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Overcome
the Challenges of Fast Changing Wireless Appliance Design
Using Agilent EEsof AMDS
By Erwin De Baetselier and Davy
Pissoort, Agilent EEsof EDA
Nowadays, wireless appliance designers face
many tough challenges. Not only do they have to fit multi-band,
multi-purpose antenna systems into small stylish housings
that are enticing to consumers, they also have to comply
with an increasing number of regulatory, operator and end-user
demands for radiation safety, high-performance functionality
and quality. Driven by intense competition, R&D processes
have increasingly adopted outsourced and modular design,
thereby creating additional challenges for project coordination,
teamwork and overall device quality. To help ensure the
development of appliances that are compliant with regulatory
and end-user performance requirements while also meeting
stringent time-to-market deadlines, today’s antenna
designers now require a new design tool, one that can adequately
address the many challenges of wireless appliance design.
Modern Product Demands
To successfully address the needs of modern wireless appliance
designers, 3-dimensional Electromagnetic (3D EM) antenna
design tools must move beyond the more conventional simulator
with a nice-looking user interface. There are a number of
reasons driving the need for such a move (see Figure
1).
They include:
• CAD environments need to facilitate seamless cooperation
between antenna designers and industrial designers who have
an increasing influence on the types and shapes of the antennas
used in modern wireless appliances.
• The effect of real-world interaction, such as the
detuning of the antenna by bringing the wireless appliance
in contact with a hand or close to a head, needs to be coupled
back to the RF antenna module.
• 3D EM antenna design tools must include information
on the antenna diversity functionality to accommodate antennas
in Multiple-Input, Multiple Output (MIMO) systems.
• Users want to reliably and efficiently check their
latest design against up-to-date compliance standards tests
such as Hearing Aid Compatibility (HAC), Over-The-Air (OTA)
performance and Specific Absorption Rate (SAR).
• The transceiver/antenna test phase has become a
critical bottleneck for time-to-market. When the appliance
finally meets the operator and regulatory demands, will
it also meet customer expectations with regards to reception,
voice quality and battery life?
Addressing these needs is critical to the overall success
or failure of modern wireless appliances.
A Better Solution
A prime example of an effective 3D EM antenna design tool
offering much more than a simulator with a nice-looking
user interface is the Antenna Modeling Design System (AMDS)
from Agilent EEsof. It is the only solution specifically
developed to enable antenna and industrial product designers
to overcome the challenges of fast changing wireless appliance
design.
AMDS works by efficiently importing, meshing and simulating
an entire wireless appliance, together with its surrounding
real-world environment, to analyze compliance standards
such as HAC, MIMO antenna diversity and SAR. By doing so,
AMDS drastically cuts design cycle time and minimizes risk
prior to the wireless appliance progressing through the
slow and expensive process of physical testing. It is the
full-wave 3D electromagnetic simulation tool for the antenna
designer with a unique feature set to:
• Efficiently import CAD data from product designers
and eliminate time-consuming EM modeling redefinition in
subsequent design iterations between antenna and product
designers.
• Guarantee antenna compliance to legal/operational
standards such as HAC, OTA and SAR. It also optimizes performance
for MIMO by analyzing antenna placement and diversity for
the entire physical wireless appliance.
• Optimize end-user product performance quality by
introducing real-world proximity interaction of the human
body into the antenna EM simulation.
A Wide Breadth Of Functionality
The AMDS 3D EM simulator is based on Finite Difference Time
Domain (FDTD) technology, which provides a full-wave solution
to the 3D EM problem and is able to handle complex, arbitrarily
shaped 3D metals and dielectrics (see Figure 2).
The inherent simplicity of the solution’s meshing
and equation set has a number of key benefits. For example,
for arbitrary shapes, it is computationally more efficient
than EM simulators based on finite element method (FEM)
or method of moment (MOM), and offers fast wideband analysis
in a single simulation run. Additionally, its easy parallelization
allows for things like accelerated simulations on hardware
graphical processor cards and multi-threaded simulations.
AMDS features an intelligent hierarchical CAD data interface
that seamlessly imports and exports complete wireless appliance
structures created by industry-standard CAD packages such
as Step, ProE, and SAT (see Figure 3).
Its design flow is completely optimized for efficient re-iteration
of complex designs, thereby allowing mobile appliance designers
to simulate a large number of prototypes (see Figure
4). Following the second design iteration, the
complete design can be imported and modeled in minutes.
Physical product shape iterations and antenna placement
analyses can be performed repeatedly without the time-consuming
and error-prone manual redefinition of materials and mesh
settings.
Using AMDS, an over 70 percent time savings (e.g., with
regard to modeling and setup) can be realized. In contrast,
other tools easily require 4 to 8 hours just to set up a
simulation. As an added benefit, AMDS’s state-of-the-art
design management allows smooth iterations between antenna
and industrial designers to create the latest look of high-performance
wireless appliances.
Meeting the Next Major Design Challenges
With its unique functionality and benefits, AMDS is ready
for the next major design challenges, whether they pertain
to antenna diversity, HAC, SAR simulation, or optimizing
the design for real-world interaction.
Antenna Diversity
MIMO systems have today become an important enabler for
Wireless LAN applications. Part of MIMO design encompasses
antenna diversity simulations, as illustrated in Figure
5 by an example that comprises two monopole antennas
mounted on an FR4-substrate. Antenna diversity guarantees
good reception, whatever the polarization or direction-of-arrival
of the incoming signal.
By default, antenna diversity parameters are typically
calculated for a cross-polarization discrimination (XPD)
of 0 dB and a uniform probability density function. In contrast,
the Advanced Antenna Diversity Options in AMDS allow the
designer to create a custom probability density function.
