Abstract: A polarizer screen for a satellite communications terminal, comprising a plurality of layers separated by dielectric material, each layer having a grid of parallel metal strips and a periodic distribution of interleaved metal dipoles, wherein a first set of dipoles is arranged to be perpendicular to the metal strips and a second set of dipoles is arranged to be parallel to the metal strips such that any linearly polarized electromagnetic waves that pass through the screen are converted into orthogonal circular polarization in different frequency bands.

Abstract: A waveguide structure including two parallels electrically conducting ground planes (1,2), each of which includes at least one row of spaced apart electrically conducting posts (3). The rows of posts are arranged substantially parallel to one another and the space bounded by the plates and posts defines a guided wave region (4) along which electromagnetic radiation may propagate. The posts are connected to only one of the planes so that there is no physical connection between the two ground planes (1,2). Actuating means may be connected to one or both of the ground planes to cause relative movement there between to thereby alter the electrical response of the waveguide. The direction of the relative movement may such that the distance between the rows of posts (3) is changed and/or the distance between the ground planes (1,2) is changed. Various device may utilize the described waveguide construction, including reconfigurable waveguide filters and antenna structures e.g. slotted waveguide arrays.

Abstract: A flat plate or slab antenna (1) is fabricated from a number of sandwiched layers in which a number of arrayed individual antenna elements (3) are formed. The antenna elements (3) each include a horn (12) with a rectangular aperture (13) feeding (or fed by) individual rectangular waveguides (15). Two orthogonal probes (17,20) protrude into each waveguide (13), each of which is connected to respective beamforming networks. The network of first probes (17) operates at a first frequency while the network of second probes (20) operates at a frequency which is different from the first frequency. In the preferred embodiment, the edges (13) of the horn apertures (12) are parallel to the sides (6, 7, 8, 9) of the antenna slab while the walls of the rectangular waveguides are at 45° to the sides (6, 7, 8, 9) of the slab. The antenna (1) is able to receive and/or transmit two orthogonally linearly polarised signal at different frequencies and is therefore capable of full duplex operation.