Band-pass filter structure and design method

Abstract

The invention relates to a band-pass filter structure and a design method, the band-pass filter structure comprises two SIW resonators which are distributed in a bilateral symmetry manner, adjacent surfaces of the two SIW resonators form a common wall, a second metal layer at least comprises a strip line resonator and a stepped strip line with two short-circuited ends, the two SIW resonators and the strip line resonator adopt a coplanar waveguide feed structure, and the two SIW resonators and the stepped strip line resonator are connected in parallel. The two SIW resonators are electrically coupled with the stepped strip line of which the two ends are short-circuited, and an inductive coupling window is arranged on a common wall to form magnetic coupling; the stripline resonator comprises a U-shaped half-wavelength stripline resonator with two short-circuited ends, an L-shaped quarter-wavelength stripline resonator or a combination of the U-shaped half-wavelength stripline resonator with two short-circuited ends and a full-wavelength stripline resonator. The number of transmission zero points is large and the positions are controllable through hybrid electromagnetic coupling, the order design of the filter is realized through the shape and the number of the combined strip line resonators, and the filter has the advantages of high selectivity and compact structure.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave filters, and particularly relates to a band-pass filter structure and a design method thereof. Background Art

[0002] Microwave filters are key components in the field of microwave technology. By selectively transmitting or attenuating signals of specific frequencies, they aim to optimize system performance, reduce interference, and improve signal transmission quality. Microwave filters are widely used in multiple fields, including wireless communication systems, radar systems, radio frequency front-end processing, and satellite communication, etc.

[0003] With the continuous development of wireless communication technology, it is particularly important to design band-pass filters with small size, low insertion loss (IL), and controllable transmission zeros (TZs). As an important breakthrough in modern microwave engineering, substrate integrated waveguide (SIW) technology combines the advantages of traditional waveguides and planar circuits. SIW resonators have the advantages of low loss, high quality factor (Q), easy integration, good shielding, flexible design, and low manufacturing cost, and are widely used in the design of microwave filters.

[0004] However, the size of SIW filters is relatively large, especially in the lower frequency bands where the wavelength is longer, resulting in the SIW structure being larger than the microstrip line. Using a hybrid structure for the filter is a good way to achieve miniaturization, and these structures can be realized by combining SIW cavities with other planar resonators. However, these planar resonators usually etch slot-line structures on the surface of the SIW cavity, resulting in a decrease in Q value and an increase in radiation loss. Using a stripline structure as a resonator can well avoid the increase in insertion loss because the stripline structure is integrated inside the SIW cavity. However, the controllability of the TZs of this filter is usually poor, and it is difficult to achieve higher orders.

[0005] Existing hybrid SIW filters have the following problems: (1) The loss of the filter is relatively high: To achieve the miniaturization of hybrid SIW filters, semi-open structures are usually used, and these semi-open structures will reduce the quality factor of SIW resonators, thereby increasing the insertion loss.

[0006] (2) The number of transmission zeros of the filter is small, the order is low, and the selectivity is poor: Although the hybrid SIW filter can effectively achieve miniaturization, the number of its TZs is small and the positions are difficult to control, and it is difficult to achieve higher orders.

[0007] (3) The size of the filter is relatively large: The SIW filter is larger in size than the microstrip filter, and higher-order filters usually require multiple resonators to be cascaded to achieve the required filtering characteristics, and the overall size is usually large.

[0008] (4) Poor resonator flexibility: The coupling strength between the traditional straight strip line and the SIW cavity is difficult to control, and it causes a large perturbation to the SIW resonator. Therefore, it is not suitable to be used as a resonator. Summary of the Invention

[0009] To solve the problems existing in the existing hybrid SIW filters, such as high loss of the filter, small number and low order of transmission zeros of the filter, poor selectivity, large size of the filter, and poor resonator flexibility, the present invention proposes a band-pass filter structure and a design method. Through hybrid electromagnetic coupling, the number of transmission zeros is large and the positions are controllable. The planar structure is optimized to achieve a compact structure with high selectivity and take into account miniaturization design.

