JP3133684B2 - Omnidirectional antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband omnidirectional antenna installed in a base station or the like.

[0002]

2. Description of the Related Art As an antenna installed in a mobile radio base station or the like, an omnidirectional antenna capable of obtaining a wide band and a high gain has conventionally been used. Broadband antennas are required because transmission and reception are at different channel frequencies and multiple channels are required. The non-directionality is set because the other party moves. FIG. 1 shows an example of a conventional high-gain omnidirectional antenna.
3 (a), (b), (c), (d), and (e).

FIG. 13A shows a collinear type antenna. A radiating element 102 composed of a folded dipole is attached to at least three stages on a side surface of a support 101 having a lightning rod 100 attached to a tip thereof. The radiating elements 102 are arranged on the side surface of the support 101 with an angle difference of 120 ° from each other. This is the radiating element 10
Since the folded dipole 2 is mounted close to the column 101, a deviation occurs in the directivity in the horizontal plane. Therefore, the column 101 has an angle difference of 120 °.
By arranging them on the side surfaces, the deviations are compensated for to be non-directional. The radiating element 102
Is an electrical length of λ / 2. Here, λ is the wavelength of the center frequency of the operating frequency band.

FIGS. 13 (b) and 13 (c) show the configuration of another conventional high-gain omnidirectional antenna, which is a coaxial stacked antenna. In this coaxial stacked antenna, as the name implies, radiating elements 102 having a coaxial structure are stacked in multiple stages. The length of the radiating element 102 is
Although the electrical length is λ / 2, the radiating element 1 is used to make the phase of the electromagnetic wave radiated from the radiating element 102 in-phase.
As shown in FIG. 2B, the connection between the cores 02 is made by connecting the core wire to the grounding portion and connecting the grounding portion to the core wire.

FIGS. 13D and 13E show the configuration of another conventional high-gain omnidirectional antenna, which is an antenna called a multistage sleeve type. In this multi-sleeve type antenna, as the name suggests, the sleeve-shaped radiating elements 102 are stacked in multiple stages. The length of the radiating element 102 is λ /
Although the electrical length of the radiating element 102 is set to 2 in order to make the phase of the electromagnetic wave radiated from the radiating element 102 the same,
Is folded back as shown in FIG.

[0006]

Since the above collinear antenna has the metal pillar 101, a lightning arrester can be installed if necessary. Therefore, there is a disadvantage that the antenna impedance is reduced because the radiating element 102 is attached. For this reason, the radiating element 102 has a folded structure to increase the antenna impedance. However, there is a problem that the number of folded lines of two or three lines is limited mechanically and the antenna impedance cannot be increased too much. there were. Therefore, when the number of stages is increased, there is a problem that the frequency band of a good voltage standing wave ratio (VSWR) becomes narrow. Further, by arranging the radiating element 102 on the side surface of the column 101 with an angle difference of 120 ° to compensate for the deviation, it cannot be made completely omnidirectional and about 2 dB. There has been a problem that a degree of deviation remains.

Further, in the coaxial stacked antenna and the multi-sleeve antenna described above, since the support and the antenna are also used, there is a problem that the lightning arrester cannot be provided even when the lightning arrester is required. there were. Further, in these antennas, since the radiating elements arranged in multiple stages are fed in series, the amount of beam tilt differs between the upper side and the lower side of the frequency band, and the gain in the horizontal plane is one in the frequency band. There is a problem that does not happen. In particular, when the number of stages of the radiating element is increased, this disadvantage becomes remarkable. Furthermore, in the multi-stage sleeve antenna, when the number of stages is increased, there is a problem that a frequency band of a favorable voltage standing wave ratio (VSWR) is narrowed.

Accordingly, an object of the present invention is to provide a broadband omnidirectional antenna which has good directivity in a horizontal plane and can obtain an arbitrary antenna impedance. A further object of the present invention is to provide an omnidirectional antenna in which a lightning arrester can be provided when necessary.

[0009]

In order to achieve the first object, an omnidirectional antenna according to the present invention comprises a cylindrical metal cylinder, and is elongated in the axial direction of a side surface of the metal cylinder. Any number of folded elements and radiators are formed,
The radiator is supplied with power from a coaxial power supply cable.

