Leaky coaxial cable

Abstract

In a leaky coaxial cable capable of radiating circularly polarized electromagnetic waves, the power of the leaked electromagnetic waves is increased to enable good use in power transmission applications. [Solution] The leaky coaxial cable comprises an inner conductor, an insulator, and an outer conductor. The outer conductor comprises a feed section, a radiating section, and an impedance matching transformer. The feed section is formed when the outer conductor surrounds the entire outer circumference of the inner conductor, resulting in a 100% coverage of the insulator surface. The radiating section is wound around the insulator in a single helix with a constant pitch to form a gap, resulting in a coverage of less than 50% of the insulator surface. The transformer is positioned between the feed section and the radiating section at a distance in the axial direction of the inner conductor, and connects the feed section and the radiating section.

Description

Technical Field

[0001] The present disclosure relates to a leaky coaxial cable capable of radiating circularly polarized waves.

Background Art

[0002] As described in Patent Document 1, an external conductor is wound in a single helix at a constant pitch on the surface of an insulator covering the periphery of a linear inner conductor, so that circularly polarized electromagnetic waves are radiated when a high-frequency signal is input. A leaky coaxial cable configured as such is known. Since this leaky coaxial cable radiates circularly polarized electromagnetic waves, on the receiving side that receives the electromagnetic waves, there is no need to adjust the orientation of the receiving antenna, which is convenient to use.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the leaky coaxial cable described in Patent Document 1, the occupancy rate of the external conductor on the insulator surface is 50% or more, preferably 69% or more, and the VSWR (voltage standing wave ratio) representing the relationship between the incident wave and the reflected wave to the leaky coaxial cable is 2.0 or less. This is because in Patent Document 1, it is assumed that the leaky coaxial cable is used for communication purposes to transmit and receive high-frequency signals in the frequency band of 800 MHz to 2400 MHz.

[0005] [[ID=3 8]] However, leaky coaxial cables can also be used for power transmission applications, such as supplying power to external devices like RFID tags with high-frequency signals in a narrow frequency band of 850MHz to 930MHz. In this case, if the occupancy rate of the outer conductor on the insulator surface is set to 50% or more, the radiated power of electromagnetic waves from the leaky coaxial cable is suppressed, resulting in the problem of not being able to supply the desired power to the external device.

[0006] One aspect of this disclosure is to increase the power of the leaked electromagnetic waves in a leaky coaxial cable capable of radiating circularly polarized electromagnetic waves, thereby enabling its use in power transmission applications. [Means for solving the problem]

[0007] One aspect of the leaky coaxial cable of this disclosure comprises an inner conductor extending along an axis, an insulator covering the inner conductor, and an outer conductor provided around the insulator. The outer conductor also comprises a power supply section, a radiating section, and an impedance matching transformer.

[0008] Of these components, the power supply section surrounds the entire outer circumference of the inner conductor and is configured to occupy 100% of the surface area of ​​the insulator. The radiating section is wound around the insulator in a single helix with a constant pitch to form a gap and is configured to occupy less than 50% of the surface area of ​​the insulator. The transformer is positioned between the power supply section and the radiating section, spaced apart in the axial direction of the inner conductor, and is configured to connect the power supply section and the radiating section.

[0009] With the leaky coaxial cable of this disclosure configured in this way, the occupancy rate on the surface of the insulator of the radiating portion is less than 50%, which allows for a higher electromagnetic wave radiating power compared to the one described in Patent Document 1, making it suitable for use in power transmission applications.

[0010] On the other hand, reducing the occupancy rate on the insulating surface of the radiating section increases the impedance difference between the power supply section and the radiating section. This makes the high-frequency signal being transmitted more easily reflected at the coupling point, worsening the reflection loss (return loss) in the leaky coaxial cable.

[0011] Therefore, in the leaky coaxial cable of this disclosure, a transformer is provided between the power supply section and the radiating section. As a result, reflection of high-frequency signals at the coupling section between the power supply section and the radiating section is suppressed, and the return loss in the leaky coaxial cable, and consequently the transmission loss of high-frequency signals, can be improved.

