Mutual Coupling (MC) is the exchange of energy between multiple antennas when placed on the same PCB, it being one of the critical parameters and a significant issue to be considered when designing MIMO antennas. It appears significantly where multiple antennas are placed very close to each other, with a high coupling affecting the performance of the array, in terms radiation patterns, the reflection coefficient, and influencing the input impedance. Moreover; it degrades the designed efficiency and gain since part of the power that could have been radiated becomes absorbed by other adjacent antennas' elements. The coupling mechanism between multiple antenna elements is identified as being mainly through three different paths or channels: surface wave propagation, space (direct) radiation and reactive near-field coupling. In this thesis, various coupling reduction approaches that are commonly employed in the literature are categorised based on these mechanisms. Furthermore, a new comparative study involving four different array types (PIFA, patch, monopole, and slot), is explained in detail. This thesis primarily focuses on three interconnected research topics for mutual coupling reduction based on new isolation approaches for different wireless applications (i.e. Narrowband, Ultra-wide-band and Multi-band). First, a new Fractal based Electromagnetic Band Gap (FEBG) decoupling structure between PIFAs is proposed and investigated for a narrowband application. Excellent isolation of more than 27 dB (Z-X plane) and 40 dB (Z-Y plane) is obtained without much degradation of the radiation characteristics. It is found that the fractal structures can provide a band-stop effect, because of their self-similarity features for a particular frequency band. Second, new UWB-MIMO antennas are presented with high isolation characteristics. Wideband isolation (≥ 31 dB) is achieved through the entire UWB band (3.1-10.6 GHz) by etching a novel compact planar decoupling structure inserted between these multiple UWB antennas. Finally, new planar MIMO antennas are presented for multi-band (quad bands) applications. A significant isolation improvement over the reference (≥ 17 dB) is achieved in each band by etching a hybrid solution. All the designs reported in this thesis have been fabricated and measured, with the simulated and measured results agreeing well in most cases.

Yes

Antenna is one of the most important components in wireless systems since signal transmission and reception are conducted through the antenna interface. Therefore, the signal quality is highly affected by the properties of the antenna. Traditional antennas integrated in devices such as laptops or cell phones have fixed radiation properties and can not be changed to adapt to different environments. Thus the performance of thefwhole system will be negatively affected since the antenna will not operate in the optimum status in different environments. To solve this problem, reconfigurable antenna, which can dynamically change its operation frequency, radiation pattern, and polarization, has gained a significant interest recently. Recongurable antennas are considered smart antennas, and can maximize the capacity of the wireless system. This dissertation focuses upon the theoretical analysis and design of smart antennas with recongurable radiation properties. The presented multi-functional reconfigurable antennas (MRAs) are aimed to applications in WLAN (wireless local area network) systems. The theoretical analysis of the MRA was rst investigated to validate the design concept, and then applied for practical applications. The multi-functional recongurable antenna array (MRAA), which is a new class of antenna array, is also created as a linear formation (4 1) of MRA, with theoretical analysis and design of the MRAA fully described. This work developed three MRA(A)s for practical implementation in WLAN systems. The rst design is the MRA operating in 802.11 b/g band (2.4-2.5 GHz), with nine beam steering directions in a parasitic layer-based MRA structure. The second is a MRA operating in 802.11ac band (5.17-5.83 GHz) with three beam steering directions in a simplied parasitic layer-based MRA structure. The third is a MRAA extension of the second design. The design process of these MRA(A)s is realized with the joint utilization of electromagnetic (EM) full-wave analysis and multi-objective genetic algorithm. All three MRA(A) designs have been fabricated and measured. The measured and simulated results agree well for both impedance and radiation characteristics. These prototypes can be directly employed in a WLAN system since practical limits have been taken into account with real switches and components implemented. Finally, this dissertation work concludes with plans for future work, which will focus on development of MRA(A)s with dual-frequency operation.

