A three-dimensional frequency selector based on a slow-wave loaded slotted line

Abstract

The present invention provides a three-dimensional frequency selector based on a slow-wave loaded slot line, which includes a plurality of periodically arranged slow-wave loaded slot line units. The slow-wave loaded slot line units adjacent along the x-axis are separated by an air layer to form a periodic gap in the x-axis direction; the slow-wave loaded slot line units adjacent along the y-axis are directly connected; the slow-wave loaded slot line unit includes a slot line in the z-axis direction and a T-shaped metal patch loaded in the slot line gap. The present invention forms a three-dimensional structure through two-dimensional periodic arrangement in the x-y plane and slot line gap extension in the z direction to realize the selection of the frequency of the incident wave; after the slot line is loaded with a T-shaped metal patch, the equivalent electrical length increases and the phase velocity decreases, enabling the structure to achieve the target spatial filtering characteristics under a compact size.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and particularly to a three-dimensional frequency selector based on a slow-wave loaded slot line. Background Art

[0002] A frequency selector is an artificial electromagnetic structure array composed of exactly the same metal, dielectric, or composite structure units arranged periodically along one-dimensional or two-dimensional directions. It exhibits differential selection performance for spatial electromagnetic waves with different operating frequencies, polarization states, and incident angles, and thus can be regarded as a filter for spatial electromagnetic waves. With the ability to flexibly control spatial electromagnetic waves, the frequency selector has long attracted attention and is widely used in many fields such as filters, electromagnetic stealth, satellite communication, and electromagnetic compatibility of electronic devices.

[0003] Traditional frequency selectors generally adopt a single-layer or multi-layer planar unit structure arranged periodically, and its structural plane and periodic plane are in the same plane, that is, a two-dimensional frequency selective surface. After the 1940s, with the gradual maturity of printed circuit board (PCB) processing technology, the structure of the two-dimensional frequency selective surface gradually changed from the traditional form to metal patches or slots etched on the PCB, and further developed into a multi-layer structure.

[0004] However, after more than a hundred years of research and development, although the design of the two-dimensional frequency selective surface has become increasingly mature and perfect, it has gradually become rigid, and its regulation performance is subject to certain limitations. In contrast, a three-dimensional frequency selector has more design dimensions, is easier to construct multiple-mode resonance paths, and can form transmission poles at multiple frequency points. By flexibly adjusting the unit structure, these transmission poles can form a transmission passband to achieve more complex and wider application range filtering characteristics.

[0005] Although the three-dimensional frequency selector has greatly improved performance, it is difficult to avoid the problems of high profile and high cost. As the size of the frequency selector increases, it will not only cause energy loss and affect transmission characteristics, but also hinder its engineering application on irregular surfaces. Thus, it can be seen that the existing technology has deficiencies and it is difficult to miniaturize the three-dimensional frequency selector. Therefore, it is necessary to draw on the experience of miniaturizing the two-dimensional frequency selective surface to effectively reduce the device size and optimize the space utilization efficiency to meet the requirements of modern electronic devices for miniaturization and lightweight, and at the same time improve the application value of the three-dimensional frequency selector in communication, stealth technology, and other electronic fields. Summary of the Invention

[0006] To solve the above problems, the present invention aims to propose a three-dimensional frequency selector based on a slow-wave loaded slot line. By arranging two-dimensionally periodically in the x-y plane and extending the slot line gaps in the z direction, a three-dimensional structure is formed to achieve the regulation of the frequency of the incident wave. After loading T-shaped metal patches on the slot line, the equivalent electrical length increases and the phase velocity decreases, enabling the structure to achieve the target spatial filtering characteristics under a compact size.

[0007] To achieve the above object, the technical solution of the present invention is realized as follows:

[0008] A three-dimensional frequency selector based on a slow-wave loaded slot line includes a plurality of periodically arranged slow-wave loaded slot line units. The slow-wave loaded slot line units adjacent along the x-axis are separated by an air layer to form a periodic gap in the x-axis direction; the slow-wave loaded slot line units are arranged periodically along the y-axis, and adjacent slow-wave loaded slot line units are directly connected; the slow-wave loaded slot line unit includes a slot line in the z-axis direction and T-shaped metal patches loaded in the slot line gap.

[0009] Further, the slow-wave loaded slot line unit includes a dielectric substrate. A first transverse metal patch and a second transverse metal patch are respectively provided at the upper and lower ends of the same surface of the dielectric substrate. There are two T-shaped metal patches in the slot line gap between the first transverse metal patch and the second transverse metal patch. The two T-shaped metal patches are arranged facing each other and connected together to form an "I-shaped metal patch", and the I-shaped metal patch is not connected to the first transverse metal patch and the second transverse metal patch.

