Microwave ablation antenna based on substrate integrated coaxial line structure

Abstract

The invention belongs to the technical field of medical instruments, and particularly relates to a microwave ablation antenna based on a substrate integrated coaxial line structure, the ablation antenna comprises a substrate coaxial line assembly, the substrate coaxial line assembly comprises a first dielectric layer, a second dielectric layer, a third dielectric layer and a fourth dielectric layer which are sequentially arranged from the upper end to the lower end, a first conductor layer is fixed between the first dielectric layer and the second dielectric layer, a second conductor layer is fixed between the third dielectric layer and the fourth dielectric layer, and a plurality of metalized through holes are uniformly arranged between the second dielectric layer and the fourth dielectric layer. Through cooperation of the central feeder line and the U-shaped branch knot, a current path is changed, electromagnetic field distribution is optimized, the microwave energy gathering effect is improved, the highly localized heat effect of the antenna tip end is achieved, meanwhile, through cooperative work of the U-shaped branch knot and the balun assembly, reverse electromagnetic waves are restrained, backward radiation heating is reduced, forward gain is improved, and the antenna tip end is more compact. And the roundness of the ablation area is obviously improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of medical devices, and particularly relates to a microwave ablation antenna based on a substrate integrated coaxial line structure. BACKGROUND

[0002] As a minimally invasive tumor treatment method, microwave ablation (MWA) has obtained wide attention in clinical treatment by causing tumor cells to necrose at high temperature through the heat effect of microwave energy. As a new type of electromagnetic structure, the substrate integrated coaxial line (SICL) structure uses two rows of metallized via arrays to construct a quasi-coaxial electromagnetic field distribution in a printed circuit board (PCB) dielectric substrate, retains the electromagnetic shielding performance of a traditional coaxial line, has the advantage of easy integration and processing of a planar circuit, breaks through the limitation of the three-dimensional structure of a traditional antenna, and can greatly reduce manufacturing complexity and cost.

[0003] The existing microwave ablation antenna has many technical limitations: the traditional coaxial feed antenna is prone to exciting electromagnetic waves on the surface of the outer conductor due to unbalanced structure, causing the ablation area to excessively extend along the axial direction of the antenna, and there is a risk of damaging the surrounding healthy tissues; although a choke coil or a floating sleeve can be used as a balun to suppress electromagnetic waves at a high impedance point, the existing choke coil or floating sleeve form increases the cross section of the antenna, which is not conducive to the implementation of minimally invasive surgery; the coaxial line-based slot antenna and helical dipole antenna do not need a balun component, but have the problems of complex manufacturing process and high cost.

[0004] Based on the above problems, the application provides a microwave ablation antenna based on a substrate integrated coaxial line structure to solve the problem that the existing microwave ablation antenna cannot simultaneously meet the requirements of compact structure, low invasiveness, easy processing, ideal ablation effect and low cost. SUMMARY

[0005] The application aims to provide a microwave ablation antenna based on a substrate integrated coaxial line structure, which changes the current path, optimizes the electromagnetic field distribution, improves the microwave energy concentration effect, realizes the highly localized heat effect of the antenna tip, and at the same time, through the synergistic work of the U-shaped stub and the balun component, suppresses the reverse current, reduces the backward radiation heating, improves the forward gain, and significantly improves the roundness of the ablation area.

