JP6533718B2 - Multifrequency collinear antenna - Google Patents

Description

  The present invention relates to a multi-frequency collinear antenna used, for example, in a base station of a mobile communication system.

  In a mobile communication system such as a cellular phone system or a PHS (Personal Handyphone System), for example, a collinear antenna is used as a communication antenna (see, for example, Patent Document 1). There are a series feeding system and a parallel feeding system as a feeding system in the collinear antenna. The series feeding method generally narrows a band in which a good voltage standing wave ratio (VSWR) can be obtained. On the other hand, in the parallel feeding system, since each radiating element is configured close to a dipole antenna, using a relatively wide band antenna enables a good VSWR over a wide band even if feeding as a collinear array in principle. It is possible to maintain

JP, 2011-089919, A

  However, the radome diameter of the collinear antenna is generally restricted. For this reason, when the antennas are multi-tiered, the feeding cables bundled for parallel feeding are close to the radiation element, and the characteristics of the radiation element are deteriorated, thereby causing the deterioration of the VSWR characteristics and directivity as the entire collinear antenna. Therefore, just by adopting the parallel feeding method, it is not always possible to obtain good VSWR characteristics.

  In addition, regardless of whether the feeding method is in series or in parallel, conventional collinear antennas have restrictions on the arrangement intervals of the radiation elements (for example, 0.5 to 0.95 λ), so the arrangement of the distributors and matching circuits is limited. Be In general, the radiation element is constituted by a 0.35 to 0.5 λ element. Moreover, in order to obtain stable excitation, it is not possible to arrange an unintended conductor in the vicinity of the radiation element. Therefore, the lower limit of the distance between the radiation elements is approximately 0.5λ.

  Furthermore, when the antennas are arrayed, it is necessary to prevent grating lobes. Grating lobes are generated when the distance between the radiation elements is 1.0 λ or more, and when grating gloves are generated, the gain is greatly reduced. In addition, even if the distance is shorter than this, the side lobe tends to be large and the gain is likely to be reduced due to the influence of the radiation element, the divider and the like. Therefore, the upper limit of the distance between the radiation elements is approximately 0.95λ. However, when the maximum dimension of the antenna is constant and the number of stages of radiating elements changes, parallel feeding must take into consideration the number, distribution, and size of distributors according to the number. In a series feed scheme, the phase shift circuit must be changed as the spacing of the radiating elements changes. However, the distributor and the phase shift circuit must be arranged in a limited space between the radiating elements and can not be easily changed.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to obtain good VSWR characteristics over a wide band, suppress side lobes, improve the gain, and further operate frequency and beam It is an object of the present invention to provide a multi-frequency collinear antenna that can easily cope with changes in tilt angle.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a dielectric substrate having a ground pattern disposed on a first surface and a second surface open on the back side with respect to the first surface. A first radiation comprising a composite right-handed / left-handed transmission line comprising a feed section on one end and a matching termination on the other end of the second surface of the dielectric substrate. Arrange the elements. At the same time, a second radiation element comprising the same right / left handed composite transmission line as the first radiation element is formed parallel to the first radiation element on the second surface of the dielectric substrate. And the feed section and the matching end section are arranged in the opposite direction. And it is comprised so that the high frequency electric power of equal amplitude and an antiphase may be supplied to the feed part of the said, 1st and 2nd radiation element.

  According to a second aspect of the present invention, the lumped constant of the lumped constant line provided in the right / left handed composite transmission line of the first and second radiation elements is set according to the operating frequency to be transmitted and received. It is characterized by

  According to a third aspect of the present invention, in the first and second radiation elements, the lumped constant of the lumped constant line included in the right-handed / left-handed compound transmission line corresponds to the tilt angle of the radiation beam to be obtained. The first and second radiation elements may be set to different values.

  According to the first aspect of the present invention, since the right-hand / left-handed composite transmission line operates as a traveling wave antenna, it is possible to provide an antenna capable of obtaining a good VSWR over a wide band. In addition, the right-hand / left-handed composite transmission line has a configuration in which a plurality of units constituting a lumped constant line are closely arranged in series, and each unit also serves as a radiation element, a divider and a phase circuit, The occurrence of side lobes can be kept low, which can improve the gain. Furthermore, the tilt angles of the radiation beams by the first and second radiation elements are combined, and as a result, the radiation pattern can be directed in the front direction orthogonal to the dielectric substrate surface regardless of the frequency.

