Abstract: A dual-mode microwave applicator for treating tissue comprises a control unit, a rod-shaped element, a coaxial line, and a metal sleeve. The control unit controls the applicator in an application mode and a sensing mode. In the application mode microwave radiation is applied and during the sensing mode tumorous tissue is detected. The rod-shaped element comprises a tip. The coaxial line is formed in the rod-shaped element to relay microwaves to the tip for treatment of the tissue. The coaxial line comprises an inner conductor and an outer conductor. The outer conductor includes a slot of a slot length formed at a slot distance from the tip. The metal sleeve at a sleeve distance from the slot. The sleeve distance is about 0.55 mm, the slot length is about 1.75 mm, and the slot distance is about 7.7 mm.