A six-order high-temperature superconducting very narrow band pass filter

Abstract

The application discloses a kind of topological structure and six-order high-temperature superconducting extremely narrow band band-pass filter, belong to microwave communication technical field.Aiming at the problems, such as low control degree of freedom, large size or frequency disturbance, that existing extremely narrow band filter is difficult to accurately control interstage coupling coefficient under fixed size, a kind of six-order loading stub interdigital resonator array structure based on HTS film is provided.The structure includes six same-frequency resonant units, each unit integrates upper interdigital capacitance enhancement part, lower double-helix magnetic field decoupling part, and adjustable coupling stub part around the interdigital part;By adjusting the length difference of two sides stub, the odd mode coupling coefficient between adjacent resonators is dynamically controlled under the premise of keeping the total electrical length constant, and high-precision coupling control is realized without changing the pitch and center frequency.The filter center frequency in the application is 1170.6 MHz, the 3-dB relative bandwidth is 0.09%, and the insertion loss is less than 0.1 dB, with the characteristics of miniaturization, high selectivity and high reliability.

Description

Technical Field

[0001] This invention relates to the field of microwave communication technology, and more specifically, to a sixth-order high-temperature superconducting ultra-narrow bandpass filter. Background Technology

[0002] Radio astronomy observations place extremely high demands on the sensitivity and spectral purity of the front-end receiver. Among these requirements, the radio frequency bandpass filter must achieve "zero" loss signal passage within an extremely narrow bandwidth, while suppressing out-of-band radio interference.

[0003] Current research on ultra-narrow bandpass filter design mainly focuses on weakly coupled resonators and the introduction of secondary coupling structures. However, weakly coupled resonators generally face the problem of low degree of freedom in controlling the coupling coefficient; their coupling degree largely depends on the fine-tuning of the resonator spacing, which limits design flexibility. On the other hand, while introducing secondary coupling structures can improve performance, it significantly increases the overall size of the device, and the additional coupling it may generate can interfere with the resonator's natural frequency, further increasing design complexity. These inherent limitations severely restrict the design freedom of filters in complex application scenarios.

[0004] High-temperature superconducting (HTS) thin films, as a novel material, possess extremely low surface resistivity and excellent out-of-band rejection capability, while significantly reducing insertion loss. Combining metamaterial coupling structures with resonators, and precisely controlling the coupling coefficients between resonators, holds promise for a comprehensive improvement in filter performance. However, existing HTS ultra-narrowband filter technology still has significant shortcomings in miniaturization, coupling accuracy, batch consistency, and power capacity. A new resonance and coupling mechanism is urgently needed to achieve an integrated design of high-order, ultra-narrowband, high selectivity, and high reliability without sacrificing the low insertion loss advantage of superconductivity. Summary of the Invention

[0005] In view of the shortcomings of existing technologies, this invention provides a sixth-order high-temperature superconducting ultra-narrow bandpass filter. This invention achieves precise control of the coupling coefficient of the sixth-order ultra-narrow bandpass filter by loading an array of interdigital resonators with adjustable stubs onto an HTS thin film, realizing an integrated design of ultra-narrow band, high selectivity, and high reliability.

[0006] The technical means employed in this invention are as follows:

[0007] A sixth-order high-temperature superconducting ultra-narrow bandpass filter includes an input feed line, an output feed line, and six resonant units arranged sequentially along the signal transmission direction on a high-temperature superconducting thin film substrate. Each resonant unit has the same resonant frequency and forms a coupled resonant chain. The input feed line and the output feed line are respectively coupled to the first and last resonant units to realize energy excitation and extraction. Each of the resonant units integrates a composite resonant structure, which includes a magnetic field decoupling section at the top, an interdigital capacitance enhancement section at the bottom, and adjustable coupling stub sections disposed on both sides of the magnetic field decoupling section and the interdigital capacitance enhancement section. The interdigital capacitance enhancement section is composed of interdigital microstrip lines arranged on the left and right; the magnetic field decoupling section is a microstrip line structure with a double helix configuration; the adjustable coupling stub section is composed of a pair of stubs whose lengths can be independently adjusted but whose total electrical length remains constant; the electromagnetic field of the adjustable coupling stub section is strongly coupled with the interdigital capacitance enhancement section and participates in the overall resonance; by adjusting the length difference between the two stubs, the odd-mode coupling coefficient between adjacent resonant units is dynamically controlled. The input feed line and the output feed line are symmetrically coupled to the adjustable coupling stub of the first and last resonant units, so that the external excitation is directly controlled by the adjustment state of the coupling coefficient.

