Leaky coaxial cable type antenna

Abstract

To provide a leaky coaxial cable type antenna comprising a slot and enabling increase of intensity of an electromagnetic wave radiated from the slot.SOLUTION: An antenna 1 is a leaky coaxial cable type antenna for use in communication at 850 MHz to 930 MHz bands. The antenna 1 comprises a cable portion including an inner conductor extending in one direction, an insulator covering the inner conductor, and an outer conductor 4 in which at least one slot 4a is formed. A termination 1b of the cable portion can reflect electric power input from an input end 1a. A circumferential dimension of the slot 4a ranges from 35 to 95% with respect to a full circumference of the outer conductor 4. An outer diameter of the insulator is 5 mm or more. An attenuation amount of electric power which is reflected by the termination 1b and arrives at the input end 1a is 8 dB or more in 850 MHz to 930 MHz bands with respect to electric power input from the input end 1a.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a leaky coaxial cable type antenna.

Background Art

[0002] In recent years, RFID (radio frequency identifier) tags have been used for individual item management of products and the like. The information of the RFID tag is read by an antenna. In order to read the information of the RFID tag, a leaky coaxial cable type antenna may be used (for example, see Patent Document 1). Patent Document 1 discloses a leaky coaxial cable type antenna including an inner conductor, an insulator, and an outer conductor formed with slots.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above-described antenna, the intensity of the electromagnetic wave radiated from the slot may be weak.

[0005] One aspect of the present invention is to provide a leaky coaxial cable type antenna capable of increasing the intensity of the electromagnetic wave radiated from the slot.

Means for Solving the Problems

[0006] One aspect of the present invention is a leaky coaxial cable type antenna used for communication in the 850 MHz to 930 MHz band, which has a cable portion including an inner conductor extending in one direction, an insulator covering the inner conductor, and an outer conductor covering the insulator and having at least one slot formed therein. The end opposite to the input end of the cable portion can reflect the power input from the input end. The peripheral dimension of the slot is within the range of 35% to 95% with respect to the entire circumference of the outer conductor. The outer diameter of the insulator is 5 mm or more. The attenuation amount of the power reflected at the end and reaching the input end with respect to the power input from the input end is 8 dB or more in the 850 MHz to 930 MHz band, and a leaky coaxial cable type antenna is provided.

[0007] According to the above configuration, since the attenuation amount (RL) is large, the intensity of the electromagnetic wave radiated from the slot is strong. Therefore, an antenna suitable for RFID communication in the 850 MHz to 930 MHz band can be provided.

[0008] The longitudinal dimension of the slot is preferably 10 mm or more.

[0009] A plurality of the slots are formed, and a plurality of the slots are formed in the outer conductor at intervals in the longitudinal direction of the inner conductor. When the repeating dimension of the arrangement of the plurality of slots in the longitudinal direction is P, the wavelength of the signal to be transmitted is λ, the wavelength shortening rate is ν, and νλ is the propagation wavelength λg, it is preferable to satisfy λg / (1 + 0.766ν) < P < 3λg / (1 + ν).

[0010] The total length of the cable portion in the longitudinal direction is preferably 10 m or less.

[0011] A plurality of slots including the slot are formed in the outer conductor at intervals in the longitudinal direction, and the peripheral dimension of each of the plurality of slots may increase toward the end side in the signal propagation direction.

Effects of the Invention

[0012] According to one aspect of the present invention, it is possible to provide a leaky coaxial cable type antenna that can enhance the intensity of electromagnetic waves radiated from slots.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Modes for Carrying Out the Invention

[0014] The leaky coaxial cable type antenna of the embodiment will be described with reference to the drawings. [Leaky Coaxial Cable Type Antenna] (First Embodiment) FIG. 1(A) is a perspective view of the cable portion of the leaky coaxial cable type antenna 1 according to the first embodiment. The leaky coaxial cable type antenna is also simply referred to as an "antenna". FIG. 1(B) is a cross-sectional view of the cable portion of the antenna 1. FIG. 2 is a side view showing the structure of the antenna 1.

[0015] As shown in FIGS. 1(A) and 1(B), the cable portion of the antenna 1 includes an inner conductor 2, an insulator 3, an outer conductor 4, and a sheath 5. The insulator 3 covers the inner conductor 2. The outer conductor 4 covers the insulator 3. As shown in FIGS. 1(A) and 2, a plurality of slots 4a are formed in the outer conductor 4.

