Low-loss flexible patch antenna and deformable transmission line for millimeter wave transmission device

Abstract

A low loss flexible copper clad laminate (FCCL) for millimeter wave transmission has a dielectric layer formed between conductive copper layers, the dielectric layer comprising an electrospun nanoweb of cyclized polyacrylonitrile. The cyclized polyacrylonitrile has improved thermal stability over its uncyclized form, maintaining high porosity, which further enables injection of a second resin having a low dielectric constant to increase adhesion with the conductive copper layer and fibers or between fibers, this further enhances the dielectric properties and structural stability of the FCCL. The FCCL has a low dielectric constant and performance equivalent to that of an existing ultra-low loss material, is lower in cost, can be used as a passive radio frequency device in a high-frequency transmission system, comprises components in a high-frequency transmission device, such as a flexible antenna and a transmission line, reduces loss of signal conversion heat energy and time delay of signals, and improves the transmission efficiency of the high-frequency transmission system. The cable is especially suitable for various high-frequency signal transmission applications.

Description

Technical Field

[0001] The present invention generally relates to millimeter-wave signal transmission. More specifically, the present invention relates to a dielectric layer having an electrospun nanofiber web for high-frequency signal transmission. Background Art

[0002] As millimeter-wave (mmWave) radars and transmissions become increasingly popular, and with the development of electrical devices that utilize millimeter-wave transmissions, which include but are not limited to high-capacity and high-speed communication systems, advanced driver assistance systems (ADAS) for automobiles, signal transmission using higher-frequency waves is inevitable.

[0003] Thus, in the case where high-frequency millimeter-wave signals typically range from 30 GHz to 300 GHz (which corresponds to wavelengths of approximately 1 mm - 10 mm), the selection of dielectric materials becomes increasingly critical because their electrical properties directly affect signal propagation, transmission efficiency, and thus the overall performance of the communication system.

[0004] When selecting a suitable material as a dielectric substrate, the dielectric constant (Dk) and dielectric loss (Df) of the material are key factors to consider. A lower Dk will increase the signal propagation speed and reduce signal delay. On the other hand, a lower Df will reduce signal attenuation and improve system efficiency.

[0005] Conventional printed circuit boards (PCBs) or wiring boards typically use epoxy resins or polyimide resins as dielectric materials. However, their Dk and Df are not low enough, so their signal transmission speed is low and the transmission loss becomes very high, especially when the system is used for high-frequency signal transmission above 28 GHz. Additionally, the thermal stability of epoxy resins and polyimide resins is not high enough to withstand high-frequency transmission. The combination of these two drawbacks results in signal delay, attenuation, and component heating problems.

[0006] In response to this technical bottleneck, the industry has developed various chemical structures and methods to minimize both the dielectric constant and dielectric loss of polymer films, which include the use of poly(phenylene ether), modified polyimide (m-PI) with fluorinated substituents, and liquid crystal polymer (LCP).

[0007] However, the above solutions generally have cost and performance issues. For example, LCP has a high cost and may be difficult to process; and a design with both low Dk and low Df has not been achieved with m-PI. Therefore, there is a need in the art for a dielectric material that has ideally low Dk and Df values and good mechanical properties for high-frequency signal transmission at a reasonably low cost. Summary of the Invention

[0008] The present invention provides a flexible copper-clad laminate for millimeter-wave signal transmission with lower loss than prior art.

[0009] The flexible copper-clad laminate in the present invention includes at least one dielectric sheet layer and at least one copper conductor layer, and the dielectric sheet layer is a nanofiber web formed by electrospinning of a first resin.

[0010] The above nanofiber web includes micropores or nanopores, and a second resin is injected therein.

[0011] One important feature of the flexible copper-clad laminate of the present invention is that the difference in dielectric constant between the first resin and the second resin is less than 1.0.

[0012] The flexible copper-clad laminate in the present invention has good dielectric properties, and its Dk value is not higher than 2.5 and its Df value is not higher than 0.005 during millimeter-wave transmission.

[0013] The above structure also helps to reduce the mismatch loss caused by the braiding effect to less than 1%.

