Pattern Reconfigurable MIMO Antennas for Multiband LTE Operation

Nowadays, multiple antennas are becoming widely used in small mobile terminals as they can significantly improve wireless communication performance in terms of link reliability and spectral efficiency. Also, pattern reconfiguration is another new trend for antenna design as it enables the antennas to adapt to different propagation and user scenarios. However, due to the limited space in the terminals, it is difficult to implement both techniques and obtain good antenna performance, especially for frequency bands below 1 GHz. This is because the mobile chassis is often shared by different antennas as the main radiator, regardless of the antenna structure, which leads to high mutual coupling and correlation. In this thesis, a dual-band (824-894 MHz and 1850-1990 MHz) MIMO antenna system with pattern reconfiguration at the low band was designed based on the theory of characteristic modes (TCM). The work began with the design of a single reconfigurable antenna that can be switched between an inverted-F antenna (IFA) mode and a bezel mode, with low envelope correlation of around 0.2 between the states. This was followed by the implementation of a second antenna (i.e., a single-side T-strip) for MIMO operation. The inclusion of the second antenna required the antenna system to be re-optimized, and several performance trade-offs were observed and investigated, including the tradeoff in the mutual coupling between the MIMO antennas in different states as well as the tradeoff between the mutual coupling and the inter-state correlation. The final design of the pattern reconfigurable MIMO antennas yields an inter-state correlation of around 0.3, and an intra-state correlation of below 0.1 and 0.2, respectively. All the studies were carried out in CST Microwave Studio and Matlab.In modern days, mobile phones play quite an important role in people’s life. Besides sending messages and making phone calls, applications such as surfing web, listening to music, watching videos etc. becomes more and more popular. In order to meet the incredibly fast development of mobile market, faster and more stable wireless communication system are required. The theoretical download speed of LTE (4G standard) could reach 100 Mbps, which is 10000 times faster than that (9.6Kbps) for GSM (2G standard). Antenna is a key element in wireless communication, which has great influence on the data rate. In Fig. 1, a Multiple Input Multiple Output (MIMO) system is presented with “x” representing the transmit side, “y” representing the receive side and “H” representing the channel. MIMO system is employed in modern LTE standard, which uses multiple antennas at both the transmitting and receiving sides, so that the data rate can be linearly increased without additional frequency spectrum and transmit power. Another technique regarding antenna is reconfiguration, especially pattern reconfiguration for reliable links. By directing the main beam to the signal and the null to the interference, the reliability of the communication link can be greatly increased. pand one of these techniques. In this way, transmitting speed, reliability and error rates could be apparently improved in MIMO system. Moreover, is another technique comes out in recent years which could modify automatically antenna itself into different states according to different needs (e.g. frequency band, radiation pattern) in different scenarios. As a result, better antenna performance is achieved. When it comes to real antenna design, size limitation can lead to high correlation between multiple antennas and also low reconfiguration effect. Thus, designing an efficient reconfigurable multiple antenna system is quite an important topic. In this thesis, in order to design as efficient mobile antenna system, Theory of Characteristic Modes (TCM) is studied. TCM basically explains that any antenna structure inherently holds a set of orthogonal modes, and any current on the antenna can be expressed as the superposition of the weighted modes. By exciting different orthogonal modes, the TCM analysis can help design uncorrelated MIMO antenna and reconfigurable antennas with distinct patterns. In this thesis, a dual-band (824-894 MHz and 1850-1990 MHz) MIMO antenna system with pattern reconfiguration at the low band was designed based on TCM. One antenna is a T-strip antenna along the length of the chassis. The second antenna can be reconfigured between bezel state and IFA state. These three antennas are situated on the edge over a 30 mm × 65 mm × 7 mm chassis, saving more space for other electrical devices in the handset. The simulated final structure is presented in Fig. 2. Simulations are carried out in commercial software Computer Simulation Technology (CST) studio, and the final simulated results are compared with the theoretical results from TCM to confirm whether the right modes are excited

Considerations on Configurable Multi-Standard Antennas for Mobile Terminals Realized in LTCC Technology

