A unidirectionally radiating monopole slot antenna

A wideband planar antenna with unidirectional characteristics is demonstrated based on the monopole slot antenna. By utilizing a stub-protruded feedline and adding two symmetrical stubs at the slot edge, the impedance-matching condition is improved. The resonance frequency of the monopole slot antenna is significantly shifted down, and the impedance bandwidth is enlarged. By changing the width of the ground plane, connecting one metallic finger at the upper right corner, and etching two asymmetrical slits in the ground plane as reflectors, the radiation directivity of the monopole slot antenna can be enhanced. The proposed antenna achieves a measured 97.4 % bandwidth for S₁₁ <; -10 dB at the center frequency of 2.31 GHz, better than 10 dB front-to-back ratio.