GB865367A - Improvements in or relating to microwave supporting structures - Google Patents

Abstract

865,367. Waveguides; coaxial lines; cavity resonators. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Aug. 28, 1958 [Aug. 28, 1957], No. 27073/57. Class 40(8) A microwave supporting structure has at least one reflecting wall comprising a quarterwave layer of dielectric material spaced a quarter-wave from a metal surface, the dielectric constant and loss factor of the dielectric material bearing a specified relation to the conductivity and permeability of the metal surface and the angular frequency of the supported microwave such that there is greater reflection from the combination of dielectric surface and metal surface than from the metal surface alone. Dielectric materials comprising ceramics consisting mainly of titanium dioxide are referred to. Laminated dielectric/air material can be used provided the electric field is substantially normal to the direction of lamination. As shown in Fig. 2 the dielectric surfaces 5 extend between the broad faces of the rectangular waveguide 6. In the construction shown in Fig. 3 a coaxial dielectric layer 7 is spaced from the guide wall 8 by a layer 9 of expanded polyethylene or polystyrene, the thickness of the layer 7 being small compared with that of the guide radius. In the cylindrical resonant cavity shown in Fig. 4 two #/4 discs 10 of dielectric material are spaced #/2 apart and #/4 from the end walls 11 of the cavity which is fed by an input loop 12 opposite an output loop 13. Cavity losses can be further reduced by increasing the radius of the side wall 14 and adding a cylindrical #/4 dielectric liner spaced #/4 from the side wall between the discs 10. The reduction in endwall losses is substantially independent of whether H- or E-mode waves are propagated, provided the dielectric constant of the material is greater than 10, except near the cut-off frequency.