IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 60, NO. 9, SE PTEM BER 20 12 2925
A Novel Reader Architecture Based on UWB
Chirp Signal Interrogation for Multiresonator-Based
Chipless RFID Tag Reading
Randika V. Koswatta, Student Member, IEEE,andNemaiC.Karmakar, Senior Member, IEEE
Abstract—A very low-cost RFID reader architecture comprised
of a voltage-controlled oscillator (VCO), a mixer, and a low-pass
filter (LPF) for reading an ultra-wideband chipless RFID tag is
proposed. The VCO generates a linear chirp (swept) frequency in-
terrogation signal. The reader, which is a coherent frequency-mod-
ulated continuous-wave radar, interrogates a tag and decodes the
tag’s identification data in both amplitude and phase information.
A signal-processing technique based on Hilbert transform (HT)
is used and accurate detection of a 9-b tag is achieved. The new
reader needs only on e VCO and does not need any calibration tag
to decode data as needed for its predecessors.
Index Terms—Chipless radio frequency identification (RFID),
Hilbert transform, ultra wideband (UWB), UW B RFID reader.
I. INTRODUCTION
T
HE radio frequency identification (RFID) technology pro-
vides wireless identifications of tagged objects. The block
diagram of a
generic RFID system is shown in Fig. 1. The
data-carrying device is called a tag o r a transponder. A reader
or an interrogator is used to read and write the tag’s information
[1], [2]. T
he reader sen ds the interrogation signal. In response,
the tag transmits the data relat ed to the identity o f the object.
The total comm unication uses electromagnetic (EM) waves in
the RF ra
nge. RFIDs offer nonline-of-sight, long-distance, and
all-weather r eading. RFIDs also offer larger data carrying ca-
pacity than an optical barcode can offer. The conven tio nal ap-
plicat
ion-specific integrated circuit (ASIC) RFID tags use dig-
ital communication techniques such as amplitude shift keying
(ASK) and binary phase-shift keying (BPSK) for the d ata com-
munic
ation [1]. Some chipped and chipless tags u se backscatter
modulation [3], [4] as w ell as UWB pulses [5]–[7] for data
transfer.
Chipl
ess RFID tags do n ot contain an ASIC chip. They are
fully passive. Different techniques, such as time-domain reflec-
tometry (TDR), back-scattering modulations, and frequency
sig
natures, are used to encode data in chipless RFID tags.
Therefore, the reader design must address the technology used
in the chipless RFID tag design [8]. As an exam ple, RF surface
Manuscript received March 22, 2012; revised April 19, 2012; accepted April
23, 2012. Date of publication July 12, 2012; date of current version August 28,
2012. This work was supported in part by Monash University under P roof of
Concept Grant 2008, the A ustralian Research Council’s Linkage Project under
Grant LP0989652., Securency International Pty. Ltd., and SatNet Pty. Ltd.
The authors are with the Department of Electrical and Computer Systems En-
gineering, Monash University, Clayton, VIC, 3800 Australia (e-mail: randika.
koswatta@monash.edu; nemai.karmakar@monash.edu).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Dig
ital Object Identifier 10.1109/TMTT.2012.2203929
Fig. 1. Block diagram of a general RFID system.
acoustic w ave (SAW) t ags use TDR for data encoding [3]. A
reader system based on counting the reflected pulses f rom the
SAW tag is reported in [3], [9]. Another TDR-based chipless
RFID tag reported in [10] uses distributed shunt capacitors for
informatio n encoding. No dedicated reader design is reported
for this tag. A high-speed digital storag e oscilloscope (DSO)
is used to decode the data in a laboratory setting. An arra y of
capacitively loaded printed dipolesasachiplesstagisreported
by Jalaly and Robertson [11].
A chipless RFID tag made of a reactively loaded microstrip
patch antenna is reported in [12], [13]. A detection technique
based on soft computing for these tags is recently reported by
the same group in [14]. From the above review of the reported
works on the chip less RFID tags and readers, there exists a re-
search gap in developing a low-cost reader architecture for a
chipless RFID tag reading. This paper aims to fill the research
gap.
II. C
HIPLESS RFID DEVELOPMENT
The complete architecture of three frequency signatu re-based
chiples
s RFID tag readers has been reported in [4] and
[15]–[18]. The multiresonator-based chipless RFID tag shown
in Fig. 2(a) uses frequency signatures to encode data [15].
Readin
g of the multiresonator-based chipless RFID tag re-
quires a frequency-domain measurement. Either the amplitude
or the p hase of the transmission coefficient of the tag can be
used f
or decoding data. However, both amplitude and phase
measurements improve the efficacy of the reader. In the labora-
tory, a vector network analyzer (VNA) can be used to measure
the f
orward transmission coefficient
versus frequency to
identify encoded data [15], [16]. However, it is not a conven -
tional reading technique as the VN A is an expensive piece of
equ
ipment.
We have reported three generations of chipless RFID tag
readers [4], [15]–[18]. The fi rst- and second-generation (Gen.
1an
d Gen. 2) readers are an amplitude only detector and
a amplitude and phase detector, respectively. Both readers
operate over the 2.0–2.5-GHz frequency band and are capab le
of
reading 5 b of data. The third-generation (Gen. 3) reader
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