[0008] Furthermore, the interdigital capacitor enhancement section includes approximately 28 interdigital microstrip lines arranged in an interlaced manner, with the spacing between adjacent interdigital microstrip lines not exceeding 0.1 mm.

[0009] Furthermore, in the adjustable coupling stub section of any resonant unit, the length of the stubs on both sides is adjusted as follows: the sum of the stub lengths is 13.24 mm, and the length difference range is ±0.18 mm.

[0010] Furthermore, the center frequency of the filter is 1170.6 MHz ± 5 MHz, the 3-dB relative bandwidth is 0.09% ± 0.01%, and the insertion loss in the passband does not exceed 0.1 dB.

[0011] Furthermore, the high-temperature superconducting thin film substrate is a double-sided YBCO thin film MgO wafer with a thickness of 0.5 mm and a dielectric constant of 9.78.

[0012] Furthermore, the spacing between the six resonant units is 0.28mm, 0.32mm, 0.32mm, 0.32mm and 0.28mm respectively.

[0013] Furthermore, the filter is applied to the front end of a radio astronomy receiver, a deep space exploration communication system, or a quantum sensing signal conditioning circuit.

[0014] Compared with the prior art, the present invention has the following advantages: The high-order high-temperature superconducting ultra-narrow bandpass filter of this invention can be applied to communications with strong anti-interference and high selectivity, and has a simple structure. The structure comprises six interdigital resonant units with loaded stubs, each with the same resonant frequency. To achieve precise control of the interstage coupling coefficient without changing the interstage resonator distance and the overall filter size, the coupling coefficient is precisely controlled by loading stubs and adjusting their lengths. Through reasonable design and circuit optimization, a sixth-order superconducting ultra-narrow bandpass filter was finally designed. The circuit size is 0.126 × 0.068 mm. ,in With a waveguide wavelength of 1170.6 MHz and a compact size, the miniaturization effect of the loaded stub interdigital resonator is verified.

[0015] Furthermore, this invention employs an ultra-narrow bandpass filter made of high-temperature superconducting dielectric material, which exhibits low loss and can improve the sensitivity of communication systems. The center frequency of the superconducting ultra-narrow bandpass filter is located at 1170.6 MHz, with a 3-dB relative bandwidth (FBW) of 0.09% and an insertion loss of less than 0.1 dB within the operating frequency band, demonstrating the excellent low insertion loss performance of superconducting technology. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of a sixth-order high-temperature superconducting ultra-narrow bandpass filter structure in an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the filter unit structure in an embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the magnetic field decoupling unit in an embodiment of the present invention.

[0020] Figure 4 This is a schematic diagram showing the relationship between the stub length and coupling coefficient of a sixth-order high-temperature superconducting ultra-narrow bandpass filter in an embodiment of the present invention.

[0021] Figure 5 This is a schematic diagram showing the relationship between the frequency and S-parameters of a sixth-order high-temperature superconducting ultra-narrow bandpass filter in an embodiment of the present invention.

[0022] In the figure: 1. Input feed line; 2. Output feed line; 3. Resonant unit; 301. Left loading stub; 302. Right loading stub; 3031. Right cross-finger microstrip line; 3032. Left cross-finger microstrip line; Right cross-finger connecting microstrip line; 3034. Left cross-finger connecting microstrip line; 304. Magnetic field decoupling unit. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0024] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0025] like Figure 1 As shown, this invention provides a sixth-order high-temperature superconducting ultra-narrow bandpass filter, including an input feed line 1, an output feed line 2, and six resonant units 3 arranged sequentially along the signal transmission direction on a high-temperature superconducting thin film substrate. Each resonant unit 3 has the same resonant frequency and forms a coupled resonant chain. The input feed line 1 and the output feed line 2 are respectively coupled to the first and last resonant units to achieve energy excitation and extraction. In this embodiment, the high-temperature superconducting thin film substrate is a double-sided YBCO thin film MgO wafer with a thickness of 0.5 mm and a dielectric constant of 9.78. The input feed line 1 and the output feed line 2 are symmetrically coupled to the adjustable coupling stubs of the first and last resonant units, so that the external excitation is directly controlled by the adjustment state of the coupling coefficient.

