PURPOSE: To make an apparatus smaller, as it maintains insulating properties, and to eliminate machining to reduce a manufacturing cost by forming the longitudinal section of a central conductor into an H-shape and by providing a first groove shaped into a ring, in the manner of coaxially facing the central conductor, and a second groove.
CONSTITUTION: A central conductor 21 forms an H-shape in the longitudinal section, and an insulator 22 is formed by a main body part 23 on the central conductor 21 side, a flange 24 thinner than the main body part 23 on the outer peripheral end side and a U-shaped groove 25 as a first groove. Also, a semicircular groove 26 is provided as a second groove in the vicinity of the boundary between the insulator surface 22a and U-shaped groove 25. The H-shielded central conductor 21 forms a recessed part in the boundary of the insulator 23, the central conductor 21 and an insulating gas to prevent a triple junction. When the width of the U-shaped groove is selected in a specified manner, it is possible to suppress the electric field strength of the insulator surface. Thus, the diameter of a spacer is reduced and working properties are improved.
YOSHIDA TETSUO
MASAKI NOBUO
