A wideband stepped-impedance open-slot antenna with end-fire directional radiation characteristics

In this paper, new techniques are proposed to increase the front-to-back ratio of the stepped-impedance (SI) open-slot antenna for operation from 1.67 GHz to 4.25 GHz, covering the required frequency bands of the wireless communications systems, such as DCS, PCS, IM-2000, and WLAN. By designing a stub-protruded feedline and adding two symmetrical stubs at the edge of a quarter-wavelength slot, additional capacitance is introduced to the resonator. Hence, the impedance-matching condition of the SI open-slot antenna is not only effectively improved, but also the resonance frequency of the slot antenna is significantly shifted down and then an improvement in impedance bandwidth is achieved. In order to decrease the back radiation, two pairs of symmetrical open slots with uniform width are etched at the back of the blocking open slot such that the currents along the longitudinal edges of the ground plane cannot flow to the back direction. In addition, by embedding an array of seven slits beside the radiating slot, the back lobe at the upper frequency bands can be reduced. Two pairs of three-element metal strips are utilized as a power director to increase the forward power and enhance the front-to-back ratio of the SI open-slot antenna. Compared to conventional unidirectional radiation antennas, the proposed antenna demonstrates improved wideband unidirectional radiation characteristics and relatively smaller size.