Integrated Dual Band GSM Antenna Design

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Integrated Dual-Band GSM Antenna

design Marli Strydom CST AG

CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Problem description / specification

Embedded antenna design using Antenna Magus

Fullwave 3D simulation using CST STUDIO SUITE

Antenna matching using Optenni Lab

Conclusion

Outline


Problem Description

Theft and predator

alert device

Task: Replace an off-the-shelf dual

band GSM antenna with a cheaper,

printed, integrated antenna.

All images courtesy of Etse Electronics (www.etse.co.za) off-the-shelf antenna obscured


Possible Advantages

Planar nature allows antenna to be printed on PCB

reduction in manufacturing costs

reduction in assembly costs

Higher antenna efficiency

Longer amplifier & battery life

Possible Disadvantages

Engineering time and effort

Software cost?

Integrated Antenna Design


Dual band GSM 890 MHz – 960 MHz

1710 MHz – 1879.8 MHz

Antenna Specifications

Substrate - 4-layer FR4

Maximum available distance between two

metal layers is 1.203 mm

Max. antenna dimension: 70 mm x 10.5 mm

70 mm

10.5mm antenna

off-the-shelf antenna model obscured


Initial Integrated Antenna Design

using Antenna Magus


Finding the Right Antenna

2 templates matched 3/3 keywords – select the IFA

Printed inverted-F antenna (IFA)

Known antennas(>500)

Antennas in Magus (>200)

“GSM” (55)

“Planar” (44)

“Printed” (2)


Design Printed IFA


Estimated Performance (Single Elements)

Export Model

to CST MWS...


Simulated Results: Combined Elements

Simulation results on simplified

dielectric board

Retune antenna by quick

parameter sweep

900 MHz

element

1800 MHz

element

element length: l

detuned performance: l = 2.3 mm retuned performance: l = 3 mm


Model and Simulate

New Antenna in CST MWS


The following changes have to be made:

Reduce the substrate/ground plane size

Add components and tracks

Adjust Antenna Size

18 mm 10.5 mm


Effect of Fitting Antenna on Reduced Substrate

10.5 mm /0.41 inches

Real impedance has

changed from 44 to 8 Ohm


Antenna Magus Guidelines: Change Design

Shorting stub to compensate for

capacitance

Reduced height = decreased

input impedance

Design Guidelines

Info Browser


Antenna fits inside design area and

real impedance at 1800 is increased

from 8 to 30 Ω.

Match Impedance by

Adding an Extra Shorting Stub

Add stub to

compensate for

added capacitance

1800 band

element

moved


Import PCB into CST MWS


Simulation now includes: Reduced 900 MHz and

1800 MHz elements

Tracking device PCB

Battery

Housing

Simulation Including PCB, Battery

Discrete port (via onto RF chip)

Lengthen elements

Simulation time < 30 min


Design well matched at centre of both bands

Small substrate size results in reduced impedance

bandwidth

Required: good match

across GSM bands!

Simulation Results

GSM 900 and 1800 bands


Matching Network Design

using Optenni Lab


Fast and easy-to-use matching circuit optimization

tool for antenna designers

Main features:

Fast automatic matching circuit generation

Estimation of bandwidth potential

Two-way link to CST STUDIO SUITE

Mupti-port matching

Matching Network using Optenni Lab


Target: GSM 900 and

GSM 1800 bands

Original minimum

efficiency (red bars):

-4.2 dB in 900 band

-10.4 dB in 1800 band

Antenna Without Matching

Blue curve: S11

Green curve: efficiency


Bandwidth potential for a

lossless two-component

matching circuit at 6dB

return loss level

GSM 900: 33 MHz

(wanted: 70 MHz)

GSM 1800: 46 MHz

(wanted: 170 MHz)

Thus: antenna is difficult

to match!

Bandwidth Potential


Minimum efficiency

about -3.6 dB (45%)

Performance drops by

0.5 dB when losses are

considered

Dual Band Matching Circuit


Antenna in Realistic Environment


Impedance match

unchanged

Farfield changes

Device in More Realistic Environment 900 MHz

1.8 GHz

tracker positioned 9 cm from sheep

simulation took about 1.5 hours


Friis Range Comparison

GSM bands

Integrated antenna

With matching

Frequency [GHz]

Range [

km

]

Friis parameters:

Pt = 2 W; Pr = -80 dBm

S11,r = -40 dB

Gr = 9 dBi

900 MHz: Gt between 0 and 2.8 dBi

1800 MHz: Gt between 0 and 4.5 dBi

best case:

30 km

worst case:

22 km best case: 18km

worst case: 11 km

Matching improvement

2

,11

2

,11

2

114

rtrt

t

r SSR

GGP

P


A new customised integrated antenna was designed for

this particular tracking device to operate in the GSM

900 band and GSM 1800 bands.

The design process was made easier by using advanced

tools like Antenna Magus, CST MICROWAVE STUDIO, and

Optenni Lab.

The printed design can reduce unit cost per tracking

device by replacing an off-the-shelf antenna and

reducing the labour required to assemble the antenna,

and can have better performance.

Conclusion

Integrated Dual Band GSM Antenna Design

Documents

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