Surface acoustic wave trap

Abstract

This invention discloses a surface acoustic wave (SAW) notch filter, belonging to the field of radio frequency (RF) technology. The resonator group of this SAW notch filter includes a series arm resonator and a parallel arm resonator; the series arm resonator includes an interdigital transducer and reflectors located on both sides of the interdigital transducer. When the spacing p2 between the reflectors and the spacing p1 between the interdigital transducers satisfy 0.94×p1 ≤ p2 ≤ 0.98×p1, a second mode is controllably excited between the resonant frequency and the anti-resonant frequency, effectively suppressing the clutter frequency response on the high-frequency side of the notch filter. When the spacing p3 between the interdigital transducers and the reflectors satisfies p3=T×(p1+p2) / 2, and 0.92≤T≤0.96, p2 and p3 work synergistically to further improve the suppression effect. This invention, by precisely controlling the reflector spacing and the spacing between the interdigital transducers and the reflectors, excites the second mode to reduce the clutter frequency response on the right side of the anti-resonant point, while simultaneously obtaining a lower S21 value, a steeper transition band characteristic, and better rectangularity.

Description

Technical Field

[0001] This invention relates to the field of radio frequency technology, and more particularly to surface acoustic wave (SAW) notch filters. Background Technology

[0002] A notch filter is a filter that can suppress signals of specific frequencies and is widely used in applications such as interference suppression, signal clarity improvement, and system stability enhancement. In modern communication systems, many unwanted interference signals exist, which can affect the normal operation of the system. Therefore, designing an efficient and flexible surface acoustic wave (SAW) notch filter to accurately control and suppress these interference frequencies is of great significance for improving communication quality.

[0003] Existing surface acoustic wave (SAW) notch filters typically employ a trapezoidal topology, consisting of multiple series-arm resonators and parallel-arm resonators. In this structure, the frequency response characteristics of the resonators are mainly determined by geometric parameters such as the electrode finger spacing of the interdigital transducers, the electrode finger spacing of the reflectors, and the spacing between the interdigital transducers and the reflectors.

[0004] However, existing surface acoustic wave (SAW) notch filters still have the following technical problems in practical applications: In existing resonator designs, when the spacing between reflectors is equal to or close to the spacing between interdigital transducers, the resonator exhibits a strong parasitic response to the right of the anti-resonance point (high-frequency side). This parasitic response leads to a decrease in the notch filter's suppression effect, an increase in insertion loss, and affects the signal quality of the system.

[0005] The transition band between the passband and stopband of existing notch filters is not steep enough, resulting in poor frequency selectivity and difficulty in accurately distinguishing adjacent frequency signals, which limits their application in dense frequency band communication systems.

[0006] Existing notch filters typically require maintaining perfect periodicity of the resonator structure, but this exacerbates parasitic responses on the high-frequency side. Adjusting structural parameters to suppress parasitic responses may, in turn, impair the quality factor at the anti-resonance point, affecting the stopband suppression depth. This interrelationship among performance indicators makes it difficult for existing surface acoustic wave (SAW) notch filters to simultaneously achieve a comprehensive performance of high suppression depth, low insertion loss, and a steep transition band.

[0007] Existing technologies generate additional modes between the resonant frequency and the anti-resonant frequency, which degrades the performance of the resonator. In order to reduce the generation of spurious modes, there is a lack of active utilization of additional modes to improve filter performance.

[0008] Therefore, how to controllably introduce additional modes in a surface acoustic wave (SAW) notch filter by precisely controlling the geometric parameters of the resonator, while maintaining the high performance of the main resonant mode, thereby suppressing parasitic responses, improving the steepness of the transition band, and optimizing the overall filtering performance, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0009] This invention proposes a surface acoustic wave notch filter to address how to improve the suppression of parasitic responses to the right of the anti-resonant frequency, how to improve the transition band characteristics between the passband and stopband and increase the steepness of the transition band, and how to achieve controllable additional mode excitation and use it to improve filter performance.

[0010] The core technical solution of this invention is as follows: by setting the geometric relationship between the reflector spacing p2 and the IDT spacing p1, and the geometric relationship between the IDT and the reflector spacing p3, the second mode can be controllably excited between the resonant frequency and the anti-resonant frequency; the parasitic response on the right side of the anti-resonant frequency is suppressed, and the performance of notch filter clutter suppression and transition band steepness is improved through the synergistic optimization of p2 and p3.

