High-coupling planar Balun and radio frequency front-end module

Abstract

The utility model discloses a high-coupling planar Balun and a radio frequency front-end module. The high-coupling planar Balun comprises a primary coil, a secondary coil, a balanced signal port and a non-balanced signal port which are arranged on the same layer of metal, a hollow area is formed in the middle of the primary coil, one part of the secondary coil is located in the hollow area, and the secondary coil is connected through a bonding wire to form a complete loop structure. According to the utility model, the primary coil and the secondary coil are designed on the same metal layer, and the secondary coil is partially positioned in the hollow area of the primary coil, so that the high coupling of the primary coil and the secondary coil is realized, the manufacturing process is simplified, the cost is reduced, and the signal conversion efficiency is remarkably improved. Meanwhile, as the primary coil and the secondary coil are located on the same plane, through hole connection and interlayer interconnection are reduced, the influence of parasitic parameters is reduced, and the performance of the Balun in high-frequency application is improved.

Description

Technical Field

[0001] This utility model relates to the field of radio frequency circuits, and in particular to a high-coupling planar balun and radio frequency front-end module. Background Technology

[0002] A balun (balance-to-unbalance) is a circuit device that converts an unbalanced signal into a balanced signal. It is widely used in radio frequency systems, especially in connecting differential power amplifiers and single-ended antennas.

[0003] The principle of a balun is to transfer radio frequency energy between the primary and secondary coils through magnetic coupling, such as... Figure 1 As shown. The coupling coefficient k of the balun characterizes the magnetic coupling strength between the two coils. The magnetic coupling strength is directly proportional to the coupling coefficient k; the larger the coupling coefficient k, the lower the loss of the balun. To achieve a high-coupling balun, a multi-layer vertical coupling structure is usually used (such as...). Figure 2 (as shown) and single-layer planar coupled structures (such as) Figure 3 (As shown).

[0004] In a multi-layer vertically coupled structure, the primary and secondary coils are coupled together in the vertical direction, forming a multi-layer structure. The advantage of this design is that as much primary magnetic flux as possible can pass through the secondary coil, thus achieving efficient magnetic coupling. While multi-layer vertically coupled baluns exhibit excellent magnetic coupling efficiency and performance, their manufacturing process is complex, costly, and has a low yield. Furthermore, this structure is relatively large, making heat dissipation difficult, especially in high-power applications where heat buildup can negatively impact performance and lifespan. In addition, its operating frequency range is limited, and high-frequency losses are significant. Regarding mechanical stability, the multi-layer structure may be affected by vibration or shock environments, and long-term use may lead to problems such as interlayer delamination, affecting reliability.

[0005] In a single-layer planar coupled structure, the primary and secondary coils are located in the same plane, typically implemented using a single layer of metal. Because the inner coil is smaller than the outer coil, the magnetic flux generated by the outer coil cannot completely pass through the inner coil, resulting in a smaller coupling coefficient k. To improve coupling strength, the spacing s between the inner and outer coils needs to be minimized, and the area of ​​the inner coil needs to be increased. Different manufacturing processes (such as back-end chip manufacturing, integrated passive devices (IPD), low-temperature co-fired ceramic (LTCC), etc.) can reduce the spacing s to less than 1.0 μm, but this still cannot match the efficiency of vertical coupling. For low-cost substrate implementations, the substrate spacing is typically at least 20 μm, leading to a lower coupling coefficient k in the planar balun and consequently increased losses. Utility Model Content

[0006] The purpose of this invention is to provide a highly coupled planar balun and an RF front-end module, which solves the technical problems of complex multi-layer balun design and low coupling in the prior art, while reducing the design complexity and manufacturing cost of the RF front-end with a simpler structure.

[0007] To solve the above technical problems, this utility model provides a high-coupling planar balun and an RF front-end module. The high-coupling planar balun includes a primary coil, a secondary coil, a balanced signal port, and an unbalanced signal port disposed on the same metal layer. A hollow area is formed in the middle of the primary coil, a part of the secondary coil is located in the hollow area, and the secondary coil is connected by bonding wires to form a complete loop structure.

[0008] The primary coil is connected to the balanced signal port, the secondary coil is connected to the unbalanced signal port via the bonding wire, and the high-coupling planar balun is used to realize signal conversion between the balanced signal port and the unbalanced signal port.

