3D printing five-order band-pass filter based on thin plate cross coupling structure

Abstract

The invention provides a 3D printing five-order band-pass filter based on a thin plate cross-coupled structure, relates to the technical field of band-pass filters, is applied to an S-band communication system, and comprises a five-order resonator and two cross-coupled thin plate structures, the five-order resonators are sequentially arranged along a main transmission path of the filter, adopt a rectangular waveguide cavity structure and work in a TE101 fundamental mode, and the adjacent resonators realize interstage coupling through inductive diaphragms; according to the cross coupling thin plate structure, the height of a third resonant cavity is reduced, a thin plate is stacked above and below the third resonant cavity respectively, the thin plates are connected with a second-order resonator and a fourth-order resonator to form two sets of independent non-adjacent resonator cross coupling channels, and each thin plate is provided with a pair of irises to control the coupling strength. The filter has the technical advantages of high selectivity, low loss, strong out-of-band rejection, low processing cost and high precision.

Description

Technical Field

[0001] This invention relates to the technical field of bandpass filters, and more particularly to a 3D-printed fifth-order bandpass filter based on a thin-plate cross-coupling structure. Background Technology

[0002] In radio frequency microwave systems such as radio astronomy and deep space exploration, the S-band (2–4 GHz) has become a core application frequency band in fields such as ground communication, shipborne radar, and spacecraft telemetry and control due to its advantages of long signal transmission distance and moderate penetration capability. With the rapid development of wireless communication technology, spectrum resources are becoming increasingly scarce, and systems are placing more stringent requirements on the selectivity, out-of-band suppression capability, and low-loss characteristics of filters. It is necessary not only to accurately screen S-band target signals, but also to efficiently suppress out-of-band clutter interference (such as leakage from adjacent frequency bands and harmonic components), while reducing insertion loss to ensure system energy efficiency.

[0003] With the increasing application of S-band (2-4 GHz) technology in fields such as radio astronomy and deep space exploration, higher demands are being placed on filter performance. The loss of microstrip circuits increases with power, leading to a series of problems. Therefore, the low-loss characteristics of cavities become more advantageous. Currently, traditional S-band bandpass filters mostly employ all-pole topologies or simple cascaded structures. While these offer advantages such as simple structure and ease of manufacturing, they also have significant limitations: Firstly, the lack of effective cross-coupling mechanisms makes it difficult to introduce transmission zeros, resulting in insufficient out-of-band suppression and inability to meet the anti-interference requirements in high-density spectrum environments. Secondly, some high-performance solutions achieve cross-coupling through complex folded structures, which improves selectivity but suffers from large size, high fabrication difficulty, and poor loss control, making it difficult to adapt to the trend of miniaturized and integrated systems. Furthermore, existing cross-coupling-based filter designs often rely on metal pillars, probes, or ring structures for coupling, resulting in insufficient flexibility in coupling strength adjustment and high risk of parasitic resonance, further limiting the performance optimization space of the filters.

[0004] In conclusion, developing an S-band bandpass filter with innovative structure, high selectivity, low loss, and strong out-of-band suppression characteristics is a key direction for overcoming existing technological bottlenecks and meeting the application needs of modern radio frequency systems. Summary of the Invention

[0005] To address the stringent performance requirements of S-band communication systems for filters, particularly regarding high selectivity, low loss, and strong out-of-band suppression, this invention provides a 3D-printed fifth-order bandpass filter based on a thin-plate cross-coupling structure. This filter comprises a fifth-order resonator and two thin plates, with cross-coupling achieved through the plates, resulting in two transmission zeros, high selectivity, low loss, and strong out-of-band suppression. This invention aims to introduce an innovative design method into the field of S-band filters, improving performance and overcoming the limitations of existing technologies.

