JP3188980B2 - Multi-frequency 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 microstrip antenna, and more particularly to a multi-frequency microstrip antenna.

[0002]

2. Description of the Related Art In recent years, various types of mobile communication systems, particularly systems for communicating with vehicles (satellite communication systems or roadside communication systems) have been constructed for practical use. In communication in these systems, it is planned to use a plurality of different frequency bands, and a vehicle requires an antenna for each of these frequency bands. Therefore, as a communication antenna, a multi-frequency antenna is preferable in order to prevent the antenna from being disturbed. What is desired as an in-vehicle antenna is a low-profile antenna that does not impair the beauty of a car. For this reason, a microstrip antenna (hereinafter, referred to as MSA) that shares multiple frequencies is most suitable as an in-vehicle antenna used in a mobile communication system.

Meanwhile, the MSA is an antenna using a radiation loss of an open planar resonance circuit having a structure in which conductor plates are mounted on both sides of a dielectric plate, and has a low profile, a light weight, a compact size, and easy manufacture. Although it has features, it is an antenna that originally has a narrow band characteristic and exhibits a function in a specific frequency band. For this reason, various measures such as providing a plurality of resonance points so that they can be used in a wide band of frequencies are provided.
We are trying to share multiple frequencies. Conventional multi-frequency shared MS
As A, there is, for example, the MSA disclosed in JP-A-1-82803. Focusing on the fact that two independent orthogonal modes can be excited, this MSA is a three-resonance MSA in which the first mode has two frequencies.

[0004]

Problems to be Solved by the Invention
In the case of the MSA disclosed in
The frequency separation width is determined by the ratio between the radiating element and the stub width. In other words, there are separation widths that cannot be realized due to constraints on the separation widths of the frequencies in the two-frequency conversion,
The operating frequency band cannot be set freely.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multi-frequency MSA that does not have any particular restrictions on the frequency separation width in multi-frequency operation.

[0006]

FIG. 5 shows a conventional rectangular MS.
It is a perspective view of A. 11 is an a1 × b1 rectangular radiating element made of copper foil, 12 is a dielectric substrate having a thickness h, and 13 is a ground conductor made of copper foil. Also, the thickness h of the dielectric substrate 12
Is very thin with respect to the used wavelength λo (h≪λo). In this case, the electromagnetic field generated by this antenna is Ez, H
x and Hy components only, and the internal electromagnetic field mode is TMm
n.

FIG. 6 shows the electromagnetic field distribution in the TMmn mode (m = 0, n = 1) and the TMmn mode (m = 1, n = 0), which are the basic modes of the MSA shown in FIG.
Represents Ez, and the solid line 15 represents Hx, Hy, that is, the magnetic current. In FIG. 7A showing the electromagnetic field distribution in the TM01 mode, it can be seen that the electric field is zero when y = b / 2. Similarly, from the same figure (b) showing the electromagnetic field distribution of the TM10 mode, x =
It can be seen that the electric field becomes zero at a / 2. Also, (x = a
/ 2, y = b / 2) is the basic mode of the MSA (TM
This is the point where the electric field in the 10 mode and the TM01 mode) becomes zero. When the electric field is zero, the potential difference becomes zero, and it can be equivalently treated as a short-circuit point. This indicates that loading any load on this point does not affect the electromagnetic field distribution for the fundamental mode of the MSA. Therefore, in the present invention, a feeding point is newly provided at a point where the electric field becomes zero, and excitation is performed at a frequency different from the excitation frequency in the basic mode.

That is, the multistrip microstrip antenna of the present invention has a dielectric plate member (2) sufficiently thin with respect to the wavelength used; a rectangular plate mounted on one surface of the dielectric plate member (2). A radiation conductor plate member (1); a ground conductor (3) mounted on the other surface of the dielectric plate member (2); a predetermined frequency (foc) located on the center line or diagonal line of the radiation conductor plate member (1). ) first feed point of excitation (5); in microstrip antenna comprising, on the radiating conductor plate member (1), the first feed
To position the electric field becomes 0 when the point (5) was excited at a predetermined frequency (foc), characterized by providing a second feed point (4). The symbols in parentheses indicate the corresponding elements in the embodiments described later.

