Mutual coupling suppression in multiple microstrip antennas for wireless applications

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonMutual 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

Antenna Designs for 5G/IoT and Space Applications

This book is intended to shed some light on recent advances in antenna design for these new emerging applications and identify further research areas in this exciting field of communications technologies. Considering the specificity of the operational environment, e.g., huge distance, moving support (satellite), huge temperature drift, small dimension with respect to the distance, etc, antennas, are the fundamental device allowing to maintain a constant interoperability between ground station and satellite, or different satellites. High gain, stable (in temperature, and time) performances, long lifecycle are some of the requirements that necessitates special attention with respect to standard designs. The chapters of this book discuss various aspects of the above-mentioned list presenting the view of the authors. Some of the contributors are working strictly in the field (space), so they have a very targeted view on the subjects, while others with a more academic background, proposes futuristic solutions. We hope that interested reader, will find a fertile source of information, that combined with their interest/background will allow efficiently exploiting the combination of these two perspectives

A bra monitoring system using a miniaturized wearable ultra-wideband MIMO antenna for breast cancer imaging

This paper represents a miniaturized, dual-polarized, multiple input–multiple output (MIMO) wearable antenna. A vertically polarized, leaf-shaped antenna and a horizontally polarized, tree-shaped antenna are designed, and the performance of each antenna is investigated. After designing the MIMO antenna, it is loaded with stubs, parasitic spiral, and shorting pins to reduce the coupling effects and remove the unwanted resonances. Afterward, the two-port MIMO cells are spaced by 2 mm and rotated by 90° to create three more cells. The antennas are designed using two layers of denim and felt substrates with dielectric constants of 1.2 and 1.8, and thicknesses of 0.5 mm and 0.9 mm, respectively, along with the ShieldIt™ conductive textile. The antenna covers a bandwidth of 4.8–30 GHz when the specific absorption rate (SAR) meets the 1 g and 10 g standards. Isolation greater than 18 dB was obtained and mutual coupling was reduced after integrating shorting pins and spiral parasitic loadings. A maximum radiation efficiency and directive gain of 96% and 5.72 dBi were obtained, respectively, with the relatively small size of 11 × 11 × 1.4 mm3 for the single element and final dimensions of 24 × 24 × 1.4 mm3 for the full assembly. The antenna’s performance was examined for both on-body (breast) and free space conditions using near-field microwave imaging. The achieved results such as high fidelity, low SAR, and accuracy in localization of the tumour indicate that the MIMO antenna is a decent candidate for breast cancer imaging

A broadband resonant cavity antenna using a metamaterial superstrate consisting of two indentical patch arrays

This thesis presents the research work on the development of a broadband resonant cavity antenna (RCA) using a two-layer metamaterial based superstrate and a wideband patch antenna as a primary source. It is shown that the resonant effect in a metamaterial consisting of two identical patch arrays can be used to design an RCA device for broadband performance. The large radiation bandwidth of 40∼47% with 1-dB-ripple flat band response and the maximum gain of ∼13 dBi have been achieved over the frequency band of 8∼12 GHz. The dimensions of the compact RCA device are 45x45x24 mm3 (or 1.5λx1.5λx0.8λ at 10 GHz). The two-layer metamaterial superstrate is based on an assembled structure using the two liquid crystal polymer (LCP) film substrates each with a printed patch array and separated by an air spacer of 4 mm. This air-based superstrate contributes antenna efficiency; it is lighter and requires less dielectric material. For comparison, the two-layer metamaterial superstrate design is implemented using an FR4 board and it has also been demonstrated to provide similar broadband performance in an RCA device. The Fano resonance effect in the two-layer metamaterial design has been studied. It has been discovered that a sharp resonance can be obtained in such metamaterials when a dielectric spacer is very thin (~100 µm). Analysis of current and electric field distributions shows that the observed electromagnetically induced transparency (EIT) associated with the enhanced transmission originates from the effect of trapped-mode resonance in the two-layer metamaterials. The experimental work was carried out using both FR4 and LCP based dielectric spacers. It is shown that the LCP based metamaterials can also be used as an effective absorber near a design frequency of 10 GHz. A broadband source antenna is based on an optimised coplanar waveguide (CPW) fed and aperture coupled patch antenna design. By exploiting the coupling effects of a triple resonances associated with the CPW structure, the aperture, and the patch element, the broadband patch antenna was obtained and used successfully in the development of the broadband RCA device. Impedance and radiation bandwidths of the practical device are measured to be as large as 41% and 43%, respectively. The new fabrication and assembly methods based on laser micromachining of the PMMA polymer have been developed for a successful construction of metamaterial structures and antenna devices

Design and analysis of wideband passive microwave devices using planar structures

A selected volume of work consisting of 84 published journal papers is presented to demonstrate the contributions made by the author in the last seven years of his work at the University of Queensland in the area of Microwave Engineering. The over-arching theme in the author’s works included in this volume is the engineering of novel passive microwave devices that are key components in the building of any microwave system. The author’s contribution covers innovative designs, design methods and analyses for the following key devices and associated systems: Wideband antennas and associated systems Band-notched and multiband antennas Directional couplers and associated systems Power dividers and associated systems Microwave filters Phase shifters Much of the motivation for the work arose from the desire to contribute to the engineering o