JP4704844B2 - Discone antenna - Google Patents

Description

  The present invention relates to a discone antenna, and more particularly to a discone antenna that is suitably improved for a mobile phone, a wireless local area network (wireless LAN), an ultra wideband wireless (UWB), and the like.

  In a mobile phone system or a wireless LAN system, a communication network is constructed by connecting a base station or relay station connected to a trunk line and a mobile phone using radio waves.

  However, there are places where communication is difficult due to radio wave propagation characteristics, usage locations, etc. depending on the radio wave format, radio wave intensity, frequency used, etc., which are permitted for use of mobile phones and information terminal devices. For example, in underground malls and buildings, it is difficult to use a mobile phone or the Internet because radio waves from a base station in a corresponding external area are difficult to enter.

As a countermeasure against this, a system that relays repeaters in an underground shopping center or a building and relays between an external base station or an indoor line installed in the place and a mobile phone or the like is promising. The repeater generally includes a wireless communication device connected to a line and a plurality of antennas arranged on a ceiling or the like. For example, Japanese Patent Application Laid-Open No. 8-204425 discloses an example of a base station antenna of a mobile phone attached to a ceiling.
JP-A-8-204425

  However, there are a plurality of communication providers that provide communication services for mobile phones and information terminal devices, and a plurality of radio waves are used. It is desirable for the repeater to relay a plurality of communication radio waves from each operator. Further, the output radio waves of mobile phones and information terminal devices and the output radio waves allowed for the relay are as weak as about 10 [mW]. For this reason, an antenna used for a repeater is required to have a broadband characteristic and good transmission / reception efficiency. Specifically, the SWR (standing wave ratio) is required to be 2 or less over the entire range including a plurality of communication radio waves. In a specific band, SWR is required to be 1.5 or less.

  Therefore, an object of the present invention is to provide a highly efficient antenna with wideband characteristics.

  Another object of the present invention is to provide a small and compact antenna that is a broadband antenna with high efficiency and can be easily installed on a ceiling or the like.

In order to achieve the above object, the discone antenna of the present invention includes a disk portion including a plate-shaped conductor, a cone portion including a conical conductor, a central portion of the plate-shaped conductor, and a top portion of the conical conductor. A feed end set respectively, and a frequency characteristic adjustment circuit of an antenna connected between the tops of the plate-like conductor and the conical conductor, and the frequency characteristic adjustment circuit has a low frequency range of a use frequency band. It includes an inductor that sets the characteristics and a capacitor that sets the high frequency characteristics of the used frequency band .

  By adopting such a configuration, it is possible to improve the characteristics of a discone antenna that generally has a wide band characteristic but is difficult to obtain a high gain at the time of transmission. Also, different frequency characteristics can be obtained using discone antennas having the same shape.

  Preferably, the conical conductor extends in the horizontal direction from the middle of the slope. Thereby, the height of the antenna can be reduced, and the entire antenna device can be configured compactly, which is convenient.

  The conical conductor can expand (bend) in the horizontal direction from the lower end of the slope to a portion of about 60% upward. Even in this case, the required SWR characteristics can be obtained, and the antenna device can be more compactly formed. If the conical conductor is horizontally developed at a portion closer to the disk portion, the developed portion can also function as a capacitor component with the disk portion.

  Preferably, the ratio between the diameter A of the plate conductor and the slope length B of the conical conductor is from an optimum value of a discone antenna (for example, A: B = 0.2λ: 0.3λ) that obtains wideband characteristics. Set to deviate. Here, λ is the wavelength of the usable lower limit frequency of the antenna. Thereby, the frequency characteristic of the discone antenna is broken, and the frequency characteristic can be changed by inserting the impedance.

  Preferably, the frequency characteristic adjusting circuit includes an inductor that sets a low frequency characteristic of a use frequency band and a capacitor that sets a high frequency characteristic of the use frequency band. Thereby, it is possible to improve the SWR characteristic (antenna gain characteristic) in the used frequency band.

  Preferably, the diameter of the plate-like conductor is 0.08 to 0.2 wavelength, more preferably 0.13 wavelength with respect to the wavelength λ of the usable lower limit frequency of the antenna.

  Preferably, the slope length of the conical conductor is 0.32 to 0.5 wavelength, more preferably 0.3 wavelength with respect to the wavelength of the lower limit frequency of the use frequency band of the antenna.

Preferably, the lower one third of the conical conductor extends in the horizontal direction from the middle of the slope. Thereby, the height of the antenna can be lowered to make it easy to install on the ceiling, for example, a truncated cone shape.

