CN102255129A - Planar superconductive microstrip line resonator - Google Patents

Abstract

The invention relates to a planar superconducting microstrip line resonator, which belongs to the field of microwave technology. The resonator includes an upper superconducting thin film, a lower superconducting thin film and a dielectric substrate between the two superconducting thin films. It is characterized in that: The upper superconducting thin film is composed of a continuous and complete superconducting strip line spirally wound clockwise or counterclockwise for two to four turns from the inside to the outside. The present invention can significantly push up the spurious frequency, and push up the second harmonic frequency to about three times of the fundamental frequency. Another advantage of the planar superconducting microstrip line resonator is that it is suitable for making superconducting filters with a very wide range of relative bandwidth from 0.5% to 20%.

Description

A Planar Superconducting Microstrip Resonator

technical field

The invention belongs to the field of microwave technology, in particular to a planar superconducting microstrip line resonator.

Background technique

The filter has the function of frequency selection, that is, the signal of the required frequency is passed, and the signal of the unnecessary frequency is suppressed. It is a very important microwave component in the field of microwave engineering technology and is widely used in mobile communications, satellite communications, radar and other microwaves. communications and other fields. Since the conductivity of superconducting materials in the microwave band is two to three orders of magnitude higher than that of conventional metal materials, they are used to make filters with better performance.

The coupled resonant filter composed of microstrip line resonators is a very important realization form of microwave filter. The cross section of the planar superconducting microstrip line is shown in Fig. 1, which is composed of an upper superconducting thin film 11, a lower superconducting thin film 12 and a dielectric substrate 13 between the two superconducting thin films.

The upper superconducting thin film 11 is usually composed of a straight strip line with both ends open, and the length is about half of the corresponding wavelength of the resonant frequency on the microstrip line dielectric substrate. Due to the periodicity of the frequency response of the distribution parameter circuit of the microstrip line, this half-wavelength linear microstrip line resonator generates the second harmonic frequency and the third harmonic frequency at integer multiples of the fundamental frequency such as double frequency and triple frequency. Wait for the parasitic resonant frequency, so that the filter composed of half-wavelength microstrip line resonators produces a parasitic passband at a certain distance from the design passband. The rejection of the filter at the spurious passband is very low, causing unwanted frequency signals to pass through the filter, thereby affecting the performance of the filter. Especially when the passband of the filter is located in the dense electromagnetic spectrum area where various microwave communications such as mobile communication and cable TV are relatively dense, the requirements for the characteristics of the parasitic passband are more stringent, and the filter needs a wide stopband range outside the passband Has a good degree of inhibition.

In recent years, researchers have proposed a variety of resonator structures to improve the parasitic passband characteristics of filters. Using a 1/4 wavelength microstrip line resonator structure short-circuited at one end can make the spurious frequency appear only at odd multiples of the fundamental frequency (the second harmonic frequency is located at three times the fundamental frequency, and the third harmonic frequency is located at three times the fundamental frequency. 5 times), thereby improving the parasitic channel characteristics of the filter. However, the requirement for grounding at the short-circuit end of the 1/4 wavelength microstrip line will increase the complexity of the fabrication process, and it is also difficult to achieve grounding on brittle substrates (such as magnesium oxide MgO, lanthanum aluminate LaAlO ₃ ) (Zhou J , Lancaster M J, Huang F, IEEE Trans. Applied Supercond., 14(2004), 28). Using zigzag coupled microstrip line structure (Kuo J, Hsu W, Huang W, IEEE Microw.Wireless Compon. Lett., 12(2002), 383) and substrate suspension structure (KuoJ, Jiang M, Chang H, IEEE Trans.Microw.Theory Tech., 52(2004), 83), the purpose of suppressing frequency multiplication and spurious passband response can be achieved by balancing the odd and even mode phase velocities in the coupled microstrip line, but these two methods have great influence on the preparation process higher requirements. Using a step impedance resonator structure (Jin S, Wei B, Zhang X, et al, Microwave opt.tech.lett., 49(2007), 2097) can also move the parasitic passband of the filter to high frequencies, however The step impedance structure is generally suitable for higher frequency bands, but at low frequency bands, it faces the difficulty of large resonator size and difficulty in miniaturization.

