Wideband circularly polarized metasurface backed aperture antenna
Date of Issue2012
School of Electrical and Electronic Engineering
A wideband, unidirectional, single feed, circularly polarized octagonal-aperture antenna backed by single and double layered meta-surface has been proposed and studied. The octagonal-aperture antenna is fed by an L-shaped strip to excite two orthogonal modes for generating circularly polarized radiation. An impedance transformer is used to improve the matching of the antenna. The unidirectional circularly polarized radiation has been achieved using a 00 reflection phase metasurface in place of conventionally used planar metal reflector. The octagonal-aperture antenna with three different reflector surfaces: single and double layered meta-surface and planar metal surface was designed and optimized using CST MWS EM software. All three antennas were then fabricated on a low cost FR4 substrate and measurements were taken. Measured results of the octagonal aperture antenna over all three surfaces have been compared to validate the proposed antenna designs. As observed through simulations and justified by theory, octagonalaperture radiator gives wider axial ratio and impedance bandwidths for single and double layered meta-surfaces as compared to that of metal surface in measurements. The measured results of the octagonal-aperture antenna prototype over the single layered meta-surface are 26.7 % (5.30-6.90 GHz) for 3-dB axial ratio bandwidth and 36.2% (4.97-7.14 GHz) for VSWR<2 impedance bandwidth. The measured gain is 6.33 dBic at 6.0 GHz band in the boresight direction. The measured results for the octagonal-aperture antenna prototype over the double layered meta-surface are 33.2% (5.20-7.19 GHz) for 3-dB axial ratio bandwidth and 36.2% (5.04-7.21 GHz) for VSWR<2 impedance bandwidth. The measured gain is 6.97 dBic at 6.0 GHz band in the boresight direction. For planar metal surface backed octagonal-aperture antenna, the measured axial ratio bandwidth is greater than 5 dB and VSWR<2 impedance bandwidth is 99.7 %. The overall antenna volume for the proposed designs is 0.72 1...0 x 0.60 1...0 x 0.19 1...0 at 6.00 GHz. In conclusion, unidirectional wideband circularly polarized aperture antenna backed with meta-surfaces has been proposed and designed. These antennas have met design specifications suitable for wireless communication such as WLAN applications.
DRNTU::Engineering::Electrical and electronic engineering::Antennas, wave guides, microwaves, radar, radio