JP2016152589A - Array antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an array antenna in which the electrical tilt angle can be made deeper for a higher frequency band.SOLUTION: An array antenna includes a half wavelength delay circuit 7 provided in a branch feeding line 6 branching downward at the m-th branch, when the n-th step branch 3 counting from a radiation element 2 side is the n-th branch, and delaying half wavelength for a preset reference wavelength, and an N wavelength delay circuit 8 provided in a branch feeding line 6 branching downward at the n-th branch, where n is larger than m, and delaying 2wavelengths for the reference wavelength. The feeding direction of the radiation element 2 being fed via the half wavelength delay circuit 7 is the reverse direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an array antenna used for a base station antenna or the like.

  As a feeding system in an array antenna having a plurality of radiating elements, a series feeding system and a parallel feeding system are known.

  The series feeding method is a feeding method used for collinear antennas, leaky coaxial cables, etc., and has a structure in which radiating elements are arranged in series from the feeding point, so that the feeding phase as the signal travels on the transmission line Are gradually delayed. The arrangement interval of the radiating elements is generally set to about 0.5 to 1 wavelength, and when traveling through the transmission line during this period, the wavelength is shortened by a dielectric or the like, and the phase is changed accordingly, and power is supplied. It will be.

  Therefore, in the series power feeding method, the radiation direction (electrical tilt angle) of radio waves can be adjusted by adjusting the interval between the radiating elements and the dielectric constant of the dielectric. However, it is known that in the series power feeding method, when used over a wide band, the electrical tilt angle differs significantly between the lower limit and the upper limit of the frequency.

  On the other hand, the parallel power feeding method has a structure in which power is supplied in parallel by distributing in multiple stages from the feeding point to the radiating elements. In the parallel feeding method, since the distance from the feeding point to each radiating element is constant, even when used over a wide band, the radio wave radiation direction can be constant (same electric tilt angle).

  In recent years, since base station antennas are often used in a wide band, parallel power feeding methods are frequently used for base station antennas.

  As prior art document information related to the invention of this application, there are Patent Documents 1 and 2.

JP 2012-134904 A Japanese Patent No. 5186343

  By the way, in recent years, mobile phone systems and the like are in the direction of adopting a method with a higher transmission speed in a higher frequency band. As the construction of the service area at this time, it is desired that the area becomes narrower (the electric tilt angle is deeper) in the higher frequency band based on the concept of a small cell.

  However, in the series power feeding method, the electric tilt angle can be changed for each frequency band, but the electric tilt angle is not necessarily deeper as the frequency band is higher, and it is difficult to finely control power distribution. There is a problem that there is. In addition to this, there is a problem that the side lobe cannot be suppressed because it is difficult to adjust the power supply in the series power feeding method.

  On the other hand, in the case of the parallel power feeding method, there is a problem that the electric tilt angle is the same in each frequency band, which does not meet the needs of recent area construction.

  Accordingly, an object of the present invention is to provide an array antenna that can solve the above-described problems and can increase the electrical tilt angle in a higher frequency band.

The present invention was devised to achieve the above object, and includes a plurality of radiating elements arranged in the vertical direction for transmitting and receiving a desired polarization, and a multistage branching section, from a feeding point to each of the radiating elements. A multi-frequency array antenna used in a plurality of frequency bands, wherein the branching unit branches the feed line into two vertically. When the n-th branch portion counted from the radiating element side is the n-th branch portion, it is provided in a branch feed line that branches downward at the m-th branch portion, and is set to a preset reference wavelength. N wavelength for delaying by 2 ^(nm-1) wavelengths with respect to the reference wavelength provided by a half-wavelength delay circuit for delaying by half-wavelength and a branch feed line that branches downward in an n-th branch path where n is greater than m A delay circuit, through the half-wave delay circuit This is an array antenna in which the feeding direction of the radiating element to be fed is reversed.

  The radiating element is a dipole antenna or a slot antenna, and the connection of the signal line and the ground line of the feeding line to the radiating element fed through the half-wave delay circuit does not go through the half-wave delay circuit. It may be configured to be opposite to the radiating element that is fed to the power source.

  The radiating element includes a ground plate arranged in parallel to a vertical direction, a radiating plate arranged in parallel to be separated from the ground plate, and a feed pin that electrically connects the ground plate and the radiating plate. A connecting position of the feed pin to the radiation plate in the radiating element that is fed through the half-wavelength delay circuit, and in the radiating element that is fed without going through the half-wavelength delay circuit. The connection position of the feed pin to the radiation plate is relative to the center between the radiation element fed through the half-wave delay circuit and the radiation element fed through the half-wave delay circuit. It may be a symmetrical position.

