GB2318236A

GB2318236A - Radiation detector arrangements

Info

Publication number: GB2318236A
Application number: GB8424759A
Authority: GB
Inventors: David Richmond Houldcroft
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1983-10-01
Filing date: 1984-10-01
Publication date: 1998-04-15
Anticipated expiration: 2004-10-01
Also published as: GB2318236B; GB8424759D0; FR2874250A1; GB8326361D0

Abstract

A radiation detector arrangement for detecting radio radiation and optical radiation which includes antenna means 10 for detecting radio radiation, and optical detector apparatus 14, 13 for detecting optical radiation, said optical detector apparatus including optical detector means 14 and optical reflector means 13 adapted to reflect optical radiation onto said detector means and being located substantially coincident with or forwardly of said antenna means, the arrangement being adapted so that said optical radiation and radio radiation pass through a generally common aperture prior to being detected.

Description

RADIATION DETECTOR ARRANGEMENTS This invention relates to radiation detector arrangements, and in particular to such arranyements for detecting radio radiation and optical radiation.

In this Specification, the term "radio radiation" is intended to mean radiation which is processed according to radio frequency techniques and the term "optical radiation" is intended to mean radiation which is processed according to optical techniques.

The growing interest in multiband guidance systems for missiles and other uses often requires the use of multiple radiation acceptors to cover the wavebands adopted. Where a system utilizes an optical and radio combination of guidance such acceptors can comprise an object lens and an antenna each having a respective separate aperture which passes radiation. In some applications, it is found to be impractical to provide two separate apertures because of the limited space available for installation of the two guidance systems, particularly where each aperture is to receive radiation from substantially the same common direction.

According to one aspect of this invention, there is provided a radiation detector arrangement for detecting radio radiation and optical radiation (as hereinbefore defined) which includes antenna means for detecting radio radiation and optical detector apparatus for detecting optical radiation, said optical detector apparatus including optical detector means and optical reflector means, adapted to reflect optical radiation onto said detector means and being located substantially coincident with or forwardly of said antenna means the arrangement being adapted so that said optical and radio radiation pass through a generally common aperture prior to being detected.

Preferably, the antenna means comprises an electrically conductive antenna element provided on a dielectric substrate, and the reflecting means comprises a stacked dielectric reflectance filter provided on a dielectric substrate.

In one embodiment, the antenna means and the reflecting means are formed on a single dielectric substrate.

In another embodiment, the antenna element is provided on the surface of the dielectric reflectance filter.

The reflecting surface of the reflecting means may be planar; alternatively it may be curved.

Further aspects will become apparent from the following description, which is by way of example only, reference being made to the following drawings, in which: Figure 1 is a perspective view of a wide band, cavity backed spiral antenna, Figure 2 is a schematic side section view through a first embodiment of dual band radiation detector, Figure 3 is a schematic side section view through a second embodiment of dual band radiation detector, and Figure 4 is a schematic side section view through a third embodiment of dual band radiation detector, Referring initially to Figure 1, there is illustrated a wide band cavity backed spiral microwave antenna which comprises a metallic spiral antenna element 10 which is plated on to a dielectric substrate 11. The substrate 11 is backed by a cavity formed by a metallic casing 12 which ensures one way emission and/or reception. The element 10 is of spiral form, having arms which extend from a central region. The width of the arms increases away from the central region so as to increase the bandwidth emitted or received by the antenna. A discussion of spiral antennae is to be found in the 'International Countermeasures Handbook' June 1976.

Referring now to Figures 2, 3 and 4, there are shown embodiments of dual band radiation detector adapted to receive both radio radiation at microwave frequencies and optical radiation at infra red frequencies, through a substantially common aperture and along substantially coincident axes. Each of the embodiments employs an antenna for receiving radio radiation similar to the spiral antenna of Figure 1, although the form of the antenna element may be varied to suit the requirements of a particular system.

Referring now particularly to Figure 2, the dual band radiation acceptor illustrated comprises an antenna element 10 plated on to a substrate 11 of dielectric material, the substrate being backed by a cavity formed by casing 12. On the portions of the substrate 11 not covered by the element 10 is deposited a stacked dielectric reflectance filter 13 adapted to be reflective to optical radiation in the operating range of frequencies of optical detector 14. The exposed surface of antenna element 10 is also caused to be reflective to the operating frequencies, for example by plating with gold. The composite element formed by substrate 11, antenna element 10, and stacked dielectric filter 13 thus performs both as a radio radiation detector, and as a primary reflective optical element which reflects optical radiation on to optical detector 14.

