4g mimo antenna using genesys and design & · pdf filestandards affect antennas for base...

4G MIMO ANTENNA

DESIGN & Verification

Using Genesys And

Momentum GX To Develop

MIMO Antennas

© Copyright 2008 Agilent Technologies, Inc.

Agenda

• 4G Wireless Technology

• Review Of Patch Technology

• Review Of Antenna Terminology

• Design Procedure In Genesys

• Verifying Antenna Performance

• Using Genesys To Determine Multi-Element Patterns


• Using Genesys To Determine Multi-Element Patterns

• Verifying Method With Momentum GX

• Conclusion

4G Wireless: LTE, WiMAX, Mobile WiMAX, 802.11n

Fourth Generation Wireless Infrastructure:

• Higher Data Rates

– Up to 150 Mbs downlink, 50Mbs uplink

• Multi-Data Formats


• Multi-Data Formats

– Edge, GSM, FTE, UMTS etc.

• Speedy Mobiles 100 km/hr

Selection criteria for antenna type:

• Beam pattern

• Gain

• Power handling capability

• Directivity

Antenna Parameters


• Directivity

• Bandwidth

• Manufacturability

• Cost

Patch antenna topologies:

• Advantages

– Ease of manufacture

– Form complicated antenna patterns

– Flexible substrates

– Variety of shapes and structures

Patch Antenna Characteristics


– Variety of shapes and structures

– Weight

– Cost

• Disadvantages

– Substrate material limits efficiency

– Lossy, lower radiation efficiency means increased transmit power

– Power limited

There is an almost endless number of antenna feed topologies:

• Rectangular, Circular, Arrays

• Shapes affect bandwidth, radiation patterns and polarization

• Spacing and phase affect directivity, gain and radiation pattern

Patch Antenna Shapes


Patch Patterns

Series Feed

Parallel Feed

θE

E

Radiation Patterns

Fields defined by E-theta and E-phi

• Etotal is the vector sum of both components

• Etheta sweeps from the North Pole 0o to 90o

• Ephi sweeps from 0o to 180o around the North Pole


φE

Note relationship of the field to theX and Y axis of the circuit board

Orientation In Antenna Patterns

Patch antennas Rarely Have Symmetrical Pattern

• Due to current distribution on patch(s)


Phi=0o Phi=90o

Antenna Design Procedure

Use linear analysis to evaluate physical dimensions

Verify design with Momentum GX

• Determine additional matching circuitry using MATCH

• Examine prototype with far field analysis


Design and verify a steer-able beam array

• Develop a mathematical model of the far field pattern

• Apply procedure to dual antenna pattern

• Verify multi-element pattern with Momentum

20=Wν

∗+∗−

++

=hrr 121

11 εεε

Start with a rectangular design

• Resonance is determined by length along the feed axis

– Length is approximately

– Width is loosely equal to length, however maximum efficiency is given for width by (1)

2

λ

Patch Design


1

2

2

0

+∗=

rrfW

ε

ν

∗+∗

−+

+=

W

hrreff 121

2

1

2

1 εεε

( )

( )

+⋅−

+⋅+

∗=∆

8.0258.0

264.03.0

412.0

h

W

h

W

h

L

eff

eff

ε

ε

Fringe Effect

Lf

Leffr

∆⋅−⋅⋅

= 22

0

ε

ν

L∆ L∆L

W

Patch Design

Frequency requirements for LTE band II

• Approximately 7.5% bandwidth

• Transmit band is 60 MHz wide, 1850-1910 MHz

• Receive band is 60 MHz wide, 1930-1990 MHz


The design will then center at 1920 MHz

• Start a patch Length =1440 mils, with a Width =1860 mils

• Substrate is FR4 Er=4.5, height = .059 inches

Using Linear Modeling

Start with simple transmission line model to verify the length


Using Momentum GX

First simulation establishes resonant frequency


Of course transmission line does not model radiation

Markers show band edges for the transmit and receive bands

Reducing Patch Width And Optimizing Length

Reducing patch width has small effect on response but reduces footprint

Length =1434.5 mils

Width =1200 mils


Evaluating Matching Structures

Using Genesys MATCH we can determine the optimum matching structure

Start with settings dialog we set the frequency band of match

• The settings represent the full band 1850-1990 MHz with 50 pts


Using Antenna Data For Match

In Sections Tab We Point MATCH To The Momentum Data Set As The Terminating Impedance