  The N wavelength delay circuit and the half wavelength delay circuit may comprise a coaxial cable or a microstrip line.

  The reference wavelength may be a wavelength corresponding to a center frequency of a frequency band to be used.

  According to the present invention, it is possible to provide an array antenna capable of increasing the electrical tilt angle as the frequency band increases.

It is a schematic block diagram of the array antenna which concerns on one Embodiment of this invention. In this invention, it is a figure explaining the reverse phase electric power feeding of a patch antenna. (A) is a directivity diagram according to an array factor at a frequency of 1900 MHz, (b) is 2560 MHz, and (c) is 3500 MHz.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of an array antenna according to the present embodiment.

  As shown in FIG. 1, an array antenna 1 is a multi-frequency array antenna used in a plurality of frequency bands, and includes a plurality of radiating elements 2 arranged in the vertical direction and transmitting / receiving a desired polarization, A tree-like (tournament-like) feed line 5 including the branching portion 3 and formed from the feed point 4 to each radiation element 2 is provided. That is, the array antenna 1 adopts a parallel feeding system as a feeding system. In the present embodiment, the tree-like (tournament-like) feed line 5 is formed so that the line lengths from the feed point 4 to each radiation element 2 are equal.

  Here, a case will be described in which the array antenna 1 is an antenna shared by three frequency bands of 1.9 GHz band, 2.5 GHz band, and 3.5 GHz band. Although FIG. 1 shows the case where the radiating element 2 is a vertically polarized dipole antenna, the specific structure of the radiating element 2 is not limited to this.

  The branch part 3 is configured to branch the feed line 5 into two vertically. Here, branching up and down refers to branching into a branch feed path 6 that feeds power to the radiating element 2 arranged in the vertical direction and a branch feed path 6 that feeds power to the radiating element 2 arranged in the vertical direction. This means that it is not necessary to wire up and down in the immediate vicinity of the branch part 2.

  Hereinafter, the n-th branch part 3 counted from the radiating element 2 side is referred to as an n-th branch part. In the present embodiment, as an example, a case where the feed line 5 has a three-stage configuration will be described. In FIG. 1, the first branch portion is indicated by 3a, the second branch portion is indicated by 3b, and the third branch portion is indicated by 3c.

  In the present embodiment, a block is formed for each of a plurality (two in this case) of radiating elements 2, and a branch point in the first branch part 3a is a feeding point of each block. That is, the 1st branch part 3a is a part which branches to supply electric power to each radiation element 2 of each block. Here, although the number of the radiating elements 2 in each block is two, the number of the radiating elements 2 may be one or more, and usually two to four. Therefore, the first branch part 3a may have three or more branches, and may be omitted when the number of the radiating elements 2 is one. Thus, the number of the radiating elements 2 is not limited to an even number.

The array antenna 1 according to the present embodiment is provided in a branch feed line 6 that branches downward at the m-th branch, and is a half-wavelength delay circuit 7 that delays half a wavelength with respect to a preset reference wavelength (delays). N-wavelength delay circuit 8 provided in branch feed line 6 that branches downward at an n-th branch path where n is greater than m, and delays 2 ^(nm-1) wavelengths with respect to the reference wavelength. (N is an integer, and the phase angle to be delayed is 360 × N degrees).

Here, m = 2, a half-wavelength delay circuit 7 is provided in the branch feed line 6 that branches downward in the second branch portion 3b, and the branch feed line 6 that branches down in the third branch path 3c An N-wavelength delay circuit (one-wavelength delay circuit) 8 that delays 2 ^(3-2-1) = 1 wavelength with respect to the wavelength is provided.

In the case of a four-stage configuration, an N-wavelength delay circuit (two-wavelength delay circuit) 8 that delays 2 ^(4-2-1) = 2 wavelengths in the branch feed line 6 that branches downward in the fourth branch path. When a five-stage configuration is provided, an N wavelength delay circuit (four wavelength delay circuit ^{) that} delays 2 ^(5-2-1) = 4 wavelengths in the branch feed line 6 that branches downward in the fifth branch path. ) 8 may be provided.

  The N wavelength delay circuit 8 and the half wavelength delay circuit 7 may be configured by a coaxial cable or a microstrip line. Here, the reference wavelength is a wavelength corresponding to the center frequency of the frequency band to be used, but the reference wavelength can be selected as appropriate, and may be a wavelength corresponding to the lowest frequency of the frequency band to be used, for example.

