Efficient Dual-Band Single-Port Rectifier for RF Energy Harvesting at FM and GSM Bands

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Efficient Dual-Band Single-Port Rectifier for RF
Energy Harvesting at FM and GSM Bands
Nastouh Nikkhah
RF and Communication Technologies
(RFCT) research laboratory, Faculty of
Engineering and IT
University of Technology Sydney
Ultimo, NSW 2007, Australia
Food Agility CRC Ltd.
175 Pitt St, NSW 2000, Australia
Nastouh.Nikkhah@student.uts.edu.au
Justin Lipman
RF and Communication Technologies
(RFCT) research laboratory, Faculty of
Engineering and IT
University of Technology Sydney
Ultimo, NSW 2007, Australia
Justin.Lipman@uts.edu.au
Rasool Keshavarz
RF and Communication Technologies
(RFCT) research laboratory, Faculty of
Engineering and IT
University of Technology Sydney
Ultimo, NSW 2007, Australia
Rasool.Keshavarz@uts.edu.au
Negin Shariati
RF and Communication Technologies
(RFCT) research laboratory, Faculty of
Engineering and IT
University of Technology Sydney
Ultimo, NSW 2007, Australia
Food Agility CRC Ltd.
175 Pitt St, NSW 2000, Australia
Negin.Shariati@uts.edu.au
Mehran Abolhasan
RF and Communication Technologies
(RFCT) research laboratory, Faculty of
Engineering and IT
University of Technology Sydney
Ultimo, NSW 2007, Australia
Mehran.Abolhasan@uts.edu.au
Abstract—This paper presents an efficient dual-band
rectifier for radiofrequency energy harvesting (RFEH)
applications at FM and GSM bands. The single-port rectifier
circuit, which comprises a 3-port network, optimized T-
matching circuits and voltage doubler, is designed, simulated
and fabricated to obtain a high RF-to-DC power conversion
efficiency (PCE). Measurement results show PCE of 26% and
22% at 20 dBm, and also 58% and 51% at 10 dBm with a
maximum amount of 69% and 65% at 2.5 dBm and 5
dBm, with single tone at 95 and 925 MHz, respectively.
Besides, the fractional bandwidth of 21% at FM and 11% at
GSM band is achieved. The measurement and simulation
results are in good agreement. Consequently, the proposed
rectifier can be a potential candidate for ambient RF energy
harvesting and wireless power transfer (WPT). It should be
noted that a 3-port network as a duplexer is designed to be
integrated with single-port antennas which cover both FM
and GSM bands as a low-cost solution. Moreover, based on
simulation results, PCE has small variations when the load
resistor varies from 10 to 18 kΩ. Therefore, this rectifier can
be utilized for any desired resistance within the range, such as
sensors and IoT devices.
Keywords—single port rectifier, voltage doubler, RF-to-DC
power conversion, ambient RF energy harvesting
I. INTRODUCTION
Radiofrequency energy harvesting (RFEH) technology
has been notably considered as it enables devices to be used
easily in environments where it would not be feasible to
replace batteries. Moreover, RFEH can diminish
environmental pollution by reducing battery production [1].
Consequently, RFEH system can be functional in self-
sustainable low power applications, such as the Internet of
Things (IoT) devices which are used in many areas
comprising the manufacturing industry, agriculture,
healthcare, wireless sensor networks (WSN), radio
frequency identification devices (RFID) and intelligent
transportation systems [2-5].
Radiofrequency energy harvesting from ambient signals
can transfer power through free space. Since RF signals
such as FM (88-108 MHz) and cellular (GSM-900) are
accessible broadly and perpetually in the environment,
RFEH systems are a promising solution to supply power for
electronic devices. Previous research has demonstrated the
feasibility of RF energy scavenging through RF field
investigations in Australia [6]. FM signals can be useful for
EH due to providing stable, continuously and lower pass
loss in free space ambient RF source with an appropriate
power level than other RF signals at different locations. In
this regard, some works have been concentrated on the
lower side of the RF spectrum [7-9]. In addition, GSM-900,
which supports cellular communications, due to having a
high number of based stations in urban and suburb areas,
can be a good candidate for EH.
Rectifying antenna (rectenna) can be used to convert RF
signals to DC power in RFEH scenario. A rectenna includes
an antenna as an RF power receiver and a rectifier circuit to
convert RF to DC power. Since ambient RF signals
propagate in any direction, using antennas with
omnidirectional patterns can be a suitable choice for RFEH
systems [10-12]. Furthermore, the ambient RF power level
received by a rectenna can alter unpredictably, depending
on various factors such as power source level, distance from
RF stations and RF source polarization. Consequently, the
RF-to-DC conversion efficiency (PCE) is a crucial
parameter in rectifier design [7]. Although some rectifiers
have gained high RF to DC conversion efficiency, they are
not suitable for ambient RFEH since these structures can
harvest high input power levels. Comparatively, several
rectennas have been designed using different kinds of
rectifier topology, such as single series rectifier [13-15],
Villard voltage doubler [16], differential-output topology
rectifier [17], full-wave Greinacher [18] and voltage doubler
rectifier [19, 20]. It should be noted that the voltage doubler
topology can be well utilized in low power rectification
design [2].
