JP2004112394A - Microstrip antenna and radio communication apparatus using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microstrip antenna wherein impedance matching is easy in spite of the adoption of a plural point power supply system using side power supply. <P>SOLUTION: The microstrip antenna 10 is fabricated from a substrate 11 made from a dielectric, a radiation electrode 12 formed on one of the main surfaces of the substrate 11, a grounded electrode formed on the other of the main surfaces of the substrate 11, a plurality of feed lines 13 which are formed between the tip and the electrode 12 with a gap G therebetween and supply signals with specified phase differences from a signal source to the electrode 12, and a stub 16 extending from the lines 13 in the direction crossing the length direction of the lines 13 and formed by patterning a metal conductor. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a microstrip antenna used as a built-in antenna of a mobile phone or a mobile terminal as a wireless communication device.
[0002]
[Prior art]
Mobile terminals such as GPS and ETC have a built-in circularly polarized antenna in order to obtain stable transmission and reception performance. Here, a typical example of a circularly polarized antenna is a microstrip antenna.
[0003]
The feed mode of the microstrip antenna includes pin feed through a feed line penetrating the base and directly connected to the radiation electrode, and side feed through a feed line formed from the side surface of the base to the surface on which the radiation electrode is formed. is there. The side power supply is used in many microstrip antennas because the power supply line can be formed by a printing technique and the mass production effect is low and the cost is high.
[0004]
Then, in the microstrip antenna, circularly polarized waves are radiated by feeding power from one point while slightly changing the electrical lengths of two adjacent sides of the rectangular radiation electrode formed on the base (1). Point feeding method). Alternatively, a circularly polarized wave is radiated (multiple points) by feeding a signal by shifting the power supply phase by 90 degrees from a plurality of (two or four) power supply points rotated by 90 degrees with respect to a square radiating electrode. Power supply system).
[0005]
Here, in the one-point feeding method, since the frequency characteristic of the axial ratio of the radiated circularly polarized wave is deteriorated and the frequency band is narrowed, a multi-point feeding method is used to avoid these problems. .
[0006]
[Problems to be solved by the invention]
However, when the multi-point feeding method is adopted in the side feeding, it is difficult to achieve impedance matching, and a reflection loss of energy occurs at a connection point.
[0007]
Therefore, an object of the present invention is to provide a microstrip antenna that can easily achieve impedance matching while adopting a multi-point feeding method with side feeding, and a wireless communication device using the same.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, a microstrip antenna according to the present invention includes a base made of a dielectric, a radiation electrode formed on one main surface of the base, and a radiation electrode formed on the other main surface of the base. A plurality of feed lines that are provided with a gap formed between the tip and the radiation electrode, and that supply a signal from a signal source to the radiation electrode with a predetermined phase difference; A stub that extends in a direction intersecting the length direction and is formed by patterning a metal conductor.
[0009]
In order to solve the above problems, a microstrip antenna according to the present invention includes a base made of a dielectric, a radiation electrode formed on one main surface of the base, and a radiation electrode formed on the other main surface of the base. A plurality of feed lines provided in conduction with the formed ground electrode and the radiating electrode, for feeding a signal from a signal source to the radiating electrode with a predetermined phase difference, and intersecting the feed line with the length direction of the feed line. And a stub that is provided to extend in a direction in which the metal conductor is formed.
[0010]
According to such an invention, the impedance characteristic can be adjusted to a desired value by adjusting the stub extending from the feed line, so that the impedance matching can be easily performed in the multi-point feeding microstrip antenna with side feeding. It becomes possible to plan.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described more specifically with reference to the drawings. Here, in the attached drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted. The embodiment of the present invention is a particularly useful embodiment in which the present invention is implemented, and the present invention is not limited to the embodiment.