  According to the discone antenna of the present invention, the size of the disc portion of the discone antenna is made smaller than the normal value, the ratio of the disc portion and the cone portion is removed from the optimum value, and (at the optimum value) constant input impedance characteristics The frequency characteristic of the discone antenna is changed according to the added impedance. Then, a required frequency characteristic is set by the frequency characteristic adjusting circuit. Thereby, a plurality of frequency band characteristics can be set using discone antennas having the same outer shape. An antenna having an SWR of 2 or less over the selected required frequency band can be obtained.

(Discorn antenna)
Embodiments of the present invention will be described below with reference to the drawings.

  First, the discone antenna will be described.

  FIG. 1 shows the shape of a discone antenna. A disk portion 10 that is a disk-shaped conductor and a cone portion 20 that is a conical conductor are combined to form the center of a coaxial cable 40. The conductor 42 is connected to the center of the disk portion, and the outer conductor 44 is connected to the top of the cone portion 20.

  The discone antenna is a practically modified version of an infinite-length biconical antenna. The infinite length biconical antenna is a typical self-similar antenna, and has a characteristic that the input impedance is constant regardless of the frequency. For this reason, the discone antenna has a very wide band and the input impedance is substantially constant at 50 [Ω]. Coaxial cables having a wave impedance of 75 [Ω] or 50 [Ω] are commercially available, and there is an advantage that a coaxial cable of 50 [Ω] can be directly connected to a discone antenna.

  Such a discone antenna is vertically polarized and omnidirectional, and is used as a wideband reception for a fixed station or a transmission / reception antenna that uses a frequency portion with good specific characteristics for transmission.

Example 1
FIG. 2 shows a first embodiment of the present invention. In the figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

  In the present embodiment, the SWR of the required frequency band (width) is set to 1.5 or less by setting the values of the diameter A of the disk portion 10, the length (slope) B, the inductance L, and the capacitance C of the cone portion 20, or The object is to keep the SWR at 2 or less over a wide frequency range. Specifically, the discone antenna of the embodiment is designed as an antenna corresponding to a plurality of bands of 800 MHz band, 1500 MHz band, and 2000 MHz band that are frequency bands for mobile phones.

  Therefore, in the present invention, the ratio (A: B) of the diameter A of the disc portion 10 of the discone antenna to the slope length B of the cone portion 20 is an experimental or empirical optimum value (normal value). .2λ: In order to make the setting deviate from 0.3λ, the diameter A of the disk portion 10 is set to 0.13λ which is about 60%. The lower limit wavelength of the used frequency band is determined by the slope length B. By setting the parameters as described above, the frequency characteristics of the discone antenna exhibiting the broadband characteristics with the constant input impedance under the optimum conditions are affected by the external connection impedance. The slope length B of the cone part 20 is 0.3λ and the half apex angle of the cone part is 45 degrees, which is the same as that of a normal discone antenna.

  Next, as shown in FIG. 2, a frequency characteristic adjusting circuit 30 including a parallel connection circuit of an inductance L and a capacitance C is provided in the power feeding portion of the antenna to set the frequency characteristics of the SWR. The inductance L is for low frequency adjustment, and the low frequency SWR is improved by the value of the inductance L. Capacitance C is for high-frequency adjustment, and improves the high-frequency SWR characteristics that are deteriorated by inductance L. Since the discone antenna is basically broadband, the characteristics can be improved with a frequency bandwidth about three times the lower limit frequency.

  The disk part 10 mentioned above can be comprised by a printed wiring circuit board (PCB), for example, and a disk conductor is formed of the metal conductor formed in the single side | surface of the said board | substrate. The inductance L can be formed by an inductance pattern formed on the opposite surface of the substrate.

As shown in FIG. 6 described later, the cone portion 30 can be developed in the horizontal direction from the middle of the slope of the conical conductor. Even when bent in this way, the frequency characteristics of the SWR are the same. Even if the slope length part of about 60% is bent upward from the lower end of the slope of the conical conductor, the influence on the frequency characteristics of the SWR is small within the frequency range of 3fo, which is about three times the lower limit frequency fo. . Further, the characteristics can be adjusted by the frequency characteristic adjusting circuit 30. Therefore, this feature can be used to make the antenna device compact.
The capacitance C of the frequency characteristic adjusting circuit 30 can be formed by coupling the disk conductor and the top of the cone portion 30. Further, when the expanded portion of the cone portion 30 is enlarged, the capacitor C can be formed by the disk portion 10 and the expanded portion.

  FIG. 3 shows SWR characteristics when the discone antenna is designed as a two-frequency antenna that is used in two frequency bands of 810 to 960 [MHz] and 1470 to 1530 [MHz].