This paper is an extended version of a paper presented at the EuCAP 2009 conference [1]. We present part of a long term research project that aims on designing a (re-)configurable multi-standard antenna element for 4G (4th Generation) mobile terminals based on LTCC (Low Temperature Co-fired Ceramic) technology. The antenna itself is a coupling element [2] that efficiently excites the chassis of the mobile terminal to radiate as an entire antenna. Coupling is optimized by a reactive tuning circuit. Several of these tuning circuits are realized in a single LTCC component and can be multiplexed to the antenna by a SPnT (Single Pole n Thru) antenna switch integrated into the LTCC component. The coils and capacitor in the LTCC component are configurable on the top-layer of the component. Thus, the component is configurable according to different mobile terminal chassis configurations and multiple bands

Design of low profile MIMO antennas for mobile handset using characteristic mode theory

Designing highly integrated and efficient MIMO antennas for mobile handset is challenging, especially for low frequency bands below 1 GHz. In this work, by analyzing and manipulating the characteristic modes of a mobile handset, we propose a low profile dual-band MIMO antenna with high integration ability. Both antennas cover a bandwidth of 100 MHz at the center frequency of 0.9 GHz. The isolation between the antennas is over 10 dB, and the envelope correlation is below 0.1, which ensures high efficiency of the antenna system and good MIMO performance

Antenna System Design for 5G and Beyond – A Modal Approach

Antennas are one of the key components that empower a new generation of wireless technologies, such as 5G and new radar systems. It has been shown that antenna design strategies based on modal theories represent a powerful systematic approach to design practical antenna systems with high performance. In this thesis, several innovative multi-antenna systems are proposed for wireless applications in different frequency bands: from sub-6 GHz to millimeter-wave (mm-wave) bands. The thesis consists of an overview (Part I) and six scientific papers published in peer-reviewed international journals (Part II). Part I provides the overall framework of the thesis work: It presents the background and motivation for the problems at hand, the fundamental modal theories utilized to address these problems, as well as subject-specific research challenges. Brief conclusions and future outlook are also provided. The included papers of Part II can be divided into two tracks with different 5G and beyond wireless applications, both aiming for higher data rates.In the first track, Papers [I] to [IV] investigate different aspects of antenna system design for smart-phone application. Since Long Term Evolution (LTE) (so-called 3.5G) was deployed in 2009, mobile communication systems have utilized multiple-input multiple-output antenna technology (MIMO) technology to increase the spectral efficiency of the transmission channel and provide higher data rates in existing and new sub-6 GHz bands. However, MIMO requires multi-antennas at both the base stations and the user equipment (mainly smartphones) and it is very challenging to implement sub-6 GHz multi-antennas within the limited space of smartphones. This points to the need for innovative design strategies. The theory of characteristic modes (TCM) is one type of modal theory in the antenna community, which has been shown to be a versatile tool to analyze the inherent resonance properties of an arbitrarily shaped radiating structure. Characteristic modes (CMs) have the useful property of their fields being orthogonal over both the source region and the sphere at infinity. This property makes TCM uniquely suited for electrically compact MIMO antenna design.In the second track, Papers [V]-[VI] investigate new integrated antenna arrays and subarrays for the two wireless applications, which are both implemented in a higher part of the mm-wave frequency range (i.e. E-band). Furthermore, a newly developed high resolution multi-layer “Any-Layer” PCB technology is investigated to realize antenna-in-package solutions for these mmwave antenna system designs. High gain and high efficiency antennas are essential for high-speed wireless point-to-point communication systems. To meet these requirements, Paper [V] proposes directive multilayer substrate integrated waveguide (SIW) cavity-backed slot antenna array and subarray. As a background, the microwave community has already shown the benefits of modal theory in the design and analysis of closed structures like waveguides and cavities. Higher-order cavity modes are used in the antenna array design process to facilitate lower loss, simpler feeding network, and lower sensitivity to fabrication errors, which are favorable for E-band communication systems. However, waveguide/cavity modes are confined to fields within the guided media and can only help to design special types of antennas that contain those structures. As an example of the versatility of TCM, Paper [VI] shows that apart from smartphone antenna designs proposed in Papers [I]-[IV], TCM can alsobe used to find the desirable modes of the linear antenna arrays. Furthermore, apart from E-band communications, the proposed series-fed patch array topology in Paper [VI] is a good candidate for application in 79 GHz MIMO automotive radar due to its low cost, compact size, ability to suppress surface waves, as well as relatively wide impedance and flat-gain bandwidths