[0010] To achieve the above object, the first aspect of the present invention proposes a band-pass filter structure, which includes a first metal layer, a second metal layer, and a third metal layer. A first dielectric layer is provided between the first metal layer and the second metal layer, and a second dielectric layer is provided between the second metal layer and the third metal layer. The first dielectric layer, the second dielectric layer, and the first metal layer are correspondingly provided with via arrays. The first metal layer, the third metal layer, and the via arrays form two SIW resonators, and the two SIW resonators are symmetrically distributed left and right. The adjacent surfaces of the two SIW resonators form a common wall. The second metal layer includes at least one strip line resonator and a stepped strip line short-circuited at both ends. The first metal layer is provided with a center conductor strip and two grounded conductor strips on both sides. The two SIW resonators and the strip line resonator adopt a coplanar waveguide feeding structure. The two SIW resonators and the stepped strip line short-circuited at both ends form an electrical coupling, and via arrays are also correspondingly provided at the position of the common wall. There is an inductive coupling window between the via arrays on the common wall to form a magnetic coupling; The strip line resonator includes a U-shaped half-wavelength strip line resonator short-circuited at both ends, an L-shaped quarter-wavelength strip line resonator, or a combination of a U-shaped half-wavelength strip line resonator short-circuited at both ends and a full-wavelength strip resonator.

[0011] This structure is composed of a first metal layer, a second metal layer, a third metal layer, and the first dielectric layer and the second dielectric layer sandwiched therein. Two symmetrically distributed SIW resonators are formed by the via arrays and the metal layers. The second metal layer is provided with various strip line resonators and stepped strip lines, and a hybrid electronic coupling is realized by combining the coplanar waveguide feeding structure, electrical coupling, and magnetic coupling. The design of the stepped strip line short-circuited at both ends is adopted to achieve a large number of transmission zeros with controllable positions.

[0012] Based on this structure, filters of various different orders such as third order, fourth order, and fifth order can be designed according to different requirements. For example, by adjusting the type and number of strip line resonators, the order and filtering characteristics of the filter can be changed to meet the diverse requirements of different fields such as wireless communication and radar systems.

[0013] Furthermore, feeding holes are symmetrically arranged on both sides of the first metal layer. The feeding holes are in a T shape, and a feeding line is arranged in the middle of the transverse section of the feeding holes. The feeding line and the first metal layer are of an integrated structure.

[0014] In the second aspect of the present invention, a filter design method for a band-pass filter structure is proposed, including: Step 1: Set the operating frequency, order, relative bandwidth, and the number and positions of transmission zeros of the filter; Step 2: Determine the number of SIW resonators and strip-line resonators according to the order, determine the dielectric substrate material based on the relative permittivity, loss tangent, and cost, and calculate the sizes of the SIW resonators and strip-line resonators according to the expected operating frequency of the filter; Step 3: Increase the transmission zeros of the filter by a stepped strip line short-circuited at both ends, select the order of the filter by designing the strip-line resonator, establish an equivalent topological structure and a coupling matrix, and define the electric coupling and magnetic coupling coefficients between the resonators; Step 4: Establish a simulation model of the hybrid SIW filter, optimize the simulation model to make the performance of the filter meet the requirements; Step 5: Detect the filter effect by comparing the simulation results with the response of the coupling matrix.

[0015] By setting parameters such as the operating frequency, order, relative bandwidth, and the number and positions of transmission zeros of the filter, the number and sizes of the SIW resonators and strip-line resonators are determined, and an equivalent topological structure and a coupling matrix are established. This design method brings significant benefits: on the one hand, through precise calculation and simulation optimization, it can ensure that the filter meets the performance requirements, reduce the number of design iterations, and improve the design efficiency; on the other hand, its parametric design idea enables designers to flexibly adjust the order, passband characteristics, and transmission zero distribution of the filter to meet the requirements of different application scenarios and reduce the development cost.

[0016] In the third aspect of the present invention, a third-order hybrid SIW filter based on hybrid electromagnetic coupling, a band-pass filter structure, is proposed. The strip-line resonator includes a U-shaped half-wavelength strip-line resonator short-circuited at both ends. The U-shaped half-wavelength strip-line resonator short-circuited at both ends includes a U-shaped section and a blind-hole section. The U-shaped section is in a U shape, and blind-hole sections are arranged at the two end positions of the U-shaped section. The U-shaped section and the blind-hole section are of an integrated structure; The U-shaped half-wavelength strip-line resonator short-circuited at both ends is arranged in parallel with the stepped strip line short-circuited at both ends, and the midpoints of the U-shaped half-wavelength strip-line resonator short-circuited at both ends and the stepped strip line short-circuited at both ends are both located on the common wall; Two SIW resonators and a U-shaped half-wavelength strip line resonator shorted at both ends adopt a coplanar waveguide feeding structure. The two SIW resonators are electrically coupled with a stepped strip line shorted at both ends, and the two SIW resonators and a capacitive coupling window form a magnetic coupling to generate transmission zeros near the two passbands.

