Design Feature

SHUAI JI | Engineer

HUA QI | Engineer

HUIFENG ZHANG | Engineer

The 20th Institute of China Electronics Technology Group Corp.,

Xian, Peoples Republic of China; e-mail: jishuai19871222@163.com

Rectenna Serves 2.45-GHz

Wireless Power
Transmission

This fairly simple and straightforward rectenna design can be applied for
conversion of energy at RF/microwave frequencies to usable DC power.

ireless applications inject a great

deal of excess electromagnetic (EM)
energy into the environmentenergy that can be reused if properly
recovered. A rectifying antenna, or rectenna as it is popularly
known, is one such means for recovering that energy. To demonstrate the capabilities of such a design, a novel rectenna
was developed for low-power operation at a single IndustrialScientific-Medical (ISM) frequency of 2.45 GHz.
The rectenna consists of a highly efficient photonic-bandgap (PBG) structure, a microstrip lowpass filter (LPF) with
Impedance matching
and filtering

Antenna

Rectification

Load

1. This diagram shows the main function blocks of the rectenna circuit.
b
W1
a

W2

W3
2. This schematic diagram presents the linearly polarized PBG
antenna for use at 2.45 GHz.

102

defected ground structure (DGS) circuitry, and a Schottky

diode. To evaluate the rectenna, it was fabricated on a lowcost FR-4 printed-circuit-board (PCB) material with relative
dielectric constant (r) of 4.4 in the z-direction at 10 GHz and
thickness of 1 mm. As will be shown, the rectenna achieves RFto-DC conversion efficiency of 63% when processing received
power of +18 dBm at 2.45 GHz.
Studies of wireless transmissions, and methods for preserving and conserving the power from those transmissions, have
continued since the first wireless power transmissions (WPTs)
by Nikola Tesla in 1899. Rectennas have been of interest
for their capabilities to convert RF energy to DC power,
and provide the opportunities to reuse some of this transmitted wireless power. In recent years, microstrip circuit technology has been widely used for the development of receiving rectifier antennas, with RF-to-DC conversion efficiency
representing one of the most important parameters of any
rectenna design.1-3
A rectenna is an antenna with additional components,
including a LPF and a rectifying circuit. The rectenna
receives microwave energy from the antenna.4-6 A Schottky
rectifier diode converts the received RF energy to DC power.7-9 The amount of power that can be transmitted is limited, and the amount of RF/microwave power is reduced from
the source through attenuation, mainly due to free-space
signal path loss. For use in portable devices that, in general,
usually have small dimensions, an effective rectenna design
should also have small dimensions.
To achieve higher-order harmonic rejection of unwanted
signals, the rectenna design employs a miniature microstrip
LPF with DGS.10,11 The simple DGS is applicable on 50-
feeder lines to achieve the required lowpass filtering performance. The LPF with DGS can suppress and isolate second-

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MICROWAVES & RF

and third-order harmonic signals from

the rectifying circuitry, allowing the
rectenna to achieve its target high RFto-DC conversion efficiency without
processing unwanted signals.

