Ultra-wideband three-dimensional frequency selector with wide out-of-band rejection characteristics

Abstract

The application provides an ultra-wideband three-dimensional frequency selector with wide out-band suppression characteristics, comprising a plurality of filter units arranged two-dimensionally periodically along an x-axis and a y-axis; adjacent filter units along the x-axis are separated by an air layer to form a periodic gap, and adjacent filter units along the y-axis are directly connected; the filter unit comprises a slow-wave loaded slot line structure and a matching structure; the slow-wave loaded slot line structure comprises a plurality of slot line structures extending along a z-axis direction and at least one group of distributed LC networks; and the matching structure is a gradually changing slot line matching structure and is arranged at both ends of the slow-wave loaded slot line structure. The application introduces a slow-wave effect by loading a distributed LC network inside a slot line gap, forms a transmission zero point outside a passband, and realizes wide-band suppression of out-band signals; an impedance gradually changing matching structure is introduced at both ends of the structure, and port matching is effectively improved through smooth transition, so that the frequency selector can maintain excellent out-band suppression performance while obtaining a wide passband response and low insertion loss.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to an ultra-wideband three-dimensional frequency selector with wideband out-of-band suppression characteristics. It can be applied to scenarios such as electromagnetic filtering, satellite communication, electromagnetic compatibility of electronic equipment, stealth and radomes, to achieve selective transmission of electromagnetic waves in specific frequency bands and wideband out-of-band suppression. Background Technology

[0002] A frequency selector is a periodic array of unit structures made of metal, dielectric, or their composite materials. It can exhibit differentiated transmission and reflection characteristics according to the frequency, polarization state, and incident angle of electromagnetic waves, and is equivalent to a "space electromagnetic filter". With the development of wireless communication technology, the demand for frequency selectors in many fields is increasing, especially the requirements for the coordinated performance of "wide passband" and "wideband external suppression" are becoming more stringent.

[0003] Traditional frequency selectors primarily utilize two-dimensional frequency selection surfaces, achieving filtering functionality by etching metal patches or gaps on a dielectric substrate. Some employ multi-layer stacked structures to extend bandwidth and angular stability. However, the performance control capabilities of two-dimensional structures have inherent limitations: achieving wide bandwidth stopband characteristics requires multi-layer stacking, leading to increased overall structural thickness, higher manufacturing difficulty, and high requirements for inter-layer alignment accuracy. Furthermore, the design process relies on large-scale full-wave optimization, resulting in long cycles and high costs, making it difficult to meet the needs of complex scenarios.

[0004] To overcome the limitations of two-dimensional structures, researchers have proposed three-dimensional frequency selectors. By introducing multiple geometric dimensions and coupling paths, transmission poles can be formed at multiple frequency points, achieving multi-passband or multi-stopband characteristics. However, existing three-dimensional frequency selectors still have key drawbacks: on the one hand, out-of-band suppression is limited to specific frequency bands, and the ability to suppress higher harmonics weakens as the frequency increases, failing to cover a wide frequency range; on the other hand, expanding the passband width significantly weakens the out-of-band filtering performance, resulting in insufficient stopband depth and narrow width, making it difficult to simultaneously meet the dual requirements of "ultra-wideband passband" and "efficient out-of-band suppression." Therefore, how to achieve synergistic optimization of wide passband and wideband out-of-band suppression in three-dimensional frequency selectors has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the aforementioned issues, this invention aims to propose an ultra-wideband three-dimensional frequency selector with wideband out-of-band suppression characteristics. It achieves frequency modulation of the incident wave by forming a three-dimensional structure through a two-dimensional periodic arrangement in the xy-plane and the extension of slot lines in the z-direction. Furthermore, it enhances out-of-band suppression by introducing a slow-wave loading structure within the slot lines and employs impedance-gradient matching structures at both ends to obtain excellent transmission characteristics within a wide passband.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] An ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics includes multiple filter units arranged in a two-dimensional periodic pattern along the x-axis and y-axis; adjacent filter units along the x-axis are separated by an air layer to form periodic gaps, and adjacent filter units along the y-axis are directly connected; each filter unit includes a slow-wave loaded slot line structure and a matching structure, the slow-wave loaded slot line structure includes a multi-slot line structure extending along the z-axis and at least one set of distributed LC networks, and the matching structure is a gradient slot line matching structure and is disposed at both ends of the slow-wave loaded slot line structure.

