JPH09153723A - Microstrip antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microstrip antenna with a small-sized simple configuration and ease of design and manufacture by devising the antenna to revise a characteristic impedance and a resonance frequency specific to the antenna and also its directivity. SOLUTION: An antenna element 2, a feeder 3, and a matching line are formed by coating a metallic film as a looped circuit to a surface of a dielectric board whose thickness is thinner than a radiation wavelength. Small sized metallic rectangular film sets 41 -44 are sticked to part on the looped circuit to change its old characteristics or the like of the looped circuit. The degree of this change depends on the size and sticked position of the metallic film pieces to be sticked and the resonance wavelength, the impedance characteristic and the directivity are changed. Thus, various characteristics of an electromagnetic wave emitted from the antenna element are changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna for a wireless communication system, and more particularly to an antenna suitable for use as a wireless base station antenna for a mobile communication system.

[0002]

2. Description of the Related Art Various antennas are used as radio base station antennas in mobile communication systems. For example, a collinear antenna is used for a PHS system, which is a typical mobile radio system in Japan. Other,
Brown antennas, sleeve antennas, etc. are also used. These antennas are called linear antennas, and most of them are currently in a form in which electromagnetic waves are transmitted from linearly formed antenna elements. With the advent of high-quality and inexpensive dielectric plates in recent years, the above antenna is a linear antenna of the type in which a metal film is deposited on the surface of the dielectric plate-this is usually called a microstrip antenna-
Is used. On the other hand, there is an antenna type called "folded dipole antenna" in which the tips of the dipole antennas are connected to each other and one of these dipoles is fed in the center. Generally, an antenna that forms an electric circuit in which the entire antenna is closed when viewed from the power feeding section is called a loop antenna, but a "folded dipole antenna" also falls within this category. The "folded dipole antenna" is also widely used in amateur radio and special communications.
However, it does not seem to be used as a radio base station antenna for mobile communication systems.

[0003]

The "folded dipole antenna" (hereinafter abbreviated as loop antenna) is not used as a radio base station antenna of a mobile communication system for the following reason. It is difficult to obtain an antenna having a high gain. When the frequency used is given, the total length of the antenna that resonates with it is determined, and the antenna length cannot be changed to an arbitrary value. Given the shape of the antenna, its characteristic impedance is fixed and cannot be changed. Therefore, the cable feeding the antenna must be chosen so that the characteristic impedance of the cable matches that of the antenna. The shape of the antenna usually has to be included in a two-dimensional plane, and the directional characteristics of the electromagnetic wave transmitted from the antenna are determined according to the shape, so in order to obtain arbitrary directivity, Other circuits / means must be used. The weather resistance of the antenna is inferior to that of the linear antenna. In a nutshell, the above items are difficult to use, and some improvements have been desired.

[0004]

In order to improve the electrical characteristics of the solid loop antenna (folded dipole antenna) described above, the present invention uses a recent good-quality and inexpensive dielectric plate, and has a metal film on the surface thereof. A microstrip antenna was formed by forming and depositing a circular shape, a rectangular shape, a loop-shaped circuit shape, or the like to form an antenna element. Further, by depositing a small metal film such as a rectangular shape on a part of the loop circuit, the characteristics which the loop circuit has in the past are changed, and accordingly, the electromagnetic wave emitted from the antenna element is changed. The various characteristics of can be changed. In addition, the drawback of the weather resistance is inferior to the conventional linear antenna is that the operating frequency is higher than 1 GHz (hence the wavelength is 30 cm or less), and the entire antenna can be downsized. It was possible to solve this by covering it with a resin material from the outside.

[0005]

In the antenna of the present invention, a loop-shaped circuit formed on the surface of the dielectric plate is partially covered with a small metal film such as a rectangular metal film so that the loop-shaped antenna circuit has a conventional structure. The characteristic impedance characteristic was changed. The degree of this change has various aspects depending on the size of the metal film piece to be attached, the relative position of the metal film piece to be attached to the loop antenna circuit, and the like. That is, various effects such as a place that greatly affects the resonance wavelength (resonance frequency) of the antenna, a place that affects the characteristic impedance, a place that changes the directional characteristics, a place that affects both of the above two, etc. Will be done.

