Communications: radio wave antennas – Antennas – With spaced or external radio wave refractor
Reexamination Certificate
2000-05-18
2001-11-20
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With spaced or external radio wave refractor
C343S787000
Reexamination Certificate
active
06320551
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a device which is adapted to be positioned in the path of a beam of electromagnetic radiation propagating in free space which changes characteristics of the beam. The invention is particularly, but not exclusively, concerned with microwave devices.
The term microwave refers to the part of the electromagnetic spectrum substantially in the frequency range 0.2 to 300 GHz. It includes that part of the spectrum referred to as millimeter wave (having a frequency in the range 30 to 300 GHz).
In a known device for controlling the direction of a microwave beam, the microwave beam passes through a rectangular block of dielectric material formed by two wedge-shaped pieces, one being of ferrite material and one being of non-ferrite material, the pieces having their sloping faces in juxtaposition. An external magnetic field is applied to the block in a direction perpendicular to the direction of propagation of the microwave beam. The magnetic field is substantially constant across the block.
Applied magnetic field induces magnetization in the material which is substantially uniform across the block. A microwave beam passing through the magnetised material will interact with it and this interaction changes relative velocity across the beam. If a microwave beam is directed through the block so as to travel in turn through a thickness of the ferrite and then through a thickness of the non-ferrite material, certain parts of the beam will travel through a different length of ferrite material compared to certain other parts of the beam thus causing a differential phase shift across the block. The phase at one edge will lag when compared to the phase at the other edge and the beam will be deflected. Altering the direction of the magnetic field will cause the beam to deflect in an opposite direction.
In another embodiment of a device for controlling the direction of a microwave beam, the beam passes through a cylinder of material formed by two wedge-shaped pieces one being of ferrite and one being of non-ferrite material, the pieces having the sloping faces in juxtaposition. The cylinder is located within an external solenoid which is used to apply a magnetic field along the longitudinal axis of the cylinder which is substantially parallel to the direction of propagation of the beam. The magnetic field is substantially constant across the cylinder. The device operates by Faraday rotation. For circularly polarized beams such a device induces a differential phase shift in the beam thus causing deflection of the beam. Linearly polarized beams are equivalent to a combination of two circularly polarized beams rotating in opposite directions and so such a device splits a linearly polarized beam into two separate circularly polarized beams leaving the device at angles +&thgr;° and −&thgr;° to the direction of propagation of the original beam.
Devices of this kind are difficult to construct and cause in-line loss due to beam reflection at the junction between the ferrite and non-ferrite wedge shaped pieces. Such devices provide beam deflection in one plane only and so two devices in series would be required to produce conical steering.
Another device for controlling the direction of a microwave beam comprises a body of ferrite material having magnetic coils which apply a magnetic field across the body which induces a gradient in magnetization across the body. The resultant direction of the beam leaving the device is perpendicular to the gradient in the magnetic field across the body. Therefore the degree of deflection in the beam is controlled by the gradient in the magnetization. The device differs from the two devices described above in that all parts across the width of a microwave beam pass through the same thickness of ferrite material. However magnetization induced varies across the ferrite material through which the microwave beam passes.
A disadvantage with this device is that the thickness of the body is governed by its width. If the body is relatively thin compared to its width, magnetic flux tends to concentrate around the coils and so does not penetrate sufficiently across the width of an aperture through which the beam passes and little or no magnetic flux passes through the body in a central region of the aperture. However, the width of the material is governed by the width of the beam which the device is to steer and so cannot be chosen independently. As a result devices of this type need to have a thickness and a width which are comparable. This causes the devices to be bulky, heavy, cumbersome and expensive. Furthermore a thicker material causes greater insertion loss in a system.
SUMMARY OF THE INVENTION
According to a first aspect the invention provides a device for controlling the direction of a beam of radiation comprising a body of magnetic material having an aperture for the beam of radiation and means for applying a gradient in magnetization across the aperture characterized in that there is a variation in material composition of the body such that a greater amount of magnetic field penetrates through a central region of the body than would be the case in a body of uniform material composition.
According to a second aspect of the invention provides a device for controlling the direction of beam of radiation comprising a body of magnetic material having an aperture for the beam of radiation and means for applying a gradient in magnetization across the aperture characterized in that across the aperture there is a variation in reluctance from a front face of the body through to a rear face of the body.
The aperture may be one of a plurality of sub-apertures which together form a complete single aperture of the device.
There may be a variation in reluctance and/or material composition in certain regions through the body and a lack of variation in certain other regions.
Preferably the beam of radiation is microwave radiation.
Preferably the body is of composite material. Preferably the material composition of the body varies from a front face of the aperture to a rear face of the aperture. The body may have a plurality of layers wherein the layers are perpendicular to the direction of propagation of the beam of radiation. At least one of the layers may extend from a first side of the aperture to a second opposite side. Alternatively, the material composition of the body may vary across the aperture from the first side to the opposite second side.
A magnetic material is one in which its internal magnetization is effected by magnetic field. Preferably the magnetic material is an electrical insulator. It may be a ferrite. Ferrite materials may be particularly suitable since they combine high permeability with low conductivity and low losses. Due to the low conductivity, ferrite materials are easily penetrated by microwaves.
Preferably the device comprises at least one magnetic field generating means. Preferably there are two magnetic field generating means. The magnetic field generating means may be a single wire or coils. Preferably the magnetic field generating means are provided in one or more pairs on opposite sides of the aperture. Preferably the or each pair of magnetic field generating means is adapted to produce lines of magnetic force in opposite directions to induce the gradient in magnetization. If the lines of magnetic force are in opposite directions on opposite sides of the beam, the resultant flux along the direction of propagation of the beam will be zero in the center of the aperture.
Preferably there are two gradients in magnetization which are in directions perpendicular to one another. This enables the direction of the beam to be controlled in azimuth as well as in elevation to achieve conical beam steering. In this event, pairs of coils would be located in proximity to faces of the body through which the beam of radiation does not pass. Preferably the gradient or gradients in the magnetization are substantially linear.
Conveniently the body comprises a first material containing at least one region of a s
Bae Systems Electronics Limited
Kirschstein et al.
Nguyen Hoang
Wong Don
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