[0006] The technical solutions adopted by the application are as follows: A microwave ablation antenna based on a substrate integrated coaxial line structure, comprising a substrate coaxial line assembly, the substrate coaxial line assembly comprising a first dielectric layer, a second dielectric layer, a third dielectric layer and a fourth dielectric layer arranged in sequence from an upper end to a lower end, a first conductor layer fixed between the first dielectric layer and the second dielectric layer, a second conductor layer fixed between the third dielectric layer and the fourth dielectric layer, a plurality of metallized vias uniformly arranged between the second dielectric layer and the fourth dielectric layer, and the first conductor layer and the second conductor layer being electrically connected through the plurality of metallized vias, further comprising: a radiation assembly assembled between the second dielectric layer and the third dielectric layer, the radiation assembly comprising an inner conductor layer, a center feed line and a U-shaped stub, the inner conductor layer being fixed between the second dielectric layer and the third dielectric layer, the center feed line being arranged at one end of the inner conductor layer, and the U-shaped stub being arranged outside the center feed line; a balun assembly assembled on the first dielectric layer and the fourth dielectric layer, the balun assembly being configured to suppress reverse electromagnetic waves, reduce backward radiation and improve the forward gain of the antenna; wherein the U-shaped stub is configured to change the current path and the electromagnetic field distribution, concentrate microwave energy to a target ablation area, and improve power transmission efficiency.

[0007] In a preferred embodiment, the length of the center feed line is denoted as L1, the length of the U-shaped stub is denoted as L2, and the length of the balun assembly is denoted as L3, L1≥0.75λ eff , L2≥0.25λ eff , L3≤0.75λ eff , wherein λ eff represents the effective wavelength of electromagnetic waves in tissue.

[0008] In a preferred embodiment, the balun assembly is a choke coil structure.

[0009] In a preferred embodiment, the choke coil structure comprises a first metal layer, a first metal column, a second metal layer and a second metal column, the first metal layer is fixed to the upper end of the first dielectric layer, the first metal column is fixed to the inside of the first dielectric layer, and the first conductor layer and the first metal layer are electrically connected through the first metal column, the second metal layer is fixed to the lower end of the fourth dielectric layer, the second metal column is fixed to the inside of the fourth dielectric layer, and the second conductor layer and the second metal layer are electrically connected through the second metal column.

[0010] In a preferred embodiment, the horizontal cross-sectional shape of the first metal layer and the second metal layer is rectangular.

[0011] In a preferred embodiment, L1=15mm, L2=3mm, and L3=8mm.

[0012] In a preferred solution, the balun assembly is a floating sleeve structure.

[0013] In a preferred solution, the floating sleeve structure comprises a third metal layer and a fourth metal layer, the third metal layer is fixed to the upper end of the first dielectric layer, and the fourth metal layer is fixed to the lower end of the fourth dielectric layer.

[0014] In a preferred solution, the third metal layer and the fourth metal layer are both rectangular in horizontal cross-sectional shape.

[0015] In a preferred solution, L1=15mm, L2=3mm, and L3=7mm.

[0016] In a preferred solution, the first dielectric layer, the second dielectric layer, the third dielectric layer, and the fourth dielectric layer are made of any one of the following materials: FR4, CEM1, and Teflon.

[0017] A microwave ablation needle employing the microwave ablation antenna based on the integrated coaxial line structure according to any one of the preceding solutions.

