This paper presents a design of a small size antenna in the L-band for applications of microwave hyperthermia treatment and microwave imaging of the human head. The design is intended to provide an increase of the power radiated toward the human and concentrate the specific absorption rate (SAR) values in the tumor tissue. Size reduction is achieved here by adding a high dielectric layer just above the antenna, and the best suitable material for this application is found to be the fresh water. The design depends on a short circuit triangular slotted shaped on a thick foam substrate to enhance its bandwidth. Analysis is performed using the IE3D and SEMCAD-X simulators, and the obtained overall antenna size is 404014 mm3. The resonance frequency in air is 2.35 GHz at free space, which is reduced near the head to 1.4 GHz, using a 5-mm water layer pad. Simulation analysis is provided of the SAR patterns associated with this antenna.