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Communications Engineering volume 3, Article number: 111 (2024 ) Cite this article Oil And Filter
Electrical cables, as the industry’s blood vessels and nervous system, require evolving distributed filtering for complex electromagnetic environment adaptability. This article introduces a filter cable design featuring an insulated cylinder coated with a defected conductor transmission structure (DCTS). The DCTS, with a well-designed etched pattern, functions as a boundary condition for transmitting specific frequency electromagnetic waves, similar to a lumped filter circuit. To validate this method, a low-pass filter cable is proposed with six-slot-ring defected structures, utilizing polytetrafluoroethylene as the inner dielectric, encased within a flexible printed circuit board (FPCB)-manufactured DCTS. The proposed cable, with precise dimensions (2.4 mm diameter, 340 mm length), demonstrates minimal insertion loss ( < 0.38 dB below 6 GHz) in the passband and rejection exceeding 23 dB at 7.7-25 GHz in the stopband. Further enhancements achieve attenuation exceeding 50 dB in the stopband (7.1 GHz to 20 GHz). Compared to traditional cables, this filter cable addresses electromagnetic compatibility (EMC) by cutting off the interference coupling path.
Electrical cables1, as current-carrying conductors, act as the coupling path of undesirable electromagnetic interference (EMI)2, which can potentially impact the proper operation of electronic devices. According to the basic framework of any electromagnetic compatibility (EMC) design3, electrical cables not only conduct EMI, leading to symptoms of conducted emissions (CE) and conducted susceptibility (CS)4,5, but also radiate electromagnetic energy6, causing issues with radiated emissions (RE) and radiated susceptibility (RS)7,8. Moreover, with the rapid advancements in technology, including the smart grid, next-generation communication technologies9, the Internet of Things (IoT)10, unmanned systems, and artificial intelligence, the development and application of critical infrastructure and advanced intelligent equipment and systems have become pivotal factors in achieving reliable and secure operations. In this regard, ensuring reliability in a complex electromagnetic environment is a critical consideration for the effective functioning of various intelligent equipment systems11. Electrical cables, known as the blood vessels and nervous system of the industry, require the evolution of distributed filtering capabilities depicted in Fig. 1 to address the intricate requirements of electromagnetic environment adaptability.
CE conducted emissions, CS conducted susceptibility, RE radiated emissions, RS radiated susceptibility.
The evolutionary trajectory of filter cables12 begins with conventional microstrip filters13,14 and defected ground structure (DGS) filters15, transitions to planar filtering transmission lines16, further evolves into filtering cables that utilize a defected conductor layer (DCL)17,18, and transforms into filter cables with defected conductor transmission structures (DCTSs)19 to address the issue of radiation caused by DCL. Over the past two decades, a large number of etched patterns on DGS filters have been studied to achieve different functions. These include the equilateral U- shaped DGS low-pass filter20, differential bandpass filters with dumbbell-shaped DGS21, bandstop filters using dumbbell DGS and spiral DGS integrated with U-slots22, tunable bandstop filters with an embedded metamaterial-based DGS23, tunable phase shifter with liquid crystal and DGSs24, and an absorptive common-mode filter with three dumbbell-shaped apertures of meandering ribbons25. Generally, the traditional DGS filters are manufacture by rigid substrates with epoxy or ceramics. A commonly employed approach involves the utilization of a flexible printed circuit board (FPCB) to design and fabricate a flexible transmission filter, which serves as a transitional form from a DGS filter to a filter cable. This FPCB incorporates 10 asymmetric Pi-shaped DGSs16. Moreover, the filtering capability can be achieved by enclosing the wire with a DCL featuring dumbbell-shaped defected structures and surface-mounted capacitors26, as well as by employing a DCL with asymmetric spiral-shaped defected structures17. However, due to the slots on the DCL-based filtering cable, there are deficiencies in terms of electromagnetic radiation27. Therefore, an alternative implementation of a filter cable with distributed filtering functionality is required.
