A filter cable

Abstract

This application belongs to the field of coaxial cable technology and relates to a filter cable, comprising: a coaxial cable including, from the inside out: an inner conductor, a dielectric layer, and an outer conductor; the outer conductor has a groove, the groove including: a first part and two second parts, both the first part and the second parts being strip-shaped structures, the two ends of the first part being connected to the two second parts respectively, so that the groove forms an axisymmetric "H" shape; the first part is arranged along the circumference of the outer conductor, the second parts are arranged parallel to the axial direction of the outer conductor, and the first part connects to the non-midpoint of the second part; the first part is provided with a picofarad capacitor. This application enables the coaxial cable to be compatible with filtering functions and has multiple filtering frequency points within the operating frequency band, realizing wideband band-stop filtering.

Description

Technical Field

[0001] This application relates to the field of coaxial cable technology, and in particular to a filter cable. Background Technology

[0002] Coaxial cable is one of the most commonly used transmission media in radio frequency, microwave and broadband electromagnetic signal transmission systems. It is widely used in communication systems, radar systems, measurement and control systems, electromagnetic compatibility testing, antenna feed networks and interconnection scenarios of various electronic devices.

[0003] Traditional coaxial cables are primarily used for low-loss signal transmission, and their structure typically consists of an inner conductor, a dielectric layer, an outer conductor, and an outer sheath. These cables generally lack frequency selectivity; when a system needs to suppress specific interference frequencies, unwanted frequency bands, or sensitive frequency bands, a band-stop filter, notch filter, or other frequency selector device must be added in series in the transmission link. However, external filter solutions have several drawbacks. First, additional components increase system size, weight, and connection complexity, hindering lightweight, integrated, and miniaturized designs. Second, connectors and transition structures introduce additional insertion loss, impedance mismatch, and parasitic effects, impacting the overall transmission performance of the link. Third, traditional filters are often independent devices, their structure separate from the coaxial cable itself, making them unsuitable for applications with limited space, complex wiring, or requiring distributed filtering along the cable.

[0004] In existing technologies, to integrate cable and filtering functions, periodic structures, slotted structures, or defective conductor structures can be introduced into the outer conductor of the coaxial cable, giving the cable body specific frequency selectivity characteristics. This type of method integrates filtering functionality into the transmission line body, reducing the number of external components and improving system integration.

[0005] However, the above structure can only achieve filtering at a certain frequency point, and it is difficult to achieve wideband band-stop filtering. Summary of the Invention

[0006] Therefore, it is necessary to provide a filter cable that can make the coaxial cable compatible with filtering functions and has multiple filtering frequency points within the operating frequency band to achieve wideband band-stop filtering.

[0007] A filter cable includes: a coaxial cable, wherein the coaxial cable comprises, from the inside out: an inner conductor, a dielectric layer and an outer conductor, which are sequentially arranged. The outer conductor is provided with a groove, the groove comprising: a first part and two second parts, both the first part and the second parts being strip-shaped structures, the two ends of the first part being connected to the two second parts respectively, so that the groove forms an axially symmetrical "H" shaped structure; the first part is arranged along the circumference of the outer conductor, the second part is arranged parallel to the axial direction of the outer conductor, and the first part is connected to the non-midpoint of the second part; The first part is equipped with a picofarad capacitor.

[0008] In one embodiment, the first portion connects to a corresponding end of two second portions to form an axisymmetric "U"-shaped structure in the groove.

[0009] In one embodiment, the capacitance value of the capacitor is adjustable.

[0010] In one embodiment, the groove further includes: two third portions; The third part is a strip structure with multiple 90° bends. The two ends of one third part are connected to the two ends of one second part, and the two ends of another third part are connected to the two ends of another second part, so that the two third parts and the two second parts form two handleless comb-shaped structures.

[0011] In one embodiment, the handleless comb-shaped structure includes: a comb back and comb teeth; The comb back is arranged parallel to the axial direction of the outer conductor, and the comb teeth are arranged along the circumference of the outer conductor; All the teeth on the comb are collinear at the ends furthest from the back of the comb, and the two handleless comb-shaped structures have two axes of symmetry. In one embodiment, the length of the third part is increased to shift the filter frequency to a lower frequency.

[0012] In one embodiment, the first part, the second part, and the third part are all equal-width structures.

[0013] In one embodiment, the ratio of the length of the comb back to the length of the comb teeth satisfies [2, 3], and the ratio of the width of the comb back to the width of the comb teeth satisfies [1, 2].

[0014] In one embodiment, the ratio of the circumferential length of the groove to the circumference of the outer conductor satisfies [0.85, 0.95], and the ratio of the axial length of the groove to the axial length of the outer conductor satisfies [0.5, 0.7].

