GB761764A - Microwave transmission line - Google Patents

Abstract

761,764. Transmission line arrangements. STANDARD TELEPHONES & CABLES, Ltd. May 1, 1953 [May 8, 1952], No. 12113/53. Class 40 (8). The lateral extent of the dielectric layer in a microwave strip transmission line is adjusted to promote propagation of the TEM mode with minimum loss. The transmission line is of the type described in Specifications 704,050 and 708,601 and comprises two conductors 1, 2 printed or otherwise disposed on either side of a dielectric layer 3b a small fraction of a quarter line-wavelength thick. It is shown in the Specification that coupling with undesired modes of propagation can be minimized by making the dielectric layer 3b, Fig. 4, extend to either side of the line by a distance #e/2, where #c is the free-space wavelength in the dielectric. The same object may be achieved (Fig. 5) by making the lateral extent equal to #s/2, where #s is the wavelength of TM mode surface waves propagated parallel to the surface of a plane conductor coated with a thin layer of dielectric. For practical purposes #s=#o, where #o is the free-space wavelength. In this case the conductor 2a is arranged to extend the full width of the dielectric. In a further arrangement (Fig. 7) the dielectric extends for a distance #s/4 and is provided with conductive coatings 14 on its outer edges. In a modification of this arrangement the conductor 2b extends to the outer conductive edges 14. The same effect can be obtained where the lateral extension equals #e/2 by replacing the conductive strips 14 by strips of ferrite material. Fig. 10 shows an example of a double line based on the arrangements shown in Figs. 5 and 7. A multiple line may be formed by arranging dielectric layers on either side of a tubular copper braid 21 forming a common conductor for the inner and outer lines 23, 27. The spacing of the lines is similar to that shown in the arrangement of Fig. 10.