university of patras electrical & computer eng. dept. laboratory of electromagnetics compact...

UNIVERSITY OF PATRASELECTRICAL & COMPUTER ENG. DEPT.LABORATORY OF ELECTROMAGNETICS

Compact Printed Antennas for Small Diversity and MIMO Terminals

Professor V. Makios

Laboratory of Electromagnetics

Department of Electrical and Computer Engineering

University of Patras

Patras, Greece



Professor C. Soras (Director)

Dr. M. Karaboikis

Dr. G. Tsachtsiris

V. Papamichael

Antenna group

Laboratory of Electromagnetics


Outline

• Introduction

• Multi Element Antenna (MEA) Systems Evaluation

• Compact Printed MEA Systems Design

• Diversity and MIMO Systems Performance

• Conclusions


Modern Antenna Systems Demands

1. Mitigation of fading in wireless communications

Diversity techniques at the receiver

2. Requirements for higher data rate communications

Multiple Input Multiple Output (MIMO) wireless systems


Printed versus Non Printed Antennas

1. Zero-cost

2. Ease of fabrication

3. Ease of integration in small terminals

So far in the major part of literature for Diversity and MIMO applications

• Non-printed antennas (Planar Inverted F Antennas or dipole arrays)

• Up to 3-element printed antennas have been proposed

Advantages of Printed Antennas


Trade-off in Diversity/MIMO Performance

Increasing the number of integrated antennas

Diversity and MIMO performance is enhanced

What is the maximum number of printed elements in a compact Diversity/MIMO system terminal for maximum performance ?

Restricted space of small terminal device

Strong mutual coupling among antenna elements

Query


MEA Systems Evaluation

Criteria for achieving Diversity/MIMO performance

Diversity performance metric MIMO performance metric

• Mean Effective Gain (MEG)

• Envelope Correlation Coefficient (ρe)

•Effective Diversity Gain (EDG) • MIMO capacity (C)


Criteria in Non Uniform Environment

* * 2i j i j

eiji i j j

| (XPR ( ) ( ) ( ) ( ) ( ))d |

(XPR G ( ) ( ) G ( ) ( ))d (XPR G ( ) ( ) G ( ) ( ))d

Mean Effective Gain (MEG) :

Envelope correlation coefficient (ρe) :

XPR 1MEG P (Ω) G (Ω) P (Ω) G (Ω) d Ωθ θ φ φ1 XPR 1 XPR

G (Ω) : active gain pattern

E(Ω) : active electric field pattern

P(Ω) : angular density function

XPR : cross polarization power ratio

MEGi 1MEG j

ρ < 0.5eij Environment

Characteristics


Criteria in Uniform Environment



radeMEG

2

XPR 1

P P 1/ 4πθ φ

Uniform Environment

eij

2* *S S S Sii ij ji jj

2 2 221 S S 1 S Sii ji jj ij

erad : radiation efficiency


Effective Diversity Gain Calculation

+

Effective Diversity Gain (EDG)

CDF of SNR of the combined signal(CDF : Cumulative Distribution Function)



Pdiv : the received power level of the combined signal

Pideal : the received power level of a dual-polarized isotropic radiator with unit

radiation efficiency operating in the same environment

Pdiv and Pideal are read at the same probability level in a CDF versus SNR plot

div

ideal

PEDG

P


MIMO Capacity CalculationThe Capacity (C) of a N x N MIMO system when the channel state

information is not known at the transmitter:

HT2 N 2

PC log det

N

I TT

The Transfer matrix T elements are evaluated using a generic

MIMO channel model:

n m

Lj

nm R R T T1

T e

E a E

Complex channel gainNumber of

multipath

components

Direction of Arrival Direction of Departure

PT : transmitted power

σ2 : noise power

IN : NxN Identity matrix


Investigated MEA Systems Design

The layouts of the investigated

compact printed Multi Element

Antenna (MEA) systems

Compact due to the use of :

device’s ground plane

fractal concepts (Minkowski monopole)

short circuit (Inverted F Antenna (IFA))