[0010] Further, the slow-wave loaded slot line unit includes a dielectric substrate. A first transverse metal patch and a second transverse metal patch are respectively provided at the upper and lower ends of the same surface of the dielectric substrate. Two T-shaped metal patches are installed in the slot line gap between the first transverse metal patch and the second transverse metal patch. The two T-shaped metal patches are arranged back to back and not connected together to form a "double T-shaped metal patch", and the double T-shaped metal patch is connected to the first transverse metal patch and the second transverse metal patch.

[0011] Further, the slow-wave loaded slot line unit includes a dielectric substrate. A first capacitor-loaded metal patch and a second capacitor-loaded metal patch facing each other are respectively provided at the upper and lower ends of the same surface of the dielectric substrate. The first capacitor-loaded metal patch is T-shaped, and the second capacitor-loaded metal patch is in the shape of an inverted T; a lumped capacitor is connected between the vertical patches of the first capacitor-loaded metal patch and the second capacitor-loaded metal patch. There is an I-shaped metal patch in the gap on each side of the lumped capacitor between the first capacitor-loaded metal patch and the second capacitor-loaded metal patch, and the I-shaped metal patches are not connected to the first capacitor-loaded metal patch and the second capacitor-loaded metal patch.

[0012] Further, the slow-wave loaded slot-line unit includes a dielectric substrate. On the upper and lower ends of the same surface of the dielectric substrate, a first capacitively loaded metal patch and a second capacitively loaded metal patch facing each other are respectively provided. The first capacitively loaded metal patch is T-shaped, and the second capacitively loaded metal patch is in an inverted T shape. A lumped capacitor is connected between the vertical patches of the first capacitively loaded metal patch and the second capacitively loaded metal patch. There is a double-T-shaped metal patch in the slot-line gaps on both sides of the lumped capacitor for the first capacitively loaded metal patch and the second capacitively loaded metal patch. The double-T-shaped metal patch is connected to both the first capacitively loaded metal patch and the second capacitively loaded metal patch.

[0013] Further, the slow-wave loaded slot-line unit includes a dielectric substrate. On the upper and lower ends of the same surface of the dielectric substrate, a first capacitively loaded metal patch and a second capacitively loaded metal patch facing each other are respectively provided. The first capacitively loaded metal patch is T-shaped, and the second capacitively loaded metal patch is in an inverted T shape. A lumped capacitor is connected between the vertical patches of the first capacitively loaded metal patch and the second capacitively loaded metal patch. There is a double-T-shaped metal patch in the gap on the left side of the lumped capacitor for the first capacitively loaded metal patch and the second capacitively loaded metal patch. The double-T-shaped metal patch is connected to both the first capacitively loaded metal patch and the second capacitively loaded metal patch. There is an I-shaped metal patch in the gap on the right side of the lumped capacitor for the first capacitively loaded metal patch and the second capacitively loaded metal patch. The I-shaped metal patch is not connected to either the first capacitively loaded metal patch or the second capacitively loaded metal patch.

[0014] Further, the slow-wave loaded slot-line unit includes a dielectric substrate. On the upper and lower ends of the same surface of the dielectric substrate, two sets of first capacitively loaded metal patches and second capacitively loaded metal patches facing each other are respectively provided. The first capacitively loaded metal patch is T-shaped, and the second capacitively loaded metal patch is in an inverted T shape. The vertical patches of the first capacitively loaded metal patch and the second capacitively loaded metal patch are connected through a lumped capacitor. There is an I-shaped metal patch in the slot-line gap between the two lumped capacitors for the two sets of first capacitively loaded metal patches and second capacitively loaded metal patches. The I-shaped metal patch is not connected to the first capacitively loaded metal patches and the second capacitively loaded metal patches on its left and right.

[0015] Further, the lumped capacitor is used to enhance the slow-wave effect and jointly act with the vertical patches of the first capacitively loaded metal patch and the second capacitively loaded metal patch at both ends thereof and the wire-introduced inductance to form a low-frequency transmission zero point.

[0016] Further, the lumped capacitor, the T-shaped metal patch, the first capacitively loaded metal patch, and the second capacitively loaded metal patch are combined to form a multi-order frequency selector for achieving a target frequency response.

[0017] Further, the width of the slot line gap is determined by the characteristic impedance value required for the design. The wider the width, the higher the characteristic impedance; the narrower the width, the lower the characteristic impedance.

