Waveguide corner junction with improved operation by use of diaphragms reflective at glancing angle

摘要

905,774. Waveguide bends and junctions. STANDARD TELEPHONES & CABLES Ltd. March 30, 1961, No. 11765/61. Class 40 (8). Two inclined rectangular waveguides are joined by a junction including a reflecting surface and dielectric diaphragms on either side of the junction, the material and dimensions of the diaphragms being such that they reflect energy incident on them at a glancing angle. Fig. 1 shows an H-plane section of a junction between two rectangular waveguides 1, 2 utilizing the H 01 mode of propagation. The waveguide mode may be considered to be the resultant of ordinary plane waves travelling at the velocity of light at an angle # = #/2a to the axis 7 and suffering repeated reflection from the walls of the guide. Since the dielectric diaphragms 5, 6 do not disturb the direction of wave fronts incident at near normal angles (# is exaggerated in the Figure), wave fronts whose paths are shown at 8 and 11 in guide 1 result in wave fronts 8SP1/SP and 11SP1/SP in guide 2 and no change in the manner of propagation arises. However, if both the diaphragms were transparent to wave fronts such as those shown in guide 1 at 9 and 10, wave fronts indicated by broken lines would result in both guides with consequent perturbation of the normal mode. According to the invention, the dimensions and dielectric constant of the diaphragms are such that where these wave fronts are incident at a glancing angle (at P and G) they suffer reflection and result in wave fronts 9SP1/SP, 10SP1/SP propagating in guide 2 in the desired direction. It is shown in the Specification that the dielectric constant of the diaphragms must be small and the width a of the guide large compared with the operating wavelength # if the desired results are to be obtained over a wide, e.g. 20%, band. The material may be foamed polystyrene having a dielectric constant of 4/3 and the width of the guide may be increased up to five wavelengths. The invention may be applied to a known kind of hybrid junction in which energy incident in either of guides 24, 27 is divided by a halfsilvered mirror between guides 25, 26. Diaphragms 30-33 are located between the junction and each of the guides. In the band separation filter of Fig. 4, a multi-layer dielectric sandwich filter 39 allows one frequency channel to be transmitted to guide 37 and reflects all other channels into guide 36. The junction between guides 35 and 36 is bounded by diaphragms 40, 41.