[0014] The above first resin can be selected from a variety of polymers including cyclized polyacrylonitrile, polyphenylene ether, m-polyimide, polytetrafluoroethylene, polyether ether ketone or poly-p-phthalic acid.

[0015] The above second resin can be selected from polyethylene, polyether ether ketone, polyethylene naphthalate, polyethylene terephthalate or polyimide.

[0016] The dielectric losses of the above first resin and second resin are both lower than 0.005.

[0017] The flexible copper-clad laminate of the present invention is specially designed, and the diameter of the nanofibers formed by electrospinning is 300 nanometers to 500 nanometers.

[0018] The micropores or nanopores of the above nanofiber web have an average size of 900 nanometers to 2.5 micrometers; and the porosity of the nanofiber web is 75% to 90%.

[0019] The flexible copper-clad laminate of the present invention has a coefficient of thermal expansion lower than 3.6 ppm / K, which is beneficial to maintaining signal integrity during millimeter-wave transmission and the stability of the laminate body structure.

[0020] On the other hand, the present invention also provides a high-frequency transmission device for high-frequency transmission, including the above flexible copper-clad laminate, and the device is a passive radio frequency device including but not limited to an antenna or a transmission line.

[0021] In the flexible copper-clad laminate of the above passive radio frequency device, the diameter of the nanofibers in the dielectric layer is 300 nanometers to 500 nanometers; the micropores or nanopores of the nanofiber network have an average size of 900 nanometers to 2.5 micrometers; and the porosity of the nanofiber network is 75% to 90%.

[0022] In the flexible copper-clad laminate of the above passive radio frequency device, the first resin is selected from cyclized polyacrylonitrile, polyphenylene ether, m-polyimide, polytetrafluoroethylene, polyetheretherketone or polyterephthalic acid; the second resin is selected from polyethylene, polyetheretherketone, polyethylene naphthalate, polyethylene terephthalate or polyimide; and the difference in dielectric constant between the selected first resin and the second resin is less than 1.0.

[0023] In the above passive radio frequency device, the dielectric losses of the first resin and the second resin in the flexible copper-clad laminate are both less than 0.005; and the mismatch loss caused by the weaving effect is less than 1%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Embodiments of the present invention are described in more detail below with reference to the drawings, in which:

[0025] Figure 1 is a SEM image of the structure of the flexible copper-clad laminate in the present invention, where 101 represents the copper layer and 102 represents the nanofiber network layer injected with adhesive. It should be noted that the nanofiber network layer injected with adhesive has a thickness of 30μm - 50μm, providing different thickness material options for the design of high-frequency passive devices.

[0026] Figure 2 is a sliced SEM image of the flexible copper-clad laminate in the present invention to more effectively observe its layered structure.

[0027] Figure 3A 、 3B and 3C are schematic diagrams of the structures of the antennas used in Examples 1, 2, and 3 respectively. 101 represents the copper layer, 102 represents the nanofiber network layer injected with adhesive, and 103 represents the additional dielectric layer.

[0028] Figure 4A and 4B show the overall setup of the antenna corresponding to Example 1 below. Figure 4A shows a top view of the antenna, and Figure 4B shows a side view of the antenna structure.

[0029] Figure 5A shows the return loss of the antenna in the frequency band from 26 GHz to 30 GHz. Figure 5B shows a comparison of the insertion losses of the transmission lines from the IC to the antenna of a conventional flexible printed circuit board (FPCB) and the antenna of the present invention.

[0030] Figure 6 Shows the setting for the test signal delay of the FPCB and the antenna of the present invention. The lengths of the transmission lines for both the antenna with the FCCL of the present invention and the conventional FPCB with PI are fixed at 18.4 mm.

[0031] Figure 7A and 7B Shows the overall setting of the antenna corresponding to Example 2 below. Figure 7A Shows a top view of the antenna, and Figure 7B shows a side view of the antenna structure.

[0032] Figure 8A Shows the return loss of the antenna in the frequency band from 23 GHz to 26 GHz. Figure 8B Shows the comparison of the peak gain of the antenna with frequency. Figure 8A and 8B Both are plotted using data obtained from antennas with dielectric layers of different total thicknesses.