pass characteristics with improved

harmonic-suppression characteristics
in the high-frequency stopband. The
proposed DGS LPF exhibits sharp filter
cutoff characteristics, with low in-band
insertion loss, wide stopband, compact
RECTENNA DESIGN
size, and relatively easy fabrication.
Figure 1 shows a block diagram of the
The U-shaped slot is combined with
proposed rectenna design. In developa rectangular groove measuring 3.8
ing this design, the PBG antenna, DGS
5.5 mm and a pair of gaps measuring
LPF, and rectifier circuits were all first
0.50 7.25 mm.
designed, fabricated, and characterized 3. The plot offers measured results of return
To achieve enhanced performance
separately. Then they were combined to loss for the PBG antenna.
from the LPF, symmetric stubs were
realize a complete rectenna.
introduced to increase the filters bandRadiation pattern 1
The linearly polarized PBG antenstop suppression in the high-frequency
0
na was fabricated on 1-mm-thick
band. Figure 5 presents the structure
30
30
-2.00
FR-4 substrate with a relative dielecof the DGS LPF used in the rectenna.
-9.00
tric constant of 4.4 at 10 GHz in the
The optimal dimensions for the DGS
60
60
-16.00
z-direction of the material (Fig. 2). The
LPF are as follows: W4 = 3.6 mm; W5 =
-23.00
dimensions of the 50- feed line were
5.5 mm; W6 = 1.5 mm; and g = 0.5 mm.
20 1.9 mm. The dimensions of the
For good bandstop characteristics, the
90
90
PGB antenna were 30 31 mm. The
length of the symmetric stubs can be of
photonic-band-gap (PBG) structure in
great importance.
the ground is designed to improve the
As can be observed, the value of L
120
120
gain as well as the directionality of the
greatly influences the band-notched
antenna. This increase in gain correfrequency, as shown in Fig. 6. The
150
150
sponds to improved power transmitting
bandstop frequency varies from 3.0 to
180
efficiency.
6.0 GHz as the value of L is varied from
Mag
Ang
Name
Theta
The square hole in the ground is
0 to 18 mm.
m1 360.0000 -0.0000 3.6908
designed for the PBG structure and
In the rectenna design, the purpose
m2 180.0000 180.0000 -12.3883
it measures 6.6 7.0 mm. For some
of the rectifier is to directly convert
measure of the PGB antenna per- 4. These are computer-simulated results of
RF/microwave energy into DC electriformance, Fig. 3 shows the antennas the gain for the PBG antenna.
cal energy. For this purpose, Schottky
return loss while Fig. 4 offers its gain
diodes are the preferred means of concharacteristics.
version for their low-voltage drops and high-speed response
The rectennas DGS LPF was also designed and fabricated and processing capabilities. In addition, Schottky diodes conon FR-4 substrate material with relative dielectric constant sume the least amount of power due to conduction and switchof 4.4. With the U-slot added to it, the DGS offers good low- ing of alternative RF-to-DC conversion approaches.
The commercial Schottky diode chosen for use in the recg
tenna design was model HSMS-286C from Avago TechnolW6
ogies (www.avagotech.com). This is a compact lead-free,
surface-mount semiconductor that is usable from 915 MHz
to 5.8 GHz. It features high detection sensitivity of as good as
W3
50 mV/W at 915 MHz, 35 mV/W at 2.45 GHz, and 25 mV/
W at 5.8 GHz. The miniature surface-mount package helps
save PCB space.
Within the rectifier circuit, the Schottky diode exhibits
W
W5
W4 5
low parasitic circuit elements through about 6 GHz. High
performance was achieved by modifying the basic parasitic
5. The schematic diagram represents the DGS LPF in the
circuit values and comparing them against the return-loss
rectenna design.
characteristics contained in the data sheet for the HSMS-

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Directive Rectenna
5

L = 0 mm

0
-5

S21dB

-10
-15

L = 18 mm

-20
-25
-30

L = 6 mm

-35
-40

L = 12 mm
0

10

12
7. This schematic diagram represents the model used for the

FrequencyGHz
6. The curves show simulated values of S21 for different values of L.

rectennas impedance matching input circuit.

286C. The main parameters for the HSMS-286C include series

resistance, Rs = 5 ; capacitance of Cj0 = 0.18 pF; and Vbr = 7
V. The next step was to create a matching input circuit for the
diode, with matching done for the 2.45-GHz input. Figure 7
shows the simulated circuit module.
A matching circuit between the 50- feed line and the
RF-to-DC rectifying circuit is shown in Fig. 8(a). A peak
efficiency of 63%, measured with a 250- load, occurred at
roughly +18 dBm received power, which is the maximum

power rating of the diode. Loads of 200 and 300 were also
measured and produced nearly identical results. Figure 8(b)
shows the conversion efficiency for the RF-to-DC rectifying
circuit of these loads.
The rectenna shown in Fig. 9 was fabricated on a 1-mmthick FR-4 substrate. It is designed to receive microwave energy in free space from a horn antenna with transmitted power
levels to 4 W. The light-emitting diode (LED) is used as the
low-power consumption load to verify the performance of the
rectenna. Figures 10 and 11 offer glimpses of the test system
used for this characterization. The rectenna was used to drive
a single LED at a distance of 1 m and a voltage of +1.7 VDC.
The energy received by the rectenna was +7.3 dBm, which
translates to an efficiency of 13.9%. The rectenna also drove
an LED array formed by three LEDs at a distance of 75 cm and
voltage of +1.8 VDC. The efficiency of the rectenna in this
case can reach as high as 45.5%.
The rectenna with PBG antenna operating at the single
ISM-band frequency of 2.45 GHz represents a fairly simple

(a)
70

Load = 200
Load = 250
Load = 300

Efficiency%

60
50
40
30
20
10
(b)

+2

+4

+6

+8

+10

+12

+14

+16

+18

Input powerdBm

8. The proposed (a) matching circuit for the rectenna is shown

9. The proposed rectenna was fabricated on a 1-mm-thick FR-4

next to its (b) measured electrical behavior

substrate.