[0009] Optionally, the main coil includes a first part and a second part, the first part and the second part are adjacent and together form a ring structure, and the hollow area is located inside the ring structure.

[0010] Optionally, the secondary coil includes a first part and a second part, the first part being located between the first part and the second part of the primary coil, and the second part being located within the hollowed-out area. Both the first part and the second part of the secondary coil are concentrically and similarly arranged with the annular structure of the primary coil.

[0011] Optionally, the first part of the secondary coil includes multiple coil segments, which are connected to different parts of the secondary coil via the bonding wire, so that the secondary coil forms the complete loop structure.

[0012] Optionally, the balanced signal port is located below the main coil; the unbalanced signal port may be located to the left, right, or above the main coil.

[0013] Optionally, the number of turns of the main stage coil is 1.

[0014] Optionally, the number of turns of the secondary coil is 2.

[0015] A radio frequency front-end module includes the aforementioned highly coupled planar balun, and further includes a radio frequency power amplifier and a matching network;

[0016] The radio frequency power amplifier includes two amplifiers that form a differential output, with the output of each amplifier connected to one end of a decoupling capacitor and the other end of the decoupling capacitor grounded.

[0017] The balanced signal port of the high-coupling planar balun is connected to the two outputs of the RF power amplifier, the unbalanced signal port of the high-coupling planar balun is connected to the input of the matching network, and the output of the matching network is connected to the antenna.

[0018] The primary coil of the highly coupled planar balun is grounded via a first capacitor.

[0019] Optionally, the matching network includes a high-frequency band matching network, which includes:

[0020] The second capacitor has one end connected to the unbalanced signal port of the highly coupled planar balun;

[0021] The first inductor has one end connected to the other end of the second capacitor, and the other end grounded.

[0022] The second inductor is connected at one end to the unbalanced signal port of the highly coupled planar balun;

[0023] The third capacitor has one end connected to the other end of the second inductor;

[0024] The third inductor has one end connected to the other end of the third capacitor and the other end connected to the antenna;

[0025] The fourth inductor has one end connected to the other end of the third capacitor and the other end grounded.

[0026] The fourth capacitor has one end connected to the other end of the third capacitor, and the other end grounded.

[0027] Optionally, the matching network includes a low-frequency band matching network, which includes:

[0028] The second capacitor has one end connected to the unbalanced signal port of the highly coupled planar balun;

[0029] The first inductor has one end connected to the other end of the second capacitor, and the other end grounded.

[0030] The second inductor is connected at one end to the unbalanced signal port of the highly coupled planar balun;

[0031] The third capacitor has one end connected to the other end of the second inductor;

[0032] The third inductor has one end connected to the other end of the third capacitor, and the other end grounded.

[0033] A fourth inductor and a fourth capacitor are connected in parallel, with one end of the parallel connection connected to the other end of the second inductor;

[0034] The fifth capacitor and the fifth inductor are connected in series. One end of the series connection is connected to the other end of the fourth inductor and the fourth capacitor connected in parallel, and the other end is grounded.

[0035] The sixth inductor has one end connected to the other end of the fourth inductor and the fourth capacitor connected in parallel, and the other end connected to the antenna.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects:

[0037] The high-coupling planar balun proposed in this invention achieves high coupling between the primary and secondary coils by designing the primary and secondary coils on the same metal layer and positioning the secondary coil portion within the hollowed-out area of ​​the primary coil. This simplifies the manufacturing process, reduces costs, and significantly improves signal conversion efficiency. Furthermore, because the primary and secondary coils are located on the same plane, via connections and interlayer interconnections are reduced, minimizing the impact of parasitic parameters and enhancing the balun's performance in high-frequency applications. Attached Figure Description

[0038] Figure 1 This is the schematic diagram of a balun.

[0039] Figure 2 A schematic diagram of a traditional planar baron design;

[0040] Figure 3 Another schematic diagram for a traditional planar baron design;

[0041] Figure 4 This is a schematic diagram of one embodiment of the present invention;

[0042] Figure 5 This is a graph comparing the coupling coefficient k of an embodiment of the present invention with that of a traditional planar balun;

[0043] Figure 6 This is a schematic diagram of the structure of a radio frequency front-end module in one embodiment of the present invention;

[0044] Figure 7 This is a schematic diagram of the structure of another radio frequency front-end module in one embodiment of the present invention.