[0033] Figure 9A and 9B Shows the overall setting of the antenna corresponding to Example 3 below. Figure 9A Shows a top view of the patch antenna with FSS, and Figure 9B shows the multi-layer integrated structure of the antenna with FSS.

[0034] Figure 10 Shows a high-quality eye diagram formed when the dielectric constant difference between the first resin and the second resin is less than 1.0. Detailed Description

[0035] The present invention relates to a low dielectric constant and loss flexible copper-clad laminate (FCCL) customized for millimeter-wave transmission. The FCCL includes a unique nanofiber network-based dielectric layer and a copper conductor layer, thereby providing high signal transmission efficiency, excellent flexibility, and good thermal stability. Incorporating a specific resin into the nanofiber network minimizes the weaving effect of the printed circuit board, thereby reducing signal distortion and attenuation during transmission. The superior properties of the FCCL make it an ideal material for high-frequency transmission devices such as antennas and transmission lines.

[0036] The low-loss flexible copper-clad laminate (FCCL) for millimeter-wave transmission described herein is designed to meet the challenges associated with high-frequency signal transmission. In one embodiment, the FCCL includes at least one dielectric sheet layer composed of an electrospun nanofiber web formed with a first resin, particularly cyclized polyacrylonitrile. As used herein, the expression "cyclized polyacrylonitrile" refers to polyacrylonitrile in which the nitrile groups have been at least partially converted to a cyclic structure under heat in the range of 200 °C to 300 °C. In this way, the material exhibits enhanced properties such as increased fiber rigidity, higher electrospun fiber web porosity for the injection of an adhesive, and lower polarizability.

[0037] The nanofiber web is characterized by the presence of micropores or nanopores, which can be through-holes or blind holes. A blind hole is a hole through which a liquid or fluid cannot pass, and a through-hole is a hole through which a liquid or fluid can pass. These micropores or nanopores contribute to the improved dielectric properties of the FCCL.

[0038] In addition, in certain embodiments, the micropores or nanopores in the nanofiber web are injected with a second resin. The second resin can be selected from one or more resins including polyethylene, polyetheretherketone, polyethylene naphthalate, polyethylene terephthalate, and polyimide, and the resin also acts as an adhesive. Injecting with this second resin helps to improve the weave effect of the printed circuit board, reduce the dielectric constant of the overall structure, and minimize signal loss during transmission.

[0039] The difference in dielectric constant between the first resin and the second resin forming the nanofiber web results in the losses caused by the printed circuit board weave effect and the eye diagram as shown in the following table. From Table 1 below and Figure 10 it can be seen that when the difference in dielectric constant between the first resin and the second resin is less than 1.0, the transmission line impedance mismatch loss caused by the weave effect can be less than 1%, and a high-quality eye pattern is formed.

[0040] Table 1: <![CDATA[ΔDk (Difference between the first resin and the second resin D K difference)]]> Loss (%) 0 0 1 0.4 2 1.2 3 2.2

[0041] In addition, the diameter of the nanofibers in the dielectric layer falls within the range of 300 nm to 500 nm, thus ensuring optimal dielectric properties and mechanical stability. The size of the micropores or nanopores in the nanofiber web can be in the range of 900 nm to 2.5 μm, thus contributing to the overall low-loss characteristics and improved flexibility of the FCCL.

[0042] In addition, the porosity of the nanofiber web in the dielectric layer can be in the range of 75% to 90%, thus providing the desired balance between low signal loss for effective millimeter-wave transmission and mechanical flexibility, and optimizing the injection with the second resin as an adhesive.

[0043] In one aspect, the FCCL exhibits a low coefficient of thermal expansion with a value below 3.6 ppm / K, ensuring stable performance over a wide range of operating temperatures and preventing performance degradation and structural instability due to heat generated during signal transmission.

[0044] The superior dielectric properties of the FCCL result in minimal dielectric loss with a value less than 0.005, ensuring efficient millimeter-wave transmission.

[0045] In addition, the FCCL exhibits low woven-effect-induced loss for millimeter-wave transmission with a value less than 1%, ensuring minimal signal attenuation during transmission.

[0046] The applications of the low-loss flexible copper-clad laminate described herein extend to various high-frequency transmission devices, including antennas and transmission lines, suitable for efficient and reliable high-frequency signal transmission.