104

SEPTEMBER 2014

MICROWAVES & RF

design and an effective means of converting RF signals to DC

energy at that frequency. The gain of the rectenna is 4.29 dBi
at 2.45 GHz, with RF-to-DC conversion efficiency of as high
as 63%. This particular rectenna design can operate effectively
with low-power loads at these ISM frequencies using a lowcost LED to aid in the conversion.
This rectenna design can contribute to low-power energyharvesting applications at the ISM frequency band of 2.45
GHz. It was fabricated on relatively low-cost circuit substrate
material with effective results, with the LED serving to assist
in the operational stability while also indicating the proper
operation of the rectenna circuitry. With its high gain and
high RF-to-DC conversion efficiency, the rectenna represents a simple circuit addition for ISM-band products and
an efficient means of reusing some of the energy that might
otherwise have been lost. For compact and portable products,
ideally the rectenna can be made with relatively small dimensions and at low cost.
This simple and straightforward conversion design can
be applied to achieve power supplies for low-power loads,
and can be useful in powering such applications as radiofrequency identification (RFID), wireless sensor networks,
and micro-mechanical systems.

REFERENCES
1. Hucheng Sun, Yong-xin Guo , Senior Member, IEEE , Miao He, and Zheng
Zhong, Design of a High-Efficiency 2.45-GHz Rectenna for Low-Input-Power
Energy Harvesting, IEEE Antennas and Wireless Propagation Letters, Vol. 11,
2012, pp. 929-932.
2. J.O. McSpadden, L. Fan, and K. Chang, Design and experiments of high conversion efficiency 5.8 GHz rectenna, IEEE Transactions on Microwave Theory &
Techniques, Vol. 46, No. 12, December 1998, pp. 2053-2060.
3. W.-H. Tu, S.H. Hsu, and K. Chang, Compact 5.8-GHz rectenna using steppedimpedance dipole antenna, IEEE Antennas and Wireless Propagation Letters, Vol.
6, 2007, pp. 282-284.
4. Ugur Olgun, Chi-Chih Chen, and John L. Volakis, Wireless Power Harvesting
with Planar Rectennas for 2.45 GHz RFIDs, 2010 URSI International Symposium
on Electromagnetic Theory, 2010, pp. 329-331.
5. Z. Harouni, L. Cirio, L. Osman, A. Gharsallah, S. Member, and O. Picon, A
dual circularly polarized 2.45 GHz rectenna for wireless power transmission, IEEE
Antennas and Wireless Propagation Letters, Vol. 10, 2011, pp. 306-309.
6. U. Olgun, C.-C. Chen, and J.L. Volakis, Investigation of rectenna array configurations for enhanced RF power harvesting, IEEE Antennas and Wireless Propagation Letters, Vol. 10, 2011, pp. 262265.
7. Y.-Y. Gao, X.-X. Yang, C. Jiang, and J.-Y. Zhou, A circular polarized rectenna
with low profile for wireless power transmission, Progress In Electromagnetics
Research Letters, Vol. 13, 2010, pp. 4149.
8. G.M. Yang, R. Jin, et al., Ultrawideband bandpass filter with hybrid quasilumped
elements and defected ground structure, Microwaves and Antenna Propagation,
Vol. 1, No. 3, 2007, pp. 733-736.
9. J.S. Park, C.S. Kim, J. Kim, et al., Modeling of a photonic bandgap and its
application for the lowpass filter design,Asia-Pacific Microwave Conference, Vol.
4, 1999, pp. 331-334.
10. Yasushi Horii and Makoto Tsutsumi, Harmonic Control by Photonic Bandgap
on Microstrip Patch Antenna, IEEE Microwave and Guided Wave Letters, Vol. 9,
No. 1, 1999, pp. 13-15.
11. S. Riviere, F. Alicalapa, A. Douyere, and J.D. Lan Sun Luk, A Compact Rectenna Device at Low Power Level, Progress In Electromagnetics Research, Vol.
16, 2010, pp. 137-146.

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