The existing half-wavelength microstrip line resonator with the simplest structure is a linear resonator 21, as shown in FIG. 2(a). The substrate material used in the resonator is magnesium oxide MgO with a thickness of 0.5 mm and a dielectric constant ε _r of 9.71. The width of the microstrip line is 0.08mm, and the length is 96.04mm. Using the electromagnetic simulation software Sonnet to simulate the linear resonator, it can be seen that the fundamental resonance frequency (fundamental frequency) 22 is 640.85MHz, the second resonance frequency (secondary frequency) 23 is 1282.1MHz, and the third resonance frequency (third frequency) 24 It is 1924MHz, as shown in Fig. 2(b). The second resonant frequency and the third resonant frequency are about 2 times and 3 times of the fundamental resonant frequency, respectively. When the resonator resonates at the fundamental frequency, the schematic diagram of the distribution of the current along the length of the linear resonator is shown in Figure 2(c). At the same time, it flows to the other end of the microstrip line. The current in the middle of the linear resonator is large, the current at both ends is small, the port current is zero, and it is distributed in half a sine cycle; when the linear resonator resonates at the second harmonic frequency, the schematic diagram of the current distribution with the length of the linear resonator is shown in the figure As shown in 2(d), the current direction of the left and right halves of the linear resonator is opposite, the two ports and the middle current are zero, and the current is the largest at 1/4 of the total microstrip line length from both ends, showing a sinusoidal periodic distribution.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and proposes a planar superconducting microstrip line resonator, which can significantly push up the spurious frequency, and push the second harmonic frequency up to about three times the fundamental frequency Location. Another advantage of the planar superconducting microstrip line resonator is that it is suitable for making superconducting filters with a very wide range of relative bandwidth from 0.5% to 20%.

In order to achieve the above-mentioned purpose of the invention, the present invention proposes a planar superconducting microstrip resonator, comprising an upper superconducting film, a lower superconducting film and a dielectric substrate between the two superconducting films, characterized in that the The upper layer of superconducting thin film is composed of a continuous and complete superconducting strip line spirally wound clockwise or counterclockwise for two to four turns from the inside to the outside.

The above-mentioned strip lines may be formed by connecting straight strip segments, or may be formed by connecting arc-shaped strip segments.

The line width of the above-mentioned strip lines may preferably be 0.01 mm to 0.50 mm.

The line-to-line distance of the above strip lines may preferably be 0.01 mm to 0.10 mm.

Features and effects of the present invention

The invention utilizes the characteristics of the current distribution of the half-wavelength microstrip line resonator to propose a planar superconducting microstrip line resonator, which can significantly push up the spurious frequency and push the second harmonic frequency to about three times the fundamental frequency s position.

Another advantage of the planar superconducting microstrip line resonator is that due to the single helical structure of the resonator, the electromagnetic field at the fundamental frequency is relatively divergent, so it can generate a large coupling with adjacent resonators, thereby realizing a broadband filter the design of. By adjusting the distance between adjacent resonators to change the coupling coefficient, a superconducting filter with a very wide range of relative bandwidth from 0.5% to 20% is fabricated.

Description of drawings

Figure 1 is a cross-sectional view of a planar superconducting microstrip line.

Fig. 2a is a schematic diagram of a half-wavelength linear microstrip line resonator circuit.

Fig. 2b is a simulation frequency response characteristic curve of a half-wavelength linear microstrip line resonator.

Fig. 2c is a schematic diagram of the current distribution at the fundamental frequency of the half-wavelength linear microstrip line resonator.

Fig. 2d is a schematic diagram of the current distribution at the second harmonic frequency of the half-wavelength linear microstrip line resonator.

Fig. 3a is a schematic diagram of the structure of the upper superconducting thin film in the first embodiment of a planar superconducting microstrip line resonator proposed by the present invention.

Fig. 3b is a simulated frequency response characteristic curve of the structure of the first embodiment of a planar superconducting microstrip line resonator proposed by the present invention.