[0012] Therefore, by using the leaky coaxial cable of this disclosure in power transmission applications that transmit high-frequency signals with a limited frequency bandwidth, it becomes possible to transmit or receive high-frequency signals efficiently with low loss. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic side view showing the configuration of the leaky coaxial cable of the embodiment. [Figure 2] This is an explanatory diagram showing the outer conductor shown in Figure 1 unfolded around the axis of the inner conductor. [Figure 3] This graph shows the simulation results of return loss when the metal coverage ratio of the transformer section on the insulator surface is changed. [Figure 4] This graph, similar to Figure 3, shows the simulation results of the transmission loss when the metal coverage ratio of the transformer section is changed. [Figure 5] This graph shows the simulation results of the return loss used to confirm the configurable range of the metal coverage ratio in the transformer section. [Figure 6] This graph, similar to Figure 5, shows the simulation results of the transmission loss when the metal coverage ratio of the transformer section is changed. [Figure 7] These are graphs showing the directivity of a leaky coaxial cable. Figure 7A shows the directivity of the leaky coaxial cable in the embodiment, and Figure 7B shows the directivity of a leaky coaxial cable without a transformer. [Figure 8] A graph representing a comparison of the simulation results of the return loss of the leaky coaxial cable of the first modified example with that of a leaky coaxial cable without a transformer section. [Figure 9] A graph representing a comparison of the simulation results of the transmission loss of the leaky coaxial cable of the first modified example with that of a leaky coaxial cable without a transformer section. [Figure 10] A graph representing a comparison of the simulation results of the return loss of the leaky coaxial cable of the second modified example with that of a leaky coaxial cable without a transformer section. [Figure 11] A graph representing a comparison of the simulation results of the transmission loss of the leaky coaxial cable of the second modified example with that of a leaky coaxial cable without a transformer section.

Embodiments for Carrying Out the Invention

[0014] Embodiments of the present disclosure will be described below. The leaky coaxial cable 10 of the present embodiment is a leaky coaxial cable used for power transmission applications that operates each of these parts by supplying power to an RFID tag or various sensors.

[0015] Therefore, during power supply, a transmitter (not shown) that generates a high-frequency signal of a predetermined frequency for power supply is connected to one end of the leaky coaxial cable 10 via a connector 26 shown by a dotted line in FIG. 1 or the like. Also, the other end of the leaky coaxial cable 10 is terminated or open-circuited with a dummy resistor having a resistance value corresponding to the characteristic impedance of the coaxial cable.

[0016] In the present embodiment, as the high-frequency signal for power supply, for example, a narrow-band high-frequency signal in the 920 MHz band such as 918 MHz or 919.2 MHz is used.

[0017] [Configuration] As shown in FIG. 1, the leaky coaxial cable 10 has a linear inner conductor 20 extending along the axis 12. For the inner conductor 20, for example, copper wire is used, and the outer peripheral surface of the inner conductor 20 is covered by a cylindrical insulator 22 provided concentrically. And an outer conductor 30 is provided on the outer peripheral surface of the insulator 22.

[0018] As the material of the insulator 22, for example, polyethylene, polytetrafluoroethylene, vinyl chloride, or foams thereof can be used. Further, the inner diameter of the outer conductor 30 (in other words, the outer diameter of the insulator 22) is set according to the specifications of coaxial cables such as 5C, 8C, 5D, 8D, etc.

[0019] Also, the outer diameter of the inner conductor 20 is appropriately adjusted in consideration of the relative dielectric constant εr of the insulator 22 so that the characteristic impedance of the leaky coaxial cable 10 becomes 75 Ω or 50 Ω, which is the characteristic impedance corresponding to the coaxial cable specifications 5C, 8C or 5D, 8D.

[0020] Note that the outer peripheral surface of the outer conductor 30 is covered by an electrically insulating sheath (not shown). As the material of the sheath, for example, polyethylene, vinyl chloride, or a non-halogen-based flame retardant can be used.

[0021] The outer conductor 30 includes a power feeding portion 32 to which a connector 26 is attached, a radiation portion 34 for high-frequency signals, and a transformer portion 36 that functions as an impedance matching transformer. Among these, the power feeding portion 32 surrounds the entire outer periphery of the inner conductor 20 and is configured such that the occupancy rate on the surface of the insulator 22 is 100%. That is, the power feeding portion 32 constitutes a general coaxial cable.

[0022] Next, the radiation portion 34 is wound in a single-layer spiral shape at a constant pitch P so as to form a gap around the insulator 22. For example, the radiation portion 34 is formed by winding a metal tape coated with an adhesive on a single strip-shaped metal foil around the insulator 22 at a constant pitch P in a single-layer spiral shape.

[0023] For example, copper, aluminum, or silver can be used as the metal foil constituting the radial portion 34. Furthermore, this metal foil may have a thickness of, for example, 20 μm to 300 μm.

