The
Art
of
UHF
RFID
Antenna
Design:
Impedance-Matching
and
Size-Reduction
Techniques
Gaetano
Marrocco
Dipartimento
di
Informatica
Sistemi
e
Produzione,
University
of
Roma
'Tor
Vergata"
Via
del
Politecnico,
1,
00133,
Roma,
Italy
Tel:+39
06
72597418,
Fax:+39
06
72597460;
E-mail:
marrocco@disp.
uniroma2.
it
Abstract
Radio-frequency
identification
technology,
based
on
the reader/tag
paradigm,
is
quickly
permeating several
aspects
of
everyday
life.
The
electromagnetic
research mainly
concerns
the
design
of
tag
antennas
having
high
efficiency
and
small
size,
and
suited
to
complex
impedance
matching
to
the
embedded electronics.
Starting from the
available
but
fragmented
open
literature,
this
paper
presents
a
homogeneous
survey of
relevant
methodologies
for
the design
of
UHF
passive
tag
antennas. Particular
care
is
taken
to
illustrate,
within
a
common framework, the basic
concepts
of
the
most-used
design
layouts.
The
design
techniques
are
illustrated
by
means
of
many
noncommercial
examples.
Keywords: Antennas;
REID;
tag;
impedance
matching;
T-match;
meander
line
antenna;
small
antenna;
PlEA;
lEA
1.
Introduction
T
he
idea
of
radio-frequency
identification
(RFTD)
of
objects
and
remote
control
of
devices
was
first
introduced
in
late
1948
by
H.
Stockman
[1].
After
the
big
efforts
produced
by
the
devel-
opment
of
microelectronic technology
in
the
1970s
[2],
and
the
continuing
evolution
of
the
last
decade
[
3,
4],
REID
is
now
becoming
a
pervasive technology
[5,
6]
in
everyday
life
[7].
It
is
also
being
used
in
more
advanced
applications, involving
logistics,
inventory
management,
systems
for
disabled people,
homeland
and
personal
security,
distributed
sensor
networks
[8],
and
mobile
healthcare
[9].
A
basic
RFID
system
comprises
a
radio-scanner
unit, called
a
reader,
and
a
set
of
remote transponders, denoted
as
tags.
The tags
include
an
antenna
and
a
microchip transmitter with
internal
read/write memory.
In
passive
tags,
the
energy
required
to
drive the
microchip
comes
from
the
interrogation
system
itself.
A
backscattering
modulation
is
achieved
when
the
microchip
acts
as
a
switch,
to
match
or
mismatch
its
internal load
to
the
antenna.
Several
frequency
bands
have
been standardized
for
this
tech-
nology. Low-frequency
(LF,
125-134
kHz)
and
high-frequency
(HF,
13.56
MHz) systems
are
the
most
mature
and
worldwide
dif-
fused
technology.
They
are
based
on
quasi-static
magnetic
flux
coupling
among
the
reader's
and
tag's
coils.
Ultra-high-frequency
(UHF,
860-860
MHz)
and
microwave
(2.4
GHz
and
5.8
GHz)
systems instead involve electromagnetic
interaction
among
true
antennas
and
permit
longer
communication
links,
and
they
are
the
emerging technology.
Together
with
the
power
sensitivity
of
the
microchip,
the
tag's
antenna plays
a
key role
in
the
overall RFID system
perform-
ance
factors, such
as
the
overall
size,
the
reading
range,
and
the
66
ISSN
1045-9243/2008/$25
@2008
IEEE
compatibility
with
tagged
objects.
Most
of
the
antennas
for
IJHF
ominidirectional
tags
are
commonly
fabricated
as
modified
printed
dipoles.
The
design
goal
is
to
achieve
the
inductive input
reactance
required
for
the
microchip conjugate impedance
matching,
and
to
miniaturize
the
antenna
shape.
Several
tricks
are
used,
and the
resulting
tags
sometimes
exhibit
charming
and
nearly artistic
lay-
outs.
Although
many
tag
configurations
can
be retrieved
in
scien-
tific papers,
or
even
in
the
catalogs
of
commercial products,
there
is
a
lack
of
systematization
of
the design
methodology.
A
first
tuto-
rial
paper
was
available
in [10],
where
the
concept
of
conjugate
impedance
matching
to
the
microchip
was
reviewed, some
per-
formance
parameters
were
introduced,
and
fabrication
and
meas-
urement
procedures were
described
in
some detail.
This
paper provides
a
unitary
and
general
survey
of
the
most-
used
design procedures
for
miniaturized
tag
antennas
with
a
com-
plex
impedance
matched
to
the
microchip
load.
Attention
is
devoted
to
the
rationale
and
to
the
main features
of
basic
configu-
rations,
by
the
modification
and
combination
of
which
a
great
vari-
ety
of
tag
layouts
can
be
easily
obtained. For
each design
solution,
the role
of
the
main geometrical parameters over
the
complex
impedance tuning
are
investigated
here
by
introducing
matching
charts,
which
are
a
useful
tool
to
get
the
same
antenna
configura-
tion
to
suit
different
kinds
of
microchips.
The
rest
of
this
paper
is
organized
into
four
main
sections.
Section
2
introduces
several
techniques
for
achieving
complex
impedance
matching,
such
as
the
T-mach,
the
proximity-loop,
and
the
nested-slot
layouts.
Miniaturization
and
bandwidth
issues
are
addressed
in
Section
3,
with
references
to
meandered
and
inverted-
IEEE
Antennas
and
Propagation
Magazine,
Vol. 50,
No.
1,
February
2008
Authorized licensed use limited to: Intel Corporation via the Intel Library. Downloaded on December 6, 2009 at 18:28 from IEEE Xplore. Restrictions apply.