[0017] The hybrid electromagnetic coupling method enables the controllable position of the transmission zeros, can effectively suppress the interference signals on both sides of the passband, improves the passband selectivity, and has a stronger stopband suppression ability compared with the traditional third-order filter. The structure is compact, and the third-order filtering function is completed in a limited space, and the volume is significantly reduced compared with the traditional SIW third-order filter. The combination of the U-shaped half-wavelength strip line resonator and the SIW resonator does not occupy extra space, realizes miniaturized design, and is suitable for portable devices with strict volume requirements. The fourth aspect of the present invention proposes a fourth-order hybrid SIW filter based on hybrid electromagnetic coupling, which adopts a band-pass filter structure. The strip line resonator includes two L-shaped quarter-wavelength strip line resonators. The L-shaped quarter-wavelength strip line resonator includes a horizontally placed L-shaped section and a blind hole section. The vertical section of the horizontally placed L-shaped section faces upward, and the blind hole section is arranged on the side of the vertical section away from the horizontal section. The horizontally placed L-shaped section and the blind hole section are an integrated structure. The two L-shaped quarter-wavelength strip line resonators are symmetric along the common wall, and the L-shaped quarter-wavelength strip line resonator is parallel to the stepped strip line shorted at both ends; Two SIW resonators are respectively inserted into an L-shaped quarter-wavelength strip line resonator, and both the SIW resonator and the L-shaped quarter-wavelength strip line resonator adopt a coplanar waveguide feeding structure; The two SIW resonators, the two L-shaped quarter-wavelength strip line resonators and the stepped strip line shorted at both ends form a main coupling path and three cross-coupling paths to generate three transmission zeros.

[0018] The fourth-order hybrid SIW filter has more transmission zeros and cross-coupling paths, further enhances the selectivity of the filter, makes the passband edge steeper, can better separate the target frequency band from the interference frequency band, and meets the communication scenarios with high requirements for signal purity. Compared with the traditional cascaded fourth-order filter, the structure is more compact, reduces the loss in the signal transmission process, and improves the overall electromagnetic compatibility at the same time. The unique design of the L-shaped quarter-wavelength strip line resonator realizes the fourth-order filtering function while maintaining the miniaturization of the structure; and by adjusting the size and position of the strip line, the coupling strength and the position of the transmission zeros can be flexibly controlled to adapt to different design requirements.

[0019] The fifth aspect of the present invention proposes a fifth-order hybrid SIW filter based on hybrid electromagnetic coupling, which adopts a band-pass filter structure. The stripline resonator includes a combination of a U-shaped half-wavelength stripline resonator short-circuited at both ends and two full-wavelength stripline resonators. The U-shaped half-wavelength stripline resonator short-circuited at both ends includes a U-shaped section and a blind-hole section. The U-shaped section is in a U shape, and blind-hole sections are arranged at the two end positions of the U-shaped section. The U-shaped section and the blind-hole section are an integrated structure; The U-shaped half-wavelength stripline resonator short-circuited at both ends, the stepped stripline short-circuited at both ends, and the two full-wavelength stripline resonators are arranged in parallel. One of the full-wavelength stripline resonators is arranged above the U-shaped half-wavelength stripline resonator short-circuited at both ends, and the other full-wavelength stripline resonator is arranged below the stepped stripline short-circuited at both ends; Two SIW resonators, two full-wavelength stripline resonators, and the U-shaped half-wavelength stripline resonator short-circuited at both ends adopt a coplanar waveguide feeding structure. The two SIW resonators, the two full-wavelength stripline resonators, the U-shaped half-wavelength stripline resonator short-circuited at both ends, and the stepped stripline short-circuited at both ends form three main coupling paths and three cross-coupling paths, generating five transmission zeros.