Further, in the above omnidirectional antenna,
The grounding portion to which the shield wire of the coaxial cable is connected may be formed in a sleeve shape.

In order to achieve the second object,
Another antenna of the present invention includes a support column having a lightning rod attached to the tip thereof, a cylindrical metal cylinder, and an arbitrary number of folded elements that are elongated in the axial direction of the side surface of the metal cylinder, and a radiator. A cylindrical radiating element that is formed, and a coaxial cable that supplies power to the radiator of the cylindrical radiating element, wherein the cylindrical radiating element is fitted to the column and attached to the column. The coaxial cable is inserted into the support.

Further, in the omnidirectional antenna,
The cylindrical radiating element may be attached to the support in multiple stages, and the multi-stage cylindrical radiating element may be fed in parallel from the coaxial cable. Further, in the cylindrical radiating element, an earth portion to which a shield wire of the coaxial cable is connected may be formed in a sleeve shape.

According to the present invention, since the radiating element has a cylindrical shape, it can be made omnidirectional in a horizontal plane. Further, since a large number of folded elements can be provided due to its structure, the antenna impedance can be set to a desired value by adjusting the number of folded elements and the width thereof.

[0014]

FIG. 1 shows the configuration of an omnidirectional antenna according to an embodiment of the present invention. The omnidirectional antenna shown in FIG. 1 is an antenna including a cylindrical radiating element 1, and has an outer shape of a cylinder as shown in the figure. Three elongated notches are formed in the cylindrical side surface of the cylindrical radiating element 1, whereby two elongated folding elements 2 are formed.
And an elongated radiator 3 are formed. In this case, the upper end and the lower end of the cylindrical radiating element 1 are formed in a ring shape, and the upper end and the lower end of the ring-shaped part are connected by the folded element 2 and the radiator 3. The length in the axial direction of the cylindrical radiating element 1 is approximately λ / 2 of the wavelength λ of the operating center frequency. The radiator 3 has a shape in which the folded element 2 is substantially cut in half, and a coaxial cable 5 is connected to a power supply point 4 at an end of the radiator 3 to supply power.

This power is supplied from the core 5-1 of the coaxial cable 5.
Is connected to the radiator 3 on the hot side, and the shield wire 5-2 is connected to the ground side. The antenna impedance of the tubular radiating element 1 configured as described above is determined by the number of the folded elements 2 and the width thereof. Therefore, in order to obtain a desired antenna impedance, the number and the width of the folded elements 2 may be adjusted. Note that the folded element 2 and the radiator 3 are arranged at substantially equal intervals. For example,
When the number of the radiator 3 and the folding element 2 is three, the antenna impedance becomes about 70 to 80Ω, and when the number of the radiator 3 and the folding element 2 is four, the antenna impedance becomes about 100Ω. If the number of the radiator 3 and the folded element 2 is five, the antenna impedance is about 130 to 15
It becomes 0Ω.

FIG. 2 shows an embodiment in which such a tubular radiating element 1 is attached to a support 11. As shown in FIG. 2, a lightning rod 10 is attached to the tip of a metal support 11, and the cylindrical radiating element 1 is a ring-shaped insulating spacer 12.
Is attached so as to be inserted into the support column 11 via. Accordingly, it is possible to prevent the cylindrical radiating element 1 from being affected by the metal support 11 as much as possible. FIG.
3 is a top view of the omnidirectional antenna shown in FIG.
3A shows a case where the number of the radiator 3 and the folding element 2 is three, and FIG. 3B shows a case where the number of the radiator 3 and the folding element 2 is four. Since the cylindrical radiating element 1 has a cylindrical shape, the directivity in the horizontal plane is substantially omnidirectional.