[0024] Next, the transformer section 36, acting as a transformer, is positioned between the power supply section 32 and the radiating section 34, with a gap in the axial direction of the internal conductor 20, and connects the power supply section 32 and the radiating section 34. As shown in Figure 2, the transformer section 36 is constructed by widening the width around the axis 12 of the main body portion extending from the radiating section 34 toward the power supply section 32 on the surface of the insulator 22 compared to the radiating section 34. For this reason, the transformer section 36 can be constructed, for example, by attaching a metal tape, which is a strip of metal foil coated with adhesive, around the insulator 22, similar to the radiating section 34.

[0025] In this way, by attaching strip-shaped metal foil to the surface of the insulator 22 using adhesive as the radiating portion 34 and the transforming portion 36, it is possible to suppress changes in the shape of the radiating portion 34 and the transforming portion 36 relative to the insulator 22, even if the leaky coaxial cable 10 is deformed during transportation or other events.

[0026] Furthermore, when winding the radiating portion 34 and transformer portion 36 onto the surface of the insulator 22, it is not always necessary to use an adhesive to attach the strip-shaped metal foil to the insulator 22. For example, after winding the radiating portion 34 and transformer portion 36 onto the surface of the insulator 22, these portions may be fixed to the surface of the insulator 22 by pressing them from the outside with a sheath or the like.

[0027] Here, the pitch P of the radiating portion 34 is the winding period of the metal foil in the axial direction of the leaky coaxial cable 10, and is the length the metal foil advances in the axial direction of the internal conductor 20 when it completes one revolution around the insulator 22. In this embodiment, the length of the metal foil in the axial direction along the axis 12 of the internal conductor 20 in the radiating portion 34 is called the outer conductor width Wm.

[0028] The pitch P of the radial portion 34 is greater than the width Wm of the outer conductor, and the radial portion 34 is wound around the outer surface of the insulator 22 while forming a single helical groove (gap). In this embodiment, as shown in Figure 2, the distance between radial portions 34 in a direction perpendicular to the side edge of the radial portion 34 when the outer conductor 30 is projected onto the outer surface plane of the insulator 22 around the axis 12 of the inner conductor 20 is called the gap width Wg.

[0029] In the leaky coaxial cable 10 of this embodiment, the relationship shown in equation (1) below holds true in the radiating section 34, similar to that described in Patent Document 1. In equation (1), εr is the relative permittivity of the insulator 22, λo is the wavelength of the applied high-frequency signal (design wavelength), and P is the winding pitch of the radiating section 34. The relative permittivity εr of the insulator 22 is frequency-dependent, but naturally, it is the value at the frequency of the applied high-frequency signal.

[0030]

number

[0031] Furthermore, in this embodiment, the leaky coaxial cable 10 is configured such that the occupancy rate of the radiating portion 34 (in other words, the metal foil constituting the radiating portion 34) on the outer surface of the insulator 22 is less than 50%. The occupancy rate (%) of the radiating portion 34 on the outer surface of the insulator 22 can be calculated as "(Wm / P) × 100" by dividing the outer conductor width Wm by the pitch P.

[0032] On the other hand, since the transformer section 36 is constructed by widening the width around the axis 12 of the internal conductor 20 compared to the radiating section 34, the occupancy rate of the transformer section 36 (in other words, the metal foil constituting the transformer section 36) on the outer surface of the insulator 22 is greater than that of the radiating section 34.

[0033] In this embodiment, the occupancy rate of the radiating portion 34 and the transformer portion 36 on the outer surface of the insulator 22 is also referred to as the metal cover rate. As described above, in this embodiment, a transformer section 36 is provided between the power supply section 32 and the radiating section 34. This is because, although reducing the metal coverage ratio of the radiating section 34 to less than 50% would increase the leakage power from the radiating section 34 compared to the one described in Patent Document 1, it would worsen the return loss, and as a result, it may not be possible to supply the desired power to external equipment.

[0034] In other words, in this embodiment, by providing a transformer section 36 with a metal coverage ratio greater than that of the transformer section 36 between the power supply section 32 and the radiating section 34, the return loss of the leaky coaxial cable 10 is improved, and the desired power can be supplied to external equipment.