This article presents a filter cable design method with a defected conductor transmission structure (DCTS). The DCTS with specific etched pattern serves as a boundary condition for selectively transmitting electromagnetic waves in frequency band as a filter circuit. By examining the equivalent circuit, preliminary transmission characteristics of each defected resonance unit can be derived. Subsequently, the transmission characteristics of the longitudinally varying, serially connected six-slot-ring structure filter cable can be enhanced and fine-tuned using advanced full-wave simulation software. The feasibility of implementing the filter cable based on the defected conductor transmission structure (DCTS) can be substantiated by conducting a comparative analysis between physical prototypes and simulation results, thereby validating the credibility and efficacy of the design. This paper delves into the effects of parameter variations in the six-slot-ring structure on its performance, as well as investigates the impact of cable bending on its performance.
Figure 2 shows various structures and parameters of the proposed filter cable with 40 six-slit-ring defected structures. As depicted in Fig. 2a, the composition of the filter cable, from outermost to innermost layers, encompasses a shielding layer, a transmission dielectric, the defected conductor transmission structure (DCTS), and an inner cylinder dielectric.
a The arrangement of the characteristic filter cable, illustrating the sequence of layers from the outermost to the innermost: shielding layer, transmission dielectric, DCTS, and inner cylinder dielectric. b 3D representation of the DCTS in the proposed filter cable, illustrating 40 cascaded six-slot-ring structures. c DCTS with 40 cascaded structures consisting of six-slot-ring. d Parameter diagram depicting two individual six-slot-ring structures within the DCTS.
Similar to coaxial cables, the filter cable’s outermost layer boasts a complete shielding layer, imparting exceptional electromagnetic shielding capabilities. This design effectively thwarts any interference from external electromagnetic waves, thus safeguarding the integrity of the filter cable. The transmission dielectric within the cable, akin to the transmission medium found in coaxial cables, acts as a conduit for electromagnetic and magnetic fields. Commonly composed of polytetrafluoroethylene (PTFE) or other low-loss insulating materials, this dielectric ensures the efficient transmission of signals.
As illustrated in Fig. 2b, the DCTS of the filter cable consists of a conductor layer that envelopes the dielectric inner cylinder and incorporates deliberate defected structures. Current flows through this layer, leveraging the presence of these defects to create the desired filtering circuitry effect. The inner cylinder dielectric is a cylindrical object composed of flexible insulating material, serving as a substrate for the DCTS. However, the electromagnetic field within it is negligible compared to that of the transmission dielectric.
Regarding the specific case of the low-pass filter cable discussed in this paper, Fig. 2b showcases a 3D representation of the DCTS. It consists of 40 sequentially arranged six-slot-ring defected structures, encircling the inner cylinder dielectric. All the six-slot-ring defected structures share a similar configuration. These modified rings are systematically arranged in a uniform pattern, following a proposed technique that maintains a consistent width for the six-slot-ring structure while progressively elongating it from the inner to the outer regions, all while upholding symmetry around the central point.
Figure 2c illustrates the configuration of the expanded DCTS, consisting of 40 six-slot-ring defected structures. Each of these structures can be considered as a fundamental resonant unit. As the DCTS needs to encircle the inner cylinder dielectric of the cable, the width of the six-slot-ring structure should be less than the circumference of the inner cylinder dielectric. Nonetheless, it is possible to substantially extend their length, although it would still be slightly shorter than that of the filter cable.
Figure 2d presents an enlarged view of two adjacent six-slot-ring defected structures, with geometric parameters labeled for reference. It can be observed that their configuration is rectangular, exhibiting a symmetrical structure.
As shown in Fig. 3, the DCTS-based filter cable can be considered as an approximation of a non-uniform waveguide model featuring intricate boundary conditions. Fields within the transmission dielectric of the filter cable can be derived using potential functions, which satisfy the Laplace equation. In cylindrical coordinates, it can be expressed as:
The schematic diagram of a non-uniform waveguide structure with intricate boundary conditions.
It is apparent that, similar to coaxial cables, the shielding layer of the filter cable also possesses a continuous conductor on its outer surface, resulting in zero electrical potential.
On the boundary of a defected conductor transmission structure, it is evident that the tangential component of the electric field is zero. Due to its incomplete nature and the presence of defects, any DCTS structure can be described by the following equation:
where f is a Boolean function associated with the coordinate position, then the boundary conditions of DCTS satisfy the following:
which shows that the ABCD matrix of the cascade connection of the two networks is equal to the product of the ABCD matrices representing the individual two ports.
