This paper explores the application of the concept of characteristic modes on the chassis of a mobile phone to purposeful design of its radiation characteristics. Focus is on the resonant chassis modes which dominate the overall radiation properties. Modal radiation quality factors are derived from characteristic mode eigenvalues. Antenna -chassis coupling, previously only considered in terms of equivalent circuits, is discussed from a field theoretic point of view. A numerical approach for characteristic mode analysis is presented which is an eigenmode solver extension to the well known NEC2 code. Numerical results are given for wire grid models of a bar-type and a folder-type phone chassis.
The essential role of the resonant modes of the surface current density distribution on the chassis of a small size handheld terminal for its multiband radiation properties is discussed. An easy-to-implement practical approach for chassis mode analysis by post-processing of output data from standard CEM software packages is presented. The purposeful utilization and the tuning of chassis modes for the design of multiband radiation characteristics on generic bar-type and folder-type geometries is demonstrated and numerical results are given for several canonical examples.
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