[0006]

1 (a) to 1 (e) are plan views showing an embodiment of the present invention, that is, a view of an antenna of the present invention seen from vertically above. First, FIG. 1A shows a basic circuit of a loop antenna circuit. In FIG. 1A, 1 is a dielectric plate that is thinner than the wavelength of the radiated electromagnetic wave, 2 is an antenna element using a loop circuit, 3 is a feeder line, and a matching line (not shown) is provided at this tip. It is provided. 1 (b) to (e)
Is another rectangular small metal film 4 on the dielectric plate 1 including the metal film forming the loop antenna circuit of FIG.
Shows a plan view of which has deposited a _{1-4 4.} FIG. 1 (a)
When the dielectric plate 1 shown in (e) to (e) is formed by using, for example, a glass cloth base material fluororesin copper clad laminate, the dielectric plate 1 is formed by removing an unnecessary metal film by a method similar to the printing method. The antenna element 2 and the feed line 3 are adhered and formed on the surface of the. When a simple dielectric plate is used as the dielectric plate 1, the antenna element 2 and the feed line 3 are formed by depositing a film of copper or the like on the surface by means such as vapor deposition. These fabrication methods are applicable to all the antennas of the present invention. Naturally, the metal of the loop-shaped circuit and the metal film deposited on it are in close contact with each other to the extent that they are electrically considered to be the same metal, and the current is created so that it flows as if it were the same metal. ing.

FIG. 1 (b) shows an example in which a rectangular small metal film, which is orthogonal to the circuit, is deposited on the metal film forming the loop circuit at the position shown in the figure. When the small metal film is deposited on such a place, the resonance wavelength (resonance frequency) of the original loop circuit moves to a low frequency. It is judged that this is physically due to the increase in the total length of the loop circuit. 1 (c) is shown in FIG.
An example in which the small metal film shown in (b) is deposited in the loop circuit is shown. When a small metal film is deposited on such a place, the resonance wavelength (resonance frequency) of the original loop circuit moves to a low frequency as in the case of FIG. 1 (b), but the degree is the former. Get bigger.

FIG. 1 (d) shows an example in which a rectangular small metal film is deposited near the feeding point of the loop circuit as shown in the figure. By depositing a small metal film on such a place, the characteristic impedance of the original loop circuit can be changed. This is theoretically difficult to elucidate, and is the result obtained experimentally as described below. FIG.
(E) is the position where the small metal coating is installed as shown in Fig. 1 (b).
However, the installation state is different from that of FIG. 1B, but an example in which the metal film forming the loop circuit is applied in parallel is shown. In this case, it can be used to change the main direction of the radio wave emitted from the antenna element.

The results of measuring the characteristics of the prototype antenna of the present invention will be described below. The actual dimensions of the antenna element using the loop circuit shown in FIG. 1 (a) are 5.1 cm in width (longitudinal direction of the dielectric plate), 2.9 cm in height (both are external peripheral length), and 0.2 cm in width. Yes, the standard thickness of the metal coating is 0.03 cm. In theoretical calculation, the characteristic impedance of the loop antenna is about 50 ohms,
The resonance wavelength (resonance frequency) is about 15.5 cm, (about 1.9
4 GHz). FIG. 2A shows the standing wave ratio of the antenna originally possessed by the loop antenna element. That is, there is a loop-shaped microstrip antenna formed on the surface of a dielectric plate, and the original standing wave ratio (SWR) characteristic is shown when there is no other metal film piece on the metal film. The standing wave ratio mentioned here indicates the ratio of the input wave and the reflected wave at the antenna feeding terminal point. The characteristic impedance of the power supply line to this antenna is 50 ohms. In FIG. 2A, the markers 1 to 3 have frequencies of 1.9 GHz, 2.1 GHz and 1.9 G, respectively.
The standing wave ratio measurement result at the time of Hz is shown, and the value is 1.289 for each as shown in the upper right of the figure.
4, 2.8494 and 4.0884. The marker 4 indicates the resonance frequency of the loop-shaped microstrip antenna, the frequency is 1.94 GHz and the standing wave ratio is 1.10. The characteristic impedance of the antenna at this frequency is 50.30 + j4.30 ohms.

