CN112563699B

CN112563699B - Miniaturized spiral surface-mountable band-pass filter based on multilayer PCB structure

Info

Publication number: CN112563699B
Application number: CN202110207749.3A
Authority: CN
Inventors: 董元旦; 杨丹宇; 杨涛
Original assignee: Chengdu Pinnacle Microwave Co Ltd
Current assignee: Chengdu Pinnacle Microwave Co Ltd
Priority date: 2021-02-25
Filing date: 2021-02-25
Publication date: 2021-05-11
Anticipated expiration: 2041-02-25
Also published as: CN112563699A

Abstract

The invention discloses a miniaturized spiral surface-mountable band-pass filter based on a multilayer PCB structure, which comprises four layers of dielectric substrates, five layers of metal copper layers, three layers of prepreg bonding layers, four quarter-wavelength short-circuit spiral resonators, a spiral coupling window, a through metallized through hole and a coplanar waveguide type feed port. The invention designs the quarter-wavelength short-circuit spiral resonator in the metal shielding cavity by utilizing the multilayer PCB laminating technology, embeds the quarter-wavelength short-circuit spiral resonators in the horizontal direction, and stacks the quarter-wavelength short-circuit spiral resonators in the vertical direction, thereby having the characteristics of miniaturization, compactness, easy design, surface mounting, high selectivity, high out-of-band rejection, low loss and high power capacity, and being beneficial to the application of scenes with small size and high performance requirements, such as base station systems, handheld devices and the like.

Description

Miniaturized spiral surface-mountable band-pass filter based on multilayer PCB structure

Technical Field

The invention relates to the technical field of band-pass filters, in particular to a miniaturized spiral surface-mountable band-pass filter based on a multilayer PCB structure.

Background

The filter is an indispensable important device in radio frequency circuits and wireless communication systems, and the performance of the filter determines the performance and quality of the whole microwave system. With the overall progress of communication technologies represented by 5G, there is a strong demand for a miniaturized high-performance bandpass filter satisfying N78 frequency bands (3300 MHz to 3800 MHz) at 6GHz or less. The band-pass filter is an important branch of the filter, is a main component of signal selection and interference suppression in a microwave system, and is widely used in the aspects of mobile communication, integrated circuits and the like.

Currently, commonly used band pass filters are roughly classified into lumped element band pass filters, metal cavity band pass filters, microstrip line band pass filters, Substrate Integrated Waveguide (SIW) band pass filters, low temperature co-fired ceramic technology (LTCC) based band pass filters, Surface Acoustic Wave (SAW) band pass filters, and the like according to the structure of the filter. The lumped element band-pass filter is characterized in that a lumped element capacitor and an inductor are connected in series in a main circuit and in parallel in a branch circuit respectively to form a transmission pole and a transmission zero point, and finally the transmission pole and the transmission zero point are cascaded together to construct band-pass response. The metal cavity body band-pass filter is characterized in that an electric wall formed by metal binds an electromagnetic signal in a closed cavity body, and the electromagnetic wave oscillates in the metal cavity body. The electromagnetic wave at the resonance frequency is retained and the electromagnetic waves of the remaining frequencies are attenuated in the oscillation, thereby constructing a band-pass response. The microstrip line band-pass filter utilizes the distribution parameter characteristics of microstrip lines to construct a resonator, and controls the coupling coefficient in a direct coupling or space coupling mode through the position arrangement between the microstrip lines, so that band-pass response is constructed. The substrate integrated waveguide band-pass filter utilizes through metallized through holes to replace electric walls on the left and right narrow sides of a waveguide, integrates the whole structure on a printed circuit board, and mutually couples TE _ n0 modes between the same or different cavities so as to construct band-pass response. Based on a low temperature co-fired ceramic (LTCC) band-pass filter, the characteristics of multilayer circuit layout and high-density packaging of the LTCC technology are utilized, and multilayer layout and high-density integration are carried out on a distributed parameter circuit inside an LTCC substrate, so that band-pass response is constructed. The surface acoustic wave band-pass filter utilizes the positive and negative piezoelectric effect of the piezoelectric substrate to carry out mutual conversion on an electric signal and an acoustic signal, and designs a proper transfer function so as to construct band-pass response.

