Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Reexamination Certificate
1999-02-23
2001-09-18
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
C343S795000
Reexamination Certificate
active
06292154
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an antenna device of a compact, thin design having wideband frequency characteristics.
2. Description of the Related Art
Recently, mobile satellite communications, using a mobile means (e.g. an airplane, a ship or a car) and a communication satellite, have come into wide use. With the spread of the mobile satellite communications, there has now been a stronger demand for a compact, high-performance antenna. As is well known, in order to achieve a compact antenna design, there has been proposed a meandering-type antenna in which a radiation element of the antenna comprises a wire-like conductor formed or bent into a meandering configuration. One example of such antenna is disclosed in JP-A-6-90108.
Generally, the frequency bandwidth of a conventional antenna is about several % in terms of the specific band, and when the length of a radiation element was reduced so as to achieve a compact design, a problem was occurred that the band was further narrowed. When the transmitting band and the receiving band were larger than the specific band thereof, a problem was occurred that a plurality of antennas for transmitting and receiving purposes were required.
FIGS. 13A
to
13
B are a plan view showing the construction of a conventional antenna,
FIGS. 13B and 13C
are views showing the installation of the conventional antenna, and
FIG. 13D
is a graph showing resonance characteristics of the conventional antenna. The resonance frequency of the conventional antenna is a single resonance, and therefore the conventional antenna can not deal with a plurality of frequency bands (that is, the frequency band between 137.0 MHz and 138.0 MHz for a down-line and the frequency band between 148.0 MHz and 150.05 MHz for an up-line) assigned to a mobile satellite communication system which effects a ground-satellite-ground data communication using a satellite orbiting in a low orbit. Namely, the resonance frequency fr is determined by the length L of a radiation element, and this has resulted in a problem that the resonance occurred only for the single frequency.
In the installation of the antenna on a mobile means such as a vehicle, it is desirable that the antenna should have a low posture (reduced antenna height) in order to reduce the wind pressure, acting on the antenna open surface, and also to prevent damage to the antenna upon contact with other objects. Particularly, when the antenna is installed on a container, the antenna height is about 0.5 m as a result of the stacking of the containers even if the above ¼-wavelength grounded-type antenna is used, and therefore the installation of the antenna is impossible. If the conventional antenna, shown in
FIG. 13A
, is mounted vertically on the vehicle body as shown in
FIG. 13B
, in addition to the above bandwidth problem, further problems concerning the reduction of the wind pressure and the damage to the antenna upon contact with other object will be occurred. If the antenna is mounted horizontally on the vehicle body as shown in
FIG. 13C
, the impedance is lowered as the antenna approaches an electrically-conductive panel or plate of the vehicle body, and also the resonance frequency is shifted, so that the impedance matching between the antenna and the feeder line is adversely affected, which has resulted in a problem that the transmitting and receiving operation can not be operated.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an antenna device which can deal with more frequencies, and has a compact design and a low posture, and is hardly influenced by a box-like metal body such as a vehicle body.
In order to achieve the object of present invention an antenna device of the present invention comprising radiation elements, feed means for feeding electric power to the radiation elements, a ground plate, and a cover member covering the radiation elements and the feed means, which is mounted on metal cubic and using short circuit between ground plate and metal cubic, wherein a value, obtained by dividing the distance (H) between the radiation elements and the ground plate by a wavelength (&Lgr;), is 1÷250≦H&Lgr;≦1÷80, and preferably 1÷200≦H÷&Lgr;1÷100.
With this construction, an overall loss of the antenna can be suppressed while suppressing the decrease of the antenna impedance, and therefore there can be provided the antenna device of high reliability which can positively operate under a wide range conditions of use.
The plurality of radiation elements and the feed equipment are formed on a common antenna board, and therefore as compared with the case where such elements are formed on separate boards, the antenna construction can be simplified, and the productivity can be enhanced, and besides the compact, thin design of the antenna can be achieved. Furthermore, since the different line lengths are provided, a plurality of wavelengths can be transmitted and received.
Particularly, by setting the line length to about 25% of the corresponding wavelength, the optimum transmitting and receiving operation becomes possible corresponding to wavelength, and also the polarization characteristics of the antenna can be enhanced.
Electric power is fed to the plurality of radiation elements through the single feed equipment, and therefore the area of the antenna board, which is occupied by the feed equipment can be reduced, then the antenna board size can be reduced. Besides, since the power is fed to the plurality of radiation elements through the common feed equipment, the power can be fed to the plurality of radiation elements under the same condition, and therefore there can be provided the antenna of high reliability having excellent antenna characteristics each frequency to which the plurality of radiation elements correspond, respectively.
REFERENCES:
patent: 4464663 (1984-08-01), Lalezari et al.
patent: 4849765 (1989-07-01), Marko
patent: 4987424 (1991-01-01), Tamura et al.
patent: 5936583 (1999-08-01), Sekine et al.
patent: 0777293A1 (1997-06-01), None
patent: 0690108 (1994-03-01), None
patent: WO9627219 (1996-09-01), None
European Search Report dated Mar. 1, 2000.
Patent Abstract of Japan, JP 05 291 825 A, Nov. 5, 1993.
Patent Abstract of Japan, JP 11 251 825 A, Sep. 17, 1999.
European Search Report dated Nov. 5, 1999.
Patent Abstract of Japan, JP 05 291 825, Nov. 5, 1993.
Deguchi Futoshi
Nakashima Kazuyuki
Tate Sumio
Matsushita Electric - Industrial Co., Ltd.
Stevens Davis Miller & Mosher LLP
Wimer Michael C.
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