[0016] As shown in FIG. 1(A), the inner conductor 2 extends in one direction. The direction along the central axis O of the inner conductor 2 is referred to as the longitudinal direction and is represented by the Z axis. The direction orthogonal to the central axis O is referred to as the radial direction. The direction of orbiting around the central axis O is referred to as the circumferential direction. The longitudinal direction is also the direction in which a signal propagates through the antenna 1. The terminal side in the direction in which the signal propagates is defined as the +Z side, and the signal source side is defined as the -Z side. The signal propagates toward the +Z side. The -Z side end of the cable portion of the antenna 1 is the input end 1a (see FIG. 2). The +Z side end of the cable portion of the antenna 1 is the terminal end 1b (see FIG. 2).

[0017] The inner conductor 2 is formed of a metal such as copper. The cross-sectional shape orthogonal to the length direction of the inner conductor 2 is, for example, circular. The inner conductor 2 may be a stranded wire formed by twisting a plurality of fine conductor wires.

[0018] The insulator 3 covers the inner conductor 2 from the outside in the radial direction. The insulator 3 is formed of, for example, resin. Examples of the resin constituting the insulator 3 include polyolefin resins such as foamed polyethylene. The insulator 3 is formed coaxially with respect to the inner conductor 2.

[0019] The outer conductor 4 covers the insulator 3 from the radially outer side. The outer conductor 4 is, for example, a conductor layer formed by winding a tape (metal tape) made of a metal such as copper around the insulator 3. An insulating base material and an adhesive layer for adhering the insulating base material to the outer conductor 4 may be provided on the inner peripheral surface of the outer conductor 4. As the insulating base material, a polyester resin (for example, polyethylene terephthalate (PET), etc.), a polyolefin resin (polypropylene, polyethylene, etc.) can be adopted. As the adhesive layer, for example, an ethylene-based ionomer resin can be adopted. Openings corresponding to the slots 4a may not be formed in the insulating base material and the adhesive layer. The inner diameter of the outer conductor 4 is substantially the same as the outer diameter of the insulator 3, or slightly larger than the outer diameter of the insulator 3. An air layer may be provided between the insulator 3 and the outer conductor 4. The outer conductor 4 is not limited to a metal tape and may be constituted by a metal braid. The outer conductor 4 may be constituted by a combination of a metal tape and a metal braid.

[0020] A plurality of holes (slots 4a) are formed in the outer conductor 4. The plurality of slots 4a are formed at different positions in the length direction of the outer conductor 4 (the length direction of the cable portion of the antenna 1). The plurality of slots 4a are formed at intervals in the length direction of the outer conductor 4.

[0021] The shape of the slot 4a is, for example, rectangular. Specifically, the slot 4a is a rectangular shape whose longitudinal direction (long side direction) is along the length direction of the cable portion of the antenna 1. The shapes of the plurality of slots 4a are the same as each other. The directions of the plurality of slots 4a are the same as each other. The sizes of the plurality of slots 4a are the same as each other. The slot 4a is rectangular even in the flat state of the tape before the tape that becomes the outer conductor 4 is wound around the insulator 3.

[0022] The dimension of the slot 4a in the longitudinal direction is referred to as the longitudinal dimension W1. The dimension of the slot 4a in the circumferential direction is referred to as the circumferential dimension W2. The repeating dimension of the arrangement of the slots 4a in the longitudinal direction is referred to as the "slot pitch P". The slot pitch P is the sum of the longitudinal dimension W1 and the longitudinal interval between the slots 4a.

[0023] In the leaky coaxial cable 1, when considering the propagation of electromagnetic waves only in the +Z direction, if the radiation angle θn of the electromagnetic waves is set to 0 for the radiation angle perpendicular to the central axis O and the radiation direction inclined toward the terminal side is taken as positive, it is expressed by the following formula (1).

[0024] θn = sin -1 (nλ / P + 1 / ν) …(1)

[0025] However, n is the radiation mode (negative integer), λ is the wavelength in free space, and ν is the wavelength shortening ratio of the leaky coaxial cable 1. The wavelength shortening ratio ν is expressed by the following formula (2) based on the effective relative permittivity εs obtained from the volume ratio of the insulator 3 and the hollow portion between the inner conductor 2 and the outer conductor 4.

