GB756192A - Improvements relating to microwave phase-shifting devices - Google Patents

Abstract

756,192. Microwave phase-shifting circuits. FERRANTI, Ltd. Feb. 14, 1955 [Feb. 17, 1954], No. 4613/54. Class 40 (8). A microwave phase-shifting device for a transmission system in which the transmission path is required to have one or other of two electrical lengths according to whether the power transmitted is above or below a certain level comprises a waveguide " turnstile " junction with a gas discharge cell in the circular-section branch. The turnstile junction comprises four similar rectangular guides 11, 12, 13, 14 assembled with their broad sides in the same plane to form a rectangular cross from the centre of one side of which extends a circular guide 15 with its axis normal to the broad sides of the rectangular guides. The circular guide 15 contains a circular sealed resonant aperture 16 and a short-circuiting disc 18 the space between these elements being filled with an ionizable gas. The guides 12, 14 are shortcircuited at distances from the junction which differ by a quarter-wavelength of the transmitted energy. Half the energy arriving at the junction from the input guide 11 is coupled directly into the circular guide 15 whilst the remaining half divides equally between the guides 12, 14. These two components are reflected back to the junction in antiphase and are coupled into the circular guide 15. The wave energies coupled directly and indirectly into the guide 15 are plane-polarized in mutuallyperpendicular directions. The positions of the short-circuits in guides 12, 14 are preferably arranged so that the direct and indirect components are in phase quadrature and produce a circularly-polarized wave in the guide 15. This wave is reflected either at the aperture 16 or at the disc 18 according to whether its energy is sufficient or insufficient to cause discharge of the gas cell. Thus for a path difference of a halfwavelength between high- and low-energy wave the distance between the aperture 16 and the short-circuit 18 is made equal to a quarterwavelength. The whole of the output appears in guide 13. In a modification the guide 15 is extended axially to form a reservoir for the gas cell, the disc 18 being provided with a small communicating aperture. The Specification refers to a known arrangement for achieving the above results in which the input energy is divided equally between two branch guides having matched cells and short-circuits beyond the cells.