[0011] The specific solution of the present invention is as follows: A surface acoustic wave trap, comprising: A resonator group consisting of multiple resonators, the resonator group including multiple series arm resonators and multiple parallel arm resonators; The resonator includes an interdigital transducer; and reflectors disposed on both sides of the interdigital transducer along the direction of surface acoustic wave propagation. The interdigitated transducer includes multiple first electrode fingers and multiple second electrode fingers inserted in an alternating manner; the reflector includes multiple third electrode fingers arranged periodically. The spacing between adjacent first electrode fingers and second electrode fingers is set as p1, the spacing between adjacent third electrode fingers is set as p2, and the spacing between adjacent third electrode fingers and first electrode fingers, or adjacent third electrode fingers and second electrode fingers, is set as p3. At least one series arm resonator, when p2 satisfies the condition 0.94×p1≤p2≤0.98×p1, excites a second mode that coexists with the main resonant mode between the resonant frequency and the anti-resonant frequency of the resonator. The second mode is used to suppress the clutter frequency response to the right of the anti-resonant frequency.

[0012] Furthermore, when the frequency response of the second mode is enhanced, the position of the resonant frequency and the anti-resonant frequency of the main resonant mode is not changed, while the clutter frequency response to the right of the anti-resonant frequency is reduced.

[0013] Furthermore, when p2 satisfies the condition 0.96×p1≤p2≤0.98×p1, as p2 decreases, the S21 value of the surface acoustic wave notch filter tends to 0, and the rectangularity of the surface acoustic wave notch filter remains stable with a change rate of less than 3%.

[0014] Furthermore, when p2 satisfies the condition 0.94×p1≤p2≤0.96×p1, as p2 increases, the rectangularity of the surface acoustic wave notch filter tends to decrease to 1. When p2 is less than 0.94×p1, the rectangularity of the surface acoustic wave notch filter undergoes a nonlinear abrupt change.

[0015] Furthermore, the p3 condition satisfies p3=T×(p1+p2) / 2. When 0.92≤T≤0.96, the decrease of T causes the clutter frequency response to the right of the anti-resonance frequency to decrease simultaneously.

[0016] Furthermore, the p3 condition satisfies p3=T×(p1+p2) / 2, and when 0.92≤T≤0.96, the value of the surface acoustic wave notch filter S21 is -0.757dB to -0.73dB.

[0017] Furthermore, when p2 and p3 are optimized together, the value of the surface acoustic wave notch filter S21 is less than the value of the surface acoustic wave notch filter S21 when p2 or p3 is optimized alone.

[0018] The present invention has the following technical effects: Effectively suppress high-frequency parasitic response This invention precisely controls the geometric parameters of the resonator, setting the reflector spacing p2 to satisfy 0.94×p1≤p2≤0.98×p1, and setting the IDT and reflector spacing p3 to satisfy p3=T×(p1+p2) / 2, 0.92≤T≤0.96. Within this parameter range, a second mode is excited, and the clutter frequency response of the resonator to the right of the anti-resonance frequency is effectively suppressed, improving the notch filter's ability to suppress high-frequency interference signals and improving the system's signal quality.

[0019] 2. Increase the steepness of the transition zone and enhance frequency selectivity. This invention changes the impedance characteristics of the resonator in the transition band region by controllably introducing a second mode between the resonant frequency and the anti-resonant frequency, resulting in lower loss and a steeper transition band in the notch filter between the passband and stopband, reduced rectangularity, and improved frequency selectivity.

[0020] 3. The main resonant mode and the second mode coexist, and p2 and p3 work together to improve the overall filtering performance. This invention effectively excites the second mode and suppresses parasitic response by synergistically optimizing p2 and p3 without affecting the main resonant mode. Compared with optimizing p2 or p3 alone, synergistic optimization enables the notch filter to have comprehensive performance of high suppression depth, low insertion loss and steep transition band.