Since there are typical single-port antennas that resonate
with both FM and GSM bands [21-23], a single-port
rectifier can be an appropriate candidate to be easily
integrated with these antennas. For this purpose, a 3-port
network that operates as a duplexer is required to obtain a
single-port rectifier. In this case, the rectifier harvests
without the need for a power divider device and an extra

SMA connector. Consequently, the proposed system is low-
cost, compact and can be fabricated easily.
This paper describes an efficient dual-band rectifier for
RF energy harvesting operating over a single port in FM and
GSM bands. The proposed RF energy harvester comprises
a 3-ports network, optimal T-matching circuits including
radial stubs and a voltage doubler structure which is
designed, simulated and measured. The results of the
rectifier demonstrate a noticeable fractional bandwidth
where the reflection coefficient is defined below 10 dBm.
Furthermore, the high conversion efficiency is achieved
over a proposed input power range. Further, the efficiency
is relatively stable for variations of the load resistor. Hence,
this system can be used for any desired sensor with
resistance between 10 to 18 kΩ. The rest of the paper is
organized as follows: Section II describes the proposed
rectifier design and presents simulation and measurement
results. Finally, Section III concludes this paper.
II. RECTIFIER DESIGN, SIMULATION AND
MEASUREMENT
The block diagram of the proposed RF energy harvester
is illustrated in Fig. 1, which comprises an antenna as an RF
signal receiver, a 3-port network to obtain a single-port
structure, a T-matching circuit to transfer maximum power
from the antenna to load, a voltage doubler to convert input
RF energy (AC signal) to DC voltage and a load section.
The proposed single-port dual-band rectifier circuit, which
harvests energy from FM and GSM bands simultaneously,
is presented in Fig 2. It should be noted that the rectifier
design is simulated and optimized using Advance Design
System (ADS) software.
Fig.1. Block diagram of the proposed RF energy harvester.
Low turn-on voltage Schottky diode HSMS-2850 (Cj0 =
0.18 pF, RS = 25 Ω, IS = 3e−6 A) is chosen as a rectification
device in voltage doubler structure, which is used especially
in a small signal application at frequency bellow 1.5 GHz
due to its low series resistance (RS) and also junction
capacitance (Cj0) [24]. In addition, the HSMS-2850 diode
has a low threshold voltage with high saturation current,
which is a critical factor for rectification at low input power
levels [2].
Different rectifiers topologies have been proposed, such
as bright type, single series, single shunt, and voltage
doubler rectifiers. A voltage doubler rectifier is used due to
its desired advantages, including, first, the total amplitude
of the output voltage is boosted since two diodes are added
in series. Second, using a voltage doubler rectifier decreases
diodes' junction resistance and enhances the detection
sensitivity at low power levels as the produced current of the
first diode provides external bias for the second diode [25].
A resistance load is added at the end of the voltage
doubler to sense the DC voltage. Since the resistance values
of applied sensors are relatively near to the range of 10 to
18 kΩ [20], this range is chosen for optimization in ADS
software at low input power levels to maximize the RF to
DC power conversion efficiency. In this case, 14 kΩ was
achieved as an optimum value for the load resistance.
Fig.2. Topology of the proposed rectifier. Dimensions (mm), inductors
(nH), capacitors (pF) and loads (kΩ) are presented in Table I.
TABLE I. PARAMETERS OF THE PROPOSED STRUCTURE SHOWN IN FIG. 2.
[W1]
[W2,3]
[R3]
[W4]
[W5]
[W6]
[W7]
[W8]
0.5
1.6
1.6
1.6
1.6
1.5
1.5
8
[W9]
[W10]
[W11]
[W12]
[W13]
[W14]
[W15]
[W16]
1.1
2
1
1
1
2
2
2
[W17]
[W18]
[W19]
[W20]
[W21]
[W22]
[W23]
[W24]
2
2
2
1
1
1.1
1.2
1.6
[W25]
[W26]
[W27]
[L1]
[L4]
[L5]
[L7]
[L8]
6
1
1.6
18
15.8
7.6
9.6
11
[L9]
[L10]
[L11]
[L13]
[L14]
[L16]
[L17]
[L18]
4.5
2
1
5
5
4
10
1
[L19]
[L20]
[L22]
[L23]
[L25,27]
[L26]
Ang8,26
Ang17
32.4
1
1.1
1.5
6
3.4
90o
45o
U1
U2
U3
U4
U5
C1,2
C3
RL
230
1970
3.2
55
3
20
100
14
Furthermore, the impedance matching network section
is optimized based on T-circuits, allowing the upper stage
of the rectifier to receive the maximum FM signal from an
input port. At the same time, the lower one can capture GSM
band signals. It is noteworthy to mention that a radial stub
used in the matching section with different dimensions can
maintain the rectifier performance over different load
resistors. Moreover, the radial stubs (parts 8, 26 and 17
shown in Fig. 2) were used instead of capacitors,
simplifying the rectifier design as any desired values can be
achieved at a low cost. In addition, using the radial stub at
the end of the rectifier as a capacitor role (part 17) can save
energy due to the imaginary input impedance of the
transmission line and smooth the output DC signal as a low
pass filter.
