International audienceAs an answer to the self-interference problem inherent to RFID systems, this work proposes a dual-band backscat-tering architecture. A dual-band RFID system architecture can bring several advantages to the RFID technology. In fact, a dual-band reader could operate without any self-interference cancellation circuit that currently limits its sensitivity; moreover, its dual-band architecture would be compatible with software defined radio-based cellphones. Dual-band readers will need to talk with low-powered dual-band tags that up-convert, modulate, and backscatter the impinging signal from the fundamental frequency to the 2 nd harmonic without weakening the communication link. This article reports on the UHF dual-band Harmonic Tun-neling Tag capable of backscattering and amplifying a 900 MHz signal when receiving an input carrier at 450 MHz. The Harmonic Tunneling Tag provides positive conversion gains (+7 dB) that improve the communication link by a factor of 2 and operates under a very low bias voltage of 0.16 V

Amato, Francesco

Hemour, Simon

English

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The Harmonic Tunneling Tag: a Dual-Band Approach to
Backscattering Communications
Francesco Amato, Simon Hemour
To cite this version:
Francesco Amato, Simon Hemour. The Harmonic Tunneling Tag: a Dual-Band Approach to Backscat-
tering Communications. 2019 IEEE International Conference on RFID Technology and Applications
(RFID-TA), Sep 2019, Pisa, Italy. ￿hal-02311456￿
The Harmonic Tunneling Tag: a Dual-Band
Approach to Backscattering Communications
Francesco Amato, Member, IEEE, and Simon Hemour, Senior Member, IEEE
Abstract—As an answer to the self-interference problem inher-
ent to RFID systems, this work proposes a dual-band backscat-
tering architecture. A dual-band RFID system architecture can
bring several advantages to the RFID technology. In fact, a
dual-band reader could operate without any self-interference
cancellation circuit that currently limits its sensitivity; moreover,
its dual-band architecture would be compatible with software de-
fined radio-based cellphones. Dual-band readers will need to talk
with low-powered dual-band tags that up-convert, modulate, and
backscatter the impinging signal from the fundamental frequency
to the 2nd harmonic without weakening the communication link.
This article reports on the UHF dual-band Harmonic Tun-
neling Tag capable of backscattering and amplifying a 900 MHz
signal when receiving an input carrier at 450 MHz. The Harmonic
Tunneling Tag provides positive conversion gains (+7 dB) that
improve the communication link by a factor of 2 and operates
under a very low bias voltage of 0.16 V.
Index Terms—RFID, backscattering, tunnel diode, tunneling
tag, reflection amplifier, harmonic tunneling tag, 5G, dual-band,
UHF.
I. INTRODUCTION
F IFTH generation (5G) wireless communication systemswill reshape the way cellphones are used and designed.
Therefore, one of the opportunities that electrical engineers
should not overlook is the possibility to embed RFID readers
within the hardware of future 5G phones.
RFID, in fact, struggles in finding a widespread use in com-
mercial applications other than supply-chains and in becoming
as pervasive as Bluetooth Low Energy (BLE). One reason
is that RIFD backscattering does not operate on two bands
links as cellphones do requiring, therefore, a whole different
hardware that does not integrate well within the cellphone
architecture. Readers, moreover, by sending and receiving
signals in the same frequency band, experience leakage of the
transmitted carrier directly into the receiver causing extreme
self-interference that limits their sensitivities and reduce the
communication range.
Introducing in RFID systems the dual-band communication
paradigm already used by cellphones would make the reader
architecture less complex and open the possibility to integrate
RFID readers into cellphones. Harmonic readers and tags can
be the approach for developing dual-band RFIDs where the
Francesco Amato is with the Pervasive Electromagnetic Lab, Department
of Civil and Computer Science Engineering, University of Roma Tor Vergata,
00133 Roma, Italy (e-mail: f.amato@ing.uniroma2.it); Simon Hemour is with
the CNRS and IMS Research Center, Department of Science and Technol-
ogy, University of Bordeaux, F-Talence, France (e-mail: simon.hemour@u-
bordeaux.fr).
reader sends a signal at the fundamental frequency f0 to
interrogate a tag that reflects and modulates a higher harmonic
(e.g.: 2f0) detectable by the reader [1]. The transponder,
therefore, requires a dual-band antenna and a non-linear de-
vice, such as a diode. Researchers have already explored the
dual-band solutions for RFID transponders [2], [3], but the
generation of harmonics comes with conversion losses that
significantly affect the link performances. In fact, there are
typically 30 dB of conversion losses at a typical input RF
power of 1 µW.