[0026] ν = 1 / (εs) 1 / 2 …(2)

[0027] Normally, usually only the so-called -1st mode with n = -1 is often used. Empirically, the radiation angle of the -1st mode is -50° to +30° as the practical limit angle. Therefore, the slot pitch P preferably falls within the range of the following formula (3).

[0028] λg / (1 + 0.766ν) < P < 3λg / (1 + ν) …(3)

[0029] λg is the propagation wavelength in the leaky coaxial cable 1, and λg = νλ. For example, when the frequency of the signal is 920 MHz (λ ≒ 325.9 mm) and the wavelength shortening ratio ν is 0.8, the range of the slot pitch P is preferably in the range of 161 mm to 434 mm.

[0030] Note that the shape of the slot is not limited to a rectangular shape. The slot may be an oval shape, a rounded square shape (a rectangular shape with rounded corners), a rectangular shape, a parallelogram shape, etc. The slot may be formed such that its longitudinal direction is inclined with respect to the length direction of the cable portion of the antenna. The number of slots formed in the outer conductor is not limited to a plurality, and may be one. That is, the number of slots can be at least one.

[0031] The outer conductor 4 is formed, for example, by winding a metal tape having a slot 4a formed therein in advance around the insulator 3. Thereby, the slot 4a can be formed at a predetermined position.

[0032] The inner conductor 2 is electrically connected to an external signal source and propagates a high-frequency signal supplied from the signal source. Along with the propagation of the high-frequency signal, electromagnetic waves are radiated from the inner conductor 2. In the longitudinal direction of the cable portion of the antenna 1, at a portion where the slot 4a is not formed in the outer conductor 4, the electromagnetic waves are shielded by the outer conductor 4. Therefore, the electromagnetic waves do not leak to the outside of the antenna 1. On the other hand, at a portion where the slot 4a is formed, the electromagnetic waves leak to the outside of the antenna 1 through the slot 4a. In the antenna 1, wireless communication can be performed by the leaked electromagnetic waves.

[0033] The sheath 5 covers the outer conductor 4. The sheath 5 is made of resin, rubber, etc.

[0034] No terminator is provided at the terminal 1b of the cable portion of the antenna 1. The terminal 1b can reflect the power input from the input terminal 1a. The terminal 1b may have a short-circuit structure or an open structure.

[0035] The antenna 1 is used, for example, as an antenna for communicating with a passive RFID tag. In a passive RFID tag, generally, a high-frequency signal in the UHF band (for example, 850 MHz to 930 MHz) is used.

[0036] When using a high-frequency signal, to maintain a good communication state with a distance of about 1 m, for example, between the antenna 1 and the passive RFID tag, it is preferable that the coupling loss is within 40 dB, for example. To reduce the coupling loss, it is required to increase the energy of the electromagnetic wave emitted from the antenna 1. Since the antenna 1 is used by increasing the energy of the emitted electromagnetic wave, it is not suitable for long-distance transmission exceeding, for example, 100 m. Considering the application of communicating with the passive RFID tag, the total length of the cable portion of the antenna 1 is preferably 10 m or less.

[0037] Figure 3 is a graph showing the results of Test 1. The vertical axis in Figure 3 indicates the reflection attenuation amount (RL: Return Loss) in the antenna. RL represents the attenuation amount of the power that is input from the input end of the cable portion, reflected at the terminal, and reaches the input end (see Figure 2). The horizontal axis in Figure 3 indicates the frequency. Figure 4 is an enlarged graph of Figure 3.

[0038] The conditions of Test 1 are as follows. Total length of the cable portion of the antenna: 1030 mm Material of the insulator 3: Foamed polyethylene (wavelength shortening rate 0.8) Longitudinal dimension W1: 110 mm Shape of the slot 4a as viewed from the side: Rectangular Number of slots 4a: 4 Interval between the slots 4a in the longitudinal direction: 118 mm No terminator is provided at the terminal of the cable portion of the antenna.

[0039] As shown in Figures 3 and 4, in Test 1, in the band of 850 MHz to 930 MHz (for example, 915 MHz to 930 MHz), RL was about 2 dB. Thus, in the band of 850 MHz to 930 MHz, RL was relatively small.