Yes / This paper presents the results of a study on developing an effective technique to increase the performance characteristics of antenna arrays for sub-THz integrated circuit applications. This is essential to compensate the limited power available from sub-THz sources. Although conventional array structures can provide a solution to enhance the radiation-gain performance however in the case of small-sized array structures the radiation properties can be adversely affected by mutual coupling that exists between the radiating elements. It is demonstrated here the effectiveness of using SIW technology to suppress surface wave propagations and near field mutual coupling effects. Prototype of 2 × 3 antenna arrays were designed and constructed on a polyimide dielectric substrate with thickness of 125 μm for operation across 0.19-0.20 THz. The dimensions of the array were 20 × 13.5 × 0.125 mm3. Metallization of the antenna was coated with 500 nm layer of Graphene. With the proposed technique the isolation between the radiating elements was improved on average by 22.5 dB compared to a reference array antenna with no SIW isolation. The performance of the array was enhanced by transforming the patch to exhibit metamaterial characteristics. This was achieved by embedding the patch antennas in the array with sub-wavelength slots. Compared to the reference array the metamaterial inspired structure exhibits improvement in isolation, radiation gain and efficiency on average by 28 dB, 6.3 dBi, and 34%, respectively. These results show the viability of proposed approach in developing antenna arrays for application in sub-THz integrated circuits. / Ministerio de Ciencia, Innovación y Universidades, Gobierno de España (MCIU/AEI/FEDER, UE) under Grant RTI2018-095499-B-C31, in part by the Innovation Programme under Grant H2020-MSCA-ITN-2016 SECRET-722424, and in part by the U.K. Engineering and Physical Sciences Research Council (EPSRC) under Grant EP/E022936/1.

No / This paper presented a planar printed multiple-input-multiple-output (MIMO) antenna with a dimension of 100 x 45 mm2. It composed of two crescent shaped radiators placed symmetrically with respect to the ground plane. Neutralization line applied to suppress mutual coupling. The proposed antenna examined both theoretically and experimentally, which achieves an impedance bandwidth of 18.67% (over 2.04-2.46 GHz) with a reflection coefficient < -10 dB and mutual coupling minimization of < -20 dB. An evaluation of MIMO antennas is presented, with analysis of correlation coefficient, total active reflection coefficient (TARC), capacity loss and channel capacity. These characteristics indicate that the proposed antenna suitable for some wireless applications.

Neste trabalho é apresentado o projeto de uma antena planar de formato de F-invertido (PIFA) com ranhura-T para aplicação nos sistemas de comunicações sem fio GSM/UMTS/WCDMA. As larguras de banda da antena são aumentadas em função do aproveitamento dos modos ressonantes implícitos no plano de terra. Uma análise paramétrica é feita visando a obtenção de desempenho equilibrado na antena. As diversas simulações do desempenho da antena são realizadas com o software SEMCAD, que utiliza o método das diferenças finitas no domínio do tempo (FDTD). No trabalho é avaliada a diferença de desempenho da antena com e sem a presença do aparelho celular e também próximo à cabeça do usuário. Deste modo, é observada uma influência negativa sobre o desempenho da antena causada pela presença da cabeça do usuário. Adicionalmente, boa concordância é observada entre os dados do modelo simulado e os resultados medidos do protótipo. / This work presents the design and implementation of a planar inverted F-type antenna (PIFA) slot-T for wireless mobile communications GSM/UMTS/WCDMA. The excitation of the ground plane modes is used to increase the antenna bandwidth. A parametric analysis is done to obtain a balanced performance of the antenna. The several antenna performance simulations are performed with the SEMCAD software, which use the finite difference time domain (FDTD) method. In addition the differences in performance of the antenna are evaluated with and without the presence of the cell phone housing and the user's head, thus, negative influence on the antenna performance caused by the presence of the user's head is observed. Finally a prototype is implemented to get an idea of the real behavior of the proposed antenna. Good agreement is observed between data of the simulated model and measured results of the prototype.