[0008] Furthermore, the multi-slot structure includes a first transverse metal strip and a second transverse metal strip extending along the z-axis direction. The first transverse metal strip and the second transverse metal strip are placed in a mirror image symmetrically along the center line of the filter unit in the y-axis direction. The first transverse metal strip is connected to the second transverse metal strip of the unit adjacent in the y-axis direction, and the second transverse metal strip is connected to the first transverse metal strip of the unit adjacent in the y-axis direction.

[0009] Furthermore, the distributed LC network is located between the first transverse metal strip and the second transverse metal strip, and includes a first longitudinal metal structure, a second longitudinal metal structure, a first transverse metal structure, and a second transverse metal structure; the first longitudinal metal structure and the second longitudinal metal structure are symmetrically placed along the centerline of the filter unit's y-axis direction to provide an inductive effect for the distributed LC network; the first transverse metal structure and the second transverse metal structure are symmetrically placed along the centerline of the filter unit's y-axis direction to provide a capacitive effect for the distributed LC network.

[0010] Furthermore, the upper end of the first longitudinal metal structure is connected to the first transverse metal strip, and the lower end is connected to the first transverse metal structure; the lower end of the second longitudinal metal structure is connected to the second transverse metal strip, and the upper end is connected to the second transverse metal structure.

[0011] Furthermore, the shapes of the first longitudinal metal structure and the second longitudinal metal structure are straight or bent structures that realize the inductive effect.

[0012] Furthermore, the first longitudinal metal structure and the second longitudinal metal structure of the distributed LC network are respectively connected to the first transverse metal strip and the second transverse metal strip, and the connection position is at the junction of adjacent slot line structures to form a slow wave loading at the position; all slot line structures have the same slot width, and their length is determined according to the series inductance value required for the filter design, and are used to form multiple equivalent series inductance units.

[0013] Furthermore, multiple sets of the distributed LC networks form multiple parallel LC series resonant branches; the order of the overall structure is determined by the number of the distributed LC networks and the number of slotted line structures in front of, behind and between them, ultimately forming an elliptical filter topology structure composed of multiple passive resonant units cascaded together, used to achieve the filtering effect of elliptical response characteristics.

[0014] Furthermore, the capacitive effect of the first transverse metal structure and the second transverse metal structure increases with their own length and the distance between them decreases; the inductive effect of the first longitudinal metal structure and the second longitudinal metal structure increases with their own width and length.

[0015] Furthermore, the matching structure includes a first matching structure and a second matching structure placed at both ends of the slow-wave loading slot line structure; the slot width of the matching structure is continuously or monotonically varying in segments, and the slot line shape includes straight lines and curves; in the matching structure, the slot width on the side connected to the slow-wave loading slot line structure is smaller, corresponding to the low impedance region, and the slot width gradually increases along the direction away from the slow-wave loading slot line structure, corresponding to the high impedance region.

[0016] Furthermore, the slot width of the slow-wave loaded slot structure is relatively large, while the slot width of the matching structure on the side connected to the slow-wave loaded slot structure is relatively small, resulting in a significant difference in slot width between the two, in order to achieve an elliptic filtering response.

[0017] Beneficial effects: This invention introduces a slow wave effect by loading a distributed LC network inside the slot gap, forming a transmission zero outside the passband and achieving wideband suppression of out-of-band signals; at the same time, an impedance-gradient matching structure is introduced at both ends of the structure, which effectively improves port matching through smooth transition, so that the frequency selector can obtain wide passband response and low insertion loss while maintaining excellent out-of-band suppression performance. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0019] Figure 1 This is a schematic diagram of the structure of the ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics according to an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of the filter unit structure of the ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics according to an embodiment of the present invention;

[0021] Figure 3This is a schematic diagram of the slow-wave loaded slot line structure of the ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics according to an embodiment of the present invention;

[0022] Figure 4 This is a transmission characteristic parameter curve of the ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics described in an embodiment of the present invention. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0024] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] Example 1

[0026] See Figure 1-4 An ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics includes multiple filter units 1 arranged in a two-dimensional periodic pattern along the x-axis and y-axis; adjacent filter units 1 along the x-axis are separated by an air layer to form a periodic gap, and adjacent filter units 1 along the y-axis are directly connected; each filter unit 1 includes a slow-wave loaded slot line structure 2 and a matching structure 3, the slow-wave loaded slot line structure 2 includes a multi-slot line structure 4 extending along the z-axis and at least one set of distributed LC networks 5, and the matching structure 3 is a gradient slot line matching structure and is disposed at both ends of the slow-wave loaded slot line structure 2.