By incorporating the port characteristics at both ends of the filter cable, it is theoretically possible to analytically solve the field distribution within the transmission dielectric and achieve the transmission characteristics of the filter cable. However, due to the complexity of the DCTS, a more practical approach is to analyze its equivalent circuit properties and conduct research using full-wave simulation methods.
Due to the highly intricate DCTS, it is impractical to solve it using analytical methods. Instead, equivalent circuit analysis and full-wave simulation can be used for the design of the filter cable.
By employing quasi-static analysis, it becomes possible to derive an equivalent circuit topology model for each resonant unit within the DCTS-based filter cable. The proposed low-pass filter cable incorporates a DCTS composed of 40 cascaded six-slot-ring defected structures, wherein each unit showcases comparable filtering characteristics. As a result, it is feasible to initially examine the equivalent structures, wherein each unit showcases comparable
filtering characteristics. As a result, it is feasible to initially examine the equivalent circuit acquired from a single six-slot-ring defected structure unit, relying on its current distribution diagram, and subsequently extrapolate the filtering characteristics of the entire cable by cascading these units.
Since the DCTS is a thin and flexible layer that wraps around the inner cylinder dielectric, comprehending the characteristics of current distribution intuitively becomes challenging due to the curved nature of the DCTS. To address this, the current distribution diagram of the six-slot-ring can be analyzed within a planar filter, yielding the equivalent circuit of this structure. Figure 4a showcases the current distribution on the ground, illustrating the transmission of current from port 1 to port 2 in the presence of the six-slot-ring defected structure. The current distribution displays noticeable discontinuities at the four right angles and six slots of the defected structure. These discontinuities serve as the basis for extracting the discontinuous structures of the six-slot-ring structure into equivalent circuits. Upon analysis, the current distribution indicates that the microstrip discontinuitiespredominantly used in this case are gaps, right-angle bends, and T-junctions28.
a Current distribution in a single six-slot-ring defected structure. b Equivalent circuit representation of the gap. c Equivalent circuit representation of the right-angle bend. d Equivalent circuit representation of the T-junction. e The equivalent circuit diagram of a single resonant unit of the proposed filter cable. (This data has been published in ref. 19)
Figure 4b presents the equivalent circuit of the gap, which is a pai-network. The shunt capacitance C1 is attributed to the irregularities in the electric field distribution along the strip’s edge. The series capacitance C12 emerges from the interaction between the strip conductors that establish the gap. Evidently, as the gap spacing increases and approaches infinity, C12 is expected to decrease. In the case of infinite spacing, C12 should approach zero, while C1 should be equivalent to the end capacitance for an open-ended line. Figure 4c demonstrates the equivalent circuit of the right-angle bend, which includes a shunt capacitance Cb and a series inductance ΔLb. Figure 4d showcases the representation of the T-junction through its equivalent circuit. This circuit encompasses series inductances ΔL1 in the main line and ΔL2 in the stub arm, as well as the junction capacitance CT28.
By conducting an analysis of the current distribution and obtaining the equivalent model for the discontinuous structure, the equivalent circuit of the six-slot-ring resonant unit has been derived, as depicted in Fig. 4e. Upon traversing the inductor L1, the current originating from the microstrip line bifurcates into two paths. One segment flows downward through L26, returning to point A. Simultaneously, another segment flows upward through L27, also returning to point A. Subsequently, the combined current proceeds towards point B via L28. At point B, another division occurs, with one portion flowing through L29 and returning to L55, while the remaining portion proceeds through L32 and also returns to L55. This delineates the current distribution and the directions of flow within this equivalent circuit diagram.
This section examines the impact of structural parameters on the S-parameters of two six-slot-ring DCTSs. The primary focus of this study lies in the S21 curve, with particular attention directed toward observing the changes in resonance frequencies and stopband characteristics resulting from adjustments to various structural parameters. The objective of this analysis is to facilitate the optimization of six-slot-ring DCTS. The parameters associated with the six-slot-ring DCTS encompass the following: the length LU of the ring, the width WU of the ring, the width G1 of the central slit of the six-slot-ring structure, the width G2 of the slit on both sides of the six-slot-ring structure, the distance L1 between the inner side of the ring and the nearest slit edge, the distance S1 between the inner and outer sides of the ring, the distance M between the units and the number N of the six-slot-ring resonator. Moreover, the arrangement of the defected structures in this investigation follows a gradually symmetrical pattern, wherein the gradual symmetry pertains to the progressive alignment of the lengths of the six-slot-ring structures.