Neste trabalho é apresentado o projeto de uma antena planar de formato de F-invertido (PIFA) com ranhura-T para aplicação nos sistemas de comunicações sem fio GSM/UMTS/WCDMA. As larguras de banda da antena são aumentadas em função do aproveitamento dos modos ressonantes implícitos no plano de terra. Uma análise paramétrica é feita visando a obtenção de desempenho equilibrado na antena. As diversas simulações do desempenho da antena são realizadas com o software SEMCAD, que utiliza o método das diferenças finitas no domínio do tempo (FDTD). No trabalho é avaliada a diferença de desempenho da antena com e sem a presença do aparelho celular e também próximo à cabeça do usuário. Deste modo, é observada uma influência negativa sobre o desempenho da antena causada pela presença da cabeça do usuário. Adicionalmente, boa concordância é observada entre os dados do modelo simulado e os resultados medidos do protótipo. / This work presents the design and implementation of a planar inverted F-type antenna (PIFA) slot-T for wireless mobile communications GSM/UMTS/WCDMA. The excitation of the ground plane modes is used to increase the antenna bandwidth. A parametric analysis is done to obtain a balanced performance of the antenna. The several antenna performance simulations are performed with the SEMCAD software, which use the finite difference time domain (FDTD) method. In addition the differences in performance of the antenna are evaluated with and without the presence of the cell phone housing and the user's head, thus, negative influence on the antenna performance caused by the presence of the user's head is observed. Finally a prototype is implemented to get an idea of the real behavior of the proposed antenna. Good agreement is observed between data of the simulated model and measured results of the prototype.

Neste trabalho é apresentado o projeto de uma antena planar de formato de F-invertido (PIFA) com ranhura-T para aplicação nos sistemas de comunicações sem fio GSM/UMTS/WCDMA. As larguras de banda da antena são aumentadas em função do aproveitamento dos modos ressonantes implícitos no plano de terra. Uma análise paramétrica é feita visando a obtenção de desempenho equilibrado na antena. As diversas simulações do desempenho da antena são realizadas com o software SEMCAD, que utiliza o método das diferenças finitas no domínio do tempo (FDTD). No trabalho é avaliada a diferença de desempenho da antena com e sem a presença do aparelho celular e também próximo à cabeça do usuário. Deste modo, é observada uma influência negativa sobre o desempenho da antena causada pela presença da cabeça do usuário. Adicionalmente, boa concordância é observada entre os dados do modelo simulado e os resultados medidos do protótipo. / This work presents the design and implementation of a planar inverted F-type antenna (PIFA) slot-T for wireless mobile communications GSM/UMTS/WCDMA. The excitation of the ground plane modes is used to increase the antenna bandwidth. A parametric analysis is done to obtain a balanced performance of the antenna. The several antenna performance simulations are performed with the SEMCAD software, which use the finite difference time domain (FDTD) method. In addition the differences in performance of the antenna are evaluated with and without the presence of the cell phone housing and the user's head, thus, negative influence on the antenna performance caused by the presence of the user's head is observed. Finally a prototype is implemented to get an idea of the real behavior of the proposed antenna. Good agreement is observed between data of the simulated model and measured results of the prototype.

Yes / This paper presented a planar printed multiple-input-multiple-output (MIMO) antenna with a dimension of 100 x 45 mm2. It composed of two crescent shaped radiators placed symmetrically with respect to the ground plane. Neutralization line applied to suppress mutual coupling. The proposed antenna examined both theoretically and experimentally, which achieves an impedance bandwidth of 18.67% (over 2.04-2.46 GHz) with a reflection coefficient < -10 dB and mutual coupling minimization of < -20 dB. An evaluation of MIMO antennas is presented, with analysis of correlation coefficient, total active reflection coefficient (TARC), capacity loss and channel capacity. These characteristics indicate that the proposed antenna suitable for some wireless applications.

Yes / This paper presented a planar printed multiple-input-multiple-output (MIMO) antenna with a dimension of 100 x 45 mm2. It composed of two crescent shaped radiators placed symmetrically with respect to the ground plane. Neutralization line applied to suppress mutual coupling. The proposed antenna examined both theoretically and experimentally, which achieves an impedance bandwidth of 18.67% (over 2.04-2.46 GHz) with a reflection coefficient < -10 dB and mutual coupling minimization of < -20 dB. An evaluation of MIMO antennas is presented, with analysis of correlation coefficient, total active reflection coefficient (TARC) and capacity loss. These characteristics indicate that the proposed antenna suitable for some wireless applications.