Characteristic mode based pattern reconfigurable antenna for mobile handset

Pattern reconfigurability is a desirable feature of mobile handset antennas, as it enables the antennas to adapt to non-stationary propagation environments. However, it is difficult to vary the radiation pattern of a handset antenna at frequencies below 1 GHz because the entire chassis commonly acts as the main radiator. Hence, designing pattern reconfigurability based on the antenna element (secondary radiator) alone can severely limit the achievable pattern diversity. In this work, a dual-band (0.85-0.90 GHz and 1.93-2.11 GHz) handset antenna with pattern reconfigurability at the low band is designed by loading the periphery of the chassis with a metal bezel. The bezel loading adds a new resonant characteristic mode to the chassis, on top of the fundamental resonant mode. These two modes are selectively excited for pattern reconfigurability using a suitable feed and two PIN diodes, which yield an envelope correlation of below 0.2 in the low band (0.07 at 0.87 GHz). Moreover, since the proposed antenna is fully integrated into the bezel structure, it does not occupy any extra space on the chassis, which also allows more antennas to be implemented, e.g., for MIMO applications.