[0045] Reference numerals: 1. Primary coil; 101. First part of the primary coil; 102. Secondary coil; 2. Secondary coil; 201. First part of the secondary coil; 202. Secondary coil; 3. Bonding wire; 4. Decoupling capacitor; C1. First capacitor; C2. Second capacitor; C3. Third capacitor; C4. Fourth capacitor; C5. Fifth capacitor; L1. First inductor; L2. Second inductor; L3. Third inductor; L4. Fourth inductor; L5. Fifth inductor; L6. Sixth inductor. Detailed Implementation

[0046] Based on the teachings of this specification, those skilled in the art can form new technical solutions by combining different implementation methods without creating technical contradictions. Such variations should be considered to fall within the protection scope of this patent.

[0047] The following is a more detailed description of a high-coupling planar balun and RF front-end module of the present invention, with reference to the accompanying drawings, which illustrate preferred embodiments of the present invention. It should be understood that those skilled in the art can modify the present invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the present invention.

[0048] The present invention will be described in more detail below by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0049] Example 1

[0050] like Figure 4 As shown, this embodiment of the invention proposes a highly coupled planar balun, including a primary coil 1, a secondary coil 2, a balanced signal port, and an unbalanced signal port disposed on the same metal layer. A hollow area is formed in the middle of the primary coil 1, a portion of the secondary coil 2 is located within the hollow area, and the secondary coil 2 is connected by bonding wires 3 to form a complete loop structure.

[0051] The primary coil 1 is connected to the balanced signal port, the secondary coil 2 is connected to the unbalanced signal port via the bonding wire 3, and the high-coupling planar balun is used to realize signal conversion between the balanced signal port and the unbalanced signal port.

[0052] In this embodiment, the primary coil 1 and the secondary coil 2 are disposed on the same metal layer, eliminating interlayer dielectric interference in traditional multilayer structures and improving electromagnetic coupling efficiency. The hollowed-out area design allows the secondary coil 2 to be partially embedded within the primary coil 1, forming a three-dimensional interlaced structure, further enhancing the coupling between coils. The use of the bonding wire 3 solves the problem of single-layer coils being unable to close, while maintaining the characteristics of a single-layer metal.

[0053] In this embodiment, the primary coil 1 includes a first part and a second part. The first part 101 and the second part 102 of the primary coil are adjacent and together form a ring structure, thereby forming a continuous conductive circuit. The hollowed-out area is located inside the ring structure. The hollowed-out area is set to reserve space for the secondary coil 2, so that the primary and secondary coils can achieve high coupling on the same metal layer, simplifying the manufacturing process and reducing costs.

[0054] Preferably, the annular structure can be circular, elliptical, or other closed curve shapes. The hollowed-out area has a similar shape to the annular structure but is slightly smaller and is located at the center of the annular structure. For example, when the annular structure is circular, the hollowed-out area can be a concentric circle.

[0055] Furthermore, the secondary coil 2 includes a first part and a second part. The first part 201 of the secondary coil is located between the first part 101 and the second part of the primary coil, and the second part 202 of the secondary coil is located within the hollowed-out area. Both the first part 201 and the second part of the secondary coil are concentrically and similarly arranged with the annular structure of the primary coil 1, ensuring that the bending radius and rotation angle of the primary coil 1 and the secondary coil are completely consistent, thereby increasing the coupling area and improving signal conversion efficiency. Simultaneously, the use of a single-layer metal structure reduces parasitic impedance and signal loss.

[0056] In this embodiment, the first part 201 of the secondary coil includes multiple coil segments, which are connected to different parts of the secondary coil 2 via the bonding wire 3, thus forming the complete loop structure of the secondary coil 2. Using the bonding wire 3 to connect the different parts of the secondary coil 2 avoids complex through-hole designs, simplifies the manufacturing process, and reduces production costs. Furthermore, this structure offers good flexibility, allowing the shape and size of the coil to be adjusted according to actual needs to adapt to different application scenarios.