FIG. 2 (b) shows the standing wave ratio characteristic of the microstrip antenna when a small metal film is deposited on the loop-shaped antenna element at the position shown in FIG. 1 (b). The size of the small metal film is 1.3 cm in length and 0.5 c in width.
The standard value of m and thickness was 0.07 cm. Note that FIG.
The experimental results shown in (c) to FIG. 2 (e) also used the small metal film of this size. In this case, it can be seen that the resonance frequency of the antenna has moved to a low frequency of 1.86 GHz as shown by the marker 4 in FIG. The standing wave ratio at this time is 1.1.
5, the characteristic impedance was 49.73-j2.6. FIG. 2 (c) shows the loop antenna element shown in FIG.
The standing wave ratio characteristic of the microstrip antenna when a small metal film is deposited on the position shown in (c) is shown.
In this case, the resonance frequency of the antenna is the marker 4 of FIG.
As shown in, it can be seen that the frequency has moved to a frequency as large as 1.799 GHz. At this time, the standing wave ratio was 1.087 and the characteristic impedance was 54.37-j0.17 ohm.

FIG. 2 (d) shows the standing wave ratio characteristic of the microstrip antenna when a small metal film is deposited on the loop-shaped antenna element at the position shown in FIG. 1 (d). In this case, the resonant frequency of the antenna is not obtained, indicating that the characteristic impedance has changed from 50 ohms to a significantly different value. The measured value of the characteristic impedance is 6 for marker 1 (frequency 1.90 GHz).
8.3-j4.23 ohms, marker 4 (frequency 1.94
GHz) was 48.85-j11.37 ohms. FIG. 2 (e) shows the loop antenna element shown in FIG.
The standing wave ratio characteristic of the microstrip antenna when a small metal film is deposited at the position shown in (e) is shown.
In this case, it was experimentally confirmed that the directivity of the antenna (the main direction of the radio wave emitted from the antenna element) was changed downward. If it is desired to direct the main directional characteristics upward, a metal film piece may be attached to the lower part of the loop antenna element.

[0012]

Since the antenna of the present invention can change the characteristic impedance, the resonance frequency and the directivity peculiar to the antenna, the shape of the antenna is different from the conventional one, including the ease of matching between the antenna and the feed line. The antenna can be shaped, and the antenna design can be facilitated and the antenna can be easily downsized. Further, since the antenna can be downsized, a large number of antennas can be coupled in multiple stages, and it is possible to increase the gain of the loop antenna, which has been difficult in the past. Therefore, the effect of the present invention is great.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing various characteristics of the antenna of the present invention.

[Explanation of symbols]

1 Dielectric Plate 2 Antenna Element 3 Feed Line 4 ₁ to 4 ₄ Metal Film Piece

Claims (4)

[Claims] 1. An antenna element having a structure in which a metal film is attached to and formed on a loop-shaped circuit on the surface of a dielectric plate that is thinner than the radiation wavelength so that the loop-shaped circuit changes the characteristics that it has conventionally. In addition, a small metal film having a rectangular shape or the like is attached to a part of the loop circuit to change the electromagnetic wave emitted from the antenna element, thereby making it possible to change the antenna characteristics. . 2. In an antenna element having a structure in which a metal film is deposited and formed on a loop-shaped circuit on the surface of a dielectric plate that is thinner than the radiation wavelength, the loop-shaped circuit changes the characteristics that it has conventionally. A microstrip antenna in which the resonance frequency that the loop circuit has conventionally can be changed by depositing a small metal film such as a rectangle on a part of the loop circuit. 3. An antenna element having a structure in which a metal film is attached to and formed on a loop-shaped circuit on the surface of a dielectric plate that is thinner than the radiation wavelength, so that the loop-shaped circuit changes the characteristics that the conventional circuit has. A microstrip antenna in which the characteristic impedance of the loop circuit can be changed by depositing a small metal film such as a rectangle on a part of the loop circuit. 4. An antenna element having a structure in which a metal film is applied to and formed on a loop-shaped circuit on the surface of a dielectric plate that is thinner than the radiation wavelength, so that the characteristics that the loop-shaped circuit has conventionally are changed. A microstrip antenna in which the directivity characteristic of the loop circuit can be changed by applying a small metal film such as a rectangle on a part of the loop circuit.