JP2006295630A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device capable of efficiently transmitting and receiving vertical, horizontal, right-handed, and left-handed polarized waves by the same frequency even in a wide band area. <P>SOLUTION: The antenna device is constituted of printing a right/left symmetrical loop pattern 2 for central feeding and a ground plane 3 on the surface of a double-sided substrate and printing a taper-like microstrip line 4 on the rear face. A wide-band area circularly polarized wave plane antenna capable of preventing the deterioration of an antenna conductor by laminated structure can control frequency so as to reduce it. The antenna device can efficiently receive or transmit vertical, horizontal, right-handed, and left-handed polarized waves by the same frequency even in a wide band and can be applied in an environment for wirelessly connecting terminals in which a degree of polarization identification is not important. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an antenna device used for transmission / reception of a radio signal, and more particularly to an antenna device used in a MIMO communication system that performs high-speed data transmission on a transmission path using spatial multiplexing, for example.

  More particularly, the present invention relates to an antenna device used in a communication environment that connects wireless communication terminals without regard to polarization discrimination, and in particular, each of vertical, horizontal, right-handed, and left-handed turns at the same frequency. The present invention relates to an antenna device that can efficiently transmit and receive polarized waves.

  A wireless network is attracting attention as a system free from wiring in the conventional wired communication system. As a standard for a wireless network, IEEE (The Institute of Electrical and Electronics Engineers) 802.11 or the like can be cited.

  Further, although the IEEE 802.11a standard supports a modulation scheme that achieves a communication speed of 54 Mbps at the maximum, a wireless standard capable of realizing a higher bit rate is required. MIMO (Multi-Input Multi-Output) communication is attracting attention as one of the technologies for realizing high-speed wireless communication. This is a communication system that includes a plurality of antenna elements on both the transmitter side and the receiver side, and realizes a spatially multiplexed transmission path (hereinafter also referred to as “MIMO channel”). That is, transmission data is distributed and transmitted to a plurality of antennas in a transmitter. On the other hand, each signal can be extracted without crosstalk by performing signal processing on spatial signals received by a plurality of antennas in the receiver (see, for example, Patent Document 1).

  In wireless communication such as wireless LAN and PAN (Personal Area Network), information transmission is performed via an antenna. In MIMO communication that uses a broadband of 5 GHz band, etc., a communication environment is assumed in which wireless communication terminals are connected without regard to the degree of polarization discrimination, and vertical, horizontal, right-handed, and left-handed polarized waves are used at the same frequency. An antenna structure that can efficiently transmit and receive is required.

  An antenna is composed of a radiating element, a feed line that feeds the radiating element, and a ground that grounds the radiating element. As a loop antenna that is fed from the center, a “central feeding loop antenna” is known (for example, (See Non-Patent Document 1). The basic structure is that, as shown in FIG. 23, two loops having a tightly coupled common plane are compressed into one and fed through a center line connected to the loop at the symmetry axis of the loop. It is.

  FIG. 24 shows the relationship between the current moment of the central feed loop antenna and the current distribution. As can be seen from the figure, it can be considered as “3-wire folded-dipole antenna”, that is, it is treated as an electrically small antenna.

As shown in FIG. 23, the configuration of the central feed loop antenna is a shape having a circular loop conductor having a radius _Rb and a center line having a length of 2b, and the conductors are all perfect conductors. Various antennas can be configured using this structure as a basic antenna (see, for example, Non-Patent Document 2). For example, the triangular twin loop antenna shown in FIG.

  Since the central feed loop antenna is composed of only a complete conductor, it has a simple structure. However, since the intended use is the UHF band, there is a problem in terms of size and weight, and the structure of the feed section is complicated. Become.

  In addition, a loop antenna capable of selectively transmitting and receiving horizontal and vertical polarized waves by feeding power from a feed conductor to a loop element by electromagnetic coupling, and further selectively transmitting and receiving left and right circularly polarized waves Proposals have been made (see, for example, Patent Document 2).

  As a conventional circularly polarized antenna, two dipole antennas, called crossed dipole antennas, cross each other at a right angle at the center and feed each other with a phase difference of 90 degrees to generate circularly polarized waves. A rectangular or circular radiating conductor is formed on the top surface of the antenna or dielectric ceramic (see FIG. 26), and two spatially orthogonal biaxial resonance modes are used, and each of the two feeding points is 90 degrees. A dielectric ceramic patch antenna or the like that generates a circularly polarized wave by supplying power with a phase difference is known (see FIG. 27).