[0027] This embodiment introduces a slow wave effect by loading a distributed LC network inside the slot gap, forming a transmission zero outside the passband and achieving wideband suppression of out-of-band signals. At the same time, an impedance-gradient matching structure is introduced at both ends of the structure to effectively improve port matching through a smooth transition, so that the frequency selector can achieve wide passband response and low insertion loss while maintaining excellent out-of-band suppression performance.

[0028] In the specific implementation, the period intervals are Px and Py, with Px = 5mm and Py = 10mm. Therefore, the I / O port impedance satisfies Z0 = ηPy / Px = 753.4Ω.

[0029] In a specific example, the multi-slot structure 4 includes a first transverse metal strip 41 and a second transverse metal strip 42 extending along the z-axis direction. The first transverse metal strip 41 and the second transverse metal strip 42 are placed in a mirror image symmetrically along the center line of the filter unit 1 in the y-axis direction. The first transverse metal strip 41 is connected to the second transverse metal strip 42 of the unit adjacent in the y-axis direction, and the second transverse metal strip 42 is connected to the first transverse metal strip 41 of the unit adjacent in the y-axis direction.

[0030] The mirror-symmetric arrangement and the conductive connection structure across units in this embodiment (i.e., the first transverse metal strip is connected to the second transverse metal strip of the adjacent unit) form a continuous and symmetrical conductive path, ensuring that the electromagnetic signal is transmitted uniformly in the y-axis direction and avoiding frequency shift caused by structural asymmetry.

[0031] The symmetrical structure reduces the impact of processing errors on performance. Even with slight deviations in local dimensions, the overall electromagnetic response remains stable, improving the consistency of mass production.

[0032] In a specific example, the distributed LC network 5 is located between the first transverse metal strip 41 and the second transverse metal strip 42, and includes a first longitudinal metal structure 51, a second longitudinal metal structure 52, a first transverse metal structure 53, and a second transverse metal structure 54; the first longitudinal metal structure 51 and the second longitudinal metal structure 52 are symmetrically placed along the centerline of the filter unit 1y-axis direction to provide an inductive effect for the distributed LC network 5; the first transverse metal structure 53 and the second transverse metal structure 54 are symmetrically placed along the centerline of the filter unit 1y-axis direction to provide a capacitive effect for the distributed LC network 5;

[0033] The upper end of the first longitudinal metal structure 51 is connected to the first transverse metal strip 41, and the lower end is connected to the first transverse metal structure 53; the lower end of the second longitudinal metal structure 52 is connected to the second transverse metal strip 42, and the upper end is connected to the second transverse metal structure 54.

[0034] The shapes of the first longitudinal metal structure 51 and the second longitudinal metal structure 52 are straight and bent structures that realize the inductance effect;

[0035] The first longitudinal metal structure 51 and the second longitudinal metal structure 52 of the distributed LC network 5 are respectively connected to the first transverse metal strip 41 and the second transverse metal strip 42, and the connection position is at the junction of adjacent slot line structures 4 to form slow wave loading at the position; all slot line structures 4 have the same slot width, and their length is determined according to the series inductance value required by the filter design, and are used to form multiple equivalent series inductance units.

[0036] Multiple sets of the distributed LC networks 5 form multiple parallel LC series resonant branches; the order of the overall structure is determined by the number of the distributed LC networks 5 and the number of the slot line structures in front, behind and between them, ultimately forming an elliptical filter topology structure composed of multiple passive resonant units cascaded together, which is used to achieve the filtering effect of elliptical response characteristics.

[0037] The capacitive effect of the first transverse metal structure 53 and the second transverse metal structure 54 increases with their own length and the distance between them decreases; the inductive effect of the first longitudinal metal structure 51 and the second longitudinal metal structure 52 increases with their own width and length.