[0057] In some of the aforementioned solutions, the layout of the balanced and unbalanced signal ports of the high-coupling planar balun may limit signal transmission efficiency and make it difficult to adapt to the spatial layout requirements of different RF front-end modules. Therefore, in this embodiment, it is further proposed that the balanced signal port be located below the main coil 1, and can be directly connected to the bottom of the annular structure of the main coil 1, thereby shortening the wiring distance between it and the differential output of the RF power amplifier and reducing signal transmission loss. The unbalanced signal port can be located on the left, right, or top of the main coil 1, with the specific location determined by the relative layout of the power amplifier and antenna in the RF front-end module. For example, when the unbalanced signal port is located on the left side of the main coil 1, it is connected to the loop end of the secondary coil 2 through the bonding wire 3; when it is located on the right side, it is connected to the loop start end of the secondary coil 2; when it is located above, it is connected to the middle region of the secondary coil 2 through a vertically bridging bonding wire 3. The diverse configuration of the unbalanced signal port position allows the balun to adapt to the packaging requirements of RF modules of different sizes, while maintaining the integrity of the coupling area between the main and secondary coils.

[0058] In this embodiment, the main stage coil 1 has one turn. This single-turn design simplifies the structure of the main stage coil 1 and reduces manufacturing complexity. Furthermore, the single-turn main stage coil 1 can reduce the parasitic capacitance of the coil, achieving a wider operating bandwidth while maintaining good electromagnetic coupling.

[0059] In this embodiment, the secondary coil 2 has a coil number of 2, thereby increasing the coupling area between the secondary coil 2 and the primary coil 1 and improving the coupling coefficient. Simultaneously, the double-coil structure can reduce the equivalent resistance of the secondary coil 2, reducing signal transmission losses. Furthermore, the design of the secondary coil 2 with a coil number of 2 allows for a wider operating frequency band while maintaining the miniaturization of the balun, meeting the requirements of multi-band mobile communication systems.

[0060] Based on the technical solution proposed in Embodiment 1, under the same outer ring size and 20µm metal pitch conditions, the planar balun proposed in Embodiment 1 and Figure 2 and Figure 3 The traditional planar balun was compared with the simulation results shown below. Figure 5 As shown in the figure. The black curve in the figure represents the planar balun proposed in this embodiment, and the blue curve represents... Figure 2 The display shows a traditional flat baron, with the red curve being... Figure 3 Another traditional planar baron is on display.

[0061] Figure 5As shown, within the LTE band B2 and LTE band B3 transmission frequency bands (i.e., 1710-1910MHz), the coupling coefficient k of the balun proposed in this embodiment at the 1710MHz and 1910MHz frequency points is 23% higher than that of the conventional planar balun.

[0062] In summary, the primary coil 1 of this embodiment is divided into two parts, with a portion of the secondary coil 2 embedded inside the primary coil 1. This allows the primary current to be more evenly distributed across the two parts of the primary coil 1, effectively enhancing the magnetic coupling strength. Simultaneously, by optimizing the coil layout, energy loss caused by eddy currents generated inside and outside the secondary coil 2 due to the primary coil 1 is reduced, resulting in higher efficiency and lower losses in high-frequency applications.

[0063] Example 2

[0064] like Figure 6-7 As shown, this embodiment proposes a radio frequency front-end module, including the highly coupled planar balun described in Embodiment 1, and also including a radio frequency power amplifier and a matching network.

[0065] Specifically, the RF power amplifier includes two amplifiers forming a differential output. The output terminal of each amplifier is connected to one end of a decoupling capacitor 4, and the other end of the decoupling capacitor 4 is grounded. The balanced signal port of the high-coupling plane balun is connected to the two output terminals of the RF power amplifier, the unbalanced signal port of the high-coupling plane balun is connected to the input terminal of the matching network, and the output terminal of the matching network is connected to the antenna. The main coil 1 of the high-coupling plane balun is grounded through a first capacitor C1.

[0066] The RF front-end module achieves efficient signal conversion through a single-layer metal layout of primary and secondary coils and a matching network, and further suppresses common-mode noise through the first capacitor C1. High-frequency interference is filtered out through the decoupling capacitor 4 at the output of the differential power amplifier, and wide-band impedance matching is achieved through the multi-stage inductor and capacitor combination of the matching network, thereby improving the signal integrity and anti-interference capability of the RF front-end module.