  The antenna parameters in this case are: disk portion diameter A = 0.13λ, cone portion slope length B = 0.3λ, cone portion half apex angle = 45 degrees, inductor L = 5 [nH], capacitor C = 3 [PF].

  FIG. 3 shows the SWR characteristics observed with an oscilloscope when a high-frequency signal having a power supply of 10 [mW] is supplied to the antenna and the frequency is swept from 600 [MHz] to 2.5 [GHz].

In the figure, the vertical axis represents the SWR value, and the scale is 0.2. The horizontal axis is frequency, and one scale is 190 [MHz]. Marker 1 indicated by a triangle in the graph is 810 [MHz], marker 2 is 958 [MHz], marker 3 is 1429 [MHz], marker 4 is 1501 [MHz], marker 5 is 1920 [MHz], The marker 6 indicates 2170 [MHz].

  As can be seen from the SWR characteristics of the figure, according to the discone antenna of the first embodiment, good characteristics of SWR 1.5 or less are obtained in all the two frequency bands. Incidentally, SWR1.5 corresponds to a power efficiency of 96%.

(Example 2)
FIG. 4 shows a second embodiment of the present invention, in which the above-described discone antenna is used in three frequency bands of 810 to 960 [MHz], 1470 to 1530 [MHz], and 1900 to 2200 MHz. The SWR characteristic at the time of designing as an antenna is shown.

  The antenna parameters in this case are: disk portion diameter A = 0.13λ, cone portion slope length B = 0.3λ, cone portion half apex angle = 45 degrees, inductor L = 3 [nH], capacitor C = 1. [PF].

  FIG. 4 shows the SWR characteristics observed with an oscilloscope when a high-frequency signal having a power supply of 10 [mW] is supplied to the antenna and the frequency is swept from 600 [MHz] to 2.5 [GHz]. In addition, the frequency of the markers 1-6 is the same as that of FIG.

  As shown in the figure, the performance of SWR 1.8 or less (power efficiency 92% or more) is obtained in all the three frequency bands. Moreover, in two frequency bands of 810 to 960 [MHz] and 1470 to 1530 [MHz], it is 1.6 or less, which is favorable.

Also in Example 2, the cone part 30 can be developed in the horizontal direction from the middle of the slope of the conical conductor, as shown in FIG. Even when bent in this way, the frequency characteristics of the SWR are the same. Even if the slope length part of about 60% is bent upward from the lower end of the slope of the conical conductor, the influence on the frequency characteristics of the SWR is small within the frequency range of 3fo, which is about three times the lower limit frequency fo. . Further, the characteristics can be adjusted by the frequency characteristic adjusting circuit 30. Therefore, this feature can be used to make the antenna device compact.
The capacitance C of the frequency characteristic adjusting circuit 30 can be formed by coupling the disk conductor and the top of the cone portion 30. Further, when the expanded portion of the cone portion 30 is enlarged, the capacitor C can be formed by the disk portion 10 and the expanded portion.

(Comparative example)
FIG. 5 shows, as a comparative example, an example of the SWR frequency characteristics of a discone antenna manufactured for a microwave band with normal antenna parameters.

  In general, a discone antenna is composed of a disc portion having a diameter of 0.2 wavelength and a cone portion having a length of 0.3 wavelength with respect to the wavelength of the lower limit frequency at which the antenna can be used.

  Therefore, the antenna parameters of the comparative example are set such that the diameter A of the disk portion is 0.2λ, the slope length B of the cone portion is B = 0.3λ, and the half apex angle of the cone portion is 45 degrees. A coaxial cable with a wave impedance of 50 [Ω], which is the usual usage, was directly connected to the feeding point of the antenna. The frequency characteristic adjusting circuit 30 is not provided. The SWR is observed with an oscilloscope when a high frequency signal with a power supply of 10 [mW] is supplied to the antenna and the frequency is swept from 600 [MHz] to 2.5 [GHz].

In the figure, the vertical axis represents the SWR value, and the scale is 0.2. The horizontal axis is frequency, and one scale is 190 [MHz]. Marker 1 indicated by a triangle in the graph is 810 [MHz], marker 2 is 958 [MHz], marker 3 is 1429 [MHz], marker 4 is 1501 [MHz], marker 5 is 1920 [MHz], The marker 6 indicates 2170 [MHz].

  As can be seen from the figure, in the normal configuration, the SWR is about 1.8 to 2.4 at 800 MHz to 2 GHz, and the condition that should be less than or equal to SWR2 in the entire band cannot be cleared. Moreover, in the frequency band of the mobile phone in the 800 MHz band and the 1500 MHz band, SWR 1.5 is preferably obtained, but about 1.8 is the limit.