[0006] The technical means employed in this invention are as follows: A 3D-printed fifth-order bandpass filter based on a thin-plate cross-coupled structure is applied to an S-band communication system, comprising: a fifth-order resonator and two cross-coupled thin-plate structures; The fifth-order resonators are arranged sequentially along the main transmission path of the filter, employing a rectangular waveguide cavity structure and operating at TE. 101 The fundamental mode, adjacent resonators achieve interstage coupling through inductive diaphragms; the cross-coupling thin plate structure is as follows: the height of the third resonant cavity is reduced, and a thin plate is stacked above and below the third resonant cavity. The thin plate connects the second-order and fourth-order resonators, forming two sets of independent non-adjacent resonator cross-coupling channels. Each thin plate is provided with a pair of irises to control the coupling strength.

[0007] Furthermore, the S-band frequency range is 2-4 GHz, the center frequency of the filter is fixed at 3.35 GHz, and the passband width is 0.5 GHz.

[0008] Furthermore, the thin plate is an ultra-thin structure with a thickness of 1 mm, and the coupling gap between the thin plate and the resonator cavity is 1 mm.

[0009] Furthermore, by adjusting the electric field coupling strength between the thin plate and the resonator, a transmission zero is generated on the upper and lower sides of the passband of the two sets of cross-coupled channels, forming a double transmission zero filtering response.

[0010] Furthermore, when the center frequency of the filter is lower than the frequency of the thin plate, the cross coupling is inductive coupling, and the transmission zero is located on the right side of the passband; when the center frequency of the filter is higher than the frequency of the thin plate, the cross coupling is capacitive coupling, and the transmission zero is located on the left side of the passband.

[0011] Furthermore, the coupling windows between the first-order resonator and the second-order resonator, and between the fourth-order resonator and the fifth-order resonator, are all set on the adjacent cavity walls.

[0012] Compared with the prior art, the present invention has the following advantages: The filter of this invention combines the technical advantages of high selectivity, low loss, strong out-of-band suppression, low processing cost, and high precision. By adjusting the electric field coupling strength between the thin plate and the resonator, two transmission zeros are generated on both sides of the S-band passband. Combined with changing the position of the coupling window in the middle of the resonator, the steepness of the passband edge reaches below -70dB, effectively distinguishing the passband and stopband signals, and significantly attenuating out-of-band interference signals. It solves the problems of passband transition bandwidth and poor interference suppression in the prior art, and significantly improves frequency selectivity and out-of-band suppression capability. Meanwhile, the resonator has been optimized in coupling design to reduce additional losses, achieving an insertion loss of less than -0.5dB in the S-band passband, overcoming the high loss defect of traditional microstrip bandpass filters. In addition, the complex structure is processed by 3D printing, which is simpler and cheaper than traditional machining, and the resulting device has higher precision. The overall solution has a reasonable structural design, combining practicality and economy, and has good prospects for industrial application. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a three-dimensional structural diagram of a fifth-order bandpass filter based on a thin-plate cross-coupling structure provided in an embodiment of the present invention, where a1=72.14mm, b1=34.04mm, c1=49.2mm, a2=54.1mm, c2=48.8mm, a3=65.3mm, c3=51.1mm, a4=71.7mm, c4=50.5mm, a5=67.5mm, c5=5 0.7mm, a6=53mm, c6=49.1mm, l1=43.8mm, l2=36.7mm, l3=27.3mm, l4=29.4mm, l5=43.4mm , l6=47.8mm, l7=36mm, l8=57mm, a7=27mm, a8=62.5mm, b2=30.04mm, b3=1.0mm, h=1.0mm; Figure 2 The side view of a fifth-order bandpass filter based on a thin-plate cross-coupled structure provided in an embodiment of the present invention is shown, wherein b1=34.04mm, b2=30.04mm, b3=1.0mm, c1=49.2mm, c2=48.8mm, c4=50.5mm, c6=49.1mm, and h=1.0mm. Figure 3The S11 and S21 parameter curves of a fifth-order bandpass filter based on a thin-plate cross-coupled structure are shown. Figure 4 A detailed plot of the insertion loss S21 parameter curve for a fifth-order bandpass filter based on a thin-plate cross-coupled structure; Figure 5 This is a schematic diagram of the standing wave of a fifth-order bandpass filter based on a thin-plate cross-coupling structure. Detailed Implementation