[0038] It should be noted that the dimensions of each structure in the distributed LC network can be determined through electromagnetic simulation and theoretical calculation according to design requirements, so as to ensure that the capacitance and inductance values ​​required for the parallel LC series resonant branch in the elliptic filter are realized, thereby achieving the target frequency response and out-of-band suppression effect.

[0039] In its implementation, to achieve excellent passband flatness and high out-of-band rejection performance, this invention employs a fifth-order elliptic filter as the design objective. Elliptic filters introduce transmission zeros outside the passband, thereby achieving steeper cutoff characteristics and higher out-of-band rejection levels under finite order conditions.

[0040] The basic circuit topology of a fifth-order elliptic filter consists of five passive resonant units arranged sequentially, including three series inductor units and two parallel LC series resonant branches. In this topology, the series inductors determine the transmission characteristics within the passband and, together with the load impedance, affect the filter's center frequency and bandwidth. The parallel LC series resonant branches generate transmission zeros at specific frequency points, thereby significantly improving out-of-band rejection characteristics. By rationally designing the values ​​of the inductors and capacitors, rapid out-of-band attenuation can be achieved while ensuring low insertion loss within the passband.

[0041] In the filtering unit, a slow-wave loaded slotted line structure is used to achieve a fifth-order elliptic filter response. Specifically, it can be a three-slotted line structure and a loading slotted line structure with two sets of distributed LC networks. The first and second longitudinal metal structures of the distributed LC networks are connected to the first and second transverse metal strips, respectively, at the junctions of adjacent slotted line structures to form a slow-wave loading. All slotted line structures have the same slot width, and their length is determined according to the series inductance value required for the filter design, forming three equivalent series inductance units. The two sets of distributed LC networks form two parallel LC series resonant branches, ultimately forming a fifth-order elliptic filter topology structure composed of five cascaded passive resonant units, achieving a filtering effect with elliptic response characteristics.

[0042] A distributed LC network is a local structure loaded within the gaps of a slot line. It can be considered as a point loaded on the slot line, with an equivalent electrical length approximately zero. While it doesn't significantly change the overall electrical length of the slot line, it can significantly induce a slow-wave effect at that location, substantially altering the local characteristic impedance. Specifically, the impedance at this point is greatly reduced, making the characteristic impedance of adjacent pure slot line segments, when externally equivalent, much higher than that of connected structures, thus exhibiting significant inductive characteristics. Based on this, a pure slot line segment can be equivalent to a series inductor unit in a circuit topology.

[0043] To quantitatively characterize the equivalent inductance of the aforementioned pure slot segment, a two-port equivalent method based on S-parameters is employed. Its equivalent inductance value can be obtained using the following formula:

[0044]

[0045] Where B is the parameter of the ABCD matrix, Let be the angular frequency. Therefore, based on the S-parameters obtained from the simulation, the equivalent inductance value of the slot segment can be extracted, and the physical length and geometric dimensions of the slot can be further determined.

[0046] In this embodiment, the first and second transverse metal structures provide capacitance for the distributed LC network. The longer their length and the smaller the distance between them, the greater the capacitance effect. The first and second longitudinal metal structures are used to achieve inductance. The narrower their width and the longer their length, the stronger the inductance effect. To increase the inductance value, a bent structure can also be used. The dimensions of each structure in the distributed LC network can be determined by electromagnetic simulation and theoretical calculation according to design requirements to ensure that the capacitance and inductance values ​​required for the parallel LC series resonant branch in the elliptic filter are achieved, thereby achieving the target frequency response and out-of-band suppression effect.

[0047] The distributed LC network loaded inside the slot line exhibits a single stopband over a wide frequency range; therefore, its equivalent circuit can be characterized by a second-order series resonant circuit. By combining the scattering parameters obtained through electromagnetic simulation software with the equivalent circuit model, the equivalent inductance and capacitance values ​​of the distributed LC network can be calculated.

[0048] For a series LC resonant network, its impedance function can be expressed as:

[0049]

[0050] Where f is the frequency, L is the equivalent inductance, and C is the equivalent capacitance.

