4x4 Dual-Band MIMO Antenna with Low Mutual Coupling Using a Novel Structure of Neutral Line

A 4x4 dual- band MIMO Fractal-PIFA antenna with high isolation is designed and fabricated. The antenna operates at 2.6 GHz and 5 GHz with large bandwidth of 13.4% and 20.4% respectively for wide-band applications in portable terminals. Based on self affinity and lengthened shorting pin of PIFA structure, the single antenna is miniaturized up to nearly 90% comparing to traditional patch one. Being on RO 4350B substrate with the thickness of 1.52 mm, the proposed antenna gets compact size with approximate radiation patch size of 10.8x11mm(2) and total one of 74x75 mm(2). To get high isolation between radiation elements of MIMO antenna at so close distance of 3.13 mm from edge to edge, a novel structure of neutral line is presented with equivalent circuit model. The mutual coupling is lower than -20dB for both operating bands. All are simulated based on CST software.