Band-pass filter

Abstract

The invention provides a band-pass filter, which belongs to the technical field of filters and comprises a dielectric substrate and a microstrip line wiring layer arranged on the surface of the dielectric substrate. The microstrip line wiring layer comprises an input feeder line, an output feeder line and a resonance network located between the input feeder line and the output feeder line. The resonant network comprises (2n + 1) linear terminal short-circuit resonators and 2n L-shaped terminal short-circuit resonators which are sequentially arranged in parallel at intervals, the 2n L-shaped terminal short-circuit resonators are sequentially arranged between every two adjacent linear terminal short-circuit resonators in a penetrating manner, and n is a positive integer; the (2k-1) th L-type terminal short-circuit resonator and the 2k-th L-type terminal short-circuit resonator are distributed in an axial symmetry manner relative to the 2k-th linear terminal short-circuit resonator, and are provided with coupling sections which are opposite to each other and are arranged at intervals, the open-circuit end of the 2k-th linear terminal short-circuit resonator is configured to terminate outside a spacing area between the coupling sections, and k is a positive integer and is smaller than or equal to n.

Description

Technical Field

[0001] This application relates to the field of filter technology, and more particularly to a bandpass filter. Background Technology

[0002] With the widespread application of carrier aggregation (CA) technology in modern and future communication systems, the spectrum environment is becoming increasingly congested, and mutual interference between transmitted and received signals, as well as between different aggregated frequency bands, is becoming more and more severe, including local oscillator leakage, image frequencies, and out-of-band modulation interference. As the core frequency selection device in the RF front end, the bandpass filter can retain the useful signal within the passband while suppressing interference signals outside the passband.

[0003] Microstrip bandpass filters typically employ an interdigital structure, consisting of multiple linear resonators arranged side-by-side at intervals. Signal transmission primarily occurs through cascaded coupling between adjacent resonators, exhibiting an all-pole response. However, interdigital all-pole bandpass filters have a slow stopband roll, meaning a wide transition band from the passband to the stopband. To achieve steeper sidebands and improve frequency selectivity, the number of resonators needs to be increased. But this not only significantly increases the physical size of the filter but also introduces greater insertion loss, making it difficult to meet the combined requirements of miniaturization, low loss, and high selectivity in modern communication systems.

[0004] Therefore, how to overcome the limitations of the all-pole characteristics of traditional interdigital filters and achieve steep sideband suppression without increasing circuit size is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This application provides a bandpass filter that achieves negative coupling between non-adjacent resonators by introducing an L-type resonator and constructing a clearance space in the physical structure. The positive and negative coupling between the source and the load cancel each other out, thereby generating a transmission zero. While meeting the requirements of device miniaturization, it significantly improves the frequency selectivity and out-of-band rejection capability of the filter.

[0006] This application provides a bandpass filter, including a dielectric substrate and a microstrip wiring layer disposed on the surface of the dielectric substrate; The microstrip wiring layer includes an input feed line, an output feed line, and a resonant network located between the input feed line and the output feed line; The resonant network includes (2n+1) linear short-circuit resonators and 2n L-type short-circuit resonators. The (2n+1) linear short-circuit resonators are arranged in parallel intervals, and the 2n L-type short-circuit resonators are arranged interlaced between two adjacent linear short-circuit resonators. n is a positive integer. The (2k-1)th L-type terminal short-circuit resonator and the 2kth L-type terminal short-circuit resonator are axially symmetric about the 2kth linear terminal short-circuit resonator. The (2k-1)th L-type terminal short-circuit resonator and the 2kth L-type terminal short-circuit resonator have mutually facing and spaced coupling segments. The open-circuit end of the 2kth linear terminal short-circuit resonator is configured to terminate outside the spaced area between the coupling segments. k is a positive integer and k≤n.

[0007] In some embodiments, the signal transmission path between the input feed line and the output feed line includes a first path and a second path; the first path passes through the 2kth linear short-circuit resonator, and the second path does not pass through the 2kth linear short-circuit resonator; the signal transmitted through the second path is used to generate destructive interference with the signal transmitted through the first path to generate a transmission zero.

[0008] In some embodiments, the spacing between the interval regions between the coupling segments is configured to be adjustable to control the frequency position of the transmission zero point.

[0009] In some embodiments, the coupling segments are coupled with open-circuit coupling or short-circuit coupling; Specifically, the transmission zero is generated by coupling the open-circuit segment to the low-frequency side of the passband, and the transmission zero is generated by coupling the short-circuit end to the high-frequency side of the passband.

