an example embodiment, the first stroke may enable the conductive plate to form a groove with e.g. 80%of the target stamping depth. For example, if the punching process requires forming a groove with the depth of e.g. 2mm in the conductive plate, the process of the first stroke of the punch head may be that the punch head may punch the conductive plate to form a groove with the depth of e.g. 1.6 mm. And it should be understood that the specific depth of the groove may be determined based on the specific shape and usage of the conductive plate and the material type, and the present disclosure is not limited thereto. Then, during the process of the second stroke by the punch head, the conductive plate may be clamped and further punched into the predetermined shape. Since the conductive plate may have been performed by first stroke, the yield rate for mass production may be significantly improved, comparing with the conductive plate formed by only one stroke. Following the punching process, the groove portions of the conductive plate may be cut, and then the rough shape of the low-pass filter 300 may be finished. As a terminal-user product, it may be polished.

In an example embodiment, the step 504 of removing portions of the conductive plate to form a plurality of conductive stubs with stub rods connected physically and electrically to the conductive beam and coupling-enhancing structures. The conductive stub comprising the stub rod and the coupling-enhancing structure may be arranged to be connected to the conductive beam physically and electrically, which may extend and provide a signal flow path. The two adjacent stub rods and the portion of conductive beam therebetween are connected physically and electrically. The two adjacent stub rods may be perpendicular to the conductive beam and parallel to each other. The coupling-enhancing structure may comprise two protrusions projecting from a distal end of the stub rod, which may extend in a direction substantially parallel to the conductive beam. The conductive stub, with the stub rod and the coupling-enhancing structure, may have a "T" shape substantially. The distance between two adjacent coupling-enhancing structures may be less than or equal to a half of the wavelength of the resonant frequency of the corresponding conductive stub, or preferably less than or equal to one eighth of the wavelength of the resonant frequency of at least one of the corresponding conductive stubs. In this way, the coupling-enhancing structures may be coupled with each other, and contribute one transmission zero point to the filter response. Consequently, the low-pass filter herein may achieve a broader stopband bandwidth and higher rejection. The distributed inductance of the conductive stub 304 comprising the stub rod 3042 and the coupling-enhancing structure 3044, may depend on the width of the conductive stub rod 3032, the height of the conductive stub 304, the thickness of the conductive stub 304 and the width of the conductive housing 306. In some other example embodiments, the coupling-enhancing structures may comprise only one protrusion projecting from a distal end of the stub rod, which has an "L" shape substantially. The distance between two adjacent conductive stubs may be less than or equal to one eighth of a wavelength of the resonant frequency of the corresponding conductive stub, in order to achieve better coupling effect. Quantity and position of protrusions forming the coupling-enhancing structure 3044 are not limited to the above example embodiments. In some other example embodiments, the coupling-enhancing structure may have two protrusions disposed at the same side of the distal end of the stub rod and are perpendicular to the stub rod. In some other example embodiments, the coupling-enhancing structure formed by at least one protrusion structure may extend in a direction substantially parallel to the signal flow path. In some example embodiments, the stub rods 3032may have substantially identical height.

In some example embodiments, two adjacent conductive stubs may have the coupling-enhancing structures, and the stub rods of the at least two adjacent conductive stubs may have different height such that the coupling-enhancing structures of the at least two adjacent conductive stubs may be separated from each other in the height direction and overlap with each other in the direction substantially parallel to the signal flow path. In this case, the coupling manner between the two coupling-enhancing structures 3044 is increased because the two coupling-enhancing structures 3044 may have an increased overlapping area. In addition, the lower coupling-enhancing structure may extend below the higher coupling-enhancing structure to vicinity of the adjacent stub rod supporting the higher coupling-enhancing structure, which also increases the coupling capacitance of the coupling-enhancing structure. The distance between the two adjacent coupling-enhancing structures in the height direction and the distance between the lower coupling-enhancing structure and the adjacent stub rod in the signal flow path direction each may be less than or equal to a half of the wavelength of the resonant frequency of the corresponding conductive stub, or preferably less than or equal to one eighth of the wavelength of the resonant frequency of at least one of the corresponding conductive stubs, for the purpose of achieving broader stopband bandwidth and higher rejection performance.

