JP2002271131A - Planar antenna - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To make a planar antenna thin and have wideband characteristics. A feed line has one end connected to a coaxial receptacle, and the other end connected to a feed point of an antenna element via a via hole formed in a dielectric flat plate. In an antenna in which a transmission line 1 composed of a metal conductor antenna element 2 and a strip conductor feeding the antenna element is formed on a dielectric flat plate 15, two antennas having the same width and different lengths at substantially the same location on the transmission line 1. Stubs 4 and 5 are formed. An antenna for feeding power at least partially using the transmission line 1 is characterized in that a plurality of stubs 4 and 5 having different shapes are provided at substantially the same location on the transmission line 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat antenna, more specifically, a patch of a metal conductor (hereinafter also referred to as an antenna element) on a dielectric flat plate and a strip-shaped transmission line for feeding the antenna element. The present invention relates to a so-called planar antenna formed, and more particularly to a structure of a thin planar antenna having broadband characteristics used for a communication terminal such as a wireless LAN or an intelligent transport system (ITS) or a base station.

[0002]

2. Description of the Related Art At present, various services using radio such as wireless LAN and ITS are being studied. It is desired that an antenna mounted on a wireless device mounted on a car for ITS application has high performance and small size from the viewpoint of aesthetics and installation space. Further, it is desirable that the wireless device used in the wireless LAN be small and thin so that the antenna and its peripheral portion can be housed in a package with the same thickness as the PC card. The antenna used in these systems includes a patch antenna, that is, a planar antenna. The band of the patch antenna is narrower when the dielectric substrate constituting the antenna is thinner, and the unit price of the substrate is generally lower when the substrate is thinner. When the thickness of the substrate constituting the patch antenna is reduced to reduce the thickness and cost, the band becomes narrower, so that the patch antenna needs to have a wider band.

As this type of planar antenna, there is known a planar antenna in which a plurality of antenna elements are formed on a dielectric flat substrate and a feed line of a conductor feed pattern is provided for each of the antenna elements as shown in FIG. (Japanese Patent Laid-Open No. 20
00-134028). FIG. 10 is a plan view showing only the surface of the planar antenna on which the feeder transmission line is formed. A plurality of antenna elements are not shown, and the plurality of antenna elements are on the opposite side of the surface on which the transmission line is formed. Formed on the surface.

That is, a feed transmission line composed of a strip line extending from a coaxial feed point to a feed point of a plurality of antenna elements and branching from one side of a substrate is provided on one surface of the substrate.
A stub 25a is formed in the middle of
A stub 25b is also formed in the middle of 4b. Stubs 25a, 25
The width of the strip line beyond b is wider than the feed point side of the coaxial cable. Further branched tracks 26a, 2
6b, 26c, 26d also have stubs 27a, 27b, 27c, 2
7d is formed, and the width of the line is similarly varied. As described above, the impedance matching is realized by providing the stub with the branch part of the transmission line interposed between the feeding transmission lines.

[0005]

The above-mentioned conventionally known planar antenna has a plurality of antenna elements arranged. Therefore, two stubs (for example, the stub 25a and the stub 27a) are provided in the feed transmission line at positions apart from the branch point up to the feed points of the plurality of antenna elements (patches). The stub provided at the same place among the plurality of stubs provided on the feed transmission line is used for impedance matching and for canceling radiation by making the current flow in the opposite direction. It is formed so as to be targeted.

[0006] Further, a plurality of stubs for one antenna element are provided at different widths of the transmission line and formed at distant positions. That is, the above-described conventionally known antenna does not consider the miniaturization and broadening of the band width of an antenna having a single antenna element.

An object of the present invention is to reduce the area required for arranging transmission lines and stubs used for feeding a planar antenna, and to realize a planar antenna having good wideband characteristics.

[0008]

In order to achieve the above object, a planar antenna according to the present invention has a transmission line formed of a metal conductor antenna element and a strip conductor feeding the antenna element on one surface of a dielectric flat plate. In the planar antenna, a plurality of stubs having different shapes are provided at substantially the same location on the transmission line.

