Axial Ratio Extension of Circularly Polarized Patch Antennas using Diamond-shaped Metasurface

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Abstract
This talk presents bandwidth enhancement technique of axial ratio (AR) in 1 -point-fed circularly polarized (CP) microstrip antennas using metasurface (MS). In these structures, MSs consisting of a rectangular unit cell have been used for widening the impedance bandwidth in addition to the AR bandwidth. The author called this structure artificial ground structure (AGS) for the dual purpose. The AGS has been installed underneath the patch antenna with two truncated corners, and the substrates have a relative permittivity of ε r = 2.2 and loss tangent of tan δ = 0.001 (ROGERS RT/Duroid 5880). The AGS has the function of an AMC for expanding the -10-dB S 11 bandwidth. Also, the AGS can convert the incident wave of linear polarization (LP) or elliptical polarization (EP) to CP reflected wave. This mechanism can extend the AR bandwidth. However, this expansion is sometimes limited by resonances in related to the outer circumference of the MS structure. If the circumference is rectangular, that is the dimension along x is different from that along y, an extra difference of phase causes in x- and y- components of the radiated field resulting in deteriorated AR.