In some example embodiments, the two adjacent conductive stubs, comprising the two coupling-enhancing structures 3044 respectively supported by the stub rods 3042, may be substantially formed to be oriented coplanar to each other. In some example embodiments, the two adjacent conductive stubs 304 may be provided opposite to each other at both sides of the conductive beam. And the conductive beam 302 may be substantially in a cube shape and extend in a linear direction which may be substantially parallel to the signal flow path. In some other example embodiments, the conductive beam may be bent to form a plurality of portions, and at least one portion of the plurality of portions may extend along a direction different from a neighboring portion connected to each other.

The method 500 may further comprise a step 506 of bending the conductive beam at one or more parts such that the conductive beam extends in a two dimensional plane or a three dimensional space. Following the steps of 502 and 504, referring to FIG. 4A and FIG. 5, the conductive beam may be bent to form a plurality of

portions

4021, 4022, 4023, 4024, 4025 and 4026 extending towards a direction different from a neighboring portion connected to each other. As the illustration in FIG. 4A, the

portions

4021, 4022, 4023, 4024, 4025 and 4026 may be constructed substantially in a three dimensional space, and a plurality of sets of conductive stubs may be provided along the one side of the

portions

4025 and 4026 respectively. The plurality of conductive stubs may be disposed at predetermined intervals, and the size of the predetermined intervals may be identical or not identical. The conductive beam with the

portions

4021, 4022, 4023, 4024, 4025 and 4026, may provide a signal flow passage. When signals are supplied to the input terminal 408, the signals may be transmitted along the bent conductive beam with the plurality of portions, as shown in FIG. 4B. And in an example embodiment, a set of

conductive stubs

4041, 4042, 4043 and 4044 may be disposed at one side of the portion 4021 of the conductive beam, and may be oriented coplanar therewith. Each of the

conductive stubs

4041, 4042, 4043 and 4044 may be physically and electrically connected to the portion 4021 of the conductive beam respectively, and a coupling-enhancing structure with two protrusions projecting from a distal end of the stub rod. The set of

conductive stubs

4041, 4042, 4043 and 4044 may have a "T" shape substantially, and it may cause the coupling effect generated by the ends of the protrusions of two adjacent conductive stubs, such as the adjacent

conductive stubs

4041 and 4043. For the purpose of achieving coupling effect, the distance between two adjacent coupling-enhancing

structures

4041 and 4043 may be less than or equal to a half of the wavelength of the resonant frequency of the corresponding conductive stub, or preferably less than or equal to one eighth of the wavelength of the resonant frequency of at least one of the corresponding conductive stubs. The coupling-enhancing structures of the set of

conductive stubs

4041, 4042, 4043 and 4044 may have two protrusions projecting from a distal end of the corresponding stub rod and be parallel to the portions 4021 of the conductive beam and perpendicular to the corresponding stub rod. And the shapes of the set of

conductive stubs

4041, 4042, 4043 and 4044 may have a "T" shape substantially. The coupling-enhancing structure of the conductive stubs 4045 may have only one protrusion projecting from a distal end of the corresponding stub rod and be parallel to the portions 4021 of the conductive beam and perpendicular to the corresponding stub rod. And the shape of the conductive stubs 4045 may have an "L" shape substantially. Quantity and position of protrusions forming the coupling-enhancing structure are not limited to the above example embodiments. In some example embodiments, more conductive stubs may be disposed along the portion 4021 of the conductive beam 402 depending on size and shape.

The method 500 may further comprise a step 508 of bending one or more conductive stubs at the proximal end of the stub rod such that the one or more conductive stubs are oriented perpendicular to the conductive beam. Referring back to FIG. 4E, two pairs of the

conductive stubs

4046a and 4047a, 4046b and 4047b may be less than or equal to a half of the wavelength of the resonant frequency of the corresponding conductive stub, or preferably less than or equal to one eighth of the wavelength of the resonant frequency of at least one of the corresponding conductive stubs. And the

conductive stubs

The method 500 may further comprise a step 510 of mounting the conductive beam into a cavity enclosed by a conductive housing, at least one of the plurality of conductive stubs being oriented substantially parallel to a wall of the cavity. Referring back to FIG. 3A, in an example embodiment, the N-stepped resonant element array may be arranged within the conductive housing 306 enclosing a cavity for accommodating to the N-stepped resonant element array. The N resonant elements may be disposed along the conductive beam 302, wherein each having a stub rod connected physically and electrically to the conductive beam and a coupling-enhancing structure supported by the stub rod; and each of the coupling-enhancing structures 3044 may be coupled with the conductive housing 306.

