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.

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