GB814310A - Improvements in or relating to highly active wide-band absorbers for short radio waves - Google Patents

Abstract

814,310. Radio wave absorbers. GENEST GESELLSCHAFT FUR ISOLIERUNGEN, W. Feb. 22, 1956 [Feb. 23, 1955], No. 5567/56. Class 40 (7). A wide-band radio wave absorber for preventing reflection by a wall comprises a plurality of electric or magnetic dipoles arranged in front of, at or in the surface of the wall, each dipole being associated with two resonant systems one of which is damped. Each magnetic dipole may comprise a conductive loop or a slot in a conductive surface. When the dipoles are resonant, e.g. #/2 conductors or slots, each dipole constitutes one resonant system and the other is provided by (1) spacing the dipoles from the wall, the space between the dipoles and the wall being preferably filled with lossy or loss-free dielectric or insulating material, Figs. 1-4, and Fig. 11 (not shown); or (2) coupling each dipole to a resonant circuit, Figs. 9 and 10 (not shown). When the dipoles are non-resonant, e.g. short linear conductors or small loop elements, each dipole is coupled to a resonant circuit and the other resonant system is provided by (1) spacing the dipoles from the wall, Figs. 7 (not shown), and Fig. 8; or (2) coupling each dipole to two interconnected resonant circuits. When the dipoles are spaced from the wall the spacing is (2n + 1)#/4 for electric dipoles and n#/2 for magnetic dipoles. Electric dipoles may be formed of conductive or lossy strips, e.g. conductive lacquer, graphite paper, colloidal graphite or impedance foil, applied to the solid filling the space between the dipoles and the wall; loss-free dipoles should be connected to a dissipative load, e.g. a graphite wedge, or damped resonant system, located behind the wall, Fig. 6 (not shown). When loop elements are employed, each loop element 15, Fig. 8, is arranged perpendicularly to the wall and may be formed of metal wire or graphite paper coupled to a resonant system 9 behind the wall 1 by a coaxial line 5. The resonant system 9 may comprise (1) lossy dielectric layers spaced from a conductive termination of the line 5, (2) grooves in the metallic or lossy inner and outer conductors of the line, or (3) a layer of iron powder in the coaxial line 5 and loss-free dielectric. When slot elements are employed the elements may be made lossy by filling the slots with lossy material or by forming the slots in an impedance foil; the associated resonant circuit may comprise a cavity resonator coupled to the slot by a waveguide. When resonant #/2 elements are employed they are spaced parallel to each other with a separation less than #/2 but non-resonant elements may be arranged in a random manner. Crossed dipoles may be employed to make the absorption independent of the polarization of the incident radiation; alternatively this may be effected by using parallel electric and magnetic dipoles.