[0010] In some embodiments, the L-shaped terminal short-circuit resonator consists of a parallel segment, a vertical segment, and a bent connecting segment connecting the parallel segment and the vertical segment. The parallel segment is the coupling segment, and the extension direction of the parallel segment is parallel to the extension direction of the input feed line and the output feed line. The extension direction of the vertical segment is perpendicular to the extension direction of the input feed line and the output feed line. The extension direction of the linear terminal short-circuit resonator is perpendicular to the extension directions of the input feed line and the output feed line.

[0011] In some embodiments, the resonant length of the L-shaped terminal short-circuit resonator is the total length of the parallel segment, the bent connecting segment, and the vertical segment, and the resonant lengths of the L-shaped terminal short-circuit resonator and the linear terminal short-circuit resonator are determined based on 1 / 4 wavelength of the center frequency of the bandpass filter.

[0012] In some embodiments, the bent connecting section is a 45-degree chamfered structure or a circular arc bending structure.

[0013] In some embodiments, a microstrip reference ground layer is provided on the bottom surface of the dielectric substrate, and the short-circuit ends of the (2n+1) linear terminal short-circuit resonators and the 2n L-type terminal short-circuit resonators are all electrically connected to the microstrip reference ground layer through metallized vias penetrating the dielectric substrate.

[0014] In some embodiments, the dielectric substrate is an alumina ceramic substrate having a coefficient of thermal expansion that matches the active circuit, and the microstrip reference ground layer is configured to be assembled with an external circuit board via a conductive adhesive process.

[0015] In some embodiments, the bandpass filter operates in the Ka band.

[0016] The bandpass filter provided in this application has (2n+1) linear short-circuit resonators and 2n L-type short-circuit resonators arranged sequentially in a resonant network. The L-type short-circuit resonators are arranged between adjacent linear short-circuit resonators using a bending structure. This arrangement effectively reduces the physical size of the circuit without reducing the number of resonant stages, and achieves device miniaturization while maintaining high-performance filtering characteristics. The (2k-1)th L-type short-circuit resonator and the 2kth L-type short-circuit resonator have mutually targeted and spaced coupling sections, and the open end of the 2kth linear short-circuit resonator in the middle does not enter the coupling interval region. This layout constructs a signal multipath transmission mechanism between two non-directly adjacent L-type short-circuit resonators, which can effectively improve the sideband steepness and selectivity. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is one of the structural schematic diagrams of the bandpass filter provided in the embodiments of this application; Figure 2 This is a second schematic diagram of the bandpass filter provided in the embodiments of this application; Figure 3 This is a schematic diagram of the signal transmission path of the bandpass filter provided in the embodiments of this application; Figure 4 This is the third schematic diagram of the bandpass filter provided in the embodiments of this application; Figure 5 This is a schematic diagram of the dimensions of the bandpass filter provided in an embodiment of this application; Figure 6 This is a schematic diagram of the S-parameter simulation curve of the bandpass filter provided in the embodiments of this application; Figure label: 1-Microstrip line wiring layer; 2-Dielectric substrate; 3-Microstrip line reference ground layer; 4-Input feed line; 5-Output feed line; 6-First linear termination short-circuit resonator; 7-Second linear termination short-circuit resonator; 8-Third linear termination short-circuit resonator; 9-First L-type termination short-circuit resonator; 10-Second L-type termination short-circuit resonator; 11, 12-Parallel segments (coupling segments); 13, 14-Vertical segments; V-Metallized via. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Figure 1 This is one of the structural schematic diagrams of the bandpass filter provided in the embodiments of this application, such as... Figure 1 As shown, the filter is mainly composed of a microstrip wiring layer 1, a dielectric substrate 2, and a microstrip reference ground layer 3 from top to bottom. Specifically, the microstrip wiring layer 1 is disposed on the surface of the dielectric substrate 2, and the microstrip reference ground layer 3 is disposed on the bottom surface of the dielectric substrate 2.

[0021] The microstrip wiring layer 1 includes an input feed, an output feed, and a resonant network located between the input and output feeds. This resonant network employs a modified hybrid interdigital topology, consisting of two sets of resonators of different types interleaved. Specifically, the resonant network includes a linear resonator group and an L-type resonator group.

[0022] The linear resonator group consists of (2n+1) linear short-circuit resonators with termination, and the L-type resonator group consists of 2n L-type short-circuit resonators with termination. Here, n is a positive integer. The (2n+1) linear short-circuit resonators with termination are arranged in parallel intervals, and the 2n L-type short-circuit resonators with termination are arranged alternately between adjacent linear short-circuit resonators.