The simulation then yields the typical antenna correlation
parameters (see Figure 6).
Hearing Aid Compatibility (HAC)
RF signals from mobile phones can couple to hearing aids,
generating noise that prevents acceptable use of such phones
by hearing aid users. By February 2008, all wireless carriers
in the U.S. must ensure that 50 percent of their phones
are hearing-aid compatible (see Figure 7).
AMDS allows the designer to evaluate the hearing aid compatibility
between wireless communications devices and hearing aids
very early in the design cycle. This compatibility is verified
in accordance with the IEEE American National Standard Methods
of Measurement of Compatibility (ANSI C63.19-2006). Following
simulation, a single-screen evaluation tool is opened which
displays the various wireless standards used in the phone
(e.g., GSM or CDMA). Each standard creates different hearing
aid interferences which can be taken into account by simply
adjusting the tool’s Articulation Weighting Factor
(AWF). Being able to get detailed information on the total,
tangential and normal electric/magnetic fields on the HAC
scan area is of tremendous help to the designer when optimizing
the design of a mobile phone to comply with a higher HAC
category (see Figure 8).
SAR (Specific Absorption Rate) Simulation
The SAR is the unit of measure commonly used to determine
the interaction of electromagnetic fields with human tissue.
Most regulations involving devices producing electromagnetic
fields must not exceed some specified exposure limit --
typically defined in terms of the SAR averaged over a cubical
volume of tissue. The IEEE sets exposure levels in terms
of one gram averaging volumes for the majority of the body,
with a ten gram averaging volume being applied to extremities
such as the ears or fingers.
In AMDS, SAR calculations with 1 and 10 gram averages, whole
body average and locate peak SARs are conducted in accordance
with the protocol of the latest C95.3 standard. A wide set
of human body phantoms containing the latest Standard Anthropomorphic
Model (SAM) standards complements AMDS’s SAR and bio-temperature
calculations. This ensures that the designer is able to
meet the highest benchmark specifications in the industry
(see Figures 9 and 10).
Note that the simulation time for a typical handheld wireless
appliance, next to the SAM head, is less then 30 minutes.
Optimize for Real World Interaction
AMDS allows the designer to optimize the antenna structure
and its placement within the wireless appliance for maximal
performance in the presence of, for example, a human head
or hand (see Figure 11). In this manner,
the designer can determine the detuning by, and sensitivity
to, real-world interaction and meet end-user performance
requirements before the bottleneck in prototype testing
which often dramatically increases the actual time-to-market.
As an example of AMDS’s ability to optimize real-world
interaction, the impact of a hand and head on the performance
of the Bluetooth and GSM antenna inside a cell phone (e.g.,
wireless appliance) were investigated. The results are displayed
in Figure 12.
A Rapid Design Cycle
In the above example of a complete cell phone, AMDS can
perform the entire wideband simulations in roughly 15 minutes
with a memory consumption of less than 400 Mb. The hierarchical
CAD data management guarantees over a 70 percent time savings
on modeling and setup of iterated designs. This fast cycle
time enables the designer to simulate various setups of
a mobile phone to assure optimal performance in all circumstances
before its actual physical assembly. AMDS also comes standard
with the ability to take advantage of the latest evolution
in multiprocessor and multi-core platforms for even faster
computation. The designer can even use Message Passing Interface
(MPI) technology to run AMDS on computer farms to solve
very large problems.
AMDS uses the latest hardware acceleration-engines-based
GPU technology from Acceleware (www.acceleware.com). As
a result, speed-ups of 35 times compared to non-accelerated
simulations on regular processors are possible.
Conclusion
Successfully addressing the needs of modern wireless appliance
designers is a difficult task -- one that is not adequately
addressed by today’s conventional simulators with
a nice-looking user interface. AMDS is the only full-wave
3D electromagnetic simulation tool designed specifically
for the antenna designer with unique functionality ranging
from the ability to efficiently import CAD data to guaranteeing
antenna compliance to legal/operational standards. It also
allows the designer to simulate antenna structure and placement
within a wireless appliance in the presence of real-world
proximity effects, such as the human head and hand, to determine
parameters such as detuning and sensitivity. These capabilities
help ensure the development of wireless appliances that
are compliant with regulatory and end-user performance requirements,
while also meeting today’s stringent time-to-market.
For the antenna designer, the benefits of using AMDS are
obvious – better designed wireless appliances with
an increased chance of success in the marketplace.
About the Authors
Davy Pissoort received electrical engineering and PhD
degrees from Ghent University in 2001 and 2005, respectively.
From October 2001 until October 2006 he worked at the Department
of Information Technology of Ghent University as a doctoral
and post-doctoral researcher of the Fund for Scientific
Research-Flanders (Belgium) (F.W.O.-Vlaanderen). In June
and July 2004 he was a visiting scientist at the Department
of Electrical and Computer Engineering of the University
of Illinois at Urbana-Champaign (UIUC), IL, USA. In November
2006, he joined Agilent Technologies as a research engineer.
Erwin De Baetselier holds a BS degree in Medical Sciences,
an engineering degree in Applied Physics and a PhD degree
in electronics. He worked as a researcher in the Faculty
of Medicine at the VUB (Brussels University) and at the
Electronics and Information Systems department of the Ghent
University. He joined Hewlett Packard/Agilent EEsof EDA
in 1997 as a research engineer in the SI domain. As off
1999 he was the Agilent EEsof EDA technical support manager
for Europe. For the last year, he has been program manager
for the AMDS product.
Agilent Technologies
www.agilent.com
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