The Type Of Matching Structure Is Selected Next

• We will try to use distributed matching for incorporation into the layout


Stepped Impedance Network

Stepped impedance provides a good match at band center but the band edges are not improved


Quarter Wave Matching Line

A simple quarter wave provides improvement at band center but again the band edges are not improved


Match For Transmit Band

The patch antenna chosen is inherently narrow band

• Focus on matching for the transmit frequencies since a poor match can result in watts of power loss

• Re-center resonant frequency for transmit band center 1880 Mhz


Slight increase in antenna length decreases center frequency

Synthesize Matching Network

Using MATCH Again To Find Best Structure

• In this case a simple quarter wave transmission provides an adequate match at band center and edges

Length =1434.5 mils


Final Momentum Analysis

Final analysis places center frequency at ~1880 MHz

• Quarter wave matching line gives us -36 dB return loss at ~1880

• Transmit band edges provide ~-10 dB return loss

• Receive band has the worst match of -6.5 -> -3 db, possible second antenna


Plotting Field Patterns

We must have performed a Momentum simulation first!


Etotal Compared To Phi

Select antenna graph measurement then select phi cut

• Radiation pattern is dependent upon rotation around phi axis


Antenna Patterns

Field pattern is a function of φ

90=φ

0=φ


θ

00=φ

θ

090=φ

90=φ

Standards affect antennas for base stations and mobiles devices

Base stations need to provide data to multiple users while compensating for multi-path and delay

Mobiles also need to compensate for multi-path and fading

MIMO Networks Require Agile Antennas


Networks Require Agile Antennas

Variety of antenna function and types

Omni Directional

Steer-able Array

Diversity


Switched or Multi-Beam

Patch Antenna Types

MIMO- Steerable Antenna

Use Genesys to develop MIMO Antennas

Design and evaluation of steerable MIMO Antennas

• We use the results of our antenna design to predict the contributions from an array

• If the patch antennas are reasonably isolated Smn~ 0, then linear superposition can be used to plot the far field contributions (2)


mnsuperposition can be used to plot the far field contributions (2)