[0012]
1 is a perspective view showing a microstrip antenna according to an embodiment of the present invention, FIG. 2 is a plan view of the microstrip antenna of FIG. 1, FIG. 3 is a side view of the microstrip antenna of FIG. 1, and FIG. FIG. 5 is a graph showing a change in input impedance with respect to a stub length in a microstrip antenna according to an embodiment of the present invention; FIG. 5 is a graph showing frequency characteristics of input impedance in a microstrip antenna according to an embodiment of the present invention; 6 is a graph showing the VSWR frequency characteristic of the microstrip antenna according to one embodiment of the present invention, FIG. 7 is a graph showing the radiation pattern of the microstrip antenna according to one embodiment of the present invention, and FIG. Axial ratio ratio in a microstrip antenna according to an embodiment of the invention FIG. 9 is a graph showing frequency characteristics of gain in a microstrip antenna according to one embodiment of the present invention, and FIG. 10 is a perspective view showing a microstrip antenna according to another embodiment of the present invention. It is.
[0013]
As shown in FIGS. 1, 2 and 3, the microstrip antenna 10 of the present embodiment has a rectangular base 11 made of a dielectric, and is provided on one main surface of the base 11. Has a square radiation electrode 12, and a ground electrode (not shown) formed on the other main surface. In the present embodiment, the radiation electrode 12 is square, but may be rectangular, elliptical, circular, or various other shapes. In this specification, the rectangular shape broadly means a square including not only a rectangle but also a square.
[0014]
Four power supply lines 13 are formed from the four side surfaces of the rectangular base 11 to the surface on which the radiation electrode 12 is formed. The feed line 13 has a gap G between its tip and the radiation electrode 12 and is electromagnetically coupled to the radiation electrode 12. Then, signals from a signal source (not shown) are shifted from the feeding points located on the four sides of the radiation electrode 12 by 90 degrees in the feeding phase between the feeding points on two sides adjacent to each other. Power to the radiation electrode 12.
[0015]
In this specification, the power supply line is a conductive line such as a microstrip line or a single line.
[0016]
As shown, the microstrip antenna 10 is mounted on a mounting substrate 14 made of a dielectric material backed by a metal plate. A power supply conductor (not shown) connected to the power supply line 13 of the microstrip antenna 10 and a ground conductor 15 connected to a ground electrode are formed on the mounting substrate 14.
[0017]
Here, in the microstrip antenna 10 of the present embodiment, in order to improve the axial ratio characteristics of the radiated circular polarization, four feed lines 13 are formed, and the feed phases between the feed points are shifted by 90 degrees. And four-point power supply. However, it is sufficient that a plurality of power supply lines 13 are formed, and the number is not limited to four. That is, it is sufficient that there are a plurality of feeding points, and it is not necessary to use four-point feeding. Further, the phase difference between the power supply phases may be other than 90 degrees.
[0018]
In the case of two power supply lines 13, the power supply lines 13 are formed from two mutually adjacent side surfaces of the base 11 to the surface on which the radiation electrode 12 is formed. Then, a signal from a signal source is supplied to the radiation electrode 12 from two power supply points located on two mutually adjacent sides of the radiation electrode 12 with the power supply phase shifted by 90 degrees.
[0019]
A metal conductor is formed on the side surface of the base 11 by extending from the power supply line 13 in a direction intersecting with the length direction of the power supply line 13 (one direction orthogonal to the direction shown in the figure) and patterning a metal conductor. A stub 16 for adjusting the impedance characteristics of the strip antenna 10 is formed.
[0020]
That is, the present inventor has found that the impedance characteristic of the microstrip antenna 10 changes when such a stub 16 is provided and its line length, formation position, line width, and the like are changed. Therefore, even in the case of the microstrip antenna 10 of the side feeding method and the multi-point feeding method in which impedance matching is difficult, by providing the stub 16 and adjusting the line length or the like, a desired impedance (for example, 50Ω) can be easily obtained. I learned that it would be possible to do so. The relationship between the length of the stub 16 and the impedance will be described later.
[0021]
Here, the stubs 16 may be formed at two places on one side or both sides of the power supply line 13, and the extending directions may not be orthogonal directions. Further, if desired impedance characteristics can be obtained, it is not necessary to extend to adjacent side surfaces as shown in the figure.
