In this paper, we propose an asymmetric dipole antenna utilizing the metal case as a ground radiator for a pen-type wireless presenter which operates in the ISM frequency band(2.4~2.48 GHz). A normal mode helix mounted on the top end of the long metallic cylinder case which acts as the ground plane takes the form of the asymmetric dipole structure in the proposed antenna. The metallic cylinder case which performs as a radiating element increases the inherent narrow bandwidth and low gain of the helix. The effects of the hand contacts with the metal case on the antenna performance are measured and analyzed with a specially designed human phantom. Experimental results show that the -10 dB return loss bandwidth of the proposed antenna in free space(no hand contact) is 200 MHz that ranges from 2.3 to 2.5 GHz and the maximum gain is measured to be 5 dBi. Under the normal operating condition where the metal case is contacted with a human hand, the bandwidth is 480 MHz from 2.24 to 2.72 GHz. The maximum gain is 2 dBi, lowered by 3 dB due to the hand contact.
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