Abstract
This paper presents a miniaturized dual-mode handset antenna design. A quadrifilar helix antenna (QHA) is utilized to work at higher band (1980-2010 MHz and 2170-2200 MHz) with circular polarization. By cutting off a circular slot on the outer conductor of the QHA feedline and introducing four quarter-wavelength short-circuited stubs, the QHA radiator and its feedline can also work as a monopole antenna at lower band (440-560 MHz) with linear polarization. With this radiator-sharing technique, the dual-mode characteristics can be achieved utilizing only a QHA; therefore, the antenna dimension can be reduced remarkably since it is unnecessary to design an additional monopole antenna. Moreover, the short-circuited stubs are designed with stripline and integrated with the one-to-four power divider and phase shifter for further miniaturization. The measured S11 is less than -8 dB. The typical gain is higher than 0.5 dBi at lower band and 2.5 dBi at higher band. The AR of the QHA is better than 1.3 dB, and the head SAR values are much lower than the international standard at both lower and higher bands. The proposed miniaturized dual-mode antenna can be applied to portable handsets to realize the intercom and satellite communications.
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