[0040] Figure 5 is a graph showing the results of Test 2. The vertical axis in Figure 5 indicates RL in the antenna. The horizontal axis in Figure 5 indicates the frequency. Figure 6 is an enlarged graph of Figure 5.

[0041] The conditions of Test 2 are as follows. Total length of the cable part of the antenna: 770 mm Material of Insulator 3: Foamed polyethylene (wavelength shortening rate 0.8) Longitudinal dimension W1: 86 mm Shape of Slot 4a as viewed from the side: Rectangular Number of Slots 4a: 4 Spacing between Slots 4a in the longitudinal direction: 86 mm No terminator is provided at the end 1b of the cable part of the antenna.

[0042] As shown in FIGS. 5 and 6, in Test 2, in the 850 MHz to 930 MHz band, RL (reflection attenuation) was about 14 dB to about 22 dB. In Test 2, it can be seen that the RL in the 850 MHz to 930 MHz band increased because the form of Slot 4a was different from that of the antenna in Test 1. In the 850 MHz to 930 MHz band, since RL is large, it can be inferred that the intensity of the electromagnetic wave radiated from Slot 4a is strong.

[0043] In the 850 MHz to 930 MHz band, RL of 8 dB or more is required. When RL is 8 dB or more, the intensity of the electromagnetic wave radiated from Slot 4a becomes strong. In the 850 MHz to 930 MHz band, RL of 10 dB or more is preferable.

[0044] FIG. 7 is a graph showing the results of Test 3. The vertical axis of FIG. 7 shows RL in a plurality of antennas in which the number of Slots 4a is any one of 4 to 8. The horizontal axis of FIG. 7 shows the frequency. For example, "4slots" means that the number of Slot 4a is 4. Other conditions of Test 3 were in accordance with Test 2. As shown in FIG. 7, in Test 3, in the 850 MHz to 930 MHz (for example, 915 MHz to 930 MHz) band, RL differed greatly depending on the number of Slots 4a.

[0045] FIG. 8 is a graph showing the results of Test 4. The vertical axis of FIG. 8 shows the number of slots 4a and the RL in the antenna in which the length Lt (see FIG. 2) is adjusted. The length Lt is the distance between the slot 4a on the most rear end side and the terminal 1b. The horizontal axis of FIG. 8 shows the frequency. For example, "4slots 86mm" means that the number of slots 4a is 4 and Lt is 86 mm. Other conditions of Test 4 were in accordance with Test 2.

[0046] As shown in FIG. 8, in Test 4, by adjusting the length Lt (see FIG. 2), the RL in the 850 MHz to 930 MHz band became 8 dB or more. In the 850 MHz to 930 MHz band, since the RL is large, it can be inferred that the intensity of the electromagnetic wave radiated from the slot 4a is strong.

[0047] The antenna 1 propagates energy by an electric field called the TEM mode. An electric current flows in the longitudinal direction in the outer conductor 4. By forming the slot 4a extending in the circumferential direction and the longitudinal direction in the outer conductor 4, the electric current flowing in the outer conductor 4 is partially cut off, a potential difference is generated between the signal source side and the terminal side of the slot 4a, and energy is released to the outside of the antenna 1 as an electric field. Increasing this energy can be achieved by increasing the longitudinal dimension W1 and the circumferential dimension W2 of the slot 4a. According to the results studied by the inventors of the present application, it is preferable that the longitudinal dimension W1 is 10 mm or more and the circumferential dimension W2 is 35% or more of the entire circumference of the outer conductor 4. This will be described in detail below.

[0048] FIG. 9 shows the relationship between the longitudinal dimension W1 and the coupling loss. The conditions of Test Examples 1-1 and 1-2 are as shown in Table 1. "Circumference of outer conductor" in Table 1 indicates the total circumferential length of the portion of the outer conductor 4 where the slot 4a is not formed. "Circumferential opening ratio R" is the ratio of the circumferential dimension W2 to the circumference of the outer conductor.

[0049]

Table 1

[0050] As shown in Fig. 9, in both Test Examples 1-1 and 1-2, the longitudinal dimension W1 of the slot 4a was varied and the coupling loss was measured. In both Test Examples 1-1 and 1-2, in the region where the longitudinal dimension W1 is 50 mm or less, the larger the longitudinal dimension W1, the smaller the coupling loss. This is because the larger the longitudinal dimension W1, the larger the amount of electromagnetic waves leaking from the slot 4a. Also, Test Example 1-1 tended to have a smaller coupling loss than Test Example 1-2. This is because Test Example 1-1 has a larger peripheral dimension W2 and peripheral opening ratio R than Test Example 1-2.

