JPH0682973B2 - Microstrip antenna - Google Patents

Description

Description: TECHNICAL FIELD The present invention uses a slot feed system having a triplate feed line to provide a slot having a diameter approximately equal to the diameter of a circular microstrip antenna to reduce the resonance frequency. The present invention relates to a microstrip antenna that has been reduced in size and has been made smaller and thinner.

2. Description of the Related Art In recent years, portable mobile station antennas used in mobile communication systems are required to be small and lightweight, have a wide bandwidth, and be efficient. Since the electric field on the y-axis 22 of the microstrip antenna 21 shown in FIG. 8 is zero, the electromagnetic field distribution does not change even if the y-axis of the microstrip antenna 21 is short-circuited. F is the feeding point. Therefore, as the mobile station antenna, the λ / 4 type microstrip antenna 23 formed on the dielectric substrate 20 shown in FIG. 9 is used. This antenna is the width of the antenna x
The axial length is related to the frequency band, and the shorter the width, the narrower the band width.

Further, it is well known that, when the antenna is downsized, the characteristics of the antenna efficiency η and the bandwidth BW generally deteriorate. In the antenna short-circuited in the y-axis direction, V when the relative permittivity εr of the dielectric substrate is 2.55 and the substrate thickness h / λ is 0.005
The result of calculating the bandwidth below SWR2 with b / a as a parameter is document 1 (Journal of the Institute of Electronics, Information and Communication Engineers '88 / 11 Vol.J.
71-B No. 11). The results are shown in FIG. For example, a normal antenna with b / a of 1 (Fig. 10 (a)) has a bandwidth of 0.76% and b / a of 0.5 (Fig. 10 (b)).
The antenna bandwidth with λ / 4 in both x and y axis directions is 0.4
%.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above, when the area of the antenna becomes 1/4 of the normal state, the bandwidth becomes narrow. Further, since the antenna is short-circuited, it becomes necessary to connect the antenna element and the ground conductor plate. Therefore, a through hole must be provided between the antenna conductor and the ground conductor plate. Alternatively, the antenna conductor must be bent on the x-axis and soldered to the ground conductor plate.
As described above, the miniaturization of the antenna element narrows the bandwidth and complicates the manufacturing process, which causes a problem that the manufacturing cost is increased when the array is formed.

It is an object of the present invention to provide a microstrip antenna that can perform impedance matching between an antenna and a feed line without inserting a matching circuit, and that can be manufactured in a small size and easily manufactured.

Means for Solving the Problems A microstrip antenna according to the present invention includes a dielectric between a circular microstrip antenna formed of a conductor plate and a power supply line provided at a position facing the circular microstrip antenna. A ground conductor plate is sandwiched between the ground conductor plate and the ground conductor plate. The ground conductor plate has a length substantially equal to the diameter of the circular microstrip antenna and a width equal to or smaller than the radius of the antenna. A slot for exciting an electromagnetic wave with respect to the circular microstrip antenna has a center of the slot substantially coincident with a center of the circular microstrip antenna and intersects with the feed line immediately below the circular microstrip antenna. It is characterized by being provided as follows.

Operation FIG. 8 shows a conventional general rectangular patch antenna. twenty one
Is a rectangular patch conductor. F is the feeding point, the resonance frequency of the antenna is determined by the length in the x-axis direction, and the input impedance depends on the length in the y-axis direction. When the rectangular patch antenna is fed at the feeding point F, the electric field between the antenna and the ground conductor becomes maximum at the edge of the rectangular patch antenna and becomes zero at the center of the rectangular patch antenna. Therefore, even if this point is short-circuited, it operates as an antenna. Further, the input impedance decreases as the length in the y-axis direction becomes narrower. Thereby, the antenna can be downsized. However, as shown in FIG. 10, the matching frequency range is narrowed and the bandwidth is reduced. For example, as will be described later in detail, as is clear from FIG. 10 (a),
The bandwidth of an antenna with a size of λ / 4 in both the x and y axis directions is 0.4%
Is.

On the other hand, the microstrip antenna of the present invention can be downsized by increasing the slot to the diameter of the antenna element to lower the resonance frequency, but the VSWR frequency bandwidth can be 0.76%. That is, by using the microstrip antenna of the present invention, it is possible to solve the decrease in the frequency bandwidth of VSWR caused by the miniaturization of the antenna.

Further, as is clear from FIG. 6, even if the slot width is expanded to the radius of the antenna, the resonance frequency and the input resistance hardly change. Therefore, the slot of the circular microstrip antenna of the present invention is characterized by having a length substantially equal to the diameter of the antenna and a width equal to or smaller than the radius of the antenna.