[0021] In summary, the surface acoustic wave notch filter provided by this invention, through precise design of the resonator geometry parameters, can controllably introduce a second mode while maintaining the performance of the main resonant mode unaffected, thereby effectively suppressing parasitic responses, improving the steepness of the transition band, and enhancing filtering performance. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a surface acoustic wave resonator 100 in the prior art; Figure 2 A schematic diagram showing the spacing p1 of the IDT, the spacing p2 of the reflector, and the spacing p3 between the IDT and the reflector; Figure 3 This is a topological schematic diagram of the surface acoustic wave notch filter 200 of the present invention; Figure 4 Admittance / conductance-frequency curves for different N values; Figure 5 The S21-frequency comparison diagram of the surface acoustic wave notch filter 200 when N is 0.96, 0.97, 0.98, 0.99 and 1 respectively; Figure 6 The S21-frequency comparison diagram of the surface acoustic wave notch filter 200 when N is 0.96, 0.95, 0.94, 0.93 and 0.92 respectively; Figure 7 Admittance / conductance-frequency curves for different voltage levels (T); Figure 8 The S21-frequency comparison diagram shows the surface acoustic wave notch filter 200 with T values ​​of 0.96, 0.95, 0.94, 0.93 and 0.92 respectively. Figure 9 The graph shows the S21 value of the surface acoustic wave trap 200 as a function of T. Figure 10 The S21-frequency comparison diagram of the surface acoustic wave notch filter 200 when T is 0.92 and 1 respectively. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 are within the scope of protection of the present invention.

[0024] It should be noted that the terms "first" and "second" used in the following description are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "multiple" means two or more.

[0025] Device Description: Figure 1 A schematic top view and cross-sectional view of a typical surface acoustic wave (SAW) resonator 100 based on a piezoelectric substrate are shown. The SAW resonator 100 based on the piezoelectric substrate 1 consists of an interdigital transducer (IDT) and a reflector formed on the piezoelectric substrate 1, wherein the reflectors are disposed on both sides of the IDT in the direction of SAW propagation. The piezoelectric substrate 1 is a single-layer or multi-layer substrate made of a piezoelectric material, such as lithium niobate, lithium tantalate, gallium nitride, aluminum nitride, or zinc oxide.

[0026] Admittance: A physical quantity describing the response of a circuit element to alternating current and voltage, usually denoted by the symbol Y. For a circuit element, its admittance Y is equal to the ratio of its conductance G to its susceptance B, i.e., Y = G + jB, where j is the imaginary unit. In this embodiment, admittance (dB) can be expressed by the formula Y = 20 × log0 10 |Y| is obtained.

[0027] Furthermore, the interdigital transducer includes multiple first electrode fingers 2a and multiple second electrode fingers 2b inserted in an alternating manner, and a first busbar 4a and a second busbar 4b that are opposed to each other in the extension direction of the first electrode fingers 2a and the second electrode fingers 2b; the reflector includes multiple third electrode fingers 2c arranged periodically, and a third busbar 4c and a fourth busbar 4d that are opposed to each other in the extension direction of the third electrode fingers 2c.

[0028] The direction parallel to the x-axis in the coordinate system is defined as the electrode finger arrangement direction, which is also the surface acoustic wave propagation direction. The direction parallel to the y-axis in the coordinate system is defined as the electrode finger extension direction. The direction parallel to the z-axis in the coordinate system is defined as the height direction of the surface acoustic wave resonator 100.

[0029] like Figure 2As shown, the distance λ between adjacent first (or second) electrode fingers is typically referred to as the "wavelength" of the IDT. The overlap distance AP between the first and second electrode fingers is typically referred to as the "aperture" of the IDT. The distance p1 between adjacent first and second electrode fingers is typically referred to as the "spacing" of the IDT. The distance p2 between adjacent third electrode fingers is typically referred to as the "spacing" of the reflector, and the distance p3 between adjacent third electrode fingers and the first (or second) electrode fingers is typically referred to as the "spacing" of the IDT and the reflector.

[0030] Figure 3 A topological schematic diagram of the surface acoustic wave (SAW) notch filter 200 provided in Embodiment 1 of the present invention is shown. Specifically, the SAW notch filter 200 includes an input port (IN), an output port (OUT), and a resonator group. The resonator group includes multiple series resonators and multiple parallel resonators. The signal is input from the IN port and output from the OUT port after processing. The series resonators are connected to the main signal transmission path from IN to OUT, and one end of the parallel resonator is connected to the signal path, while the other end is grounded, forming a branch path from the signal to ground. The impedance characteristics of the series and parallel resonators are used to achieve a filtering effect. At frequencies where the signal needs to pass, the series resonators exhibit low impedance, allowing the signal to pass smoothly; while the parallel resonators exhibit high impedance, preventing the signal from flowing to ground. At frequencies where suppression is needed, the situation is reversed: the series resonators exhibit high impedance, blocking the signal, while the parallel resonators exhibit low impedance, short-circuiting the interference signal to ground, thereby achieving the notch filtering function.

