Abstract: An iris and shutter arrangement for a camera, particularly a CCD camera, in which a first liquid crystal display is formed of a plurality of concentric annuli of liquid crystal material and a second liquid crystal display is provided as a further plurality of coaxial annuli each of which overlies the space separating one annuli from the next in the first display. The first display also includes a relatively clear central circular area, defining the smallest aperture desired, which is covered by a circular area of liquid crystal material in the second display. The annuli in both cases are continuous save for breaks along a line forming a path for control conductors deposited upon the faceplates of the two displays.

Abstract: A thyratron comprises an anode and control grids between which is located a double layer screen grid. Thermionic cathode material is inserted in an aperture in the part of the screen grid furthest from the anode, and in operation this is heated to the required temperature by hot plasma which surrounds it, thus eliminating the need for a cathode heater.

Abstract: A gas discharge device includes an anode, an enclosure member having an aperture therein and substantially enclosing a volume of a gas filling, and a mechanism for injecting electrons into the volume of gas filling to produce ionization of the gas filling within the volume so that during operation of the device, the enclosure member and the ionization within the enclosure member constitute a cathode, and a conduction path is established between the interior of such cathode and the anode through the aperture of the enclosure member.

Abstract: A coupled cavity travelling wave tube has a coupling wall/ferro-magnetic pole piece formed as an iron-copper-iron sandwich with a coolant channel therein defined at least in part by the inner copper member of the sandwich. Where the coolant channel is defined also in part by a surface of an outer ferromagnetic member, at least that surface is electroplated.

Abstract: A coupled cavity TWT comprises a hollow copper tube having a plurality of tranverse walls of iron which define cavities. The walls each include an aperture on the longitudinal axis of the tube through which an electron beam passes during operation of the TWT. Any energy dissipated by electrons colliding with the surfaces of the apertures is conducted as heat away from the walls along thermal conduction paths which include copper elongate members.

Abstract: Klystrons are inherently non-linear and have an amplification characteristic which is frequency dependent on both signal amplitude and beam current. This may be compensated for by applying suitable correcting signals to a beam controlling electrode of the klystron thereby changing its electron beam current over the whole excursion of a modulating signal. A klystron arrangement in accordance with the invention is particularly suitable for use in a television transmitter, enabling full time modulation to be carried out with a significant improvement in the operating efficiency of the klystron.

Abstract: To determine some spatial characteristic, such as size or shape, of an object, the object is viewed with a television camera that employs an image sensor such as a CCD device. An image is formed on a television screen and a set of measurement markers (or cursors) are superimposed on the image at desired positions. The CCD timing signals are used to accurately determine the position of the cursors and hence the desired spatial characteristic.

Abstract: An external cavity klystron vacuum tube has a ceramic cylindrical wall surrounded by an external cavity within which is an output probe. The cylindrical wall section is sealed at its ends to other components of the tube--to enable the interior to be evacuated--by sealing means such as to avoid a sharp edge projecting inwardly towards the interior of the cavity.

Abstract: A coupled cavity travelling wave tube of the space harmonic type is provided wherein the interaction gaps in successive cavities are alternately offset towards the input end of the slow wave structure and towards the output of the slow wave structure, whereby beam electrons which are synchronous at band edge frequencies tend to experience a phase reversal in the electro-magnetic wave propagating in the slow wave structure, at each successive interaction gap.

Abstract: A thyratron includes an envelope containing a gas filling, an anode, an intermediate grid, control grids and a cylindrical structure which acts as a cathode heat shield in a conventional thyratron. In operation the intermediate grid is maintained at cathode potential and, when triggering pulses are applied to the control grids, the gas filling ionizes and the thyratron becomes conducting. The main part of the current comes from the intermediate grid which acts as a "hollow" cathode, and enables the thermionic cathode conventionally used to be dispensed with if desired.

Abstract: The present invention provides apparatus for forming electron beams, which may be advantageously employed in many applications, for example in display devices or thyratrons. A cathode member has a hole in its front surface. All the surfaces of the cathode member, except for the wall and base of the holes, are covered in an electrically insulating material such as glass. The cathode member and an anode member are contained within an envelope which also contains a gas filling. On application of a suitably high voltage between the cathode and anode members an electron beam is formed extensive in a direction away from the hole. The anode member may be located behind the front surface of the cathode member, and an electron beam still forms in front of the front surface.

