Mobile terminal antennas implemented using optimized direct feed

A novel antenna structure based on optimized direct feed is presented in this paper. The antenna structure consists of the chassis of a mobile terminal, a feed structure and a matching circuitry. The chassis is cut in two pieces, which are connected with an inductor. The value of the inductor is tuned so that the lowest resonant frequency of the chassis equals the center frequency of the operating band. The feed structure excites very strongly the resonant wavemode of the chassis and thus very large bandwidth is available. The feed structure can be integrated e.g. on the PCB of a mobile terminal and thus the antenna is very low-profile. The antenna structure has been demonstrated with a simulated and measured prototype that covers the GSM850/900 systems.