[0018] The present application has the following technical effects: In the process of transmitting microwaves from the inner conductor layer to the center feed line and the U-shaped branch, the number of conductors increases from one to three, the current path is changed through the cooperation of the center feed line and the two branches of the U-shaped branch, the electromagnetic field distribution is optimized, the microwave energy concentration effect is improved, the high local thermal effect of the antenna tip is realized, at the same time, the two branches of the U-shaped branch play a role in inhibiting the reverse current on the center feed line, further improving the microwave energy concentration effect, and effectively concentrating the microwave energy to the target ablation area. The U-shaped branch and the balun assembly work together to not only effectively suppress the reverse current along the axial direction, reduce the backward radiation heating, and improve the forward gain of the device, but also significantly improve the roundness of the ablation area compared with the traditional structure. In the present application, by reconstructing the structure of the microwave ablation antenna, the overall size of the antenna is significantly reduced compared with the prior art, making it more suitable for application in minimally invasive surgery, and further reducing the damage to the patient during invasive tumor treatment. Compared with the coaxial structure-based balun antenna, slot antenna and spiral dipole antenna, the balun assembly based on the substrate integrated coaxial line in the present embodiment has the advantages of simple structure, simple manufacturing process and low cost. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the overall structure schematic diagram in the embodiment one of the present application; Figure 2 is the overall structure schematic diagram in the embodiment two of the present application Figure 1An enlarged view of the middle A; Figure 3 An overall structural exploded view of the embodiment one of the present application; Figure 4 An overall structural sectional view of the embodiment one of the present application; Figure 5 A structural schematic view of the radiation assembly in the embodiment one of the present application; Figure 6 A partial structural schematic view of the embodiment one of the present application; Figure 7 A S parameter schematic view of the device in the embodiment one of the present application; Figure 8 An overall structural schematic view of the embodiment two of the present application; Figure 9 An overall structural schematic view of the embodiment two of the present application Figure 8 An enlarged structural schematic view of the middle B; Figure 10 An overall structural exploded view of the embodiment two of the present application; Figure 11 An overall structural sectional view of the embodiment two of the present application; Figure 12 A S parameter schematic view of the device in the embodiment two of the present application; Figure 13 A physical view of the overall structure in the embodiment one of the present application; Figure 14 A physical view of the overall structure in the embodiment two of the present application; Figure 15 A SAR simulation distribution diagram of the working condition A in the embodiment two of the present application; Figure 16 A SAR simulation distribution diagram of the working condition B in the embodiment two of the present application; Figure 17 A SAR simulation distribution diagram of the working condition C in the embodiment two of the present application; Figure 18 A SAR simulation distribution diagram of the working condition D in the embodiment two of the present application.

[0020] In the drawings, the components represented by each reference numeral are listed as follows: 10, substrate coaxial assembly; 11, first dielectric layer; 12, second dielectric layer; 13, third dielectric layer; 14, fourth dielectric layer; 15, first conductor layer; 16, second conductor layer; 17, metallized via; 20, radiation assembly; 21, inner conductor layer; 22, center feed line; 23, U-shaped stub; 31, first metal layer; 32, first metal post; 33, second metal layer; 34, second metal post; 41, third metal layer; 42, fourth metal layer. DETAILED DESCRIPTION

[0021] In order to make the above objectives, features and advantages of the present application more clear and easily understood, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0022] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details given herein. In other instances, well-known methods have not been described in detail in order to avoid unnecessarily obscuring the present application. Therefore, the specific details set forth hereinafter are merely exemplary and should not be construed as limiting the scope of the present application.

[0023] Secondly, the "one embodiment" or "an embodiment" as used in this specification means that a specific feature, structure or characteristic described in connection with the embodiment can be included in at least one implementation of the present application. The "in one preferred embodiment" appearing in different places in this specification does not mean the same embodiment, nor does it mean an embodiment that is separate from or mutually exclusive with other embodiments.

[0024] Thirdly, the present application is described in detail in connection with the schematic drawings. In the detailed description of the embodiments of the present application, the sectional view of the device structure is partially enlarged without the general proportion for the convenience of description, and the schematic drawings are only examples, which should not limit the scope of protection of the present application. In addition, the three-dimensional spatial dimensions of length, width and depth should be included in the actual manufacture.

