JP3033030B2 - Linearly polarized microstrip antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linearly polarized microstrip antenna, and more particularly to a technique for miniaturizing a linearly polarized microstrip antenna.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a conventional microstrip antenna (hereinafter, referred to as an MS antenna). The MS antenna has a rectangular element (x1 × y1), and can independently excite the x and y directions depending on the feeding position. Further, when the feeding point position is on a diagonal line of x1 × y1, circular polarization can be generated. Hereinafter, from the viewpoint of the size of the rectangular element and the size of the grounding conductor, M
The S antenna will be described.

(1) Rectangular element size A resonance mode exists independently in the x direction and the y direction. Here, the conventional method will be described in the x direction. In order to excite in the x direction, the position of the feeding point is set to be parallel to the x axis at y1. In the basic mode, the length of x1 is x1 ≒ λg / 2
= C / (2f√Er) = λo / (2√Er). Here, λg is the guide wavelength (meaning the wavelength on the antenna), λo is the free space wavelength, and Er is the permittivity. That is, in order to reduce the size of the antenna, it is desirable to increase the dielectric constant of the substrate. On the other hand, as shown in FIG. 7, FIG. 8, FIG. 9, FIG. 10, and FIG.
There are problems such as a large Q factor and a narrow bandwidth.

In general, about 1 ≦ Er ≦ 5 is selected, and 0.
23λo ≒ x1 ≒ 0.5λo. In the basic mode,
the current on the element surface in the x direction is zero at x1 / 2,
That is, there is disclosed a technique for reducing the size by a one-side short-circuit type MS antenna utilizing the electric field (Ez = 0) between the ground conductor plate and the element (Japanese Patent Application Laid-Open No. 61-717).
No. 02 and JP-A-62-131609).

(2) Size of ground conductor plate The size of the element and the ground conductor plate (dielectric plate) affects the radiation directivity. In particular, when the ratio approaches 1, sufficient directivity cannot be obtained. This also results in reduced gain. If the ground conductor plate is large enough compared to the element,
The radiation directivity is Z> 0 and the broadside direction shown in FIG. 6, and does not radiate when Z <0. Generally, the size of the ground conductor plate is experimentally determined from required radiation directivity.

[0006]

The above-mentioned Japanese Patent Application Laid-Open No. 61-7 / 1986
In the antenna disclosed in Japanese Patent No. 1702, the element length x1
Although operation has been confirmed at ≒ λg / 4, it has been found that the radiation directivity tilt and the bandwidth become narrower at the cost of miniaturization. In the antenna disclosed in Japanese Patent Application Laid-Open No. 62-131609, means for eliminating the tilt of the directivity is disclosed. However, the low profile, which is an advantage of the MS antenna, is lost, and the bandwidth is narrow. Therefore, it is necessary to correct the resonance frequency disclosed in Japanese Utility Model Laid-Open No. 63-12931. That is, there are the above-mentioned two problems in reducing the size of the antenna. When designing an MS antenna, whether the matching is sufficient, the radiation directivity is satisfactory, the gain and antenna efficiency are large,
Need to be considered. It is an object of the present invention to reduce the size of an MS antenna based on dimensions determined theoretically for matching, gain, and antenna efficiency, and experimentally for radiation directivity, based on dimensions determined. Note that the present invention uses a rectangular M
It is specified for the S antenna, and is mainly intended for use in the L band.

[0007]

A linearly polarized microstrip antenna according to the present invention has a dielectric plate member (2) which is sufficiently thin with respect to a wavelength to be used; and is mounted on one surface of the dielectric plate member (2). A rectangular radiating conductor plate member (3) having one side larger than よ り 小 さ い times and smaller than 倍 times the in-tube wavelength λg; and a pair of opposing rectangular radiation conductor plate members (3). A rectangular stub (4a, 4b) extending at a length smaller than 1/4 of the in-use wavelength λg is provided at the center of the two sides.