[0031] Optimization of reflector spacing p2 After determining the circuit topology, the reflector spacing p2 of the series arm resonator was further refined. In conventional resonators, the generation of other modes between the resonant frequency and the anti-resonant frequency degrades the resonator's performance. In this invention, p2 = N*p1 is set for any series arm resonator. Through the optimized design of N, the aim is to enable the resonator to excite a second mode in addition to the main resonant mode.

[0032] Generally speaking, the appearance of a second mode between the resonant frequency and the anti-resonant frequency of a resonator will increase the insertion loss and ripple of the filter's operating band. However, for a notch filter, a moderate increase in the insertion loss and ripple of the operating band will not affect the overall performance of the notch filter.

[0033] The second mode is controlled to occur between the resonant frequency and the anti-resonant frequency of the resonator. This second mode does not affect the main resonant mode; instead, it suppresses the clutter frequency response to the right of the anti-resonant frequency. The second mode coexists with the main resonant mode in the frequency domain. The excitation of the second mode does not change the position of the resonant frequency and the anti-resonant frequency of the main resonant mode, and the amplitude of the clutter frequency response to the right of the anti-resonant frequency decreases.

[0034] Figure 4 The admittance / conductance-frequency curves of the series arm resonator with different values ​​of N are shown. From the conductance curves, it can be seen that in the range of N = 0.94 to 1.04, as N increases, for example, approaching or exceeding 1, a significant parasitic peak appears to the right of the anti-resonant frequency, and the frequency response to the right of the anti-resonant frequency gradually strengthens. These parasitic responses deteriorate the notch filter's suppression performance at high frequencies. As N decreases to less than 1, a second mode appears between the resonant frequency and the anti-resonant frequency, in addition to the main resonant mode. The response strength of this second mode is inversely proportional to the frequency response to the right of the anti-resonant frequency. As shown in the figure, the stronger the second mode frequency response, the better the suppression of clutter frequency response to the right of the anti-resonant frequency.

[0035] In a notch filter, S21 represents the scattering parameters (S-parameters) of the signal from the input port to the output port. S21 is an important parameter for evaluating the performance of a notch filter, reflecting the degree of signal attenuation and frequency characteristics as the signal passes through the device. By observing the S21 curve, the passband, stopband, and transition band characteristics of the notch filter can be determined.

[0036] To further refine this change, Figure 5 The diagram shows the S21-frequency comparison for surface acoustic wave (SAW) notch filter 200 with N values ​​of 0.96, 0.97, 0.98, 0.99, and 1. The curves show that when N is between 0.96 and 0.98, the right-side clutter frequency response of the SAW notch filter 200 is relatively small. When N is 0.98, the maximum S21 value corresponding to the right-side clutter frequency response of the SAW notch filter 200 is -0.87 dB. As N decreases, the absolute value of the S21 value of the right-side clutter frequency response of the SAW notch filter 200 decreases, and the S21 value tends to be 0. However, when N is 0.99 and 1, the S21 values ​​corresponding to the right-side clutter frequency response of the SAW notch filter 200 are -0.98 dB and -1.11 dB, respectively. This abrupt change in the right-side clutter frequency response of the SAW notch filter 200 deteriorates its performance.

[0037] Furthermore, when N is 0.96~0.98, the rectangularity of the surface acoustic wave notch filter 200 is stable at 1.25, with a change rate of less than 3%. Therefore, when N changes within this range, it will not have a significant impact on the rectangularity of the surface acoustic wave notch filter 200.

[0038] Therefore, when 0.96≤N≤0.98, as N decreases, the S21 value of the clutter on the right side of the surface acoustic wave notch filter 200 tends to 0 from -0.87dB, while maintaining a stable rectangularity.

[0039] Similarly, Figure 6 The S21-frequency comparison diagrams of surface acoustic wave notch filters 200 with N values ​​of 0.96, 0.95, 0.94, 0.93, and 0.92 are shown.

[0040] When N is 0.96, the maximum S21 value corresponding to the right-side clutter frequency response of the surface acoustic wave notch filter 200 is -0.78 dB. As N decreases, the absolute value of S21 of the right-side clutter of the surface acoustic wave notch filter 200 decreases, and the S21 value tends to 0. This follows the same pattern as when N is 0.96~0.98. Although reducing N can optimize the S21 value, the steepness of the transition band must also be considered. Therefore, the influence of N on the rectangularity needs to be further explored.

