Broad-band and circularly polarized space-filling-based slot antennas

Based on the use of space-filling curves, broad-band and circularly polarized microstrip-fed slot antennas are proposed. Broad-band performance is achieved through merging different downscaled versions of a composition of "island-like" space-filling slot antennas without increasing the overall antenna size. This technique provides different resonant slot lengths corresponding to a wide range of frequencies. By merging three downscaled versions of a composite second-iteration Moore slot antenna, a broad-band slot antenna is developed. The proposed antenna has a bandwidth (VSWR<2) of 87.6% around 4.5 GHz, which is higher by a factor of 13.5 compared to the square ring slot antenna, and by a factor of 3 compared to the nested square rings slot antenna. The developed slot antenna has a maximum gain of 5 dB and a total area of 3×3 cm². Furthermore, by introducing asymmetry in the proposed slot antenna, which is implemented by replacing all parallel slots on one side of the structure and all inner slots by a ground plane, circular polarization is achieved. The circularly polarized slot antenna version has a 3-dB axial ratio bandwidth of 22% with VSWR<2. The design and simulation of the proposed slot antennas have been performed using a moment-method-based full-wave electromagnetic simulator. Measurements of fabricated antennas are in good agreement with simulation results.