[0035] Here, the transformer section 36 has its axial length of the internal conductor 20 and its metal cover ratio set according to general design methods. In other words, the axial length Lt (see Figure 2) of the internal conductor 20 of the transformer section 36 is set to be 1 / 4 (i.e., λ / 4) of the wavelength λ of the high-frequency signal. However, this wavelength λ is the wavelength that takes into account the wavelength shortening factor in the coaxial structure.

[0036] Furthermore, the metal coverage ratio of the transformer section 36 is set such that, when the characteristic impedance of the power supply section 32 is Z1 and the characteristic impedance of the radiating section 34 is Z2, the characteristic impedance of the transformer section 36 is the geometric mean of these two values, "√(Z1 × Z2)".

[0037] However, the metal coverage ratio of the transformer section 36 does not need to be precisely adjusted so that the characteristic impedance of the transformer section 36 matches the above-mentioned geometric mean value; it is sufficient to set it to be within a predetermined range centered on the above-mentioned geometric mean value (for example, within ±6%).

[0038] The basic configuration of the leaky coaxial cable 10 in this embodiment is, for example, an 8D size coaxial cable in which the diameter of the inner conductor 20 is 3 mm, the diameter of the outer conductor 30 is 7.8 mm, and the relative permittivity of the insulator 22 is 1.32. As shown in Table 1, the pitch P of the radiating section 34 is 158 mm, the outer conductor width Wm is 52.2 mm, the gap width Wg is 16.2 mm, and the metal coverage ratio of the radiating section 34 is 33%. The length Lt of the transformer section 36 is 70 mm, and the metal coverage ratio of the transformer section 36 is 50%.

[0039] [Table 1]

[0040] [effect] In the leaky coaxial cable 10 of this embodiment, configured as described above, the return loss was measured (simulated) with the axial length (total length) of the radiating section 34 set to 2m, and as shown in Table 1, the return loss was 23.8dB.

[0041] In contrast, the return loss of the leaky coaxial cable without the transformer section 36 was 9.9 dB. Therefore, it can be seen that the return loss can be improved with the leaky coaxial cable 10 of this embodiment compared to the leaky coaxial cable without the transformer section 36.

[0042] The return loss represents the attenuation (in other words, reflection loss) of the power of the high-frequency signal input from the power supply section 32 of the leaky coaxial cable 10, which is reflected at the end of the leaky coaxial cable 10 and reaches the input end. The return loss listed in Table 1 is the worst-case value within the frequency band of 900 MHz to 1 GHz.

[0043] Thus, with the leaky coaxial cable 10 of this embodiment, even though the metal coverage rate of the radiating section 34 is less than 50% (33%), the return loss caused by impedance mismatch between the power supply section 32 and the radiating section 34 can be improved by providing the transformer section 36. Furthermore, simulations described later confirmed that the transmission loss of high-frequency signals (in other words, insertion loss) can also be improved.

[0044] Therefore, the leaky coaxial cable 10 of this embodiment can be used for power transmission applications that transmit high-frequency signals with a limited frequency bandwidth (920 MHz band in this embodiment), enabling efficient transmission or reception of high-frequency signals with low loss.

[0045] Furthermore, in this embodiment, the leaky coaxial cable 10 can improve return loss by providing a transformer section 36 between the power supply section 32 and the radiating section 34, and adjusting its metal coverage ratio through calculations or other means.

[0046] Therefore, the design work for the leaky coaxial cable 10 can be simplified compared to improving return loss in a leaky coaxial cable that does not have a transformer section 36. In other words, in conventional leaky coaxial cables that do not have a transformer section 36, the return loss can be improved by adjusting the winding pitch of the metal tape constituting the radiating section 34. However, this requires adjusting the winding pitch over the entire axial direction of the radiating section 34, making the design work for improving the return loss complicated. Therefore, with the leaky coaxial cable 10 of this embodiment, the design work for improving the return loss can be performed much more easily compared to conventional leaky coaxial cables.

[0047] Next, we will explain the simulation conducted to confirm the effects obtained by providing the transformer section 36 described above. [Simulation 1] In Simulation 1, the metal coverage ratio of the transformer section 36 was varied from 33% (the same as the radiating section 34) to 66% in 5.5% increments, and the return loss and through loss of the leaky coaxial cable 10 were measured (simulated). The simulation results are shown in Figures 3 and 4.

[0048] In Simulation 1, similar to the return loss simulation shown in Table 1 above, an 8D size coaxial cable was used, with the axial length of the radiating section 34 set to 2m and the metal coverage of the radiating section 34 set to 33%. The pitch P of the radiating section 34, the outer conductor width Wm, the gap width Wg, and the length Lt of the transformer section 36 are as shown in Table 1.