[0051] When f is the resonant frequency f0, the series LC impedance is 0, that is, ZLC(f0) = 0. At this time, the relationship between the inductor and the capacitor can be derived as follows:

[0052]

[0053] When f is the cutoff frequency fc, the corresponding frequency point where the transmission coefficient S21 is -3.0dB, the impedance of the series LC circuit is Z0 / 2, that is:

[0054]

[0055] Based on the above conditions, the specific equivalent inductance and capacitance values ​​of the distributed LC network can be obtained from the port impedance, transmission zero, and cutoff frequency as follows:

[0056]

[0057] Based on the above relationships, the specific equivalent inductance and capacitance values ​​of the distributed LC network can be determined according to the design requirements of the fifth-order elliptic filter response, and the specific structure and size of the distributed LC network can be determined.

[0058] In a specific example, the matching structure 3 includes a first matching structure 31 and a second matching structure 32 placed at both ends of the slow-wave loading slot line structure 2; the slot width of the matching structure 3 is continuous or monotonically varying in segments, and the slot line shape includes straight lines and curves; in the matching structure 3, the slot width on the side connected to the slow-wave loading slot line structure 2 is smaller, corresponding to the low impedance region, and the slot width gradually increases along the direction away from the slow-wave loading slot line structure 2, corresponding to the high impedance region.

[0059] It should be noted that the first matching structure and the second matching structure have the same dimensions, and the slot width changes are both gradual slot width structures, which are composed of multi-level slot width change units. The size of each level of slot width is determined according to the calculation formula of the matching line impedance. From the side view, along the z-axis electromagnetic wave incident direction, the gap of the slot line shows a gradual structure that monotonically decreases from the outside to the inside.

[0060] In practical implementation, to achieve optimal equiripple impedance transition characteristics, both the first and second matching structures adopt the Klopfenstein gradient line form. The Klopfenstein gradient is derived from the step Chebyshev impedance transformer when the number of sections increases to infinity. Compared with other gradient lines, for a given gradient length, the reflection coefficient of the Klopfenstein impedance gradient is the smallest throughout the entire passband; in other words, when the maximum reflection coefficient specification is limited within the passband, the Klopfenstein gradient can provide the shortest matching section.

[0061] The natural logarithm of the Klopfenstein graded characteristic impedance variation is:

[0062]

[0063] In the formula, the function Defined as

[0064]

[0065] In the formula, It is the modified Bessel function, which determines the impedance variation along the length of the gradient line and is the key to achieving minimum reflection matching.

[0066] However, directly using integral forms for numerical calculations is complex and difficult to apply efficiently in engineering design. Therefore, a simplified calculation method based on numerical analysis is adopted: by performing a series expansion of the incomplete Bessel function and utilizing its […]. The uniform convergence within the interval [1,1] allows for the expansion and integration of the integral term by term, resulting in a fast-converging power series expression. Furthermore, by introducing a recurrence relation, the calculation of coefficients can be significantly simplified, avoiding the tedious steps of successive integration.

[0067] Based on this method, the calculation of the function φ(x,A) can achieve high accuracy with only a finite number of iterations. In specific implementation, a recursive algorithm of the following form can be used: during the iteration process, the coefficient terms are obtained recursively from the calculation results of the previous term. The iteration terminates when the correction amount of the result by the iteration term is less than a preset threshold, thus ensuring the efficiency and convergence of the calculation. Practice shows that the results obtained by this method are completely consistent with the numerical results of the original Klopfenstein integration method, while the computation time is only a tiny fraction of that of the traditional integration method. Therefore, using this improved method, the characteristic impedance distribution function value of the Klopfenstein gradient line can be obtained quickly while ensuring accuracy, thus providing an efficient computational tool for the design of filters and transmission line matching structures.

[0068] In a specific example, the slot width of the slot structure 4 in the slow-wave loaded slot structure 2 is relatively large, and the slot width of the matching structure 3 on the side connected to the slow-wave loaded slot structure 2 is relatively small. The two exhibit a significant difference in slot width to achieve an elliptic filtering response.

[0069] In the specific implementation, the elliptic filter was designed using ADS simulation software, and the values ​​of the three series inductors were obtained as follows: 2.18nH, 9.56nH, and 5.02nH; the capacitance of the first parallel LC series resonant branch was 75.80Ff, and the inductance was 7.94nH; the capacitance of the second parallel LC series resonant branch was 139.78Ff, and the inductance was 2.11nH, with a filter port of 242Ω.

