Antenna Systems & Technology - Spring 2014 - (Page 10)

FEATURE ARTICLE Antenna Design for LTE Enabled Tablets By Derek Campbell and Peter Futter - EM Software and Systems Long-term evolution (LTE) is a predominant 4th generation (4G) mobile wireless communication standard that incorporates several innovative technologies and provides a roadmap for integrating future developments. In addition, LTE offers the flexibility to operate at frequencies ranging from 400 to 4,000 MHz. Lower frequencies were allocated in North America, because better coverage and building penetration expedites deployment in rural and suburban areas. Higher frequencies were allocated in Europe and Asia, because larger bandwidths are potentially available. [1] A key LTE standard is supporting multiple antenna elements. Currently, a maximum of four antenna elements is supported on both the base station and mobile device. Although increasing the number of antenna elements theoretically increases channel capacity, research has shown that strong mutual coupling deteriorates MIMO performance when more than five antenna elements are integrated within thin mobile devices. Systems with more antennas do, however, become advantageous when operating as a reconfigurable two-element system.[2] Various techniques have been developed to these isolation challenges. Diversity antennas have combined separate antennas into a single structure to minimize space requirements and maximize polarization/pattern diversity.[3] Characteristic mode analysis (CMA) has also been exploited by a systematic design procedure developed to meet isolation requirements for a geometry confined within a specified size and shape.[4] The emergence of robust wireless communication standards has shifted the paradigm in the consumer electronics market from traditional desktop computers to mobile devices. In this paper, a complete system level analysis is therefore provided for two identical antennas integrated into an LTE enabled handheld tablet. The antennas were designed to address multiband flexibility as well as provide low mutual coupling and envelope correlation.[5] A multiport matching network was then designed to optimize the efficiency of power transfer between the antennas and their respective sources. Finally, the entire system underwent further analysis to determine specific absorption rate (SAR) when operating near the explicit presence of human hands. Antenna Design Antenna engineers often choose printed ultra-wideband (UWB) planar monopoles for wireless communication due to low-cost, thin shape and the flexibility to operate at several frequencies. A meandering microstrip line can also extend from the antenna to incorporate an additional resonance.[5] Method of Moment (MoM) simulations within the FEKO Software Suite 6.3 [6] demonstrated that the antenna offers suitable reflection coefficients across five LTE frequency bands. The planar monopole antenna has a near omnidirectional radiation pattern as illustrated in Figure 1, which is advantageous when communicating from a base-station to a handheld tablet with an unknown orientation. The physical dimensions can be further optimized based on radiation characteristics and S-parameters to fine tune the frequency bands for a specific geographical region. Figure 1. Array Design Hand-held tablets are multimedia infotainment systems that drive an increasing demand for mobile broadband services ranging from SMS messaging to streaming IPTV. Mobile broadband services therefore require wireless communication channels to be established throughout urban environments. Multiple copies of a single transmitted signal can be created from reflections and diffractions off clusters of buildings in the environment. Multipath effects occur when several copies of the transmitted signal are then received at different times. Signal strength fluctuates and in some cases performance is significantly deteriorated 10 Antenna Systems & Technology Spring 2014 www.AntennasOnline.com http://www.AntennasOnline.com

Table of Contents for the Digital Edition of Antenna Systems & Technology - Spring 2014

Editor’s Choice
What's So Exciting About the Future of M2M? Everything
Antenna Design for LTE Enabled Tablets
Recent Progress on Plasma Antennas
Guest Column: Don't Let Your Choice of Tool Hinder Your Cable and Antenna Testing
Antennas
Components/Subsystems
Short-Range Wireless
Software / System Design
Test & Measurement
Industry News
Marketplace

Antenna Systems & Technology - Spring 2014