  The latter dielectric ceramic patch antenna is often used in a car navigation system using GPS (Global Positioning System). As a feature, it is possible to reduce the size by increasing the relative dielectric constant, but it is a narrow band. For this reason, it is thought that it is unsuitable as antennas, such as wireless LAN which uses a comparatively wide band. Further, since the antenna structure is complicated and the constituent materials are effective, it is disadvantageous in terms of manufacturing cost and material cost.

  In addition, a dual-polarized antenna (for example, refer to Patent Document 3) that can switch or simultaneously transmit and receive two orthogonal polarized waves, and a wideband and low-profile polarized-wave antenna (for example, Patent Document 4). (Refer to the above)) Circularly polarized wave antenna with a small size in the radiation direction and an occupied area in a plane perpendicular to the radiation direction, a wide frequency band, and a large isolation between left-handed circularly polarized waves and right-handed circularly polarized waves ( For example, see Patent Document 5).

JP 2002-44051 A JP-A-11-220317 JP 2002-76767 A JP 2000-31732 A JP 2004-88185 A T.A. Tsujii, M .; E. , “Analysis of center-line-driver-loop-antenna” (M.I.E.C.E. (Japan) PROC.IEE, Vol 121, No. 11, Nov. 1974, pp. 1355-1359) Tsukiji Takehiko “Introduction to Radio and Antennas” (pp. 184-190)

  An object of the present invention is to provide an excellent antenna device used in a communication environment in which wireless communication terminals are connected without regard to polarization discrimination.

  A further object of the present invention is to provide an excellent antenna device capable of efficiently transmitting and receiving vertical, horizontal, right-handed and left-handed polarized waves at the same frequency.

The present invention has been made in consideration of the above problems,
A substantially planar substrate;
A loop-shaped radiating element pattern formed on the surface of the substrate and having a substantially symmetrical shape,
A ground plane formed on the same plane as the radiating element pattern of the substrate and short-circuiting the radiating element pattern at both ends of the loop;
A central feed line formed from approximately the center of the radiating element pattern toward the center of the loop;
An antenna device comprising:

  In wireless communication, information transmission is performed via an antenna. However, in MIMO communication using a broadband of 5 GHz band, a communication environment in which wireless communication terminals are connected without assuming polarization discrimination importance is assumed. An antenna structure that can efficiently transmit and receive vertical, horizontal, right-handed, and left-handed polarized waves is required.

  The antenna device according to the present invention is configured, for example, by using a double-sided substrate, printing a loop pattern and a ground plane on the front surface of the substrate, and printing a microstrip line on the back surface. Here, the loop pattern as the radiating element has a semicircular shape, for example, and is short-circuited to the ground plane at both ends of the pattern. A central feed line is formed from the approximate center of the loop pattern toward the center of the loop. A through hole leading to the back surface of the substrate is formed at substantially the front end of the central power supply line, and connected to a tapered microstrip line printed on the back surface side through the through hole. It operates to resonate in the low frequency band with the size outside the loop pattern, and to resonate in the high frequency band with the length of the central feed line.

  The antenna device according to the present invention can be easily configured with such a planar substrate structure, and is a very simple, low-cost and smart antenna device.

  In addition, in order to strengthen the ground of the antenna, a ground plane region is provided on both sides of the microstrip line formed on the back surface of the substrate, and the structure is shared with the ground plane on the substrate surface by a plurality of through holes. Also good.

  In addition, the antenna conductor can be prevented from deteriorating and the wavelength shortening effect can be obtained by using a multilayer structure in which a substrate material or dielectric material is laminated on the substrate surface on which a loop pattern or the like is printed. The frequency can be adjusted to decrease.

  Further, as a modification of the antenna device according to the present invention, a coplanar structure in which a loop pattern, a feed line, and a ground plane are all mounted on one side of a substrate is also conceivable. For example, a conductive line is formed from the tip of the central feed line, and a ground plane is formed on both sides of this conductive line. In such a case, it can be manufactured more easily and at low cost.

  ADVANTAGE OF THE INVENTION According to this invention, the outstanding antenna apparatus used in the communication environment which connects between terminals without considering polarization | polarized-light discrimination degree can be provided.

  Further, according to the present invention, it is possible to provide an excellent antenna device capable of efficiently transmitting and receiving vertical, horizontal, right-handed, and left-handed polarized waves at the same frequency.

  The antenna device according to the present invention is configured by printing a centrally fed left-right symmetric loop pattern and a ground plane on the surface of a double-sided board, and printing a tapered microstrip line on the back surface. By adopting such an alignment, it is possible to efficiently receive or transmit vertical, horizontal, right-handed, and left-handed polarized waves at the same frequency while having a wide band.