Fig. 4a is a schematic diagram of the structure of the upper superconducting thin film in the second embodiment of a planar superconducting microstrip line resonator proposed by the present invention.

Fig. 4b is a simulated frequency response characteristic curve of the structure of the second embodiment of a planar superconducting microstrip line resonator proposed by the present invention.

Fig. 5a is a schematic diagram of the structure of the upper superconducting thin film in the third embodiment of a planar superconducting microstrip line resonator proposed by the present invention.

Fig. 5b is a simulated frequency response characteristic curve of the structure of the third embodiment of a planar superconducting microstrip line resonator proposed by the present invention.

Fig. 6 is the implementation structure of several other variants of the upper superconducting film of a planar superconducting microstrip line resonator proposed by the present invention.

Figure 6a shows the structure of the superconducting thin film on the upper layer of the three-circle rectangular ring belt.

Figure 6b shows the structure of the superconducting thin film on the upper layer of the two-circle rectangular ring.

Figure 6c shows the structure of the upper superconducting thin film with three circles of square rings.

Figure 6d shows the structure of the superconducting thin film on the upper layer of the four-circle square ring.

Figure 6e shows the structure of the superconducting thin film on the upper layer of the three-circle fat cross-shaped annulus.

Figure 6f shows the structure of the superconducting thin film on the upper layer of the three-circle arched rectangular ring.

Figure 6g shows the structure of the upper superconducting thin film with three semicircular rings.

Figure 6h shows the structure of the superconducting thin film on the upper layer of the three-circle circular annulus.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments.

first embodiment

With reference to Fig. 1, utilize a complete microstrip line, this microstrip line is the planar superconducting microstrip line, comprises the upper layer superconducting film 11, the lower layer superconducting film 12 and the dielectric substrate 13 between two layers of superconducting films . The structure of the upper superconducting thin film 11 of this embodiment is shown in FIG. 3( a ), which is a superconducting strip line with both ends open, and the strip line is formed by three circles 31 in a counterclockwise direction from the inside to the outside. In this embodiment, the upper and lower superconducting films are made of high-temperature superconducting films, and the dielectric substrate 13 is made of magnesium oxide MgO with a thickness of 0.50 mm and a dielectric constant of 9.71.

Fig. 3(a) is a planar superconducting microstrip line resonator structure designed in this embodiment given that the fundamental frequency is 427.1MHz. The coils in this structure are all rectangular coils 31, and the outer contour of the outermost coil is 2.32 mm long and 14.4 mm wide. The total length of the strip line is 96.04 mm, the line width is 0.08 mm, and the adjacent spiral coils are equally spaced and the interval is 0.04 mm.

Fig. 3 (b) is the frequency response characteristic curve obtained by electromagnetic simulation software Sonnet simulation of the present embodiment, its fundamental frequency resonant frequency 32 is 427.1MHz, the second harmonic frequency 33 is 1220.65MHz, and the third harmonic frequency 34 is 2016.5MHz , the second harmonic frequency of the resonator is 2.87 times of the fundamental frequency, which significantly improves the spurious frequency response characteristics compared with the linear microstrip line resonator whose second harmonic frequency is about twice the fundamental frequency.

It can be seen from the above embodiments that the reason why the resonator structure of the present invention improves the spurious frequency characteristics of the resonator is that when the resonator resonates at the fundamental frequency, the current directions on adjacent microstrip lines are the same, which will generate a larger Self-inductance, which leads to the reduction of the fundamental resonant frequency of the resonator, makes the fundamental frequency of the resonator shown in Figure 3(a) only 427.1MHz, which is much lower than the fundamental frequency of the linear resonator in Figure 2(a) 640.85 MHz. When the resonator resonates at the second harmonic frequency, the current directions on adjacent microstrip lines are not exactly the same, and the self-inductance is small, which has little influence on the second harmonic frequency of the resonator, as shown in Figure 3(a) The second harmonic frequency simulation result of the resonator is 1220.65MHz, which is not much different from the second harmonic frequency 1282.1MHz of the linear resonator in Fig. 2(a). Based on the above reasons, the ratio of the second harmonic frequency to the fundamental frequency of the resonator of the present invention is much larger than that of the linear resonator, thereby improving the spurious frequency response characteristics of the resonator.