Embodiment FIG. 1 is a diagram for explaining an embodiment of the present invention.
Is a circular microstrip antenna made of a circular conductor having a radius r, 2 is a thickness h ₁ , a dielectric substrate having a permittivity εγ ₁ is 3, a ground conductor plate, 4 is a slot, 5 and 7 are thickness h ₂ , a dielectric Body εγ ₂
Of the dielectric substrate, 6 is a triplate feed line.

As shown in FIG. 1, the microstrip antenna 1 is provided on the surface of the dielectric substrate 2. A grounding conductor plate 3 is provided between the dielectric substrates 2 and 5, and a rectangular slot 4 is formed in the grounding conductor plate 3, and the center of the slot 4 substantially coincides with the center of the microstrip antenna 1. Further, it is provided immediately below the microstrip antenna 1 so as to face the center thereof. Further, the dielectric substrate 5 is provided on the dielectric substrate 7, and the feed line 6 extends between the both 5 and 7 so as to be orthogonal to the longitudinal direction of the slot 4 and beyond the slot 4 by a predetermined length. Is provided as follows.

A ground conductor plate 8 is provided on the lower surface of the dielectric substrate 7.

In the antenna configured as described above, when a microwave current is fed from the feeding line 6, the electromagnetic wave of the microwave reaches the microstrip antenna 1 through the slot 4 and excites the microstrip antenna, Electromagnetic waves of microwaves are radiated from the microstrip antenna 1.

Now, as an antenna element, a circular microstrip antenna 1 having a radius r on one surface of a dielectric substrate 2 having a thickness h ₁ and a dielectric constant εγ ₁ shown in FIG.
2, a slot 4 having a width Ws and a length Ls is provided so as to face the center of the circular microstrip antenna 1, and a dielectric substrate 2 having a thickness h ₂ and a dielectric constant εγ ₂ is provided.
Consider a circular microstrip antenna composed of a triplate feed line 6 for feeding the slot 4 having a narrowed space.

Fig. 3 shows that the characteristic impedance of the feed line 6 is 50Ω, power is fed at the center of the slot, and the dielectric constant εγ of each dielectric substrate 2, 7 is 2.5.
5, thickness d ₁ is 0.8 mm, h ₂ , h ₃ , is 1.6 mm, and the radius r of the circular microstrip antenna 1 is 33.81 mm, the relationship between the length Ls of the slot 4 and the resonance frequency / input resistance The measured value of is shown. At this time, the reactance of the circular microstrip antenna is matched by adjusting the length S1 of the stub.

Next, the microstrip antenna 1 is shown in FIGS.
Shows a frequency characteristic of reflection loss when the radius r is 33.81 mm, the slot width Ws is 1.5 mm, and the slot length L is 65.0 m and 26.0 mm.

The radius r of the circular microstrip antenna 1 is shown in FIG.
= 33.81 mm, slot length Ls = 65.0 mm, slot width Ws
The measured value of the relationship between the resonance frequency and the input resistance when is expanded is shown. FIG. 7 shows the reflection directivity of the circular microstrip antenna when the radius r = 33.81 mm, the slot length Ls = 65.0 mm, and Ws = 1.5 mm.

From Fig. 4 and Fig. 5, the resonance frequency is the dimension of the slot 4.
Although it decreases monotonically as Ls becomes longer, the input resistance has a maximum value at Ls of 50 mm. When the slot length Ls is 65mm, which corresponds to the antenna diameter, the input resistance becomes 50Ω, and the resonance frequency drops to 867.5MHz. From this, it can be seen that the resonance frequency is halved by expanding the slot to about the antenna diameter, as compared to the case of the normal probe feeding system without a slot (resonance frequency 1.6 GHz). That is, in order to obtain the same resonance frequency, by using this slot coupling method, the radius of the antenna is about half and the area is 1/4 as compared with the normal probe feeding method.

Further, it can be seen from FIG. 6 that the resonance frequency and the input resistance do not change much even if the slot width Ws is expanded to about the antenna radius.

Furthermore, from the experimental results of the reflection loss in FIGS. 4 and 5, the bandwidth at which the reflection loss is -10 dB or less is 0.6 when Ls = 26 mm.
%, 0.75% at 65 mm. The bandwidth of the λ / 4 short-circuit type microstrip antenna is, as shown in Reference 1, for example, the bandwidth of a normal antenna with b / a of 1 (Fig. 10 (a)) is 0.76%, and b / a is 0.5 (Fig. 10 (a)),
The bandwidth of the λ / 4 antenna in both the x and y directions is 0.4%.
As described above, generally, the bandwidth becomes narrower as the size of the antenna is made smaller, but if this slot coupling system is used, the bandwidth is hardly changed even if the size of the antenna is made smaller.

