Variable-impedance matching between the antenna and the RF-frontend provides several potential advantages, including changing operational frequency, compensating for unintentional mismatch, improving scanning capability, and reducing noise and interference signal levels. In this article a concept of tuning the operational band of an antenna by variable-impedance matching is presented. In this investigation a 65 nm CMOS RF-frontend capable of changing its input-impedance is used to tune the operational band of a microstrip antenna. It is shown that by properly selecting the input-impedance of the RF-frontend, the operating frequency of the antenna can be shifted, which increases the total operational bandwidth from 10 MHz to more than 30 MHz.