In the conventional lumped element bandpass filter, the lumped element capacitor and inductor are limited by the distribution parameters at a high frequency, and the capacitance and inductance of the capacitor cannot maintain the nominal values and are not easy to control, so that the lumped element bandpass filter is not easy to design at a high frequency.

As for the commonly used metal cavity band-pass filter at present, the metal cavity structure and the production limit have the defects of large volume, heavy weight and the like, and the filter has the defects of single structure, inflexible design and the like.

As for the microstrip line band-pass filter commonly used at present, due to the limitation on the microstrip line structure, the open space structure makes the electric field at the edge of the microstrip not be completely bound in the dielectric substrate, and partial energy radiates into the surrounding open space, so that the defects of relatively large loss and the like exist; meanwhile, due to the lack of a corresponding shielding structure, the energy radiated by the microstrip band-pass filter is easy to interfere with other circuit elements in the same system, and is also easy to interfere with other electromagnetic energy, so that the microstrip band-pass filter has the defect of relatively weak electromagnetic compatibility.

For the substrate integrated waveguide band-pass filter commonly used at present, due to the limitation of the transmission mode of the substrate integrated waveguide, the defect that the electromagnetic signal below the cut-off frequency of the waveguide cannot be transmitted in the substrate integrated waveguide exists; meanwhile, the method is limited by the limit of the resonance principle of the substrate integrated waveguide, and has the defects of relatively large volume and the like.

For the band-pass filter based on the low-temperature co-fired ceramic technology, which is commonly used at present, the band-pass filter is limited by a processing technology, and the LTCC needs to adopt a ceramic material with a high relative dielectric constant and simultaneously adopts high-density integration, so that the band-pass filter has the defects of high cost and the like.

As for the existing common surface acoustic wave band-pass filter, the surface acoustic wave filter generally has relatively large insertion loss and cannot be well integrated into a circuit; and is generally only suitable for communication systems below 2GHz, and has the defects of difficult application to high frequency under the condition of high power, and the like.

In summary, the conventional lumped element bandpass filter has the disadvantages of difficult application to high frequency, etc.; the metal cavity band-pass filter is limited by a metal structure and has the defects of large volume, heavy mass, inflexible design and the like; the microstrip line band-pass filter is positioned in an open space, and has the defects of large radiation loss, easy interference with other circuit elements and interference by other elements; the substrate integrated waveguide band-pass filter is limited by a resonance principle and has the defect of relatively large volume; the low-temperature co-fired ceramic technology band-pass filter is limited by a processing technology and has the defects of high cost and the like; the surface acoustic wave band-pass filter has the defects of relatively large insertion loss, difficulty in being applied to high frequency and high power and the like.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a miniaturized spiral surface-mountable band-pass filter based on a multilayer PCB structure.

In order to achieve the purpose of the invention, the invention adopts the technical scheme that:

a miniaturized spiral surface-mountable band-pass filter based on a multilayer PCB structure comprises a metal layer structure and a medium substrate structure which are sequentially stacked;

the metal layer structure comprises a first metal layer, a second metal layer, a third metal layer, a fourth metal layer and a fifth metal layer, and the first metal layer and the fifth metal layer and first through metallized through holes arranged on the outer sides of the periphery form a metal shielding cavity; the second metal layer and the fourth metal layer are respectively provided with a spiral resonator structure, the third metal layer is provided with a spiral coupling window opposite to the spiral resonator structure, and the first metal layer is respectively provided with an input feed port and an output feed port which are connected with the spiral resonator structures on the second metal layer and the fourth metal layer;

the dielectric substrate structure comprises a first dielectric substrate, a second dielectric substrate, a third dielectric substrate and a fourth dielectric substrate.

Further, the spiral resonator structure disposed on the second metal layer specifically includes a first spiral resonator and a second spiral resonator embedded in each other, and an input end of the first spiral resonator is connected to the input feed port through a second through metallized via.

Further, the ground terminal of the first spiral resonator is connected to the first metal layer and the fifth metal layer through the first ground via.