[0022]
The radiation electrode 12, the ground electrode, the power supply line 13, and the stub 16 are formed by patterning a metal conductor layer such as copper or silver. Specifically, it is formed by, for example, a method of pattern printing and baking a metal paste such as silver, a method of forming a metal pattern layer by plating, and a method of patterning a thin metal film by etching.
[0023]
In the microstrip antenna 10 having the above configuration, when the signal from the signal source is fed to the radiation electrode 12 with the above-described phase difference via the four feed lines 13, the radiation electrode 12 resonates in two orthogonal directions. . Since these two resonance currents have a phase difference of 90 degrees, the radio waves radiated from each resonance current are linearly polarized waves whose directions are orthogonal to each other and whose phases are shifted by 90 degrees. Therefore, these are superimposed to emit a circularly polarized radio wave.
[0024]
Here, the base 11 is made of, for example, a high-frequency ceramic dielectric material having a relative dielectric constant of about ε _r1 = 37, and has a resonance frequency of f = 2.4 GHz (λ _2.4 = 125 mm). In the case of the microstrip antenna 10 of the embodiment, the thickness is B ₁ = 4 mm (= 0.032λ _2.4 ), and the length of one side is S ₁ = 12 mm (= 0.096λ _2.4 ). I have. The mounting substrate 14 has, for example, a relative dielectric constant of ε _r2 = 4.8, a thickness of B ₂ = 1 mm (= 0.008λ _2.4 ), and a length of one side of S ₂ = 40 mm (= 0.320λ). _2.4 ).
[0025]
The length of one side of the radiation electrode 12 is S _P = 9 mm (= 0.072λ _2.4 ), the width of the feed line 13 and the stub 16 is W = 1 mm (= 0.008λ _2.4 ), The height from the lower part to the stub 16 is H = 1.5 mm (= 0.012λ _2.4 ).
[0026]
Here, the change of the input impedance with respect to the length (L) of the stub 16 is shown in FIG.
[0027]
As shown in the figure, when the length (L) of the stub 16 is changed, the impedance greatly changes. When L = 0.076λ _2.4 (9.5 mm), the reactance component X _in becomes 0Ω and the resistance component R _in is 50Ω. Therefore, when achieving impedance matching with 50Ω is, it is sufficient to set the length of the stub 16 in L = 0.076λ _2.4.
[0028]
FIG. 5 shows the frequency characteristics of the input impedance in the microstrip antenna 10 of the present embodiment in which the length of the stub 16 is set to L = 0.076λ _2.4 in this manner, and the VSWR (Voltage / Standing Wave Ratio) FIG. 6 shows the frequency characteristics of (/ standing wave ratio).
[0029]
As shown in FIG. 5, in the microstrip antenna 10 of the present embodiment, it can be seen that the input impedance is 50 + j0Ω when the frequency f = 2.4 GHz. Also, as shown in FIG. 6, at a frequency f = 2.39 to 2.405 GHz, that is, at a frequency f = about 2.40 GHz, the VSWR at an input impedance of 50Ω is 2 or less. It can be seen that the gain is good.
[0030]
Further, FIG. 7 shows a radiation pattern on the xz plane (see FIG. 1) and FIG. 8 shows an axial ratio pattern in the microstrip antenna 10 of the present embodiment. The frequency at this time is f = 2.40 GHz. Further, in FIG. 7, the solid line radiation pattern of right-handed circularly polarized wave E _R, the broken line shows the radiation pattern of the left hand circular polarization E _L. From these figures, it can be seen that the beam half width is calculated to be 104 degrees and the beam width having an axial ratio of 3 dB or less is calculated to be 150 degrees, and that a circularly polarized wave having an excellent axial ratio characteristic is emitted.
[0031]
Further, FIG. 9 shows the frequency characteristic of the gain in the microstrip antenna 10 of the present embodiment. As shown in the figure, the right-handed circularly polarized wave gain is about 5 dB near the frequency f = 2.40 GHz where the VSWR is 2 or less.