[0020] The fifth-order hybrid SIW filter has five transmission zeros, enabling the filter to have excellent passband selectivity and stopband rejection ability. It can accurately screen out target signals in a complex electromagnetic environment, effectively suppress out-of-band interference, and meet the application scenarios with extremely high filtering performance requirements such as high-end radars and satellite communications. The fifth-order box topology is realized in a planar structure, and the structure is highly integrated. Compared with the traditional fifth-order SIW filter, the volume is greatly reduced, providing the possibility for the miniaturization and high-density integration of equipment. The combination of various stripline resonators enables designers to finely adjust the coupling matrix and the distribution of transmission zeros according to actual needs, quickly optimize the filter performance in different frequency bands and application scenarios, and shorten the product R & D cycle.

[0021] Through the above technical solutions, the beneficial effects of the present invention are as follows: (1) The hybrid SIW filters of the present invention all use a hybrid electromagnetic coupling structure (a stepped stripline short-circuited at both ends), enabling the filter to have multiple transmission zeros with controllable positions, and making the filter have high selectivity. By selecting the structure and shape of the stripline resonator, the order of the filter can be flexibly designed, making the filter have good structural compactness.

[0022] (2) The present invention uses a stripline structure as the resonator, without etching slot lines and other structures on the filter surface, avoiding radiation loss, improving the quality factor, and increasing the shielding ability for nearby circuits.

[0023] (3) The hybrid SIW filter of the present invention uses a U-shaped strip line as a resonator, and the coupling strength is easy to control, which is suitable for various wireless communication systems.

[0024] (4) The present invention is realized by integrating multiple strip line resonators into the left and right SIW resonators. The multiple strip line resonators do not occupy extra space, and the volume is reduced by 60% compared with the traditional SIW filter, significantly improving the miniaturization level. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of a band-pass filter of the present invention.

[0026] Figure 2 It is a schematic structural diagram of a third-order hybrid SIW filter based on hybrid electromagnetic coupling of the present invention; Figure 3 It is an equivalent topology diagram of a third-order hybrid SIW filter based on hybrid electromagnetic coupling of the present invention; Figure 4 It is a simulation and synthesis response curve diagram of a third-order hybrid SIW filter based on hybrid electromagnetic coupling of the present invention; Figure 5 It is a schematic structural diagram of a fourth-order hybrid SIW filter based on hybrid electromagnetic coupling of the present invention; Figure 6 It is an equivalent topology diagram of a fourth-order hybrid SIW filter based on hybrid electromagnetic coupling of the present invention; Figure 7 It is a simulation and synthesis response curve diagram of a fourth-order hybrid SIW filter based on hybrid electromagnetic coupling of the present invention; Figure 8 It is a schematic structural diagram of a fifth-order hybrid SIW filter based on hybrid electromagnetic coupling of the present invention; Figure 9 It is an equivalent topology diagram of a fifth-order hybrid SIW filter based on hybrid electromagnetic coupling of the present invention; Figure 10 It is a simulation and synthesis response curve diagram of a fifth-order hybrid SIW filter based on hybrid electromagnetic coupling of the present invention; Figure 11 It is a schematic structural diagram of a strip line resonator and a stepped strip line short-circuited at both ends of a band-pass filter structure of the present invention.

[0027] Attached reference numerals: first metal layer 1, second metal layer 2, third metal layer 3, first dielectric layer 4, second dielectric layer 5, via array 6, common wall 7, stripline resonator 8, U-shaped half-wavelength stripline resonator 801 shorted at both ends, L-shaped quarter-wavelength stripline resonator 802, full-wavelength stripline resonator 803, stepped stripline 9 shorted at both ends, feed hole 10, feeder 11. Detailed implementation

[0028] Embodiment 1 As Figure 1 and 11 shown, a band-pass filter structure includes a first metal layer 1, a second metal layer 2 and a third metal layer 3. A first dielectric layer 4 is provided between the first metal layer 1 and the second metal layer 2, and a second dielectric layer 5 is provided between the second metal layer 2 and the third metal layer 3. Via arrays 6 are correspondingly formed in the first dielectric layer 4, the second dielectric layer 5 and the first metal layer 1. The first metal layer 1, the third metal layer 3 and the via array 6 form two SIW resonators, and the two SIW resonators are symmetrically distributed left and right. The adjacent surfaces of the two SIW resonators form a common wall 7. The second metal layer 2 includes at least one stripline resonator 8 and a stepped stripline 9 shorted at both ends. The first metal layer 1 is provided with a center conductor strip and two side ground conductor strips. The two SIW resonators and the stripline resonator 8 adopt a coplanar waveguide feeding structure. The two SIW resonators and the stepped stripline 9 shorted at both ends form an electrical coupling. Via arrays 6 are also correspondingly provided at the position of the common wall 7, and an inductive coupling window is left between the via arrays 6 on the common wall 7 to form a magnetic coupling; The stripline resonator 8 includes a U-shaped half-wavelength stripline resonator 801 shorted at both ends, an L-shaped quarter-wavelength stripline resonator 802, or a combination of a U-shaped half-wavelength stripline resonator 801 shorted at both ends and a full-wavelength stripline resonator 803.

