DIPOLE CONFIGURATIONS WITH STRONGLY IMPROVED RADIATION EFFICIENCY FORHAND-HELD TRANSCEIVERS

In this paper the design criteria for antenna structures with improved radiation efficiency while operating in close vicinity to a biologica l scatterer were investigated. The study was performed using a simple lambda/2 dipole combined with a directive or reflective element. The o ptimization criteria were the effective radiation efficiency, the spat ial peak specific absorption rate (SAR), and the sensitivity of the in put resistance to the distance from the scatterer. It could be demonst rated that the primary design criterion to improve the radiation effic iency is not directivity but the reduction of the maximum incident mag netic field strength in the exposed skin area of the user's head. For the reflectively coupled dipole, all performance parameters could be i mproved by several decibels compared to a standard lambda/2 dipole, wh ereas for some other directive structures, the performance was impaire d. The study was conducted with the generalized multipole technique (G MT) numerical simulation method, the results of which were validated b y measurement methods.