Further, the spiral resonator structure disposed on the fourth metal layer specifically includes a fourth spiral resonator and a third spiral resonator embedded in each other and disposed opposite to the first spiral resonator and the second spiral resonator, respectively, and an output end of the fourth spiral resonator is connected to the output feed port through a third through metalized via.

Further, a ground terminal of the fourth spiral resonator is connected to the first metal layer and the fifth metal layer through a second ground via.

Further, the first, second, third and fourth spiral resonators are embodied as quarter-wave short-circuited spiral resonators.

Further, the second spiral resonator and the third spiral resonator are connected to the first metal layer and the fifth metal layer through a third ground via.

Further, the input feed port and the output feed port are embodied as coplanar waveguide feed ports.

Furthermore, an adhesive layer structure is also arranged between the metal layer structure and the dielectric substrate structure;

the adhesive layer structure comprises a first adhesive layer arranged between the second metal layer and the second medium substrate, a second adhesive layer arranged between the third metal layer and the third medium substrate, and a third adhesive layer arranged between the fourth metal layer and the fourth medium substrate.

Further, the first adhesive layer, the second adhesive layer, and the third adhesive layer are specifically prepreg adhesive layers.

The invention has the following beneficial effects:

(1) the quarter-wavelength short-circuit spiral resonators are embedded in the horizontal plane, the space in the horizontal direction is fully utilized, the strength of electric field coupling is controlled by adjusting the space distance between the two resonators, and the resonators are arranged compactly. Compared with the conventional parallel coupling line and the conventional step impedance line, the parallel coupling line and the step impedance line have the advantages that unnecessary space is reduced, and the size is further reduced.

(2) The invention utilizes multilayer PCB laminating technology to stack quarter-wavelength short-circuit resonators in the vertical direction, fully utilizes the space in the vertical direction, makes the structure further compact, compared with an LTCC filter, does not need to be limited by a medium with high relative dielectric constant and a complex processing technology, can realize superior performance at lower cost, has larger application market, and can be widely applied to base stations and handheld devices.

(3) The metal shielding cavity is constructed by connecting the fifth metal layer at the top layer, the first metal layer at the bottom layer and the first through metalized through holes at the periphery. Compared with the common microstrip line filter, the introduction of the topmost metal layer increases the resonant parallel capacitance, so that lower resonant frequency is generated under the same size, and the miniaturized design is realized. The introduction of a metallic shielding cavity also reduces radiation losses and enhances the electromagnetic compatibility of the filter. And simultaneously, the filter has a higher Q value and higher power capacity.

(4) According to the invention, the spiral coupling window is designed on the middle third metal layer, and on the premise of not changing the position of the resonator, the strength of electric field coupling between the second spiral resonator and the third spiral resonator which are arranged in the vertical direction can be adjusted by adjusting the size of the coupling window, so that more design freedom is provided, the design principle is clear, and the design steps are simple.

(5) The magnetic coupling generated between the input and output ports of the first metal layer positioned at the bottommost layer generates a transmission zero point on each side of a pass band in the topological structure, so that the filter has high selectivity and enhances out-of-band rejection. The transmission zero point introduced by the higher mode further improves the out-of-band rejection degree.

(6) The input/output port of the first metal layer at the bottommost layer is designed as a coplanar waveguide line, has the characteristic of surface mounting, can be directly tested by an evaluation board (EVB), and can be applied to a base station system and handheld equipment.

(7) The filter has relatively large bandwidth and relatively excellent performance at high frequency, can make up the defects of low frequency and narrow bandwidth of the surface acoustic wave filter, and has wide application scenes in a 5G millimeter wave Ka band.

(8) The invention has the characteristics of miniaturization, compactness, easy design, surface mounting, high selectivity, high out-of-band rejection, low loss and high power capacity, and is beneficial to the application of small-size scenes with high performance requirements, such as base station systems, handheld equipment and the like. The application of the multilayer PCB laminating technology is beneficial to reducing the production cost and is suitable for large-scale production and application in the 5G communication era.