[0025] Embodiment one Please refer to the accompanying drawings Figures 1 to 5 As shown in the drawings, the first embodiment of the present application provides a microwave ablation antenna based on a substrate integrated coaxial line structure, which comprises a substrate coaxial line assembly 10, the substrate coaxial line assembly 10 comprises a first dielectric layer 11, a second dielectric layer 12, a third dielectric layer 13 and a fourth dielectric layer 14 arranged in sequence from the upper end to the lower end, one end of the first dielectric layer 11, the second dielectric layer 12, the third dielectric layer 13 and the fourth dielectric layer 14 is provided with a piercing end, a first conductor layer 15 is fixed between the first dielectric layer 11 and the second dielectric layer 12, a second conductor layer 16 is fixed between the third dielectric layer 13 and the fourth dielectric layer 14, a plurality of metalized vias 17 are uniformly arranged between the second dielectric layer 12 and the fourth dielectric layer 14, the upper end and the lower end of the metalized via 17 respectively penetrate the inside of the second dielectric layer 12 and the fourth dielectric layer 14, and the first conductor layer 15 and the second conductor layer 16 are electrically connected through the plurality of metalized vias 17, the first conductor layer 15, the second conductor layer 16 and the metalized via 17 constitute an outer conductor unit, further comprising: The radiation assembly 20 is assembled between the second dielectric layer 12 and the third dielectric layer 13, and includes an inner conductor layer 21, a center feed line 22 and a U-shaped stub 23. The inner conductor layer 21 is fixed between the second dielectric layer 12 and the third dielectric layer 13 and located at an end away from the piercing end. The center feed line 22 is integrally formed at an end of the inner conductor layer 21 close to the piercing end. The horizontal cross-sectional shape of the center feed line 22 is U-shaped. The U-shaped stub 23 is integrally formed outside the center feed line 22. The balun assembly is assembled on the first dielectric layer 11 and the fourth dielectric layer 14, and is configured to be capable of suppressing reverse electromagnetic waves, reducing backward radiation and improving the forward gain of the antenna. The U-shaped stub 23 is configured to be capable of changing the current path and the electromagnetic field distribution, concentrating microwave energy to the target ablation area, and improving the power transmission efficiency.

[0026] It should be noted that the materials of the first dielectric layer 11, the second dielectric layer 12, the third dielectric layer 13 and the fourth dielectric layer 14 are any one of the following materials: FR4, CEM1, Teflon or other high molecular materials with insulating properties. In this embodiment, the materials of the first dielectric layer 11, the second dielectric layer 12, the third dielectric layer 13 and the fourth dielectric layer 14 are preferably FR4.

[0027] Further, please refer to Figure 6 As shown, the length of the center feed line 22 is L1, the length of the U-shaped stub 23 is L2, and the maximum length of the balun assembly is L3. L1≥0.75λ eff , L2≥0.25λ eff , L3≤0.75λ eff , where λ eff represents the effective wavelength of the electromagnetic wave in the tissue.

[0028] It should be noted that the device is also used with a microwave generating device. The microwave generating device and the inner conductor layer 21, the microwave generating device and the first conductor layer 15, and the microwave generating device and the second conductor layer 16 are electrically connected by a suitable method. The microwave generating device can deliver electromagnetic wave energy (i.e. microwave) to the inner conductor layer 21. The specific connection method can refer to the prior art, and will not be described further here.

[0029] In this embodiment, the microwave is transmitted to the inner conductor layer 21 by the microwave generating device, and the microwave is transmitted to the center feed line 22 and the U-shaped branch 23 through the inner conductor layer 21. Due to the U-shaped cross-sectional shape of the U-shaped branch 23, the number of conductors increases from one to three (three conductors are the end of the center feed line 22 away from the inner conductor layer 21 and the two branches on the U-shaped branch 23) during the transmission of the microwave. Through the cooperation of the three conductors, the local microwave energy is concentrated, and the two branches on the U-shaped branch 23 can suppress the reverse current on the center feed line 22, further improving the microwave energy concentration effect. Through the cooperation of the center feed line 22 and the U-shaped branch 23, the current path can be changed, the electromagnetic field distribution can be optimized, the highly localized thermal effect of the antenna tip can be realized, the microwave energy can be effectively concentrated to the target ablation area, in addition, the U-shaped branch 23 can also adjust the impedance characteristics of the antenna, so as to more accurately match the impedance of the microwave source and the biological tissue, thereby further improving the power transmission efficiency. At the same time, through the cooperation of the U-shaped branch 23 and the balun assembly, on the one hand, the reverse electromagnetic wave along the axial direction can be effectively suppressed, and the backward heating is reduced (about 33%); on the other hand, the roundness of the ablation area is obviously improved compared with the ordinary structure, and has the characteristics of easy processing, low cost, compact antenna structure and high ablation area roundness. It shows potential application value in improving the safety of minimally invasive tumor ablation treatment.