Fluid Antenna Systems

Over the past decades, multiple antenna technologies have appeared in many different forms, most notably as multiple-input multiple-output (MIMO), to transform wireless communications for extraordinary diversity and multiplexing gains. The variety of technologies has been based on placing a number of antennas at fixed locations which dictates the fundamental limit on the achievable performance. By contrast, this paper envisages the scenario where the physical position of an antenna can be switched freely to one of the N positions over a fixed-length line space to pick up the strongest signal in the manner of traditional selection combining. We refer to this system as a fluid antenna system (FAS) for tremendous flexibility in its possible shape and position. The aim of this paper is to study the achievable performance of a single-antenna FAS system with a fixed length and N in arbitrarily correlated Rayleigh fading channels. Our contributions include exact and approximate closed-form expressions for the outage probability of FAS. We also derive an upper bound for the outage probability, from which it is shown that a single-antenna FAS given any arbitrarily small space can outperform an L-antenna maximum ratio combining (MRC) system if N is large enough. Our analysis also reveals the minimum required size of the FAS, and how large N is considered enough for the FAS to surpass MRC.Comment: 26 pages, 5 figure

Capacity Enhancement by Pattern-Reconfigurable Multiple Antenna Systems in Vehicular Applications

This work presents a design methodology for pattern reconfigurable antennas in automotive applications. Channel simulation is used to identify the relevant beam directions prior to the design of the antenna. Based on this knowledge several reconfigurable multiple antenna systems are designed. These antennas are evaluated by the channel capacity calculation from virtual and real-world test drives. An increase of the channel capacity by a factor of 2 compared to a conventional system is observed

Tunable decoupling and matching concepts for compact mobile terminal antennas

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Mutual Coupling Considerations in the Development of Multi-feed Antenna Systems

In the design of any multi-port network with more than one antenna, mutual coupling between these different ports must be accounted for. In an effort to investigate and control these mutual coupling effects, we have selected three structures to be thoroughly analyzed. Furthermore, they have been fabricated and tested to develop relevant design guides for these selected structures to have minimal mutual coupling effects. These selected structures included a feed network for a multi-port antenna, a dual feedhorn for a large reflector antenna, as well as a set of Multi- Input Multi-Output (MIMO) laptop antennas. In the first study, we analyzed a 30- port radial splitter that can be used for an in-phase feeding of a 30-high power transmitter. Our objectives here have been geared towards estimating the mutual coupling between the 30 ports and exploring the port and alignment failure analysis, its graceful degradation results, and relevant efficiency performance for such high power multi-port network will be presented. In the second study, we investigated the mutual coupling of a multifeedhorn structure of a large reflector antenna in order to allow multi-beam radiation or reception. This high gain antenna utilizes integrated feeds with precise physical tight spacing and could suffer from strong inter-coupling. Mutual coupling effects here include input match deterioration, beam width broadening, and cross-polarization degradation due to the proximity coupling of these various feeds. Our study derived accurate feed location expressions as well as methods to improve the decoupling between the feeds that have been implemented. These results will be discussed. For the third study, we carried out extensive investigates into the mutual coupling effects amidst wireless laptop antennas for a MIMO system implementation. For a laptop use, it is required to determine the best location, optimum spacing, and orientations of these antennas in order to achieve the maximum benefits of the system’s diversity. First, we studied the coupling between two antennas as a function of their spacing, types, and orientations. Subsequently, we extended the study to a controlled multi-antenna system for a MIMO implementation. Design rules for such implementation have been derived and will be discussed in detail