JP3619971B2 - Indoor antenna - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an antenna installed indoors, and is particularly applicable to a radio base station antenna of a mobile phone in an underground shopping center, a tunnel, or the like.
[0002]
[Prior art]
In order to use mobile phones in underground malls, tunnels, etc., wireless base stations are installed at these locations. A monopole antenna or a loop antenna can be used as an antenna of such a radio base station, and these antennas are installed on a wall or ceiling as shown in FIGS. 3A and 3B. The directivity characteristic in the vertical plane of such an antenna is as shown in FIG. 3C and can receive a wide range of radio signals.
[0003]
[Problems to be solved by the invention]
The mobile phone receives uplink radio signals and transmits downlink radio signals using the radio base station antenna described in the previous section. Compared to general land radio base stations, mobile phones are more likely to approach such base station antennas in underground malls and tunnels. When the portable device approaches the base station antenna, the received power of the base station antenna becomes extremely high. For this reason, the low noise amplifier connected to the rear stage of the antenna is saturated. When such saturation occurs, the gain of the low noise amplifier decreases and intermodulation distortion occurs, making it difficult to receive the uplink radio signal of the mobile phone far from the base station antenna. An object of the present invention is to prevent saturation of a low noise amplifier that occurs when a mobile phone approaches a base station antenna.
[0004]
[Means for Solving the Problems]
In order to reduce the received power of the antenna when the mobile phone approaches the antenna attached to the ceiling or wall, a reflector is installed below the monopole antenna or the loop antenna. Further, in order to reduce the shape of the reflector, the reflector and these antennas are wrapped with a dielectric having a high dielectric constant.
[0005]
Since the uplink radio signal from the mobile phone in the vicinity of the antenna is reflected by this reflector, the received power at the antenna can be reduced in such a case.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
(1) Embodiment of Claim 1 As shown in FIG. 1A, the invention of claim 1 comprises a ground plate 1, a monopole antenna 2, a reflector plate 5, and a support bar 6. The difference from the conventional antenna is that the reflector 5 and the support bar 6 are provided.
[0007]
In the present invention, the reflecting plate 5 is placed in parallel with the ground plate 1. Thereby, the lower gain of the monopole antenna can be reduced as shown in FIG. 1C. The support bar 6 is provided to fix the reflecting plate 5 on the ground plate 1, and its relative dielectric constant is set to 1 to suppress the influence of the support bar on the directivity characteristics of the antenna.
By providing such a reflector 5, the antenna received power can be reduced when the mobile phone approaches the lower side of the antenna. As a result, gain reduction and cross modulation due to saturation of the low-noise amplifier connected to the subsequent stage of the antenna can be suppressed. Therefore, it is possible to suppress the distortion of the uplink radio signal transmitted from the mobile phone below the antenna and to maintain good communication quality. In addition, since a decrease in gain can be suppressed, a signal from a distant mobile phone can be received well.
[0008]
(2) Embodiment of Claim 2 The invention of claim 2 comprises a ground plate 1, a loop antenna 4, a reflector 5, and a support bar 6, as shown in FIG. 1B. The present invention has a configuration in which the monopole antenna 2 of the invention of claim 1 is replaced with a loop antenna 4. In the case of the loop antenna 4 as well, the same effect as in the first aspect can be obtained by placing the reflector 5.
[0009]
(3) Embodiment of Claim 3 The invention of claim 3 comprises a ground plate 1, a monopole antenna 2, a reflector 5, a first dielectric 7, and a second dielectric 8, as shown in FIG. 2A. The difference from claim 1 is that the monopole antenna 2 and the reflector 5 are wrapped with a dielectric having a large relative dielectric constant.
Antennas installed indoors must be small. Therefore, the indoor antenna of the present invention is miniaturized by wrapping the monopole antenna 2 and the reflector 5 with the first dielectric 7. When the relative dielectric constant of the first dielectric 7 is ε _r1 , the wavelength λ ₁ inside the first dielectric is λ ₁ = λ ₀ / √ε _r1
Shortened to However, λ ₀ represents the wavelength in free space. Since the wavelength can be shortened in this way, electromagnetic waves incident from the lower side of the monopole antenna can be sufficiently reflected even if a small reflector is used.
[0010]
On the other hand, the second dielectric is provided to buffer the mismatch of the propagation impedance between the free space and the first dielectric 7. Accordingly, the electromagnetic wave propagating in the free space can be received by the monopole antenna 2 without being reflected by the first dielectric 7. Also, the electromagnetic wave radiated from the monopole antenna 2 is radiated to free space without being reflected by the first dielectric surface. Here, the dielectric constant epsilon _r2 of the second dielectric, when the free space permittivity and _{ε r0 ε r2 = (ε r0} ε r1) 1/2
Choose as follows. Further, the thickness t is equal to the wavelength λ ₂ in the second dielectric,
t ≒ λ _2/4
Set to. Substituting λ ₂ = λ ₀ / √ε _r2 into the above equation,
t≈λ ₀ / 4√ε _r2
It becomes.
[0011]
By wrapping the monopole antenna 2 with the dielectrics 7 and 8 as described above, a small indoor antenna having a large gain attenuation on the lower side of the antenna can be realized. For example, ceramic can be used as the first and second dielectrics 7 and 8.
(4) Embodiment of Claim 4 The invention of claim 4 has a configuration in which the monopole antenna 2 of the invention of claim 3 is replaced with a loop antenna 4 as shown in FIG. 2B, and the same effect as in claim 3 is obtained. It is done.
[0012]
【The invention's effect】
In the indoor antenna of the present invention, the reception power can be kept small by the reflector 5 when approaching the lower side of the antenna of the mobile phone. Further, by using the dielectrics 7 and 8 having a high dielectric constant, such received power can be reduced even with a small reflector. Also, the entire antenna can be miniaturized.
[0013]
With the antenna of the present invention, gain reduction and cross modulation caused by saturation of a low-noise amplifier at the rear stage of the antenna can be suppressed, the communication quality can be kept good, and a transmission signal of a mobile phone far from the antenna can be received well.
[Brief description of the drawings]
FIGS. 1A and 1B are front views of the principle of the first and second embodiments, respectively, and FIG.
FIGS. 2A and 2B are cross-sectional views illustrating the principle of claims 3 and 4 respectively.
FIGS. 3A and 3B are front views showing the principle of a conventional indoor antenna, and FIG. 3C is a diagram showing directional characteristics in a vertical plane of A or B;