Drawings

FIG. 1 is a schematic structural diagram of a miniaturized spiral surface-mountable band-pass filter based on a multi-layer PCB structure according to the present invention;

FIG. 2 is a front view of a miniaturized spiral surface-mountable bandpass filter based on a multi-layer PCB structure according to the present invention;

FIG. 3 is a top view of the miniaturized spiral surface-mountable band-pass filter based on the multi-layer PCB structure of the present invention;

FIG. 4 is a schematic diagram of a resonator structure of a miniaturized spiral surface-mountable band-pass filter based on a multi-layer PCB structure according to the present invention;

FIG. 5 is a schematic diagram of a stacked structure of a miniaturized spiral surface-mountable bandpass filter based on a multi-layer PCB structure according to the present invention;

FIG. 6 is a coupling topology diagram of a miniaturized spiral surface-mountable band-pass filter based on a multi-layer PCB structure according to the present invention;

FIG. 7 is a graph of the 1-10GHz frequency response of the miniaturized spiral surface-mountable band-pass filter based on a multi-layer PCB structure according to the invention.

Wherein the reference numerals are: 1-a first spiral resonator, 2-a second spiral resonator, 3-a third spiral resonator, 4-a fourth spiral resonator, 5-a first through metalized via, 6-an input feed port, 7-an output feed port, 8-a second through metalized via, 9-a third through metalized via, 10-a first ground via, 11-a second ground via, 12-a third ground via.

Detailed Description

The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.

The invention provides a novel miniaturized, compact and easy-to-design high-performance band-pass filter implementation mode based on technologies such as a quarter-wavelength short-circuit spiral resonator (lambda/4 short-circuited spiral resonator), a spiral coupling window, a metal shielding cavity (Shielded metal housing), a Through metalized via (Through metal via), a coplanar waveguide feed (CPW feeding structure), multilayer PCB lamination and the like by taking an N78 frequency band (3300-.

As shown in fig. 1, a miniaturized spiral surface-mountable bandpass filter based on a multilayer PCB structure according to an embodiment of the present invention includes a metal layer structure and a dielectric substrate structure stacked in sequence;

the metal layer structure comprises a first metal layer, a second metal layer, a third metal layer, a fourth metal layer and a fifth metal layer, and the first metal layer and the fifth metal layer form a metal shielding cavity with first through metallized through holes 5 arranged on the outer sides of the periphery; the second metal layer and the fourth metal layer are respectively provided with a spiral resonator structure, the third metal layer is provided with a spiral coupling window opposite to the spiral resonator structure, and the first metal layer is respectively provided with an input feed port 6 and an output feed port 7 which are connected with the spiral resonator structures on the second metal layer and the fourth metal layer;

The invention sequentially stacks four layers of dielectric substrates and five layers of metal layers, the metal layers above and below the dielectric substrates are supported by the dielectric substrates, the fifth metal layer at the topmost layer and the first metal layer at the bottommost layer are used as equivalent ground of the filter and form a metal shielding cavity together with the surrounding through metalized via holes, the spiral resonator structure is designed in a closed metal cavity formed by the top and bottom metal floors and the surrounding through metalized via holes, and the resonance parallel capacitance at the upper layer is equivalently increased, so that lower resonance frequency is generated under the same size, and the miniaturization effect is realized. Due to the metal shielding cavity, the electromagnetic compatibility of the component is improved while the radiation loss is reduced.

In the present embodiment, the spiral resonator structure provided on the second metal layer specifically includes a first spiral resonator 1 and a second spiral resonator 2 embedded in each other; the spiral resonator structure provided on the fourth metal layer comprises in particular a fourth spiral resonator 4 and a third spiral resonator 3 embedded in each other and arranged opposite to the first spiral resonator 1 and the second spiral resonator 2, respectively.

The first spiral resonator 1, the second spiral resonator 2, the third spiral resonator 3 and the fourth spiral resonator 4 are quarter-wavelength short-circuit spiral resonators, the length and the width of a spiral line are adjusted according to an equivalent RLC circuit of a transmission line, the value of equivalent LC is changed, and the change of the resonant frequency of the filter can be realized.