The antenna impedance of the omnidirectional antenna of the present invention comprising the cylindrical radiating element 1 shown in FIGS. 2 and 3 can be adjusted to a desired value by adjusting the number and the width of the folded elements 2 as described above. It can be a value.
Next, a modified example of the cylindrical radiating element 1 is shown in FIG. In the modification, the ground side of the cylindrical radiating element 1 is constituted by the sleeve element 6. Also in this case, the folded element 2
The antenna impedance can be set to a desired value by adjusting the number and the width thereof. Power is supplied to the cylindrical radiating element 1 of the modified example by the core 5-1 of the coaxial cable 5.
Is connected to the radiator 3 on the hot side, and the shield wire 5-2 is connected to the ground side constituted by the sleeve element 6. The axial length of the cylindrical radiating element 1 of the modified example is approximately λ / 2 of the wavelength λ of the operating center frequency.

Next, the appearance of the omnidirectional antenna of the present invention constituted by the above-mentioned cylindrical radiating element 1 is shown in FIG.
FIG. 5A shows the power supply method. The power feeding method shown in FIG. 5A is a case in which the cylindrical radiating elements 1 are stacked in two stages, and the parallel power feeding in which the two-stage cylindrical radiating elements 1 are connected in parallel by the coaxial cable 5 to feed power is performed. Is going. In this case, if the characteristic impedance of the coaxial cable 5 is 50Ω, the two-stage cylindrical radiating element 1 is connected in parallel. Therefore, if the antenna impedance of the cylindrical radiating element 1 is about 100Ω, the coaxial cable 5 Impedance matching can be obtained.

The interval between the cylindrical radiating elements 1 stacked in two stages is approximately 0.9λ of the wavelength λ of the operating center frequency,
The axial length of the cylindrical radiating element 1 is approximately λ / 2 of the wavelength λ of the operating center frequency, and the electrical length (distance) between the cylindrical radiating element 1 and the parallel connection point is the operating center frequency. Wavelength λ
Is an integral multiple of approximately λ / 2. However, the omnidirectional antenna of the present invention is not limited to this size, and, for example, the interval between the stacked cylindrical radiating elements 1 can be arbitrary. However, the gain will decrease somewhat.
As described above, since the stacked cylindrical radiating elements 1 are fed in parallel, there is no change in the beam tilt within the operating frequency band unlike the conventional series feeding.

FIG. 6A shows the external appearance of the cylindrical radiating element 1 in the case where the cylindrical radiating element 1 is stacked in four stages, and FIG.
(B). The power supply method shown in FIG. 6B shows a case where the cylindrical radiating elements 1 are stacked in four stages, and the four cylindrical radiating elements 1 are connected in parallel by the coaxial cable 5 two by two, Further, parallel feeding is performed in which the power is branched by the matching unit 13. In this case, assuming that the characteristic impedance of the coaxial cable 5 is 50Ω, the cylindrical radiating element 1 having two stages is provided.
Are connected in parallel, and if the antenna impedance of the cylindrical radiating element 1 is set to about 100Ω, impedance matching with the coaxial cable 5 can be achieved.

The interval between the cylindrical radiating elements 1 stacked in four stages is approximately 0.9λ of the wavelength λ of the operating center frequency,
The axial length of the cylindrical radiating element 1 is approximately λ / 2 of the wavelength λ of the operating center frequency, and the electrical length (distance) between the cylindrical radiating element 1 and the parallel connection point is the operating center frequency. Wavelength λ
Is an integral multiple of approximately λ / 2. However, as described above, the omnidirectional antenna of the present invention is not limited to this size. As described above, since the cylindrical radiating elements 1 stacked in four stages are fed in parallel, the beam tilt does not change in the operating frequency band unlike the conventional series feeding.

In the omnidirectional antennas stacked as shown in FIGS. 5 and 6, a lightning rod 10 is attached to the tip of the pole 11, and when lightning strikes the lightning rod 10, the lightning rod 10 passes through the ground through the pole 11. The lightning is applied by passing the current through it. As the cylindrical radiating element 1, FIG.
Alternatively, any of the cylindrical radiating elements 1 shown in FIG. 4 may be employed. In this case, the cylindrical radiating element 1 is mounted on the column 11 via the insulating spacer 12 as shown in FIG.

Next, FIG. 7 shows the change of the antenna impedance with respect to the frequency when the number of the folded elements 2 and the radiators 3 is 3, 4, and 5. The center frequency in this case is 385 MHz. As shown in the figure, when the number of the radiator 3 and the folding element 2 is three, the antenna impedance is about 70 to 80Ω, and when the number of the radiator 3 and the folding element 2 is four, the antenna impedance is about Around 100Ω,
It can be seen that when the number of radiators 3 and folded elements 2 is 5, the antenna impedance is about 130 to 150Ω.

