New short backfire antennas for wireless applications

A low-cost wideband short backfire antenna (SBA) and a circularly polarized (CP) SBA are presented. The low-cost SBA designed for the 5 GHz UNII band is excited by a planar monopole which is printed on a dielectric substrate and fed by a microstrip line. By splitting the printed monopole with a slot, wideband performance is achieved. It is demonstrated that the low-cost SBA can achieve an impedance bandwidth of 15% (VSWR<2). The CP SBA is excited by a cross aperture with an unbalanced feed that consists of two orthogonal H-shaped slots with a pair of capacitive stubs. It is shown that the CP SBA can achieve an axial ratio (≤3 dB) bandwidth of 4.2% with a VSWR bandwidth of 6.5% (VSWR<1.2) and a gain of 14 dBi. As high-gain and low-cost wideband/CP directional antennas, the new SBAs can find applications in various wireless communications systems (such as LMDS, WLAN, and the emerging WiMAX networks) and wireless power transmission.