[0041] The transition band is a short transition region connecting the passband and the stopband. The transition band determines the rectangularity. The steeper the transition band and the narrower its width, the closer the rectangularity is to 1.

[0042] As can be seen from the curves, when N is between 0.94 and 0.96, the transition band of the surface acoustic wave (SAW) notch filter 200 is steeper, while when N is between 0.93 and 0.92, the transition band is gentler. Specifically, this represents the ratio of the bandwidth of the stopband with an S21 value of -5 dB to the bandwidth of the stopband with an S21 value of -20 dB.

[0043] When N is 0.94, the rectangularity of the surface acoustic wave notch filter 200 is 1.27. As N increases, the rectangularity of the surface acoustic wave notch filter 200 gradually decreases, that is, it gets closer to 1.

[0044] When N is 0.93, the rectangularity of the surface acoustic wave notch filter 200 is 2.01. The rectangularity undergoes a nonlinear abrupt change, showing a significant deterioration.

[0045] Therefore, when 0.94≤N≤0.96, the S21 value of the surface acoustic wave (SAW) notch filter 200 is less than -0.78dB, and the rectangularity of the transition band is less than or equal to 1.27. However, when N is 0.93, the rectangularity of the SAW notch filter 200 is 2.01, which is abrupt and deteriorates the performance of the SAW notch filter 200.

[0046] In summary, preferably, p2 satisfies: 0.94×p1≤p2≤0.98×p1. Within this range, the performance of the main resonant mode remains unaffected, while the second mode is effectively excited, suppressing the clutter frequency response to the right of the anti-resonant frequency. This achieves a good balance between the S21 value and the rectangularity, thus improving the notch filter performance.

[0047] Optimization of IDT and reflector spacing p3 After determining the optimal range for p2, the spacing p3 between the IDT and the reflector, another key geometric parameter, was optimized. p3 is defined as the distance between an adjacent third electrode finger (reflector electrode) and the first electrode finger (or second electrode finger). p3 determines the phase relationship between the sound wave excited by the IDT and the sound wave reflected by the reflector. A suitable p3 ensures that the reflected wave and the incident wave are superimposed in phase within the IDT region, enhancing the resonance effect. An unsuitable p3 leads to phase mismatch and increased energy loss.

[0048] Specifically, set p3 = T × (p1 + p2) / 2 for any series arm resonator.

[0049] Figure 7 The admittance / conductance-frequency curves of the series arm resonator at different values ​​of T are shown, where N is kept at 0.96. From the conductance curves, it can be seen that when 0.92 ≤ T ≤ 0.96, as T increases, the distance between the IDT and the reflector increases, causing a change in the phase difference between the reflected and incident waves. This phase mismatch results in a strong parasitic response of the resonator to the right of the anti-resonance frequency (high-frequency side). This strong response to the right of the anti-resonance frequency leads to a decrease in the suppression effect of the notch filter on the high-frequency side. A second mode, besides the main resonant mode, always exists between the resonant frequency and the anti-resonance frequency. When T is less than or equal to 0.96, the clutter frequency response to the right of the anti-resonance frequency remains at a relatively low level.

[0050] To quantify this phenomenon, Figure 8 The diagram shows the S21-frequency comparison for surface acoustic wave (SAW) notch filter 200 with T values ​​of 0.96, 0.95, 0.94, 0.93, and 0.92. The curves show that when T is 0.96, the maximum S21 value corresponding to the right-side clutter frequency response of the SAW notch filter 200 is -0.757 dB. As T gradually decreases, the absolute value of S21 corresponding to the right-side clutter frequency response of the SAW notch filter 200 decreases, and the S21 value tends towards 0. The right-side clutter frequency response of the SAW notch filter 200 also decreases. Compared to optimizing only N to 0.96, where the S21 value corresponding to the right-side clutter frequency response of the SAW notch filter 200 is -0.78 dB, the right-side clutter frequency response of the SAW notch filter 200 is even smaller when T is 0.96.

[0051] To further verify the improvement of the notch filter by the technical solution of this application, an optimization comparison experiment was conducted on p2 and p3. Under the condition that other structures and parameters of the notch filter are the same, the values ​​of N and T associated with p2 and p3 were adjusted, and the corresponding S21 values ​​were recorded as follows: The results show that optimizing p2 and p3 independently helps improve the right-side clutter frequency response of the surface acoustic wave notch filter 200. The optimization of the two also has a synergistic effect. Optimizing p2 and p3 simultaneously improves the right-side clutter frequency response of the surface acoustic wave notch filter 200, further enhancing the performance of the surface acoustic wave notch filter 200.