Here, the difference in the shape of the stub means that at least one of the length and the width is different. The same location means that a point at which the center lines of the plurality of stubs and the center line of the transmission line intersect is substantially one point. The plurality of stubs may be arranged on both left and right sides or only one side of the transmission line.

Further, when the planar antenna is a circularly polarized antenna with two-point feeding, the stub is provided between a branch point for dividing the feeding power to the antenna element into two and a feeding point to the antenna element. It is provided on a transmission line equally distant from each feeding point of each of the two transmission lines connecting them.

The planar antenna of the present invention can be made smaller in planar shape only by forming a single antenna element and a plurality of stubs as shown in the following embodiments, and also for the following reasons. In addition, it is possible to expand the band of use, that is, the frequency range where the reflection coefficient is equal to or less than a certain range. When an antenna element (patch) is connected to the tip of a transmission line having a constant characteristic impedance, the reflection coefficient viewed from the power supply side of the transmission line is represented as a Smith chart in FIG. When the frequency is changed, the reflection coefficient S11 becomes a curve 16
It changes like In this curve 16, the reflection coefficient S11 is below a certain value (for example, -10 dB or less) in the range of the inside of the circle 17 (thick line) indicating the reflection coefficient S11. In the two cases, since the internal curve of the circle changes monotonically, the frequency fluctuation range (range of frequency 1 or frequency 2) inside the circle is narrow. When a plurality of stubs having a predetermined shape and different characteristics are provided in the middle of the transmission line, the curve in the circle 17 showing the reflection coefficient S11 when the frequency is changed changes complicatedly as shown in FIG. Then, the frequency fluctuation range (range of frequency 3 to frequency 4) inside the circle is expanded, and the band of the planar antenna is expanded. In the above-mentioned conventional invention, no consideration is given to miniaturization and broadening of the bandwidth of an antenna having a single antenna element, and a plurality of stubs are also arranged at intervals. On the other hand, the present invention has been made by newly finding that the same effect can be obtained even when a plurality of stubs having different shapes are provided at substantially the same position on the transmission line.
Therefore, the gap previously provided between the stubs can be formed in the film nest, and the antenna can be reduced in size.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. In all the drawings for describing the embodiments, those having the same functions and components are denoted by the same reference numerals, and a repeated description thereof will be omitted.

FIGS. 1 and 2 are a plan view and a sectional view, respectively, showing the configuration of a first embodiment of the planar antenna according to the present invention. As shown in the cross-sectional view, the antenna of the present embodiment has an antenna in which a dielectric plate 15 is provided with a metal conductor antenna element 2 and a transmission line 1 composed of a strip conductor for feeding the antenna element. Two stubs 4 and 5 having the same width and different lengths are formed in substantially the same place. One end of the feed line 1 is connected to the coaxial receptacle 6, and the other end is connected to the feed point of the antenna element 1 via the via hole 3 formed in the dielectric plate 15. As shown in the cross-sectional view of FIG. 2, the dielectric flat plate 15 includes a first dielectric layer 9 and a second dielectric layer 8 formed above and below the conductor layer 7 forming the ground. The transmission line 1 and the plurality of stubs 4 and 5 are formed on the first dielectric layer 9. A feed section of the transmission line 1 to the antenna element 2 is provided from a tip end of the transmission line 1 via a dielectric plate (8, 9) and a via hole 3 formed through a ground 7. In this embodiment, the resonance frequency of the patch antenna 2 is 5.8 GHz
And The thickness of the dielectric layer 8 between the patch 2 and the ground 7 is 0.8 mm, and the thickness of the dielectric layer 9 between the ground 7 and the feed line 1 is 0.8 mm.
Was 0.2 mm thick. The dielectrics 7 and 8 used were Teflon (registered trademark) substrates having a relative dielectric constant of 2.6 and a dielectric loss tangent of 0.0015. The feed line 1 was formed by a microstrip line having a characteristic impedance of 50 ohms.
The width of the open stubs 4 and 5 is the same, 0.58 mm,
The length was 7.0 mm and 10.4 mm, respectively.