  The antenna device according to the present invention can be used in an environment in which wireless communication terminals that do not care about polarization discrimination are wirelessly connected. The structure can be easily constructed from a planar substrate structure, and a very simple, low-cost and smart antenna device can be provided.

  The broadband circularly polarized wave planar antenna according to the present invention is low in manufacturing cost and material cost, and a band having an axial ratio of 3 dB or less is obtained with respect to the used frequency.

  Moreover, the wideband circularly polarized wave planar antenna according to the present invention can prevent deterioration of the antenna conductor by adopting a laminated structure, and can adjust the frequency to be reduced.

  Other objects, features, and advantages of the present invention will become apparent from more detailed description based on embodiments of the present invention described later and the accompanying drawings.

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

  1 and 2 show the structures of the front surface and the back surface of an antenna device according to an embodiment of the present invention, respectively. The illustrated antenna device is configured by printing the loop pattern 2 and the ground plane 3 on the front surface of the double-sided board and printing the microstrip line 4 on the back surface. The structure can be easily constructed from a planar substrate structure, and is a very simple, low-cost and smart antenna device. In addition, the laminated structure can prevent the antenna conductor from being deteriorated, and the frequency can be adjusted to be reduced.

  The loop pattern 2 serving as a radiating element has a bilaterally symmetric shape, and typically draws an arc as shown. The ground plane 3 is connected to the radiating element at both ends of the loop pattern 2. Further, from substantially the center of the loop pattern 2, the central feed line 5 extends toward the center of the arc. Further, a through hole connected to the back surface of the double-sided substrate is formed at the tip of the central power supply line 5, and a tapered microstrip line 4 connected to the central power supply line 5 through the through hole on the back surface side. Is formed.

The loop pattern 2 printed on the surface of the double-sided substrate 1 is a radiating element depicting a semicircle, the inner radius r ₁ is 0.73λ _g , the radius r ₂ is 0.78λ _g , and the outer radius r ₃ is 0.83λ _g and the perimeter is 1.21λ _g (where λ _g is the wavelength of the desired signal). Further, the end portions of the loops of the loop pattern 2, is shorted to the ground plane 3 of G1 = 0.83λ _g. The width W1 of the central feed line 5 connected approximately at the center of the loop pattern 2 is 0.037λ _g .

  On the back surface of the double-sided substrate 1, a microstrip line 4 having a taper shape from a microstrip line width of 50Ω to a feed line width W1 on the surface is printed. A through hole having an inner diameter φ of 0.01387λ for supplying power to the antenna on the surface of the double-sided substrate is provided at the tip of the microstrip line 4.

  Note that the shape of the loop pattern 2 is not necessarily limited to an arc, and may be, for example, a rectangle. However, by using a shape without an edge such as an arc, radiation from the edge can be reduced.

  In order to strengthen the ground of the antenna, as shown in FIGS. 3 and 4, ground plane regions 3 ′ and 3 ″ are provided on both sides of the microstrip line 4 on the back surface, and the double-sided substrate 1 is formed by a plurality of through holes. A structure in which a reference potential is shared with the ground plane 3 on the front surface side may be used.

  In addition, the shape itself which short-circuited the front-end | tip of the antenna to the ground is well-known in this industry (for example, refer nonpatent literature 2).

  The antenna device according to the present embodiment is an environment antenna that wirelessly connects, for example, wireless communication terminals used in a 5 GHz band. 5 and 6 show in detail the configuration of the antenna pattern when the antenna device shown in FIGS. 3 and 4 is used in the 5 GHz band (the unit of size described in the figure is Mm).

  The back surface of the double-sided substrate 1 has a taper-shaped microstrip line 4 that is 22.5 [mm] long and narrows to a width of 1.9 to 1.0 [mm] using the ground plane 3 region on the front surface. is there. At the tip, there is a through hole with an inner diameter φ of 0.8 [mm] for connection to the antenna on the surface.

  On the surface of the double-sided substrate 1, there is a central feed line 5 having a width of 1 [mm] and a length of 19.5 [mm], and the end of the line is symmetrical about an inner diameter of 19.5 [mm] and an outer diameter of 22 There is a loop element 2 whose arc-shaped tip forming 0.5 mm is short-circuited to the ground plane 3. This can add a phase difference by 90 degrees symmetrically and is operated so as to easily form a circularly polarized wave. In addition, it operates so as to resonate a low frequency band with the size of the outside of the antenna, and resonates with a high frequency by the length of the slit-shaped central feed line 5 inside the antenna pattern. To make it work.