RFin @f0
RFout
and
RFout
@f0
Tx/Rx
Single- or 
dual-band
RFID reader
@2f0
Low voltage 
source
bias
modulation
RF choke
DC block
tunnel 
diode
Fig. 1: A concept of the Harmonic Tunneling RFID tag
communicating with either a dual-band or a single-band legacy
RFID reader.
This work proposes to use a single tunnel diode to design
low-powered dual-band RFID tags up-converting the input
carrier frequency with positive conversion gain. The particular
structure of a tunnel diode makes it suitable for different kind
of applications; it can be used, for example, as impedance
tuner [4] or as a reflection amplifier [5]. In RFIDs it can
improve the read range [6] and allow the long-range tracking
of tagged objects [7]. In this paper, we demonstrate the circuit
design and preliminary measurement results of a Harmonic
Tunneling Tag (Fig. 1) that uses non-linearities in tunnel diodes
for generating amplified harmonics that improve the link
budget and enables the deployment of dual-band RFID readers
with no self-interference. The prototype uses tunnel diode
AI301A [8] operating at f0 = 450 MHz and backscattering
an amplified signal (+7 dB) at UHF (2f0 = 900 MHz) by
using a very low biasing voltage. Although bulkier and less
efficient than other tunnel diodes available in the market,
the inexpensive and easy-to-buy tunnel diode AI301A from
former soviet union was used for this work because of its
high robustness that makes it suitable for early-stage tests and
proof-of-concept development.978-1-7281-0589-5/19/$31.00 c©2019 IEEE.
2019 IEEE International Conference on RFID Technology and Applications (RFID-TA)
978-1-7281-0589-5/19/$31.00 ©2019 IEEE 244
(a)
0 0.5 1 1.5 2 2.5 3
-80
-70
-60
-50
-40
-30
-20
-10
0
(b)
Fig. 2: a) Measurement setup with VNA E5080A. Inset: tunnel
diode under test on substrate with r = 2.2 and 30 µm
thickness. b) R1 and A1 at fundamental frequencies (f0 ∈ [1
MHz, 3 GHz]), A1,2 and A1,3 of 2nd (2f0 ∈ [2 MHz, 6 GHz])
and 3rd (3f0 ∈ [3 MHz - 9 GHz]) harmonics, respectively.
Input power level Pin = -20 dBm at power-calibrated port 1;
Vbias = 0.16 V.
II. NON-LINEARITIES IN TUNNEL DIODES
To test the tunnel diode capabilities in reflecting and ampli-
fying higher order harmonics VNA E5080A was used taking
advantage of its frequency offset mode. Since the junction
resistance and capacitance of the tunnel diode depend on
the input signal power levels Pin and frequencies f0, it is
necessary to perform a full 1-port calibration as well as both
source and receiver calibration. The block diagram in Fig.
2a summarizes the measurement setup: the power levels at
source R1 impinging on the tunnel diode at the fundamental
frequencies f0 ∈ [1 MHz, 3 GHz] were collected together
with the power levels A1,n of the n-th reflected harmonics
at frequencies nf0, n ∈ N at the receiver. Fig. 2b shows the
impinging power level R1 at the fundamental frequency range
as well as the reflected power levels of both the fundamental
frequencies (n = 1) and 2nd, and 3rd harmonics for input
power level Pin = -20 dBm. The reflected gains (or losses)
of fundamental and higher order harmonics can be computed
as A1,nR1 , with the S11 parameter corresponding to the case of
n = 1.