[0008]

[Function] Even if the length of one side of the radiation conductor plate member (3) is constant, the desired resonance frequency can be matched by adjusting the width and length of the stubs (4a, 4b). . Therefore, the radiation conductor plate member (3) can be formed in a rectangular shape having one side larger than １ ／ times and smaller than 倍 times the used wavelength, and matching can be achieved. Also, generally, a dielectric plate member
(2) The length of the radiating conductor plate member (3) must be twice as long as the radiating conductor plate member (3). ) Is reduced, and the antenna can be reduced in size. Furthermore, since only one set of stubs is required, the manufacturing is relatively easy and the manufacturing cost can be reduced.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0010]

FIG. 1 shows a microstrip (MS) of the present invention.
The outline of an antenna is shown. This will be described below with reference to FIG.
The rectangular MS antenna has independent resonance modes in the x and y directions. In the present invention, since it is used as a linearly polarized antenna, it is used only in the resonance mode in the x direction. Hereinafter, the resonance mode in the x direction will be described. In an MS antenna 1 having a dielectric constant Er and a thickness h on one side of a thin copper dielectric material, and the other as an element, the element 3 includes stubs 4a and 4b having a length Lx1 and a width Wy in the x direction Ly0 /.
This is a rectangular element of Lx0 × Ly0 loaded at the position 2, and the thickness of the dielectric is sufficiently smaller than the free space wavelength λo. When the imaginary number of the input admittance Yinx in the x direction becomes zero, the resonance condition can be obtained from the equivalent circuit of FIG. In FIG. 2, Yx0 and Yx1 are Ly0,
Wy is the characteristic admittance of the microstrip line, and βx0 and βx1 are their phase constants. Since radiation is emitted from each opening at the end of the element, its contribution is represented by radiation admittance Ya. In this embodiment, since the thickness h of the dielectric is sufficiently smaller than the free space wavelength λo, Ya ≦ Yx0, Yx1. So Ya
Assuming that = 0, the equivalent circuit is simplified, and the resonance condition where the imaginary number of Yinx becomes zero is obtained by the following equation.

[0011]

(Equation 1)

In the present invention, λg / 4 <Lx0 <λ
g / 2, 0 <Lx1 <λg / 4 to use tan (βx
0) (Lx0) <0, tan (βx1) (Lx1)> 0, which is a condition for determining the mathematical expression shown in Expression 1. FIG. 3 is a graph of the mathematical formula shown in Expression 1. This will be described below with reference to FIG.
The horizontal axis represents Lx0 and Lx1 normalized by the guide wavelength λg. Also, λg ≒ λo / √Er. The vertical axis is number 1
Are the values on the right and left sides of the equation shown in FIG. The stub 4a,
The characteristic admittance Y1 of the stub determined by the width Wy of 4b is included. As an example, Wy = 0.05λg, Wy =
The resonance conditions of 0.09λg and Wy = 0.12λg are shown. In the basic mode excitation by the conventional method of Lx0 = 0.5λg, resonance occurs at the stub length Lx1 = 0. Wy = 0.0
At 5λg, when Lx0 = 0.34λg, Lx1 = 0.
Resonates at 19λg. The resonance condition is determined as described above.

Next, the gain will be examined. The gain is determined by (antenna efficiency) × (directivity gain). As shown in FIG. 9, the antenna efficiency decreases as the dielectric constant increases, resulting in a decrease in gain. In the present invention, since no condition is set for the dielectric constant, there is no deterioration in antenna efficiency. The directivity gain changes depending on the size of the element 3, but within the scope of the present invention, it hardly changes, and the decrease in gain is within a negligible range.

When examining the radiation directivity, in order to obtain sufficient radiation directivity, the element shape, in this case, a ground conductor plate (dielectric) of about twice the distance of each opening contributing to radiation at the end of the element, is required. Generally required. In the present invention, the length of the dielectric is equivalent to 2Lx0, which is shorter than the conventional element length of 0.5λg. Therefore, the length of the dielectric 2 can be shortened accordingly, and the antenna can be miniaturized.