[0018] Beneficial effects: By loading an I-shaped metal patch or a double-T-shaped metal patch in the middle of the slot line gap, the present invention can increase the equivalent electrical length of the z-direction structure, thereby reducing the profile of the traditional three-dimensional frequency selector while ensuring the target resonance characteristics. Description of the Drawings

[0019] The drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0020] Figure 1 is a schematic structural diagram of a three-dimensional frequency selector based on a slow-wave loaded slot line according to an embodiment of the present invention;

[0021] Figure 2 is a front view and a side view of an I-shaped metal patch loaded on a slow-wave loaded slot line unit of a three-dimensional frequency selector based on a slow-wave loaded slot line according to an embodiment of the present invention;

[0022] Figure 3 is a front view and a side view of a double-T-shaped metal patch loaded on a slow-wave loaded slot line unit of a three-dimensional frequency selector based on a slow-wave loaded slot line according to an embodiment of the present invention;

[0023] Figure 4 is a schematic diagram of the combination of an I-shaped metal patch and a lumped capacitor loaded on a slow-wave loaded slot line unit of a three-dimensional frequency selector based on a slow-wave loaded slot line according to an embodiment of the present invention Figure 1 ;

[0024] Figure 5 is a schematic diagram of the combination of a double-T-shaped metal patch and a lumped capacitor loaded on a slow-wave loaded slot line unit of a three-dimensional frequency selector based on a slow-wave loaded slot line according to an embodiment of the present invention;

[0025] Figure 6 is a schematic diagram of the combination of an I-shaped metal patch, a double-T-shaped metal patch and a lumped capacitor loaded on a slow-wave loaded slot line unit of a three-dimensional frequency selector based on a slow-wave loaded slot line according to an embodiment of the present invention;

[0026] Figure 7 is a schematic diagram of the combination of an I-shaped metal patch and a lumped capacitor loaded on a slow-wave loaded slot line unit of a three-dimensional frequency selector based on a slow-wave loaded slot line according to an embodiment of the present invention Figure 2 ;

[0027] Figure 8 Schematic diagram of the structure of a third - order narrow - band band - pass three - dimensional frequency selector based on a slow - wave loaded slot - line according to an embodiment of the present invention;

[0028] Figure 9 Transmission characteristic parameter curve graph of a third - order narrow - band band - pass three - dimensional frequency selector based on a slow - wave loaded slot - line according to an embodiment of the present invention. Detailed implementation manners

[0029] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0030] The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0031] Embodiment 1

[0032] Refer to Figures 1-9 : A three - dimensional frequency selector based on a slow - wave loaded slot - line, including a plurality of periodically arranged slow - wave loaded slot - line units 1. The slow - wave loaded slot - line units 1 adjacent along the x - axis are separated by an air layer to form a periodic gap in the x - axis direction; the slow - wave loaded slot - line units 1 are arranged periodically along the y - axis, and adjacent slow - wave loaded slot - line units 1 are directly connected; the slow - wave loaded slot - line unit 1 includes a slot - line in the z - axis direction and a T - shaped metal patch 2 loaded in the slot - line gap.

[0033] In this embodiment, a three - dimensional structure is formed through two - dimensional periodic arrangement in the x - y plane and slot - line gap extension in the z - direction to realize the selection of the incident wave frequency; after the slot - line is loaded with T - shaped metal patches, the equivalent electrical length increases and the phase velocity of the guided wave decreases, enabling the structure to achieve the target filtering characteristics under a compact size; the periodic structure resonates at a specific frequency to form band - pass or band - stop characteristics; the loaded patches adjust the equivalent circuit parameters LC resonance to achieve the target frequency response.

[0034] In a specific example, refer to Figure 2 : The slow - wave loaded slot - line unit 1 includes a dielectric substrate 101. At the upper and lower ends of the same surface of the dielectric substrate 101, there are respectively a first transverse metal patch 102 and a second transverse metal patch 103. There are two T - shaped metal patches 2 in the slot - line gap between the first transverse metal patch 102 and the second transverse metal patch 103. The two T - shaped metal patches 2 are arranged opposite to each other and connected together to form an "I - shaped metal patch 21", and the I - shaped metal patch 21 is not connected to the first transverse metal patch 102 and the second transverse metal patch 103.

[0035] The I - shaped metal patch in this embodiment forms a distributed capacitance - inductance network, enhancing the equivalent dielectric constant and equivalent magnetic permeability of the slot - line, reducing the phase velocity of electromagnetic waves, and realizing the slow - wave effect.

[0036] In a specific example, refer to Figure 3 : The slow-wave loaded slot-line unit 1 includes a dielectric substrate 101. At the upper and lower ends of the same surface of the dielectric substrate 101, a first transverse metal patch 102 and a second transverse metal patch 103 are respectively provided. There are two T-shaped metal patches 2 in the slot-line gap between the first transverse metal patch 102 and the second transverse metal patch 103. The two T-shaped metal patches 2 are arranged back to back and not connected together to form a "double T-shaped metal patch 22", and the double T-shaped metal patch 22 is connected to the first transverse metal patch 102 and the second transverse metal patch 103.