Determining Far Fields

Far Field value is the superposition of each radiator

22 ))cos(*())sin(*(1 dRRFp −+= θθ

FAR FIELD

FAR FIELD


θ

4/λ=d

R

Fp1 Fp2

θ

R )sin(* θR

dR −)cos(* θ

dR +)cos(* θ

22 ))cos(*())sin(*(2 dRRFp ++= θθ

α∠A β∠B

Mathematically Generated Pattern

v2k

Antk

B cos δk( )⋅ B sin δk( )⋅ i+( )⋅:=

v1k

Antk

A cos γk( )⋅ A sin γk( )⋅ i⋅+( )⋅:=

δk β 2π Fk

⋅−:=

γk α 2π Ek

⋅−:=

Fk

R cos θkπ

2−

⋅ K−

2

R sin θkπ

2−

⋅

2

+:=Ek

R cos θkπ

2−

⋅ K+

2

R sin θkπ

2−

⋅

2

+:=

Antk

.5 cos θk π−( )( )1.0⋅ .5cos θk π−( )−:=β 0deg:=α 0deg:=

D 2 K⋅:=K nλ

4⋅:=R 100 λ⋅:=n 1:=λ 1:=

B .5:=A .5:=θk kπ

180⋅:=k 0 360..:=

Superposition of Fields


0

15

30

45

607590105

120

135

150

165

180

195

210

225

240255 270 285

300

315

330

345

0.8

0.6

0.4

0.2

0Vk

θ k

0

15

30

45

607590105

120

135

150

165

180

195

210

225

240255 270 285

300

315

330

345

0.8

0.6

0.4

0.2

0Ant k

θ k

Vk

v1k

v2k

+:=

30

45

607590105

120

135

150

0.8

0.6 30

45

607590105

120

135

150

0.8

0.6

Far Field plot of two omni-directional antennas

• Driven with equal amplitude and in phase

• Note the new directionality

Superposition Of A Two Element Array


0

15

30150

165

180

195

210

225

240255 270 285

300

315

330

345

0.4

0.2

0Ant k

θ k

0

15

30150

165

180

195

210

225

240255 270 285

300

315

330

345

0.6

0.4

0.2

0Vk

θ k

Single Antenna Pattern Result Of Far Field Superposition

Antenna Interference

An intuitive look at interference vs. spacing

• Like colors or phases add while unlike colors or phases subtract

A


+

+

++

A B

Front Sided Antenna

45

607590105

120

135 0.8

0.6

45

607590105

120

135 0.8

Little or no backward radiation

• Pattern becomes narrower with little side lobe radiation

• Typical of patch antenna


0

15

30150

165

180

195

210

225

240255 270 285

300

315

330

345

0.6

0.4

0.2

0Ant k

θ k

0

15

30150

165

180

195

210

225

240255 270 285

300

315

330

345

0.6

0.4

0.2

0Vk

θ k

Changing The Feed Phase

0

15

30

45

607590105

120

135

150

165

180

0.8

0.6

0.4

0.2

0Vk

β 90− deg:=

Varying the phase and amplitude of the elements

• Results in controlling the tilt or angle of maximum radiation


0

15

30

45

607590105

120

135

150

165

180

195

210

225

240255 270 285

300

315

330

345

0.8

0.6

0.4

0.2

0Vk

θ k

β 60− deg:=

0180

195

210

225

240255 270 285

300

315

330

345

0

θ k

β 90− deg:=

0

15

30

45

607590105

120

135

150

165

180

195

210

225

240255 270 285

300

315

330

345

0.8

0.6

0.4

0.2

0Vk

θ k

β 180− deg:=

Pattern Array

Field patterns for an array of antenna elements can be analyzed or synthesized by*….

1) Knowing the single element radiation pattern

2) The amplitude and phase of the sources driving each element

3) Knowing the spacing or separation between elements

Method may be extended to multiple elements


Method may be extended to multiple elements

*Interference or coupling between elements is zero or nearly zero

d d d

α∠A β∠B χ∠C δ∠D

Array Design In Genesys

Applying the same trigonometry within Genesys

• We start with the single patch antenna from before

• Using Momentum far field data we obtain the element pattern

• Genesys’ rich set of math functions allows us to project far field data from the captured single element pattern

• This method may be extended to two or more element arrays


• This method may be extended to two or more element arrays

• The ability to tune parameters such as feed amplitude and phase as well as antenna distance gives full control over the far field

• When applied to a large number of elements, optimization reduces the time and effort

Extracting The Element Pattern

Run a Momentum GX analysis of the proposed antenna

Extract Momentum E-field dataset values for single element


New Data Vector

With Field Values

Using Genesys Math Functions

Trigonometric equations relating far-field value to element pattern characteristics

