Design of a Microstrip Monopole Slot Antenna With Unidirectional Radiation Characteristics

A design procedure for a wideband planar unidirectional antenna is presented based on the monopole slot antenna. Owing to the additional capacitance contributed by a stub-protruded feedline and two symmetrical stubs at the slot edge, the impedance-matching condition is improved; meanwhile, the resonance frequency of the monopole slot antenna is significantly shifted down, and an improvement in impedance bandwidth is achieved. By modifying 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.