[0037] The capacitive structure formed by the double T-shaped metal patches in this embodiment forms a distributed capacitance-inductance network, makes the capacitive effect more concentrated, further enhances the equivalent dielectric constant of the slot line, reduces the electromagnetic wave phase velocity, and enhances the slow-wave effect.

[0038] In a specific example, refer to Figure 4 : The slow-wave loaded slot-line unit 1 includes a dielectric substrate 101. At the upper and lower ends of the same surface of the dielectric substrate 101, a first capacitive loading metal patch 104 and a second capacitive loading metal patch 105 facing each other are respectively provided. The first capacitive loading metal patch 104 is T-shaped, and the second capacitive loading metal patch 105 is in the shape of an inverted T; a lumped capacitor 3 is connected between the vertical patches of the first capacitive loading metal patch 104 and the second capacitive loading metal patch 105. There is an I-shaped metal patch 21 in the gap between the first capacitive loading metal patch 104 and the second capacitive loading metal patch 105 on both sides of the lumped capacitor 3, and the I-shaped metal patches 21 are not connected to the first capacitive loading metal patch 104 and the second capacitive loading metal patch 105.

[0039] In this embodiment, the synergistic effect of the lumped capacitor and the I-shaped structure enables LC series resonance circuits to be formed at both the slot line gap and the I-shaped patches on both sides, realizing the filtering characteristics of double poles and double zeros. By adjusting the value of the lumped capacitor, the positions of the low-frequency poles and zeros can be flexibly controlled, and then the frequency ranges of the passband and the stopband can be adjusted. The relative bandwidths of the low-frequency stopband, high-frequency stopband and passband of this structure can all reach 40%, providing a high degree of tunability and performance optimization space. In addition, with the enhancement of the slow-wave effect, a 70% size reduction effect can be achieved through this structure, significantly improving the space utilization rate of the design.

[0040] In a specific example, refer to Figure 5: The slow-wave loaded slot-line unit 1 includes a dielectric substrate 101. On the upper and lower ends of the same surface of the dielectric substrate 101, there are respectively a first capacitively loaded metal patch 104 and a second capacitively loaded metal patch 105 facing each other. The first capacitively loaded metal patch 104 is T-shaped, and the second capacitively loaded metal patch 105 is in the shape of an inverted T. A lumped capacitor 3 is connected between the vertical patches of the first capacitively loaded metal patch 104 and the second capacitively loaded metal patch 105. There is a double-T metal patch 22 in the slot-line gap between the first capacitively loaded metal patch 104 and the second capacitively loaded metal patch 105 on both sides of the lumped capacitor 3, and the double-T metal patch 22 is connected to both the first capacitively loaded metal patch 104 and the second capacitively loaded metal patch 105.

[0041] The combination of the lumped capacitor and the double-T metal patch structure with bilateral capacitors in this embodiment can also achieve flexible regulation of the passband and stopband ranges. The relative bandwidth of the stopband range provided by the double-T patch structure can still reach 40%. However, compared with the I-shaped patch structure, the passband shows obvious narrowband characteristics, and the maximum relative bandwidth does not exceed 15%. Although the passband is narrow, this structure has a better slow-wave effect and can achieve a size reduction effect of nearly 80%, which is especially suitable for narrowband application scenarios.

[0042] In a specific example, refer to Figure 6 : The slow-wave loaded slot-line unit 1 includes a dielectric substrate 101. On the upper and lower ends of the same surface of the dielectric substrate 101, there are respectively a first capacitively loaded metal patch 104 and a second capacitively loaded metal patch 105 facing each other. The first capacitively loaded metal patch 104 is T-shaped, and the second capacitively loaded metal patch 105 is in the shape of an inverted T. A lumped capacitor 3 is connected between the vertical patches of the first capacitively loaded metal patch 104 and the second capacitively loaded metal patch 105. There is a double-T metal patch 22 in the gap between the first capacitively loaded metal patch 104 and the second capacitively loaded metal patch 105 on the left side of the lumped capacitor 3, and the double-T metal patch 22 is connected to both the first capacitively loaded metal patch 104 and the second capacitively loaded metal patch 105. There is an I-shaped metal patch 21 in the gap between the first capacitively loaded metal patch 104 and the second capacitively loaded metal patch 105 on the right side of the lumped capacitor 3, and the I-shaped metal patch 21 is not connected to both the first capacitively loaded metal patch 104 and the second capacitively loaded metal patch 105.