[0023] In some embodiments, the short-circuit ends of the (2n+1) linear terminal short-circuit resonators and the 2n L-type terminal short-circuit resonators in the resonant network are all electrically connected to the microstrip reference ground layer 2 through metallized vias V that penetrate the dielectric substrate 2.

[0024] The resonant network has specific local coupling units. Taking the kth (k is a positive integer and k≤n) local coupling unit as an example, the kth local coupling unit includes the (2k-1)th L-type terminal short-circuit resonator, the 2kth L-type terminal short-circuit resonator, and the 2kth linear terminal short-circuit resonator.

[0025] The (2k-1)th L-type terminal short-circuit resonator and the 2kth L-type terminal short-circuit resonator are axially symmetric about the 2kth linear terminal short-circuit resonator. This symmetrical structure can simplify the design and simulation optimization process, and also ensure the consistency of the input and output port impedances, thus improving return loss.

[0026] The (2k-1)th L-type terminal short-circuit resonator and the 2kth L-type terminal short-circuit resonator each contain a coupling segment. The two coupling segments are opposite to each other and spaced apart, with a gap region.

[0027] The physical length of the 2kth linear short-circuit resonator located between the (2k-1)th L-type terminal short-circuit resonator and the 2kth L-type terminal short-circuit resonator is specially configured. Specifically, the open end of the 2kth linear short-circuit resonator is configured to terminate outside the gap region between the coupling segments and cannot actually extend into the gap region between the coupling segments of the two L-type terminal short-circuit resonators.

[0028] In this embodiment, (2n+1) linear short-circuit resonators and 2n L-shaped short-circuit resonators are interspersed in the resonant network. The L-shaped short-circuit resonators are arranged between adjacent linear short-circuit resonators using a bending structure. This arrangement effectively reduces the physical size of the circuit without reducing the number of resonant stages, and achieves device miniaturization while maintaining high-performance filtering characteristics. The (2k-1)th L-shaped short-circuit resonator and the 2kth L-shaped short-circuit resonator have mutually targeted and spaced coupling sections, and the open end of the 2kth linear short-circuit resonator in the middle does not enter the coupling interval region. This layout constructs multiple signal transmission paths between two non-directly adjacent L-shaped short-circuit resonators, which can effectively improve sideband steepness and selectivity.

[0029] Furthermore, this local coupling unit constructs a unique signal multipath transmission mechanism. Specifically, the mutually opposing and spaced coupling segments in the k-th local coupling unit, i.e., the relative portions of the (2k-1)-th L-type terminated short-circuit resonator and the 2k-th L-type terminated short-circuit resonator, are configured to establish non-adjacent negative coupling. This negative coupling mechanism forms two parallel signal transmission paths between the filter's input and output feed lines: First path (main path): The signal is transmitted through the 2kth linear terminal short-circuit resonator.

[0030] Secondary Path: The signal is transmitted without passing through the 2kth linear short-circuit resonator. Since the open end of the 2kth linear short-circuit resonator is configured to terminate outside the gap between the coupling segments, it cannot actually extend into the gap between the coupling segments of the two L-type short-circuit resonators. Therefore, the signal can be transmitted by bypassing the intermediate 2kth linear short-circuit resonator through the capacitive or inductive coupling between the (2k-1)th and 2kth L-type short-circuit resonators.

[0031] At the edge of the operating frequency band, i.e., the passband edge, by properly designing the coupling strength, the signals transmitted through the second path and the first path can have approximately equal amplitudes but opposite phases. This allows the signals transmitted through the two paths to produce destructive interference, generating transmission zeros at the corresponding frequency positions. These transmission zeros cause the filter's amplitude-frequency response curve to drop rapidly at the passband edge, thus exhibiting high selectivity.

[0032] In this embodiment, during signal transmission, in addition to the main path passing through the L-type terminated short-circuit resonator, the linear terminated short-circuit resonator, and the L-type terminated short-circuit resonator in sequence, an auxiliary coupling path is formed that directly crosses the two L-type terminated short-circuit resonators. The signals transmitted through these two paths will undergo destructive interference at a specific frequency. This interference effect significantly accelerates the signal attenuation speed of the filter at the passband edge, thereby achieving extremely steep sideband transition characteristics and greatly enhancing the filter's ability to suppress interference signals outside the passband and its frequency selectivity performance.

[0033] Furthermore, the generation of transmission zeros depends on the destructive interference of signals transmitted through the two paths, and the coupling strength directly affects the amplitude and phase characteristics of the signal transmitted through the second path.

