Thermal loss becomes an issue for narrow-band tunable antennas in fourth generation handsets

Antenna tuning is a very promising technique to cope with the expansion of the mobile communication frequency spectrum. Tunable antennas can address a wide range of operating frequencies, while being highly integrated. In particular, high-Q antennas (also named narrow-band antennas) are very compact, thus are good candidates to be embedded on fourth generation handsets. This study focuses on `high-Q´ tunable antennas and contributes with a characterisation of their loss mechanism, which is a major parameter in link-budget calculations. This study shows, through an example, that the tuner loss is not sufficient to explain the total loss of tunable antennas. It is found that thermal loss -because of the metal conductivity of the antenna itself - plays a major role in the loss mechanism of narrow-band tunable antennas. The investigated high-Q planar inverted F antenna designs exhibit a significant thermal loss; at 1400 MHz nearly 2 dB are lost solely because of the copper conductivity. Thermal loss poses a limitation to achievable performance of tunable antennas and to antenna miniaturisation.