[0043] The hybrid structure of this embodiment uses both I-shaped patches and double-T patches, combining the advantages of both, and can achieve a better balance among broadband, high performance, and compact design, which is suitable for complex applications with multiple performance requirements.

[0044] In a specific embodiment, refer toFigure 7 The slow-wave loaded slot-line unit 1 includes a dielectric substrate 101. On the upper and lower ends of the same surface of the dielectric substrate 101, there are two sets of opposed first capacitive-loaded metal patches 104 and second capacitive-loaded metal patches 105. The shape of the first capacitive-loaded metal patch 104 is T-shaped, and the second capacitive-loaded metal patch 105 is an inverted T-shaped. A lumped capacitor 3 is connected between the vertical patches of the first capacitive-loaded metal patch 104 and the second capacitive-loaded metal patch 105. There is an I-shaped metal patch 21 in the slot-line gap between the two lumped capacitors 3 for the two sets of first capacitive-loaded metal patches 104 and second capacitive-loaded metal patches 105. The I-shaped metal patch 21 is not connected to the first capacitive-loaded metal patch 104 and the second capacitive-loaded metal patch 105 on its left and right.

[0045] In this embodiment, a combination of double lumped capacitors and an I-shaped metal patch is adopted, and the passband exhibits narrow-band characteristics with a relative bandwidth not exceeding 15%. However, this structure shifts the low-frequency transmission zero point to the high-frequency region, broadening the out-of-band rejection ability in the high-frequency band, and the relative bandwidth of the stopband can reach 65%. At the same time, through the optimization of the slow-wave effect, this structure realizes a size reduction of more than 60%.

[0046] In a specific example, the lumped capacitor 3 is used to enhance the slow-wave effect, and jointly acts with the vertical patches of the first capacitive-loaded metal patch 104 and the second capacitive-loaded metal patch 105 at both ends of it and the inductance introduced by the wire to form a low-frequency transmission zero point.

[0047] The lumped capacitor and the wire of this embodiment form an LC resonance unit, and a transmission zero point is formed in a specific frequency band. By optimizing the capacitance value (0.05 - 10 pF) and the wire length, the zero point position can be accurately adjusted within the range of 2 - 18 GHz, and the stopband rejection reaches -30 dB.

[0048] In a specific example, the lumped capacitor 3, the T-shaped metal patch 2, the first capacitive-loaded metal patch 104, and the second capacitive-loaded metal patch 105 are combined to form a multi-order frequency selector for achieving the target frequency response.

[0049] The multi-order structure of this embodiment realizes a filtering response of 3 orders and above through the hierarchical setting of the T-shaped patch spacing (0.2 - 0.5 mm) and the lumped capacitance value.

[0050] In a specific embodiment, there is a positive correlation between the slot line gap width and the characteristic impedance, that is, the wider the slot line gap width, the higher the characteristic impedance, and vice versa. However, the value of the characteristic impedance depends not only on the slot line gap width but is also affected by the loading structure inside the slot line gap. Specifically, based on the electromagnetic bandgap of the slow-wave structure, the characteristic impedance of the main mode of the electromagnetic wave gradually decreases to zero as the frequency increases, which greatly expands the impedance adjustment range of the slot line and provides greater flexibility in the design process. Here, taking the loading of a T-shaped metal patch as an example, in order to enhance the slow-wave effect, the lateral branch of the T-shaped metal patch is usually made as long as possible and the spacing as small as possible to achieve the best capacitive effect. On this basis, the slot width is adjusted to obtain a suitable impedance range.

[0051] In this embodiment, the design range of the slot line gap width is 2 - 9 mm, which can provide sufficient space for the internal loading components. To ensure the performance of the overall system, accurate impedance matching is required between the lumped capacitance loading part, the T-shaped patch loading part, and the input and output ports, where the impedance of the input and output ports Z0 = ηpy / px. Under this design, the adjustment of the characteristic impedance not only depends on the slot line gap width but also needs to be optimized in coordination with the loading components inside the slot line gap to ensure the high-efficiency transmission and stability of the system.

[0052] In the specific implementation, referring to Figure 8 , a three-dimensional frequency selector based on a slow-wave loaded slot line is proposed, specifically a third-order narrowband band-pass three-dimensional frequency selector. The adjacent slow-wave loaded slot line units 1 along the x-axis are separated by an air layer to form a periodic gap in the x-axis direction; the slow-wave loaded slot line units 1 are arranged periodically along the y-axis, and the adjacent slow-wave loaded slot line units are directly connected; the periodic intervals are px and py respectively, and px and py = 10 mm.