(Example 3)
FIG. 6 shows a third embodiment of the present invention, and is an explanatory diagram for explaining an example of downsizing a discone antenna. In the figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

  In this embodiment, about 30% (about 1/3) of the lower portion of the cone portion 20 of the above-described discone antenna according to the present invention is bent in the horizontal direction to reduce the height of the entire antenna. Even in this case, the frequency bandwidth 3fo which is about three times the usable low frequency fo has no effect on the characteristics.

As described above, in the configuration of the implementation examples 1 and 2, bent in the horizontal direction of the cone portion 20, from the lower end of the cone portion 20 to 60% of the upward (about 2/3) in the horizontal direction Even if it is bent, the frequency characteristics of the antenna do not change much (there is no difference from the unexpanded one) Therefore, the height of the whole antenna can be further reduced.
As described above, since the embodiment includes the frequency characteristic adjusting circuit, the frequency characteristic of the SWR can be adjusted in an unbalanced state from the optimum value of the size ratio between the disk portion and the deformed cone portion.

  FIG. 7 is a cross-sectional view for explaining an example in which the modified discone antenna shown in FIG. 6 is housed in a dome. 7, parts corresponding to those in FIG. 6 are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 7, the discone antenna is mounted on a base plate 110 that is a circular insulator and is covered with a pot-shaped dome 120. A coaxial cable connected to a high frequency power source (not shown) is connected to the connector 130. The connector 130 and the feeding point of the discone antenna are connected by an internal coaxial cable 44.

  In the discone antenna of the embodiment, since the disk portion 10 is about 60% of the length of a general diameter and the height is about 2/3, for example, the height is 80 mm and the bottom width is about 200 mm. In addition, the entire antenna device can be made compact and compact.

  The antenna device 100 assembled in this way is attached to the ceiling in an underground shopping mall or building in the reverse direction and used.

  In addition, although the Example demonstrated the discone antenna comprised by the plate-shaped object, this can be comprised by a linear radial element. This also belongs to the discone antenna.

As described above, according to the embodiment of the present invention, the diameter of the disc portion of the discone antenna is set to about 0.13 wavelength, and the optimum condition of the disc portion and the cone portion in the discone antenna (for example, the optimum condition) The ratio A: B = 0.2λ: 0.3λ) is changed from a state having a stable broadband characteristic to a state in which the characteristics of the discone antenna are affected by the connected inductance and capacitance, and the low-frequency SWR is caused by the inductance. Since the capacitor is adjusted so as to improve the characteristics, and the high-frequency SWR characteristics that deteriorate with this adjustment are improved by the capacitor, a discone antenna having good SWR characteristics in a relatively wide frequency band as required Can be obtained.

  Further, by expanding the cone portion of the discone antenna in the horizontal direction, the height of the antenna device can be reduced, and a compact antenna device can be obtained, which is convenient when installed on a ceiling surface or the like.

FIG. 1 is an explanatory diagram for explaining a discone antenna. FIG. 2 is an explanatory diagram for explaining the characteristics of the discone antenna of the embodiment. FIG. 3 is a graph for explaining the SWR characteristics of the first embodiment. FIG. 4 is a graph for explaining the SWR characteristics of the second embodiment. FIG. 5 is a graph for explaining the SWR characteristics of the comparative example. FIG. 6 is an explanatory diagram for explaining the third embodiment. FIG. 7 is a cross-sectional view illustrating the assembled state of the antenna of the third embodiment.

Explanation of symbols

10 disk section, 20 cone section, 30 frequency adjustment circuit 40 coaxial cable

Claims (5)

A disk portion including a plate-shaped conductor;
A cone portion including a conical conductor;
A feeding end set to each of a central portion of the plate-like conductor and a top portion of the conical conductor;
And a frequency characteristic adjusting circuit of an antenna which is connected between the top portion mutually the conical conductor and said plate-shaped conductor,
The frequency characteristic adjusting circuit is a discone antenna including an inductor that sets a low frequency characteristic of a use frequency band and a capacitor that sets a high frequency characteristic of a use frequency band .   The discone antenna according to claim 1, wherein the conical conductor extends in the horizontal direction from the middle of the slope.   The discone antenna according to claim 1 or 2, wherein a ratio between a diameter of the plate-like conductor and a slope length of the conical conductor is set so as to deviate from an optimum value of the discone antenna that obtains a broadband characteristic. The diameter of the plate-like conductor is 0.13λ to the wavelength λ of the available lower limit frequency of the antenna, the slope length of the conical conductor is 0.3Ramuda, in any one of claims 1 to 3 Discone antenna described. The discone antenna according to any one of claims 1 to 4 , wherein a lower side 1/3 of the conical conductor is expanded in a horizontal direction.

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