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Antenna Design Considerations for LTE
Enabled Tablets
Rensheng (Ray) Sun, Ph.DEM Software & Systems (USA), Inc.
Hampton, VA 23666
Mobile Antenna Systems ConferenceDenver, CO
September 18-19, 2012
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Outline
LTE-MIMO and antenna design challenges
Multiband planar monopole antenna for LTE MIMO systems
Antenna arrays on tablet computer Impedance matching improvements Channel capacity analysis Conclusion
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LTE-MIMO and Antenna Design Challenges
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LTE-MIMO
MIMO technologies have been widely used in LTE todeliver enhanced performance, such as higher user datarates, improved system capacity and coverage, reducedlatency, etc.
Tx 1
Tx 2
Tx 3
Tx 4
Base station
Rx 1
Rx 2
Rx 3
Rx 4
Mobile terminal
Signal Separator
Transmission Channel
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Design Implementations and Challenges
LTE antennas offer many practical design andimplementation challenges due to the size of theportable terminal on which they areimplemented/designed
Challenges in designing antennas for a LTE/MIMOsystem Antenna matching Isolation between the antennas Cross-correlation Interactions with neighboring components on mobile
devices
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Challenge - Isolation Techniques
Placing the antennas half a wavelength apart as a ruleof thumb for low enough correlation Not attractive because of the space required for separation
Using branch line hybrid with passive inductors andcapacitors to decouple the antenna ports1
Orthogonally polarized elements offer significant portisolation
Characteristic modes analysis for surface currentdistributions to provide orthogonal decoupling throughsystematic approach
1. Rashid Ahmad Bhatti, Soongyu Yi, and Seong-Ook Park, Compact Antenna Array With Port Decoupling for LTE-Standardized Mobile Phones, IEEE Antennas & Wireless Propagation Letters, Vol. 8, 2009
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Compact Dual Port Antenna for LTE mobile phone applications
Two orthogonal radiating elements areused to achieve pattern diversity
The problem of separation between theantennas for the isolation is overcomeby having zero separation
Qinjiang Rao and Dong Wang, A Compact Dual-Port Diversity Antenna for Long-Term Evolution Handheld Devices, IEEE Transactions onVehicular Technology, Vol. 59, No. 3, March 2010
There are no additional neutralization stubs(or) hybrids used to provide isolation
The zero separation leads to size reductionresulting in compact design Dual port inverted
PIFA
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Meander-line Loaded Planar Monopole Antenna for
Multiband LTE MIMO Systems
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Planar Monopole Antenna for Multiband LTE
The planar antenna covers five frequency bands for LTE applications, including 746-787 MHz, 1710-1755 MHz, 2110-2155 MHz, 2305-2400 MHz, and 2500-2690 MHz
The ultra-wideband planar monopole itself covers 1700 MHz to 2900 MHz
Meandering microstrip line is loaded to provide resonance at LTE 700 MHz band
Overall size: 88mm x 50mm x 1.6mm
Yuan Yao, etc., Multiband Planar Monopole Antenna for LTE MIMO Systems, International Journal of Antennas and Propagation, Vol.2012, Article ID 890705.
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Reflection Coefficient for a Single Antenna Itself
Good matching across five bands: 746-787 MHz, 1710-1755 MHz, 2110-2155 MHz, 2305-2400 MHz, and 2500-2690 MHz
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Triangular Surface Mesh for MoM/SEP solver
Solved using MoM/SEP (surface equivalence principle)
Mesh size: 1.74 mm
Surface triangles: 7,282
Peak memory: 3.48 GB
Runtime: 10 minutes/freq with 8-processor parallel solver
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Surface Currents & Radiation Pattern at 760 MHz
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Surface Currents & Radiation Pattern at 2.6 GHz
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Two Antenna Elements Integrated on a Generic Tablet
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Antennas Integrated with Generic Tablet
The model includes two antennas, case, LCD panel, battery, PCB
Dimensions (W x H x D)7.6 x 4.8 x 0.39 inches
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Antennas Integrated with Generic Tablet(cut plane view)
Dimensions (W x H x D)7.6 x 4.8 x 0.39 inches
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Tetrahedral Mesh for FEM/MoM solver
Solved with FEM/MoM
Mesh size: 3.15 mm
Surface triangles: 5,093
Tetrahedra: 74,942
Peak memory: 10.13 GB
Runtime: 36 minutes/freq with 8-processor parallel solver
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Radiation Pattern (Both Antennas Excited; 2.6 GHz)
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Radiation Pattern (#1 excited; #2 terminated)
Gaintotal
Gaintheta
Gainphi
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Radiation Pattern (#2 excited; #1 terminated)
Gaintotal
Gaintheta
Gainphi
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S-parameters for the two antennas on tablet
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Impedance Matching Improvement with Optenni Lab
* Thanks to Mr Jussi Rahola at Optenni for helping with the optimization
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Matching Circuit Design in Optenni Lab
Read in the impedance data in Touchstone format
Specify the target frequency bands
Available components: inductors, capacitors, resistors, transmission lines, two-port S parameter blocks
Note: efficiency of matching circuits is optimized, not the impedance match
Multiport module containing simultaneous multiport matching (optimization of antenna efficiency) coming later this year
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Efficiency without Matching
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Matching Circuit with Discrete Components
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S-parameters
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Efficiencies
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Matching Circuit with Microstrip Lines
Microstrip lines, eps_r=4.8, thickness 1 mm. Width:T1-T3: 1mmT4 3.4 mm, T5: 2.1 mm, T6: 3.1 mm
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S parameters
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Efficiency
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Channel Capacity Analysis
* Thanks to Mr Oliver Stbler at AWE for helping with the simulations
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Channel Capacity
Channel capacity can be calculated from the channelmatrices obtained from measurements
Alternatively, The channel capacity is computed by post processing the
ray data from a fixed transmitter in a certain environment(channel) for different positions of the receiver
The channel capacity is computed as;
where,HF is the channel matrix is the SNR
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Indoor Environment
Commercial software WinProp from AWE Communications is used to calculate the channel capacity
www.awe-communications.com
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MIMO Configurations
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1x2 MIMO system
2x2 MIMO system
Channel Capacity in Indoor Environment
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Simulation along a trajectory in an urban area (1x2 MIMO)
Channel Capacity in Urban Environment
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Simulation along a trajectory in an urban area (2x2 MIMO)
Channel Capacity in Urban Environment
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Conclusion
Challenges in designing antennas for LTE-MIMO system arebriefly discussed
Simulation results for a multiband planar monopole antennais discussed
Interactions/coupling between two-element array integratedon a generic tablet is studied
Impedance matching optimization is performed to enhancethe performance of the multiband multiport system
The channel capacity of the antennas on a tablet is computedin both indoor and urban environments
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