[0053] In this embodiment, the slow-wave loaded slot line unit includes a dielectric substrate, which uses Rogers4350B with a relative dielectric constant of 3.66 and a thickness of 0.762 mm; and, on the upper and lower ends of the same surface of the dielectric substrate, there are respectively a first capacitive loading metal patch and a second capacitive loading metal patch facing each other. The first capacitive loading metal patch is T-shaped, and the second capacitive loading metal patch is an inverted T-shaped. There is a certain space reserved between the first capacitive loading metal patch and the second capacitive loading metal patch to form a first slot line gap (left slot line gap), a second slot line gap (middle slot line gap), and a third slot line gap (right slot line gap), and the slot line gaps are continuously distributed in the entire slot line structure to form a complete third-order slot line;

[0054] In this embodiment, a lumped capacitor is connected between the vertical patches of the first capacitor-loaded metal patch and the second capacitor-loaded metal patch, and there is an I-shaped metal patch in the slot line gap between the left and right of the lumped capacitor, and the I-shaped metal patches are not connected to the first capacitor-loaded metal patch and the second capacitor-loaded metal patch respectively.

[0055] When the electric field direction of the incident electromagnetic wave is perpendicular to the incident plane, that is, TE polarization, the distance between the transverse strip of the I-shaped metal patch and the first capacitor-loaded metal iron sheet and the second capacitor-loaded metal patch forms a capacitive structure. The smaller the distance, the greater the capacitive effect; at the same time, the longitudinal branch of the I-shaped metal patch forms an inductive structure. The thinner the branch, the greater the inductive effect; similarly, the double-T metal patch also provides such local capacitive effect and local inductive effect. That is to say, the loaded metal patch provides an additional distributed LC series network inside the slot line, which has a crucial impact on the performance of the frequency selector.

[0056] First, since the phase constant ( ), the propagation speed of the electromagnetic wave (v), and the relative permittivity ( ) and relative permeability of the propagation medium are related ( ), that is:

[0057] =w / v=w

[0058] where w is the angular frequency of the electromagnetic wave. The capacitor changes the energy density of the electric field in the medium by affecting the electric field distribution in the structure, enhances the local concentration effect of the electric field, and has an additional binding effect on the propagation of the electromagnetic wave, increasing the relative permittivity of the structure ; similarly, the inductor increases the storage and exchange of magnetic field energy by enhancing the interaction between the electric field and the magnetic field, thereby increasing the relative permeability of the structure . The introduction of the capacitor and the inductor will both increase the phase constant of the electromagnetic wave, which means that at the same frequency, the propagation speed of the electromagnetic wave in the structure becomes slower and the wavelength is shortened. Therefore, although the frequency of the electromagnetic wave remains unchanged, its corresponding propagation distance and the required physical space are greatly reduced, thus effectively reducing the size of the structure.

[0059] Second, the LC series structure formed by the loaded metal patch provides additional transmission zeros for the three-dimensional frequency selector, that is, the phenomenon of attenuation or complete blocking of the electromagnetic wave appears at a specific frequency. The series LC circuit is composed of an inductor (L) and a capacitor (C) connected in series. The resonance frequency of this circuit (f0) is given by the following formula:

[0060] f0=

[0061] At the resonance frequency, the capacitance and inductance of the LC circuit interact, and the transmission impedance of the structure to electromagnetic waves increases sharply, resulting in the inability of electromagnetic waves to pass through. Almost all the energy is reflected, thus forming a transmission zero point. During the design, by adjusting the values of the inductance (L) and capacitance (C), that is, adjusting the dimensions of the vertical branches and horizontal strips of the I-shaped metal patch, as well as the spacing of the structure corresponding to the capacitance effect, the position of the transmission zero point can be controlled, enabling the three-dimensional frequency selector to produce an efficient frequency selection effect within a certain frequency range.

[0062] In this embodiment, the function of the lumped capacitance is similar to that of the loaded metal patch and has a larger adjustment range. While greatly enhancing the slow-wave effect, the lumped capacitance also introduces inductance through the vertical patches and wires of the first capacitance-loaded metal patch and the second capacitance-loaded metal patch at both ends, and they work together to form a low-frequency transmission zero point, thereby optimizing the frequency selectivity of the structure.

[0063] In this embodiment, the width of the slot-line gap is determined by the characteristic impedance value required by the design. The length l of the slot-line gap is generally determined in combination with the electrical length Θ, and Θ = βl, where β is the phase constant of the electromagnetic wave. It can be seen that increasing the phase constant can effectively reduce the physical size of the structure.

