GB597923A - Wave-signal transmission line having an adjustable terminal impedance - Google Patents

Abstract

597,923. Electric resonators. HAZEL. TINE CORPORATION. Oct. 30, 1945, No. 28813. Convention date, Nov, 16, 1944. [Class 40 (iii)] The impedance at the terminals of a transmission line is varied by means of magnetic material surrounding one or both conductors and so shaped as to have a substantial coefficient of reflection. In the coaxial line 40, 41, Fig. 2, a cylinder 42 of magnetic material slides along the inner conductor 41. When it is at a current antinode it increases the distributed inductance and so lengthens the line electrically and affects the terminal impedance. The slider 42 is long rather than broad, in order to leave a clearance and so prevent arc-over and to prevent the impedance from being affected by tolerance variations ; it terminates sharply so that the resulting discontinuity of impedance may give rise to reflection. It is about oneeighth wavelength long in a quarter-wave line or about quarter wavelength long when the line is longer than half a wavelength, in order to secure a maximum range of variation. The cylinder 42 may have thin walls, Fig. 1 (not shown), in order that it may not affect the distributed capacity of the line, or it may be in contact with either the inner or the outer conductor, Figs. 3, 4 (not shown). The slider may comprise a mass of dielectric having magnetic particles embedded in it. When the slider is at a voltage node, the dielectric increases the electrical length of the line while the magnetic material has little effect. The Specification gives formulµ for determining the effective permeability and dielectric constant which will yield a required impedance characteristic, the magnetic effect predominating. The slider constructed of such material may fill the space between the conductors as at 45, Fig. 5 ; or if it has a permeability greater than 2 it may be enclosed in a conductive shell 52, Fig. 7, having a web 54 which may be central as shown or located at one end, Fig. 6 (not shown). A pair of Lecher wires 80, 81, Fig. 8, may be embraced by sliding magnetic cylinders 85, 86, joined by a web 87 of dielectric. The corners of the sliders 42 or 85, 86 may be rounded to prevent corona discharge. The device may be arranged as a resonator for tuning in oscillator, Fig. 1 (not shown). Specification 597,922 is referred to.