A Circularly Polarized Array Composed of Linear Polarized Microstrip Patches Fed by Metamaterial Transmission Line

A novel single-feed circularly polarized antenna array is constructed by a 2 × 2 array of four square linear polarized microstrip patches with orthogonal orientation and phase shift of 90° in between. The sequential rotation and suitable phasing of linear polarized microstrip patches improve the radiation pattern symmetry and input impedance matching of the array antenna. A metamaterial transmission line is designed and applied to feeding the antenna array. The metamaterial transmission line works at its zeroth order resonant mode and there is no phase shift between its four output ports. A circularly polarized antenna array at 5.8 GHz is built and demonstrated, which is fed by the metamaterial transmission line. The antenna array is compact and the whole dimension is about 1.1λ g 2. The antenna gain reaches 9 dBi, and shows a good axial ratio. Experimental results and simulation agree well.