GB597251A - Improvements in or relating to electromagnetic waveguides - Google Patents

Abstract

597,251. Wave-guides. ALLEN, W. D. June 20, 1945, No. 15789. [Classes 40 (iii), and 40 (v)] A device for effecting transformation of the mode of wave propagation in a wave-guide comprises a member of dielectric material having a dielectric constant different from that of the dielectric medium of the guide, placed in the guide, and so shaped and dimensioned that a phase change is imparted to a selected portion of the wave, so that upon recombination of the two wave portions, the desired mode change is effected. Fig. 5 shows an arrangement for changing an E01 wave in a circular guide 10 into an H11 wave in a circular guide 15. A semicylindrical block 11 of dielectric material is placed in the guide. The length and dielectric constant of the material of block 11 are such that a 180 degrees phase-shift is introduced in the radial electric component in the. lower half of the guide. On recombination of the two halves, the field pattern in that of an H11 wave. Guide 15 has a diameter which is too small to sustain an E01 mode wave, while sustaining an H11 wave. The edges of block 11 are chamfered to reduce reflection. A resonant ring 14 of the kind described in Specification 597,216 is provided to eliminate undesired modes. The block 11 may be used in a similar manner to produce an H11 wave in a circular guide when fed by a coaxial line joined end to end on a common axis (Figs. 8 and 9, not shown). Fig. 6 shows an arrangement for converting a plane polarized H11 mode wave into a circularly polarized wave. A dielectric plate 16 is diametrically disposed in the guide at an angle to the electric vector e4 such that after passing the plate, there exist two equal electric vectors e5, e6 at right angles, thus providing a circularly polarized wave. The above devices are also applicable to rectangular wave-guides.