second embodiment

With reference to Fig. 1, utilize a complete microstrip line, this microstrip line is the planar superconducting microstrip line, comprises the upper layer superconducting film 11, the lower layer superconducting film 12 and the dielectric substrate 13 between two layers of superconducting films . The structure of the upper superconducting thin film 11 of this embodiment is shown in FIG. 4( a ), which is a superconducting strip line with open circuits at both ends, and the strip line wraps around 41 twice in a clockwise direction from the inside to the outside. In this embodiment, the upper and lower superconducting films are made of high-temperature superconducting films, and the dielectric substrate 13 is made of magnesium oxide MgO with a thickness of 0.50 mm and a dielectric constant of 9.71.

Fig. 4(a) is a planar superconducting microstrip line resonator structure designed in this embodiment given that the fundamental frequency is 1180MHz. The coils in this structure are all square coils 41, and the outer contour of the outermost coil is 5 mm long and 5 mm wide. The total length of the strip line is 36.6 mm, the line width is 0.2 mm, and the adjacent coils are equally spaced with a pitch of 0.04 mm.

Fig. 4 (b) is the frequency response characteristic curve obtained by the electromagnetic simulation software Sonnet simulation of this embodiment, its fundamental frequency resonant frequency 42 is 1180MHz, and the second harmonic frequency 43 is 3553MHz, which is 3.01 times of the fundamental frequency.

third embodiment

With reference to Fig. 1, utilize a complete microstrip line, this microstrip line is the planar superconducting microstrip line, comprises the upper layer superconducting film 11, the lower layer superconducting film 12 and the dielectric substrate 13 between two layers of superconducting films . The structure of the upper superconducting thin film 11 of this embodiment is shown in FIG. 5( a ), which is a superconducting strip line with open circuits at both ends, and the strip line is composed of four circles 51 in a clockwise direction from inside to outside. In this embodiment, the upper and lower superconducting films are made of high-temperature superconducting films, and the dielectric substrate 13 is made of magnesium oxide MgO with a thickness of 0.50 mm and a dielectric constant of 9.71.

Fig. 5(a) is a planar superconducting microstrip line resonator structure designed in this embodiment given that the fundamental frequency is 488.4MHz. The coils in this structure are all square coils 51, and the outer contour of the outermost coil is 5 mm long and 5 mm wide. The total length of the strip line is 76.56 mm, the line width is 0.04 mm, and the adjacent spiral coils are equally spaced and the interval is 0.02 mm.

Fig. 5 (b) is the frequency response characteristic curve obtained by the electromagnetic simulation software Sonnet simulation of this embodiment, its fundamental frequency resonant frequency 52 is 488.4MHz, and the second harmonic frequency 53 is 1465.7MHz, which is 3.0 times of the fundamental frequency.

The above-mentioned embodiment is only an example to illustrate the present invention, but the present invention is not limited thereto, and various deformations and different numbers of turns can be carried out on this basis, such as but not limited to the rectangle in Fig. 6(a)-(h), Square, cross, rectangle with an arch at one end, semicircle, and circle. In addition, although the magnesium oxide MgO substrate is selected in the above embodiment, substrates of other materials such as lanthanum aluminate LaAlO ₃ substrate and sapphire can be used as required. These deformations should also belong to the same design concept of the present invention, and all should be within the protection scope of the present invention.

Claims (4)

1. A planar superconducting microstrip line resonator, comprising an upper superconducting film, a lower superconducting film and a dielectric substrate positioned between two layers of superconducting films, is characterized in that, said upper superconducting film is a A continuous and complete superconducting strip line consists of two to four helical turns clockwise or counterclockwise from the inside to the outside. 2 . The resonator according to claim 1 , wherein the strip lines are formed by connecting linear strip segments or by connecting arc-shaped strip segments. 3 . 3. The resonator according to claim 1, wherein the strip line has a line width of 0.01 mm to 0.50 mm. 4. The resonator according to claim 1, wherein the distance between the strip lines is 0.01 mm to 0.10 mm.

Images