[0067] In one specific embodiment, the matching network includes a high-frequency matching network, which includes a first inductor L1, a second inductor L2, a third inductor L3, a fourth inductor L4, a second capacitor C2, a third capacitor C3, and a fourth capacitor C4.

[0068] One end of the second capacitor C2 is connected to the unbalanced signal port of the high-coupling planar balun. One end of the first inductor L1 is connected to the other end of the second capacitor C2, and the other end is grounded. The first inductor L1 and the second capacitor C2 are connected in series and then grounded to adjust the high-frequency impedance. One end of the second inductor L2 is connected to the unbalanced signal port of the high-coupling planar balun. One end of the third capacitor C3 is connected to the other end of the second inductor L2. One end of the third capacitor C3 is connected to the other end of the third capacitor C3, and the other end is connected to the antenna. One end of the fourth inductor L4 is connected to the other end of the third capacitor C3, and the other end is grounded. One end of the fourth capacitor C4 is connected to the other end of the third capacitor C3, and the other end is grounded. The second inductor L2, the third capacitor C3, and the fourth capacitor C4 form the main signal transmission path, reducing high-frequency phase distortion. The fourth inductor L4 and the fourth capacitor C4 are connected to the main signal transmission path and grounded, forming a high-frequency harmonic absorption circuit to further prevent high-frequency harmonic interference. The high-frequency matching network forms an impedance matching network at different nodes through a combination of multi-level inductors and capacitors, effectively suppressing high-frequency harmonic interference and enabling low-loss transmission of high-frequency signals.

[0069] In another specific embodiment, the matching network further includes a low-frequency matching network, which includes a first inductor L1, a second inductor L2, a third inductor L3, a fourth inductor L4, a fifth inductor L5, a sixth inductor L6, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, and a fifth capacitor C5.

[0070] One end of the second capacitor C2 is connected to the unbalanced signal port of the high-coupling planar balun. One end of the first inductor L1 is connected to the other end of the second capacitor C2, and the other end is grounded. The first inductor L1 and the second capacitor C2 are connected in series and then grounded to suppress the influence of high-frequency noise on low-frequency signals. One end of the second inductor L2 is connected to the unbalanced signal port of the high-coupling planar balun. One end of the third capacitor C3 is connected to the other end of the second inductor L2. One end of the third inductor L3 is connected to the other end of the third capacitor C3, and the other end is grounded. The third capacitor C3 and the third inductor L3 are connected in series to filter out noise other than low frequencies. The fourth inductor L4 and the fourth capacitor C4 are connected in parallel, and one end of the parallel connection is connected to the other end of the second inductor L2. The fourth inductor L4 and the fourth capacitor C4 are connected in parallel to form a resonant structure, which can cancel the capacitive impedance in the low-frequency range, making it closer to a purely resistive state. The fifth capacitor C5 and the fifth inductor L5 are connected in series. One end of the series connection is connected to the other end of the parallel connection between the fourth inductor L4 and the fourth capacitor C4, and the other end is grounded. The series connection of the fifth capacitor C5 and the fifth inductor L5 is used to adjust the ratio of capacitive reactance and inductive reactance to compensate for signal phase shift. One end of the sixth inductor L6 is connected to the other end of the parallel connection between the fourth inductor L4 and the fourth capacitor C4, and the other end is connected to the antenna. The sixth inductor L6 serves as an output matching element, transmitting the optimized low-frequency signal to the antenna to ensure efficient energy radiation. The low-frequency band matching network, through the combination of multiple inductors and capacitors, achieves multiple functions such as high-frequency noise suppression, clutter filtering, impedance matching, and phase compensation. While optimizing signal transmission efficiency, it also improves the overall performance and stability of the RF system and reduces costs.

[0071] In summary, the high-coupling planar balun proposed in this invention achieves high coupling between the primary and secondary coils by designing the primary and secondary coils on the same metal layer and positioning the secondary coil portion within the hollowed-out area of ​​the primary coil. This simplifies the manufacturing process, reduces costs, and significantly improves signal conversion efficiency. Furthermore, because the primary and secondary coils are located in the same plane, the need for via connections and interlayer interconnections is reduced, minimizing the impact of parasitic parameters and enhancing the balun's performance in high-frequency applications.

