1

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

2

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

3

LTE-MIMO and Antenna Design Challenges

4

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

5

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

6

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

7

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

8

Meander-line Loaded Planar Monopole Antenna for

Multiband LTE MIMO Systems

9

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.

10

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

11

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

12

Surface Currents & Radiation Pattern at 760 MHz

13

Surface Currents & Radiation Pattern at 2.6 GHz

14

Two Antenna Elements Integrated on a Generic Tablet

15

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

16

Antennas Integrated with Generic Tablet(cut plane view)

Dimensions (W x H x D)7.6 x 4.8 x 0.39 inches

17

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

18

Radiation Pattern (Both Antennas Excited; 2.6 GHz)

19

Radiation Pattern (#1 excited; #2 terminated)

Gaintotal

Gaintheta

Gainphi

20

Radiation Pattern (#2 excited; #1 terminated)

Gaintotal

Gaintheta

Gainphi

21

S-parameters for the two antennas on tablet

22

Impedance Matching Improvement with Optenni Lab

* Thanks to Mr Jussi Rahola at Optenni for helping with the optimization

23

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

24

Efficiency without Matching

25

Matching Circuit with Discrete Components

26

S-parameters

27

Efficiencies

28

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

29

S parameters

30

Efficiency

31

Channel Capacity Analysis

* Thanks to Mr Oliver Stbler at AWE for helping with the simulations

32

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

33

Indoor Environment

Commercial software WinProp from AWE Communications is used to calculate the channel capacity

www.awe-communications.com

34

MIMO Configurations

35

1x2 MIMO system

2x2 MIMO system

Channel Capacity in Indoor Environment

36

Simulation along a trajectory in an urban area (1x2 MIMO)

Channel Capacity in Urban Environment

37

Simulation along a trajectory in an urban area (2x2 MIMO)

Channel Capacity in Urban Environment

38

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