Experimental determination of the loss mechanisms in a mobile handset chassis

Measuring the efficiency of an antenna mounted on a mobile handset chassis can generally be considered a destructive measurement as the phone has to be disassembled to reach the feed point of the antenna and to measure its radiated power e.g. in an anechoic chamber. The errors caused by the RF cable, i.e. perturbations of the radiated fields by surface currents induced on the cable shield, form a considerable problem. The solution presented is to consider the chassis-antenna combination as a resonance circuit consisting of two or more resonators, and to determine the quality factors of the chassis resonator by measuring its resonance curves in an external field, both in free space and while located in a waveguide below cut-off. From the quality factors the radiation efficiency of the chassis currents can be determined. At frequencies below 1 GHz the chassis can be considered as the main radiator, while the antenna element is merely the feed of the chassis. It is therefore important to access the chassis resonance especially at frequencies below 1 GHz. First results shown in this paper indicate that the radiation efficiency of the chassis was 90% or more for the tested 3 phone models, which amounts to less that 0.5 dB conductive and dielectric losses in the chassis