  For example, FR-4 is used for the double-sided substrate 1, and the size is 45 × 45 × 1 [mm] = vertical × horizontal × thickness, and the conductor thickness is 0.035 [mm].

  Next, the input characteristics, gain, and directivity of the antenna device according to this embodiment will be examined.

  FIG. 7 to FIG. 9 show the theoretical value and the actual measured value of return loss (reflection loss) [dB] as the input characteristics of the antenna apparatus shown in FIG. 5 and FIG. 6, and the comparison between the theoretical value and the actual measured value, respectively. ing. In either case, it can be seen that the input characteristics of −10 dB or less are satisfied in the frequency band near 5.2 GHz, resonance can be obtained in the frequency band suitable for the purpose, and the radiation efficiency is increased.

  10 to 12, the input characteristics of the antenna device shown in FIGS. 5 and 6 include theoretical values, measured values, theoretical values and measured values of VSWR (Voltage Standing Wave Ratio). Each comparison is shown. In either case, VSWR satisfies 2.0 or less in the frequency band near 5.2 GHz, and it can be seen that resonance can be obtained in the frequency band suitable for the purpose and the radiation efficiency is increased.

  Further, as a modification of the antenna device having the planar substrate structure shown in FIGS. 5 and 6, a multilayer structure may be considered using the same substrate material or dielectric material as shown in FIG. In this case, a wavelength shortening effect can be obtained by filling the air portion with a dielectric. FIG. 14 shows return loss as the antenna input characteristic when a dielectric having a thickness of 1 mm is laminated on the surface of the double-sided substrate 1 on which the loop pattern 2 is formed. Also from the figure, the frequency region for obtaining −10 dB has moved to the low frequency band, and the wavelength shortening effect can be confirmed. Further, the frequency region for obtaining VSWR 2.0 or lower in this case is also moved from 5.0 to 7.0 GHz indicated by symbol A in the figure to 4.5 to 6.4 GHz band indicated by symbol B. It can be confirmed that the shortening effect is obtained. That is, by making the antenna device a laminated structure, the antenna conductor can be prevented from being deteriorated, and the frequency can be adjusted to be reduced.

  15 to 16 show theoretical values and measured values of the directivity characteristics of the antenna device shown in FIGS. 5 and 6 in the linearly polarized wave, respectively. However, it follows that the coordinate system shown in FIG. 17 is set. From each figure, it is confirmed that there is no directivity in the vertical polarization plane, but there is directivity in the horizontal polarization plane.

  18 to 19 show theoretical values and measured values of directivity characteristics of the antenna device shown in FIGS. 5 and 6 with right-handed and left-handed circular polarization, respectively. 20 to 21 show the axial ratio and frequency characteristics of circular polarization of the antenna device. The axial ratio is measured using an antenna that radiates linearly polarized waves on the transmitting side and an antenna that radiates circularly polarized waves on the receiving side. Specifically, the orientation of the antenna under measurement is fixed in the peak direction, and the axis ratio of the transmission ellipse is rotated by 180 degrees or more, so that the level ratio between the major axis and the minor axis of the polarization ellipse is measured as the reception amplitude level. The ratio of the maximum value and the minimum value of the measured value expressed in decibels is recorded as the axial ratio.

  The antenna device shown in FIGS. 1 and 2 uses a double-sided board, and forms a loop pattern as a radiating element, a feed line and a ground plane on its surface, and a microstrip line on the back side. It is configured. As a modified example, a coplanar structure in which all of these patterns are formed on a single-sided substrate can be considered.

  FIG. 22 shows an embodiment of the present invention having a coplanar structure. On the upper surface of the substrate, a loop pattern consisting of a symmetrical semicircle is printed as a radiating element. The ground plane shorts the radiating element to ground at both ends of this loop pattern. From approximately the center of the loop pattern, the central feed line extends toward the center of the arc. And from the front-end | tip of a center electric power feeding line, the conduction line which operate | moves equivalent to a coaxial cable is formed. The pattern forming the ground plane is cut at the center to pass this conductive line.

  The present invention has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiment without departing from the gist of the present invention. That is, the present invention has been disclosed in the form of exemplification, and the contents described in the present specification should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims should be taken into consideration.

