Performance improvement of closely coupled Loop antenna by shielding effect of planar negative permeability SRR and OCSRR and Thin Wire Metamaterial

摘要

Though less physical separation between two loop antenna make the compact design but increases electromagnetic interference due to near and far field radiations and also due to surface waves. This disturbs antenna parameters. To avoid effect of mutual coupling for the same physical separation, mutual coupling between two antennas should decrease. Two loop antennas are separated by the distance of λ/16 which is approximately 7.8mm at 2.5 GHz. Array of Thin Wire Metamaterial which exhibits negative permittivity at 2.5 GHz is inserted at the center of both antennas. Insertion of this array diverts phase vector due to surface wave and near field radiations. Almost 40 dB enhancement in isolation is observed over impedance band of 800 MHz. This has also corrected far field radiation pattern. Split Ring resonator which exhibits negative permeability is etched on the patch side and Open Complementary SRR which exhibits negative permittivity is etched on ground plane for two loop antennas. The complete structure is fabricated on FR4. To neglect the loss tangent for FR4, sufficient amount of return loss in dB over the desired frequency band at plasma frequency was considered. SRR along with OCSRR lengthen the path for current propagation which optimizes the dimensions of Unit Cell Metamaterial to fit in the available space at desired plasma frequency. The proposed antenna structure is composed of two Loop antennas occupying a space with the dimensions of 47mm*24mm*2mm and three Metamaterial Unit Cells. Placement of Metamaterial cell improves the isolation almost by -45 dBs. Remarkable improvement in -10 dB impedance bandwidth had been observed at 2.5 GHz. Proposed technique improves the impedance bandwidth for loop antenna for same number of loops and also improves its radiation pattern for minimum physical separation between loop antennas. This also helps to reduce overall dimensions. This leads frequency selective system over desired band.