[0049] As shown in Figure 3, the results of Simulation 1 showed that when the metal coverage ratio of the transformer section 36 was set to 33%, the same as the radiating section 34, that is, when the transformer section 36 was absent, the return loss in the 900MHz to 1GHz frequency band was the worst. In contrast, when the metal coverage ratio of the transformer section 36 was set to 49.5%, the return loss in the 900MHz to 1GHz frequency band was the best.

[0050] Furthermore, it was found that setting the metal coverage ratio of the transformer section 36 to 49.5% significantly improved the return loss compared to cases where the metal coverage ratio of the transformer section 36 was set to 38.5%, 44%, 55%, 60.5%, or 66%.

[0051] Furthermore, as shown in Figure 4, the results of Simulation 1 showed that the pass-through loss was best in the frequency band of 900 MHz to 1 GHz when the metal coverage ratio of the transformer section 36 was set to 49.5%.

[0052] Furthermore, it was found that when the metal coverage ratio of the transformer section 36 was set to 49.5%, fluctuations in pass-through loss (so-called ripple) within the frequency band of 900MHz to 1GHz were eliminated, and the pass-through loss characteristics were greatly improved.

[0053] Therefore, the simulation results of return loss and through loss shown in Figures 3 and 4 clearly show that the return loss and through loss of the leaky coaxial cable 10 can be improved by providing a transformer section 36 between the power supply section 32 and the radiating section 34.

[0054] Furthermore, it can be confirmed that if the metal coverage ratio of the radiating section 34 is 33%, setting the metal coverage ratio of the transformer section 36 to 49.5% is beneficial in order to better improve the return loss and through loss of the leaky coaxial cable 10.

[0055] On the other hand, when the metal coverage ratio of the transformer section 36 was set to 49.5%, the characteristic impedance of the transformer section 36 was found to be 62.7Ω when analyzed using a two-dimensional waveguide analysis (so-called 2D analysis). In contrast, the 2D analysis result for the characteristic impedance of the power supply section 32, where the metal coverage ratio is 100%, was 48.9Ω, and the 2D analysis result for the characteristic impedance of the radiating section 34, where the metal coverage ratio is 33%, was 75.4Ω.

[0056] Therefore, it can be seen that the characteristic impedance of the transformer section 36 should be set within a predetermined range centered on the geometric mean value "√(Z1×Z2)" of the characteristic impedance Z1 of the feed section 32 and the characteristic impedance Z2 of the radiating section 34, in accordance with the design method of a quarter-wavelength matching circuit.

[0057] In other words, if we assume from the above 2D analysis results that Z1 is 48.9Ω and Z2 is 75.4Ω, then the geometric mean is 60.7Ω. Furthermore, from the above 2D analysis results, the characteristic impedance of the transformer section 36 is 62.7Ω. Therefore, the metal coverage ratio of the transformer section 36 should be adjusted so that its characteristic impedance is close to the geometric mean of the characteristic impedances Z1 and Z2 of the power supply section 32 and the radiating section 34.

[0058] [Simulation 2] In Simulation 2, a simulation was performed to confirm the range of metal coverage of the transformer section 36 that can actually be set, based on the geometric mean of the characteristic impedances Z1 and Z2 of the power supply section 32 and the radiating section 34 described above: 60.7Ω.

[0059] Specifically, the metal coverage ratio of the transformer section 36 was varied to approximately 53.625%, which corresponds to a geometric mean of 60.7 Ω, and the return loss and through loss of the leaky coaxial cable 10 were measured (simulated).

[0060] In Simulation 2, the materials and dimensions of each part of the leaky coaxial cable 10 are the same as in Simulation 1, and the only difference from Simulation 1 is the metal coverage ratio (in other words, characteristic impedance) of the transformer section 36.

[0061] In other words, in Simulation 2, as shown in Figures 5 and 6, the metal coverage ratio of the transformer section 36 was set to 46.75%, 48.125%, 49.5%, 50.875%, 52.25%, 53.625%, and 55%.

[0062] The characteristic impedance of the transformer section 36 is 64.2Ω when the metal coverage is 46.75%, 62.75Ω when the metal coverage is 49.5%, 61.25Ω when the metal coverage is 52.25%, and 59.95Ω when the metal coverage is 59.95%.

