The present invention relates to an antenna system (1, 101, 201, 301, 401, 501) for tracking of a position of a target area (33, 133, 233, 333, 433, 533) within a body (5, 105, 205, 305, 405, 505), comprising a first antenna device (3, 103, 203, 303, 403, 503) and a second antenna device (9, 109, 209, 309, 409, 509), at least said second antenna device (9, 109, 209, 309, 409, 509) is to be located outside said body (5, 105, 205, 305, 405, 505), wherein an interface region (13, 113, 213, 313, 413, 513) between said body (5, 105, 205, 305, 405, 505) and at least said second antenna device (9, 109, 209, 309, 409, 509) at least partially consist of a dielectric medium having a relative permittivity closer to the permittivity of material within the body (5, 105, 205, 305, 405, 505) than the permittivity of air.