[0009]

According to this , the first conductor on the radiation conductor plate member (1)
Feed point (5) to position the electric field is zero when is excited at a predetermined frequency (foc), since the second feed point (4) is provided, attaching the second feeding point The resulting load does not affect the electromagnetic field distribution with respect to the basic mode (TM10 mode, TM01 mode) of the MSA. By providing the second feeding point (4), in addition to the predetermined frequency (foc) excitation of the MSA having the first feeding point (5) as the feeding point, a new
Excitation at a frequency (fa) different from a predetermined frequency (foc) using the second power supply point (4) as a power supply point becomes possible, so that multiple frequency sharing of the MSA can be achieved. In addition, in the excitation using the second feeding point (4) as the feeding point, the excitation is performed at the frequency (fa) that is freely set. Therefore, the gain of the MSA due to this excitation is equal to the first feeding point (5).
Is naturally lower than the gain of the MSA at an excitation frequency (foc: generally a resonance frequency) at which the power supply point is used, but the gain is sufficient for use in short-distance communication such as roadside communication.
There is no particular restriction on the separation width for multi-frequency A.

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

[0011]

FIG. 1 shows an example of a multi-frequency shared microstrip antenna (MSA) according to the present invention. M shown in FIG.
SA10 is a rectangular (square) MSA shared by circularly polarized multi-frequency
And on one surface of a dielectric substrate 2 having a thickness h and a dielectric constant Er,
It has a square radiating element 1 (dimension a × b) made of copper foil, and has a ground conductor 3 made of copper foil on the other surface of the dielectric substrate 2.
Is provided. The thickness h of the dielectric substrate 2 of the MSA 10 is very thin with respect to the used wavelength λo (h≪λo). Therefore, M
The electromagnetic field generated by the excitation of SA10 is Ez, Hx, H
Only the y component is present, and the internal electromagnetic field mode is TMmn.

The operation of the MSA 10 will be described. First, a feeding point 5 is provided on a diagonal line of the a × b rectangular radiating element 1 and is excited at a predetermined frequency foc. As a result, circular polarization occurs as in the case of the conventional MSA. Where a ≒ b ≒ λg / 2 = c / (2 · foc · √ (Er)) = λo /
(2√ (Er)) λg: guide wavelength c: speed of light At this time, since both the x direction and the y direction mode are the basic modes (TM10 mode and TM01 mode), (x
= A / 2, y = b / 2) The electric field becomes zero. In the MSA 10 of the embodiment, a feeding point 4 and a matching circuit 6 are newly provided at this (x = a / 2, y = b / 2) point, and the frequency foc
Is excited at a different frequency fa. By providing the feed point 4 at the point where the electric field becomes zero, the load generated by mounting the feed point 4 has no effect on the electromagnetic field distribution of the MSA 10 in the TM10 mode and the TM01 mode. Accordingly, while the excitation is performed at the frequency foc with the feeding point 5 as the feeding point, the excitation with the frequency fa different from the frequency foc with the feeding point 4 as the feeding point is also possible.

When the frequency fa is set freely,
Even if the matching circuit 6 is set to an optimum state, the gain of the MSA by excitation at the frequency fa is lower than the gain by excitation (resonance) at the frequency foc, but is sufficient for short-range communication (roadside communication). Gain. For this reason, there is no particular restriction on the separation width for multi-frequency operation.

Hereinafter, measured data when the multi-frequency shared MSA of this embodiment is excited is shown. In this embodiment, the frequency foc that becomes a circularly polarized wave and the frequency fa different from the frequency foc are designed to have a relationship of fa = 1.84 foc.

FIG. 2 shows the axial ratio at foc. FIG.
The vertical axis indicates the axial ratio (AR). Thereby, (x = a /
It can be seen that excitation was performed at the frequency foc with the feeding point 5 as the feeding point without being affected by the provision of the feeding point 4 at the (2, y = b / 2) point, and sufficient circular polarization was generated.

FIG. 3 shows the voltage standing wave ratio at fa = 1.84foc. The vertical axis in FIG. 3 is the voltage standing wave ratio (VSW).
R). As a result, it can be seen that even when the power supply point 4 is used as the power supply point and excited at the frequency fa, it has sufficient performance to perform short-range (about 10 m) communication such as roadside communication.