[0015] In one embodiment, the number of coaxial cables is two or more, and the ports of adjacent coaxial cables are connected to form a cascaded structure.

[0016] The aforementioned filter cable has grooves on its outer conductor to form a defective conductor layer, and bias capacitors are provided on the grooves to increase the resonant capacitance in the equivalent circuit of the filter cable, thereby reducing the filtering frequency to the target frequency range. The equivalent inductance and distributed capacitance formed by the defective conductor layer, together with the bias capacitor, constitute a local resonant circuit. When the frequency of the transmitted signal is close to the resonant frequency of this resonant circuit, the defective conductor layer generates a strong current resonance, causing the coaxial cable to exhibit strong reflection and a deep transmission zero at that frequency, thus realizing the band-stop filtering function in the resonant frequency band. When the frequency of the transmitted signal is far from the resonant frequency of this resonant circuit, the defective conductor layer does not generate a strong current resonance, allowing the coaxial cable to transmit signals and realize the normal transmission function in the non-resonant frequency band. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of a filter cable in one embodiment (taking a coaxial cable (i.e., a filter unit) as an example). Figure 2 This is a schematic diagram of the outer conductor unfolded structure of a filter cable in one embodiment; Figure 3 This is a schematic diagram showing the unfolded dimensions of the outer conductor of a filter cable in one embodiment. Figure 4 This is a graph showing the S21 transmission coefficient of a filter cable under different loading capacitance values ​​in one embodiment. Figure 5 This is a graph showing the S11 reflection coefficient of a filter cable under different loading capacitance values ​​in one embodiment. Figure 6 This is a current distribution diagram of the outer conductor of a filter cable in one embodiment at a frequency of 200MHz. Figure 7 This is a current distribution diagram of the outer conductor of a filter cable in one embodiment at a frequency of 500MHz. Figure 8 This is a current distribution diagram of the outer conductor of a filter cable in one embodiment at a frequency of 800MHz. Figure 9 This is a current distribution diagram of a filter cable without a third part at a frequency of 384MHz in one embodiment; Figure 10 This is a current distribution diagram of a filter cable at a frequency of 344MHz in one embodiment; Figure 11 This is a graph showing the S21 transmission coefficient of a filter cable under different bend lengths in one embodiment. Figure 12 This is a comparison diagram of a filtered cable in one embodiment, showing a broadband Gaussian time-domain signal input at one port and a filtered time-domain signal output at the other port. Figure 13 This is a comparison of the Fourier transform spectra of the input and output signals of a filter cable in one embodiment.

[0018] Explanation of reference numerals in the attached figures: Inner conductor 1; Dielectric layer 2; Outer conductor 3; first part 31, second part 32, third part 33, capacitor 34; Port 4. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0020] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0021] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of those features. In the description of this application, "multiple sets" means at least two sets, such as two sets, three sets, etc., unless otherwise explicitly specified.

[0022] In this application, unless otherwise expressly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two elements or the interaction between two elements, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0023] Furthermore, the technical solutions of the various embodiments of this application can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this application.

[0024] This application provides a filter cable, such as Figure 1 and Figure 2 As shown, in one embodiment, it includes: one or more coaxial cables. The coaxial cable includes: an inner conductor, a dielectric layer, and an outer conductor, wherein the dielectric layer is sleeved outside the inner conductor, and the outer conductor is sleeved outside the dielectric layer, that is, the inner conductor, the dielectric layer, and the outer conductor are sleeved sequentially from the inside to the outside. The outer conductor has a groove (the thickness of the groove is equal to the thickness of the outer conductor), which is coupled to the transmission direction of the coaxial cable. The groove includes a first part and two second parts; both the first and second parts are strip-shaped structures, with the two ends of the first part connected to the two second parts respectively, so that the groove forms an axisymmetric "H" shape. The first part is arranged along the circumference of the outer conductor, and the second parts are arranged parallel to the axial direction of the outer conductor, with the first part connecting to the non-midpoint of the second part. A picofarad-level capacitor is provided on the first part (i.e., the capacitor on the first part is a bias capacitor). This configuration enables the coaxial cable to be compatible with filtering functions and has multiple filtering frequency points within the operating frequency band, achieving wideband band-stop filtering.

[0025] Preferably, the first part connects to one corresponding end of the two second parts so that the groove forms an axisymmetric "U" shape to improve the resonance depth and achieve a larger filter frequency tuning range (hundreds of MHz) with a smaller capacitance value transformation range (from a few picofarads to ten picofarads).

