Helical coil, method of producing same and helical antenna using same

Abstract

A helical coil and a top-helical type antenna using the same, wherein the helical coil has a plurality of either substantially U-shaped or nearly V-shaped branch portions made of a thin metallic sheet material. The branch portions are connected continuously in a manner to place their open ends alternately inversely, and the branch portions alternatively curve toward an obverse side and a reverse side of the metallic sheet to form each turn of the coil. A method for producing the helical coil includes continuously die cutting a member on a belt-shaped strip of electrically conductive metallic sheet, and alternately placing a plurality of either substantially U-shaped or substantially V-shaped branch portions with their open ends inversely. These substantially U or V-shaped branch portions are then connected with each other in the shape of a letter, with connection to the metallic sheet being held only by linkage portions at opposite sides. The helical coil is formed by alternately curving the branch portions of each of the members in a shape of substantially circular arc toward an obverse side and a reverse side of the metallic sheet. A bobbin is formed connecting each turn of the helical coil by either insert-injection molding or outsert-injection molding of electrically nonconductive material on the individual helical coil formed on metallic sheet and subsequently the linkage portions are sheared off of the metallic sheet.