[0029] Feeding holes 10 are symmetrically arranged on both sides of the first metal layer 1. The feeding holes 10 are in a T shape, and a feeder 11 is arranged in the middle of the transverse section of the feeding holes 10. The feeder 11 and the first metal layer 1 are an integrated structure.

[0030] Embodiment 2 A filter design method for a band-pass filter structure includes: Step 1: Set the operating frequency, order, relative bandwidth, number and position of transmission zeros of the filter; Step 2: Determine the number of SIW resonators and stripline resonators 8 according to the order, determine the dielectric substrate material based on the relative dielectric constant, loss tangent and cost, and calculate the sizes of the SIW resonators and stripline resonators 8 according to the expected operating frequency of the filter; Step 3: Establish an equivalent topological structure and a coupling matrix, and define the electrical and magnetic coupling coefficients between resonators; Step 4: Establish a simulation model of the hybrid SIW filter, and optimize the simulation model to meet the requirements of the filter performance; Step 5: Detect the filter effect by comparing the simulation results with the response of the coupling matrix.

[0031] Embodiment 3 As Figures 2 - 4 shown, a third-order hybrid SIW filter based on hybrid electromagnetic coupling is made by adopting the band-pass filter structure of Embodiment 1 and the filter design method of the band-pass filter structure of Embodiment 2.

[0032] The strip-line resonator 8 includes a U-shaped half-wavelength strip-line resonator 801 shorted at both ends. The U-shaped half-wavelength strip-line resonator 801 shorted at both ends includes a U-shaped section and a blind-hole section. The U-shaped section is in a U shape, and blind-hole sections are arranged at the two end positions of the U-shaped section. The U-shaped section and the blind-hole section are an integrated structure; The U-shaped half-wavelength strip-line resonator 801 shorted at both ends is arranged in parallel with the stepped strip-line 9 shorted at both ends, and the midpoints of the U-shaped half-wavelength strip-line resonator 801 shorted at both ends and the stepped strip-line 9 shorted at both ends are both located on the common wall 7; Two SIW resonators and the U-shaped half-wavelength strip-line resonator 801 shorted at both ends adopt a coplanar waveguide feeding structure. The two SIW resonators and the stepped strip-line 9 shorted at both ends form an electrical coupling, and the two SIW resonators and the inductive coupling window form a magnetic coupling, generating transmission zeros near the two passbands.

[0033] In this embodiment, the first metal layer 1, the second metal layer 2, and the third metal layer 3 are all made of copper, and the copper-clad thicknesses are 0.035 mm, 0.07 mm, and 0.035 mm respectively. The first dielectric layer 4 and the second dielectric layer 5 both adopt Taconic TLY-5, with a thickness of 0.508 mm, a relative dielectric constant of 2.2, and a loss tangent of 0.0008.

[0034] As Figure 3 shown, the equivalent topological structure of the third-order hybrid SIW filter with hybrid electromagnetic coupling, where nodes 1 and 3 respectively represent the TE 101 mode of the two SIW resonators, node 2 represents the fundamental mode of the U-shaped half-wavelength strip-line resonator 801 shorted at both ends, and node N is a non-resonant node, representing the fundamental mode of the stepped strip-line 9 shorted at both ends, and its operating frequency is far from the center frequency of the filter.

[0035] Compared with traditional straight strip-line resonators, the U-shaped half-wavelength strip-line resonator 801 with shorted ends exhibits significant advantages. Its more compact structure is achieved through a bent structure design, enabling flexible integration into various resonator systems. This filter has the advantages of miniaturization, high selectivity, controllable transmission zeros, and self-closure.