[0034] In some embodiments, the spacing between the interval regions between the coupling segments is configured to be adjustable to control the frequency position where the transmission null is generated.

[0035] Specifically, the spacing between the interval regions of the coupling segments, that is, the physical distance between the coupling segments of the two L-shaped terminated short-circuit resonators in the local coupling unit, or simply the coupling spacing, is a key parameter for controlling the coupling strength. By changing the spacing between the interval regions of the coupling segments, the coupling strength between the two L-shaped terminated short-circuit resonators in the local coupling unit can be significantly altered. Specifically, the smaller the spacing between the interval regions of the coupling segments, the stronger the coupling; conversely, the larger the spacing, the weaker the coupling. By fine-tuning the spacing between the interval regions of the coupling segments, the frequency position of the transmission zero can be precisely controlled, thereby enabling customized design of the stopband characteristics without altering the overall filter topology.

[0036] In this embodiment, the open end of the linear terminated short-circuit resonator is configured to terminate outside the interval region between the coupling segments. This ensures that the open end of the middle linear terminated short-circuit resonator will not physically block or excessively shield the negative coupling between the two L-shaped terminated short-circuit resonators. Thus, by adjusting the spacing of the interval region between the coupling segments, the frequency position of the transmission zero point can be precisely controlled, providing good design flexibility.

[0037] In some embodiments, the extension direction of the linear terminated short-circuit resonator is perpendicular to the extension directions of the input feed line and the output feed line; the L-shaped terminated short-circuit resonator consists of a parallel segment, a vertical segment, and a bent connecting segment connecting the parallel segment and the vertical segment, wherein the parallel segment is the coupling segment; the extension direction of the parallel segment is parallel to the extension directions of the input feed line and the output feed line; the extension direction of the vertical end is perpendicular to the extension directions of the input feed line and the output feed line.

[0038] Specifically, the extension direction of each linearly terminated short-circuit resonator in the resonant network is perpendicular to the extension directions of the input and output feed lines. Each L-shaped terminated short-circuit resonator in the resonant network adopts a right-angle bend structure, consisting of three parts: a parallel segment, a perpendicular segment, and a bend connecting segment connecting the parallel and perpendicular segments.

[0039] The parallel segment, acting as the coupling segment, extends parallel to the direction of the input / output feed line. In the local coupling unit, the parallel segments of the two L-shaped terminated short-circuit resonators face each other, establishing non-adjacent negative coupling. The vertical segment extends perpendicular to the direction of the input / output feed line and is responsible for cascading coupling with the adjacent linear terminated short-circuit resonator along the main path.

[0040] To reduce signal reflection loss and radiation interference at right-angle bends, the bend connection between the parallel and vertical sections of the L-shaped terminated short-circuit resonator employs a chamfered or rounded bend structure to ensure impedance continuity. Preferably, a 45-degree chamfer structure is used to minimize reflection loss and radiation interference. This right-angle bend structure not only achieves a compact spatial layout but also effectively utilizes the parallel section to establish additional negative coupling.

[0041] In some embodiments, the resonant length of the L-shaped terminated short-circuit resonator is the total length of the parallel segment, the bent connecting segment, and the vertical segment, specifically the total length of the central conductive path along the parallel segment, the bent connecting segment, and the vertical segment. The resonant lengths of the L-shaped terminated short-circuit resonator and the linear terminated short-circuit resonator are determined based on 1 / 4 wavelength of the bandpass filter's center frequency. The initial resonant length can specifically be 1 / 4 wavelength of the bandpass filter's center frequency, and can be fine-tuned as needed in actual simulations. Traditional open-circuit microstrip line resonators require a physical length of 1 / 2 wavelength to resonate, while this application uses a terminated short-circuit resonator, utilizing the boundary conditions of the short-circuit end, requiring only 1 / 4 wavelength to resonate. Therefore, using the same operating frequency (e.g., Ka band) and the same dielectric substrate 2, the overall physical size of the filter can be significantly reduced, better meeting the requirements of miniaturized device design.

[0042] The following example, using n=1, further illustrates the technical solution provided in this application through a complete embodiment.

[0043] Figure 2 This is a second schematic diagram of the bandpass filter provided in the embodiments of this application, as shown below. Figure 2 As shown, the microstrip wiring layer 1 includes an input feed line 4, an output feed line 5, and a resonant network located between them. This resonant network employs a modified interdigital topology and specifically comprises five resonators: Linear terminated short-circuit resonators: including a first linear terminated short-circuit resonator 6, a second linear terminated short-circuit resonator 7, and a third linear terminated short-circuit resonator 8. These three linear terminated short-circuit resonators are arranged side-by-side with intervals, similar to a traditional interdigital structure. One end of each linear terminated short-circuit resonator is an open-circuit end, and the other end is a short-circuit end.