The stacked dielectric filter comprises a plurality of thin layers of dielectric materials having different refractive indices which superimposed define an element which reflects optical radiation in the band of interest. A discussion of dielectric reflectance filters is to be found in "Handbook of Optics", Editor: W G Driscoll, Assistant Editor: W Vaughan. It is believed that the selection of the particular materials and their thicknesses, having regard to the optical radiation to be reflected, is within the competence of one skilled in the art. The dielectric materials are also selected to have a low loss figure in the microwave band, so as to minimise perturbation of the radiation passing to the antenna elements.

Referring now to Figure 3, this embodiment is similar to that of Figure 1, except that the stacked dielectric filter 13 is initially deposited over the whole of the surface of the substrate 11 and then antenna element 10 is plated on top, the exposed surface of element 10 again being caused to be reflective to the optical radiation of interest by plating with gold.

Referring now to Figure 4, this embodiment is similar to that of Figures 2 and 3 except that the stacked dielectric filter 13 is formed on a separate substrate 11 located forwardly of the antenna, the antenna again being formed by plating the antenna element 10 onto the substrate 11. In this instance, the materials of which filter 13 and substrate 11 are formed should be of a low loss dielectric material so as to reduce any effect on the antenna.

In the embodiments shown in Figures 2 to 4, the optical reflecting surface defined has been plane. However a curved surface may be achieved by causing substrate 11 in Figures 2 and 3 and substrate 11 in Figure 4 to be curved to give a powered optical surface. In Figures 2 and 3 this will modify the radiation pattern received by the antenna, but the modified radiation pattern may be acceptable for the particlar application considered and may, if necessary, be modified by adjustments in the backing cavity defined by casing 12.

Claims

1. A radiation detector arrangement for detecting radio radiation and optical radiation (as hereinbefore defined) which includes antenna means for detecting radio radiation, and optical detector apparatus for detecting optical radiation, said optical detector apparatus including optical detector means and optical reflector means adapted to reflect optical radiation onto said detector means and being located substantially conincident with or forwardly of said antenna means, the arrangement being adapted so that said optical radiation and radio radiation pass through a generally common aperture prior to being detected.

2. An arrangement as claimed in Claim 1, wherein the antenna means comprises an electrically conductive antenna element provided on a dielectric substrate, and the reflecting means comprises a stacked dielectric reflectance filter.

3. An arrangement as claimed in Claim 2, wherein said antenna element and said reflector means are formed on a common substrate.

4. An arrangement as claimed in Claim 2, wherein the antenna element is provided on the surface of the dielectric reflectance filter.

5. An arrangement as claimed in any of the preceding claims wherein the optical reflecting surface of the reflector means is generally planar.

6. A missile according to claim 1, wherein said spiral antenna is provided on the front surface of said front wall and said stacked dielectric layer relfecting means is supported in front of and spaced from the antenna

7. A missile having a dual mode RF/IR radiation seeker substantially as hereinbefore described with reference to figure 1 and figure 2, 3 or 4 of the accompanying drawings.

6. An arrangement as claimed in any of Claims 1 to 4, wherein the reflecting surface of the optical reflector means is curved.

7. A radiation detector arrangement, substantially as hereinbefore described, with reference to, and as illustrated in, any of Figures 2 to 5 of the accompanying drawings.

Amendments to the claims have been filed as follows 1. A missile having a dual mode RF/IR radiation seeker which comprises a forwardfacing, cavityEacked spiral antenna for receiving radiation from within the fielof-view of the seeker, the spiral antenna being supported by the front wall, made of dielectric material, of an enclosure constituting a microwave cavity, the seeker further comprising stacked dielectric layer IR reflecting means supported by or in front of said front wall for receiving IR radiation from said field-of-view and reflecting it forwardly away from said antenna, and IR radiation detector means for receiving said IR radiation reflected by the reflecting means, and the arrangement being such as to define a generally common receiving aperture for said RF and said IR radiation.

2. A missile according to claim 1, wherein said spiral antenna is provided on the front surface of said front wall and said stacked dielectric layer reflecting means is provided on the front surface of said front wall to cover substantially all of said front surface where it is not covered by the spiral antenna, the surface of the spiral antenna being reflective to IR radiation.

3. A missile according to claim 1, wherein said stacked dielectric reflecting means is provided on the front surface of said front wall and said spiral antenna is provided on top of the reflecting means, the surface of the spiral antenna being reflective to IR radiation.

4. A missile according to claim 2 or 3, wherein said front surface is generally planar.

5. A missile according to claim 2 or 3, wherein said front surface is curved.