Antenna Design Considerations for LTE Enabled Tablets Rensheng (Ray) Sun, Ph.D EM Software & Systems (USA), Inc. Hampton, VA 23666 Mobile Antenna Systems Conference Denver, 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 to deliver enhanced performance, such as higher user data rates, improved system capacity and coverage, reduced latency, etc.
Base station
Mobile terminal
Tx 1
Rx 1
Tx 2
Rx 2 Signal Separator
Tx 3
Rx 3
Tx 4
Rx 4 Transmission Channel
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Design Implementations and Challenges •
LTE antennas offer many practical design and implementation challenges due to the size of the portable terminal on which they are implemented/designed
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Challenges in designing antennas for a LTE/MIMO system – – – –
Antenna matching Isolation between the antennas Cross-correlation Interactions with neighboring devices
components
on
mobile
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Challenge - Isolation Techniques •
Placing the antennas half a wavelength apart as a rule of thumb for low enough correlation – Not attractive because of the space required for separation
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Using branch line hybrid with passive inductors and capacitors to decouple the antenna ports1
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Orthogonally polarized elements offer significant port isolation
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“Characteristic modes” analysis for surface current distributions to provide orthogonal decoupling through systematic 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 are used to achieve pattern diversity
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The problem of separation between the antennas for the isolation is overcome by having “zero” separation
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There are no additional neutralization stubs (or) hybrids used to provide isolation
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The zero separation leads to size reduction resulting in compact design
Dual port inverted PIFA
Qinjiang Rao and Dong Wang, “A Compact Dual-Port Diversity Antenna for Long-Term Evolution Handheld Devices”, IEEE Transactions on Vehicular Technology, Vol. 59, No. 3, March 2010
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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
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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
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The ultra-wideband planar monopole itself covers 1700 MHz to 2900 MHz
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Meandering microstrip line is loaded to provide resonance at LTE 700 MHz band
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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
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Solved using MoM/SEP (surface equivalence principle)
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Mesh size: 1.74 mm
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Surface triangles: 7,282
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Peak memory: 3.48 GB
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Runtime: 10 minutes/freq with 8processor 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
Dimensions (W x H x D) 7.6 x 4.8 x 0.39 inches
The model includes two antennas, case, LCD panel, battery, PCB 15
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
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Solved with FEM/MoM
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Mesh size: 3.15 mm
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Surface triangles: 5,093
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Tetrahedra: 74,942
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Peak memory: 10.13 GB
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Runtime: 36 minutes/freq with 8processor parallel solver
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Radiation Pattern (Both Antennas Excited; 2.6 GHz)
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Radiation Pattern (#1 excited; #2 terminated) Gaintheta
Gaintotal
Gainphi 19
Radiation Pattern (#2 excited; #1 terminated) Gaintheta
Gaintotal
Gainphi 20
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
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Specify the target frequency bands
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Available components: inductors, capacitors, resistors, transmission lines, two-port S parameter blocks
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Note: efficiency of matching circuits is optimized, not the impedance match
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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: 1mm T4 3.4 mm, T5: 2.1 mm, T6: 3.1 mm 28
S parameters
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Efficiency
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Channel Capacity Analysis
* Thanks to Mr Oliver Stäbler at AWE for helping with the simulations
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Channel Capacity •
Channel capacity can be calculated from the ‘channel matrices’ obtained from measurements
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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
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The channel capacity is computed as;
where, ‘HF’ is the channel matrix ‘ρ’ is the SNR 32
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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Channel Capacity in Indoor Environment 1x2 MIMO system
2x2 MIMO system
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Channel Capacity in Urban Environment Simulation along a trajectory in an urban area (1x2 MIMO)
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Channel Capacity in Urban Environment Simulation along a trajectory in an urban area (2x2 MIMO)
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Conclusion
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Challenges in designing antennas for LTE-MIMO system are briefly discussed
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Simulation results for a multiband planar monopole antenna is discussed
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Interactions/coupling between two-element array integrated on a generic tablet is studied
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Impedance matching optimization is performed to enhance the performance of the multiband multiport system
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The channel capacity of the antennas on a tablet is computed in both indoor and urban environments
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