[0047] Compared with known liquid crystal polymer (LCP) and polytetrafluoroethylene (PTFE) ultra-low-loss transmission materials for transmission (materials defined as having a Dk value below 2.9 and a Df value below 0.003), the flexible copper-clad laminate of the present invention exhibits properties comparable to the above materials (as shown in the following examples), but at a significantly lower cost. In addition, the FCCL material provides high design flexibility for use in flexible antennas or high-speed transmission cables, which have a wide range of applications, including radar detectors for autonomous driving vehicles, high-speed high-frequency data transmission lines, and aviation and communication applications.

[0048] Examples

[0049] Table 2 below shows the properties of the FCCL of the present invention, where the property tests follow ASTM, IPC, and JIS standards. In addition, the FCCL also passes reliability tests under international standards of JIS-C5016-9.5 (regarding water absorption) and JIS-C5016-10.5 (regarding peel strength).

[0050] Table 2:

[0051] Table 3 below shows the dielectric properties of each nanofiber raw material used in the present invention.

[0052] Table 3:

[0053] Example 1 - Study on the Relationship between Nanofiber Diameter, Porosity, and Dk / Df

[0054] As shown below, when polyacrylonitrile (PAN) undergoes heat treatment at 200 °C - 300 °C under 1 atm, the nitrile groups will cyclize, thus changing the physical properties of the polymer, including pore size, porosity, and dielectric properties.

[0055] The average pore sizes of PAN samples with different average fiber diameters were studied before and after cyclization, and the results are shown in Table 4 below:

[0056] Table 4:

[0057] In addition, the dielectric properties of the cyclized PAN (cPAN) nanofibers were measured, as shown in Table 5.

[0058] Table 5:

[0059] Example 2 - Measurement of Dk and Df Values of Nanofibers

[0060] The Dk and Df values of (i) only electrospun cPAN nanofibers; (ii) only the binder; and (iii) electrospun cPAN nanofibers laminated with the binder were measured over a range of high frequencies. Different nanofibers laminated with the binder also underwent the same Dk and Df value measurements. The results are listed in Tables 6 to 10 below.

[0061] Table 6 (only cPAN nanofiber samples):

[0062] Table 7 (only PPO nanofiber samples):

[0063] Table 8 (only PTFE nanofiber samples):

[0064] Table 9 (only the binder):

[0065] Table 10 (nanofiber samples laminated with the binder):

[0066] Example 3 - Antenna and Transmission Line

[0067] In this example, the dielectric substrate of the antenna is in accordance with Figure 3AA three-layer structure arrangement, where the cPAN nanofiber mesh layer injected with an adhesive is coated with copper on both the upper surface and the lower surface to form a flexible copper-clad laminate (FCCL).

[0068] The antenna structure is a 2X2 microstrip antenna array. The upper copper layer is used to etch the antenna pattern, and the lower copper layer serves as the reflecting surface of the antenna and is grounded. The transmission line connecting the antenna to other modules or ICs in the system is a grounded coplanar waveguide (GCPW) transmission line. This form of transmission line can provide a better shielding effect for signal transmission to ensure signal transmission quality.

[0069] According to Figure 4A and 4B Design an antenna with the above FCCL and a transmission line. Subsequently, measure the return loss of the antenna and the insertion loss of the corresponding transmission line, as shown in Figure 5A and 5B respectively. The insertion loss of an FPCB transmission line with a traditional dielectric material PI is also plotted in Figure 5B for comparison. The insertion loss of the transmission line with FCCL of the present invention is lower than that of the transmission line using traditional materials in the millimeter-wave band.

[0070] Table 11 below shows the insertion losses of the transmission lines of the material of the present invention and the traditional PI material at common frequency points in the radio frequency system. It can be seen that the insertion loss of the transmission line based on the material of the present invention is lower than that of the traditional PI material in the millimeter-wave band.

[0071] Table 11:

[0072] From Figure 4A Observe the resonant frequency band, and also measure the peak gain of the antenna accordingly, as shown in Table 12 below.

