An RF sensing apparatus configured for use with a plasma processing chamber includes a penetration unit opened in an up/down direction, a main return path unit surrounding all or a portion of the penetration unit, and a secondary return path unit located between the penetration unit and the main return path unit, spaced apart from the main return path unit, and surrounding all or a portion of the penetration unit. The main return path unit and the secondary return path unit include a path through which a current flows in one of the up/down directions.