[0051] Under the conditions of Test Example 1-1 (R = 83%), by setting the longitudinal dimension W1 to 10 mm or more, the coupling loss could be made within 40 dB. Under the conditions of Test Example 1-2 (R = 70%), by setting the longitudinal dimension W1 to 30 mm or more, the coupling loss could be made within 40 dB. Note that the upper limit value of the longitudinal dimension W1 is arbitrary, but for example, when forming a plurality of slots 4a, it may be set so that the slots 4a are formed at intervals in the longitudinal direction.

[0052] Fig. 10 shows the relationship between the peripheral opening ratio R and the coupling loss. In Test Example 2, the outer diameter of the outer conductor 4 was 10 mm, the number of slots was 1, and the longitudinal dimension W1 was 100 mm. The peripheral dimension W2 (peripheral opening ratio R) was varied and the coupling loss was measured. As shown in Fig. 10, the larger the peripheral opening ratio R, the smaller the coupling loss. Under the conditions of Test Example 2, by setting the peripheral opening ratio R to 35% or more, the coupling loss could be made within 40 dB.

[0053] From the viewpoint of reducing the coupling loss in a leaky coaxial cable having only one slot 4a, the larger the circumferential opening ratio R, the more preferable. On the other hand, in a leaky coaxial cable having a plurality of slots 4a, if the circumferential opening ratio R of the slot 4a is too large, the transmission loss in the portion where the slot 4a is formed increases, and the signal energy supplied to the slot 4a on the terminal side extremely decreases. As a guideline, the circumferential opening ratio R is preferably 95% or less. If the circumferential opening ratio R is 95% or less, appropriate signal energy is also supplied to the slot 4a on the terminal side, and the coupling loss can be reduced for the entire leaky coaxial cable.

[0054] Fig. 11 shows the relationship between the inner diameter of the outer conductor 4 (the outer diameter of the insulator 3) and the coupling loss. In Test Examples 3-1 to 3-3, the outer diameters of the inner conductor 2 are 0.6 mm, 1 mm, and 2 mm, respectively. Also, the outer diameter (D) of the insulator 3 is 1.5 mm, 2.5 mm, and 5 mm. Note that the outer diameter of the outer conductor 4 is almost the same as the value obtained by adding twice the thickness of the outer conductor 4 to the outer diameter of the insulator 3. The following conditions were common for Test Examples 3-1 to 3-3. Total length of the cable portion of the antenna 1: 5 m Material of the insulator 3: Foamed polyethylene (wavelength shortening rate 0.8) Longitudinal dimension W1: 110 mm Circumferential opening ratio R: 80% Shape of the slot 4a as viewed from the side: Rectangular Number of slots 4a: 21 Interval between adjacent slots 4a in the longitudinal direction: 128 mm Frequency: 920 MHz

[0055] Note that the coupling loss was measured by arranging a measuring instrument (dipole antenna) 1.5 m away from the cable portion of each antenna 1 and moving the measuring instrument in the longitudinal direction with respect to the cable portion of the antenna 1. In Fig. 11, the horizontal axis (measurement position) indicates the position in the longitudinal direction of the cable portion of the antenna 1. Specifically, the point where the horizontal axis is 0 m corresponds to the end on the signal source side of the cable portion of the antenna 1, and the point where the horizontal axis is 5 m corresponds to the end on the terminal side of the cable portion of the antenna 1.

[0056] As shown in FIG. 11, the larger the outer diameter D of the insulator 3, the smaller the coupling loss. In particular, in the test example 3-3 in which the outer diameter D of the insulator 3 is 5 mm, the coupling loss was within 40 dB in most areas in the longitudinal direction. Even if the coupling loss exceeds 40 dB in some areas in the longitudinal direction as in the test example 3-3, communication with the passive RFID tag is possible. For example, it is sufficient to use only the area of ​​the cable part of the antenna 1 in which the coupling loss is within 40 dB (the area from 0 to 4.7 m on the horizontal axis in the test example 3-3) as the communication antenna. Alternatively, if the distance between the cable part of the antenna 1 and the passive RFID tag is made smaller than 1.5 m, the coupling loss can be adjusted to within 40 dB over the entire longitudinal length of the cable part of the antenna 1.