[0052] Figure 9 A graph showing the S21 value corresponding to the right-side clutter frequency response of the surface acoustic wave (SAW) notch filter 200 as a function of time (T) is shown. The graph shows that the absolute value of S21 corresponding to the right-side clutter frequency response of the SAW notch filter 200 decreases linearly with decreasing T, approaching 0. When T is 0.92, the S21 value corresponding to the right-side clutter frequency response of the SAW notch filter 200 is -0.73 dB; when T is 0.94, the S21 value is -0.747 dB; and when T is 0.96, the S21 value is -0.757 dB.

[0053] Based on the above experimental results, p3 is preferably satisfied with p3=T×(p1+p2) / 2, where 0.92≤T≤0.96.

[0054] Figure 10 The diagram shows the S21-frequency comparison of the surface acoustic wave (SAW) notch filter 200 when T is 0.92 and 1, respectively. The curves show that when T = 0.92, the S21 value corresponding to the right-side clutter frequency response of the SAW notch filter 200 is -0.73 dB; when T = 1, the S21 value corresponding to the right-side clutter frequency response of the SAW notch filter 200 is -0.78 dB. Therefore, the clutter frequency response of the SAW notch filter 200 on the high-frequency side is smaller when T = 0.92.

[0055] Through the synergistic optimization of p2 and p3 described above, the surface acoustic wave notch filter 200 provided in this embodiment introduces a second mode in a controllable manner while keeping the main resonant mode unaffected. This effectively suppresses the clutter frequency response to the right of the anti-resonant frequency, makes the transition band steeper, reduces the rectangularity, and improves the frequency selectivity.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A surface acoustic wave notch filter, characterized by, include: A resonator group consisting of multiple resonators, the resonator group including multiple series arm resonators and multiple parallel arm resonators; The resonator includes an interdigital transducer; and reflectors disposed on both sides of the interdigital transducer along the direction of surface acoustic wave propagation. The interdigitated transducer includes multiple first electrode fingers and multiple second electrode fingers inserted in an alternating manner; the reflector includes multiple third electrode fingers arranged periodically. The spacing between adjacent first electrode fingers and second electrode fingers is set as p1, the spacing between adjacent third electrode fingers is set as p2, and the spacing between adjacent third electrode fingers and first electrode fingers, or adjacent third electrode fingers and second electrode fingers, is set as p3. At least one series arm resonator, when p2 satisfies the condition 0.94×p1≤p2≤0.98×p1, excites a second mode that coexists with the main resonant mode between the resonant frequency and the anti-resonant frequency of the resonator. The second mode is used to suppress the clutter frequency response to the right of the anti-resonant frequency.

2. The surface acoustic wave notch filter according to claim 1, characterized by When the second mode frequency response is enhanced, the position of the resonant frequency and anti-resonant frequency of the main resonant mode is not changed, while the clutter frequency response to the right of the anti-resonant frequency is reduced.

3. The surface acoustic wave notch filter according to claim 1, wherein When p2 satisfies the condition 0.96×p1≤p2≤0.98×p1, as p2 decreases, the value of S21 of the surface acoustic wave notch filter tends to 0, and the rectangularity of the surface acoustic wave notch filter remains stable with a change rate of less than 3%.

4. The surface acoustic wave notch filter according to claim 1, wherein When p2 satisfies the condition 0.94×p1≤p2≤0.96×p1, as p2 increases, the rectangularity of the surface acoustic wave notch filter decreases towards 1. When p2 is less than 0.94×p1, the rectangularity of the surface acoustic wave notch filter undergoes a nonlinear abrupt change.

5. The surface acoustic wave notch filter according to claim 1, wherein The p3 condition satisfies p3=T×(p1+p2) / 2. When 0.92≤T≤0.96, the decrease of T causes the clutter frequency response to the right of the anti-resonance frequency to decrease simultaneously.

6. The surface acoustic wave notch filter according to claim 5, wherein The p3 condition satisfies p3=T×(p1+p2) / 2. When 0.92≤T≤0.96, the value of the surface acoustic wave notch filter S21 is -0.757dB to -0.73dB.

7. The surface acoustic wave notch filter according to claim 5, wherein When p2 and p3 are optimized together, the value of surface acoustic wave notch filter S21 is less than the value of surface acoustic wave notch filter S21 when p2 or p3 is optimized alone.

Images