From Fig. 7, it can be seen that by using this triplate type power feeding system, the unwanted radiation level to the power feeding line side can be suppressed to about -20 dB or less, and a gain of 4.1 dB can be obtained at 867.5 MHz. . In FIG. 7, the solid line shows the measurement results on the E plane and the dot-dash line shows the measurement results on the H plane. Also, r = 33.81 mm, h
_{1 = 0.8mm, h 2 = 1.6mm} , L = 65mm, Ws = 1.5mm, ground plate 45
It was set to 0 × 450 mm.

By using the configuration of FIG. 1 and extending the length of the slot 4 to a diameter of about 2r of the microstrip antenna 1, the input resistance can be the impedance of a general microwave line without sacrificing bandwidth and gain. An antenna that can match impedance to a certain 50Ω and that has a resonance frequency that is less than half that of a normal probe feeding method or a λ / 4 short-circuit type microstrip antenna can be obtained. From this, the radius of the antenna that obtains the same resonance frequency by using this slot feeding method may be about half that of the normal probe feeding method. That is, by using the present invention, a miniaturized and thin antenna can be realized.

That is, in the conventional example shown in FIGS. 8 to 10, the size is reduced by short-circuiting as described above, but there is a drawback that the antenna gain is lowered and the directivity is widened (becomes broad). Accompany. However, in the microstrip antenna of the embodiment according to the present invention, by increasing the slot length to about the diameter of the circular microstrip antenna, the input resistance can be reduced to around 50Ω, so that the input impedance should be matched. In addition, since the antenna diameter of the conventional probe feeding system can be reduced to about half, the size can be greatly reduced.

Further, by performing the triplate type power supply, it is possible to suppress the unnecessary radiation level to the power supply line side.

Although the present invention has been described with respect to the circular microstrip patch antenna, the same effect can be obtained even with a rectangular or square shape.

Although the effect of the present invention has been described by using the experimental result of the triplate feed line, the same effect can be obtained by using the microstrip line as the feed line.

This antenna element can be used not only for a mobile radio for mobile use but also as an element antenna forming an array antenna.

As described above, according to the present invention, by expanding the slot length to about the diameter of the microstrip antenna, the input resistance is reduced without sacrificing the bandwidth and the gain, and a general feed line is provided. The impedance can be matched to 50Ω, which is the same as the normal probe feeding method or λ.
Compared with the / 4 short-circuit type microstrip antenna, an antenna with a resonance frequency less than half can be obtained. Therefore, by using this slot feeding method, the radius of the antenna that obtains the same resonance frequency is about half that of the normal probe feeding method that does not short circuit. By using the present invention, an antenna which is downsized and thinned can be obtained.

As described above, by extending the length of the slot to about the diameter of the antenna, the input resistance is lowered as shown in FIG. 3, and it is generally used in microwave circuits.
Since it can be matched with the Ω feed line, there is no need to insert a matching circuit as in the conventional example, and the circuit provided in the antenna is simplified.

[Brief description of drawings]

FIG. 1 is a perspective view showing one embodiment of the microstrip antenna of the present invention, FIG. 2 is a plan view showing slots in the embodiment of FIG. 1, and FIG. 3 is a resonance frequency and an input resistance depending on the slot length. 4 and 5 are graphs showing the experimental results of the relationship, FIG. 4 and FIG. 5 are graphs showing the frequency characteristics of reflection loss, and FIG.
FIG. 7 is a graph showing the experimental results of the relationship between the resonance frequency and the input resistance when the slot width is widened, FIG. 7 is a graph showing the radiation directivity of the microstrip antenna shown in FIG. 1, and FIGS. FIG. 10 is a perspective view showing a conventional λ / 4 short-circuited microstrip antenna, and FIG. 10 is a graph showing calculation results of bandwidth and efficiency of the λ / 4 short-circuited microstrip antenna. 1 ... Circular microstrip antenna, 2 ... Dielectric substrate, 3 ... Ground conductor plate, 4 ... Slot, 5,7 ... Dielectric substrate, 6 ... Tri-plate feed line.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Koji Yasukawa, Shiraka-cho, Kyoto Prefecture, Osamu Osamu, Osamu Osamu, Hiratani, Kyoto, Japan. Report AP87-130 P. 7-P. 12 IEEE TRANSACTIONS ON ANTENNAS AND PRO PAGE VOL. AP-34, No. 12, Dec 1986, P.M. 1439-P. 1446 IEEE TRANSACTIONS ON ANTENNAS AND PRO PAGE VOL. AP-34, No. 8, Aug 1986, P.M. 977-P. 984

Claims (1)

[Claims] 1. A ground conductor plate is interposed between a circular microstrip antenna made of a conductor plate and a power supply line provided at a position facing the circular microstrip antenna, with a dielectric material interposed therebetween. The ground conductor plate has a length substantially equal to the diameter of the circular microstrip antenna and a width equal to or less than the radius of the antenna. The microstrip is provided so that the center of the slot substantially coincides with the center of the circular microstrip antenna and is directly below the circular microstrip antenna and intersects the feed line. antenna.