Abstract: A display arrangement consists of a tubular envelope with fluorescent stripes running along its length, localized portions of which are illuminated by different electron guns which produce flood beams of electrons. Field electrodes which surround each electron gun determine the angular direction at which the flood beam leaves the gun and hence which one of the fluorescent stripes is caused to emit light. The stripes can be of three different primary colors, to produce a colored display.

Abstract: A display arrangement consists of a tubular envelope with fluorescent stripes running along its length, localized portions of which are illuminated by different electron guns which produce flood beams of electrons. Each gun is situated within a switchable magnetic field which determines the angular direction at which the flood beam leaves the gun, and hence which one of the fluorescent stripes is caused to emit light. The stripes can be of three different primary colors, to produce a colored display.

Abstract: A radar system having a common antenna for transmitting and receiving signals conventionally includes a branch duplexer which is bulky and inconvenient.By using a waveguide section having an antenna port at one end and a receiver port at the other, and including a protection unit comprising p.i.n. diodes these difficulties are reduced. The diodes prevent transmitted energy from a magnetron reaching the receiver port but allow received energy, because of its lower amplitude, to pass.

Abstract: A resonant cavity device--particularly a magnetron oscillator--has a separate resonator coupled to a resonant cavity of the device. The separate resonator consists of a resonant transmission line within which are two multipactor discharge arrangements, one being positioned at a distance along a resonant transmission line which is approximately 3.lambda./4 from the end of the transmission line adjacent the cathode and the other of which is positioned at a distance along the resonant transmission line which is .lambda./4 from the same end of the transmission line. By controlling the multipactor discharges of the multipactor discharge devices appropriately three different frequencies of operation are available.

Abstract: The invention provides a travelling wave tube having a directly heated cathode. Cathode material is applied in a depression in one U-shaped member of a high resistance alloy material and the return path for heater current is provided by another U-shaped strip member beneath the first. The configurations of the two strip members are similar so that stray magnetic fields generated by the equal but opposite currents flowing therein, tend to neutralize one another. In another embodiment the two strip members are replaced by generally cylindrical members, one member being within the other. The surface of the member providing the return path for heater current is polished where it faces the member carrying the cathode material so as to reflect back heat radiated by the last-mentioned member.

Abstract: Television cameras using solid-state image sensors may be required to provide a good image of a scene under all normal night and day ambient light conditions. The available solid-state image sensors can cope satisfactorily with normal daylight, but do not have sufficient sensitivity to operate under night time conditions, so it is common to amplify the incident illumination with an image intensifier. To stop the intensifier from becoming overloaded by daylight, neutral density optical filters can be moved in front of the intensifier as the light level increases, but this is not a satisfactory solution. The invention proposes a camera incorporating two solid-state sensors, one of which is intensified and one of which is not, in the same camera head, and "switching" one or the other into operation (depending upon the ambient lighting conditions) by switching the light received by the camera to the appropriate sensor.

Abstract: A display arrangement particularly suitable for displaying video signals representing a thermal image. Successive horizontal lines of a television raster pattern are offset, or staggered, by a small amount so as to remove vertical stripe patterns which are caused by digital processing and storage of the video signal. This results in a much more acceptable visual display.

Abstract: A magnetic thyratron interrupter is provided having between an anode and a cathode a structure having an aperture therein for a discharge presenting a succession of surfaces in the direction of discharge which are contacted when the discharge is moved by applying a magnetic field transversely to the discharge direction. Examples of structure are stacks of discs having concentric holes which are alternately of larger and smaller diameter and a strip of gauze wound into a spiral.

Abstract: A display arrangement utilizes a fluorescent screen 3 to provide readily alterable bright displays. The arrangement can provide a fairly large display surface, but can be of very small thickness. It contains electron emissive cathodes 5, and field electrodes 7 positioned closely adjacent to the cathode to control the emission of free electrons. Electrons which are freely emitted are accelerated to a mesh electrode 4 which is held at a modest positive voltage. A fluorescent screen 3 having a positive potential of several thousand volts is positioned closely in front of the mesh electrode. In preferred embodiments of the invention, a number of separate cathodes and/or separate field electrodes are provided, so that selected regions of the screen can be illuminated to provide desired display patterns. Individual regions of the screen can be switched on and off (i.e. rendered bright or dark) by the application of very low switching potentials to the field electrodes and/or the cathodes.