Study On Multiple Antennas For Small Handsets

The multiple antenna design for small handsets is a difficult problem for MIMO system design because of the limited mounting space. Usually, it is desired that the multiple antenna elements have the performance of wideband, low mutual coupling and high efficiency. But the realization of the performance is severely restricted by the antenna size. It is a multi-parameter multi-objective optimization problem under the multi-bonudary conditions essentially. But it is difficult to solve mathematically. How to reduce the mutual coupling between antenna elements is one of the key problems for multiple antenna design in small mobile terminals. The technique for reducing coupling can be categorized into two kinds: one is the usage of ground branches; the other is the design of decoupling network. The antenna is affected by user's hand when using. How to avoid the hand effect and how to design the performance margin should be considered.For the techniques of ground branches for reducing the mutual coupling, firstly, a dual-element antenna is proposed, in which the T-shaped and two inverted L-shaped ground branches are used. It covers the UMTS and 2.4GHz WLAN bands with a low mutual coupling about -20dB. Secondly, a cross shaped branch with meandered lines is designed. By using this ground branch, a four-element antenna for clamshell phone is proposed. It also covers the UMTS and 2.4GHz WLAN band with less than -10dB coupling in the whole working band.For the techniques of decouling network for reducing mutual coupling, firstly, two kinds of decoupling network are proposed. One is composed of a microstrip line and match networks, the other is compsed of a hybrid coupler and matching networks. The rigorous theoretical analysis is given. Secondly, by using the decoupling network, a dual-element antenna is proposed, which works at 2.4GHz WLAN band. The error analysis is also given.For user's hand effect on the performance of antennas, firstly, the user's hand effect on bandwidth, mutual coupling and radiation patterns is studied with the simulation and measurement method. Secondly, a direct channel measurement campaign is accomplished to study the user's hand effect on the performance of MIMO systems. Corresponding conclusions can guide the multiple-antenna design for small handsets.