An RF ablation system has a hollow conductive coaxial cable comprising inner and outer coaxial tubular conductors, and an ablating member mounted at the distal end portion of the cable for delivery of radio frequency energy including microwaves to the target body tissue. The inner conductor has a central lumen and extends at least up to the ablating member. At least one electromagnetic tracking sensor coil with a magnetic core is located in the central lumen at the distal end portion of the cable, close to the distal tip of the cable, and connected to a signal processing unit. An electromagnetic field generator positioned in the vicinity of a patient undergoing treatment generates an electromagnetic field which induces a voltage in the sensor coil. The signal processing unit uses the induced voltage to calculate the position and orientation of the distal end portion or tip of the catheter in a patient's body.