[0073] Table 12: Resonant Band (GHz) Peak Gain (dBi) 28.4-28.7 4.2 (measured at 28.5 GHz)

[0074] Conduct further signal delay measurements on the cPAN transmission line of the present invention and the transmission line with PI. The signal delay test setup is shown in Figure 6 (the length of the transmission line is 18.4 mm), and the time delay measured based on the network analyzer is shown in Table 13.

[0075] Table 13: Frequency (GHz) Time Delay - cPAN (ps) Time Delay - PI (ps) Delay Percentage 1 276.88 281.94 -1.8％ 5 271.43 283.3 -4.2％ 28 249.63 312.98 -20.2％ 40 275.98 373.24 -26.1％

[0076] Referring to Table 10, the dielectric constants (Dk) of cPAN and PI are 2.1 and approximately 3.6 respectively. The Dk value can affect the transmission delay. It can be observed from the following data that cPAN not only has generally lower time delay in signal transmission, so the FCCL of the present invention based on cPAN material is more superior to the traditional FPCB in high-frequency and high-speed transmission.

[0077] Example 4

[0078] According to another embodiment of the present invention, the dielectric substrate is arranged in a five-layer structure, as Figure 3B shown, in which an additional laminated dielectric layer is inserted between the nanofiber mesh layers.

[0079] The antenna adopts the structure as Figure 7A and 7B shown. The antenna is a microstrip antenna. The upper copper layer is used for etching the antenna pattern, and the lower copper layer is used for the antenna reflecting surface and grounding.

[0080] The return loss and peak gain of antennas with different thicknesses of the same structure are measured. Each antenna is formed with the dielectric substrate structure described in the above paragraph

[0038] , but with dielectric layers of different thicknesses. The measurement results of the return loss and peak gain of the antennas are shown in Figure 8A and 8B shown.

[0081] From Figure 8A it is observed that the resonant frequency of the antenna is found in the range of 24 GHz to 25 GHz.

[0082] From Figure 8A and 8B it is observed that the increased total thickness of the dielectric layer generally improves both the return loss and gain of the antenna. It is recommended that a low-cost dielectric material (such as PI) can be used to increase the total thickness of the dielectric layer, and this will not significantly increase the dielectric material loss, and thus improve the antenna gain.

[0083] Example 5

[0084] According to another embodiment of the present invention, a multi-layer structure of a microstrip antenna integrated with frequency selective surface (FSS) units is adopted, as Figure 9A and 9B shown.

[0085] The FSS unit structure consists of two semi-circular split rings and a semi-circular metal patch placed inside the semi-circular split ring. The resonant frequency of the antenna can be changed by adjusting the lengths of the two arms of the semi-circle. The FSS is printed on a low-loss material with a nanofiber structure to further reduce the dielectric constant and loss. The above frequency selective surface is placed on top of a microstrip antenna to form a multi-layer integrated structure of the FSS and the antenna. The lens function of the FSS will be used to improve the antenna gain and achieve a high-gain, thin and light millimeter-wave antenna.

[0086] Measure the gain of the multi-layer microstrip antenna with the FSS. A microstrip antenna with the same structure but without the FSS unit is used as a reference. The results are shown in Table 14 below.

[0087] Table 14: Without FSS With FSS Percentage Increase Antenna Peak Gain at 28 GHz 5.9 dBi 7.4 dBi 25％

[0088] It is observed that the gain of the patch antenna is improved at 28 GHz by using the FSS.

[0089] The foregoing description of the invention has been provided for purposes of illustration and description. The invention is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations will be obvious to those of ordinary skill in the art.

[0090] The embodiments are chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling other persons skilled in the art to understand the various embodiments of the invention and the various modifications suitable for the particular use contemplated.

[0091] Definitions

[0092] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising" shall be understood to imply the inclusion of the stated integer or group of integers but not the exclusion of any other integer or group of integers. It should also be noted that in this disclosure and particularly in the claims and / or paragraphs, terms such as "comprises", "comprised", "comprising", etc. may have the meaning given to them in US patent law; for example, they permit the non-explicit recitation of an element, but exclude elements that are already present in the prior art or that affect the basic or novel features of the invention.