[0026] More preferably, the capacitance value of the capacitor is adjustable, so as to achieve low-frequency tuning of different filtering frequencies over a wide range while keeping the external dimensions of the filter unit unchanged (as the value of the loaded capacitor increases, the equivalent resonant capacitance increases, and the resonant frequency shifts to a lower frequency, thereby realizing capacitor tuning of the filtering frequency), which solves the problem that the resonant frequency of conventional slotted structures is determined by geometric dimensions, resulting in insufficient frequency adjustment flexibility.

[0027] In another embodiment, the groove further includes two third parts; that is, the groove includes a first part, two second parts, and two third parts. The third parts are strip-shaped structures with multiple 90° bends. The two ends of one third part are connected to the two ends of one second part, and the two ends of another third part are connected to the two ends of another second part, so that the two third parts and the two second parts form two handleless comb-shaped structures. This configuration solves the problem that traditional slotted resonant structures require large physical dimensions to achieve effective resonance. It enables low-frequency bandstop filtering within a limited cable size, meeting the filtering requirements of the hundreds of MHz frequency band, significantly reducing the size of the coaxial cable (below 100 mm), and achieving miniaturization and weight reduction.

[0028] Preferably, the handleless comb-shaped structure includes: a comb back and comb teeth; the comb back is arranged parallel to the axial direction of the outer conductor, and the comb teeth are arranged along the circumference of the outer conductor; the ends of all comb teeth away from the comb back are collinear, and the two handleless comb-shaped structures have two axes of symmetry. This configuration further reduces the size of the coaxial cable, further achieving miniaturization and weight reduction.

[0029] More preferably, the length of the third part is increased to shift the filtering frequency to a lower frequency and further reduce the size of the coaxial cable (to the tens of millimeters level), thereby achieving miniaturization and weight reduction.

[0030] More preferably, the first part, the second part, and the third part are all of equal width to further improve the resonance depth. A filtering depth of more than 30dB can be achieved using a single coaxial cable (the filtering depth will be even greater after cascading), while also achieving miniaturization.

[0031] More preferably, the ratio of the length of the comb back to the length of the comb teeth satisfies [2, 3], and the ratio of the width of the comb back to the width of the comb teeth satisfies [1, 2], so as to further improve the resonance depth, and a filtering depth of 35dB can be achieved using a single coaxial cable.

[0032] More preferably, on the outer conductor, the ratio of the circumferential length of the groove to the circumference of the outer conductor satisfies [0.85, 0.95], and the ratio of the axial length of the groove to the axial length of the outer conductor satisfies [0.5, 0.7], so as to extend the filtering frequency band and achieve a wider filtering range.

[0033] In another embodiment, there are two or more coaxial cables, and the ports of adjacent coaxial cables are connected to form a cascaded structure along the coaxial axis; different coaxial cables can use different loading capacitance values, different third part lengths, or different groove parameters to achieve multi-frequency band-stop filtering, wide-stopband filtering, or coded filtering response.

[0034] In this application, the resonant band-stop working principle can be explained using an equivalent LC resonant circuit.

[0035] Specifically, the first, second, and third parts of the outer conductor together provide the equivalent inductance and distributed capacitance, and the bias capacitance further increases the equivalent resonant capacitance. The resonant frequency of this filter unit (a coaxial cable) can be approximated as:

[0036] In the formula, This is the resonant frequency of the filter unit. The equivalent inductance is generated by the first part, the second part, and the third part. The distributed capacitance generated by the first part, the second part, and the third part, and the equivalent resonant capacitance generated by the bias capacitor; This relationship shows that when the applied capacitance increases, Increase Decrease; when the length of the third part increases, Increase Similarly, the cost is reduced. Therefore, this application achieves both filter frequency tuning and structural miniaturization by adjusting the loading capacitor value and the length of the third part, respectively.

[0037] It should be noted that the grooves can be achieved through etching, laser processing, mechanical milling, precision cutting, or other metal patterning processes. The capacitors can be fixed surface-mount capacitors, adjustable capacitors, varactor diodes, switched capacitor arrays, or other lumped elements with equivalent capacitance, enabling the filter cable to have electrically tunable or reconfigurable filtering capabilities.

