In this thesis, the effect of the hand on antenna performance and RF exposure of the hand and head, is addressed. In the first study, the effect of the hand on over-the-air (OTA) performance of the transmitter is investigated. In the second study, the influence of the user’s hand holding a mobile phone to the ear on the peak spatial specific absorption rate (psSAR) was investigated both experimentally and computationally. The last study of this part describes remaining questions regarding the exposure of the hand, i.e., the fingers and palm. The mechanisms of absorption in the hand of electromagnetic (EM) fields in the 900 to 3700 MHz frequency range was analyzed, and the envelope of the psSAR of the hand with respect to the psSAR limits calculated. The second part of this thesis focuses on developing antenna configurations that couple effectively to specific tissue regions (tumors), so called hyperthermia treatment (HT). A novel HT applicator with a phased array is proposed, developed for treatment of tumors in the head-and-neck region. The design of the antenna array as well as optimization of patient positioning based on the location of the tumor is covered.