Low-SAR capacitively coupled compact multiband antenna for smartphones

A compact planar antenna for modern multistandard smartphones is presented, which can operate in three bands: GSM (890-960 MHz), GPS (1500 MHz) and DCS (1710-1880 MHz). The proposed antenna is comprised of a feeding monopole and three radiating strips. The feeding monopole capacitively couple the RF excitation signal to the radiating strips. The length of these strips can control resonant frequencies of the antenna. The antenna is designed on a single-layered FR4 substrate. It has a total size of 37 mmx50 mmx 1.6 mm. Due to its compact structure the antenna can be directly printed on the circuit board to integrate with other parts of the circuits of a smartphone. The antenna possesses a reflection coefficient of better than -10 dB and nearly omnidirectional patterns over all the operating bands. Moreover, the directivity (>1.5 dB) and efficiencies (>70%) of the antenna are appropriate for modern smartphone applications. The effects of plastic housing, LCD screen and a human hand on the antenna performances are studied. The SAR (Specific Absorption Rate) values of the proposed antenna that absorbed into human head are also presented and it complies well with the standard of both the European Council in Europe and the Federal Communications Commission (FCC) in the United States.