[0064] Taking 4.8 GHz as the target center frequency and comprehensively considering key factors such as the position of the transmission zero point and impedance matching, in this embodiment, the dimensions of the first slot-line gap and the third slot-line gap are the same, with a length of 5 mm and a width of 7.5 mm; the length of the second slot-line gap is 2 mm and the width is 2 mm. The dimensions of the I-shaped metal patches loaded inside the first slot-line gap and the third slot-line gap are the same, with the horizontal strip size of 4.6 mm × 0.5 mm and the vertical branch size of 3.05 mm × 0.2 mm. The I-shaped metal patch is adjacent to but not connected to the first capacitance-loaded patch and the second capacitance-loaded patch, and the gap between them is 0.2 mm. The value of the lumped capacitance loaded inside the second slot-line gap is 0.51 pF.

[0065] In this embodiment, referring to Figure 9As shown, the black curve represents the two-port transmission characteristics of a third-order narrowband bandpass three-dimensional frequency selector based on a slow-wave loaded slotted line. The abscissa is the frequency with the unit of GHz, and the ordinate is the S parameter with the unit of dB. The solid line is the reflection coefficient S11, and the dashed line is the transmission coefficient S21. The passband range of this structure is 4.20 - 4.91 GHz, and the center frequency f0 is 4.56 GHz. Due to the existence of parasitic parameters, the center frequency is slightly shifted. By loading metal patches and lumped capacitors, transmission zeros are introduced at 6.3 GHz and 3.07 GHz respectively, thus forming obvious stopbands in the ranges of 2.17 - 3.56 GHz and 5.35 - 9.05 GHz, significantly improving the frequency selectivity. It should be noted that the unit size of this structure is 0.762 mm × 10 mm × 12 mm, and the profile height is only 0.18λ0 (where λ0 is the wavelength at the center frequency of the passband), demonstrating excellent spatial utilization efficiency.

[0066] To further highlight the advantages of this structure, refer to Figure 9 the frequency response of a common slotted-line three-dimensional frequency selector without a slow-wave loading structure represented by the gray curve in

[0067] It can be seen that the three-dimensional frequency selector with a slow-wave loading structure achieves high frequency selectivity while maintaining good transmission performance, significantly reducing the structural size. In particular, its profile height is reduced by 70.9% compared with the common slotted-line structure. This structure has a compact size, a low profile height, and a simple manufacturing process, being easy to process, and is especially suitable for modern communication systems, radars, stealth technologies and other fields with strict requirements for miniaturization and high integration.

[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A three-dimensional frequency selector based on a slow-wave loaded slotted line, characterized in that It includes multiple periodically arranged slow-wave loaded slot-line units (1). The slow-wave loaded slot-line units (1) adjacent along the x-axis are separated by an air layer, forming a periodic gap in the x-axis direction; the slow-wave loaded slot-line units (1) are periodically arranged along the y-axis, and adjacent slow-wave loaded slot-line units (1) are directly connected; the slow-wave loaded slot-line unit (1) includes a slot line in the z-axis direction and a T-shaped metal patch (2) loaded in the slot line gap. Two T-shaped metal patches (2) are arranged facing each other and connected together to form an "I-shaped metal patch (21)", or arranged back to back and not connected together to form a "double T-shaped metal patch (22)". The I-shaped metal patch (21) or the double T-shaped metal patch (22) is horizontally arranged in the slot line gap.

2. The three-dimensional frequency selector based on a slow-wave loaded slotted line according to claim 1, wherein, The slow-wave loaded slot-line unit (1) includes a dielectric substrate (101). At the upper and lower ends of the same surface of the dielectric substrate (101), a first transverse metal patch (102) and a second transverse metal patch (103) are respectively provided. There is an I-shaped metal patch (21) in the slot line gap between the first transverse metal patch (102) and the second transverse metal patch (103), and the I-shaped metal patch (21) is not connected to the first transverse metal patch (102) and the second transverse metal patch (103).

3. The three-dimensional frequency selector based on a slow-wave loaded slot line according to claim 1, characterized in that, The slow-wave loaded slot-line unit (1) includes a dielectric substrate (101). At the upper and lower ends of the same surface of the dielectric substrate (101), a first transverse metal patch (102) and a second transverse metal patch (103) are respectively provided. There is a double T-shaped metal patch (22) in the slot line gap between the first transverse metal patch (102) and the second transverse metal patch (103), and the double T-shaped metal patch (22) is connected to the first transverse metal patch (102) and the second transverse metal patch (103).