[0032]
As described above, according to the microstrip antenna 10 of the present application, the impedance characteristic can be adjusted to a desired value by adjusting the stub 16 extending from the feed line 13. In the antenna 10, impedance matching can be easily achieved.
[0033]
In the above description, the case where the present invention is applied to the electromagnetically coupled microstrip antenna 10 in which the gap G is formed between the tip of the feeder line 13 and the radiation electrode 12 is shown. As shown in (1), the direct feed type microstrip antenna 10 in which the feed line 13 and the radiation electrode 12 are electrically connected may be used.
[0034]
Further, each numerical value shown in the present embodiment is merely an example for specifically describing the present invention, and it is needless to say that the present invention is not limited to these numerical values.
[0035]
The microstrip antenna of the present invention can be used for various wireless communication devices such as a mobile phone, a mobile terminal, and a built-in antenna of a wireless LAN card.
[0036]
Further, as another usage of the present invention, for example, if one of two sides adjacent to each other in the radiation electrode is fed and the other is not fed, one fixed antenna can be used for horizontal polarization and vertical polarization. Application to a linearly polarized antenna system that switches between polarized waves is possible.
[0037]
【The invention's effect】
As is clear from the above description, the present invention has the following effects.
[0038]
That is, the impedance characteristic can be adjusted to a desired value by adjusting the stub extending from the feed line, so that impedance matching can be easily achieved in a microstrip antenna of a multi-point feeding system with side feeding. .
[Brief description of the drawings]
FIG. 1 is a perspective view showing a microstrip antenna according to an embodiment of the present invention.
FIG. 2 is a plan view of the microstrip antenna of FIG.
FIG. 3 is a side view of the microstrip antenna of FIG. 1;
FIG. 4 is a graph showing a change in input impedance with respect to a stub length in a microstrip antenna according to an embodiment of the present invention.
FIG. 5 is a graph showing frequency characteristics of input impedance in the microstrip antenna according to one embodiment of the present invention.
FIG. 6 is a graph showing VSWR frequency characteristics in the microstrip antenna according to one embodiment of the present invention.
FIG. 7 is a graph showing a radiation pattern in the microstrip antenna according to one embodiment of the present invention.
FIG. 8 is a graph showing an axial ratio pattern in the microstrip antenna according to one embodiment of the present invention.
FIG. 9 is a graph showing frequency characteristics of gain in the microstrip antenna according to one embodiment of the present invention.
FIG. 10 is a perspective view showing a microstrip antenna according to another embodiment of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 10 microstrip antenna 11 base 12 radiation electrode 13 feeder line 14 mounting substrate 15 ground conductor 16 stub G gap

Claims (5)

A base made of a dielectric,
A radiation electrode formed on one main surface of the base,
A ground electrode formed on the other main surface of the base,
A plurality of feed lines that are provided with a gap formed between the tip and the radiation electrode and feed a signal from a signal source to the radiation electrode with a predetermined phase difference;
A stub provided extending from the power supply line in a direction intersecting the length direction of the power supply line, and formed by patterning a metal conductor layer. A base made of a dielectric,
A radiation electrode formed on one main surface of the base,
A ground electrode formed on the other main surface of the base,
A plurality of power supply lines that are provided in conduction with the radiation electrode and supply a signal from a signal source to the radiation electrode with a predetermined phase difference,
A stub that extends from the feeder line in a direction intersecting the length direction of the feeder line and is formed by patterning a metal conductor. The radiation electrode has a rectangular shape,
The power supply to the radiation electrode by the power supply line is performed by shifting the power supply phase between the power supply points located on the four sides of the radiation electrode and the power supply points on two sides adjacent to each other by 90 degrees. The microstrip antenna according to claim 1 or 2, wherein: The radiation electrode has a rectangular shape,
The power supply to the radiation electrode by the power supply line is performed with a power supply phase shifted by 90 degrees from a power supply point located on each of two adjacent sides of the radiation electrode. Microstrip antenna. A wireless communication device using the microstrip antenna according to claim 1.

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