[0038] The aforementioned filter cable has grooves on its outer conductor to form a defective conductor layer. Bias capacitors are placed on these grooves to increase the resonant capacitance in the equivalent circuit of the filter cable, reducing the filtering frequency to the target frequency range and creating a filter cable with a tunable band-stop response. The equivalent inductance and distributed capacitance formed by the defective conductor layer, together with the bias capacitor, constitute a local resonant circuit. When the transmission signal frequency is close to the resonant frequency of this circuit (at the target resonant frequency), the defective conductor layer generates a strong current resonance, causing the coaxial cable to exhibit strong reflection and a deep transmission zero at that frequency. The transmitted signal is reflected and suppressed, achieving the band-stop filtering function in the resonant frequency band. When the transmission signal frequency is far from the resonant frequency of this circuit (at the non-resonant frequency), the defective conductor layer does not generate a strong current resonance, allowing the coaxial cable to transmit normally, and the transmitted signal is transmitted normally, achieving normal transmission in the non-resonant frequency band.

[0039] Specifically, it has the following beneficial effects: 1. By integrating the band-stop filtering function into the coaxial cable, strong resonant current is not generated at non-resonant frequency points, which can maintain the normal transmission function of the coaxial cable, and has both frequency selectivity and transmission continuity. Moreover, no additional independent filter is required, which can reduce the system size, weight and connection complexity.

[0040] 2. By creating a defective conductor layer through slotting the outer conductor and loading a bias capacitor to form an equivalent LC resonant circuit, strong resonant reflection and deep transmission zero (deep transmission suppression) can be generated at the target frequency, achieving band-stop filtering while maintaining normal signal transmission in non-target frequency bands.

[0041] 3. The filter frequency can be adjusted by changing the loading capacitor value. When the loading capacitor value is 2 pF, 3 pF, 5 pF and 10 pF, resonant filter frequencies can be formed near approximately 600 MHz, 500 MHz, 400 MHz and 280 MHz respectively, and resonant band-stop filtering can be achieved. It can cover multiple typical filter frequencies in the range of approximately 280 MHz to 600 MHz (at these frequencies, S11 is significantly enhanced, indicating that the signal is strongly reflected near the resonant frequency, and S21 shows a deep notch, indicating that the target frequency component is effectively suppressed), which has strong frequency design flexibility.

[0042] 4. By changing the length of the third part, the equivalent inductance is increased, and the distribution of the surface resonant current path is changed, so that the filter frequency point is shifted to a lower frequency without changing the unit size, thereby reducing the resonant frequency and further realizing the miniaturization of the low-frequency filter unit.

[0043] 5. It can be expanded into a multi-unit cascaded structure through multiple coaxial cables (one coaxial cable is one filter unit). By combining filter units with different capacitance values, different third part lengths or different defect conductor layer geometric parameters, multi-frequency filtering, reconfigurable filtering or coded filtering response can be achieved.

[0044] 6. By integrating the filter with the coaxial cable body, it features adjustable frequency, easy miniaturization, compact structure, and easy processing. It can be applied to RF coaxial transmission links, antenna feed networks, electromagnetic compatibility testing systems, communication equipment interconnection cables, radar and measurement and control system transmission links, anti-interference cable assemblies, and RF transmission links or electromagnetic systems that require specific frequency suppression along the cable. It is particularly suitable for application scenarios with strict requirements on size, weight, integration, and wiring space, while also requiring the suppression of specific frequency interference signals.

[0045] like Figure 3 As shown, the axial length of the outer conductor is 50 mm, and the circumferential length (circumference) is 12.5 mm. mm; the axial length of the groove is 30.8 mm, and the circumferential length is 35 mm; the width of the first part, the second part, and the third part is 1.1 mm, and the distance between the two second parts is 5 mm; the length of the comb back is 28.6 mm, the length of the comb teeth is 11 mm, the width of the comb back is 1.8 mm, and the width of the comb teeth is 1.6 mm.

[0046] like Figure 4 and Figure 5 As shown, under the same filter unit structure, different filtering frequencies can be achieved by loading different capacitor values. Specifically: when the loaded capacitor value is 2 pF, the filter cable generates a transmission notch around 600 MHz; when the loaded capacitor value is 3 pF, the filter cable generates a transmission notch around 500 MHz; when the loaded capacitor value is 5 pF, the filter cable generates a transmission notch around 400 MHz; and when the loaded capacitor value is 10 pF, the filter cable generates a transmission notch around 280 MHz. Near the above resonant frequencies, a deep notch appears at S21, indicating that the target frequency signal is significantly suppressed; S11 is close to a strong reflection state, indicating that the input signal is reflected back to the input terminal by the defective conductor resonant structure at this frequency. This result shows that this application can achieve tunable bandstop filtering function through capacitor loading.

[0047] like Figure 6 , Figure 7 , Figure 8 As shown, at the 500 MHz resonant frequency, a significant strong current distribution appears on the defective conductor layer, with the strong current mainly concentrated in the second and third regions. This phenomenon indicates that the signal near 500 MHz excites a local current resonance mode in the defective conductor layer (the filtering response at 500 MHz originates from this local current resonance mode), confining and reflecting electromagnetic energy near the defective structure, thus forming a deep transmission zero. In contrast, at non-resonant frequencies such as 200 MHz and 800 MHz, no significant strong current resonance is formed in the defective conductor layer, and the signal continues to propagate normally along the coaxial line. Therefore, the filtering effect of this application has a clear frequency selectivity.

[0048] like Figure 9 , Figure 10 , Figure 11As shown, the low-frequency miniaturization of the filter unit can be achieved by adjusting the length of the third part. While maintaining the overall dimensions of the filter unit, when the length of the third part increases from 1 mm to 12.5 mm, the filtering frequency decreases from approximately 384 MHz to approximately 344 MHz. This result indicates that increasing the length of the third part increases the equivalent inductance and lengthens the resonant current path, causing the filtering frequency to shift towards lower frequencies. Compared to directly increasing the slot size to reduce the resonant frequency, this application achieves current path compression through the third part, which is beneficial for achieving low-frequency filtering within limited cable dimensions.

[0049] like Figure 12 As shown, i1 represents the broadband Gaussian time-domain signal input at one port, and o2,1 represents the filtered time-domain output signal received at the other port. To verify the filtering function of this application in broadband time-domain signal transmission, a broadband Gaussian time-domain signal is set as the input signal at one port. Due to the band-stop effect generated by the filter cable at the target resonant frequency, the output signal undergoes a waveform change relative to the input signal, and the target frequency component is suppressed.

[0050] like Figure 13 As shown, Fourier transforms are performed on the input signal i1 at one port and the output signal o2,1 at the other port to obtain their spectral components. The spectral results show that the input signal contains spectral components over a wide frequency range, while the output signal exhibits a significant spectral dip around 500 MHz, indicating that the 500 MHz frequency component is effectively filtered out (the Fourier transform of the output signal shows that the target frequency component is filtered out). This result further proves that this application can not only achieve band-stop filtering in the frequency domain S-parameters but also suppress target frequency components during actual broadband time-domain signal transmission, thus possessing time-domain filtering capabilities.

[0051] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0052] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0053] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended application documents.

Claims

1. A filter cable, characterized in that, include: A coaxial cable, comprising, from the inside out, an inner conductor, a dielectric layer, and an outer conductor; The outer conductor is provided with a groove, the groove comprising: a first part and two second parts, both the first part and the second parts being strip-shaped structures, the two ends of the first part being connected to the two second parts respectively, so that the groove forms an axially symmetrical "H"-shaped structure; the first part is arranged along the circumference of the outer conductor, the second part is arranged parallel to the axial direction of the outer conductor, and the first part connects to the non-midpoint of the second part; The first part is equipped with a picofarad capacitor.

2. The filter cable according to claim 1, characterized in that, The first part connects to a corresponding end of the two second parts so that the groove forms an axisymmetric "U" shape.

3. A filter cable according to claim 2, characterized in that, The capacitance value of the capacitor is adjustable.

4. A filter cable according to any one of claims 1 to 3, characterized in that, The groove also includes: two third parts; The third part is a strip structure with multiple 90° bends. The two ends of one third part are connected to the two ends of one second part, and the two ends of another third part are connected to the two ends of another second part, so that the two third parts and the two second parts form two handleless comb-shaped structures.

5. A filter cable according to claim 4, characterized in that, The handleless comb-shaped structure includes: a comb back and comb teeth; The comb back is arranged parallel to the axial direction of the outer conductor, and the comb teeth are arranged along the circumference of the outer conductor; All the teeth on the comb are collinear at the ends furthest from the back of the comb, and the two handleless comb-shaped structures have two axes of symmetry.

6. A filter cable according to claim 5, characterized in that, Increase the length of the third part to shift the filter frequency to lower frequencies.

7. A filter cable according to claim 6, characterized in that, The first part, the second part, and the third part are all of equal width.

8. A filter cable according to claim 7, characterized in that, The ratio of the length of the comb back to the length of the comb teeth satisfies [2, 3], and the ratio of the width of the comb back to the width of the comb teeth satisfies [1, 2].

9. A filter cable according to any one of claims 1 to 3, characterized in that, On the outer conductor, the ratio of the circumferential length of the groove to the circumference of the outer conductor satisfies [0.85, 0.95], and the ratio of the axial length of the groove to the axial length of the outer conductor satisfies [0.5, 0.7].

10. A filter cable according to any one of claims 1 to 3, characterized in that, The number of coaxial cables is two or more, and the ports of adjacent coaxial cables are connected to form a cascaded structure.

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