[0044] The L-type terminated short-circuit resonator includes a first L-type terminated short-circuit resonator 9 and a second L-type terminated short-circuit resonator 10. The two L-type terminated short-circuit resonators are not placed independently, but are interspersed within the gaps of the linear terminated short-circuit resonators. Specifically, the first L-type terminated short-circuit resonator 9 is located between linear terminated short-circuit resonators 6 and 7, and the second L-type terminated short-circuit resonator 10 is located between linear terminated short-circuit resonators 7 and 8.

[0045] The first L-type terminal short-circuit resonator 9 and the second L-type terminal short-circuit resonator 10 are axially symmetrical about the second linear terminal short-circuit resonator 7.

[0046] The short-circuit terminals of all resonators in the resonant network are electrically connected to the bottom microstrip reference ground layer 3 through the metallized via V that penetrates the dielectric substrate 2. All resonators in the resonant network form a 1 / 4 wavelength resonant characteristic.

[0047] Both the first L-shaped terminal short-circuit resonator 9 and the second L-shaped terminal short-circuit resonator 10 are right-angle bent structures. The first L-shaped terminal short-circuit resonator 9 consists of a parallel section 11 and a vertical section 13, and the second L-shaped terminal short-circuit resonator 10 consists of a parallel section 12 and a vertical section 14. The connection section between the parallel and vertical sections of the two L-shaped terminal short-circuit resonators adopts a 45-degree chamfer structure to reduce signal reflection loss and radiation interference at the right-angle bend and ensure impedance continuity.

[0048] Parallel segments 11 and 12: Their extension directions are parallel to the extension directions of input feed line 4 and output feed line 5, corresponding to... Figure 2 In the horizontal direction, it mainly serves to resonate and couple with the adjacent linear terminal short-circuit resonator.

[0049] Vertical segments 13 and 14: Their extension directions are perpendicular to the extension directions of input feed line 4 and output feed line 5, respectively. Figure 2 The vertical direction within. Figure 2 In the middle, parallel segment 11 and parallel segment 12 are coupled segments and are directly opposite each other in space.

[0050] Furthermore, by introducing a negative coupling mechanism between non-directly adjacent L-type terminal short-circuit resonators, cross-coupling is established between different paths of the filter, realizing direct negative coupling between non-directly adjacent resonators (i.e., the first L-type terminal short-circuit resonator 9 and the second L-type terminal short-circuit resonator 10) in a compact space.

[0051] In traditional interdigital filters, coupling is mainly achieved through adjacent resonators. The transfer function is an all-pole function, resulting in slow out-of-band roll-off and insufficient stopband suppression. The intermediate resonator ( Figure 2 Specifically, the second linear terminal short-circuit resonator 7) completely blocks the electromagnetic fields of the two resonators, allowing signals to be transmitted sequentially. To overcome this limitation, Figure 2 The second linear terminal short-circuit resonator 7 is designed to avoid obstacles. The open end of the second linear terminal short-circuit resonator 7 is configured to terminate outside the interval area between parallel segment 11 and parallel segment 12, and shall not actually extend to the extension line of parallel segment 11 and parallel segment 12.

[0052] Since the open end of the second linear short-circuit resonator 7 in the middle does not actually extend to the gap area between parallel segment 11 and parallel segment 12, a gap area without metal conductor shielding is formed between parallel segment 11 and parallel segment 12, so that non-adjacent negative coupling is established between the first L-type short-circuit resonator 9 and the second L-type short-circuit resonator 10.

[0053] Non-adjacent negative coupling results in two paths for the signal from input to output. Figure 3 This is a schematic diagram of the signal transmission path of the bandpass filter provided in the embodiments of this application, referring to... Figure 2 and Figure 3 The two paths are explained as follows: First path (main path): Input → First linear terminal short-circuit resonator 6 → First L-type terminal short-circuit resonator 9 → Second linear terminal short-circuit resonator 7 → Second L-type terminal short-circuit resonator 10 → Third linear terminal short-circuit resonator 8 → Output.

[0054] Second path (negative coupling path): Input → First linear terminal short-circuit resonator 6 → First L-type terminal short-circuit resonator 9 → Second L-type terminal short-circuit resonator 10 → Third linear terminal short-circuit resonator 8 → Output.