[0015] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0016] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0017] like Figure 1 As shown, this invention provides a 3D-printed fifth-order bandpass filter based on a thin-plate cross-coupled structure, applied to an S-band communication system. The filter includes a fifth-order resonator and two cross-coupled thin-plate structures. The fifth-order resonator is arranged sequentially along the main transmission path of the filter, employing a rectangular waveguide cavity structure and operating at TE. 101 The fundamental mode, adjacent resonators achieve interstage coupling through inductive diaphragms; the cross-coupling thin plate structure is as follows: the height of the third resonant cavity is reduced, and a thin plate is stacked above and below the third resonant cavity. The thin plate connects the second-order and fourth-order resonators, forming two sets of independent non-adjacent resonator cross-coupling channels. Each thin plate is provided with a pair of irises to control the coupling strength.

[0018] Typically, when the transmission zero is located on the left side of the passband, cross-coupling should be negative. However, negative coupling structures complicate manufacturing. In this case, cross-coupling is achieved through a resonator. When the filter's center frequency is lower than the plate's frequency, the cross-coupling is inductive (positive coupling). Therefore, the transmission zero is located on the right side of the passband. Conversely, when the filter's center frequency is higher than the plate's frequency, the cross-coupling is capacitive (negative coupling), allowing the transmission zero to be placed on the left side of the passband without the need for a negative coupling structure. By adjusting the electric field coupling strength between the plate and the resonator, two sets of cross-coupled channels generate a transmission zero on the upper and lower sides of the passband, respectively, ultimately forming a filter response with two transmission zeros.

[0019] To further improve the out-of-band rejection capability of the filter, the coupling windows between the first-order and second-order resonators, and between the fourth-order and fifth-order resonators, are no longer located on the opposite cavity walls of the resonators, but rather on adjacent cavity walls. Resonance at TE 101 At that time, the magnetic field distribution around the cavity wall is basically uniform, and the new window position will not affect the fundamental mode TE. 101 Mode coupling, however for higher-order modes TE 102 In this mode, the new window position is located at the lowest point of its magnetic field component, and the new window position will not be able to effectively couple the higher-order mode TE. 102 This pattern effectively improves out-of-band inhibition capability.

[0020] This invention utilizes 3D printing technology to precisely fabricate a thin-plate cross-coupling structure. The core cross-coupling plate of the filter needs to be designed as an ultra-thin structure (only 1 mm thick), and the coupling gap between the plate and the resonator cavity is only 1 mm. The precision requirements for such a fine structure and tiny gap are difficult to achieve with traditional CNC milling. Traditional milling cutters typically have a minimum diameter greater than 1 mm, making it impossible to process ultra-thin plates and extremely fine gaps, and easily leading to structural deformation, edge burrs, and other problems, directly affecting the cross-coupling accuracy and filtering performance. 3D printing, however, can achieve micron-level machining tolerances (±0.02 mm), precisely forming the regular structure of ultra-thin plates while ensuring the uniformity and dimensional accuracy of the coupling gap. This perfectly solves the limitations of traditional machining technologies in manufacturing fine structures. Furthermore, the one-piece molding process avoids errors caused by assembling multiple parts, providing a core technological guarantee for the stable generation of dual transmission zeros and the realization of high selectivity and low loss performance of the filter.

[0021] The cascaded structure of the fifth-order resonator ensures low-loss characteristics within the passband. The synergistic effect of the two transmission zeros generated by the two partitions and the main passband significantly improves the filter's selectivity. Simultaneously, changing the position of the coupling window in the middle of the resonator enhances the out-of-passband suppression capability. Then, 3D printing is employed to manufacture the filter, providing core technological assurance for the stable generation of the dual transmission zeros and the realization of high selectivity and low-loss performance. Compared to traditional metal pillar and ring coupling structures, the cross-coupled thin-plate structure of this invention offers advantages such as flexible coupling strength adjustment, low parasitic resonance risk, and compact structure. Furthermore, the overall filter does not require complex folding design, balancing ease of fabrication and integration requirements. It is suitable for S-band communication, radar, satellite reception, and other RF microwave systems with stringent filtering performance requirements.

