Coaxial lightning arresting structure

A coaxial lightning arresting structure comprising an inner conductor, an outer conductor surrounding the inner conductor and an arrester tube located between portions of the inner and outer conductors perpendicularly to the direction of transmission and connected at its ends to the inner and outer conductors, respectively, the portion of said outer conductor provided with the arrester tube having an equivalently substantially increased inner diameter as compared with the other portions of the outer conductor so that the ratio of the inner diameter of said outer conductor portion having said increased inner diameter to the inner conductor outer diameter is greater than the ratio of the outer conductor inner diameter at the other portions thereof to the inner conductor outer diameter, which latter ratio provides the coaxial transmission line with a given characteristic impedance, said outer conductor portion having the equivalently substantially increased inner diameter also being provided with a through-hole which is relatively large with respect to the arrester tube, for insertion of the arrester tube into the lightning arresting structure such that the through-hole surrounds the inserted arrester tube, and a cylindrical cap member being fitted in said arrester tube insertion hole formed in the outer conductor portion, said cap member being formed with a hole opening toward the inner conductor for accommodating a portion of the arrester tube in said cap member in relatively close-fitting relationship.