[0055] The signals output from the two transmission paths undergo destructive interference at frequencies with equal amplitude and opposite phase, causing a sharp drop in signal amplitude and generating transmission zeros. These transmission zeros result in a very steep downward trend in the sidebands of the filter's amplitude-frequency response curve, significantly improving the filter's selectivity.

[0056] Positive coupling is achieved between resonators through gaps. The coupling strength is closely related to the spacing of the gap regions; the smaller the spacing, the stronger the coupling and the larger the bandwidth; conversely, the larger the spacing, the weaker the coupling and the smaller the bandwidth. Negative coupling between the input and output is achieved by establishing non-adjacent negative coupling between the first L-type terminated short-circuited resonator 9 and the second L-type terminated short-circuited resonator 10. By changing the spacing of the gap regions between the coupling segments (parallel segments 11 and 12), the strength of the non-adjacent negative coupling can be adjusted, and phase control can be achieved, thereby precisely controlling the number and frequency position of transmission zeros. The stronger the coupling, the farther the zeros are from the passband center; the weaker the coupling, the closer the zeros are to the passband center.

[0057] The coupling segments (parallel segments 11 and 12) can be configured as open-end coupling (primarily capacitive) or short-end coupling (primarily inductive). By adjusting the coupling polarity of the coupling segments between the first L-type terminal short-circuit resonator 9 and the second L-type terminal short-circuit resonator 10, i.e., by using open-end coupling or short-end coupling, the location of the transmission zero point on the passband can be flexibly adjusted.

[0058] If open-ended coupling is used (parallel segments 11 and 12 are used as the open ends of the L-type terminal short-circuit resonator), transmission zeros are usually generated on the low-frequency side / lower sideband of the passband (the region with frequencies lower than the passband frequency).

[0059] If short-circuit coupling is used (parallel segments 11 and 12 are used as short-circuit terminals of the L-type terminal short-circuit resonator and connected to the via terminal), transmission zeros are usually generated on the high-frequency side / upper sideband of the passband (the region with a frequency higher than the passband frequency).

[0060] By combining coupling methods of different polarities, transmission zeros can be generated on the low-frequency and / or high-frequency sides of the passband, thereby achieving symmetrical or asymmetrical out-of-band rejection characteristics. Transmission zeros effectively improve the sideband transition characteristics and out-of-band rejection characteristics of the bandpass filter, thus greatly improving the filter's selectivity.

[0061] It should be noted that, although Figure 2 The example given is n=1, but those skilled in the art will understand that when n≥2, the structure of the resonant network can be cascaded and expanded. Figure 4 This is the third schematic diagram of the bandpass filter provided in the embodiments of this application, as shown below. Figure 4 As shown, the resonant network includes 2n+1 linearly terminated short-circuited resonators and 2n L-shaped terminated short-circuited resonators. The dashed box indicates a local coupling unit, and the resonant network contains a total of n local coupling units. This extended structure can introduce more transmission zeros, further improving the stopband rejection performance of the filter.

[0062] In some embodiments, an alumina ceramic substrate is selected as the dielectric substrate 2.

[0063] Specifically, the basic parametric properties of alumina ceramics include: relative permittivity. It is approximately 9.7 (≥9.0), and the loss tangent tan δ is as low as 0.0001.

[0064] The high dielectric constant significantly shortens the physical length of the 1 / 4 wavelength microstrip line, while the extremely low loss tangent ensures that the filter has low insertion loss in the millimeter-wave band, thus better meeting the requirements of modern communication systems for device miniaturization and low loss.

[0065] In some embodiments, the alumina ceramic substrate has a coefficient of thermal expansion that matches the active circuit, and the microstrip reference ground layer 3 is configured to be assembled with an external circuit board via a conductive adhesive process.

[0066] Specifically, the coefficient of thermal expansion (CTE) of alumina ceramics is very close to that of commonly used semiconductor chips (such as GaAs and GaN). In micro-assembly processes, this filter can be directly bonded to a metal cavity or substrate using conductive adhesive. Under high-power operating environments with drastic temperature changes (such as 5G macro base station RF units), it will not cause solder joint cracking or substrate breakage due to thermal expansion and contraction mismatch, and its reliability is far superior to that of traditional PCB substrates.

[0067] In some embodiments, the bandpass filter can operate in the Ka band. In the Ka band, using a high-dielectric-constant dielectric substrate in conjunction with a quarter-wavelength microstrip structure allows for a balance between device size and insertion loss. This bandpass filter topology can also be adapted to L-band to millimeter-wave bands.

