Patent GB-1416343-A (GB)
Title: Radomes
IPC: H01Q1/42
Filed: 1972-02-16
Abstract: 1416343 Radomes DEFENCE SECRETARY OF STATE FOR 5 March 1973 [16 Feb 1972] 7081/72 Heading H4A A radome comprises at least two parallel, spaced apart dielectric material layers each having superimposed thereupon at least one polarizing grid comprising parallel wires, the wires of each grid being inclined to the wires of adjacent grids. As described, a radome comprises a pair of spaced apart dielectric material layers 1, 2, Fig. 1, each consisting of a single sheet. Mounted on the inner surface of the layer 1 is a polarizing grid 4 of parallel wires, and mounted on the outer surface of the layer 2 is a similar grid 5. The wires of the two grids are at an angle 0 to each other, and said angle should not exceed 22¢ degrees to avoid impedance matching difficulties. The thickness of each dielectric material layer is not less than # d /10 (# d  = wavelength in the dielectric material at the operating frequency), the spacing between adjacent wires in each grid is # 0 /16, and the spacing between the layers is # 0 /4 (# 0  = wavelength of oncoming radiation at the operating frequency). The space 3 between the layers 1, 2 may be filled with rigid plastic foam. The radome is mounted with the layer 1 facing a linearly polarized radiating source, and so disposed that the wires of the grid 4 are inclined at an angle 0 to the transverse to the E-field rector of the emitted waves. The grids 4, 5 then each effect a polarization rotation of 0, making 2# in all. In a second embodiment, Fig. 4 (not shown), two dielectric material layers as in Fig. 1, are each provided with polarizing grids of parallel wires on both faces. The wires of the grids on each layer are inclined at an angle 0 to each other as are the wires of the grids on each side of the space between the layers. A total polarization rotation of 40 is obtainable, i.e. with # = 22¢ degrees, a rotation of 90 degrees. In a third embodiment, shown in Fig. 6, dielectric material layers 1, 2 with polarizing grids 4, 5 as in Fig. 1 are circularly shaped and are edge driven by means of a shaft 8. A differential means 9 mounted on the shaft 8 rotates the layer 1 through a desired angle, and a second differential means 10 mounted on the shaft 8 rotates the layer 2 through twice that angle. In this way, the total polarization rotation of 2# may be adjusted as required. Such an arrangement may be mounted in front of a parabolic reflector which has a radiating waveguide feed (Fig. 7, not shown). In another embodiment, Fig. 8 (not shown), each of two circularly shaped spaced apart dielectric material layers comprises two sheets in contact and is provided with polarizing grids of parallel wires on both faces. Each sheet (carrying one polarizing grid) is rotatable by a common drive shaft through a respective differential means. If the sheet nearest the feed is rotated by a certain angle, then the other sheets in order are rotated by twice, thrice and four times that angle. A total adjustable polarization rotation of 4# is thus obtainable. The wires of the outermost polarizing grid in any embodiment may be resistive and be joined in series at their ends, when passage of an electric current will cause heating, and melt any ice which has accumulated.