In this paper, impedance modeling is presented for analyzing the metallic loading effect on the performance of a split ring resonator (SRR) antenna in (2.4-2.5)/(5.1-5.8) GHz frequency bands. Two SRR antennas of rectangular and circular rings have been designed on ANSYS HFSS software, and their return losses are obtained as -16.63/-25.26 dB at 2.7/5.8 GHz and -10/-20.09 dB at 2.2/5.2 GHz, respectively. Then the metallic loadings are incorporated in both rectangular and circular SRR antennas, which move the peak resonant frequency to 2.5/5.1 GHz with simulated return losses of -14.39/-22 dB for rectangular SRR antenna and to 2.6/5.1 GHz with -17.64/-11.10 dB, respectively for circular SRR antenna. Then, to analyze the effect of metallic loading on SRR antenna performance, a set of equations are derived from the equivalent circuit of the SRR antenna without and with metallic loading to evaluate the lumped elements values. The circular SRR antenna with metallic loading is fabricated, and its measured return loss is found to be -17.94/-15.76 dB at 2.415/5.23 GHz. The lumped component values are calculated from the measured return loss using the derived equations, and these values are compared with those obtained from the simulated return loss for circular SRR antenna. A shift in resonant frequencies towards the desired bands is observed due to the inductive effect of the metallic loading. The axial ratio values higher than 15 dB confirm that the proposed SRR antennas with metallic loadings are linearly polarised. The 2D patterns in E-plane and H-plane, as well as 3D far-field patterns, confirm an omnidirectional radiation pattern for circular SRR antenna, which is useful for WLAN applications.
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