[0068] To verify the performance of the bandpass filter provided in this application embodiment, simulation was performed using the High Frequency Structure Simulator (HFS) three-dimensional electromagnetic simulation software. The bandpass filter adopts an alumina ceramic substrate design with a substrate thickness of 0.254 mm. The metal layer thickness of the microstrip line wiring layer 1 is 3 μm, the metal layer thickness of the microstrip line reference ground layer 3 is 1 μm, and the input feed line 4 / output feed line 5 consists of transmission lines with a characteristic impedance of 50 Ω.

[0069] Figure 5 This is a schematic diagram of the dimensions of the bandpass filter provided in the embodiments of this application, as shown below. Figure 5 As shown, the specific microstrip layout and key size parameters of the bandpass filter are presented. This indicates the linewidth of input feed line 4 / output feed line 5. This width depends on the dielectric constant and thickness of the alumina substrate to match the characteristic impedance of 50Ω, ensuring good impedance matching and low reflection. This indicates the lengths of the first linear short-circuit resonator 6 and the third linear short-circuit resonator 8. This indicates the linewidth of the first linear short-circuit resonator 6 and the third linear short-circuit resonator 8. This indicates the length of the second linear terminal short-circuit resonator 7. This indicates the linewidth of the second linear terminal short-circuit resonator 7. This indicates the length of the center conductive path of the parallel segments 11 and 12 (coupling segments) of the first L-type terminated short-circuit resonator 9 and the second L-type terminated short-circuit resonator 10. This indicates the length of the center conductive path of the vertical segments 13 and 14 of the first L-type terminated short-circuit resonator 9 and the second L-type terminated short-circuit resonator 10. The linewidths of the first L-type terminated short-circuit resonator 9 and the second L-type terminated short-circuit resonator 10 are indicated. The spacing between the vertical segments 13 of the first linear short-circuit resonator 6 and the first L-type short-circuit resonator 9, and between the vertical segments 14 of the third linear short-circuit resonator 8 and the second L-type short-circuit resonator 10. The spacing between the vertical segments 13 of the second linear short-circuit resonator 7 and the first L-type short-circuit resonator 9, and the vertical segment 14 of the second L-type short-circuit resonator 10.

[0070] To ensure that each resonator has similar characteristic resistance, the initial settings are... = = To simplify design complexity and ensure process consistency, fine-tuning the resonator's linewidth in conjunction with the coupling spacing in actual simulations can better achieve the required coupling coefficient; initial settings = = ( + ), corresponding to 1 / 4 wavelength of the center wavelength of the bandpass filter, This indicates the length of the central conductive path at the bend in the connection section of the L-shaped terminal short-circuit resonator. Figure 5 Specifically, In actual simulations, to compensate for the differences in load effects caused by the different locations of the resonators, the length of the resonator is adjusted to achieve the required coupling coefficient.

[0071] The specific dimensional values ​​used in the simulation are shown in Table 1, with the unit being mm.

[0072] Table 1

[0073] in, and The ratio determines the strength of the cross-coupling, and the length of the coupling segment. The longer the length, the stronger the coupling. Setting the ratio of the two to be close to 1:1 ensures overall resonance while optimizing the coupling strength to obtain the ideal transmission zero point position.

[0074] Figure 6 This is a schematic diagram of the S-parameter simulation curves of the bandpass filter provided in the embodiments of this application, as shown below. Figure 6 As shown, the simulation results of the zero-enhanced filter provided in this application embodiment and the traditional all-pole filter in terms of S-parameters are compared. Figure 6The horizontal axis represents frequency (GHz), and the vertical axis represents amplitude (dB). The black dashed line (All pole filter S21) represents the transmission characteristic curve of a conventional interdigital filter without negative coupling. The blue solid line (Zero-Enhanced Filter S21) represents the transmission characteristic curve of the filter in the embodiment of this application. The red solid line (Zero-Enhanced Filter S11) represents the reflection characteristic curve of the filter in the embodiment of this application.

[0075] The filter in this embodiment has a center frequency of 24.375 GHz, a 3 dB relative bandwidth of 7.5%, and a minimum passband insertion loss of 0.95 dB. By introducing a transmission zero, the filter's suppression level rapidly decreases to 50 dB at an upper sideband offset from the passband of 1.2 GHz, representing an improvement of over 30 dB in suppression capability compared to traditional all-pole interdigital bandpass filters, and a significant improvement in upper sideband selectivity. Furthermore, the overall size of this filter is only 5 mm × 2.5 mm, achieving excellent electrical performance while fully meeting the urgent needs of carrier aggregation systems for device miniaturization and high performance.