[0072] Furthermore, the high coupling characteristics enable the balun to support wider bandwidths and adapt to the needs of multi-band carrier aggregation, thereby achieving a high-performance, low-cost RF front-end module.

[0073] Obviously, those skilled in the art can make various modifications and variations to this utility model without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this utility model and their equivalents, this utility model also intends to include these modifications and variations.

Claims

1. A highly coupled planar balun, characterized in that, It includes a primary coil, a secondary coil, a balanced signal port, and an unbalanced signal port, all disposed on the same metal layer; a hollow area is formed in the middle of the primary coil, a portion of the secondary coil is located within the hollow area, and the secondary coils are connected by bonding wires to form a complete loop structure; The primary coil is connected to the balanced signal port, the secondary coil is connected to the unbalanced signal port via the bonding wire, and the high-coupling planar balun is used to realize signal conversion between the balanced signal port and the unbalanced signal port.

2. The highly coupled planar balun as described in claim 1, characterized in that, The main coil includes a first part and a second part, which are adjacent to each other and together form a ring structure. The hollowed-out area is located inside the ring structure.

3. The highly coupled planar balun as described in claim 2, characterized in that, The secondary coil includes a first part and a second part. The first part is located between the first part and the second part of the primary coil, and the second part is located within the hollow area. Both the first part and the second part of the secondary coil are concentrically and similarly arranged with the annular structure of the primary coil.

4. The highly coupled planar balun as described in claim 3, characterized in that, The first part of the secondary coil includes multiple coil segments, which are connected to different parts of the secondary coil via the bonding wire, so that the secondary coil forms the complete loop structure.

5. The highly coupled planar balun as described in claim 1, characterized in that, The balanced signal port is located below the main coil; the unbalanced signal port can be located to the left, right, or above the main coil.

6. The highly coupled planar balun as described in claim 1, characterized in that, The number of turns of the main stage coil is 1.

7. The highly coupled planar balun as described in claim 1, characterized in that, The number of turns of the secondary coil is 2.

8. A radio frequency front-end module, comprising the high-coupling planar balun as described in any one of claims 1 to 7, characterized in that, It also includes an RF power amplifier and a matching network; The radio frequency power amplifier includes two amplifiers that form a differential output, with the output of each amplifier connected to one end of a decoupling capacitor and the other end of the decoupling capacitor grounded. The balanced signal port of the high-coupling planar balun is connected to the two outputs of the RF power amplifier, the unbalanced signal port of the high-coupling planar balun is connected to the input of the matching network, and the output of the matching network is connected to the antenna. The primary coil of the highly coupled planar balun is grounded via a first capacitor.

9. The radio frequency front-end module as described in claim 8, characterized in that, The matching network includes a high-frequency band matching network, which includes: The second capacitor has one end connected to the unbalanced signal port of the highly coupled planar balun; The first inductor has one end connected to the other end of the second capacitor, and the other end grounded. The second inductor is connected at one end to the unbalanced signal port of the highly coupled planar balun; The third capacitor has one end connected to the other end of the second inductor; The third inductor has one end connected to the other end of the third capacitor and the other end connected to the antenna; The fourth inductor has one end connected to the other end of the third capacitor and the other end grounded. The fourth capacitor has one end connected to the other end of the third capacitor, and the other end grounded.

10. The radio frequency front-end module as described in claim 8, characterized in that, The matching network includes a low-frequency band matching network, which includes: The second capacitor has one end connected to the unbalanced signal port of the highly coupled planar balun; The first inductor has one end connected to the other end of the second capacitor, and the other end grounded. The second inductor is connected at one end to the unbalanced signal port of the highly coupled planar balun; The third capacitor has one end connected to the other end of the second inductor; The third inductor has one end connected to the other end of the third capacitor, and the other end grounded. A fourth inductor and a fourth capacitor are connected in parallel, with one end of the parallel connection connected to the other end of the second inductor; The fifth capacitor and the fifth inductor are connected in series. One end of the series connection is connected to the other end of the fourth inductor and the fourth capacitor connected in parallel, and the other end is grounded. The sixth inductor has one end connected to the other end of the fourth inductor and the fourth capacitor connected in parallel, and the other end connected to the antenna.

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