GB1605280A - Antenna arrangements - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ANTENNA ARRANGEMENTS (71) WE, EMI LIMITED. a British Company of Blyth Road, Hays. Middlesex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to antenna arrangements, and it relates especially, though not exclusively, to such arrangements for transmitting antennae used in short range radar applications and in which separate receiving antennae are cmployed.

In some short range radar applications, for example as may be used in proximity fuzing systems for missiles arranged to fly closely adjacent a source of cluttcr, such as the sea, separate transmitting and receiving antennae are used. It has been found that clutter signals can swamp target signals and it has been proposed, in order to reduce the effcct of clutter signals, to arrange that the polarisation of the receiving antenna is rotated through about 9() as compared with the polarisation of the transmitting antenna. In practice, it is convenient to maintain the receiving antenna unchanged and to modify the design of the transmitting antenna so as to rotate its polarisation through ahout 9() . Difficulties arise, however, in providing a modified transmitting antenna which exhihits sufficicnt beam width to he useful.

According to the invention there is provided an antenna arrangement comprising a tubular waveguide of nominally rectangular crosssection having an array of slots in one wall thereof, the slotted wall being formed with relatively inclined surface portions which intersect to form an apex, substantially parallel to the waveguide axis. the slots being I)'iccd apart along said axis and disposed transversely thereto and said slots being disposed symmetrically about, and including. said apex.

In order that the invention may be clearly understood and rcadily carried into effcct, some embodiments thereof will now be described by way of example only with reference to the drawings filed with the Provisional Specification, of which: Figure I shows a conventional slotted waveguide, the slots being spaced apart along the waveguide and disposed parallel to the longitudinal axis thereof, Figure 2 shows, in perspective view, on a slotted waveguide for use in an antenna arrangement in accordance with one example of the invention, and Figures 3(a) and 3(h) show cross sectional views through two alternative forms of the waveguide shown in Figure 2.

Referring now to Figure 1, there is shown a waveguide 1 of tubular form, the waveguide being rectangular in cross section. The axis of the waveguide is shown at 2 and a plurality of radiating slots 3, 4 and 5 are formed in one wall of the waveguide, the slots being spaced apart in the axial direction of the waveguide and disposed with their larger dimension along the waveguide. This represents a conventional arningement for a transmitting antenna; the receiving antenna being similar. In the event that it is desired to rotate the polarisation of the transmitting antenna through 9()" relative to that of the receiving antenna, for the reasons described previously, it has been found that if the slots 3, 4 and 5 are merely turncd through 90 so that they lie transverse to the axis 2, the heamwidth of the antenna in the plane perpendiculir to the axis 2 is insufficient for missile fuzing purposes. The beamwidth of the antenna as shown in Figure I in the ifiorementioned plane is about IX() (as between 3dB points) whereas the corrcsponding heamwidth of an antenna similar to that shown in Figure I hut with the slots rotated through 9() , in the same pliny is only about 5(P In accordance with the invention, however, an increase ill beamwidth over the 5(1 'ichieved as described above is eficeteil hy forming the slotted wall ()f the waveguide with t inclined wall portions which intersect to form an apex which runs pirillel to the longitudinil axis of the waveguide. The slots are arranged transverse to the apex and intersect it. the apex being arranged to effectively bisect each of the sloths. Such an arrangement is shown in Figure 2, wherein a waveguide 6 has slots 7, 8, 9 and 10 firmed in one wall thereof, and the slotted wall comprises two inclined wall portions 11 and 12 which meet in an apex 13.

The apex 13 runs parallel to the longitudinal axis of the waveguide 6 and it bisects the slots, 7 to 10, which are disposed transversely of the waveguide axis. Such an arrangement has been found to have a beamwidth (between 3dB points) in the plane perpendicular to the waveguide axis of at least 1()0 .

Figures 3(a) and 3(b) show cross-sectional views of two alternative configurations for the waveguide 6. In Figure 3(a) the inclined wall portions 11 and 12 are of similar (though not necessarily identical), thickness as the remainder of the waveguide walls, whereas in Figure 3(b) the "roof" portion of the waveguide 6 is solid, apart from the slots such as 7.

In an alternative configuration, the slotted wall may constitute two inclined curved portions which abut together to form a cusp which extends parallel to the longitudinal axis of the waveguide.

What we claim is: 1. An antenna arrangement comprising a tubular waveguide of nominally rectangular cross-section having an array of slots in one wall thereof, the slotted wall being formed with relatively inclined surface portions which intersect to form an apex, substantially parallel to the waveguide axis, the slots being spaced apart along said axis and disposed transversely thereto and said slots being disposed symmetrically about. and including, said apex.

2. An antenna arrangement according to Claim 1 wherein said slotted wall comprises two relatively inclined planar portions.

3. An antenna arrangement according to Claim I wherein said slotted wall comprises two relatively inclined curved portions which abut to form a cusp at said apex.

4. An antenna arrangement substantially as herein described with reference to Figures 2 and 3(a) or 2 and 3(b) of the drawings accompanying the Provisional Specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. portions 11 and 12 which meet in an apex 13. The apex 13 runs parallel to the longitudinal axis of the waveguide 6 and it bisects the slots, 7 to 10, which are disposed transversely of the waveguide axis. Such an arrangement has been found to have a beamwidth (between 3dB points) in the plane perpendicular to the waveguide axis of at least 1()0 . Figures 3(a) and 3(b) show cross-sectional views of two alternative configurations for the waveguide 6. In Figure 3(a) the inclined wall portions 11 and 12 are of similar (though not necessarily identical), thickness as the remainder of the waveguide walls, whereas in Figure 3(b) the "roof" portion of the waveguide 6 is solid, apart from the slots such as 7. In an alternative configuration, the slotted wall may constitute two inclined curved portions which abut together to form a cusp which extends parallel to the longitudinal axis of the waveguide. What we claim is:

1. An antenna arrangement comprising a tubular waveguide of nominally rectangular cross-section having an array of slots in one wall thereof, the slotted wall being formed with relatively inclined surface portions which intersect to form an apex, substantially parallel to the waveguide axis, the slots being spaced apart along said axis and disposed transversely thereto and said slots being disposed symmetrically about. and including, said apex.

2. An antenna arrangement according to Claim 1 wherein said slotted wall comprises two relatively inclined planar portions.

3. An antenna arrangement according to Claim I wherein said slotted wall comprises two relatively inclined curved portions which abut to form a cusp at said apex.

4. An antenna arrangement substantially as herein described with reference to Figures 2 and 3(a) or 2 and 3(b) of the drawings accompanying the Provisional Specification.