  Furthermore, in the array antenna 1 according to the present embodiment, the feeding direction of the radiating element 2 fed through the half-wavelength delay circuit 7 is the reverse direction.

  In the dipole antenna used as the radiating element 2 in the present embodiment, the signal line of the feeder line 5 (center conductor in the case of a coaxial cable) is connected to one rod-shaped element, and the ground line (external conductor in the case of a coaxial cable) is already provided. A method of connecting to one rod-like element and contributing to excitation is adopted. For example, in a printed circuit board dipole antenna, a microstrip line is bent around a balun to generate an electric field to excite an antenna element.

  Thus, when feeding the radiation element 2, there is a feeding direction. If the feeding direction is reversed, the feeding is in reverse phase regardless of the frequency. That is, “the feeding direction of the radiating element 2 is reversed” means that the feeding direction is mechanically changed so that the feeding phase is reversed regardless of the frequency. Hereinafter, “setting the feeding direction of the radiating element 2 in the reverse direction” may be referred to as reverse-phase feeding.

  Since the array antenna 1 according to this embodiment uses a dipole antenna, if the connection of the signal line of the feed line 5 and the ground line is reversed, the feed direction is reversed. That is, in the array antenna 1, the radiating element to which the connection of the signal line and the ground line of the feeder line 5 to the radiating element 2 fed through the half-wavelength delay circuit 7 is fed without going through the half-wavelength delay circuit 7 2 to be reversed. This is the same when a slot antenna is used as the radiating element 2.

  When a patch antenna is used as the radiating element 2, reverse-phase power feeding can be realized by changing the position where the power feeding pins are provided. Specifically, as shown in FIG. 2, the patch antenna 21 includes a ground plate 22 arranged in parallel to the vertical direction, a radiation plate 23 spaced apart from the ground plate 22, and a ground plate 22. The power supply pin 24 is electrically connected to the radiation plate 23. The connection position of the power supply pin 24 to the radiation plate 23 is a vertically symmetrical position (with respect to the center of the radiation plate 23 in the vertical direction). By moving to a line-symmetrical position), it is possible to realize reverse-phase feeding of vertically polarized waves. It is obvious that the same means can be taken for horizontal polarization and circular polarization.

  Thus, when a patch antenna is used as the radiating element 2, the connection position of the feed pin 24 to the radiation plate 23 in the radiating element 2 fed via the half-wavelength delay circuit 7 and the half-wavelength delay circuit 7 are set. The connection position of the power feed pin 24 to the radiation plate 23 in the radiation element 2 fed without going through is not fed through the half wavelength delay circuit 7 and the radiation element 2 fed through the half wavelength delay circuit 7. The position is symmetrical (in this embodiment, vertically symmetrical) with respect to the center of the radiating element 3. When the radiating elements 2 are arranged horizontally, the connection position of the feed pin 24 to the radiation plate 23 in the radiating element 2 fed via the half-wave delay circuit 7 and the half-wave delay circuit 7 are The connection position of the feed pin 24 to the radiation plate 23 in the radiation element 2 that is fed without being interposed may be a symmetrical position.

  That is, it can be said that the reverse-phase feeding of vertically polarized waves can be realized by disposing the radiating element 2 upside down. Note that the radiating element 2 described here is merely an example, and any radiating element 2 can be used as long as it supplies power with directionality. Similarly, if the power is supplied in the opposite direction for horizontal polarization and circular polarization, the phases are reversed.

  Returning to FIG. 1, the uppermost radiation element 2 block in FIG. 1 is referred to as a first block, and the lower radiation element 2 block is sequentially referred to as a second block, a third block, and a fourth block. In the present embodiment, power is supplied to the first block without passing through the delay circuit, power is supplied to the second block via the half-wavelength delay circuit 7 and reverse phase power is supplied, and N wavelength is supplied to the third block. Power is supplied through the delay circuit 8, and the fourth block is supplied with power through the half-wavelength delay circuit 7 and the N-wavelength delay circuit 8 and is fed in reverse phase.

Therefore, the phase delay amount φi (°) of the i-th block at the reference wavelength is expressed by the following equation (1)
φi = (i−1) × 180 (1)
Can be expressed as In each block, phase delay for electric tilt angle control and amplitude control for sidelobe suppression may be individually performed on the plurality of radiating elements 2.

  Providing the N wavelength delay circuit 8 makes it possible to vary the phase for each frequency and vary the electrical tilt angle, but the phase difference increases as the operating frequency width increases. In the present embodiment, in order to correct this, the half-wave delay circuit 7 and the antiphase power supply are used in combination.