[0022] Figure 1 This is a three-dimensional structural diagram of a fifth-order bandpass filter based on a thin-plate cross-coupling structure provided in an embodiment of the present invention. The structure consists of a fifth-order filter and two partitions. Among them, a1=72.14mm, b1=34.04mm, c1=49.2mm, a2=54.1mm, c2=48.8mm, a3=65.3mm, c3=51.1mm, a4=71.7mm, c4=50.5mm, a5=67.5mm, c5=50.7mm, a6=53mm, c6=49 .1mm, l1=43.8mm, l2=36.7mm, l3=27.3mm, l4=29.4mm, l5=43.4mm, l6=47.8mm, l7=36mm, l8=57mm, a7=27mm, a8=62.5mm, b2=30.04mm, b3=1.0mm, h=1.0mm.

[0023] Waveguide basic parameters: Based on the standard rectangular waveguide dimensions of the S-band, the input and output ports of the fifth-order filter use the WR-284 waveguide, with a wide side a=72.14mm and a narrow side b=34.04mm.

[0024] Resonator: Five resonators are coupled together to generate five poles. By adjusting the coupling strength, the passband width can be controlled to achieve the desired target of 0.5 GHz and a center frequency of 3.35 GHz. The dimensions of the resonator are determined according to the following formula: ; in, This indicates the operating frequency of the design specifications. Represents the speed of light. These represent pattern ordinal numbers; they are non-negative integers and not all zero at the same time. and These represent the width and length of the resonator, respectively.

[0025] The coupling strength between the five resonators is adjusted according to the corresponding coupling coefficients in the coupling matrix. Adjacent resonators are cascaded according to preset coupling coefficients (4 sets of couplings) to ensure uniform transmission of in-band signals and attenuation of out-of-band signals through the superposition of multiple resonators, achieving high out-of-band rejection. The coupling matrix of this filter is as follows: ; From the coupling matrix, we can obtain M12=M21=0.99, M23=M32=0.83, M34=M43=0.6, M45=M54=0.6, M53=M35=-0.02, M56=M65=0.83, and M67=M76=0.99. Here, M12 and M21, M67 and M76 are the coupling coefficients between the input port, output port, and adjacent resonators, respectively. M53 and M35 are the cross-coupling coefficients between the second and fourth resonators. The others are the coupling coefficients between adjacent resonators.

[0026] Thin plates: Their length and width are closely related to the resonant frequency. Two thin plates generate two transmission zeros on both sides of the passband, making the passband edge steepness below -70dB, effectively distinguishing the passband and stopband signals and improving frequency selectivity. The thickness of the thin plates is b3=1.0mm, the length is c3=51.1mm, and the widths are a7=27mm and a8=62.5mm, respectively. The two thin plates establish an additional coupling path with the non-adjacent main resonant cavity through diaphragms. The lengths of the two diaphragms are l7=36mm and l8=57mm, and the width is h=1.0mm, respectively.

[0027] Figure 2 The side view of a fifth-order bandpass filter based on a thin-plate cross-coupling structure provided in an embodiment of the present invention is shown below, where b1 = 34.04 mm, b2 = 30.04 mm, b3 = 1.0 mm, c1 = 49.2 mm, c2 = 48.8 mm, c4 = 50.5 mm, c6 = 49.1 mm, and h = 1.0 mm. Figure 3 The S11 and S21 parameter curves of a fifth-order bandpass filter based on a thin-plate cross-coupled structure are shown. The bandwidth is 0.5 GHz and the center frequency is 3.35 GHz. Five resonators generate five poles within the bandwidth. The S11 parameter in the passband is less than -18 dB. The two thin plates generate two zeros outside the broadband, making the passband edge steepness reach below -70 dB, effectively distinguishing the passband and stopband signals and improving frequency selectivity.

