**2.1 Dual-band implantable antennas**

The medical industry is continuously developing efficient and advanced systems that are suitable for the human body. In previous years, the ISM band was mainly used for antenna design [25], but the United States Federal Communications Commission (FCC) and the European Radio-communications Committee (ERC) allocated a frequency for biomedical telemetry [24, 26]. Communication between implants and the external unit is easy with the MICS band and ISM band used to send the awake signal to an external unit. MICS band is similarly intended for data communication, the ISM band is wilful for startup signals.

To design dual-band, implantable antennas is a shift between sleep and wake-up mode for conserving energy and increasing the lifetime of antennas. The dual-mode operation generally improves the lifetime of the battery [27]. The advantage of a differentially fed dual-band implantable antenna can be connected easily with differential circuits, useful to help eliminate loss introduced by baluns and matching circuits [28, 29]. From the following **Table 1**, we can observe that Differential feed antenna is generally operated on two nearly frequencies/frequency bands such as 433.9 and 542.4 MHz [28, 34] and MICS (402–405 MHz) and ISM (2.4–2.48 GHz) [35, 36, 38]. Also dual-band antennas operated on two frequency bands such as MICS (402– 405 MHz) and ISM (2.4–2.48 GHz) [27, 29, 33, 37, 40] 1.4 and 2.4GHz [39].