Using a high precision DC power supply (E3648A) and
multi-meter 34410A1, the IV curve of tunnel diode in Fig. 3a
1Integration time defined in Number of Power Line Cycles, PLC = 10
was measured. The curve allows to identify three main areas
of interests: i) the tunneling effect region, in correspondence
of no (or low) biasing voltages; ii) the non-linear regions at
0.16 V; and iii) the negative resistance region at around 0.23 V.
The VNA was used to measure the generated reflected signals
and harmonics of the diode shown in Fig. 2a; Fig. 3b, 3c,
and 3d show the reflected fundamental signals as well as the
2nd and 3rd harmonics. When no bias is applied (Fig. 3b), no
amplification is observed and the harmonic levels are low. At
the non-linear operating point of 0.16 V (Fig. 3d), as expected,
higher gains and lower harmonics are measured. Despite the
absence of any matching network (or matched antenna), these
results already suggest a twofold use of the tunnel diode:
by operating it at the non-linear point (e.g.: at 0.16 V), it
is possible to have a mixer/doubler behavior with conversion
gain. By biasing it in the negative differential resistance region,
instead, it can be used as an high-gain reflection amplifier for
tunneling tags as already shown in [5].
III. HARMONIC TUNNELING TAG PERFORMANCE
ESTIMATION
By connecting a matching network (or a matched antenna)
to the circuit while operating it in the non-linear region, it
is possible to efficiently use the conversion gain to amplify
the 2nd harmonic and, hence, backscatter an amplified signal
at frequency 2f0 higher than the impinging one. This con-
figuration will avoid the reader self-interference, will increase
its sensitivity and will enable its integration in future dual-
band 5G cellphones. To verify this claim, the VNA was set to
transform the fixture impendance to 23+j50 Ω, which is the
conjugate impedance of the diode. The reflected signals at both
fundamental and 2nd harmonic frequencies were measured
with an input power at the VNA port of -30 dBm. As shown
in Fig. 4, at 0.16 V bias, both the fundamental at 450 MHz
and the 2nd harmonic at 900 MHz are amplified with gains
of 35 dB and 7 dB, respectively. Of significant importance
is the behaviour of the 2nd harmonic: differently from other
reported cases, where the frequency up-conversion comes at
the expenses of severe conversion losses, the tunnel diode
brings positive conversion gains. The amplified backscattered
signals show how a Harmonic Tunneling Tag can either
operate at the desired fundamental frequency f0 or operate in
dual-frequency mode and backscatter frequency up-converted
signals without any conversion losses.
Using the free-space monostatic link budget equations [9],
it is possible to compare the improved forward and backward
distances with those of a traditional monostatic UHF RFID
link for semi-passive tags mounting chip EM4325 [10]:
PT = PinGRGtτX
(
λf
4pirf
)2
(1)
and
PR = PTGRGtMX
(
λb
4pirb
)2
(2)
assuming perfect matching (τ = 1), no polarization mismatch
(X = 1). With PT being the transponder circuit sensitivity,
2019 IEEE International Conference on RFID Technology and Applications (RFID-TA)
245
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0
0.5
1
1.5
2
2.5
0 V bias
0.16 V bias
0.23 V bias
(a)
0 0.5 1 1.5 2 2.5 3
-70
-60
-50
-40
-30
-20
-10
0
10
S11
0 1 2 4 63 5
2nd
0 1.5 3 6 94.5 7.5
3rd
frequency of reflected signals (GHz)
0 V bias
(b)
0 0.5 1 1.5 2 2.5 3
-70
-60
-50
-40
-30
-20
-10
0
10
S11
0 1 2 4 63 5
2nd
0 1.5 3 6 94.5 7.5
3rd
frequency of reflected signals (GHz)
0.16 V bias
(c)
0 0.5 1 1.5 2 2.5 3
-70
-60
-50
-40
-30
-20
-10
0
10
S11
0 1 2 4 63 5
2nd
0 1.5 3 6 94.5 7.5
3rd
frequency of reflected signals (GHz)
0.23 V bias
(d)
Fig. 3: a) Measured and Fitted Tunnel Diode IV curve. A1,n/R1 data for different biasing conditions: b) 0 V; c) 0.16; and d)
0.23V.
Pin being the power transmitted by the reader, M being the
modulation factor, G denoting the antenna gains, λf/b = cff/b
being the operation wavelengths and rf/b the maximum
achievable distances in either the forward or the backward
links. The maximum achievable distances rmax are limited by
the minimum between the forward and the backward links:
rmax = min (rf , rb). A comparison can be made between
a semi-passive UHF tag and the Harmonic Tunneling Tag
(HTT) operating in dual-band mode. The parameters used for
the comparison are listed in Tab. I while Tab. II reports the
forward and backward distances for the two tag architectures.
