A frequency tunable embedded normal-mode helix antenna for portable wireless devices

A frequency tunable normal mode helical antenna is presented for wireless mobile handsets. This antenna is placed across the width of the handset chassis, which is considered as part of the radiating structure. It is shown that by keeping the length of the helix antenna constant and varying the pitch angle (height) of the antenna, the frequency of operation can be tuned to switch between various frequency bands to cover all standard 3G and 4G bands required for the next generation of mobile handsets. Variation of the helix pitch angle is implemented using a shape memory alloy (SMA) spring placed in parallel with the antenna. Extraction and contraction of this spring and therefore the antenna is controlled by passing a DC current through it. FIT simulation results (CST™) are presented for the tunable helix antenna with the SMA spring effect included in the model. Antenna design criteria are also discussed.