When the antenna impedance of the cylindrical radiating element 1 as a single element is adjusted to about 100Ω (the number of the folded elements 2 and the radiators 3 becomes three), the reactance component is lower than the center frequency. It becomes capacitive in frequency bands and inductive in higher frequency bands. If the feed line length of the coaxial cable 5 up to the connection point where the two cylindrical radiating elements 1 are connected in parallel is set to an integral multiple of λ / 2, the reactance as viewed from the connection point is changed to the center frequency by the coaxial cable 5. On the other hand, an inductive component is added in a low frequency band, and a capacitive component is added in a high frequency band, and the rate of change of the reactance with respect to the frequency is reduced as shown in FIG.

As a result, the stacked omnidirectional antenna of the present invention can have a wide band. Further, the matching unit 13 is not required when the two-stage cylindrical radiating elements 1 are connected in parallel, but only when connecting the feed lines connected in parallel, so that the feeding structure can be simplified. it can. FIG. 9 shows a change in impedance with respect to frequency at a parallel connection point when two stages are stacked. In this figure, the impedance at a frequency of 370 MHz is about 57 ohms, the impedance at a frequency of 380 MHz is about 41.3 Ω, the impedance at a frequency of 390 MHz is about 45.9 Ω, and the impedance at a frequency of 400 MHz is about 52.8 Ω.
Hz to 400 MHz, almost 5
This means that the impedance is matched to the 0Ω coaxial cable 5.

Next, FIG. 10 shows the frequency characteristics of the voltage standing wave ratio (VSWR) when the cylindrical radiating elements 1 are stacked in two stages and when the cylindrical radiating elements 1 are stacked in four stages. As shown in this figure, for a frequency band having a center frequency of 385 MHz,
A frequency band having a VSWR of 1.5 or less provides a wide frequency band of about 40 MHz. Conventionally, VSWR is 1.5
In the following frequency band, only about 5% of the center frequency can be obtained, whereas in the omnidirectional antenna of the present invention, about 10%
It can be seen from the above that the operating frequency band of the omnidirectional antenna of the present invention is wide.

Next, FIG. 11 shows the directivity in the horizontal plane of the omnidirectional antenna of the present invention. However, in this case, the cylindrical radiating elements 1 are stacked in four stages. As shown in this figure, in the frequency band of 360 MHz to 400 MHz, the deviation is within about 1 dB,
A good substantially circular omnidirectional directivity in the horizontal plane is obtained. FIG. 12 shows the directivity in the vertical plane of the omnidirectional antenna of the present invention. Also in this case, the cylindrical radiating element 1
Stacked. As shown in this figure,
In the frequency band from 360 MHz to 400 MHz, good in-plane directivity with no beam tilt is obtained. Therefore, even if, for example, the upper side of the operating frequency band is allocated to the transmission frequency and the lower side is allocated to the reception frequency, good communication can be performed without changing the antenna gain for transmission and reception.

In the present invention described above, the number of stacking stages of the cylindrical radiating element 1 is not limited to two or four, but may be any number. It is suitable. Further, the column 11 to which the cylindrical radiating element 1 is attached also functions as a conductor for grounding the lightning rod 10 to the ground. In addition, the feed line length up to the connection point where the two stacked cylindrical radiating elements 1 are connected in parallel is
Not limited to the wavelength λ of the center frequency of the operating frequency band, λ / 2
The feed line length may be an integral multiple of the following. Furthermore, the matching device 13 can perform matching using a Q match. In the above description, power is supplied in parallel to the stacked cylindrical radiating elements 1, but power may be supplied in series. However, in this case, the beam tilt amount changes within the frequency band.