[0028] Figure 4 The figure shows a detailed curve of the insertion loss S21 parameter of a fifth-order bandpass filter based on a thin-plate cross-coupling structure. The results show that the loss is less than -0.1 dB in the passband, which meets the core requirements of "high selectivity and anti-interference" for S-band bandpass filters.

[0029] Figure 5 This is a schematic diagram of the standing wave ratio (VSWR) of a fifth-order bandpass filter based on a thin-plate cross-coupling structure. The VSWR describes the impedance matching degree of the device, and the formula is: ; Ideal match ( )hour, According to the characteristics of a fifth-order bandpass filter, the reflection coefficient in the passband exhibits "equirippled" fluctuations (rather than the perfectly flat surface of an ideal filter). Therefore, the VSWR will also be "equirippled" and close to 1 (good matching). In the stopband, the reflection coefficient increases sharply, and the VSWR should rise significantly, but it usually increases smoothly or is accompanied by regular fluctuations. As can be seen from the figure, the VSWR is close to 1 in the passband, indicating that the impedance matching is good and the reflection is minimal in these frequency bands, which meets the design goal of "low reflection in the passband" for bandpass filters.

[0030] In summary, a 3D-printed bandpass filter based on a thin-plate cross-coupling structure is provided. This filter consists of a 5th-order resonator and two thin plates, and cross-coupling is achieved through the thin plates, thereby achieving several significant features such as two transmission zeros, high selectivity, low loss, and strong out-of-band suppression.

[0031] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments. In the above embodiments of the present invention, the descriptions of each embodiment have their own emphasis; parts not described in detail in a certain embodiment can be referred to in the relevant descriptions of other embodiments. It should be understood that the disclosed technical content in the several embodiments provided in this application can be implemented in other ways.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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 or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A 3D-printed fifth-order bandpass filter based on a thin-plate cross-coupling structure, characterized in that, Applied to S-band communication systems, it includes: a fifth-order resonator and two cross-coupled thin-plate structures; The fifth-order resonators are arranged sequentially along the main transmission path of the filter, employing a rectangular waveguide cavity structure and operating at TE. 101 The fundamental mode, adjacent resonators achieve interstage coupling through inductive diaphragms; the cross-coupling thin plate structure is as follows: the height of the third resonant cavity is reduced, and a thin plate is stacked above and below the third resonant cavity. The thin plate connects the second-order and fourth-order resonators, forming two sets of independent non-adjacent resonator cross-coupling channels. Each thin plate is provided with a pair of irises to control the coupling strength.

2. The 3D-printed fifth-order bandpass filter based on a thin-plate cross-coupling structure according to claim 1, characterized in that, The S-band frequency range is 2-4 GHz, the center frequency of the filter is fixed at 3.35 GHz, and the passband width is 0.5 GHz.

3. A 3D-printed fifth-order bandpass filter based on a thin-plate cross-coupling structure according to claim 1, characterized in that, The thin plate is an ultra-thin structure with a thickness of 1 mm, and the coupling gap between the thin plate and the resonator cavity is 1 mm.

4. A 3D-printed fifth-order bandpass filter based on a thin-plate cross-coupling structure according to claim 1, characterized in that, By adjusting the electric field coupling strength between the thin plate and the resonator, a transmission zero is generated on the upper and lower sides of the passband of the two sets of cross-coupled channels, forming a double transmission zero filtering response.

5. A 3D-printed fifth-order bandpass filter based on a thin-plate cross-coupling structure according to claim 4, characterized in that, When the center frequency of the filter is lower than the frequency of the thin plate, the cross coupling is inductive coupling, and the transmission zero is located on the right side of the passband; when the center frequency of the filter is higher than the frequency of the thin plate, the cross coupling is capacitive coupling, and the transmission zero is located on the left side of the passband.

6. A 3D-printed fifth-order bandpass filter based on a thin-plate cross-coupling structure according to claim 1, characterized in that, The coupling windows between the first-order resonator and the second-order resonator, and between the fourth-order resonator and the fifth-order resonator, are all set on the adjacent cavity walls.

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