Patent ID: 7317372

Claim:
An air-core coil comprising unit coil portions each having at least one conductor wound into a spiral form, the unit coil portions being arranged repeatedly axially of the coil, each of the unit coil portions comprising a plurality of unit turn portions which are different from each other in inner peripheral length and which are in direct contact with each other, the unit turn portions of small inner peripheral length being at least partly forced inwardly of the unit turn portions of great inner peripheral length, wherein the plurality of unit turn portions providing each of the unit coil portions are sequentially wound from an inner peripheral side to an outer peripheral side, or from the outer peripheral side to the inner peripheral side, one unit turn portion on an outermost periphery or on an innermost periphery being connected to another unit turn portion on an outermost periphery or on an innermost periphery, respectively, of the adjacent unit coil portion.