In this embodiment, the circularly polarized MSA using the fundamental mode (TM10 mode or TM01 mode) is shown. However, the TM10 mode or TM01 mode is used independently, and is also used as the linearly polarized MSA. it can. In this case, an example of the multi-frequency shared MSA (MSA1)
0a) is shown in FIG. The configuration is the same as that of the rectangular (square) MSA 10 shown in FIG. 1 except for the position of the feeding point 5 at a predetermined frequency (frequency fx that becomes a linearly polarized wave). (The feed point 5 shown in FIG.
(Corresponding to the feeding point 5a shown in FIG. 4). Further, in this example, the feed point 4 is located at the center of the a × b square radiating element 1, but the position where the electric field becomes 0 in each mode (y in the TM01 mode).
= B / 2, or on the center line of the square radiating element 1 where x = a / 2 in the TM10 mode.

By providing the second power supply point at a position where the electric field generated by the predetermined frequency excitation with the first power supply point as the power supply point becomes zero, the present invention can be applied to use in a higher mode.

[0019]

As described above, according to the present invention , the first feeding point (5) on the radiation conductor plate member (1) is excited at a predetermined frequency (foc) .
To position the electric field is zero when allowed to, the second feeding point
Since (4) is provided, the load generated by attaching the second power supply point is the basic mode (TM10
Mode, TM01 mode). By providing the second feeding point (4), in addition to the predetermined frequency (foc) excitation of the MSA using the first feeding point (5) as the feeding point, a second feeding point (4) is newly added. Excitation at a frequency (fa) different from the predetermined frequency (foc) as the feeding point becomes possible, and the multi-frequency use of the MSA can be achieved. In addition, in the excitation using the second feeding point (4) as the feeding point, the excitation is performed at the frequency (fa) that is freely set. Therefore, the gain of the MSA due to this excitation is determined by setting the first feeding point (5) to the feeding point. The gain is naturally lower than the gain of the MSA at the excitation frequency (foc: generally the resonance frequency), but is sufficient for use in short-distance communication such as roadside communication, and is substantially equivalent to the multifrequency of the MSA. There is no particular restriction on the separation width.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of an example of a multi-frequency microstrip antenna (MSA) of the present invention.

FIG. 2 is a graph showing actually measured axial ratio data when the MSA 10 shown in FIG. 1 is excited at a frequency foc.

FIG. 3 shows that the MSA 10 shown in FIG. 1 has a frequency fa = 1.8.
Voltage standing wave ratio (VSW ) when excited at 4 foc
It is a graph which shows the measured data of R).

FIG. 4 is a schematic perspective view showing another example of the MSA shown in FIG. 1;

FIG. 5 is a perspective view schematically showing a conventional general MSA.

6 is TMm, which is a basic mode of the MSA shown in FIG.
n mode (m = 0, n = 1) and TMmn mode (m =
FIG. 3 is a top view showing an electromagnetic field distribution at (1, n = 0).

[Explanation of symbols]

 1: square radiating element (radiating conductor plate member) 2: dielectric substrate (dielectric plate member) 3: ground conductor (ground conductor) 4: feeding point (second feeding point) 5, 5a: feeding point (first) 6: Matching circuit 10: Rectangular MSA for circularly polarized multi-frequency sharing 11: Square radiating element 12: Dielectric substrate 13: Ground conductor 10a: Rectangular MSA for linear polarization multi-frequency sharing

Claims (1)

(57) [Claims] 1. A dielectric plate member that is sufficiently thin for a wavelength to be used; a rectangular radiation conductor plate member mounted on one surface of the dielectric plate member; and a rectangular radiation conductor plate member mounted on the other surface of the dielectric plate member located in the center line or diagonal of the radiating conductor plate member, a first feeding point of the predetermined frequency excitation; ground conductor in the microstrip antenna comprising, on radiating conductor plate member, a first feed point at a predetermined frequency Excitation
The second feeding point is located at a position where the electric field becomes 0
Characterized by providing a multi-frequency sharing microstrip antenna.