Communications: radio wave antennas – Antennas – With means for moving directive antenna for scanning,...
Reexamination Certificate
2001-12-13
2003-12-23
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
With means for moving directive antenna for scanning,...
C343S757000
Reexamination Certificate
active
06667720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a steerable or directionable transponders (e.g. antennae or emitters), and especially but not exclusively to interrogator systems incorporating such transponders, and to vehicles incorporating them.
2. Discussion of Prior Art
There are times when the user (or a control processor) of electromagnetic detecting apparatus needs to look in two different directions, or when two users of a detection system each independently want to look in a different direction (for example when two people both want to have, E.M. signals analysed that come from two different directions). Sometimes signals from both directions, or fields of view, need to be analysed at substantially the same time. The immediate answer to this need is to provide two signal capture systems—for example two antennae, each under the control of a different person. This increases the cost of the overall detection system.
A second solution is to mount the signal capturer (e.g. antennae or camera) on a turntable or gimbal mechanism so that it can be rotated to look in the two directions at different times and ensure that the turntable can be moved fast enough to provided the required response time for both users (or the system) to see their desired field of view substantially simultaneously. This is difficult if a fast turning time (e.g. less than 1 second, and especially if <200 ms) is required with a substantial mass of antennae. The motor drives needed will be large and expensive, and furthermore gimbal arrangements are susceptible to mechanical failure or damage due to exposed moving parts. A gimbal also requires a large volume.
Phased arrays could in theory be used to steer the signal capturer/antennae, however at high frequencies (e.g. GHz-range) the technology is not yet mature enough to be practical or affordable, especially for the case of broad-band signals.
One area where it is believed that a steerable antennae or interrogator would be useful is in the field of vehicles. For example it is known to have radar-controlled systems on cars which prevent a car from coming too close, whilst travelling, to the vehicle in front. In order to look at a sufficiently wide field of view using cheaper, practicable, equipment it may be necessary to have more than one antenna/detector. By having a steerable antenna it is possible to provide fewer antennae and yet still look across a wide enough field of view. It may be possible to provide only one antenna on the vehicle.
It may be desirable not only to know that there is a vehicle in front, but also to identify it as being one of a known kind. For example road trains and tram convoys have been proposed in which a trailing vehicle follows a lead vehicle automatically at a controlled distance and speed, and it may be desirable for the trailing vehicle to identify the lead vehicle, for example by interrogating a transponder, or by processing some other identifying signal from the lead vehicle. It may also be desirable for the signal from the lead vehicle to contain additional data beyond that it is there, for example, its identity, what it is carrying, its braking distance, amount of fuel it has on board etc.
SUMMARY OF THE INVENTION
It is an aim of one embodiment of the present invention to enable an antenna to be steerable at a speed of the order of 100 ms or so (when operating at GHz frequencies or above).
According to a first aspect the invention comprises a steerable antenna or scanner assembly having an antenna and a steering reflector, the steering reflector being adapted to be controlled by control means.
Thus the steering reflector is moved, and not the entire assembly. This enables the lower mass reflector to be moved faster. Also, since it is a reflector it can be moved through only half of the angle the entire assembly would have to be turned (if the movement is angular movement). Preferably the antenna is of the order of 50 cm
2
or 100 cm
2
at least in area. It may be larger or smaller, depending upon the desired resolution, and upon the wavelength used.
The steering reflector is preferably capable of being moved between a first position in which the assembly has a first field of view and a second position in which the assembly has a second field of view in a time of about half-a-second or less. Most preferably the steering time is not more than about 0.2 seconds, 0.1 second, or less, possibly about 10 ms. The steerable reflector may be moved in the steering time through an angle that is at least 10°, or 20°, or 40°, or 60°, or 90°, and is preferably movable in that time through at least about 90°.
The assembly is preferably adapted to detect or emit electromagnetic radiation, preferably of millimeter wavelengths, or possibly longer or shorter wavelengths. A wavelength of 36-40 GHz, or about 77 GHz, or about 95 GHz may be chosen.
The assembly may be housed in a protective housing, which may be of the order of 5-20 cm or more wide and may be about 10-20 cm or more tall, and may be about 1-20 cm deep.
The antenna is preferably stationary (relative to a housing or mounting frame), with the steering reflector being adapted for movement.
The assembly may direct incident radiation from a chosen direction to a detector via at least one reflection of the incident radiation. This enables it to be compact. Incident radiation from the chosen direction may be directed to the detector via at least two reflections of the incident radiation within the assembly, or with only, or no more than two reflections of the incident radiation within the assembly.
There maybe a selective reflector which in use transmits at least a substantial part of an incident wave under certain conditions and which reflects at least a substantial part of an incident wave under other conditions, and in which the arrangement is such that radiation reaching a detector has been both reflected from the selective reflector and transmitted through the selective reflector. Substantially all incident radiation that encounters the selective reflector in a particular wavefront may be transmitted, or substantially all may be reflected. The steering reflector may comprise the selective reflector.
A polarisation changer maybe provided to effect a change of polarisation of radiation. The polarisation changer may provide in use the change of polarisation between the selective reflection or transmission of the incident radiation by the selective reflector and may transmit or reflect the radiation dependent upon the polarisation state of the radiation incident upon it. The assembly may be adapted to reflect off the steering reflector radiation incident upon the assembly from a chosen direction. The antenna may be a focusing antenna, and the antenna may be adapted to focus the polarity-altered radiation reflected off the steering reflector onto a detector. The polarisation changer is preferably provided in the path of the radiation between its reflection from the steering reflection and the focusing antenna, the arrangement being such that the radiation reflected off the steering reflector has its polarity altered before re-impinging upon the steering reflector and passing through the steering reflector to reach the detector.
The antenna may be arranged relative to the polarisation changer such that the radiation incident upon the assembly from a chosen direction passes through the antenna before encountering the polarisation changer.
The antenna and/or steering reflector may comprise substantially parallel lines of material. The polarisation changer may rotate the polarity of a linearly polarised wavefront by substantially 45° as the wavefront passes through it. The steering reflector may be movable angularly about an axis.
A circular polarisation to linear polarisation converter may be provided. There are certain advantages to communicating over distances using circularly polarised radiation. The circular polarisation to linear polarisation converter may be provided in front of the antenna, so that a wavefront incident from a chosen direction
Nixon & Vanderhye P.C.
Phan Tho
Qinetiq Limited
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