[0036] Embodiment 4 Such as Figures 5 - 7 A fourth-order hybrid SIW filter based on hybrid electromagnetic coupling, which adopts the band-pass filter structure of Embodiment 1 and is fabricated using the filter design method of the band-pass filter structure of Embodiment 2.

[0037] The strip-line resonator 8 includes two L-shaped quarter-wavelength strip-line resonators 802. The L-shaped quarter-wavelength strip-line resonator 802 includes a horizontally placed L-shaped segment and a blind-hole segment. The vertical segment of the horizontally placed L-shaped segment faces upward, and the blind-hole segment is arranged on the side of the vertical segment away from the horizontal segment. The horizontally placed L-shaped segment and the blind-hole segment are an integrated structure. The two L-shaped quarter-wavelength strip-line resonators 802 are symmetric about the common wall 7, and the L-shaped quarter-wavelength strip-line resonator 802 is parallel to the step-shaped strip-line 9 with shorted ends; Two SIW resonators are respectively inserted into an L-shaped quarter-wavelength strip-line resonator 802, and both the SIW resonator and the L-shaped quarter-wavelength strip-line resonator 802 adopt a coplanar waveguide feeding structure; The two SIW resonators, the two L-shaped quarter-wavelength strip-line resonators 802, and the step-shaped strip-line 9 with shorted ends form a main coupling path and three cross-coupling paths, generating three transmission zeros.

[0038] In this embodiment, the first metal layer 1, the second metal layer 2, and the third metal layer 3 are all made of copper, and the copper plating thicknesses are 0.035 mm, 0.07 mm, and 0.035 mm respectively. The first dielectric layer 4 and the second dielectric layer 5 both adopt Taconic TLY-5, with a thickness of 0.508 mm, a relative dielectric constant of 2.2, and a loss tangent of 0.0008.

[0039] Such as Figure 6 The equivalent topological structure of the fourth-order hybrid SIW filter based on hybrid electromagnetic coupling is shown, where nodes 1 and 4 respectively represent the TE 101 modes of the two SIW resonators, nodes 2 and 3 respectively represent the fundamental modes of the left and right L-shaped quarter-wavelength strip-line resonators 802, and node N represents the fundamental mode of the step-shaped strip-line 9 with shorted ends.

[0040] The filter 2 has one main coupling path and three cross-coupling paths, where 1-2-3-4 is the main coupling path, two cross-coupling paths are 1-4 and 1-N-4 respectively, and the other cross-coupling path is generated by magnetic coupling between nodes 2 and 4.

[0041] The fourth-order hybrid SIW filter with hybrid electromagnetic coupling can generate a total of three transmission zeros. Compared with the third-order hybrid SIW filter based on hybrid electromagnetic coupling, it increases the filter order and improves selectivity, while not increasing the size and maintaining the advantages of miniaturization and self-closure.

[0042] Embodiment 5 As Figures 8 - 10 A fifth-order hybrid SIW filter based on hybrid electromagnetic coupling is made by adopting the band-pass filter structure of Embodiment 1 and the filter design method of the band-pass filter structure of Embodiment 2.

[0043] The strip-line resonator 8 includes a combination of a U-shaped half-wavelength strip-line resonator 801 shorted at both ends and two full-wavelength strip resonators 803. The U-shaped half-wavelength strip-line resonator 801 shorted at both ends includes a U-shaped section and a blind-hole section. The U-shaped section is in a U shape, and blind-hole sections are arranged at the two end positions of the U-shaped section. The U-shaped section and the blind-hole section are an integrated structure; The U-shaped half-wavelength strip-line resonator 801 shorted at both ends, the stepped strip-line 9 shorted at both ends and the two full-wavelength strip resonators 803 are arranged in parallel. One of the full-wavelength strip resonators 803 is arranged above the U-shaped half-wavelength strip-line resonator 801 shorted at both ends, and the other full-wavelength strip resonator 803 is arranged below the stepped strip-line 9 shorted at both ends; The two SIW resonators, the two full-wavelength strip resonators 803 and the U-shaped half-wavelength strip-line resonator 801 shorted at both ends adopt a coplanar waveguide feeding structure. The two SIW resonators, the two full-wavelength strip resonators 803, the U-shaped half-wavelength strip-line resonator 801 shorted at both ends and the stepped strip-line 9 shorted at both ends form three main coupling paths and three cross-coupling paths, generating five transmission zeros.

