GB850528A - Improvements in or relating to electromagnetic wave guides - Google Patents

Abstract

850,528. Variable impedances for waveguides. PHILIPS ELECTRICAL INDUSTRIES Ltd. April 16, 1957 [April 19, 1956], No. 12424/57. Class 40(8). A variable impedance device comprises a grid of parallel wires D mounted in a waveguide one quarter wavelength in front of a reflecting piston Z. The grid extends across the end of a cylinder C which also accommodates the piston. Incident energy whose direction of polarization makes an angle of a degree with the wires suffers a rotation in the direction of polarization of (180-2a) degrees on reflection from the device. Thus, when a = 45 degrees the directions of polarization of the incident and reflected waves are at right angles. The directional coupler A between the guides G1 and G2 in Fig. 2 provides zero coupling for the incident wave in G1 but couples the whole of the reflected wave polarized at right angles to the incident wave into the guide G2. The phase of the reflected wave may be varied by longitudinal movement of the cylinder and piston. In the construction of Fig. 3, a strip RE of absorbtive material is arranged in a plane at right angles to the direction of polarization of the incident wave. Rotation of the cylinder C may be used to vary the amplitude of the component of the reflected wave which is absorbed by the strip RE. The phase of the unabsorbed component may be varied by longitudinal movement of the cylinder and piston.