Multi-element Antennas for Mobile Communication Systems: Design, Evaluation and User Interactions

Capacity improvement using Multiple-Input Multiple-Output (MIMO) technology necessitates multiple antennas at both transmitter and receiver ends. Antenna design challenges are related especially to mobile terminal, in which antennas need to be small, located relatively close to each other and interact with a user. Due to these limitations, mobile terminal antennas are potentially inefficient and do not provide a good MIMO performance. Traditional antenna design and characterization methods are not directly applicable to multiple antennas, and therefore research in these fields is needed. This thesis contributes two topics. First, characterization methods of multiple antennas in compact mobile terminals are studied. In the studied methods, the effects of propagation environment and user on the multiple antenna performance are taken into account. The time-varying propagation environment and user’s hand grip emulating the true scenario of the users in real-life environments are analyzed. In particular; different terminal orientations, hand grips and locations are investigated either with one or two hands holding the terminal. Second, the thesis has scientific contribution on introducing novel multi-antenna structures with elements ranging from two to eight, and frequencies ranging from 900 MHz UHF to 3500 MHz LTE bands. Specifically, this thesis advances the design, evaluation and user interaction of multiple antennas in mobile terminals operating at the 3500 MHz. The proposed structures are shown to provide good diversity and MIMO performances. Selection of suitable antenna type and their locations on the terminal chassis are shown to be important. Based on author’s experience, the proposed designs are particularly suitable for realizing a multi-element antenna structure that is tolerant to the user. Applicability of multiple antennas in compact mobile terminal for radio direction finding (RDF) is studied. Detailed analysis has also been carried out on the antenna topology on a mobile terminal and consideration of user interaction to ascertain the best use of antennas for such an application. It is found that ambiguity characterization method could be useful evaluation tool for designing a multi-antenna structure for RDF application.  

Study of user effects on two-port MIMO antennas at 2.4 GHz and 5.8 GHz for Wi-Fi and WLAN applications

In this paper, two multiple input multiple output (MIMO) antennas for Wi-Fi/WLAN mobile applications are proposed. The designed two-port MIMO antennas are made up of planar inverted-F antennas (PIFAs). The antenna elements for both designs are symmetrical and placed on the short-edged corners of the substrate used, FR4. The performance of both antennas in the presence of user’s hand is compared in terms of impedance bandwidth and efficiency. An upward shift of up to 0.17 GHz in impedance bandwidth was found for 2.4 GHz and 5.8 GHz antenna. Due to the smaller size of antennas at 5.8 GHz compared to antennas at 2.4 GHz, the antennas are less obstructed by hands and thus the exhibited total efficiency of up to 45.58 % in the presence of human hand. The designed antennas have been fabricated for validation purpose. It is shown that there is a good agreement between simulated and measured results

Performance evaluation of 2-port MIMO LTE-U terminal antenna with user’s hand effect

This paper presents the performance evaluation of 2-port MIMO antenna for LTE-U sub 6 GHz band. The evaluation focuses on the effect of user’s hand in a uniform environment and the analysis were carried out on simulation and measurement data of antenna ports. Results show that the highest performance of the design is on the frequency range from 4.5 GHz to 5.5 GHz, and the ports have low envelope correlation coefficient (ECC) less than 0.16 in both cases of without and with user’s hand. However, the presence of the user’s hand reduces mean effective gain (MEG) of ports and diversity combining gain by more than 1.6 dB compared with no-hand case. The multiplexing efficiency is around 81% and reduced by the presence of the user’s hand to 55%. Despite this reduction; the design shows high spatial multiplexing capability in both cases. The capacity carried by the second transmission eigenmode is about 39% from the total capacity under water-filling algorithm transmit power allocation

Design and Measurement-Based Evaluation of Multi-Antenna Mobile Terminals for LTE 3500 MHz Band

Design of multi-element antennas for small mobile terminals operating at higher frequencies remains challenging despite smaller antenna dimension and possibility of achieving electrically large separation between them. In this paper, the importance of the type of radiating elements operating at 3400-3600 MHz and their locations on the terminal chassis are highlighted. An isotropic radiation pattern that receives incoming signals from arbitrary directions is obtained by combining the radiation patterns of multiple antennas with localized chassis current distribution. Four multiport antennas configurations with two- and eight-element antennas are designed and evaluated experimentally in indoor propagation environments. Our proposed designs of multi-element antennas provide the highest MIMO channel capacity compared to their counterparts using antennas with less localized chassis current distribution, even in the presence of user's hand