To investigate the effect of different lengths LU of the six-slot-ring resonators on the resonant frequency of the proposed low-pass filter cable, various values of LU (LU = 3, 4, and 5 mm) were utilized while keeping other parameters remained constant in the simulation. As shown in Fig. 5a, with the increasing of LU, the center frequency of the stopband and the −3 dB cutoff frequency decreases. The stopband range below −10dB narrows and the maximum attenuation within the stopband decreases. However, this variation is not notable, as even though LU changes, the size of the gap remains constant, which does not affect the coupling effect between the gaps, thus having minimal impact on the overall current distribution. Therefore, the length parameter LU of the six-slot-ring defected structure has little influence on the cutoff frequency and characteristics of the stopband.
a For different values of LU. b For different values of WU. c For different values of G1. d For different values of G2. e For different values of L1. f For different values of S1. g For different values of M. h For different values of N.
In order to study the influence of different widths of the six-slot-ring resonator on the resonance frequency of the proposed low-pass filter cable, various values of WU (WU = 3, 4, and 5 mm) were utilized while keeping other parameters constant in the simulation. The simulation result is presented in Fig. 5b. As WU increases, the cutoff frequency gradually decreases with noticeable variation, and the overall attenuation increases. Clearly, the width parameter WU of the six-slot-ring defected structure plays a crucial role in adjusting the overall resonance frequency. An empirical formula can be derived as follows:
where F0 represents the cutoff frequency, WU denotes the width of the six-slot-ring resonator.
The impact of the width G1 of the central slit in a six-slot-ring resonator on the resonant frequency of the low-pass filter cable is studied. By maintaining other parameters constant, simulations were performed with different values of G1 (0.41, 0.61, and 0.81 mm), and the results are presented in Fig. 5c. As the gap width G1 of the six-slot-ring resonator increases, the lengths of the rectangles on both sides of the G1 decrease, resulting in a gradual shift of the cutoff frequency towards lower frequency bands. Hence, the gap width G1 along the inner opening centerline of the six-slot-ring resonator exerts an influence on the resonant frequency of the proposed filter cable, albeit with a relatively minor impact.
The investigation focuses on the impact of the width G2 of the slits on both sides of the six-slot-ring resonator on the resonant frequency of the low-pass filter cable. Several values of G2 (G2 = 0.21, 0.41, and 0.61 mm) were used in the simulation while keeping other parameters constant. The simulation results are shown in Fig. 5d. Increasing the width of G2 within the six-slot-ring resonator causes the lengths of the rectangles on both sides of the G1 to decrease starting from the part near G2, resulting in a gradual shift of the cutoff frequency towards higher frequencies. Therefore, the width G2 of the slit in the six-slot-ring resonator has an impact on the resonant frequency of the designed filter cable, but the effect is relatively small. In conclusion, for the three gaps in the six-slot-ring resonator defected structure, by changing the sizes of G1 and G2, the distribution of current on the etched defected conductor transmission structure is affected, causing changes in the resonant frequency. However, due to the limited range of conditions, the dimensions changed by G1 and G2 are small, resulting in a relatively minor change in the resonant frequency.
The distance between the inner side of the ring and the nearest slit edge of the six-slot-ring structure affects the length of the small rectangle and the position of the G2 in the ring. Simulation experiments were carried out to study the influence of the distance length by changing the value of L1 (L1 = 0.2, 0.7 and 1.2 mm), while keeping other parameters constant, as shown in Fig. 5 e). As L1 increases, the resonant frequency of the low-pass filter cable that was designed moves towards lower frequency range, resulting in a wider stopband. When the value of L1 increases, the distance between G1 and G2 decreases, causing a change in the position of slot G2. When L1 increases to a certain extent, the slots G1 and G2 merge into one, resulting in only two remaining slots in the six-slot-ring defected structure. This alteration changes the distribution structure of the six-slot-ring structure, affecting the current distribution. An empirical formula can be derived as follows:
where F0 represents the cutoff frequency, L1 denotes the distance between the inner side of the ring and the nearest slit edge.