[0076] The bandpass filter provided in this application employs a unique topology design. A straight-line terminated short-circuit resonator is designed to avoid direct proximity between two non-adjacent L-shaped terminated short-circuit resonators. This structure allows the electromagnetic field to cross the straight-line terminated short-circuit resonator, establishing a direct, non-adjacent negative coupling between the two originally non-adjacent L-shaped terminated short-circuit resonators. This non-adjacent negative coupling allows signal transmission to bypass the straight-line terminated short-circuit resonator, forming another path between the input and output, which is connected in parallel with the main path passing through the straight-line terminated short-circuit resonator. When the signals transmitted along the two paths have equal amplitude but opposite phase at the passband edges, destructive interference occurs, resulting in a transmission zero in the filter's frequency response characteristics. The generation of transmission zeros significantly improves the filter's sideband steepness and out-of-band rejection capability. To achieve the same selectivity, it requires fewer resonators than a traditional interdigital all-pole filter, effectively reducing the filter's size and achieving device miniaturization and high performance.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A bandpass filter, characterized by, The microstrip line wiring layer includes an input feed line, an output feed line, and a resonant network between the input feed line and the output feed line. The resonant network includes (2n+1) straight terminal short-circuit resonators and 2n L-shaped terminal short-circuit resonators, the (2n+1) straight terminal short-circuit resonators are arranged in parallel in sequence, the 2n L-shaped terminal short-circuit resonators are arranged in sequence between two adjacent straight terminal short-circuit resonators, and n is a positive integer. The (2k-1)th L-shaped terminal short-circuit resonator and the 2kth L-shaped terminal short-circuit resonator are axially symmetrically distributed about the 2kth straight terminal short-circuit resonator, the (2k-1)th L-shaped terminal short-circuit resonator and the 2kth L-shaped terminal short-circuit resonator have mutually opposite and spaced coupling sections, and an open end of the 2kth straight terminal short-circuit resonator is configured to terminate outside a spacing region between the coupling sections, and k is a positive integer and k≤n. A transmission path of a signal between the input feed line and the output feed line includes a first path and a second path; the first path passes through the 2kth straight terminal short-circuit resonator, and the second path does not pass through the 2kth straight terminal short-circuit resonator; and a signal transmitted by the second path is used to produce destructive interference with a signal transmitted by the first path to generate a transmission zero point.

2. The bandpass filter of claim 1, wherein, The spacing of the spacing region between the coupling sections is configured to be adjustable for controlling the frequency position of the transmission zero point.

3. The bandpass filter of claim 2, wherein, The coupling sections use open end coupling or short end coupling.

4. The bandpass filter of claim 2, wherein, The open end coupling is used to generate the transmission zero point on the low frequency side of the passband, and the short end coupling is used to generate the transmission zero point on the high frequency side of the passband. The L-shaped terminal short-circuit resonator is composed of a parallel section, a vertical section, and a bent connecting section connecting the parallel section and the vertical section, the parallel section is the coupling section, the extension direction of the parallel section is parallel to the extension direction of the input feed line and the output feed line, and the extension direction of the vertical section is perpendicular to the extension direction of the input feed line and the output feed line.

5. The bandpass filter of claim 1, wherein, The extension direction of the straight terminal short-circuit resonator is perpendicular to the extension direction of the input feed line and the output feed line. The resonant lengths of the L-shaped terminal short-circuit resonator and the straight terminal short-circuit resonator are determined based on 1 / 4 wavelength of the center frequency of the bandpass filter, and the resonant length of the L-shaped terminal short-circuit resonator is the total length of the parallel section, the bent connecting section, and the vertical section.

6. The bandpass filter of claim 5, wherein, The bent connecting section is a 45-degree cut corner structure or a circular arc bending structure.

7. The bandpass filter of claim 5, wherein, The bottom surface of the dielectric substrate is provided with a microstrip line reference ground layer, and the short-circuit ends of the (2n+1) straight terminal short-circuit resonators and the 2n L-shaped terminal short-circuit resonators are electrically connected to the microstrip line reference ground layer through metallized vias penetrating the dielectric substrate.

8. The bandpass filter of claim 1, wherein, ​ 9. The bandpass filter of claim 1, wherein, The medium substrate is an alumina ceramic substrate, which has a thermal expansion coefficient matched with an active circuit, and the microstrip line reference ground layer is configured to be assembled with an external circuit board through a conductive adhesive process.

10. The bandpass filter according to any one of claims 1 to 9, characterized in that The working frequency band of the band-pass filter is a Ka frequency band.

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