In the first embodiment, the feed point to the patch 2 is located at a position where the impedance becomes 50 ohms at the center frequency, and the via hole 3 is provided there. The open stubs 4 and 5 were located at a position 8.29 mm from the feeding point, which was the center of the width of the stub.

FIG. 3 shows the measurement results of the reflection characteristics according to the above embodiment. This measurement is indicated by a dotted line, with the result obtained by connecting the coaxial receptacle 6 to the antenna shown in FIG. Also,
As shown in FIG. 4, the solid line shows the reflection characteristics when the stub is not provided on the feed line with the same design as the antenna of FIG. According to the reflection characteristics shown in FIG. 3, when the stubs 4 and 5 are not provided, the band where the reflection characteristic S11 is 10 dB or less is about 120 MHz.
The band where 1 is less than 10 dB is about 180 MHz, and the antenna can be widened. In addition, as shown in FIG. 4, in order to obtain a band of about 180 MHz without the stubs 4 and 5, a substrate having a thickness of about 1.5 times or more is required as a substrate between the patch and the ground. As described above, according to the present embodiment, the dielectric layer 8 constituting the substrate is made thinner,
With a simple configuration in which small stubs 4 and 5 are added at the same position, it is possible to realize a wider band and a thinner antenna at the same time. FIG. 5 is a plan view showing a second embodiment of the planar antenna according to the present invention. In this embodiment, an antenna element (patch) 2, a feed line 1, and stubs 4 and 5 are formed on one dielectric layer having a ground conductor layer formed on the back surface. In the present embodiment, when the antenna element is relatively small, it can be formed most simply and compactly.

FIG. 6 is a plan view showing a third embodiment of the planar antenna according to the present invention. This embodiment is composed of three conductor layers and two dielectric layers as in the case of the patch antenna of FIG. 1, but this embodiment constitutes a circularly polarized antenna with two-point feeding. In this embodiment, in order to distribute the power equally to the two feeding points 3, the via hole 3 serving as a feeding point to the coaxial receptacle 6 and the antenna element 2 is used.
A Wilkinson-type power distributor 10 is provided therebetween.
An open stub 4 having two different shapes and an open stub 5 having two different shapes are arranged on a feed line between the power distributor 10 and the two feed points 3. The positions where the stubs 4 and 5 are provided are provided at positions evenly separated from the feeding point 3 to the antenna element 2.

In this embodiment, stubs having a length of 7.0 mm and a length of 10.1 mm are provided at 11.29 mm from the feeding point. These stubs were arranged on one side of the feed line at an angle of about 60 degrees with respect to the feed line as shown in FIG. With the feed line having such a structure, 2
It was possible to widen the band where the reflection characteristic at one feeding point was less than 10 dB, and as a result, a circularly polarized antenna with good axial ratio characteristics in a wide band was obtained.

FIG. 7 is a plan view showing a fourth embodiment of the planar antenna according to the present invention. In this embodiment, a branch line type 3 dB hybrid 11 is used in place of the Wilkinson power divider 10 shown in FIG. Also in this embodiment, the stubs are such that the same open stubs 4 and 5 are respectively arranged at positions equally distant from the feeding point on the feeding line between the 3dB hybrid 11 and the feeding point. As shown in the figure, one stub may be provided on each of the left and right sides of the feed line, or two stubs may be provided on one side of the feed line as shown in FIG.

FIG. 8 is a plan view showing a fifth embodiment of the planar antenna according to the present invention. This embodiment comprises three conductor layers and two dielectric layers as in the first embodiment. In the present embodiment, the high-frequency circuit module 12 is mounted on a substrate on which a power supply line is formed. According to the present embodiment, the stub provided for widening the band and the space required for installing the feeder line can be reduced as compared with the related art, so that the high-frequency circuit module 12 and FIG.
Although not shown, when mounting discrete components, the place where they can be mounted can be widened. Therefore, as compared with the related art, the degree of freedom in mounting the circuit components such as the high-frequency circuit module 12 and the discrete components and the wiring can be increased.