The parameter S1 is the distance between the inner and outer sides of the ring. In order to further investigate its impact on the resonant frequency, the value of S1 was changed (S1 = 0.41, 0.61, and 0.81 mm) while keeping other parameters constant for simulation. The simulation results, as shown in Fig. 5f, indicate that as S1 increases, the resonant frequency of the designed low-pass filter cable changes very little and remains essentially constant. However, the bandwidth and attenuation of the stopband have changed. From circuit analysis, it can be observed that the distance between the inner and outer sides of the ring affects the coupling degree of the circuit, but does not change the magnitude of the resonant frequency. Therefore, the parameter S1 in the six-slot-ring resonator structure is not a key influencing factor.
In order to investigate the effect of the distance between two groups of defected structures on the cutoff frequency of the proposed filter cable, we took the distance between the six-slot-ring resonators of the first and second groups as an example. We varied the value of M (M = 0.6, 0.9, and 1.2 mm) while keeping other parameters constant and obtained the simulation results shown in Fig. 5g. As M increases, the resonance frequency fluctuates around 22 GHz with a small degree of variation. This variation is primarily due to the change in M, which alters the coupling effect between the two resonators. The influence of the N variation on transmission characteristics. The aforementioned
parameter analysis is based on a single six-slot-ring resonator unit. We are interested in studying the effects of cascading multiple six-slot-ring resonator units on the proposed low-pass filter cable. Therefore, we vary the number of cascaded resonator units, denoted as N (N = 10, 16, 20, and 40). As the number of cascaded units increases, the length of the added six-slot-ring structure also increases in turn while ensuring that the lengths of the two symmetrically arranged six-slot-ring structures with respect to the center point remain equal, maintaining a symmetrical gradient arrangement. The remaining parameters are kept constant. The simulation results obtained are shown in Fig. 5h. As the number of cascaded units increases, the cutoff frequency shifts towards a lower frequency range. When N reaches 40, the cutoff frequency decreases to 6 GHz, and the attenuation within the passband is <0.38 dB. A wide stopband ranging from 7.7 to 25 GHz, with a bandwidth of 17.3 GHz, is achieved, and the transition band becomes steeper. An empirical formula can be derived as follows:
where F0 represents the cutoff frequency, N represents the number of cascaded resonant units.
As depicted in Fig. 6, the fabricated low-pass filter cable is presented with the following specifications: inner center dielectric diameter ϕin = 1.905 mm, transmission dielectric PTFE diameter ϕd = 5.626 mm, εr = 1.24, loss tan δ = 0.001, G1 = 0.81 mm, G2 = 0.21 mm, L = 340 mm, W = 5.98 mm, WU = 5 mm, L1 = 1 mm, M = 0.6 mm, S1 = 0.3 mm, LU1 = LU40 = 12 mm, LU2 = LU39 = 11.5 mm, LU3 = LU38 = 11 mm, …, LU19 = LU22 = 3 mm, LU20 = LU21 = 2.5 mm. Figure 6a illustrates the inner cylinder dielectric, which is constructed from PTFE. In Fig. 6b, the DCTS can be crafted using traditional FPCB technology. In this instance, the DCTS incorporates 40 defected six-slot-ring structures, affixed to a substrate comprised of a 10-micron-thick copper PI film, coated with gold to prevent oxidation. It can be observed that the width W of the DCTS is 0.8 mm longer than the circumference of the inner center dielectric. This is because it wraps around the inner center dielectric, overlapping by 0.8 mm to achieve a good electrical connection at the contact surface. As illustrated in Fig. 6c, the bottom side of the DCTS features 0.4 mm wide conductor edges with periodic vias, enabling improved contact when wrapped around the inner dielectric. Figure 6d illustrates the DCTS wrapped around the inner cylinder dielectric. In Fig. 6e, the transmission dielectric is composed of PTFE and is wrapped around the DCTS. Finally, Fig. 6f showcases the completed filter cable with 40 defected six-slot-ring structures. Following the wrapping of the transmission dielectric with an aluminum foil silver-plated shielding layer, a second layer of shielding is crafted by interweaving a copper-nickel-plated metal braid. N-type connectors are commonly employed at both ends.
a Inner cylinder dielectric. b Top view of the defected conductor transmission structure (DCTS) featuring 40 defected six-slot-ring structures. c Bottom view of the DCTS featuring 40 defected six-slot-ring structures. d DCTS is wrapped around the inner cylinder dielectric. e Transmission dielectric. f The completed filter cable with 40 defected six-slot-ring structures.
The measured and simulated S-parameters are shown in Fig. 7a. In the passband range below 6 GHz, it demonstrates an insertion loss of less than 0.38 dB, while offering a rejection of over 23 dB in the stopband range spanning from 7.7 to 25 GHz. Obviously, the measured results match well with the simulation results, and the small errors are mainly caused by the unavoidable accuracy errors in the production of the physical cable and the constant errors that occurred during testing.
a S-parameters of the proposed low-pass filter cable with 40 six-slot-ring defected structures on the defected conductor transmission structure (DCTS) without turning (This data has been published in Reference 19). b S-parameters of the proposed low-pass filter cable with 40 six-slot-ring defected structures on the DCTS with a turning radius of 0.5 m. c Group delay of the proposed low-pass filter cable with 40 six-slot-ring defected structures on the DCTS (This data has been published in Reference 19). d S-parameters of the low-pass filter cable with 3 groups for 40 cascaded six-slot-ring defected structure units.
The measured S-parameters for the proposed filter cable with a straight configuration and a tuning radius of 0.5 m are depicted in Fig. 7b. Regarding the tuning of the proposed cable, the S-parameters are relatively consistent, with the transition band shifting by only 0.2 GHz towards the lower frequency range.
In Fig. 7c, we present the group delay of the suggested filter cable, which is proposed with 40 cascaded six-slot-ring structures, as both simulated and measured. The group delay within the passband of the filter cable is maintained at less than 3 ns, and the simulation and measurement of the group delay exhibit a high level of agreement.
To further optimize the performance of the suggested low-pass filter cable, which incorporates 40 six-slot-ring structures, a design enhancement is introduced to achieve higher stopband suppression. By cascading three identical filter cable units, each consisting of 40 six-slot-ring structures, a total of 120 six-slot-ring units are obtained within the cable. These three groups of 40 six-slot-ring filter cables are connected using N-type double-male
adapters while ensuring that the inter-group spacing is substantially larger than the spacing between two six-slot-ring structures within each group. Simulation and measurement S-parameters are presented in Fig. 7d. It can be observed that the resulting filter cable, composed of the cascaded arrangement of three groups of 40 six-slot-ring structures, exhibits a passband below 6.6 GHz, achieving attenuation greater than 50 dB within 7.1 GHz to 20 GHz in the stopband. Additionally, the transition band demonstrates a sharp profile.
The cable model used in this article is the FSJ1-50A Andrew coaxial cable, with the outer conductor material being corrugated copper and the inner conductor material being copper-clad aluminum wire. In contrast, the inner conductor and transmission dielectric layer of the proposed filter cable are both made of PTFE, resulting in a lighter weight. At the same time, the attenuation of the FSJ1-50A cable will increase with the frequency, from 0.407 dB at 0.5 MHz to 52.747 dB at 6 GHz, causing the transmission loss to increase and reducing the efficiency of signal transmission. The proposed filter cable can achieve an insertion loss of less than 0.38 dB within the passband range, thus improving the efficiency of signal transmission.
The supplementary video illustrates the surface current distribution on the defected conductor transmission structure (DCTS) with 10 six-slot rings, which has a cut-off frequency of 13 GHz. The current distribution on the DCTS at 10 GHz within the passband demonstrates a periodic current distribution on the DCTS, allowing it to pass through with minimal attenuation. The surface distribution on the DCTS at 15.8 GHz within the stopband reveals that the surface current undergoes exponential decay along the transmission direction, and little microwave energy can penetrate it in the stopband.