Antk

.5 cos θk π−( )( )1.0⋅ .5cos θk π−( )−:=

R 100 λ⋅:=K nλ

4⋅:=n 1:=λ 1:=

β 0deg:=α 0deg:=D 2 K⋅:=B .5:=A .5:=θk kπ

180⋅:=k 0 360..:=

SUPER POSITION OF FIELDS


Vk

v1k

v2k

+:=

v2k

Antk

B cos δk( )⋅ B sin δk( )⋅ i+( )⋅:=

v1k

Antk

A cos γk( )⋅ A sin γk( )⋅ i⋅+( )⋅:=

δk β 2π Fk

⋅−:=

γk α 2π Ek

⋅−:=

Fk

R cos θkπ

2−

⋅ K−

2

R sin θkπ

2−

⋅

2

+:=Ek

R cos θkπ

2−

⋅ K+

2

R sin θkπ

2−

⋅

2

+:=

Tuning For Phase And Levels

Antenna parameters are made tunable

• Instant visualization on far field pattern


Antenna A level

Antenna B level

Phase Difference

Antenna spacing in half wavelengths

0o Phase

Result Of Phase Offsets

Antenna beam steers, side-lobes and beam width change

~28o

~42o


90o Phase

60o Phase

Additional Degrees Of Freedom

Pattern is influenced by drive levels and element separation

Added elements offer improved control over beam


Element spacing 1.3 half wavelengths Element spacing 3 half wavelengths

Verifying Predicted Pattern

Layout two element patch antenna modeled after single element previously designed and simulated

Use Momentum to generate the combined far-field with appropriate voltages and phase

Review the far-field pattern to verify the predicted performance


Verifying Isolation

At band center, 1880 MHz isolation is -43 dB


-43 dB=50 millionths

Setting Source Values

Under Momentum’s far-field options

The source levels and relative phase


Note that the phase is set at 180o …Why?

More Features For Momentum GX

3D Field Viewer


Comparing Predicted Field

Comparison of far-field predicted and Momentum GX

• Both show a half power beam width of 290

PREDICTED Momentum Momentum 3D ViewSingle Element Pattern


Adding Phase Shift At Ports

28 DegreesPREDICTED Momentum

Result of 28o difference in phase between sources

• Note identical beam values at -3dB of 38O from beam center


Note: The current version of Momentum plots half beam

Using Two Evaluations

Plotting both halves of Momentum field requires two phase evaluations

• Note values are equal between predicted and Momentum!

60 Degrees

PREDICTED Momentum


60 Degrees

Elements Driven Opposite

The extreme for two element antenna is 180 phase difference

180 Degrees

PREDICTED Momentum

Difference in magnitude due to re-normalizing in Momentum


Orientation Of Beam Relative To Board

Major cut was through phi = 0

Swept pattern steers along X-axis


00=φ

Field Pattern In Genesys

Extending the equations to four elements a narrow beam is achieved


Optimization Of Beam Pattern

Beyond two elements selecting the correct feed-phase is burdening

• We use the optimization features of Genesys to aide in finding the best set of feed amplitude and phases


Goal = 30 deg

Beam Amplitude Optimization

Additionally we optimize the feed amplitudes to compensate for beam power as a result of steering

886.1265.0

688.2271.0

374.268.0

139.1268.0

−∠=

∠=

−∠=

∠=

d

c

b

a

Angles in radians


886.1265.0 −∠=d

Other Sources Of Antenna Data

Single antenna element information can be measured and imported via TestLink


Conclusion

�An antenna design procedure was presented

�A rectangular patch was designed and verified with Momentum 3D-Planar EM Field Simulator

�A modified antenna was optimized for a LTE band and matching network incorporated

�The single patch field pattern was then used to model or predict the effect of an array of two or more elements


of an array of two or more elements

�Verification of this technique was established with Momentum field solver

�Optimization aides in extending this procedure to larger arrays

Agilent Genesys product bundles start at about $4K USD

The modules used to complete the synthesis, design and verification of MIMO antenna system presented in this paper can be found in the Genesys Non-Linear Pro GX


paper can be found in the Genesys Non-Linear Pro GX (W1426L) for about $16.6K USD

References

Antenna Theory Analysis and Design, Constantine Balanis, Wiley, second edition, Pgs 727-736

Ibid, Pgs 249-261

Fundamentals of Applied Electromagnetics, Fawwaz Ulaby, Prentice Hall,1997, Pgs 316-365

Agilent AN note “3GPP Long Term Evolution”, doc 5989-8139EN


Agilent AN “Mobile WiMAX PHY Layer Operation and Measurement”, doc 5989-8309EN

Agilent AN “MIMO Channel Modeling and Emulation Test Challenges”, doc 5989-8973EN

Agilent AN “MIMO Wireless LAN PHY Layer RF Operation & Measurement”, doc 5989-3443EN

4g mimo antenna using genesys and design & · pdf filestandards affect antennas for base...

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