A 3-port network that operates similar to a duplexer is
designed to efficiently connect the output port of any desired
single-port RF receiver (Zin=50 Ω), which supports both FM
and GSM bands, to both rectifier stages. As shown in Fig.1
and Table II, much of the input signal transmits through the
upper stage since it has a notably higher transmission
coefficient (S21) than the lower stage at the FM band. On the
other hand, the lower stage transfers GSM signals due to the
significant transmission coefficient (S31). The scattering

parameters in both bands were simulated over different
input powers.
TABLE II. S-PARAMETERS OF 3-PORT NETWORK SHOWN IN FIG.1.
Frequency
band
Input power
(dBm)
S11
(dB)
S21
(dB)
S31
(dB)
S23
(dB)
FM
2.5
24
0.14
16
16.6
5
24.1
0.13
16.2
16.8
10
24
0.11
17.1
17.6
15
23.5
0.10
18
18.4
GSM
2.5
10.2
40
0.47
37.7
5
17.1
37.7
0.12
37.7
10
17
37.1
0.13
37.7
15
14.7
35.9
0.19
37.7
The proposed rectifier is fabricated on RO4003C with a
dielectric constant of εr = 3.38, loss tangent of tan δ =
0.0027 and thickness of ts = 0.8 mm as shown in Fig.3. The
optimized parameters of the rectifier are listed in Table I.
Fig. 4 (a) and Fig. 4 (b) depict the rectifier's simulated
and measured reflection coefficient at different input power
levels from 40 to +10 dBm with the step of about 2.5 dBm.
Reasonable agreement between simulation and
measurement results is achieved at both frequency bands.
Moreover, the simulation and measurement reflection
coefficients at FM and GSM frequency bands are illustrated
in Fig. 4 (c) and Fig. 4 (d). In order to demonstrate the
impedance matching bandwidth of the rectifier at desired
frequency bands, the corresponding power levels to the
minimum reflection coefficient are chosen as input power
(2.5 dBm at 95 MHz and 5 dBm at 925 MHz based on
Fig.4). Also, Fig.4 (c) and Fig. 4 (d) show the fractional
bandwidth of 21% and 11% at FM and GSM bands,
respectively. Consequently, it can be observed that the
proposed rectifier has an acceptable impedance matching
across both frequency bands, which makes it a good
candidate to be integrated with an antenna resonating at FM
and GSM bands concurrently to realize a rectenna for RF
energy harvesting.
Fig.3. Fabricated rectifier prototype.
Efficiency is an important metric in energy harvesters
which can be defined as RF-to-DC power conversion
efficiency (PCE) and can be calculated as below,
 


 
Where VOdc is the output DC voltage in each stage, RL is the
load resistor, and Pi is the input power provided by the
signal generator to the rectifier. The evaluation of RF-to-
DC efficiency and output DC voltage are demonstrated in
Fig 5. The measured results approximately agree with the
simulations in both bands. It should be noted that ohmic
loss, specifically due to using radial stubs at T- matching
part and output of the circuit instead of a passive element,
can lead to a small difference between simulation and
measurement results. Based on the measurement results,
the proposed rectifier demonstrates an RF-to-DC efficiency
of about 26% and 21% at Pin= 20 dBm, 58% and 51% at
Pin= 10 dBm, with a maximum PCE of 69% and 65%, at
Pin= 2.5 and 5 dBm at FM and GSM bands,
respectively. For further clarification, the measurement
outputs are also presented in Table III. Furthermore, the
simulation results at fixed frequencies of 95 and 925 MHz
in Fig. 6 indicate the relation between RF-to-DC efficiency
and RL over different input power levels. RL=14 kΩ is an
optimum load for the proposed rectifier, leading to provide
higher efficiencies than other loads in both frequency
bands. Also, Fig. 6 shows that the proposed rectifier
performance achieves a relatively light variation of PCE
over the range of 10 to 18 kΩ. Consequently, the proposed
rectifier can be a proper candidate for ambient RF energy
harvesting since it presents a dual-band function with an
adequate efficiency at input power levels such as 20 dBm
(10 µW).