  According to the second aspect of the present invention, the operating frequency does not change the radiation element length only by changing the lumped constant of the lumped constant line included in the right / left handed composite transmission line of the first and second radiation elements. Can be easily changed.

  According to the third aspect of the present invention, the lumped constant of the lumped constant line provided in the right / left handed composite transmission line of the first and second radiation elements is changed to a different value between the first and second radiation elements. Thus, by changing the balance frequency, it is possible to adjust the beam tilt in an appropriate direction.

  That is, according to the present invention, it is possible to obtain good VSWR characteristics over a wide band, suppress side lobes, improve gain, and easily cope with changes in operating frequency and beam tilt angle. Can provide a multi-frequency collinear antenna.

FIG. 1 is a perspective view showing the configuration of a multi-frequency collinear antenna according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the multi-frequency collinear antenna shown in FIG. The figure which expanded and showed a part of multi-frequency collinear antenna shown in FIG. The figure which shows an example of the radiation pattern in the case of 2.5 GHz, 3.0 GHz, 3.2 GHz, and 3.5 GHz of the multi-frequency collinear antenna shown in FIG. FIG. 7 is a diagram showing frequency characteristics of VSWR obtained by the multi-frequency collinear antenna shown in FIG. 1. FIG. 2 is a diagram showing frequency characteristics of gain obtained by the multi-frequency collinear antenna shown in FIG. 1.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.
[One embodiment]
FIG. 1 is a perspective view showing the configuration of a multi-frequency collinear antenna according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view of the multi-frequency collinear antenna shown in FIG. It is the top view which expanded and showed a part of.

  In FIG. 1, reference numeral 1 denotes a dielectric substrate, and the dielectric substrate 1 is formed of, for example, a printed wiring board (printed substrate) formed in a strip shape. A ground pattern is formed on the entire back surface of dielectric substrate 1, and first and second radiation elements 2a and 2b are formed in parallel on the surface using, for example, microstrip lines.

  Each of the first and second radiation elements 2a and 2b is formed of a metaline antenna composed of a right hand / left hand composite transmission line (CRLH line). In the following, the CRLL line will be described with the same reference numerals as those of the radiating elements 2a and 2b. The CRLH lines 2a and 2b are each formed by serially connecting a plurality of units constituting a lumped constant line in the longitudinal direction, and both of them constitute a balanced line.

  In one unit, capacitance elements 22, 22, ... are loaded between one conductive portion 20 and the conductive portions 21, 21 arranged at both ends thereof, and the conductive portion 20 is further provided with inductance elements 23, 23. , ... are connected. The inductance elements 23, 23,... Have one end connected to the conductive portion 20 and the other end connected to the ground terminal 26. The ground terminal 26 is connected to the ground pattern 11 formed on the back surface of the dielectric substrate 1 through the through hole 12 as shown in FIG. One unit length is set, for example, to λ / 10, where λ is a wavelength corresponding to the operating frequency. The radiation element length is set to, for example, 1.2λ.

  A feeding conductive portion 27 is disposed at one end of the CRLH lines 2a and 2b, and a feeding point 24 is provided on the feeding conductive portion 27. A feed cable (not shown) constituting a feed line is connected to the feed point 24. Furthermore, a termination resistor 25 is connected to the end of the CRLH line 2. The termination resistor 25 matches and terminates the termination of the CRLH line 2.

  By the way, as shown in FIG. 1, the first and second CRLH lines 2a and 2b are arranged such that the feeding point 24 and the termination resistor 25 are in the opposite direction to each other. At this time, the arrangement interval of the CRLH lines 2a and 2b is set to an interval (for example, λ / 10 or more) which is not coupled to each other.

  The multi-frequency collinear antenna configured as described above operates as follows. That is, when high frequency power of equal amplitude and opposite phase is fed to the feeding points 24 and 24 of the first and second CRLH lines 2a and 2b, currents of the same amplitude and in phase are equal in each unit in these CRLH lines 2a and 2b. Is generated, whereby the CRLH lines 2a and 2b both operate as traveling wave antennas. As a result, horizontal directivity is formed in the front direction of the multifrequency collinear antenna, and beam tilt is formed in the horizontal direction.

