A choke comprising a magnetic core having a centre line that forms a closed loop, the choke has a choke axis around which the magnetic core is located, and a coil wound around the magnetic core, the coil has a plurality of turns, each of the turns has a width perpendicular to lengthwise direction of the turn, and a thickness perpendicular to both lengthwise direction of the turn and the width. The coil has a cross-section whose shape varies along lengthwise direction of the coil, such that each turn has an inner portion and an outer portion whose width is substantially greater than width of the inner portion, the outer portion is located further from the choke axis than the inner portion.