As shown in fig. 2 to 5, the coplanar waveguide Input port (Input) of the first metal layer at the lowermost layer feeds energy into the filter, which is transferred along the second through metallized via 8 to the first spiral resonator 1 at the second metal layer. The first spiral resonator 1 transfers the energy by spatial electric field coupling to a second spiral resonator 2, also in the second metal layer and embedded in each other. The second spiral resonator 2 couples energy vertically through a spiral coupling window in the third metal layer to a third spiral resonator 3 in the fourth metal layer. The coupling energy intensity of the

resonators

2 and 3 in the vertical direction is controlled by adjusting the size of the spiral coupling window. The third spiral resonator 3 transfers energy to the fourth spiral resonator 4 which is also positioned on the fourth metal layer and is embedded into the third spiral resonator through space electric field coupling again, and finally transfers the energy to a coplanar waveguide type Output port (Output) of the first metal layer positioned on the bottommost layer through a third through metallized via hole 9 to feed out, so that the design of the fourth-order band-pass filter is realized.

The invention introduces quarter-wave short circuit spiral resonators embedded with each other in the horizontal direction, and adjusts the strength of electric field coupling by controlling the space distance between the resonators so as to achieve the effect of interstage coupling; and the space can be fully utilized, so that the structure becomes more compact.

In the vertical direction, the resonators on different layers are stacked in multiple layers by utilizing the multilayer PCB laminating technology, energy is coupled in the vertical direction through the spiral coupling window on the middle layer, the coupling coefficient between the couplers arranged in the vertical direction is adjusted, the design freedom degree is improved, the effect of reasonably and fully utilizing the space in the horizontal direction and the space in the vertical direction is achieved, and the compactness of the filter structure is realized.

The invention adopts the spiral coupling window, can adjust the strength of interstage coupling by adjusting the size of the spiral coupling window on the premise of not changing the position of the resonator, provides a proper coupling coefficient to form a good passband effect, and has the advantages of simplicity and easy design.

In this embodiment, the input end of the first spiral resonator 1 and the ground end form an L-shaped structure, the input end is connected to the input feed port 6 through the second through metallized via 8, and the ground end is connected to the first metal layer and the fifth metal layer through the first ground via 10.

Similarly, the output end of the fourth spiral resonator 4 and the ground end form an L-shaped structure, the output end is connected to the output feed port 7 through the third through metallized via hole 9, and the ground end is connected to the first metal layer and the fifth metal layer through the second ground via hole 11.

Further, the spiral inner ends of the second spiral resonator 2 and the third spiral resonator 3 are connected to the first metal layer and the fifth metal layer through the third ground via 12.

Because source load coupling is generated between the input and output ports of the first metal layer positioned at the bottommost layer, a transmission zero point is respectively introduced at two sides of a pass band, the selectivity of the band-pass filter is improved, and out-of-band rejection is enhanced.

In the present embodiment, the input feed port 6 and the output feed port 7 are embodied as coplanar waveguide feed ports.

The input/output port of the first metal layer at the bottommost layer is designed into a coplanar waveguide (CPW), so that the filter has the surface mounting characteristic, is easy to integrate in a base station system and handheld equipment, and expands the application scene of the filter.

In this embodiment, an adhesive layer structure is further included between the metal layer structure and the dielectric substrate structure;

The first adhesive layer, the second adhesive layer and the third adhesive layer are prepreg adhesive layers.

The bonding layer structure, the metal layer structure and the dielectric substrate structure are arranged in a laminating mode, and the prepreg bonding layer is used as a laminating adhesive to bond the four layers of dielectric substrates into a whole. The thickness of each metal layer in fig. 2 is small relative to each dielectric substrate layer and adhesion layer and is therefore not shown.

Fig. 6 is a coupling topology of the filter, wherein E represents electrical coupling, M represents magnetic coupling, and the main coupling path is: the signal source(s) transfers energy to the first spiral resonator 1 by magnetic coupling, the first spiral resonator 1 transfers energy to the second spiral resonator 2 by electrical coupling, the second spiral resonator 2 is able to transfer energy to the third spiral resonator 3 by electrical coupling, the third spiral resonator 3 again transfers energy to the fourth spiral resonator 4 by electrical coupling, and finally the fourth spiral resonator 4 transfers energy to the load (l) by magnetic coupling. The weak coupling path is: magnetic coupling between the Source and the Load, electrical coupling between the first spiral resonator 1 and the third spiral resonator 3, electrical coupling between the first spiral resonator 1 and the fourth spiral resonator 4, and electrical coupling between the second spiral resonator 2 and the fourth spiral resonator 4.

