Numerical analysis of characteristic modes on the chassis of mobile phones

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.