5G wireless technology provides ultra high data rates, very low latency, more capacity, and good quality of service. In order to get ultrahigh data rates and high bandwidth, the technology uses mm-wave, which has a frequency spectrum from 30 GHz to 300 GHz. In 5G mobile handsets, the space left for antenna design is very small. As a result, in this thesis, we investigate multi-band phased array antennas for 5G mobile handsets that have higher bandwidth, gain and isolation. Consequently, we designed a novel multiband antenna with rectangular and circular shapes that can operate in three and four frequency bands, respectively. To enhance the bandwidth and isolation, we used the techniques of defected ground structure and metamaterials. The antenna was designed using a Rogers RT Duroid 5880 substrate with 2.2 permitivity and copper as the conducting material. The CST(Computer Simulation Technology) Microwave Studio software has been used to create the necessary antenna, while MathLab is being used for simulation and dimension calculations. The multiband eight-element array antennas have overall sizes of 70.06mm×7.89mm× 0.8mm and 80mm×12mm×0.8mm for rectangular and circular shapes, respectively. This size demonstrates that the antenna is appropriate for mobile phones. The simulation’s results show that rectangular and circular multiband antennas, respectively, have band-widths of 5.64 GHz and 7.384 GHz and isolation levels of - 40 dB and -35 dB. In addition to these performance measuring parameters, the S parameter for rectangular multiband antennas is below-26 dB and for circular multiband antennas is between -18.7 dB and -61.7 dB, with operating frequencies ranging from 27.6 GHz to 54.3 GHz for both shapes. A phased array with a rectangular or circular shape has an efficiency of more than 85%, a gain of 12.5 dB to 15.5 dB, and an envelope correlation coefficient of 0.0001/0.0002 and more than 9.93 DG(diversity gain), respectively. Key Words: Defected ground structure, Isolation, Metamaterial, Multiband, Millimeterwave,Phased array