[0026] Furthermore, such as Figure 2As shown, each of the resonant units integrates a composite resonant structure, which includes a magnetic field decoupling section 304 at the top, an interdigital capacitance enhancement section at the bottom, and adjustable coupling stub sections disposed on both sides of the magnetic field decoupling section and the interdigital capacitance enhancement section. The interdigital capacitance enhancement section is composed of a right interdigital microstrip line 3031 and a left interdigital microstrip line 3032 arranged left and right. The magnetic field decoupling section 304 is a microstrip line structure with a double helix configuration. The adjustable coupling stub section is composed of a left-loaded stub line 301 and a right-loaded stub line 302, whose lengths can be independently adjusted but whose total electrical length remains constant. The electromagnetic field of the adjustable coupling stub section is strongly coupled with the interdigital capacitance enhancement section and participates in the overall resonance. By adjusting the length difference between the two stub lines, the odd-mode coupling coefficient between adjacent resonant units is dynamically controlled.

[0027] Specifically, the interdigital capacitance enhancement section includes 14 pairs of interdigital microstrip lines arranged in a staggered pattern, with a spacing between adjacent interdigital microstrip lines not exceeding 0.1 mm. In this application, the resonant unit is based on a traditional interdigital resonator, with an interdigital structure at its upper end, which helps to lower the center frequency of the resonator. It should be noted that adding the interdigital structure increases the center frequency. f The reason for the 0-dropout technique lies in the fact that the interdigital structure greatly enhances the resonator's self-capacitance (C) at the fundamental frequency. The increase in capacitance leads to a higher resonant frequency. f The reduction to 0. In this embodiment, 28 interdigitated fingers are preferred, with an interdigitated finger spacing of 0.08 mm, thereby achieving device miniaturization. The lower end adopts a symmetrical double-helix in-helix-out-helix structure. The current directions on adjacent wires in the double-helix structure are opposite. The currents flowing in opposite directions through the helical path cause their radiated coupling fields to cancel each other in space, thereby reducing the coupling strength and effectively reducing the coupling between adjacent resonators. Furthermore, a stub is loaded at the upper end to form an enclosing structure around the interdigitated resonator and participate in the overall resonance during the resonance process. By adjusting the number of interdigitated fingers at the upper end, the overall coupling strength of the resonator can be weakened; at the same time, by precisely controlling the length of the loaded stub, the interstage coupling coefficient can be flexibly adjusted. When adjusting the stub length, if the length of one end is increased, the other end is shortened accordingly to maintain the stability of the center frequency.

[0028] In the design of extremely narrow bandpass filters, the following formula is commonly used to calculate the coupling coefficient between resonators:

[0029] in, The coupling coefficient between the i-th resonator and the (i+1)-th resonator is represented by FBW, where FBW is the relative fractional bandwidth of the filter. gi and gi+1 are the normalized trapezoidal network element parameters of the prototype low-pass filter, representing the normalized values ​​of series inductors or parallel capacitors. These values ​​can be obtained by looking up tables or through synthesis formulas based on the filter type and order. After impedance and frequency denormalization, they can be converted into actual circuit element values. In this embodiment, an extremely narrow bandpass filter is designed according to design specifications, including bandwidth, center frequency, and filter order, thereby obtaining the required coupling coefficient. Figure 4 By extracting the relationship between the coupling coefficient and the stub length, we can determine that the total stub length in this embodiment is 13.24 mm, and the length difference range of ±0.18 mm is a result obtained later in the filter performance optimization. The change in coupling coefficient corresponding to the increase in a stub length can be determined through... Figure 4 The relationship between the coupling coefficient and the stub length was derived, and Figure 4 shows the relationship between the coupling coefficient extracted from the two resonator units and the stub length. The results show that as the stub length increases, the coupling coefficient between the resonators first decreases and then increases. Combined with filter design specifications, this can be used to determine the approximate length of the loaded stub for the resonator.

[0030] This method effectively overcomes the limitations of traditional narrowband filters in coupling coefficient control. This innovative design enables precise control of the interstage coupling coefficients of high-temperature superconducting ultra-narrowband bandpass filters, without changing the resonant frequency or resonator spacing, and ensures excellent sideband selectivity.

