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Abstract
A novel compact circularly polarized microstrip antenna using left-handed transmission lines is proposed in this paper. The antenna consists of a microstrip patch unit and two left-handed transmission line (LHTL) units. The microstrip patch unit is a square patch with a small square slot embedded in the center. The left-handed transmission line units located in the center of the square patch is composed of lumped elements, which work as 3 dB power dividers and 90 degrees phase shifters. The microstrip antenna is fed by a single probe, and the two inner adjacent sides of the square patch are connected to the LHTL units for orthogonal excitation. The measured results agree with simulated results, which show that the impedance bandwidth defined by VSWR less than 2.0 is 61 MHz (2481–2542 MHz). The front-to-back ratio on the pattern is larger than 15 dB and the axial ratio in the up hemisphere less than 2 dB. The proposed antenna has the attractive features such as compact size, low axial ratio, and simple structure.