[0093] Throughout this specification and the claims, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0094] References in this specification to "one embodiment" or "an embodiment" etc. indicate that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the invention. However, each embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that, whether or not explicitly described, implementation of such feature, structure, or characteristic in connection with other embodiments is within the knowledge of persons skilled in the art.

[0095] Other definitions for selected terms used herein may be considered within the detailed description of the invention and applicable throughout the detailed description of the invention. Unless otherwise defined, all other technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0096] Persons skilled in the art will appreciate that, given these teachings, alternative embodiments may be practiced without undue experimentation or departing from the spirit or scope of the invention as set forth in the appended claims. The invention is limited only by the appended claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and drawings.

Claims

1. A low-loss flexible copper-clad laminate (FCCL) for millimeter-wave transmission, characterized in that, it comprises at least one dielectric sheet layer and at least one conductor layer, wherein: the dielectric layer is a nanofiber network, wherein the nanofibers are formed by electrospinning of a first resin; the nanofiber network comprises micropores or nanopores, wherein the micropores or nanopores are through-holes or blind holes; the nanofiber network is infused with a second resin; and wherein the conductor layer is copper; wherein the low-loss flexible copper-clad laminate has a Dk value below 2.5 and a Df value below 0.005 under millimeter-wave transmission; wherein the difference in dielectric constant between the first resin and the second resin is less than 1; and wherein the transmission line impedance mismatch loss caused by the braiding effect is less than 1%.

2. The low-loss flexible copper-clad laminate according to claim 1, characterized in that, the first resin is selected from cyclized polyacrylonitrile, polyphenylene ether, m-polyimide, polytetrafluoroethylene, polyetheretherketone or polyterephthalic acid.

3. The low-loss flexible copper-clad laminate according to claim 1, characterized in that, the second resin is selected from polyethylene, polyetheretherketone, polyethylene naphthalate, polyethylene terephthalate or polyimide.

4. The low-loss flexible copper-clad laminate according to claim 2, characterized in that, the dielectric losses of both the first resin and the second resin are less than 0.

005.

5. The low-loss flexible copper-clad laminate according to claim 1, characterized in that, the diameter of the nanofibers in the dielectric layer is from 300 nm to 500 nm.

6. The low-loss flexible copper-clad laminate according to claim 1, characterized in that, the size of the micropores or nanopores in the nanofiber network is from 900 nm to 2.5 μm.

7. The low-loss flexible copper-clad laminate according to claim 1, characterized in that, the porosity of the nanofiber network in the dielectric layer is from 75% to 90%.

8. The low-loss flexible copper-clad laminate according to claim 1, characterized in that, the laminate has a coefficient of thermal expansion below 3.6 ppm / K.

9. A high-frequency transmission device for transmitting high-frequency signals, characterized in that, it comprises the low-loss flexible copper-clad laminate according to claim 1.

10. The high-frequency transmission device according to claim 9, characterized in that, the device is a passive radio frequency device including an antenna or a transmission line, etc.

11. The high-frequency transmission device according to claim 9, characterized in that: the nanofiber network in the dielectric layer of the low-loss flexible copper-clad laminate is formed by electrospinning of a first resin, wherein the first resin is selected from cyclized polyacrylonitrile, polyphenylene ether, m-polyimide, polytetrafluoroethylene, polyetheretherketone or polyterephthalic acid; the diameter of the nanofibers in the dielectric layer of the low-loss flexible copper-clad laminate is from 300 nm to 500 nm; the size of the micropores or nanopores in the nanofiber network of the low-loss flexible copper-clad laminate is from 900 nm to 2.5 μm; The porosity of the nanofiber network in the dielectric layer of the low-loss flexible copper-clad laminate is 75% to 90%; The nanofiber network in the dielectric layer of the low-loss flexible copper-clad laminate is infused with a second resin selected from: polyethylene, polyetheretherketone, polyethylene naphthalate, polyethylene terephthalate, or polyimide; The difference in dielectric constant between the first resin and the second resin in the low-loss flexible copper-clad laminate is less than 1.0; The dielectric losses of both the first resin and the second resin in the low-loss flexible copper-clad laminate are less than 0.005; and The transmission line mismatch loss caused by the braiding effect of the low-loss flexible copper-clad laminate is less than 1%.

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