Abstract: An antenna formed by an array of dipole elements fed by a triplate or stripline system is provided with earthed posts between the dipoles. These posts prevent radiation from one dipole being received by others thereby improving the antenna efficiency.

Abstract: An improved microwave switch incorporating a fin line structure is described. Microwave switches incorporating fin line structures enable microwave energy to be passed to a load or reflected back to the source, by controlling the conductance state of diodes mounted on the fin line structure. The present invention enables the electrical performance of such switches to be greatly improved. The height of a waveguide channel in the vicinity of the fin line structure is very greatly reduced thereby forcing a waveguide mode of propagation into a slot line so that the fin line structure receives substantially all of the energy supplied to the switch. Higher order modes which are generated at the fin line structure are attenuated by lossy material positioned in choke cavities mounted on either side of the fin line structure.

Abstract: A target tracking airborne active radar system in which a reduction in transmitter power is achieved by using individual amplifiers in the aerial quadrant channels. The amplifiers provide gain on transmission and negligible loss on reception and are realized by Impatt diode/hybrid junction modules.

Abstract: The invention is concerned with the provision of a dipole radiator for feeding a parabolic reflector and provides a half wave dipole arranged at the mouth of a shallow cavity. The cavity is preferably circular with a diameter approximately three times its depth. In an example of linearly polarised radiator a cylindrical cavity is provided having a diameter of 0.72.lambda. and a height of 0.26.lambda. and the half wave dipole element is positioned 0.26.lambda. above the base of the cavity so that the dipole element extends beyond the cavity. In an example of circularly polarised radiator two crossed half wave dipole elements are provided, one of which is arranged to be inductive and the other of which is arranged to be capacitive. The cylindrical cavity has a diameter of 0.66.lambda. and a height of 0.28.lambda. and the crossed dipole elements are positioned 0.22.lambda. above the base of the cavity so as to lie flush with the mouth of the cavity.