[0070] Based on the aforementioned circuit parameters, the initial physical dimensions can be determined using a circuit parameter mapping method. Specifically, the slot width of each of the three slot structures is 9.5 mm. Using CST simulation software to measure the transmission curve and port impedance, the equivalent inductance of the slot is found to be 2.5 nH / mm, from which the lengths of the three slot structures can be calculated. Subsequently, a fitting measurement method using distributed LC networks is employed to determine the specific dimensions of the first and second distributed LC networks, thus completing the design of the slow-wave loaded slot section.

[0071] Next, the dimensions of the Klopfenstein asymptote were determined. The length of the asymptote was set to 40 mm, the source impedance to be the filter impedance of 242 Ω, the load impedance to be the I / O port impedance of the three-dimensional frequency selector of 753.4 Ω, and the transmission coefficient S21 to be -15 dB. The entire asymptote was discretized into 1000 sections, and the slot width of each section was calculated using numerical analysis. The calculation results were then curve-fitted to obtain the function of slot width variation with asymptote length. Finally, the slow-wave loaded slot section was combined with the Klopfenstein matching line to obtain the complete design result of the three-dimensional frequency selector.

[0072] It is worth noting that due to the discontinuity of the stepped impedance and the potential errors in the equivalent inductance of the slot lines and the fitting accuracy of the distributed LC network, the final dimensions need to be slightly adjusted based on the initial design results. The specific structural dimensions are as follows: In the slow-wave loaded slot line section, the slot width of the three slot line structures is 9.5 mm, and the lengths are 0.95 mm, 4.16 mm, and 2.18 mm, respectively. The first and second transverse metal structures of the first distributed LC network are both 1.5 mm long and 0.2 mm wide. The first and second longitudinal metal structures both adopt a bent structure, with a width of 0.2 mm and a total length of 7.05 mm. The first and second transverse metal structures of the second distributed LC network are both 3.3 mm long and 0.2 mm wide, and their first and second longitudinal metal structures both adopt a straight structure, with a width of 1.3 mm and a length of 1.45 mm. In addition, both the first distributed LC network and the second distributed LC network are arranged symmetrically about the central axis of the slot, and a 0.2mm gap is maintained between the first transverse metal structure and the second transverse metal structure.

[0073] The matching structure uses a gradient matching line with a total length of 40mm. Based on the design requirements, after obtaining the physical dimensions of each groove width, a third-order polynomial is used to fit the relationship between the groove width and the gradient line length. The specific form is as follows:

[0074]

[0075] Where W is the slot width and l is the gradient line length, with values ​​ranging from [0, 40]. The fitting coefficients are: a3 = 2.93E-5, a3 = 9.67E-4, a1 = 8.74E-4, a0 = 2.36. This third-order polynomial fitting effectively describes the change in slot width with the gradient line length, ensuring a smooth impedance transition of the matching structure across the entire frequency range and improving the matching performance of the frequency selector.

[0076] Figure 4 The two-port transmission characteristics of an ultra-wideband three-dimensional frequency selector with wideband out-of-band suppression are shown. The horizontal axis represents frequency in GHz, and the vertical axis represents S-parameters in dB. The solid line represents the reflection coefficient S11, and the dashed line represents the transmission coefficient S21. Using 1 dB insertion loss as an indicator, the passband range of this structure is 1.40–5.56 GHz, the center frequency is 3.48 GHz, and the relative bandwidth is 119.5%. This result demonstrates that the designed structure exhibits excellent transmission performance over a wide frequency range, with a wide passband and low insertion loss, making it suitable for high-performance applications such as ultra-wideband communication. Using 10 dB insertion loss as an indicator, the stopband range of this structure is 5.94–18.51 GHz. This result shows that the designed structure has significant out-of-band suppression capability, effectively filtering out frequency components above the passband, meeting the wideband out-of-band suppression requirements, and further improving the system's signal quality and anti-interference capability.

