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IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013 567
Design of a Miniaturization Printed Circular-SlotUWB Antenna by the Half-Cutting Method
Guo-Ping Gao, Bin Hu, and Jin-Sheng Zhang
AbstractIn this letter, the miniaturization design of a novelprinted circular slot UWB antenna is presented and investigated.By the half-cutting method and adjusting VSWR, the size ofthe proposed antenna is reduced from 40 40 to 10 20 mm .Experimental results show that the proposed antenna meets therequirement of wide working bandwidth of 3.110.6 GHz with
. Monopole-like radiation pattern is observed in both-plane and -plane. The study of transfer function (magnitude
and phase of ) and signal waveform indicate a good time-do-main characteristic of the antenna. The proposed antenna has a
compact size, good radiation characteristics, ultrawide bandwidth,and good time-domain behaviors to satisfy the requirement of the
current wireless communication systems.
Index TermsCircular-slot ultrawideband (UWB) antenna,half-cutting method, miniaturization, time-domain, transferfunction.
I. INTRODUCTION
T HE ULTRAWIDEBAND (UWB) communication sys-tems have gained much attention due to their manyadvantages including the low-spectral-density radiated power
and potential for accommodating higher data rate. Driven by
the development of UWB technology, many ultrawideband
antennas have been designed and studied. Among them, theprinted slot antennas have become the best choice for UWB
applications due to their attractive merits, such as the ultraw-
ideband characteristics, near omnidirectional radiation patterns,
simple structure, and low cost. Various printed slot antennas
with different slot shapes and feeding structures have been
presented for UWB applications [1][3].
It is well known that the UWB technology for commercialap-
plications will mainly be applied in low-power, high-data-rate,
and short-range wireless communications. The small size of the
UWB antenna is needed, and much research has been dedicated
to the miniaturization of UWB antennas by now [4][7]. The
structure of self-complementary is used in [4] and [5]. A com-
pact UWB antenna with tapered radiating slot with a G-shaped
quasi-self-complementary structure is presented in [4]; the an-
tenna dimension is 19 16 mm in physical size. In [5], the di-
Manuscript received December 06, 2012; revised March 01, 2013, March25, 2013; accepted April 16, 2013. Date of publication April 24, 2013; date ofcurrent version May 07, 2013. This work was supported by the FundamentalResearch Funds for the Central Universities under Grant lzujbky-2012-41 andthe Leading Academic Discipline Project of the State Key Laboratory of Mil-limeter Waves, Southeast University, under Grant No. K201116.
The authors are with the School of Information Science and Engineering,Lanzhou University, Lanzhou 730000, China (e-mail: [email protected]).
Color versions of one or more of the figures in this letter are available onlineat http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LAWP.2013.2259790
Fig. 1. Geometry of proposed circular-slot UWB antenna (Ant-3). The originalmode is traditional printed circular-slot UWB antenna (Ant-1) and the half-cut-ting of the Ant-1 (Ant-2).
mension of 16 25 mm is obtained. The half-cutting method
has been used in UWB antenna designs [6], [7]. A monopole
antenna is miniaturized in [6], but the volume is still too large.In [7], the LTCC antenna is designed, and the antenna dimen-
sion is 17 10 mm .
In this letter, the design of a UWB antenna based on the cir-
cular slot antenna is studied and investigated. It is found that
the lower frequency of the operation band decreases when the
antenna is half-cut, so that a smaller size of the antenna is ob-
tained. Study of the VSWR, radiation patterns, transfer function,
and time-domain characteristics indicate the wideband opera-
tion characteristics of the antenna, even if it is reduced in size.
II. ANTENNA DESIGN
Fig. 1 shows the proposed circular slot UWB antenna. It is
seen that the proposed antenna is fabricated on a substrate with
the relative dielectric constant of and thickness of
mm with width and length of and . The radiation
element is a half-circular disc that is fed by microstrip line. The
half-circular disc has a radius of . Width of the microstrip
feedline is fixed at in order to achieve 50 characteristic
impedance. The ground has a same size as the substrate, and the
inner profile of the ground is a half-circular cut with radius of
. Original mode of the proposed antenna is traditional printed
circular slot UWB antenna (Ant-1). In order to reduce the size of
Ant-1, a half-cutting circular-slot UWB antenna (Ant-2) is pro-
posed. Ant-3 exhibits a dimensional ration of 0.5 with respect to
Ant-2 considering every dimension, apart from the microstrip
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568 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013
Fig. 2. Photographs of Ant-1, Ant-2 and Ant-3. (a) Top view. (b) Back view.
Fig. 3. Comparison of VSWR for Ant-1 and Ant-2.
TABLE IDIMENSION OF THE PROPOSED ANT-1, ANT-2, AND ANT-3 (IN MILLIMETERS)
feedline width that independently adjusts characteristic
impedance to 50 . By simulation of the VSWR for antennas,the dimensions of the proposed Ant-1, Ant-2, and Ant-3 are
shown in Table I. Fig. 2 shows photographs of Ant-1, Ant-2,
and Ant-3.
CST Microwave Studio software, which is based on the
method of finite integration technology (FIT), is used in the
simulation. The simulated VSWR of Ant-1 and Ant-2 is shown
in Fig. 3. It is seen that compared to the VSWR of Ant-1,
the lower frequency of for Ant-2 is decreased
from 2.34 to 1.66 GHz. Hence, the impedance-matching band
decreases to lower frequencies by half-cutting the antenna,
then dimension of the antenna can be reduced so that it can be
used in 3.110.6-GHz UWB band. Fig. 4 shows the compared
VSWR of Ant-2 with different reduction ratios. It is seen that
the lower frequency of the operation band for Ant-2 increases
Fig. 4. Comparison of VSWR for Ant-2 with different reduction ratios.