FIG. 1 is a diagram illustrating a surface of an antenna device having a planar substrate structure according to an embodiment of the present invention. FIG. 2 is a view showing the back surface of the antenna device shown in FIG. FIG. 3 is a diagram showing a surface structure of an antenna device in which a ground plane region is provided on the back side of the substrate to enhance the ground structure of the antenna. FIG. 4 is a view showing the back surface of the antenna device shown in FIG. FIG. 5 is a diagram showing a surface structure of an antenna device configured to be used in the 5 GHz band. FIG. 6 is a view showing the back surface of the antenna device shown in FIG. FIG. 7 is a diagram showing a theoretical value of return loss (reflection loss) as the input characteristic of the antenna device shown in FIGS. 5 and 6. FIG. 8 is a diagram showing measured values of return loss (reflection loss) as the input characteristics of the antenna apparatus shown in FIGS. 5 and 6. FIG. 9 is a diagram showing a comparison between a theoretical value and an actual measurement value of return loss (reflection loss amount) as input characteristics of the antenna device shown in FIGS. 5 and 6. FIG. 10 is a diagram illustrating theoretical values of VSWRVSWR (voltage standing wave ratio) as input characteristics of the antenna device illustrated in FIGS. 5 and 6. FIG. 11 is a diagram showing measured values of VSWRVSWR (voltage standing wave ratio) as input characteristics of the antenna device shown in FIGS. 5 and 6. FIG. 12 is a diagram showing a comparison between a theoretical value and a measured value of VSWRVSWR (voltage standing wave ratio) as input characteristics of the antenna device shown in FIGS. 5 and 6. FIG. 13 is a diagram illustrating a configuration example of an antenna device having a multilayer structure using the same substrate material or dielectric material. FIG. 14 is a diagram showing return loss as the input characteristics of the antenna apparatus shown in FIG. FIG. 15 is a diagram illustrating theoretical values of directivity characteristics in the linearly polarized wave of the antenna device illustrated in FIGS. 5 and 6. FIG. 16 is a diagram illustrating measured values of directivity characteristics in the linearly polarized wave of the antenna device illustrated in FIGS. 5 and 6. FIG. 17 is a diagram illustrating a coordinate system for indicating the directivity characteristics of the antenna device with linearly polarized waves. FIG. 18 is a diagram showing theoretical values of directivity characteristics of the antenna device shown in FIGS. 5 and 6 with right-handed and left-handed circular polarization. FIG. 19 is a diagram showing measured values of directivity characteristics of the antenna device shown in FIGS. 5 and 6 with right-handed and left-handed circular polarization. FIG. 20 is a diagram illustrating the axial ratio and frequency characteristics of the circularly polarized wave of the antenna device illustrated in FIGS. 5 and 6. FIG. 21 is a diagram showing the axial ratio and frequency characteristics of the circularly polarized wave of the antenna device shown in FIGS. 5 and 6. FIG. 22 is a diagram illustrating a configuration example of an antenna device having a coplanar structure. FIG. 23 is a diagram showing a configuration example of the central feeding loop antenna. FIG. 24 is a diagram showing the relationship between the current moment of the central feed loop antenna and the current distribution. FIG. 25 is a diagram illustrating a configuration example of a triangular twin-loop antenna. FIG. 26 shows a configuration example of an antenna in which two dipole antennas called cross-dipole antennas cross each other at a right angle at the center and feed each other with a phase difference of 90 degrees to generate circular polarization. FIG. FIG. 27 is a diagram showing a configuration example of a dielectric ceramic patch antenna.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Double-sided board 2 ... Loop pattern 3 ... Ground plane 4 ... Microstrip line 5 ... Central feed line

Claims (6)

A substantially planar substrate;
A loop-shaped radiating element pattern formed on the surface of the substrate and having a substantially symmetrical shape,
A ground plane formed on the same plane as the radiating element pattern of the substrate and short-circuiting the radiating element pattern at both ends of the loop;
A central feed line formed from approximately the center of the radiating element pattern toward the center of the loop;
An antenna device comprising: A through hole leading to the back surface of the substrate is formed at substantially the front end of the central feed line, and a tapered microstrip line for supplying power to the antenna on the front surface through the through hole is formed on the back surface of the substrate. Is formed,
The antenna device according to claim 1. On the back surface of the substrate, on both sides of the microstrip line, a ground plane region shared with a ground plane on the front surface side of the substrate is formed.
The antenna device according to claim 2. Operate to resonate in a low frequency band with the outside size of the radiating element pattern;
Operates to resonate in a high frequency band with the length of the central feed line,
The antenna device according to claim 1. The radiating element is formed in a multilayer structure in which a dielectric layer is further laminated on the surface of the substrate.
The antenna device according to claim 1. On one side of the substrate, a conductive line is formed from the tip of the central feed line,
The ground plane is formed on both sides of the conductive line;
The antenna device according to claim 1.

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