[0030] Thirdly, please refer to Figure 3 and Figure 4 In this embodiment, the balun assembly is a choke coil structure, which includes a first metal layer 31, a first metal column 32, a second metal layer 33 and a second metal column 34. The first metal layer 31 is fixed to the upper end of the first dielectric layer 11, the first metal column 32 is fixed to the inside of the first dielectric layer 11, and the first conductor layer 15 and the first metal layer 31 are electrically connected through the first metal column 32. The second metal layer 33 is fixed to the lower end of the fourth dielectric layer 14, and the second metal column 34 is fixed to the inside of the fourth dielectric layer 14. The second conductor layer 16 and the second metal layer 33 are electrically connected through the second metal column 34.

[0031] Specifically, in this embodiment, L3 represents the length value of the first metal layer 31 and the second metal layer 33, and the horizontal cross-sectional shape of the first metal layer 31 and the second metal layer 33 is rectangular.

[0032] It should be noted that in this embodiment, the thicknesses of the first dielectric layer 11, the second dielectric layer 12, the third dielectric layer 13 and the fourth dielectric layer 14 are all 0.035mm, the widths of the first metal layer 31 and the second metal layer 33 are both 1.6mm, and the thicknesses of the first metal layer 31 and the second metal layer 33 are both 0.035mm. The thickness of the whole device is 0.975mm, and the width is 1.6mm. The actual picture of this embodiment can be referred to as shown in Figure 13 .

[0033] In a preferred embodiment, L1 = 15 mm, L2 = 3 mm, L3 = 8 mm, and the S parameters of the ablation antenna are obtained by simulation through software emulation (as shown in Figure 7 ).

[0034] In this embodiment, when the microwave is transmitted to the inner conductor layer 21, the center feed line 22, and the U-shaped stub 23 by the microwave generating device, the choke coil type balun assembly composed of the first metal layer 31, the first metal column 32, the second metal layer 33, and the second metal column 34 can effectively suppress the reverse electromagnetic wave, reduce the back radiation of the device, and improve the forward gain of the device. In addition, in this embodiment, the choke coil type balun assembly is integrated in the multi-layer PCB structure, avoiding the additional mechanical assembly and welding process required by the traditional three-dimensional choke coil, eliminating the assembly gap between the traditional three-dimensional choke coil and the needle rod under the condition of keeping the outer diameter of the antenna unchanged, and reducing the risk of electrical performance drift caused by mechanical looseness. Compared with the coaxial slot antenna and the spiral dipole antenna, the choke coil type balun assembly based on the substrate integrated coaxial line in this embodiment does not require precise turning or manual winding, and has the advantages of simple structure, simple manufacturing process, and low cost.

[0035] Embodiment Two This embodiment is further optimized on the basis of Embodiment One, and the main difference lies in the structure of the balun assembly, specifically: Please refer again to Figures 8 to 11 , the balun assembly is a floating sleeve type structure, which includes a third metal layer 41 and a fourth metal layer 42. The third metal layer 41 is fixed to the upper end of the first dielectric layer 11, and the fourth metal layer 42 is fixed to the lower end of the fourth dielectric layer 14.

[0036] Specifically, in this embodiment, L3 represents the length value of the third metal layer 41 and the fourth metal layer 42, and the horizontal cross-sectional shape of the third metal layer 41 and the fourth metal layer 42 is rectangular. The first conductor layer 15 and the third metal layer 41 are insulated from each other by the first dielectric layer 11, and the second conductor layer 16 and the fourth metal layer 42 are insulated from each other by the fourth dielectric layer 14.

