A Miniaturized Folded Antenna Array for MIMO Applications

In this paper, a novel cylindrical antenna array of a miniaturized structure is introduced for multi input multi output systems. The antenna array is consistent of four omega-shaped monopoles folded on a flexible cylindrical substrate of Kodak photo papers. The cylinder height is fixed to λ_o/4.5 with a diameter of λ_o/3.5, where λ_o is the free space wavelength at 2.25 GHz, with a separation distance between monopole elements of λ_o/29. The maximum mutual coupling between the monopoles elements over the frequency range from 2 to 3 GHz is found about −30 dB at the resonant frequency. Such coupling reduction is achieved by mounting conformal Spit Ring Resonators between the monopoles and backed by an electromagnetic band gap structure. An Ink-jet deposition process is used to print the array structure with sliver nano-particles on the substrate. Experimentally, S ₁₁ spectrum is measured as well as the radiation patterns on both E- and H-plans at 2.25 GHz. It is found, the proposed array exhibits a gain of 2.5 dBi with broad side radiation patterns. An excellent agreement is achieved between the measured and simulated results.