  As an example, in the array antenna 1 according to the present embodiment, directivity diagrams based on an array factor when power supply conditions and the like are set as shown in Table 1 are shown in FIGS. The conditions in Table 1 are examples of calculations, and various conditions such as the number of radiating elements 2 and the feeding phase and the feeding power ratio of each radiating element 2 depend on the required service area, etc. It can be selected as appropriate.

  As shown in FIGS. 3A to 3C, the electrical tilt angle is shallow in the 1.9 GHz band (1900 MHz), and the frequency band is increased to 2.5 GHz band (2560 MHz) and 3.5 GHz band (3500 MHz). Therefore, it can be seen that the electrical tilt angle is deep.

  A deep electrical tilt angle means a small service area, and it can be seen that the array antenna 1 can form small cells particularly in the 2.5 GHz band and the 3.5 GHz band. In the 3.5 GHz band, a large gratin glove is generated in the sky direction, but if the directivity of the radiating element 2 in the vertical plane (about 60 to 80 degrees) is taken into account, this side lobe becomes small and the sky Because it becomes the direction, there is no practical problem.

As described above, in the array antenna 1 according to the present embodiment, the half-wavelength delay circuit that is provided in the branch feed line 6 that branches downward at the m-th branch section and delays half the wavelength with respect to a preset reference wavelength. 7 and an N-wavelength delay circuit 8 provided in a branch feed line 6 that branches downward in an n-th branch path where n is larger than m, and delays 2 ^(nm-1) wavelengths with respect to a reference wavelength. The feeding direction of the radiating element 2 fed via the half-wavelength delay circuit 7 is the reverse direction.

  As a result, the electrical tilt angle can be increased as the frequency band increases. As a result, it becomes possible to meet the recent demand for a narrower service area with a higher frequency band with a simple configuration.

  Moreover, in this embodiment, since the parallel power feeding method is adopted, power distribution can be arbitrarily set, and side lobes can be suppressed as compared with the series power feeding method.

  The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

  For example, the half-wavelength delay circuit 7 and the N-wavelength delay circuit 8 may be provided in the power feeding circuit of each radiating element 2. In this case, however, a large number of half-wavelength delay circuits 7 and N-wavelength delay circuits 8 are required, resulting in high costs. From the viewpoint of cost reduction, it is desirable to provide the half-wavelength delay circuit 7 and the N-wavelength delay circuit 8 in the branch feed line 6.

DESCRIPTION OF SYMBOLS 1 Array antenna 2 Radiation element 3 Branch part 4 Feed point 5 Feed line 6 Branch feed line 7 Half wavelength delay circuit 8 N wavelength delay circuit

Claims (6)

A plurality of radiating elements arranged in the vertical direction to transmit and receive a desired polarization; and
A tree-shaped feed line including a multi-stage branch part and formed from the feed point to each of the radiating elements,
A multi-frequency array antenna used in multiple frequency bands,
The branch portion is configured to branch the feed line into two vertically.
When the nth branch portion is counted from the radiating element side as the nth branch portion,
A half-wavelength delay circuit that is provided in a branch feed line that branches downward at the m-th branch section and that delays by half a wavelength with respect to a preset reference wavelength;
an N-wavelength delay circuit provided in a branch feed line that branches downward in an n-th branch path where n is larger than m, and delays 2 ^(nm-1) wavelengths with respect to the reference wavelength;
An array antenna, wherein a feeding direction of the radiating element fed through the half-wavelength delay circuit is reversed. The array antenna according to claim 1, wherein the desired polarization is vertical polarization. The radiating element is a dipole antenna or a slot antenna;
The connection of the signal line and ground line of the feeder line to the radiating element fed through the half-wave delay circuit is opposite to the radiating element fed without going through the half-wave delay circuit The array antenna according to claim 1 or 2, wherein the array antenna is configured. The radiating element includes a ground plate arranged in parallel to a vertical direction, a radiating plate arranged in parallel to be separated from the ground plate, and a feed pin that electrically connects the ground plate and the radiating plate. Patch antenna,
The connection position of the feed pin to the radiation plate in the radiation element fed through the half-wave delay circuit, and the radiation plate in the radiation element fed without going through the half-wave delay circuit The connection position of the feed pin is a symmetrical position with respect to the center of the radiating element fed through the half-wave delay circuit and the radiating element fed without going through the half-wave delay circuit. The array antenna according to claim 1 or 2. The array antenna according to claim 1, wherein the N wavelength delay circuit and the half wavelength delay circuit are formed of a coaxial cable or a microstrip line. The array antenna according to claim 1, wherein the reference wavelength is a wavelength corresponding to a center frequency of a frequency band to be used.

Images