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    Future smartphone: MIMO antenna system for 5G mobile terminals
    (IEEE-Institute of Electrical and Electronics Engineers Inc., 2021) Abdullah, Mujeeb; Altaf, Ahsan; Anjum, Muhammad Rizwan; Arain, Zulfiqar Ali; Jamali, Abdul Aleem; Alibakhshikenari, Mohammad; Falcone, Francisco; Limiti, Ernesto
    In this article, an inverted L-shaped monopole eight elements Multiple Input Multiple Output (MIMO) antenna system is presented. The multi-antenna system is designed on a low cost 0.8 mm thick FR4 substrate having dimensions of 136 x 68 mm(2) resonating at 3.5GHz with a 6dB measured bandwidth of 450MHz, and with inter element isolation greater than 15 dB and gain of 4 dBi. The proposed design consists of eight inverted L-shaped elements and parasitic L-shaped strips extending from the ground plane. These shorted stripes acted as tuning stubs for the four inverted L-shaped monopole elements on the side of chassis. This is done to achieve the desired frequency range by increasing the electrical length of the antennas. A prototype is fabricated, and the experimental results show good impedance matching with reasonable measured isolation within the desired frequency range. The MIMO performances, such as envelope correlation coefficient (ECC) and mean effective gain (MEG) are also calculated along with the channel capacity of 38.1bps/Hz approximately 2.6 times that of 4 x 4 MIMO system. Due to its simple shape and slim design, it may be a potential chassis for future handsets. Therefore, user hand scenarios, i.e. both single and dual hand are studied. Also, the effects of hand scenarios on various MIMO parameters are discussed along with the SAR. The performance of the proposed system in different scenarios suggests that the proposed structure holds promising future within the next generation radio smart phones.
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    Isolation improvement in UWB-MIMO antenna system using slotted stub
    (MDPI, 2020) Altaf, Ahsan; Iqbal, Amjad; Smida, Amor; Smida, Jamel; Althuwayb, Ayman A.; Hassan Kiani, Saad; Alibakhshikenari, Mohammad; Falcone, Francisco; Limiti, Ernesto
    Multiple-input multiple-output (MIMO) scheme refers to the technology where more than one antenna is used for transmitting and receiving the information packets. It enhances the channel capacity without more power. The available space in the modern compact devices is limited and MIMO antenna elements need to be placed closely. The closely spaced antennas undergo an undesirable coupling, which deteriorates the antenna parameters. In this paper, an ultra wide-band (UWB) MIMO antenna system with an improved isolation is presented. The system has a wide bandwidth range from 2-13.7 GHz. The antenna elements are closely placed with an edge to edge distance of 3 mm. In addition to the UWB attribute of the system, the mutual coupling between the antennas is reduced by using slotted stub. The isolation is improved and is below -20 dB within the whole operating range. By introducing the decoupling network, the key performance parameters of the antenna are not affected. The system is designed on an inexpensive and easily available FR-4 substrate. To better understand the working of the proposed system, the equivalent circuit model is also presented. To model the proposed system accurately, different radiating modes and inter-mode coupling is considered and modeled. The EM model, circuit model, and the measured results are in good agreement. Different key performance parameters of the system and the antenna element such as envelope correlation coefficient (ECC), diversity gain, channel capcity loss (CCL) gain, radiation patterns, surface currents, and scattering parameters are presented. State-of-the-art comparison with the recent literature shows that the proposed antenna has minimal dimensions, a large bandwidth, an adequate gain value and a high isolation. It is worth noticeable that the proposed antenna has high isolation even the patches has low edge-to-edge gap (3 mm). Based on its good performance and compact dimensions, the proposed antenna is a suitable choice for high throughput compact UWB transceivers.