Fig. 5. Measured and simulated VSWR of the Ant-3.
with the reduction of the antenna volume. For UWB appli-
cation, the reduction ratio equals 0.5 with lower frequency
3.05 GHz chosen so that the Ant-3 is obtained.
III. SIMULATION AND MEASUREMENT
The prototype of Ant-3 is constructed and investigated. Themeasurement is achieved by using Agilent E8363B Vector
Network Analyzer. Fig. 5 shows the measured and simu-
lated VSWR for the constructed prototype. It is clearly seen
that both the measured and simulated results are suitable for
3.110.6-GHz UWB applications. The difference between
measurement and simulation is mainly caused by the fabrica-
tion error, the SMA connector, and numerical error.
The simulated radiation patterns at different frequencies in
the -plane and -plane are plotted in Fig. 6(a) and (b), re-
spectively. It can be seen that the -plane radiation patterns
are approximately omnidirectional over the entire operation fre-
quencies. The -plane radiation pattern at 4 GHz is similar to
a monopole antenna, while it is a little varied at 7 and 10 GHz.
Both the -plane and -plane radiation patterns are stable over
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GAO et al.: DESIGN OF MINIATURIZATION PRINTED CIRCULAR-SLOT UWB ANTENNA BY HALF-CUTTING METHOD 569
Fig. 6. Simulated radiation patterns at different frequencies. (a) -plane( -plane). (b) -plane ( -plane).
the operation band, which indicate that the antenna is suitable
for the UWB application.
IV. TRANSFER FUNCTION AND TIME-DOMAIN STUDY
A. Transfer Function Measurement
Since UWB systems use short pulses to transmit signals, it
is crucial to study the transfer function for evaluating the pro-
posed antennas performance and designing transmitted pulse
signals. For UWB applications, magnitude of the transfer func-
tion should be asflat as possible in theoperating band. Thephase
response is required to be linear over theentire band as well. The
UWB antenna can be viewed as a filter with magnitude (antenna
gain) and phase response. Thus, the study of transfer function is
used in UWB antenna design.
The transfer function measurement was taken out by using
Agilent E8363B Vector Network Analyzer as shown in Fig. 7.
A pair of the proposed antennas are used as the transmitting and
receiving antenna. The transmitter and receiver are positioned
Fig. 7. Transfer function measurement setup.
face to face ( -directions opposite) with a distance of 15 cm.
By considering the antenna system as a two-port network, the
transmission scattering parameter that indicates the transfer
function is measured. It should be noted that the measurement
was carried out in a real environment with reflecting objects in
the surrounding area.
Measured and simulated magnitude of is shown in
Fig. 8(a) and (b), respectively. Both the measured and simu-lated magnitude of is relatively flat from 3.1 to 10.6 GHz
(variation less than 10 dB), which confirms that the antenna is
suitable for UWB impulse communications. There are some
distortions from 3 to 5.5 GHz for the measurement, which is
mainly caused by the wave port and surrounding area.
Fig. 8(c) and (d) shows the measured and simulated phase
response of against frequency. Measured phase response
is nearly linear over the operation band. Meanwhile, a small
distortion is observed from 3 to 4 GHz, which corresponds with
the magnitude result in this frequency band.
B. Time-Domain Study
Time-domain study was based on the waveform of excited
signal, radiated signal, and received signal, so that the behavior
of UWB antenna can be studied. The fidelity factor is defined as
(1)
where is a delay that is varied to make the numerator in (1)
maximum. It determines the correlation between the electric
field signals and . The radiated pulse in -direction
is chosen as the reference signal , while the other
radiated pulses in -plane are set as signal . Hence, thefi
-delity factor between radiated pulses in -plane is calculated,
and the result is shown in Table II. It is observed that the mini-
mized fidelity factor in -plane is 0.9750, which shows a stable
radiation result.
Time-domain study based on the measurement setup is as
shown in Fig. 7, so the signal in -direction can be evalu-
ated. Fig. 9 shows the excited signal (ultrawideband signal),
radiated signal, and received signal, respectively. In order to
see clearly, the waveforms have been moved parallel along the
abscissa. It can be observed that the radiated signal shows the
second derivative operation, and the received signal shows the
third derivative operation as compared to the excited signal. The
result reflects the differentiator of the antenna in radiating and
receiving mode.
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570 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013
Fig. 8. Measured and simulated for the antenna systems. (a) Measured magnitude. (b) Simulated magnitude. (c) Measured phase. (d) Simulated phase.
Fig. 9. Signal waveforms for the antenna system in -direction.
TABLE IIFIDELITY FACTORBETWEEN RADIATED PULSES
V. CONCLUSION
A novel miniaturized UWB circular slot antenna is realized
from 40 40 to 10 20 mm in this letter. The study of return
loss and radiation patterns shows that the antenna has an ul-
trawide operation band and monopole-like radiation patterns.Transfer function (magnitude and phase of ) and time-do-
main result show that the proposed antenna has a good time-do-
main characteristic for UWB signal transmitting and receiving,
which correspond well with the VSWR.
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