Antenna

Details Antenna Antenna

2001-10-12

2003-03-25

Phan, Tho (Department: 2821)

Communications: radio wave antennas

Antennas

Within conductive apertured wall

C343S7000MS, C343S752000, C343S768000

Reexamination Certificate

active

06538618

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an antenna.
BACKGROUND OF THE INVENTION
A conventional antenna will be described referring to
FIGS. 33
to
36
. As well shown in
FIG. 33
, the antenna
130
comprises a chassis is configured with a grounding conductor
131
provided as the bottom surface thereof, two top conductors
135
and
118
provided as the top surface thereof opposite to the grounding conductor
131
, and side conductors
134
provided as the antenna sides. The grounding conductor
131
, the side conductors
134
, and the ceiling conductors
135
and
138
are electrically connected to each other. A feeding point
132
is provided on the grounding conductor
131
for receiving electric power from the outside. The feeding point
132
is electrically connected to one end of an antenna element
133
made of a conductive wire while the other end is connected electrically and mechanically by soldering or the like to a linear conductor
139
which is provided at the center on the top surface of the antenna. Furthermore, there is a pair of openings
136
and
137
provided symmetrically on both sides of the linear conductor
139
on the top surface of the antenna for radiation of electric waves.
FIG. 34
illustrates an example of setting dimensions of the antenna
130
. It is assumed in
FIGS. 33 and 34
that the X, Y, and Z set a three-dimensional coordinate space. The antenna
130
is arranged with the grounding conductor
131
sitting on the XY-plane, the feeding point
132
defining the origin, and the linear conductor
139
extending along the Y-axis, hence having a symmetrical structure to each of the ZY-plane and the ZX-plane. In this example, the grounding conductor
131
is formed of a square shape having each side of 0.76×&lgr; along the X and Y-axes (&lgr; being the free space wavelength) based on the free space wavelength. The height along the Z-axis of the side conductors
134
is set as 0.08×&lgr;. The length along the X-axis of the openings
136
and
137
provided on both sides of the linear conductor
139
at the center of the top surface of the antenna is 0.19×&lgr; while the side along the X-axis of the ceiling conductors
135
and
138
is set as 0.19×&lgr;. The length along the Z-axis of the antenna element
133
is set as 0.08×&lgr;.
FIG. 35
illustrates a VSWR characteristic curve of the input impedance characteristic to a 50 &OHgr; feeding line in the antenna
110
set as described. The horizontal axis in the figure is normalized by the resonance frequency f
0
. It is then apparent from the figure that the frequency band lower than 2 of VSWR extends 10% or higher, and the reflection loss is smaller throughout the wide band resulting in improvement of the impedance.
FIG. 36
illustrates the radiation directivity on the antenna
130
. The circular chart expressed the radiation directivity is 10 dB per scale and the unit is dBi based on the radiation power at the point waveform source. As apparent from the diagram, the antenna
130
has a bidirectivity of electric wave radiation along the X direction while along the Y direction is minimized. The antenna
130
having such characteristics is useful in a long, narrow interior space such as a corridor.
The antenna
130
has the openings
136
and
137
provided in the top surface thereof for radiation of electric waves. As the antenna element
133
acting as the electric wave radiation source is surrounded by the grounding conductor
131
and the side conductor
134
, the electric wave radiation effect will be negligible to the four sides and the bottom (i.e. a positional environment). According to the above characteristic, the antenna
130
can simply be mounted to any indoor location such as a ceiling with the body embedded but the top surface exposed to the radiation space so that it is flush with the ceiling surface. As a result, the antenna exhibits the projecting object from the setting surface thus being less noticeable in the view and more preferable in the appearance.
Also, in the antenna
130
, the height of the antenna element
133
is set as 0.08×&lgr; and it is lower than that of a known ¼ wavelength antenna element. This contributes to the downsizing of the antenna. Accordingly, even if the antenna is hardly embedded in the setting surface such as a ceiling, the projecting object can be minimized thus being less noticeable in the view and more preferable in the appearance.
Moreover, the antenna
130
is symmetrical structure on both the ZY-plane and the ZX-plane. This permits the directivity of electric wave radiation to be symmetrical toward each of the ZY-plane and the ZX-plane.
However, the conventional antenna
130
having the foregoing structure can be resonant only at an odd number multiple of the fundamental frequency but hardly operated at any desired group of frequencies. It is hence necessary for radiation of electric waves at different frequencies to provide a corresponding number of the antennas. The more the number of the antennas, the greater the space for installation of the antennas will be increased. Also, an increase in the number of the antennas requires a more number of transmission lines thus further increasing the installation space. Accordingly, when the installation space is too large, the antenna can hardly be mounted with less visibility thus failing to improve the appearance.
The present invention has been developed in view of the above technical drawbacks and the object is to provide an antenna which can radiate electric waves at a plurality of desired frequencies while it is made relatively simple in the structure and minimized the antenna body.
SUMMARY OF THE INVENTION
In an aspect of the present invention, there is provided an antenna comprising: a chassis consisting mainly of a grounding conductor provided as a bottom surface, a ceiling conductor provided as a top surface opposite to the grounding conductor, and side conductors provided as antenna sides; at least one opening provided in apart of said chassis, which opens for radiation of electric waves; a feeding point provided on said grounding conductor for power supply via a predetermined feeding line from the outside; and an antenna element connected to said feeding point at one end while being connected to said ceiling conductor via a frequency selectable circuit at the other end, and surrounded by the side conductors.
Said ceiling conductor may have a generally annular slit provided therein about the joint between said antenna element and the ceiling conductor, and the inner edge and the outer edge forming the slit of the ceiling conductor may be connected to each other via a frequency selectable circuit different from the frequency selectable circuit at said joint between said antenna element and the ceiling conductor.
Two or more of said generally annular slits may be provided concentrically, and the outer edge and the inner edge forming each of the slits of the ceiling conductor may be connected to each other via respective frequency selectable circuits.
Said chassis may be situated in an XYZ orthogonal coordinate system with said grounding conductor extending along the XY-plane and said feeding point sitting at the origin so that said grounding conductor, the ceiling conductor, and the side conductors are symmetrical about the ZY-plane and the opening in said chassis is symmetrical about the ZY-plane.
Said chassis may be situated in an XYZ orthogonal coordinate system so that said grounding conductor, the ceiling conductor, and the side conductors are symmetrical about the ZX-plane and the opening in said chassis is symmetrical about the ZX-plane.
Said frequency selectable circuit may be configured with a parallel resonance circuit.
Said frequency selectable circuit may be configured with a low-pass filter.
Said frequency selectable circuit may be configured with a changeover switch.
Further, said antenna may comprise a matching conductor provided to match the impedance with said feeding line and electrically connected to the grounding c

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