  By the way, the CRLH lines 2a and 2b alone have a tendency to change the radiation direction of the beam depending on the frequency. That is, the beam is emitted in the direction (front direction) perpendicular to the surface of the dielectric substrate 1 at the balance frequency, but in the low frequency band to the terminal resistor 25 and in the high frequency band to the feeding point 24 The direction of radiation of each beam changes. That is, when the CRLH lines 2a and 2b are operated alone, a tilt angle is generated in the radiation beam.

  On the other hand, in the multi-frequency collinear antenna according to the present embodiment, as described above, the first CRLH line 2a and the second CRLH line 2b are arranged in parallel at a distance such that coupling does not occur, and The directions of the lines 2a and 2b are such that the feeding point 24 and the termination resistor 25 are in opposite directions to each other. Therefore, the tilt angle θ of the radiation beam by the first CRLH line 2a and the tilt angle θ of the radiation beam by the second CRLH line 2b are combined, and as a result, in the low frequency band and the high frequency band The tilt angle θ of the radiation beam is θ = 0, and the direction of the radiation pattern is the front direction.

FIGS. 4 (a) to 4 (d) show the measurement results of radiation patterns of beams at 2.5 GHz, 3.0 GHz, 3.2 GHz and 3.5 GHz, respectively. As the measurement conditions, as illustrated in FIG. 1, the size of the dielectric substrate 1 is set to the long side GP _x = 120 mm and the short side GP _y = 50 mm, and the height B from the ground pattern 11 to the lines 2a and 2b is B = 3.2 mm, and the relative dielectric constant ε _r is ε _r = 2.6, the capacitance of the capacitance elements 22, 22, ... is 2C _z = 1.3 pF, and the inductance of the inductance elements 23, 23, ... is L _Y = 1.2 nH. As apparent from the figure, according to the multi-frequency collinear antenna according to the present embodiment, the radiation beam Eθ is in the front direction (z direction) regardless of the frequency.

  Further, as described above, both the first and second CRLH lines 2a and 2b operate as traveling wave antennas. For this reason, a good VSWR can be obtained over a wide band. FIG. 5 shows the frequency characteristics of the VSWR measured under the conditions described above. As shown in the figure, according to the multi-frequency collinear antenna according to this embodiment, the VSWR is 2 or less over the entire range from 2 GHz to 4 GHz.

  Furthermore, the first and second CRLH lines 2a and 2b have a configuration in which the radiation elements of λ / 10 are closely arranged, and since the CRLH lines 2a and 2b themselves also serve as the radiation elements and the phase shift circuit, Parts other than the radiation element such as a distributor and a phase shift circuit are unnecessary. As a result, the side lobes can be kept low and high gain can be easily obtained. FIG. 6 illustrates the measurement result of the frequency characteristic of the antenna gain. As apparent from the figure, when looking at the gain Gθ in the front direction, it is understood that a frequency band in which the gain is constant over a wide band of 2.5 to 3.5 GHz can be obtained. The 3 dB reduction band is calculated to be 33%.

  Further, in the multi-frequency collinear antenna according to the present embodiment, the frequency can be easily changed by changing the constants of the capacitance element 22 and the inductance element 23 mounted on the dielectric substrate 1. In that case, it is not necessary to change the lengths (unit lengths) of the constituent units of the CRLH lines 2a and 2b. However, the change to extremely high frequency is difficult to design because the unit length deviates from the state of being sufficiently smaller than the wavelength.

  Furthermore, the tilt angle of the radiation beam can also be easily modified. That is, at the operating frequency (balanced frequency) in the operating frequency range, the capacitances of the capacitance elements 22 of the CRLH lines 2a and 2b and the inductances of the inductance elements 23 are appropriately set individually, and the tilt angles of the radiation beams become the same direction. By doing this, it is possible to obtain the tilt angles of the radiation beams that are uniformly directed in the same direction even in the used frequency range.

  As described above in detail, in the multi-frequency collinear antenna according to the present embodiment, the first CRLH line 2a and the second CRLH line 2b are disposed in parallel at a distance such that coupling does not occur, and The directions of the lines 2a and 2b are such that the feeding point 24 and the termination resistor 25 are in opposite directions to each other. Then, high frequency power of equal amplitude and opposite phase is supplied to the feeding points 24 and 24 of the first and second CRLH lines 2a and 2b.

