Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
2001-12-20
2003-07-01
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C343S757000, C349S202000
Reexamination Certificate
active
06587076
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna used in millimeter waves or microwaves, and more particularly, to abeam scanning antenna in which the direction of a beam of radiated or absorbed electromagnetic waves can be changed by changing the phase of the electromagnetic waves.
2. Description of the Related Art
In millimeter waves or microwaves applied radar technology is well-known such type radars that in order to accurately recognize the position of an object in a wide target area, the beam of electromagnetic waves is focused and thinned, while being scanned at the same time.
On the other hand, in recent years, a millimeter wave radar has been about to be mounted on cars so that obstacles are detected while cars are running. The millimeter wave radar is to be mounted on cars, and accordingly is required to be small in size, light in weight, high in reliability and low in cost.
Beam scanning antenna of such types that switching among a plurality of antennas is carried out by a PIN diode or the like and that the antenna itself is swung are put into actual use as beam scanning antenna for car radars.
Moreover, a beam scanning antenna using a phase shifter is used in many radars although not commercialized for car radars at the present time. In the beam scanning antenna, the direction of a beam radiated from an array antenna or inputted to the array antenna is changed by accurately changing the phase of a signal fed to each element of the array antenna by use of a phase shifter such as a latched ferrite.
The conventional beam scanning antennas, however, have the following problems:
First, high reliability as a radar to be mounted to a vibrating apparatus such as a car radar can hardly be ensured in the beam scanning antenna, which swings itself, because of its mechanical driving portion, although the beam scanning antenna is easily manufactured because of its simple structure and the beam direction can finely be switched. Further, reduction in size cannot be achieved because of space for swinging the antenna.
A beam scanning antenna of such a type that switching among a plurality of antennas is carried out has an advantage of high reliability because no mechanical control is used. This type beam scanning antenna, however, has a problem of low availability of each antenna because only part of the plurality of antenna are operated at a moment, and a problem that the reduction in size of the entirety of the beam scanning antenna is hardly achieved because of necessity of the plurality of antennas. Further, since an antenna aperture of a predetermined area or more is required of the beam scanning antenna of this type irrespective of the configuration and material of the antenna elements to obtain a desired antenna gain or beam diameter, it is necessary to provide the plurality of fixed antennas with the same property to obtain the desired antenna gain or beam diameter. Consequently, it cannot be helped that the overall antenna area is large. At the same time, a switch for high frequency applications suffers large insertion loss and is difficult to operate with a high degree of efficiency. Moreover, in order to finely switch the beam direction, the number of necessary antennas increases with the result that the overall area of the antennas increases and the antenna gain decreases with increases in number of switches. Consequently, it is practically impossible to provide a beam scanning antenna in which the beam direction can be finely switched.
The beam scanning antenna using a phase shifter has a limitation of use because the phase shifter is normally large in size and expensive.
As described above, presently, no beam scanning antenna meets the requirements of being small in size, light in weight, high in reliability and low in cost although the beam scanning antenna is a technology expected to be increasingly used, particularly, for car radars in the future.
SUMMARY OF THE INVENTION
The invention is made in view of the above-mentioned problems of the related art, and an object thereof is to provide a small-size, lightweight, high-reliability and low-cost beam scanning antenna having no mechanical driving portion and capable of scanning of an electromagnetic wave beam by only electric signals.
The invention relates to a beam scanning antenna comprising two conductor plates disposed parallel to each other; a primary radiator for transmitting and receiving electromagnetic waves; and a wave collector for electromagnetic waves, shaped like a flat plate, the primary radiator and the wave collector being disposed between the two conductive plates, a plurality of input and output portions for joining the electromagnetic waves between the wave collector and the input and output portions being disposed on one of the conductive plates, the wave collector including a substrate formed of a material whose dielectric constant can be changed by an electrostatic field, a plurality of strip-shaped electrodes disposed on one principal surface of the substrate so as to be substantially parallel to one another in a direction of travel of the electromagnetic waves, and a counter electrode formed on the other principal surface of the substrate, the counter electrode extending on a substantial entirety of the other principal surface or being separated into strips so as to be opposite to the plurality of strip-shaped electrodes formed on the one principal surface,
wherein the electrostatic field is applied between the electrodes formed on the one principal surface and the counter electrode formed on the other principal surface to partially change a dielectric constant of the wave collector in a direction perpendicular to the direction of travel of the electromagnetic waves, whereby a direction of a beam of the electromagnetic waves radiated or absorbed through the input and output portions is made variable.
Moreover, in the invention, it is preferable that within a plane perpendicular to the direction of travel of the electromagnetic waves in the substrate of the wave collector, the wave collector has a dielectric constant substantially unchanged in a direction perpendicular to a shorter side of the strip-shaped electrodes formed on the one principal surface, and has in a direction parallel to the shorter side, refractive indices for the electromagnetic waves which are distributed as a quadratic function of distance with a predetermined point as a peak.
Moreover, in the invention, it is preferable that the dielectric constant of the material of the substrate whose dielectric constant can be changed by the electrostatic field is changed by 20% or more by application of the electrostatic field, and a dielectric loss thereof is 1% or less.
Moreover, in the invention, it is preferable that the material of the substrate is made of a ferroelectric of (Ba, Sr)TiO
3
, BaTiO
3
or SrTiO
3
, or a liquid crystal material such as nematic liquid crystal, cholesteric liquid crystal or smectic liquid crystal, or a liquid crystal polymer.
Moreover, in the invention, it is preferable that within a plane perpendicular to the direction of travel of the electromagnetic waves in the substrate of the wave collector, the wave collector has a highest dielectric constant at a center of the substrate in the direction parallel to a shorter side of the strip-shaped electrodes formed on the one principal surface and has dielectric constants which are reduced so that square roots of the dielectric constants decrease as a quadratic function of distance toward a periphery of the substrate, whereby the refractive indices for the electromagnetic waves are decreased as the quadratic function of distance with the center of the substrate as a peak.
The invention relates to a wave collector comprising: a substrate made of a material whose dielectric constant can be changed by an electrostatic field, in which substrate electromagnetic waves travel in a predetermined direction of travel; strip-shaped electrodes disposed on one principal surface of the substrate so as to be substantially par
Fujii Mikio
Takenoshita Takeshi
Hogan & Hartson LLP
Kyocera Corporation
Mull F H
Tarcza Thomas H.
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