[0063] Furthermore, when the metal coverage is 53.625%, the characteristic impedance is 60.6Ω, which is the closest to the geometric mean of the characteristic impedances Z1 and Z2 of the power supply section 32 and the radiating section 34: 60.7Ω.

[0064] In the return loss simulation results in Figure 5, the downward arrows indicate the point where the return loss is worst within the frequency band of 900 MHz to 1 GHz for each of the above metal coverage rates.

[0065] From these simulation results, it was found that the return loss is not best in the transformer section 36 whose characteristic impedance is closest to the geometric mean, but when the characteristic impedance of the transformer section 36 is 60.6Ω to 64.2Ω, the return loss is 15dB or less.

[0066] Furthermore, from the simulation results of the pass-through loss shown in Figure 6, it was found that when the characteristic impedance of the transformer section 36 is 60.6Ω to 64.2Ω, the fluctuation in pass-through loss (so-called ripple) becomes 0.1dB or less.

[0067] Therefore, it can be seen that the metal coverage ratio of the transformer section 36 should be set so that the characteristic impedance of the transformer section 36 is within a range of a few ohms from the geometric mean value "√(Z1 × Z2)" of the characteristic impedances Z1 and Z2 of the power supply section 32 and the radiation section 34.

[0068] [Simulation 3] In Simulation 3, the directivity of the leaky coaxial cable 10 of the above embodiment was measured (simulated) assuming that it radiates a high-frequency signal in the 920 MHz band. Similarly, the directivity of a leaky coaxial cable without the transformer section 36 was also measured (simulated).

[0069] Specifically, when a 920 MHz high-frequency signal was input to the power supply unit 32, the intensity of the left-hand and right-hand circularly polarized waves radiated from the radiating unit 34 was calculated in an angular range of -90 to +90 degrees, with the direction perpendicular to the axis 12 of the internal conductor 20 being 0 degrees. The simulation results are shown in Figures 7A and 7B.

[0070] From the results of this simulation 3, as shown in Figures 7A and 7B, the intensity of the left-hand circular polarization, which is the dominant mode, peaked at a radiation angle of -60 degrees in both coaxial cables, indicating that maximum power could be supplied to external equipment at that radiation angle. It was also confirmed that the directivity did not change significantly depending on the presence or absence of the transformer section 36.

[0071] The reason why left-hand circular polarization is the primary mode is that, in this embodiment, the leakage coaxial cable 10 has a right-handed winding at the radiating section 34 when viewed from the power supply section 32, making it easier to radiate left-hand circularly polarized electromagnetic waves.

[0072] In the above embodiments and simulations 1-3, the metal coverage ratio of the radiating portion 34 of the leaky coaxial cable 10 was assumed to be 33%. In contrast, in the following modified examples, we investigated whether the same effect could be obtained by further reducing the metal coverage ratio of the radiating portion 34. Specifically, simulations were conducted to confirm whether the technology of this disclosure could be applied even when the metal coverage ratio of the radiating portion 34 of the leaky coaxial cable 10 was set to 5% and 1%.

[0073] Below, the simulation results when the metal coverage rate of the radiating portion 34 is set to 5% are described as the first modified example, and the simulation results when the metal coverage rate of the radiating portion 34 is set to 1% are described as the second modified example.

[0074] In the first and second modified examples, the basic configuration of the leaky coaxial cable 10 is the same as in the above embodiment, being an 8D size coaxial cable with an inner conductor 20 diameter of 3 mm, an outer conductor diameter of 7.8 mm, and a dielectric constant of the insulator 22 of 1.32.

[0075] [First variation] In the first modified example, the leaky coaxial cable 10 has an axial length (total length) of the radiating section 34 of 3m, a metal coverage ratio of 5% for the radiating section 34, and a characteristic impedance of 132.1Ω for the radiating section 34.

[0076] Furthermore, as shown in Table 2, the pitch P of the radiating section 34 is 177 mm, the outer conductor width Wm is 8.5 mm, the gap width Wg is 23.1 mm, the length Lt of the transformer section 36 is 70 mm, and the metal coverage ratio of the transformer section 36 is 25%.

[0077] [Table 2]

[0078] The reason for setting the metal coverage ratio of the transformer section 36 to 25% is to make the characteristic impedance of the transformer section 36 84.8Ω, which is close to the geometric mean value "√(Z1×Z2)" of the characteristic impedances Z1 and Z2 of the power supply section 32 and the radiating section 34, which is 80.3Ω.