  Therefore, the tilt angles θ of the radiation beams of the first and second CRLH lines 2a and 2b are combined, and as a result, the radiation pattern is directed in the front direction also in the low frequency band and the high frequency band. Can. Further, since both the CRLH lines 2a and 2b operate as traveling wave antennas, it is possible to obtain good VSWR over a wide band. Furthermore, since the CRLH lines 2a and 2b themselves also serve as the radiating element and the phase shift circuit, parts other than the radiating element such as a distributor and a phase shift circuit can be eliminated, thereby suppressing the side lobe to a low level and the antenna Gain can be increased.

  In addition, by appropriately changing the lumped constants of the capacitance element 22 and the inductance element 23, it is possible to easily change the operating frequency and the tilt angle of the radiation beam. Furthermore, since a narrow diameter antenna is obtained and the structure is simple, a lightweight and robust multi-frequency collinear antenna can be provided.

  Further, since the multi-frequency collinear antenna of this embodiment can be manufactured by forming a pattern of a CRLH line on a dielectric substrate, it can be easily manufactured by the usual method of manufacturing printed wiring patterns and surface mounting of parts, Suitable for production. Therefore, the multi-frequency antenna can be provided at low cost.

[Other embodiments]
In the embodiment, one collinear antenna in which two CRLH lines 2a and 2b are arranged in parallel has been described as an example. However, the present invention is not limited thereto, and a horizontal nondirectional antenna can be configured by arranging a plurality of collinear antennas having the same configuration concentrically and orienting the respective collinear antennas in different directions in the horizontal direction. At this time, by changing the characteristic impedance of the CRLH line according to the number of collinear antennas, it is possible to eliminate the need for a distribution matching device for impedance matching with the feed line on the wireless device side. Furthermore, if a thick cable and a large number of conductors are accommodated in the inside of a cylindrical body surrounded by a plurality of collinear antennas, a narrow-diameter columnar antenna device can be configured.

  The collinear antenna described in the above embodiment may be configured in multiple stages. In this case, the antenna can be disposed so as to cover the root where the cables are concentrated, and there is an advantage that the space can be effectively used.

  In addition, the configuration and number of individual CRLH lines, the number of installation, the size, the frequency band to be covered, and the center frequency thereof can be variously modified without departing from the scope of the present invention.

  In short, the present invention is not limited to the above embodiment as it is, and at the implementation stage, the constituent elements can be modified and embodied without departing from the scope of the invention. In addition, various inventions can be formed by appropriate combinations of a plurality of components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, components in different embodiments may be combined as appropriate.

  DESCRIPTION OF SYMBOLS 1 dielectric substrate 2a, 2b right-hand / left-handed composite transmission line (CRLH line) 11 grounding pattern 12 through hole 20 21 conductive portion 22 capacitance element 23 inductance element 24 ... feeding point, 25 ... termination resistance, 26 ... grounding terminal, 27 ... conducting part for feeding.

Claims (3)

A dielectric substrate having a ground pattern disposed on a first surface and a second surface open on the back side with respect to the first surface;
A first radiation disposed on the second side of the dielectric substrate, comprising a right-hand / left-handed composite transmission line provided with a feed at one end and a matching termination at the other end. Element,
A composite right-handed / left-handed transmission line comprising a matching termination at one end and a feed at the other end, the first radiating element on the second side of the dielectric substrate A second radiating element arranged parallel to and in such a way that said feed and said matching end are in opposite directions;
What is claimed is: 1. A multi-frequency collinear antenna comprising: a feed line for feeding high-frequency power of equal amplitude and opposite phase to feed portions of the first and second radiation elements.   The first and second radiation elements are characterized in that a lumped constant value of a lumped constant line provided in the right-hand / left-handed complex transmission line is set according to an operating frequency to be transmitted / received. Multifrequency collinear antenna described.   The first and second radiation elements are the first and second radiations according to a tilt angle of a radiation beam which a lumped constant value of a lumped constant line included in the right-hand / left-handed composite transmission line is to obtain The multi-frequency collinear antenna according to claim 1, wherein the elements are set to different values.