Study of multiple antennas with defected ground slot for low-band LTE application

This study is focused on highly coupled multiple antennas with defected ground slot techniques. Two Printed Inverted-F Antenna (PIFA) are positioned at the top edge of chassis symmetrically. Both antennas are operating at low-band Long-Term Evolution (LTE) with center frequency, 829MHz. Rectangular defected ground slot is implemented to reduce the coupling effect between the antennas on the ground plane of the small chassis. Parameter study of the rectangular defected ground slot is studied with different width, W and length, L. Furthermore, the optimized dimensions of rectangular defected ground slot, W and L are simulated and presented. The optimized defected ground slot reduced the mutual coupling up to -4.5 dB. The envelope correlation coefficient (ECC) achieved less than 0.5. The ground plane of the multiple antenna structure has been further investigated by introducing another slot with a gap of 1mm between them. The achieved result is not significant in term of S-parameter and ECC compared to single defected ground slot

User’s hand effect on efficiency of 2-port 5 GHZ mobile terminal antennas

In this paper, the influence of user’s hand on mobile terminal antenna when it placed approximately on top of Multiple Input Multiple Output radiating element antennas (PIFAs) is studied extensively. The antenna is designed to operate at 5 GHz with 1.5 GHz of -6 dB bandwidth. The effect of user’s hand with different finger positions are studied at seven positions on slit at the ground plane, seven differences height above the antenna and nine different locations around the radiating element at 2 mm height from antenna. The losses due to presence of hand are studied in terms of scattering parameters, radiation efficiency and matching efficiency. The maximum loss in term of isolation in the presence of user’s hand is found at 6 mm on the slit and it decreased as the hand move away from the slitted area on the ground plane. The maximum efficiency loss is observed when the finger is placed right on top of the radiating element with -5.85 dB compare to antenna without the presence of user’s hand. On the other hand, the result for matching efficiency indicates approximately 0.2 dB losses occurred when the fingers are varied at different height and position

The influence of user mobility in mobile virus propagation: An enterprise mobile security perspective

In this paper, the authors review the usage of mobile devices in the enterprise and also the major impact from the infected mobile devices.Then the authors highlight the virus threat to enterprise mobile security and how critical the problems are.The authors then discuss the mobile virus infection dynamics which are the Bluetooth infections, mobile emails infections and mobile internet infections which are the threats to the enterprise mobile security. Then the authors discuss on the influences of user mobility issue in spreading mobile viruses before concluded this article

Textile-based flexible linear-to-circular polarizing surface for s-band pico-satellites

This paper presents a single layered textile-based flexible linear-to-circular polarizing surface. The proposed structure is designed based on a rectangular ring structure for CubeSat application in the S-band. Each unit cell is sized at 0.35λ×0.33λ×0.2λ for operation centered at 2.2 GHz. This unit cell is then multiplied into a 9x10 array to form the polarizing surface. It features a 3 dB axial ratio bandwidth (ARBW) of 34.73%, with a minimum AR of 0.28 dB. Besides that, it also offers a 90 % conversion efficiency bandwidth of up to 47.34%. The proposed structure’s performance is validated by placing it in front of a patch antenna operating at 2.2 GHz. The antenna performance indicated an increase in terms of gain from 3.14 dBi to 7.33 dBi when integrated with the polarizing surface, besides successfully converting linearly-polarized waves to circularly-polarized

Gain Enhancement of a Dual-Band Planar Slot Dipole using AMC Plane for WBAN and WLAN Applications

A dual band slot dipole antenna made from textile is proposed for Wireless Body Area Network and Wireless Local Area Network applications. The proposed antenna is integrated with an artificial magnetic conductor plane to mitigate backward radiation and reduce Specific Absorption Rate when operated on body. The artificial magnetic conductor plane is formed using a 3 x 3 array of unit cells, each consisting of a square patch integrated with diamond-shaped slot. The proposed antenna (denoted as Antenna B) is compared against another similar antenna (Antenna A) in free space and on-body, in flat condition (on chest) and under two bending axes (x- and y-axes) on the upper arm. Results indicate that Antenna B provided wider upper bandwidth to 766 MHz (in flat condition) and up to 875 MHz when bent. Besides that, higher gain of up to 5 dB with improved front-to-back ratio are also observed