The dielectric substrate material used by the band-pass filter is 0.254mm thick high-frequency version Rogers 5580; the prepreg adhesive layer was Rojess prepreg Ro4450F with a thickness of 0.1mm, a relative dielectric constant of 3.52, and a dielectric loss tangent of 0.004; the thickness of the metallic copper layer was 0.018 mm. The band-pass filter is designed to be an N78 band (3300 MHz-3800 MHz), as shown in FIG. 7, the test center frequency is 3.483GHz, the-3 dB bandwidth is 3.205 GHz-3.761 GHz, the relative bandwidth is 16%, the minimum insertion loss in the band is-1 dB, the rectangular coefficient is 0.49, the 40dB out-of-band rejection of the upper stop band reaches 2.37f0, and the 20dB out-of-band rejection of the upper stop band reaches 2.763f 0. The size of the whole filter is 10.24mm × 8.16mm × 1.406mm (0.12 λ 0 × 0.095 λ 0 × 0.016 λ 0). The return loss curve shown in S11 and the insertion loss curve shown in S21 both show that the accuracy of the measurement result and the simulation result of the invention is high. The center frequency of the test results is shifted to the left compared to the simulation results, which is caused by manufacturing errors.

The principle and the implementation mode of the invention are explained by applying specific embodiments in the invention, and the description of the embodiments is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.

It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.

Claims

1. A miniaturized spiral surface-mountable band-pass filter based on a multilayer PCB structure is characterized by comprising a metal layer structure and a medium substrate structure which are sequentially stacked;

the metal layer structure comprises a first metal layer, a second metal layer, a third metal layer, a fourth metal layer and a fifth metal layer, and the first metal layer and the fifth metal layer form a metal shielding cavity with first through metallized through holes (5) arranged on the outer sides of the periphery; a spiral resonator structure is respectively arranged on the second metal layer and the fourth metal layer, a spiral coupling window opposite to the spiral resonator structure is arranged on the third metal layer, and an input feed port (6) and an output feed port (7) which are connected with the spiral resonator structures on the second metal layer and the fourth metal layer are respectively arranged on the first metal layer; the spiral resonator structure arranged on the second metal layer specifically comprises a first spiral resonator (1) and a second spiral resonator (2) which are embedded into each other, and the input end of the first spiral resonator (1) is connected with the input feed port (6) through a second through metallized via hole (8); the spiral resonator structure arranged on the fourth metal layer specifically comprises a fourth spiral resonator (4) and a third spiral resonator (3) which are embedded into each other and are respectively arranged opposite to the first spiral resonator (1) and the second spiral resonator (2), and the output end of the fourth spiral resonator (4) is connected with an output feed port (7) through a third through metallized via hole (9); the first spiral resonator (1), the second spiral resonator (2), the third spiral resonator (3) and the fourth spiral resonator (4) are quarter-wavelength short-circuit spiral resonators;

2. The miniaturized spiral surface-mountable bandpass filter according to claim 1, characterized in that the ground terminal of the first spiral resonator (1) is connected to the first and fifth metal layers through a first ground via (10).

3. The miniaturized spiral surface-mountable bandpass filter according to claim 1, characterized in that the ground terminal of the fourth spiral resonator (4) is connected to the first and fifth metal layers through a second ground via (11).

4. A miniaturized spiral surface-mountable bandpass filter based on a multilayer PCB structure according to claim 3, characterized in that the second (2) and third (3) spiral resonators are connected to the first and fifth metal layers by a third ground via (12).

5. The miniaturized helical surface-mountable bandpass filter according to claim 1, characterized in that the input feed port (6) and the output feed port (7) are in particular coplanar waveguide feed ports.

6. The miniaturized spiral surface-mountable bandpass filter according to claim 1, further comprising an adhesive layer structure between the metal layer structure and the dielectric substrate structure;

7. The miniaturized spiral surface-mountable bandpass filter according to claim 6, wherein the first, second, and third adhesive layers are prepreg adhesive layers.