Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
1999-12-23
2001-03-13
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C343S841000
Reexamination Certificate
active
06201514
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a stereoscopic antenna for use in connection with a security detector for transmitting a radio signal indicative of detection of the presence of a person and, more particularly, to the stereoscopic antenna capable of exhibiting a uniform pattern of field radiation.
2. Description of the Prior Art
The radiation directional characteristic (directivity) and the field gain are important characteristics of the antenna. The isotropic antenna is capable of radiating energies uniformly in all directions and the curve descriptive of the directivity (directivity diagram) thereof represents a circle in all planes. Requirements for the directivity of the antenna vary depending on the application, but the antenna used in a transmitter of the security detector is desired to be isotropic because the position of the transmitter antenna relative to the receiver varies depending on the place for installation of the security detector.
The rod antenna, an elongated antenna represented by a dipole antenna, is known as a highly efficient antenna capable of exhibiting a high field gain. However, in the case of a micro dipole antenna
100
elongated in a direction z as shown in
FIG. 5A
, the micro dipole antenna
100
is not isotropic since although the non-directivity is exhibited in the plane perpendicular thereto, that is, in an x-y plane as shown by a line
101
in
FIG. 5B
, but the 8-shaped directivity is exhibited in a plane containing the micro dipole antenna
100
, that is, in the y-z plane as shown by a line
102
in FIG.
5
C. Also, in order for the rod antenna to exhibit a high efficiency, it is necessary that the length of the rod antenna as measured in a direction z which conforms to the heightwise direction has to be chosen to be of a value equal to &lgr;/2, 3&lgr;/8 or &lgr;/4 to thereby allow it to resonate at the wavelength &lgr;. This results in the rod antenna having a substantial length and, thus, in difficulty in making it compact.
A loop antenna
110
shown in
FIG. 6A
is of a design easy to make it compact. The loop antenna
110
is generally used having a perimeter chosen to be of a value equal to the wavelength &lgr;. However, even the loop antenna
110
tends to exhibit the 8-shaped directivity in a y-z plane containing the loop antenna
110
as shown by a line
112
in
FIG. 6C
, and therefore, the loop antenna is not isotropic. Also, the loop antenna
110
has a field gain smaller than that of the rod antenna.
SUMMARY OF THE INVENTION
Accordingly, the present invention is intended to provide an stereoscopic antenna which is compact in size, can exhibit a uniform field radiation pattern and has a high gain.
In order to accomplish the above described object, the present invention provides a stereoscopic antenna which comprises a planar electroconductive pattern adapted to be grounded, a loop-shaped antenna body having an axis lying perpendicular to the planar electroconductive pattern, and an antenna connection for connecting the antenna body to the planar electroconductive pattern. The ratio H/D of the longer diameter D of the antenna body, as measured in a direction along the major axis thereof, relative to the height H of the antenna body as measured from the planar electroconductive pattern is chosen to be within the range of 0.1 to 1.
According to the present invention, the stereoscopic antenna is in the form of a loop, not in the form of a long wire, and is therefore compact in size. Also, since the ratio H/D of the longer diameter D of the antenna body relative to the height H of the antenna body as measured from the planar electroconductive pattern is chosen to be not smaller than 0.1 and the steroscopic antenna of the present invention is provided with the antenna connection, the stereoscopic antenna of the present invention is quite different in structure from the loop antenna. On the other hand, since the ratio H/D of the longer diameter D relative to the height H is not greater than 1, the stereoscopic antenna of the present invention is quite different in structure from the rod antenna. Thus, by making the antenna to have a three dimensional structure including the antenna body and the antenna connection, the stereoscopic antenna having a isotropy in which the field radiation pattern is uniform can be obtained. With this structure, the capacitance component of the antenna can depend on the distance between the electroconductive pattern and the antenna body and the inductance component thereof can depend on the overall length of the antenna. Accordingly, tuning of the stereoscopic antenna can be accomplished by adjusting the distance between the electroconductive pattern and the antenna body and also the overall length of the antenna and need not be lengthened as is the case with the rod antenna which is required to be lengthened in order for the antenna to tune. Accordingly, the present invention makes it possible to compactize the antenna. Yet, by tuning the antenna, the gain of the antenna can be increased advantageously.
In a preferred embodiment of the present invention, the planar electroconductive pattern has an opposed portion extending substantially circumferentially thereof and positioned so as to axially confront the antenna body. According to this structure, since the opposed portion of the planar electroconductive pattern has a dimension on a plane which is about equal to that of the antenna body, the capacitance component can be increased to achieve the tuning of the antenna.
In another preferred embodiment of the present invention, the antenna body is formed in one to four turns. According to this structure, if the antenna body has a number of turns which is greater than four turns, the stereoscopic antenna of the present invention will have a shape approaching the shape of the rod antenna and no sufficient characteristic in terms of directivity and gain will be obtained. However, the choice of a number of turns not greater than the four turns makes it possible to provide the stereoscopic antenna having an isotropy and an increased gain.
REFERENCES:
patent: 5818398 (1998-10-01), Tsuru et al.
patent: 6034651 (1998-11-01), Enguent
Iwasawa Masashi
Miwa Ryosuke
Clinger James
Optex Co. Ltd.
Price and Gess
Wong Don
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