[0037] It should be noted that in this embodiment, the width of the third metal layer 41 and the fourth metal layer 42 is 1.6 mm, and the thickness is 0.035 mm. The overall thickness of the device is 0.975 mm, and the width is 1.6 mm. The actual picture of this embodiment can be referred to Figure 14 .

[0038] In a preferred embodiment, L1 = 15 mm, L2 = 3 mm, L3 = 7 mm, and the S parameters of the ablation antenna are obtained by simulation through software emulation (as shown in Figure 12as shown).

[0039] In this embodiment, when the inner conductor layer 21, the center feed line 22 and the U-shaped branch 23 are supplied with microwaves by the microwave generating device, the floating sleeve type balun assembly formed by the third metal layer 41 and the fourth metal layer 42 can effectively suppress the reverse electromagnetic wave, reduce the backward radiation of the device, and improve the forward gain of the device. In addition, in this embodiment, the floating sleeve type balun assembly cancels the first metal column 32 and the second metal column 34, and changes the metal column structure which needs secondary positioning or laser welding to a pure plane metal layer, thereby further reducing the processing difficulty, realizing a minimally invasive microwave ablation solution which is easier to process in batches and has lower cost.

[0040] In a specific embodiment, the following technical conditions are simulated in sequence by software to obtain SAR diagrams: Condition A: without U-shaped branch 23 and balun assembly (SAR simulation distribution diagram as shown in Figure 15 ); Condition B: with U-shaped branch 23, without balun assembly (SAR simulation distribution diagram as shown in Figure 16 ); Condition C: with U-shaped branch 23 and choke coil type balun assembly (SAR simulation distribution diagram as shown in Figure 17 ); Condition D: with U-shaped branch 23 and floating sleeve type balun assembly (SAR simulation distribution diagram as shown in Figure 18 ); It can be seen from Figure 15 and Figure 16 that under the premise that conditions A and B do not have a balun assembly, the microwave energy concentration effect and reverse current suppression effect of condition B are better than those of condition A; by comparing Figure 16 and Figure 17 and Figure 16 and Figure 18 , it can be seen that under the premise that conditions B, C and D have a U-shaped branch 23, the addition of a balun assembly greatly improves the microwave energy concentration effect, the roundness of the ablation area and the suppression effect of backward heating.

[0041] Embodiment Three A microwave ablation needle adopts the microwave ablation antenna based on an integrated coaxial line structure in any one of embodiments one or two.

[0042] The working principle of the present application is as follows: The microwave is transmitted to the inner conductor layer 21 by the microwave generating device, and is transmitted to the center feed line 22 and the U-shaped branch 23 through the inner conductor layer 21. Due to the U-shaped cross-sectional shape of the U-shaped branch 23, the current path can be changed and the electromagnetic field distribution can be optimized during the microwave transmission process through the cooperation of the center feed line 22 and the two branches of the U-shaped branch 23, so as to realize the high local thermal effect of the antenna tip, effectively concentrate the microwave energy to the target ablation area, and at the same time, the two branches of the U-shaped branch 23 can suppress the reverse current on the center feed line 22, further improve the microwave energy concentration effect, and in addition, through the cooperative work of the center feed line 22 and the balun assembly, not only can effectively suppress the reverse current along the axial direction and reduce the backward heating, but also can significantly improve the roundness of the ablation area compared with the conventional structure.

[0043] In addition, in the embodiment, the size of the antenna as a whole is significantly reduced compared with the prior art, which makes it more suitable for application in minimally invasive surgery and can further reduce the damage to the patient in the process of invasive tumor treatment. Compared with the balun antenna, the slot antenna and the spiral dipole antenna based on the coaxial structure, in the embodiment, the balun assembly based on the substrate integrated coaxial line has the advantages of simple structure, simple manufacturing process and low cost.

[0044] The above is only the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered as the protection scope of the present application. The structures, devices and operation methods not specifically described and explained in the present application are implemented according to the conventional means in the art, unless otherwise specified and limited.