The example embodiments of the present disclosure are provided only for description and illustration, rather than being exhaustive or restrictive. Many modifications and variations would be obvious to those skilled in the art. The example embodiments are chosen and described herein to elaborate principles and actual applications, making it clear to those skilled in the art that various modifications adapted to the embodiments of the present disclosure can achieve the anticipated particular technical effect.

Although the example embodiments have been described herein with reference to the drawings, it would be appreciated that the above description is not provided restrictively. Rather, without departing from the scope of disclosure or inventive idea and implementation solution of the present disclosure, those skilled in the art are allowed to make other variations and modifications.

The foregoing embodiments are only to illustrate the principle and efficacy of the present disclosure exemplarily, and are not to limit the present disclosure. A person skilled in the art can make modifications or variations on the foregoing embodiments without taking away from the spirit and scope of the present disclosure. Accordingly, all equivalent modifications or variations completed by those with ordinary skill in the art without taking away from the spirit and technical thinking disclosed by the present disclosure should fall within the scope of claims of the present disclosure.

Claims

A low pass filter comprising:

a conductive beam (302) extending to provide a signal flow path; and

a plurality of conductive stubs (304) provided along the signal flow path, the conductive stubs including a stub rod (3042) connected to the conductive beam and a coupling-enhancing structure (3044) supported by the stub rod.
The low pass filter of claim 1, wherein the conductive beam (302) has one or more bending parts so that the conductive beam (302) extends in a two dimensional plane or a three dimensional space.
The low pass filter of claim 1 or 2, wherein the coupling-enhancing structure (3044) comprises at least one protrusion projecting from a distal end of the stub rod (3042) .
The low pass filter of claim 3, wherein the at least one protrusion extends in a direction substantially parallel to the signal flow path.
The low pass filter of any one of claims 1～4, wherein at least two adjacent conductive stubs have the coupling-enhancing structures, and the stub rods of the at least two adjacent conductive stubs have different height so that the coupling-enhancing structures of the at least two adjacent conductive stubs are separated from each other in the height direction and overlaps with each other in the direction substantially parallel to the signal flow path.
The low pass filter of any one of claims 1～5, wherein a distance between the coupling-enhancing structures of two adjacent conductive stubs is less than or equal to one eighth of a wavelength of the resonant frequency of at least one of the two adjacent conductive stubs.
The low pass filter of any one of claims 1～6, wherein at least two conductive stubs having the coupling-enhancing structures are provided opposite to each other at both sides of the conductive beam (302) .
The low pass filter of any one of claims 1～7, wherein the plurality of conductive stubs have a “T” shape or an “L” shape.
The low pass filter of any one of claims 1～8, wherein one of the plurality of conductive stubs is connected to a bending part of the conductive beam (302) and bent conformal with the bending part.
The low pass filter of any one of claims 1～9, wherein the conductive beam (302) and the plurality of conductive stubs have a flat plate shape, and the plurality of conductive stubs are oriented coplanar with or perpendicular to the conductive beam (302) .
The low pass filter of any one of claims 1～10, wherein the plurality of conductive stubs are integrally formed with the conductive beam (302) .
The low pass filter of any one of claims 1～11, further comprising:

a conductive housing (306) enclosing a cavity for accommodating the conductive beam (302) and the plurality of conductive stubs, at least one of the plurality of conductive stubs being oriented parallel to a wall of the cavity.
A method for manufacturing a low pass filter, comprising:

providing a conductive plate; and

removing portions of the conductive plate to form a conductive beam and a plurality of conductive stubs connected to the conductive beam, the plurality of conductive stubs including a stub rod connected at a proximal end to the conductive beam and a coupling-enhancing structure supported at a distal end of the stub rod.
The method of claim 13, wherein removing portions of the conductive plate is performed by a punching process or a cutting process.
The method of claim 13 or 14, further comprising:

bending the conductive beam at one or more parts such that the conductive beam extends in a two dimensional plane or a three dimensional space.
The method of claim 15, wherein one of the plurality of conductive stubs connected to the bending part of the conductive beam is bent conformal with the bending part.
The method of any one of claims 13～16, further comprising:

bending one or more conductive stubs at the proximal end of the stub rod such that the one or more conductive stubs are oriented perpendicular to the conductive beam.
The method of any one of claims 13～17, further comprising:

mounting the conductive beam into a cavity enclosed by a conductive housing, at least one of the plurality of conductive stubs being oriented substantially parallel to a wall of the cavity.