Analysis of Dual-Band Helical Antenna for Diversity on Mobile Phones

Antenna diversity on a mobile phone is considered using two dual-band, GSM900/1800, helical antennas. The received signals in mobile Rayleigh fading channel are modeled using a new field simulation technique that involves the three-dimensional (3D) radiation pattern of antennas, 3D angle of arrivals (AoAs) and Doppler frequency. Statistical tools prove the validity of the field simulator. The signals correlation coefficient and diversity gain are computed for different mobile propagation environments by considering AoAs. It is shown that the diversity gain is slightly influenced by the environment models. The experimental prototype is developed and measured. Antenna characteristics: return loss, coupling, 3-D radiation patterns and antenna efficiency are obtained by the measurements and simulations. The diversity performance of the array configuration is measured in the rich wave scattering environment of a reverberation chamber (RC). Results including: signals correlation coefficient, average power of diversity branches, apparent/effective diversity gain and antenna efficiency in RC are provided. The influence of the mobile user is measured as well. Diversity gain of the helical array in both operating frequencies is fairly good. The signals correlation with user’s head increases in GSM900 and slightly decreases in GSM1800. In the former band, the diversity gain loss due to imbalance branch powers is found more important than in the later.