[0029]

According to the present invention, as described above, since the radiating element has a cylindrical shape, the directivity in the horizontal plane can be made non-directional. Also, the number of folded elements is
Since a large number can be provided on the structure, the antenna impedance can be set to a desired value by adjusting the number of folded elements and the width thereof. Therefore, the impedance can be easily matched even when stacked in multiple stages. In this case, since power is supplied in parallel to the stacked cylindrical radiating elements, it is possible to prevent a change in the amount of beam tilt within the operating frequency band. In addition, since the operating frequency bandwidth can be widened, communication of many channels can be performed with one antenna.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a cylindrical radiating element which is an embodiment of an omnidirectional antenna of the present invention.

FIG. 2 is a diagram showing a configuration of an omnidirectional antenna of the present invention in which the cylindrical radiating element shown in FIG. 1 is attached to a column.

FIG. 3 is a top view of the omnidirectional antenna of the present invention shown in FIG. 2;

FIG. 4 is a diagram showing a configuration of a modified example of a cylindrical radiating element which is an embodiment of the omnidirectional antenna of the present invention.

FIG. 5 is a diagram showing an external appearance and a feeding method of the omnidirectional antenna of the present invention in which cylindrical radiating elements are stacked in two stages.

FIG. 6 is a diagram showing the appearance and feeding method of the omnidirectional antenna of the present invention in which cylindrical radiating elements are stacked in four stages.

FIG. 7 is a diagram showing a change in antenna impedance with respect to the number of folded elements of the cylindrical radiating element in the omnidirectional antenna of the present invention.

FIG. 8 is a diagram illustrating a change in antenna impedance as viewed from a connection point side of a stacked cylindrical radiating element in the omnidirectional antenna of the present invention.

FIG. 9 is a diagram showing a change in impedance at a connection point when a two-stage cylindrical radiating element is stacked in the omnidirectional antenna of the present invention.

FIG. 10 is a diagram illustrating frequency characteristics of VSWR in a case where a two-stage cylindrical radiating element is stacked and in a case where a four-stage cylindrical radiating element is stacked in the omnidirectional antenna of the present invention.

FIG. 11 is a diagram showing directivity in a horizontal plane when four-stage cylindrical radiating elements are stacked in the omnidirectional antenna of the present invention.

FIG. 12 is a diagram showing directivity in a vertical plane when four-stage cylindrical radiating elements are stacked in the omnidirectional antenna of the present invention.

FIG. 13 is a diagram illustrating a configuration example of a conventional omnidirectional antenna.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical radiation element 2 Folding element 3 Radiator 4 Feeding point 5 Coaxial cable 5-1 Core wire 5-2 Shield wire 6 Sleeve element 10 Lightning rod 11 Strut 12 Insulating spacer 13 Matching device

Continuation of the front page (56) References JP-A-58-153405 (JP, A) JP-A-4-86004 (JP, A) JP-A-61-125206 (JP, A) JP-A-63-35239 (JP, A) JP-A-55-57163 (JP, A) JP-A-4-85807 (JP, U) JP-A-61-189610 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB H01Q 9/16-9/28 H01Q 1/00-1/10 H01Q 1/27-1/52

Claims (5)

(57) [Claims] 1. An arbitrary number of folded elements which are formed in a cylindrical metal cylinder and which are elongated in the axial direction of a side surface of the metal cylinder, and a radiator are formed, and power is supplied to the radiator from a coaxial power supply cable. An omnidirectional antenna characterized by the following. 2. The omnidirectional antenna according to claim 1, wherein an earth portion to which a shield wire of the coaxial power supply cable is connected is formed in a sleeve shape. 3. A support having a lightning rod attached to the tip thereof, a cylindrical metal cylinder, and an arbitrary number of folded elements elongated in the axial direction of a side surface of the metal cylinder, and a radiator. A cylindrical radiating element, and a coaxial cable for supplying power to the radiator of the cylindrical radiating element, wherein the cylindrical radiating element is fitted to the support and attached to the support, and the coaxial cable An omnidirectional antenna, wherein a cable is inserted into the support. 4. The multi-stage cylindrical radiating element is mounted on the column in multiple stages, and power is supplied to the multi-stage cylindrical radiating element in parallel from the coaxial cable. Omnidirectional antenna. 5. The omnidirectional antenna according to claim 3, wherein in the cylindrical radiating element, an earth portion to which a shield wire of the coaxial cable is connected is formed in a sleeve shape.