[0057] Generally speaking, when the longitudinal dimension W1 is the same, the coupling loss is determined by the ratio of the outer diameter D of the insulator 3 to the length of the edge of the slot 4a extending in the circumferential direction, so that the coupling loss is considered to be independent of the outer diameter D. However, in the test examples 3-1 to 3-3, such a result was not obtained, and the larger the outer diameter D of the insulator 3, the smaller the coupling loss. The reason for this is considered to be that the edge is coupled with other parts of the outer conductor 4 and the impedance does not increase. For example, since the slot 4a in the test examples 3-1 to 3-3 is rectangular, the corners are bent at approximately right angles, but it is considered that the current flows through the insulator 3 without passing through the outer conductor 4 due to capacitive coupling. Alternatively, it is considered that the middle part of the edge is coupled with the inner conductor 2. When such a phenomenon occurs, it is considered that even if the outer diameter D is large, the effective edge length becomes short and the coupling loss does not decrease.

[0058] Considering the results of FIGS. 9 to 11 together, in order to suppress the coupling loss to within 40 dB, it is preferable to satisfy the following condition A or condition B. Condition A: The longitudinal dimension W1 is set to 10 mm or more, the peripheral opening ratio R is set to within a range of 35 to 95%, and the outer diameter D of the insulator 3 is set to 5 mm or more. Condition B: The longitudinal dimension W1 is 30 mm or more, the circumferential opening ratio R is in the range of 70 to 95%, and the outer diameter D of the insulator 3 is 5 mm or more.

[0059] [Effects of the antenna according to the embodiment] In the antenna, RL is 8 dB or more in the 850 MHz to 930 MHz band. Since RL is large, the intensity of the electromagnetic wave radiated from the slot 4a is strong. Therefore, it is possible to provide an antenna suitable for RFID communication in the UHF band (850 MHz to 930 MHz band).

[0060] It can be speculated that the reason why the intensity of the electromagnetic wave radiated from the slot 4a becomes strong is that the interference wave generated by the interference between the traveling wave (see Fig. 2) from the input end 1a toward the terminal 1b and the reflected wave from the terminal 1b toward the input end 1a is emitted through the slot 4a.

[0061] In the antenna 1, since a plurality of slots 4a are formed at intervals in the longitudinal direction in the external conductor 4, it is possible to provide the antenna 1 capable of performing RFID communication in a wide range in the longitudinal direction of the cable portion.

[0062] [Leaky coaxial cable type antenna] (Second embodiment) Fig. 12 is a perspective view of the cable portion of the antenna 101 according to the second embodiment. As shown in Fig. 12, in the antenna 101, the circumferential dimensions of each of the plurality of slots 4a increase as going toward the terminal side in the signal propagation direction. In this case, the coupling loss can be made more uniform in the longitudinal direction.

[0063] Note that the technical scope of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. In the antenna 1 shown in FIG. 1(A) etc., the forms (shape, size, orientation, etc.) of the plurality of slots 4a are the same as each other, but the forms of two or more of the plurality of slots may be different from each other. When the forms of two or more of the plurality of slots are different from each other, it is possible to design such that the characteristics (for example, frequency characteristics) of the electromagnetic waves radiated from two or more slots with different forms are different from each other.

[0064] In the above-described embodiment, it has been described that the antenna 1 is used as an antenna for communicating with a passive RFID tag, but the antenna of the embodiment can also be suitably used for other applications. In addition, within the scope not departing from the gist of the present invention, it is possible to appropriately replace the components in the above-described embodiment with well-known components, and the above-described embodiment and modified examples may also be appropriately combined.

Example

[0065] (Example 1) The antenna 1 (see FIG. 1(A)) was fabricated. The specifications of the antenna 1 of Example 1 are as follows. Total length of the cable portion of the antenna 1: 770 mm Outer diameter of the inner conductor 2: 2 mm Material of the insulator 3: Foamed polyethylene (wavelength shortening rate 0.8) Outer diameter of the insulator 3: 5 mm Outer diameter of the outer conductor 4: 5.5 mm Longitudinal dimension W1: 86 mm Circumferential dimension W2: 13 mm Shape of the slot 4a as viewed from the side: Rectangular Number of slots 4a: 4 Interval between the slots 4a in the longitudinal direction: 86 mm No terminator is provided at the terminal 1b of the cable portion of the antenna 1.