In order to confirm the principle of operation according to the present invention, a Teflon (registered trademark) substrate having a substrate dielectric constant Er of 2.5 was used, and h = 3.2 mm, Wy = 0.09λg, Lx0}.
Exact calculation is performed at 0.34λg, and Lx1 ≒
The antenna performance was confirmed by obtaining 0.14λg. The feeding point is located at a matching point on Ly0 / 2.

FIGS. 4 and 5 show the performance of the MS antenna 1 in this embodiment. FIG. 4 shows that the power supply frequency is 1.47.
FIG. 5 is a graph showing the reflection coefficient when changing from 5 GHz to 1.675 GHz, and FIG. 5 shows the radiation directivity of the antenna 1. 4 and 5 that the matching is sufficient and that the device has sufficient directivity. Also,
The antenna gain in the maximum radiation direction was 6 dBi.

As described above, according to the present embodiment, it is possible to reduce the size of the linearly polarized microstrip antenna having sufficient matching, satisfactory radiation directivity, and sufficient gain.

[0018]

As described above, according to the present invention, even if the length of one side of the radiation conductor plate member (3) is constant, the stub (4a, 4
By adjusting the width and length of b), a desired resonance frequency can be matched. Therefore, the radiation conductor plate member
(3) can be formed in a rectangular shape having one side larger than ４ times and smaller than 倍 times the used tube wavelength λg, and matching can be achieved. Generally, the length of the dielectric plate member (2) needs to be twice as long as the radiating conductor plate member (3), but since the radiating conductor plate member (3) can be made smaller than a conventional antenna. In addition, the size of the dielectric plate member (2) is reduced, and the antenna can be reduced in size. Furthermore, since only one set of stubs is required, the manufacturing is relatively easy and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a microstrip antenna of the present invention.

FIG. 2 is an equivalent circuit in the x-axis direction of the antenna shown in FIG.

FIG. 3 is a graph in which the horizontal axis represents Lx0 and Lx1 normalized by the guide wavelength λg, and the vertical axis represents values on the right and left sides in the mathematical formula shown in Expression 1.

4 is a graph showing a relationship between a feeding frequency and a reflection coefficient of the antenna 1 shown in FIG.

FIG. 5 is a graph showing the radiation directivity of the antenna 1 shown in FIG.

FIG. 6 is a perspective view showing an example of a conventional microstrip antenna.

FIG. 7 is a graph showing a relationship between a dielectric constant and directivity in the antenna shown in FIG.

8 is a graph showing a relationship between a dielectric constant and a frequency in the antenna shown in FIG.

9 is a graph showing a relationship between a dielectric constant and a gain in the antenna shown in FIG.

FIG. 10 is a graph showing a relationship between a dielectric constant and a bandwidth in the antenna shown in FIG. 6;

11 is a graph showing a relationship between a dielectric constant and a Q factor in the antenna shown in FIG.

[Explanation of symbols]

 1: Microstrip antenna 2: Dielectric (dielectric plate member) 3: Element (radiating conductor plate member) 4a, 4b: Stub (stub)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-174404 (JP, A) JP-A-2-130004 (JP, A) JP-A-2-130003 (JP, A) JP-A-2- 130005 (JP, A) JP-A-1-243702 (JP, A) JP-A-64-82803 (JP, A) Proceedings of the 1984 IEICE National Convention 745 Transactions of the Institute of Electronics, Information and Communication Engineers B- ▲ II ▼, Vol. 72-B- ▲ II ，, No. 4, 1989, pp. 139-143. 179-181 (58) Field surveyed (Int. Cl. ⁷ , DB name) H01Q 13/08

Claims (1)

(57) [Claims] 1. A dielectric plate member which is sufficiently thin with respect to a wavelength to be used; one side attached to one surface of the dielectric plate member and having a side larger than ４ times and smaller than １ ／ times of a used guide wavelength λg. A rectangular radiating conductor plate member; and a rectangular stub extending at a central portion of each of a pair of opposing two sides of the rectangular radiating conductor plate member with a length smaller than １ ／ of the in-use wavelength λg. Linearly polarized microstrip antenna.