Patent GB-597258-A (GB)
Title: Improvements in or relating to electro-magnetic wave guide devices
IPC: H01Q3/32
Filed: 1945-07-14
Abstract: 597,258. Wave-guides ; directive radio systems. PICKUP, E., BACON, G. E., and BROOK, P. H. T. July 14, 1945, No. 18070. [Classes 40 (iii) and 40 (v)] In a wave-guide device, a suitably shaped mass of dielectric material having a dielectric constant of different value from that of the normal dielectric medium of the guide is movable within the guide between positions of different electric field strengths for varying the effective electrical length of the guide portion containing the dielectric material. In Figs. 1-3, a rectangular guide 10 carrying an H01 wave has located in it a bar 11 of dielectric material. When the bar is in positions a, a' of relatively weak electrical field strength, it has little effect. On moving to the central position b of maximum field strength, it effectively increases the electrical length of the guide section. The bar may be moved and supported by dielectric rods 12 spaced a quarter wavelength apart and passing out through apertures in the guide. To prevent reflections from the ends of the bar 11, the ends may be tapered or as shown, formed with quarter wave steps m. For use with an H02 wave, two bars moved symmetrically on either side of the central plane are employed (Figs. 7 and 8, not shown). For circular wave-guides, Fig. 9, bars 55, 56 having a curved transverse section are employed. Fig. 9 shows the arrangement for an E01 wave, in which the bars 55, 56 are supported by dielectric rods 57 so as always to be spaced symmetrically relative to the central plane. Suitable dielectrics are plastics of the polystyrene, polyethylene and polyisobutylene groups having dielectric constants of the order of 2 or 3, and very low power factors. Alternatively, the dimensions of the bars may be reduced by using ceramics having a dielectric constant of about 6 to 16. Fig. 5 shows an application to a radar system in which two reflectors 24, 25 are required to operate alternately in in-phase and anti-phase relation. The reflectors 24, 25 are connected to a common wave-guide 26 leading to transmitting and receiving apparatus, through a horn 27 and branch 28 and horn 29 and section 30 respectively. Branch section 30 contains a dielectric bar 32 which is arranged to be moved abruptly from the central position to the side position by electromagnetic means 33 to effect a phaseshift of 180 degrees. The device may be remotely controlled by switch 35. Instead of moving the bar abruptly it may be moved continuously to and fro by cam means moved by an electric motor (Fig. 6, not shown) to cause the polar diagram to scan to and fro through a predetermined angle. Fig. 4 shows an arrangement in which energy from a guide 15 is switched by means 16 alternately to reflectors 13, 14 radiating in different directions. The branch to reflector 14 includes a dielectric bar 22, the position of which can be manually adjusted by a screw-and-nut mechanism 23. The device is set up by switching to reflector 13 and adjusting for optimum radiation. Switch 16 is then operated to energize reflector 14 and the bar 22 is adjusted for optimum radiation. Specifications 597,216 and 597,217 are-referred to.