Investigated MEA Systems Design

Compact due to the use of :

device’s ground plane

fractal concepts (Minkowski monopole)

short circuit (Inverted F Antenna (IFA))

The layouts of the investigated

compact printed Multi Element

Antenna (MEA) systems


Sii parameters of MEA Systems(a) (b)

(c) (d)

(e)

(a), (b), (c) measured

(d), (e) simulated (IE3D)

• Antennas’ placement with

respect to the ground plane

• The dimensions of the

antenna elements

In all cases the antennas are

well tuned at 5.2 GHz ISM

band (5.15 – 5.35 GHz)

due to

20log( ) ii iSΓi : reflection coefficient at ith antenna port


Active Gain Patterns of MEA Systems(a) (b)

(c) (d)

(e)

In all cases the patterns exhibit

complementary performance

(pattern diversity)

Antennas’ placement with

respect to the ground

plane which affects their

radiation characteristicsAll patterns are

simulated using IE3D

due to


Radiation Efficiencies of MEA Systems

i i irad mis losse e e

N 2imis ij

j 1

e 1 S

Perpendicular orientation causes comparatively

high efficiencies

Average erad value drops as the number of

branches increase

Since |Sii| < -14dB for all cases the drop is solely attributed to the power coupled into the feed

network (|Sij|2)


MEG, ρe and EDG Results

Propagation in a Uniform Environment

XPR 1

P P 1/ 4πθ φ

Strong mutual coupling leads to

saturation behavior

Similarity of patterns due to

symmetry


EDG Results in Non Uniform Environments

Saturation behavior

The uniform environment approximates the indoor

scenarios and the elliptical distributions quite well

Simpler equations for ρe and MEG calculation can be utilized

simplifying considerably the performance evaluation

Interesting Remark


MIMO System Modeling

Tx – Rx separation distance is 10m

(dx,dy,dz) = (20m,30m,3.5m)


Propagation Scenario Description

Single bounce scattering mechanisms uniformly distributed with the constraint to reside in the far field

region of the Tx and Rx antenna arrays

The θθ, θφ, φθ and φφ scattering coefficients of the channel’s complex gain are complex Gaussian

variables with zero mean and unit variance

T matrix is realized 6000 times assuming L=21 multipath components

n m

Lj

nm R R T T1

T e

E a E

je a


MIMO Capacity Results

Propagation in the Indoor Environment

The same transmitted power is used for all MIMO systems

for a fair comparison

The effects of both the correlation properties and the power

transmission gain on channel capacity are taken into account

Saturation behavior


Conclusions

All systems satisfy the Diversity/MIMO criteria

The high directivity elliptical distribution propagation

scenario provides the maximum EDG (16.4 dB)

The maximum 1 % outage capacity achieved with unknown

channel state information at the transmitter is 20.4 bps/Hz for the

five-element system


Conclusions

Antennas’ orientation and placement has an impact

on the overall system’s performance

1. Vertical orientation of the closely spaced elements has

proven to increase the elements’ efficiency by

decreasing the corresponding mutual coupling

2. By appropriately placing the elements at the edge of the

ground plane, pattern diversity was achieved.


Conclusions

According to the results, the uniform power distribution

model is a very good approximation for the indoor

scenarios (Gaussian, Laplacian and Elliptical)

Considerable simplifications of the diversity

performance evaluation procedure


Conclusions

For both Diversity/MIMO systems an asymptotic behavior

of performance was observer as the number

of antenna elements increases

Mutual coupling among closely spaced elements which

causes radiation efficiency reduction

An upper limit of five IFA/Minkowski elements

in a PC card for the 5.2 GHz ISM band is posed

due to


Future Work

The use of compact decoupling networks in order to

increase the upper limit of efficient printed antennas

onto a small Diversity/MIMO terminal device

The performance of compact multi element antenna under

various MIMO selection algorithms should be investigated


Thank You!!!


Criteria in Uniform Environment



radeMEG

2

Γ 1

P P 1/ 4πθ φ

Uniform Environment

eij

2* *S S S Sii ij ji jj

2 2 221 S S 1 S Sii ji jj ij

university of patras electrical & computer eng. dept. laboratory of electromagnetics compact...

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