In the embodiment described above, the open stub is used as the stub, but it is apparent that the same effect can be obtained even when the shape of the stub is a short stub.

The antenna according to the present invention can simultaneously realize a wide band, a low profile, a small size, and a low price. In particular, it can be mounted on a PC card from the viewpoint of thinning. Also, a plurality of antennas of the present invention are arranged to form an array antenna, and a wireless LAN
ITS, an antenna for a base station for fixed wireless access, and an antenna for the terminal station described above.

[0022]

According to the present invention, the antenna can be broadened in bandwidth without a major change in the conventional antenna manufacturing process and without adding new components such as capacitors and switches. In addition, by providing two or more stubs provided for broadening the antenna in substantially the same place on the feed line, the area required for disposing the feed line and the stub can be reduced as compared with the conventional case, and the circuit module can be reduced. And the area on which discrete components can be mounted is increased, and the degree of freedom in installing those components is improved.

Further, if the present invention is used, the same band as that of the related art can be realized with a thinner substrate.
The cost of the antenna can be reduced.

As described above, according to the present invention, a small, thin, low-cost, wideband antenna can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of a first embodiment of a planar antenna according to the present invention.

FIG. 2 is a sectional view showing the configuration of the first embodiment of the planar antenna according to the present invention.

FIG. 3 is a reflection characteristic diagram of the first embodiment of the planar antenna according to the present invention.

FIG. 4 is a plan view showing a pattern of a feed line of a planar antenna without a stub.

FIG. 5 is a plan view showing the configuration of a second embodiment of the planar antenna according to the present invention.

FIG. 6 is a plan view showing a third embodiment of the planar antenna according to the present invention.

FIG. 7 is a plan view showing the configuration of a fourth embodiment of the planar antenna according to the present invention.

FIG. 8 is a plan view showing the configuration of a fifth embodiment of the planar antenna according to the present invention.

FIG. 9 is a Smith chart for explaining the operation of the planar antenna according to the present invention.

FIG. 10 is a plan view showing an example of a conventionally known planar antenna.

[Explanation of symbols]

1 ... feed line, 2 ... patch, 3 ... via hole, 4, 5 ...
Open stub, 6: Coaxial receptacle, 7: Ground, 8, 9: Dielectric, 10: Wilkinson type power divider, 11: Branch line type 3dB hybrid, 12
… High-frequency circuit module, 15… Dielectric plate, 1524a, 24
b, 26a, 26b, 26c, 26d ... strip line, 25a, 25b, 2
7a, 27b, 27c, 27d ... stub.

Claims (5)

[Claims] 1. An antenna in which a transmission line composed of a metal conductor antenna element and a strip conductor for feeding the antenna element is formed on a dielectric flat plate, a plurality of stubs having different shapes are provided at substantially the same location on the transmission line. A planar antenna characterized in that: 2. The antenna according to claim 1, wherein said dielectric plate comprises a first dielectric layer and a second dielectric layer formed above and below a conductor layer forming a ground, and said antenna element is , Formed on the first dielectric layer, the transmission line and the stub are formed on the second dielectric, and a feeder of the transmission line to the antenna element is provided between the transmission line and the antenna element. A planar antenna formed through a via hole formed in the antenna. 3. The planar antenna according to claim 1, wherein said antenna element, said transmission line, and said stub are formed on the same plane of said dielectric flat plate. 4. The antenna according to claim 1, wherein the antenna element is a two-point feeding circularly polarized antenna element, and the transmission line is a branch line for performing the two-point feeding. Wherein the stub is provided on a transmission line equally spaced from each feed point of each of two branch transmission lines connecting the feed point to the antenna element. 5. The antenna according to claim 1, wherein a high-frequency circuit component coupled to the transmission line is mounted on a surface of the dielectric plate on which the transmission line is formed. A planar antenna, characterized in that: