US Patent 10354838 RF antenna producing a uniform near-field Poynting vector

An apparatus for generating plasma, including a quadrupole antenna having a center region and an outer region and configured to be disposed over a dielectric window of a plasma chamber. The quadrupole antenna including a first coil defining a first SDA and a second coil defining a second SDA, the first coil being in a nested arrangement within the second coil. The nested arrangement places a turn of the first coil to be adjacent to a corresponding turn of the second coil as the first and second coils spiral from the center region to the outer region of the quadrupole antenna. Adjacent turns of each of the first and second coils are horizontally separated from one another by a distance when disposed over the dielectric window.