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.