AXIEM Application Note
Transcript of AXIEM Application Note
Polling and listening layouts as depicted in AXIEM with ports shown as well
(Design is courtesy of Rohde & Schwarz)
AXIEM®
Application Note
Design Of A Near Field Communication Antenna System
INTRODUCTIONNear field communication (NFC) is being developed as a form of contactless
communication between wireless devices like smartphones and tablets. This
technology enables users to do things like swipe their devices at the checkout
stand or wave them over another NFC-compatible device to share information
instantly without complicated setups or physical connections.
The antenna systems of these NFC-enabled devices are a critical component. In
general, the successful design of NFC antenna systems operating at 13.56MHz
requires electromagnetic (EM) simulation of both the polling and listening sides of
the antenna system, as well as the incorporation of discrete elements (including
nonlinear diode bridges that convert RF energy into DC signals). The typical analyses
performed include RF matching as a function of polling/listening distance, detection
of DC signal levels under various conditions, polling coil inductance, and generation of
harmonics at the DC port.
EM SIMULATION USING AXIEMThe sample NFC design used in this application note (monitor image below) is courtesy of
Rohde & Schwarz (R&S), a long-standing member of the NFC consortium that is respon-
sible for developing related NFC specifi cations and technology. To begin, the design is
imported into AWR’s Microwave Offi ce™/AXIEM environment by means of a Gerber fi le.
Once within AXIEM, the layout is assigned ports for the relevant discrete elements in the
design. AWR’s symbol generator wizard is then used to create a self-evident symbol.
Polling and listening layouts as depicted in AXIEM with ports shown as well
(Design is courtesy of Rohde & Schwarz)
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www.awr.tvCopyright © 2012 AWR Corporation. All rights reserved. AWR and AXIEM are registered trademarks and the AWR logo and Microwave Office are trademarks of AWR Corporation. Other product and company names listed are trademarks or trade names of their respective companies.
This more convenient and accurate method replaces the typical manual wiring of the
discrete elements using a 60-port generic block element.
Another novel and helpful feature within AXIEM is parameterization. Here, the
distances between polling and listening coils are parameterized such that a single
numerical parameter, Z, is swept over a range of values between 1mm and 100mm
(Figure 1), and, consequently, the thickness of the air layer between the coils is
controlled parametrically.
While the EM structure is for a fi nite set
of discrete Z parameters, in general Z
is continuous. In other words, while the
EM simulation is carried out at discrete
steps of 10mm (starting from 1mm),
the resulting swept model is interpolated
such that steps of 1mm are computed.
An interesting observation to note is
that if the RF matching of the polling
antenna is determined in the absence of
the listening antenna, the matching
deteriorates signifi cantly when the
listener is brought nearer. This is clearly
seen in the nonlinear matching plot on
the Smith chart in Figure 2.
CONCLUSIONThe innovative capabilities of AWR
software are well suited to the design of NFC antenna systems. With the ability to
incorporate EM models easily into nonlinear schematics, as well as support for EM
model parameterization and interpolation, AWR’s Microwave Offi ce/AXIEM software
combination is making it even easier for designers of NFC antenna systems to realize
compact designs and take their designs and productivity to new levels.
the resulting swept model is interpolated
antenna is determined in the absence of
listener is brought nearer. This is clearly
This more convenient and accurate method replaces the typical manual wiring of the
AX-NFC-2012.9.14
Figure1: Rectifi ed DC voltage vs polling/listening distances (in mm)
Figure 2: Proximity of listener circuit deteriorates RF matching at the poller input port. VSWR>2 if the distance between poller/listener is less than 18mm
— LSSnm(PORT_1,PORT_1,1,1)[1,1X] Listener_and_poller_circuit_Z — VSWR_CIR(2) Listener_and_poller_circuit_Z