Claims

1. A microwave ablation antenna based on a substrate integrated coaxial line structure, characterized in that: The coaxial line assembly (10) comprises a first dielectric layer (11), a second dielectric layer (12), a third dielectric layer (13) and a fourth dielectric layer (14) arranged in sequence from an upper end to a lower end, a first conductor layer (15) fixed between the first dielectric layer (11) and the second dielectric layer (12), a second conductor layer (16) fixed between the third dielectric layer (13) and the fourth dielectric layer (14), and a plurality of metallized vias (17) uniformly arranged between the second dielectric layer (12) and the fourth dielectric layer (14), and the first conductor layer (15) and the second conductor layer (16) are electrically connected through the plurality of metallized vias (17), and the coaxial line assembly (10) further comprises: a radiation assembly (20) assembled between the second dielectric layer (12) and the third dielectric layer (13), the radiation assembly (20) comprising an inner conductor layer (21), a center feed line (22) and a U-shaped branch (23), the inner conductor layer (21) being fixed between the second dielectric layer (12) and the third dielectric layer (13), the center feed line (22) being arranged at one end of the inner conductor layer (21), and the U-shaped branch (23) being arranged outside the center feed line (22); a balun assembly assembled on the first dielectric layer (11) and the fourth dielectric layer (14), the balun assembly being configured to suppress reverse electromagnetic waves, reduce backward radiation and improve the forward gain of the antenna; wherein the U-shaped branch (23) is configured to change the current path and the electromagnetic field distribution and concentrate microwave energy to a target ablation area.

2. A microwave ablation antenna based on a substrate integrated coaxial line structure according to claim 1, characterized in that: The length of the center feed line (22) is denoted as L1, the length of the U-shaped stub (23) is denoted as L2, and the length of the balun assembly is denoted as L3, L1≥0.75λ eff , L2≥0.25λ eff , L3≤0.75λ eff , where λ eff represents the effective wavelength of the electromagnetic wave in the tissue.

3. A microwave ablation antenna based on a substrate integrated coaxial line structure according to claim 2, characterized in that: The balun assembly is a choke coil structure.

4. The microwave ablation antenna based on the structure of substrate integrated coaxial line according to claim 3, characterized in that: The choke coil structure comprises a first metal layer (31), a first metal column (32), a second metal layer (33) and a second metal column (34), the first metal layer (31) being fixed to the upper end of the first dielectric layer (11), the first metal column (32) being fixed to the inside of the first dielectric layer (11), the first conductor layer (15) and the first metal layer (31) being electrically connected through the first metal column (32), the second metal layer (33) being fixed to the lower end of the fourth dielectric layer (14), the second metal column (34) being fixed to the inside of the fourth dielectric layer (14), and the second conductor layer (16) and the second metal layer (33) being electrically connected through the second metal column (34).

5. A microwave ablation antenna based on a substrate integrated coaxial line structure according to claim 4, characterized in that: L1=15mm, L2=3mm, L3=8mm.

6. The microwave ablation antenna based on the structure of substrate integrated coaxial line according to claim 2, characterized in that: The balun assembly is a floating sleeve structure.

7. A microwave ablation antenna based on a substrate integrated coaxial line structure according to claim 6, characterized in that: The floating sleeve structure comprises a third metal layer (41) and a fourth metal layer (42), the third metal layer (41) being fixed to the upper end of the first dielectric layer (11), and the fourth metal layer (42) being fixed to the lower end of the fourth dielectric layer (14).

8. A microwave ablation antenna based on a substrate integrated coaxial line structure according to claim 7, characterized in that: L1=15mm, L2=3mm, L3=7mm.

9. The microwave ablation antenna based on the structure of substrate integrated coaxial line according to claim 1, characterized in that: The materials of the first dielectric layer (11), the second dielectric layer (12), the third dielectric layer (13) and the fourth dielectric layer (14) are any one of the following materials: FR4, CEM1 and Teflon.

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