(a)
(b)
(c)

(d)
Fig.4. Simulated and measured reflection coefficient of the proposed
rectifier at different input RF power levels from 40 to 10 dBm (a) FM
(95MHz), (b) GSM (925MHz) frequency band and (c) FM band at
2.5dBm, (d) GSM band at 5dBm.
(a)
(b)
Fig.5. Simulated and measured results of the proposed rectifier over
different input RF power levels at FM and GSM frequency bands with14
kΩ load, (a) RF-to-DC conversion efficiency and (b) output DC voltage.
TABLE III. THE MOST IMPORTANT MEASUREMENT RESULTS.
Frequency
band
Input power
(dBm)
RF-to-DC conversion
efficiency at a single tone
VOdc
(V)
FM
2.5
69%
2.33
10
58%
0.901
20
26%
0.191
GSM
5
65%
1.69
10
51%
0.845
20
21%
0.171
Finally, Table IV compares recently reported rectifiers
with the proposed system. It is evident from Table IV that
this work has achieved higher fractional bandwidth and RF-
to-DC efficiency at a single tone compared to other works
with equal input powers. The obtained fractional
bandwidths are 21% and 11% at FM and GSM bands,
respectively. In addition, as mentioned before, high
efficiency is the critical feature of RF energy harvesters. The
proposed rectifier achieves an RF-to-DC conversion
efficiency of 58% and 51% at -10 dBm and also 26% and
22% at a low input power of -20 dBm at FM and GSM
bands, respectively. Hence, the proposed rectifier can be a
suitable candidate for ambient RF energy harvesting and
WPT systems.
(a)
(b)
Fig.6. Simulated RF-to-DC conversion efficiency of the proposed rectifier
for five samples of load (RL) over different input RF power levels at (a) FM
(95 MHz) and (b) GSM (925 MHz) frequency bands.
TABLE IV. COMPARISON OF THE PROPOSED RECTIFIER AND OTHER
REPORTED WORKS.
Ref.
Frequency
(MHz)
Fractional
bandwidth (%)
RF-to-DC conversion
efficiency at a single tone
[2]
490 (1), 860
(2)
4 (1), 2 (2)
)1( dBm 10@ 17%
7% @ 10 dBm (2)
[9]
108 - 88
23
dBm 10@ 40% dBm 20@ 18%
[14]
, )1( 925 , )2( 1820
)3( 2170
3, )2( 5, )1( 4
)3(
)1( dBm at 10@ 42%
)1( dBm at 20@ 25%
)2( dBm at 10@ 32%
)2( dBm at 20@ 18%
)3( dBm at 10@ 25%
)3( dBm at 20@ 13%
[15]
1840
7
dBm 10@ 37%
dBm 20@ 21.1%
[21]
, )1( 97.5 )2( 868
)2( 8, )1( 11
)1( dBm at 10@ 46%
)1( dBm at 20@ 27%
)2( dBm at 10@ 29%
)2( dBm at 20@ 14%
[26]
, )1( 2450
)2( 5800
)2( 2, )1( 4
)1( dBm at 10@ 20%
)1( dBm at 20@ 3%
)2( dBm at 10@ 22%
)2( dBm at 20@ 3%
This
work
,)1( 95
)2( 925
)2( 11, )1( 21
)1( dBm at 10@ 58%
)1( dBm at 20@ 26%
)2( dBm at 10@ 51%
)2( dBm at 20@ 22%

III. CONCLUSION
This paper demonstrates an efficient dual-band rectifier
to harvest RF energy from FM and GSM bands
simultaneously. The single-port dual-band voltage doubler
rectifier was designed, simulated and fabricated, which
presents a good impedance matching performance with
fractional bandwidth of 21 and 11% at FM and GSM bands,
respectively, using optimized 3-port network and T-
matching circuits. Also, the proposed energy harvester is a
low-cost solution for single-port antennas that resonate at
both FM and GSM bands due to not using the power divider
device. Measurement results of the rectifier show a
satisfactory efficiency over different low input power levels.
The proposed rectifier obtains the RF-to-DC efficiency of
58% at 95 MHz and 51% at 925 MHz when the power input
level is  dBm, respectively. The achieved efficiencies
at FM and GSM bands and over a broad input power ranges
make the proposed rectifier a good candidate for ambient
RF energy harvesting and wireless power transmission
systems.
ACKNOWLEDGMENT
This project was supported by funding from Food
Agility CRC Ltd, funded under the Commonwealth
Government CRC Program. The CRC Program supports
industry-led collaborations between industry, researchers
and the community.
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