The Harmonic Tunneling Tag in dual-band mode, improves
the read distance of backward link-limited semi-passive tags
from 10 to 18 meters. It is important to point out that these
distances were computed assuming a low dual-band reader
sensitivity that should actually improve for a dual-band self-
interference-free RFID system. Moreover, the biasing voltage
TABLE I: Link budget parameter values
Pin 30 dBm
GR 6 dBi
Gt 0 dBi
PR -74 dBm [11]
UHF Tag HTTs
Ref. [10] Dual-band
M (dB) 0 7
PT (dBm) -28* -30
f (MHz) 900 450/900
*in default battery mode settings [10]
required for the Harmonic Tunneling Tag is about one order
of magnitude lower than the bias required by the current semi-
passive ICs.
IV. CONCLUSIONS
This article demonstrated how tunnel diodes can signifi-
cantly contribute in revolutionising the UHF RFID technology.
In fact, a biasing voltage as low as 0.16 V can trigger tunnel
2019 IEEE International Conference on RFID Technology and Applications (RFID-TA)
246
0 0.5 1 1.5 2 2.5 3
-60
-50
-40
-30
-20
-10
0
10
20
30
40
@ f
0
= 450 MHz
@ 2f
0
= 900 MHz
Fig. 4: Return (S11) and conversion gains (
A1,2
R1
). Dotted gray
lines: gains measured on a 50 Ω port VNA (with frequency
offset). Solid colored lines: computation by the VNA of
fundamental return gains (+35 dB at 450 MHz) and 2nd
harmonic conversion gain (+7 dB at 900 MHz) if the power
impedance is set to 23+j50 Ω. The VNA port power Pin is set
to -30 dBm, a 3 dB attenuation is used to reduce the loading
effect of the negative resistance on the VNA generator. At
the peak gain, the RF power efficiently reaching the tunnel
junction is below -60 dBm.
TABLE II: Achievable distances
UHF tag HTT
Ref. [10] Dual Band
rf (m) 42.1 106
rb (m) 10.6 18.8
diode non-linearities to backscatter amplified 2nd harmonic
frequencies at the UHF band. A Harmonic Tunneling Tag
improves the link budget by up-converting and amplifying the
reflected signal; moreover, it allows RFID readers to operate
in dual-band mode avoiding the self-interference that currently
degrades their sensitivity.
Tunnel diodes are not the only devices that can provide
negative small signal resistance (a pair of transistors could
fairly exhibit this behavior for the same package footprint).
However, the extremely low bias voltage demonstrated in this
work would be impossible to reach. To properly operate, in
fact, the tunnel diode requires 0.16 V and draws a current
of 2 mA. Although the required current is already low, it is
important to highlight that more efficient tunnel diodes oper-
ating at much lower voltages and currents are available in the
market. This makes the Harmonic Tunneling Tags compatible
with many ambient energy harvesting techniques [12], [13],
[14] that could contribute in developing a completely passive
long-range RFID tag.
The Harmonic Tunneling Tag brings two important advan-
tages to the UHF RFID technology, both in the short and in
the long term. In fact, the added gains of the 2nd harmonic
(instead of conversion losses) would make it possible to easily
integrate dual band RFID readers within current and next-
gen cellphones that typically operate in dual band to mitigate
interference.
Moreover, the possibility of amplifying and backscatter the
impinging main carrier, further demonstrates how Tunneling
Tags can be used to improve both the current UHF RFID
technology and future RFIDs operating either at UHF, or at
microwave (e.g.: 5.8 GHz) or at mm-Wave (e.g.: 60 GHz)
frequencies.
V. ACKNOWLEDGEMENTS
The authors would like to thank Prof. P. Fay, University of
Notre Dame, for the fruitful discussions.
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2019 IEEE International Conference on RFID Technology and Applications (RFID-TA)
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The Harmonic Tunneling Tag: a Dual-Band Approach to Backscattering Communications

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The Harmonic Tunneling Tag: a Dual-Band Approach to Backscattering Communications

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