A design procedure for a dual-band CPW-fed linearly and circularly polarized (CP) antenna based on the L-shaped slot antenna is presented in this paper. The slot antenna and the feeding structure are fabricated on the same plane of the substrate so that circuit processes and position alignment can be simplified. By shortening the length of one arm of the L-slot, an additional mode with two orthogonal electrical fields with a phase difference of 90 degree is excited, so that the circularly polarized wave can also be excited. The enhancement of the resonant bandwidth is achieved by utilizing a stub-protruded feedline, adding one finger slit at the other arm slot, and tuning the dimension of the ground plane. A bandwidth of 22.0% (2.23-2.78 GHz) is achieved with an axial ratio < 3 dB for the optimized case.

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