Table 1 provides a comparison of key performance parameters between the referenced filters and filter cables in this study with the proposed low-pass filter cable. The low-pass filtering cable utilizing an asymmetric PI-shaped structure achieved a cutoff frequency of 2.2 GHz using PI film material with dimensions of 100 mm×2.6 mm×0.254 mm16. A dual-frequency bandpass filtering cable based on an asymmetric spiral structure achieved an insertion loss over 35 dB from 0.86 to 0.96 GHz in the first band and an insertion loss over 15 dB from 1.25 to 1.43 GHz in the second band, with a length of 200 mm and a diameter of 1.66 mm17. A low-pass filtering cable with ring-structured resonators achieves over 50 dB attenuation19. A passband filtering cable utilizes a DCL with a length of 1500 mm and a diameter of 8 mm, using PTFE as transmission medium29. A low-pass filtering cable with a length of 100 mm and a diameter of 0.84 mm achieved a wide stopband ranging from 3.9 GHz to 10 GHz30. A tunable band-stop filter cable for wide-bandwidth interference suppression was realized by cascading with 21 resonator units31. A translucent flexible low-pass filter with the size of 150 mm × 7.8 mm × 0.148 mm was achieved based on an asymmetric Pi-shaped structure32. A differential signal wideband common-mode suppression filtering cable based on a DGS with a single-unit size of 20 mm × 5 mm × 1 mm was realized33.
This paper introduces a low-pass filter cable incorporating 40 six-slot-ring structures on defected conductor transmission structure (DCTS). The filter cable’s design encompasses an inner cylinder dielectric, the six-slot-ring DCTS, a transmission dielectric, and a shielding layer, arranged in a layered configuration. The DCTS consists of 40 symmetrically arranged six-slot-ring structures, gradually distributed. By manipulating the parameters of these 40 structures, it is possible to adjust the S-parameters of the cable accordingly. The proposed filter cable boasts a length of 340 mm and a diameter of 2.4 mm. Experimental results reveal an impressive insertion loss of under 0.38 dB below 6 GHz in the passband, along with a stopband spanning from 7.7 to 25 GHz, showcasing an impressive rejection capability of exceeding 23 dB. In comparison to conventional cables, this filter cable offers improved versatility, compactness, and exceptional filtering capabilities.
By using DCTS to substitute a portion of the coaxial cable’s inner conductor, it becomes possible to design a filter cable with distributed filtering capability. The DCTS, crafted by FPCB, offers several advantages such as lightweight construction, low water absorption, and cost-effectiveness. A low-pass filter cable with 40 gradually symmetrically arranged six-slot-ring defected structures on the DCTS enables the attainment of adjustable low-pass filtering characteristics.
To facilitate the design and simulation of both the proposed filter cable and its individual resonator units, we employ the High-Frequency Structural Simulation software (HFSS)34 and Advanced Design System 2020. Firstly, a filter cable with DCTS was designed using HFSS 2018, and multiple six-slot-ring structures with gradient symmetry were etched on the DCTS. Through analysis of the S-parameters, the geometric parameters of the six-slot-ring structure were modified to identify the key parameters that cause changes in the performance of the filter cable. Then, the equivalent circuit of a single hexagonal slot-ring structure was obtained through simulation using ADS 2020. To measure the S-parameters and radiation of the filter cables, we utilize the Keysight network analyzer (PNA N55524B), which has been accurately calibrated by the N4691 calibration system, within an anechoic chamber.
The Video in this study has been deposited in the video database. The video is the surface current distribution on the DCTS and the shielding layer within the passband and the stopband. All data generated or analyzed during this study are included in this published article and its supplementary files. The datasets used and analyzed during the current study available from the corresponding author on reasonable request.
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We acknowledge financial support from National Natural Science Foundation of China under Grant 62271033 and the Beijing Natural Science Foundation under Grant 8202036.
Department of the College of Information Science and Technology, Beijing University of Chemical Technology, Beijing, China
Han Yunan, Cuilian Jiang, Shuangqing Xiong & Zhaohan Liu
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All authors conceived the experiments, Y.H. and C.J. designed and realized the filter cable; All authors carried out the measurements; Y.H. and C.J. worked on the theoretical modeling and data analysis; Y.H. and C.J. co-wrote the paper. All authors discussed the results and commented on the manuscript.
Correspondence to Han Yunan or Zhaohan Liu.
The authors declare no competing interests.
Communications Engineering thanks the anonymous reviewers for their contribution to the peer review of this work. Primary Handling Editors: Anastasiia Vasylchenkova. A peer review file is available.
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Yunan, H., Jiang, C., Xiong, S. et al. Filter cable design with defected conductor transmission structures. Commun Eng 3, 111 (2024). https://doi.org/10.1038/s44172-024-00262-9
DOI: https://doi.org/10.1038/s44172-024-00262-9
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