[0079] As shown in Figure 8, the return loss of the first modified leaky coaxial cable 10 is 16.946 dB at frequency f1: 918 MHz and 17.118 dB at frequency f2: 919.2 MHz. In contrast, the return loss of the leaky coaxial cable without the transformer section 36 is 5.603 dB at frequency f1 and 5.682 dB at frequency f2.

[0080] Therefore, it can be seen that in a leaky coaxial cable with a metal coverage ratio of 5% for the radiating section 34, providing a transformer section 36 with a metal coverage ratio of 25% improves the return loss in the high-frequency signal usage frequency band by more than 10 dB compared to a cable without the transformer section 36.

[0081] Furthermore, as shown in Figure 9, the pass-through loss of the first modified example of the leaky coaxial cable 10 is 5.088 dB at frequency f1 and 5.095 dB at frequency f2. In contrast, the return loss of the leaky coaxial cable without the transformer section 36 is 8.735 dB at frequency f1 and 8.623 dB at frequency f2.

[0082] Therefore, it can be seen that in a leaky coaxial cable with a metal coverage ratio of 5% for the radiating section 34, providing a transformer section 36 with a metal coverage ratio of 25% improves the transmission loss in the high-frequency signal usage frequency band by 3 dB or more compared to a cable without the transformer section 36.

[0083] [Second variation] In the second modified example, the leaky coaxial cable 10 has an axial length (total length) of the radiating section 34 of 3m, a metal coverage ratio of 1% for the radiating section 34, and a characteristic impedance of 168.8Ω for the radiating section 34.

[0084] Furthermore, as shown in Table 3, the pitch P of the radiating section 34 is 177 mm, the outer conductor width Wm is 8.5 mm, the gap width Wg is 23.1 mm, the length Lt of the transformer section 36 is 70 mm, and the metal cover ratio of the transformer section 36 is 20%.

[0085] [Table 3]

[0086] The reason for setting the metal coverage ratio of the transformer section 36 to 25% is to make the characteristic impedance of the transformer section 36 93.7Ω, which is close to the geometric mean value "√(Z1×Z2)" of the characteristic impedances Z1 and Z2 of the power supply section 32 and the radiating section 34, which is 90.9Ω.

[0087] As shown in Figure 10, the return loss of the leaky coaxial cable 10 of the second modified example is 15.349 dB at frequency f1 MHz and 16.337 dB at frequency f2. In contrast, the return loss of the leaky coaxial cable without the transformer section 36 is 5.004 dB at frequency f1 and 6.275 dB at frequency f2.

[0088] Therefore, it can be seen that even when a transformer section 36 with a metal coverage ratio of 20% is provided in a leaky coaxial cable with a metal coverage ratio of 1% in the radiating section 34, the return loss in the frequency band used for high-frequency signals can be improved by more than 10 dB compared to when the transformer section 36 is not provided.

[0089] Furthermore, as shown in Figure 11, the pass-through loss of the second modified example of the leaky coaxial cable 10 is 5.495 dB at frequency f1 and 5.461 dB at frequency f2. In contrast, the return loss of the leaky coaxial cable without the transformer section 36 is 10.015 dB at frequency f1 and 9.669 dB at frequency f2.

[0090] Therefore, it can be seen that even when a transformer section 36 with a metal coverage ratio of 20% is provided in a leaky coaxial cable with a metal coverage ratio of 1% in the radiating section 34, the transmission loss in the high-frequency signal usage frequency band can be improved by 4 dB or more compared to when the transformer section 36 is not provided.

[0091] Thus, from the simulation results of the first and second modified examples, it was confirmed that even if the metal coverage ratio of the radiating section 34 is further reduced from 33% in the above embodiment, the return loss and through loss of the leaky coaxial cable 10 can be improved by providing the transformer section 36.

[0092] [Other embodiments] While embodiments and variations of the present disclosure have been described above, the present disclosure is not limited to the embodiments and variations described above and can be implemented in various modified forms.

[0093] For example, in the above embodiment, the leaky coaxial cable 10 was described as radiating a high-frequency signal in the 920 MHz band, but the technology of this disclosure can be applied in the same manner as in the above embodiment to any leaky coaxial cable that radiates a high-frequency signal used for power transmission applications.

[0094] In other words, as shown in Table 4, high-frequency signals used for power transmission include not only the 920 MHz band, but also the 2.4 GHz band and the 5.7 GHz band. While the usage conditions of these high-frequency signals are limited, such as the radiated power from the leaky coaxial cable 10, considering the effects on the human body, the leaky coaxial cable can be used to supply power to external equipment by configuring it in the same way as in the embodiment described above.