[0066] The measurement of the coupling loss was performed by placing the measuring instrument (dipole antenna) 30 cm away from each antenna 1 in the height direction and moving the measuring instrument with respect to antenna 1. Ex is the coupling loss when the moving direction of the measuring instrument is parallel to antenna 1. Ey is the coupling loss when the moving direction of the measuring instrument is perpendicular to antenna 1 in the horizontal plane. Ez is the coupling loss when the moving direction of the measuring instrument is in the height direction.

[0067] Figure 13 is a graph showing the results of Example 1. In Figure 13, the horizontal axis (measurement position) indicates the position in the longitudinal direction of antenna 1. The point where the horizontal axis is 0 cm corresponds to the end on the signal source side of antenna 1, and the point where the horizontal axis is 77 cm corresponds to the end on the termination side of antenna 1.

[0068] (Comparative Example 1) An antenna was fabricated. The specifications of the antenna in Comparative Example 1 are as follows. Total length of the cable part of antenna 1: 1030 mm Outer diameter of the inner conductor 2: 2 mm Material of the insulator 3: Foamed polyethylene (wavelength shortening rate 0.8) Outer diameter of the insulator 3: 5 mm Outer diameter of the outer conductor 4: 5.5 mm Longitudinal dimension W1: 110 mm Circumferential dimension W2: 13 mm Shape of the slot 4a viewed from the side: Rectangular Number of slots 4a: 4 Interval between the slots 4a in the longitudinal direction: 118 mm The antenna in Comparative Example 1 is provided with a terminator at the end of the cable part.

[0069] Figure 14 is a graph showing the results of Comparative Example 1. In Figure 14, the horizontal axis (measurement position) indicates the position in the longitudinal direction of the cable part of antenna 1. The point where the horizontal axis is 0 cm corresponds to the end on the signal source side of antenna 1, and the point where the horizontal axis is 103 cm corresponds to the end on the termination side of the cable part of antenna 1.

[0070] As shown in FIGS. 13 and 14, in the antenna 1 of Example 1, the coupling loss could be reduced.

Description of Signs

[0071] 1,101… antenna (leaky coaxial cable type antenna), 1a… input end, 1b… terminal, 2… inner conductor, 3… insulator, 4… outer conductor, 4a… slot, D… outer diameter of insulator, W1… longitudinal dimension, W2… circumferential dimension.

Claims

1. A leaky coaxial cable type antenna used for communication in the 850 MHz to 930 MHz band, an inner conductor extending in one direction, an insulator covering the inner conductor, and a cable portion including an outer conductor covering the insulator and having a plurality of slots formed at intervals in the longitudinal direction of the inner conductor, wherein the end opposite to the input end of the cable portion is capable of reflecting the power input from the input end, the peripheral dimension of the slot is within a range of 35% to 95% with respect to the entire circumference of the outer conductor, the outer diameter of the insulator is 5 mm or more, the attenuation amount of the power reflected at the end and reaching the input end with respect to the power input from the input end is 8 dB or more in the 850 MHz to 930 MHz band, the dimension of the slot in the direction along the central axis of the inner conductor is 10 mm or more, when the repeating dimension of the arrangement of the plurality of slots in the longitudinal direction is P, the wavelength of the signal to be transmitted is λ, the wavelength shortening rate is ν, and νλ is the propagation wavelength λg, λg / (1 + 0.766ν) < P < 3λg / (1 + ν) is satisfied, the distance between the slot on the rearmost end side and the end of the cable portion is determined such that the attenuation amount is 8 dB or more in the 850 MHz to 930 MHz band, a leaky coaxial cable type antenna.

2. The leaky coaxial cable type antenna according to claim 1, wherein the total length of the cable portion in the longitudinal direction is 10 m or less.

3. In the outer conductor, a plurality of slots including the slot are formed at intervals in the longitudinal direction, and the peripheral dimension of each of the plurality of slots increases toward the end side in the signal propagation direction. The leaky coaxial cable type antenna according to claim 1 or 2.

Images