[0044] As Figure 9 The equivalent topological structure of the fifth-order hybrid SIW filter based on hybrid electromagnetic coupling as shown has three main coupling paths: 1-2-5, 1-3-5 and 1-4-5. Among them, 1-3-5 is the coupling path introduced by the U-shaped half-wavelength strip-line resonator 801 shorted at both ends, and 1-2-5 and 1-4-5 are two negative coupling paths introduced by the upper and lower full-wavelength strip resonators 803 respectively. These two negative coupling paths can generate two transmission zeros near the passband.

[0045] The fifth-order hybrid SIW filter based on hybrid electromagnetic coupling has multiple cross-coupling paths. One of the cross-coupling paths is generated by the fundamental mode of the stepped strip line 9 short-circuited at both ends and is represented by the non-resonant node (N), which can generate a lower stopband transmission zero. The other two coupling paths are generated by the hybrid electromagnetic coupling in 1-5. 1-5 can be divided into two coupling paths. One is the magnetic coupling path generated by the coupling window, and the other is the electric coupling path generated by the first higher-order mode of the stepped strip line 9 short-circuited at both ends. This hybrid electromagnetic coupling can generate 1 transmission zero. Additionally, considering the second higher-order mode of the U-shaped half-wavelength strip line resonator 801 short-circuited at both ends, this mode can also act as a non-resonant node to generate an upper stopband transmission zero far from the passband.

[0046] In summary, the fifth-order hybrid SIW filter based on hybrid electromagnetic coupling can generate a total of five transmission zeros. Compared with the third-order hybrid SIW filter and the fourth-order hybrid SIW filter based on hybrid electromagnetic coupling, it increases the filter order and the number of transmission zeros, improves the selectivity, and at the same time maintains the advantages of miniaturization, self-closure, and controllable transmission zeros.

[0047] The above embodiments are only the preferred embodiments of the present invention and do not limit the scope of implementation of the present invention. Therefore, any equivalent changes or modifications made according to the structure, characteristics, and principles of the scope of the present invention patent should be included in the scope of the patent application of the present invention.

Claims

1. A band-pass filter structure includes a first metal layer (1), a second metal layer (2), and a third metal layer (3). A first dielectric layer (4) is provided between the first metal layer (1) and the second metal layer (2), and a second dielectric layer (5) is provided between the second metal layer (2) and the third metal layer (3). Through-hole arrays (6) are correspondingly formed in the first dielectric layer (4), the second dielectric layer (5), and the first metal layer (1). The first metal layer (1), the third metal layer (3), and the through-hole arrays (6) form two SIW resonators, and the two SIW resonators are symmetrically distributed left and right. The adjacent surfaces of the two SIW resonators form a common wall (7), and it is characterized in that, The second metal layer (2) includes at least one strip line resonator (8) and a stepped strip line (9) short-circuited at both ends. The first metal layer (1) is provided with a center conductor strip and ground conductor strips on both sides. The two SIW resonators and the strip line resonator (8) adopt a coplanar waveguide feeding structure. The two SIW resonators and the stepped strip line (9) short-circuited at both ends form an electrical coupling. At the position of the common wall (7), a via array (6) is also correspondingly provided. There is an inductive coupling window between the via arrays (6) on the common wall (7) to form a magnetic coupling; The strip line resonator (8) includes a U-shaped half-wavelength strip line resonator (801) short-circuited at both ends, an L-shaped quarter-wavelength strip line resonator (802), or a combination of a U-shaped half-wavelength strip line resonator (801) short-circuited at both ends and a full-wavelength strip resonator (803).

2. A band-pass filter structure according to claim 1, characterized in that, Feeding holes (10) are symmetrically arranged on both sides of the first metal layer (1). The feeding holes (10) are in a T shape. A feeder line (11) is arranged in the middle of the transverse section of the feeding holes (10). The feeder line (11) and the first metal layer (1) are of an integrated structure.

3. A filter design method for a band-pass filter structure based on claim 1, characterized in that, Comprising: Step 1: Set the operating frequency, order, relative bandwidth, and the number and positions of transmission zeros of the filter; Step 2: Determine the number of SIW resonators and strip line resonators (8) according to the order. Determine the dielectric substrate material based on the relative permittivity, loss tangent, and cost. Calculate the sizes of the SIW resonators and strip line resonators (8) according to the expected operating frequency of the filter; Step 3: Increase the transmission zeros of the filter through the stepped strip line (9) short-circuited at both ends. Select the strip line resonator (8) to design the order of the filter, establish an equivalent topological structure and a coupling matrix, and define the electrical coupling and magnetic coupling coefficients between the resonators; Step 4: Establish a simulation model of the hybrid SIW filter, optimize the simulation model to make the performance of the filter meet the requirements; Step 5: Detect the filter effect by comparing the simulation results with the response of the coupling matrix.

