Hassan, Muhammad Mateen creator Supervised by Dr. Adnan Ahmed Khan text Rawalpindi MCS (NUST) 2021 monographic xiv, 119 p Modern wireless communication systems demand multi–band operation, higher data rate, channel capacity and better link reliability. Such requirements can be met by the usage of multiple input multiple output (MIMO) antenna system. The complexity of the MIMO antenna system has been reduced by the implementation of frequency reconfiguration approach. The frequency reconfiguration characteristics has been achieved by introducing radio frequency micro–electro– mechanical–system (RF MEMS) switches in the antenna system. The features of RF MEMS switch that distinguish it from other existed active switches include low power loss, wide impedance bandwidth, low insertion loss and high isolation. The thesis presents a novel design of two element MIMO frequency reconfigurable antenna system consisting of two semi–circular ring–shaped strip–lines with a rectangular slot on the top conducting layer and a U–shaped slot on the bottom side of the substrate. The dimensions of the proposed antenna system are 32 × 98 × 1 mm3. Frequency reconfigurable characteristics of the proposed MIMO antenna system has been achieved by using single pole four throw (SP4T) RF MEMS switch. To achieve the better performance from the proposed antenna system, the SP4T switch has been used in the U–shaped slot etched in the ground plane of the substrate. The frequency reconfigurability of antenna system has been switched at the frequencies of 600 MHz, 1.8 GHz, 2.4 GHz, 3.5 GHz and 5.5 GHz bands. Isolation greater than 15 dB has been achieved at all the operating bands without addition of any decoupler structure. The measured peak gains of 3.4 dB, 3.8 dB, 4.3 dB, and 4.4 dB have been achieved at 1.8 GHz, 2.45 GHz, 3.5 GHz, and 5.5 GHz respectively. Average peak radiation efficiency of 59% has been observed at all operating bands of MIMO frequency reconfigurable antenna system. The calculated envelop correlation coefficient (ECC) less than 0.04, diversity gain (DG) greater than 9.8 dB and total active reflection coefficient (TARC) less than –10 dB have been observed at all operating bands during operation. Muhammad Mateen Hassan PhD Electrical Engineering Thesis PhD EE Thesis 621.382,HAS 20260207120110.0