[0095] [Table 4]

[0096] Furthermore, in the above embodiment, a connector 26 is attached to the power supply section 32 of the leaky coaxial cable 10, and the metal coverage ratio of the insulator 22 by the outer conductor 30 protruding from the connector 26 is set as described above, thereby forming the transformer section 36 and the radiating section 34.

[0097] However, the transformer section 36 does not necessarily have to protrude from the connector 26; at least a portion of the transformer section 36 may be housed within the connector 26. In this case, the connector 26 itself may have an outer conductor with a metal cover ratio that functions as the transformer section 36.

[0098] Furthermore, in the above embodiment, the transformer section 36 was described as being constructed by widening the width of the metal tape constituting the outer conductor 30 between the power supply section 32 and the radiating section 34 compared to the radiating section 34. However, the structure of the transformer section 36 may be similar to that of a general microstrip line transformer, such as a tapered type or a stub type.

[0099] Furthermore, the transformer section 36 may be a multi-stage type composed of multiple transformers. By making the transformer section 36 a multi-stage type, the frequency bandwidth of the return loss improved by the transformer section 36 can be widened, thereby widening the bandwidth of the leaky coaxial cable 10.

[0100] Furthermore, in the above embodiment, it was explained that a strip-shaped metal tape, in which an adhesive is applied to a metal foil, is used for the radiating portion 34 and the transformer portion 36. The leaky coaxial cable 10 was described as being constructed by spirally winding this metal tape around the surface of the insulator 22. In contrast, the radiating portion 34 and the transformer portion 36 may be constructed, for example, by forming a strip of multiple metal wires and spirally winding them around the surface of the insulator 22.

[0101] In this case as well, it is preferable to apply adhesive between the metal wire and the insulator 22 to prevent the winding position of the outer conductor 30 around the insulator 22 from shifting when the leaky coaxial cable 10 is bent and deformed.

[0102] Furthermore, multiple functions of one component in the above embodiment may be realized by multiple components, or one function of one component may be realized by multiple components. Also, multiple functions of multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. In addition, some parts of the configuration of the above embodiment may be omitted. In addition, at least some parts of the configuration of the above embodiment may be added to or replaced with the configuration of other above embodiments.

[0103] Furthermore, in addition to the leaky coaxial cable 10 described above, this disclosure can also be realized in various forms, such as a system that uses the leaky coaxial cable 10 as a component, and a method for manufacturing the leaky coaxial cable 10. [Explanation of Symbols]

[0104] 10...Leaky coaxial cable, 20...Inner conductor, 22...Insulator, 30...Outer conductor, 32...Power supply section, 34...Radiation section, 36...Transformer section.

Claims

1. An internal conductor extending along the axis, An insulator covering the internal conductor, An outer conductor provided around the aforementioned insulator, Equipped with, The aforementioned external conductor is A power supply section that surrounds the entire outer circumference of the inner conductor and occupies 100% of the surface area of ​​the insulator, A radial portion is wound around the insulator in a single helix with a constant pitch so as to form a gap, and its occupancy rate on the surface of the insulator is less than 50%. Between the power supply section and the radiating section, an impedance matching transformer is provided, which is positioned at a distance from the axial direction of the internal conductor and connects the power supply section and the radiating section. A leaky coaxial cable equipped with [specific feature].

2. In the aforementioned transformer, The axial length of the internal conductor is set to λ / 4, where λ is the wavelength of the high-frequency signal transmitted or received in the leaky coaxial cable, taking into account the wavelength shortening factor in the coaxial structure. The occupancy rate of the outer conductor on the surface of the insulator is set such that, when the characteristic impedance of the power supply section is Z1 and the characteristic impedance of the radiating section is Z2, the characteristic impedance of the transformer falls within a predetermined range centered on the geometric mean value of the characteristic impedances Z1 and Z2, "√(Z1 × Z2)". The leaky coaxial cable according to claim 1.

3. The aforementioned radiation unit is When the wavelength of the high-frequency signal to be transmitted or received is λo, the relative permittivity of the insulator at the said wavelength is εr, and the pitch of the windings of the outer conductor in the axial direction of the inner conductor is P, then the following equation: [Math 1] A leaky coaxial cable according to claim 1 or claim 2, satisfying the relationship shown.

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