4. A third-order hybrid SIW filter based on hybrid electromagnetic coupling, characterized in that, Adopting the band-pass filter structure of claim 1, the strip line resonator (8) includes a U-shaped half-wavelength strip line resonator (801) short-circuited at both ends. The U-shaped half-wavelength strip line resonator (801) short-circuited at both ends includes a U-shaped section and a blind hole section. The U-shaped section is in a ∪ shape. Blind hole sections are arranged at the two end positions of the U-shaped section. The U-shaped section and the blind hole section are of an integrated structure; The U-shaped half-wavelength strip line resonator (801) short-circuited at both ends is arranged in parallel with the stepped strip line (9) short-circuited at both ends, and the midpoints of the U-shaped half-wavelength strip line resonator (801) short-circuited at both ends and the stepped strip line (9) short-circuited at both ends are both located on the common wall (7); The two SIW resonators and the U-shaped half-wavelength strip line resonator (801) short-circuited at both ends adopt a coplanar waveguide feeding structure. The two SIW resonators and the stepped strip line (9) short-circuited at both ends form an electrical coupling. The two SIW resonators and the inductive coupling window form a magnetic coupling to generate transmission zeros near the two passbands.

5. A fourth-order hybrid SIW filter based on hybrid electromagnetic coupling, characterized in that, Adopt the band-pass filter structure of claim 1. The stripline resonator (8) includes two L-shaped quarter-wavelength stripline resonators (802). The L-shaped quarter-wavelength stripline resonator (802) includes a horizontally placed L-shaped section and a blind-hole section. The vertical section of the horizontally placed L-shaped section faces upward, and the blind-hole section is arranged on the side of the vertical section away from the horizontal section. The horizontally placed L-shaped section and the blind-hole section are of an integrated structure. The two L-shaped quarter-wavelength stripline resonators (802) are symmetric along the common wall (7). The L-shaped quarter-wavelength stripline resonator (802) is parallel to the stepped stripline (9) short-circuited at both ends. Two SIW resonators are respectively inserted into an L-shaped quarter-wavelength stripline resonator (802). Both the SIW resonator and the L-shaped quarter-wavelength stripline resonator (802) adopt a coplanar waveguide feeding structure. The two SIW resonators, the two L-shaped quarter-wavelength stripline resonators (802), and the stepped stripline (9) short-circuited at both ends form a main coupling path and three cross-coupling paths, generating three transmission zeros.

6. A fifth-order hybrid SIW filter based on hybrid electromagnetic coupling, characterized in that, Adopt the band-pass filter structure of claim 1. The stripline resonator (8) includes a combination of a U-shaped half-wavelength stripline resonator (801) short-circuited at both ends and two full-wavelength stripline resonators (803). The U-shaped half-wavelength stripline resonator (801) short-circuited at both ends includes a U-shaped section and a blind-hole section. The U-shaped section is in a U shape, and blind-hole sections are arranged at the two end positions of the U-shaped section. The U-shaped section and the blind-hole section are of an integrated structure. The U-shaped half-wavelength stripline resonator (801) short-circuited at both ends, the stepped stripline (9) short-circuited at both ends, and the two full-wavelength stripline resonators (803) are arranged in parallel. One of the full-wavelength stripline resonators (803) is arranged above the U-shaped half-wavelength stripline resonator (801) short-circuited at both ends, and the other full-wavelength stripline resonator (803) is arranged below the stepped stripline (9) short-circuited at both ends. The two SIW resonators, the two full-wavelength stripline resonators (803), and the U-shaped half-wavelength stripline resonator (801) short-circuited at both ends adopt a coplanar waveguide feeding structure. The two SIW resonators, the two full-wavelength stripline resonators (803), the U-shaped half-wavelength stripline resonator (801) short-circuited at both ends, and the stepped stripline (9) short-circuited at both ends form three main coupling paths and three cross-coupling paths, generating five transmission zeros.

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