[0077] Therefore, the ultra-wideband three-dimensional frequency selector with wideband out-of-band suppression characteristics proposed in this invention can obtain a wide passband response while maintaining excellent out-of-band suppression characteristics. Moreover, it has a simple structural design, simple manufacturing process, and high engineering feasibility, further deepening the application potential of three-dimensional frequency selectors in modern communication systems.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics, characterized in that, It includes multiple filter units (1) arranged in a two-dimensional periodic pattern along the x-axis and y-axis; adjacent filter units (1) along the x-axis are separated by an air layer to form a periodic gap, and adjacent filter units (1) along the y-axis are directly connected; the filter unit (1) includes a slow-wave loaded slot line structure (2) and a matching structure (3), the slow-wave loaded slot line structure (2) includes a multi-slot line structure (4) extending along the z-axis and at least one set of distributed LC networks (5), and the matching structure (3) is a gradient slot line matching structure and is set at both ends of the slow-wave loaded slot line structure (2); The multi-slot structure (4) includes a first transverse metal strip (41) and a second transverse metal strip (42) extending along the z-axis direction. The first transverse metal strip (41) and the second transverse metal strip (42) are placed in a mirror image symmetrically along the center line of the filter unit (1) in the y-axis direction. The first transverse metal strip (41) is connected to the second transverse metal strip (42) of the unit adjacent in the y-axis direction, and the second transverse metal strip (42) is connected to the first transverse metal strip (41) of the unit adjacent in the y-axis direction. The distributed LC network (5) is located between the first transverse metal strip (41) and the second transverse metal strip (42), and includes a first longitudinal metal structure (51), a second longitudinal metal structure (52), a first transverse metal structure (53), and a second transverse metal structure (54). The first longitudinal metal structure (51) and the second longitudinal metal structure (52) are symmetrically placed along the center line of the y-axis direction of the filter unit (1) to provide inductive effect for the distributed LC network (5). The first transverse metal structure (53) and the second transverse metal structure (54) are symmetrically placed along the center line of the y-axis direction of the filter unit (1) to provide capacitive effect for the distributed LC network (5). The upper end of the first longitudinal metal structure (51) is connected to the first transverse metal strip (41), and the lower end is connected to the first transverse metal structure (53). The lower end of the second longitudinal metal structure (52) is connected to the second transverse metal strip (42), and the upper end is connected to the second transverse metal structure (54).

2. The ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics according to claim 1, characterized in that, The first longitudinal metal structure (51) and the second longitudinal metal structure (52) are straight and / or bent structures that realize the inductive effect.

3. The ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics according to claim 1, characterized in that, The first longitudinal metal structure (51) and the second longitudinal metal structure (52) of the distributed LC network (5) are connected to the first transverse metal strip (41) and the second transverse metal strip (42) respectively, and the connection position is at the junction of adjacent slot line structures (4) to form slow wave loading at the position; the slot width of all slot line structures (4) is consistent, and its length is determined according to the series inductance value required for filter design, and is used to form multiple equivalent series inductance units.

4. The ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics according to claim 1, characterized in that, Multiple sets of the distributed LC networks (5) form multiple parallel LC series resonant branches; the order of the overall structure is equal to the sum of the number of distributed LC networks (5) and the number of slotted line structures (4) in front of, behind and between them, and finally forms an elliptical filter topology structure composed of multiple passive resonant units cascaded together, which is used to achieve the filtering effect of elliptical response characteristics.

5. The ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics according to claim 1, characterized in that, The capacitive effect of the first transverse metal structure (53) and the second transverse metal structure (54) increases with their own length or the distance between them decreases; the inductive effect of the first longitudinal metal structure (51) and the second longitudinal metal structure (52) increases with their own width or length.

6. The ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics according to claim 1, characterized in that, The matching structure (3) includes a first matching structure (31) and a second matching structure (32) placed at both ends of the slow-wave loading slot line structure (2); the slot width of the matching structure (3) is continuously or monotonically changing in segments, and the slot line shape includes straight lines and / or curves; in the matching structure (3), the slot width on the side connected to the slow-wave loading slot line structure (2) is smaller, corresponding to the low impedance region, and the slot width gradually increases along the direction away from the slow-wave loading slot line structure (2), corresponding to the high impedance region.

7. The ultra-wideband three-dimensional frequency selector with wideband external suppression characteristics according to claim 1, characterized in that, The slot width of the slot structure (4) in the slow-wave loading slot structure (2) is relatively large, and the slot width of the matching structure (3) on the side connected to the slow-wave loading slot structure (2) is relatively small. The two exhibit a significant difference in slot width to achieve elliptic filtering response.

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