4. The three-dimensional frequency selector based on a slow-wave loaded slot line according to claim 1, wherein, The slow-wave loaded slot-line unit (1) includes a dielectric substrate (101). At the upper and lower ends of the same surface of the dielectric substrate (101), a first capacitive loading metal patch (104) and a second capacitive loading metal patch (105) facing each other are respectively provided. The first capacitive loading metal patch (104) is T-shaped, and the second capacitive loading metal patch (105) is in the shape of an inverted T; a lumped capacitor (3) is connected between the vertical patches of the first capacitive loading metal patch (104) and the second capacitive loading metal patch (105). There is an I-shaped metal patch (21) in the slot line gap on the left and right sides of the lumped capacitor (3) for the first capacitive loading metal patch (104) and the second capacitive loading metal patch (105) respectively, and the I-shaped metal patches (21) are not connected to the first capacitive loading metal patch (104) and the second capacitive loading metal patch (105).

5. The three-dimensional frequency selector based on a slow-wave loaded slot line according to claim 1, characterized in that The slow-wave loaded slot line unit (1) comprises a dielectric substrate (101); the upper and lower ends of the same surface of the dielectric substrate (101) are respectively provided with a first capacitor loaded metal patch (104) and a second capacitor loaded metal patch (105) facing each other; the first capacitor loaded metal patch (104) is T-shaped, and the second capacitor loaded metal patch (105) is in an inverted T-shape; a lumped capacitor (3) is connected between the vertical patches of the first capacitor loaded metal patch (104) and the second capacitor loaded metal patch (105); the first capacitor loaded metal patch (104) and the second capacitor loaded metal patch (105) are respectively provided with a double T-shaped metal patch (22) in slot line gaps on the left and right sides of the lumped capacitor (3); the double T-shaped metal patch (22) is connected to both the first capacitor loaded metal patch (104) and the second capacitor loaded metal patch (105).

6. The three-dimensional frequency selector based on a slow-wave loaded slot line according to claim 1, characterized in that The slow-wave loaded slot line unit (1) comprises a dielectric substrate (101); the upper and lower ends of the same surface of the dielectric substrate (101) are respectively provided with a first capacitor loaded metal patch (104) and a second capacitor loaded metal patch (105) facing each other; the first capacitor loaded metal patch (104) is in a T-shape, and the second capacitor loaded metal patch (105) is in an inverted T-shape; a lumped capacitor (3) is connected between the vertical patches of the first capacitor loaded metal patch (104) and the second capacitor loaded metal patch (105); The patch (105) has a double T-shaped metal patch (22) in the slot line gap on the left side of the lumped capacitor (3), and the double T-shaped metal patch (22) is connected to both the first capacitor loading metal patch (104) and the second capacitor loading metal patch (105); the first capacitor loading metal patch (104) and the second capacitor loading metal patch (105) have an I-shaped metal patch (21) in the slot line gap on the right side of the lumped capacitor (3), and the I-shaped metal patch (21) is not connected to both the first capacitor loading metal patch (104) and the second capacitor loading metal patch (105).

7. The three-dimensional frequency selector based on a slow-wave loaded slot line according to claim 1, wherein The slow-wave loaded slot-line unit (1) includes a dielectric substrate (101). On the upper and lower ends of the same surface of the dielectric substrate (101), there are two sets of opposed first capacitive-loaded metal patches (104) and second capacitive-loaded metal patches (105). The shape of the first capacitive-loaded metal patch (104) is T-shaped, and the second capacitive-loaded metal patch (105) is an inverted T-shaped. The vertical patches of the first capacitive-loaded metal patch (104) and the second capacitive-loaded metal patch (105) are connected by a lumped capacitor (3). There is an I-shaped metal patch (21) in the slot-line gap between the two lumped capacitors (3) of the two sets of first capacitive-loaded metal patches (104) and second capacitive-loaded metal patches (105). The I-shaped metal patch (21) is not connected to the two sets of first capacitive-loaded metal patches (104) and second capacitive-loaded metal patches (105).

8. The three-dimensional frequency selector based on a slow-wave loaded slotted line according to any one of claims 4-7, characterized in that, The lumped capacitor (3) is used to enhance the slow-wave effect and jointly act with the vertical patches of the first capacitive-loaded metal patch (104) and the second capacitive-loaded metal patch (105) at both ends of it and the inductance introduced by the wire to form a low-frequency transmission zero point.

9. The three-dimensional frequency selector based on a slow-wave loaded slotted line according to any one of claims 4-7, wherein The lumped capacitor (3), the T-shaped metal patch (2), the first capacitive-loaded metal patch (104), and the second capacitive-loaded metal patch (105) are combined to form a multi-order frequency selector for achieving the target frequency response.

10. The three-dimensional frequency selector based on a slow-wave loaded slotted line according to any one of claims 2-7, characterized in that, The width of the slot-line gap is determined by the characteristic impedance value required by the design. The wider the width, the higher the characteristic impedance, and the narrower the width, the lower the characteristic impedance.

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