[0031] The magnetic field decoupling unit 304 is located in the upper region of each loaded stub interdigital resonant unit, such as... Figure 3 As shown, it consists of symmetrically arranged microstrip lines extending in a planar spiral: the input-side spiral trace starts from the input feed line or the coupling point of the preceding resonant unit, circles clockwise (or counterclockwise) 1.5–2 times, terminates at one side of the bottom of the resonator body, and connects to the output-side spiral trace. Starting from the other side, it circles in the same direction in the opposite direction 1.5–2 times, then connects to the output feed line. The geometric centers of the spiral traces coincide, the linewidth matches the substrate dielectric thickness, and the spiral spacing is controlled at 0.08 mm.

[0032] In this embodiment, the spacing between the six resonant units in the filter is 0.28mm, 0.32mm, 0.32mm, 0.32mm and 0.28mm respectively, and the center frequency of the filter is 1170.6 MHz ± 5 MHz, the 3-dB relative bandwidth is 0.09% ± 0.01%, and the insertion loss in the passband does not exceed 0.1 dB.

[0033] Furthermore, the filter of the present invention can be applied to the front end of a radio astronomy receiver, a deep space exploration communication system, or a quantum sensing signal conditioning circuit.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sixth-order high-temperature superconducting ultra-narrow bandpass filter, comprising an input feed line, an output feed line, and six resonant units arranged sequentially along the signal transmission direction on a high-temperature superconducting thin film substrate. Each resonant unit has the same resonant frequency and forms a coupled resonant chain. The input feed line and the output feed line are respectively coupled to the first and last resonant units to realize energy excitation and extraction. Its features are, Each of the resonant units integrates a composite resonant structure, which includes a magnetic field decoupling section at the top, an interdigital capacitance enhancement section at the bottom, and adjustable coupling stub sections disposed on both sides of the magnetic field decoupling section and the interdigital capacitance enhancement section. The interdigital capacitance enhancement section is composed of interdigital microstrip lines arranged on the left and right; the magnetic field decoupling section is a microstrip line structure with a double helix configuration; the adjustable coupling stub section is composed of a pair of stubs whose lengths can be independently adjusted but whose total electrical length remains constant; the electromagnetic field of the adjustable coupling stub section is strongly coupled with the interdigital capacitance enhancement section and participates in the overall resonance; by adjusting the length difference between the two stubs, the odd-mode coupling coefficient between adjacent resonant units is dynamically controlled. The input feed line and the output feed line are symmetrically coupled to the adjustable coupling stub of the first and last resonant units, so that the external excitation is directly controlled by the adjustment state of the coupling coefficient.

2. A sixth-order high-temperature superconducting ultra-narrow bandpass filter according to claim 1, characterized in that, The interdigital capacitor enhancement section includes approximately 28 interdigital microstrip lines arranged in an interlaced manner, with the spacing between adjacent interdigital microstrip lines not exceeding 0.1 mm.

3. A sixth-order high-temperature superconducting ultra-narrow bandpass filter according to claim 1, characterized in that, In the adjustable coupling stub section of any resonant unit, the length of the stubs on both sides is adjusted as follows: the sum of the stub lengths is 13.24 mm, and the length difference range is ±0.18 mm.

4. A sixth-order high-temperature superconducting ultra-narrow bandpass filter according to claim 1, characterized in that, The filter has a center frequency of 1170.6 MHz ± 5 MHz, a 3-dB relative bandwidth of 0.09% ± 0.01%, and an insertion loss of no more than 0.1 dB within the passband.

5. A sixth-order high-temperature superconducting ultra-narrow bandpass filter according to claim 1, characterized in that, The high-temperature superconducting thin film substrate is a double-sided YBCO thin film MgO wafer with a thickness of 0.5 mm and a dielectric constant of 9.

78.

6. A sixth-order high-temperature superconducting ultra-narrow bandpass filter according to claim 1, characterized in that, The spacing between the six resonant units is 0.28mm, 0.32mm, 0.32mm, 0.32mm and 0.28mm respectively.

7. A sixth-order high-temperature superconducting ultra-narrow bandpass filter according to claim 1, characterized in that, The filter is used in the front end of radio astronomy receivers, deep space exploration communication systems, or quantum sensing signal conditioning circuits.

Images