Claims (4)

A monopole antenna protruding from the bottom surface of the ground plate installed on the indoor ceiling ,
Away from the tip of the monopole antenna, a metallic reflecting plate disposed in facing and the ground plate,
A support member for supporting opposed to the lower surface of the ground plate The reflective plate,
An indoor antenna comprising: A loop antenna protruding from the bottom surface of the ground plate installed on the indoor ceiling ;
Away from the tip of the loop antenna, a metallic reflecting plate disposed in facing and the ground plate,
A support member for supporting opposed to the lower surface of the ground plate The reflective plate,
An indoor antenna comprising: A monopole antenna protruding from the bottom surface of the ground plate installed on the indoor ceiling ,
Away from the tip of the monopole antenna, a metallic reflecting plate disposed in facing and the ground plate,
A first dielectric which is deposited on the lower surface of the ground plate so as to fill the monopole antenna and the reflector,
A second dielectric enveloping the surface of the first dielectric,
Said first and second dielectric respective relative dielectric constant epsilon _r1, epsilon _r2, when the the epsilon _r0 free space dielectric constant,
ε _r2 ≈ (ε _r0 ε _r1 ) ^1/2
Selected
The indoor antenna characterized in that the thickness of the second dielectric is set to approximately ¼ of the wavelength λ ₂ in the second dielectric. 4. An indoor antenna using a loop antenna instead of the monopole antenna according to claim 3.

Images