Communications: radio wave antennas – Antennas – With means for moving directive antenna for scanning,...
Patent
1998-03-05
1999-10-05
Le, Hoanganh
Communications: radio wave antennas
Antennas
With means for moving directive antenna for scanning,...
343761, H01Q 300
Patent
active
059631740
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an antenna device for emitting and/or receiving electromagnetic radiation, such as radar radiation in, for example, a car radar apparatus. The antenna device comprises a rotatable reflector, a feeder which is fixed relative to the antenna device and interacts with the reflector, a motor for driving the reflector and a tachometer for monitoring the rotation of the reflector and for controlling the drive motor.
BACKGROUND OF THE INVENTION
In certain applications, for example within the car radar field, there is a need for an antenna device having an antenna beam which can sweep a limited range of angle in the order of magnitude of some ten degrees, for example 20.degree., but which does not need to cope with large angle sectors or a complete revolution.
A conventional method for sweeping a region is to rotate both the feeder and the antenna reflector. In this way, both small and large ranges of angle can be swept. Known realizations of this method have proved however to be both costly and space-consuming and are not suitable for use in a car radar, for example, in which the space which might be available for use is very limited and the need for a low price is extremely important.
It is also known to realize the sweeping electronically using a fixed antenna. In order to realize a sweeping of the region according to the above, as is required in a car radar, the solutions remain complicated and expensive and limitation to a smaller sweeping range in which simpler solutions can be utilized has an adverse effect upon the functioning and reliability of the car radar.
In order to realize sweeping within a limited region, it has previously been proposed to utilize a rotatable reflector in combination with a fixed feeder. The reflector can in this case be driven, for example, by means of a stepping motor.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an antenna device according to the principle of the preceding paragraph, having a fixed feeder and a rotatable reflector, which is simple, strong, compact and reliable, while at the same time demanding a low price. This is achieved by an antenna device having a drive motor for driving the reflector and a tachometer for monitoring the rotation of the reflector in the form of two interacting flag motors (voice coil motors). The antenna device is here characterized in that the drive motor and the tachometer are constituted by so-called flag motors, i.e. motors having flat coils fitted so as to move in a magnetic field created by permanent magnets and having the coil ends directed towards the permanent magnets, the rotors of the motors being mutually rigidly connected to each other mechanically.
It is worth pointing our that flag motors per se are known and are used, among other things, for positioning in hard disks and CD-players. In this case, no use is made of the interaction between two motors and the field of application in question is totally different, having different drive and control requirements.
According to an advantageous embodiment, the rotors of the flag motors are arranged so as to rotate about a common rotary axle, which common rotary axle is arranged to support the reflector of the antenna device. This embodiment has advantageous characteristics in terms of, among other things, compactness and motional stability. The rotors of the flag motors can herein advantageously be constituted by a common component which is designed in one piece. Furthermore, a bearing member supporting the reflector of an antenna device can be designed in one piece with the rotor of the drive motor and/or tachometer.
According to another advantageous embodiment, the drive motor is disposed behind and the tachometer in front of the common rotary axle which supports the reflector of the antenna device. This positioning of the drive motor and tachometer enables effective use of the space available in the antenna device. In order to make even more effective use of the space, according to yet anot
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Andersson Thomas
Larsson Thomas
Silen Arne
Celsiustech Electronics AB
Ho Tan
Le Hoang-anh
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