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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: bh@lzu.edu.cn).

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.

REFERENCES

[1] H.-D. Chen, Broadband CPW-fed square slot antennas with a

widened tuning stub, IEEE Trans. Antennas Propag., vol. 51, no. 8,pp. 19821986, Aug. 2003.

[2] Y. F. Liu, K. L. Lau, Q. Xue, and C. H. Chan, Experimental studies ofprinted wide-slot antenna for wide-band applications, IEEE Antennas

Wireless Propag. Lett., vol. 3, pp. 273275, 2004.

[3] P. Li, J. Liang, and X. Chen, Study of printed elliptical/circularslot antennas for ultrawideband applications, IEEE Trans. Antennas

Propag., vol. 54, no. 6, pp. 16701675, Jun. 2006.[4] L. Guo, S. Wang, X. Chen, andC. G. Parini,Study of compact antenna

for UWB applications,Electron. Lett., vol. 46,pp. 115116,Jan.2010.

[5] L. Guo, S. Wang, X. Chen, and C. G. Parini, A small printedquasi-self-complementary antenna for ultrawideband systems, IEEE

Antennas Wireless Propag. Lett., vol. 8, pp. 554557, 2009.

[6] L. Guo, S. Wang, Y. Gao, X. Chen, and C. G. Parini, Miniaturisationof printed disc UWB monopoles, in Proc. iWAT, 2008, pp. 9598.

[7] M. Sun, Y. P. Zhang, and Y. Lu, Miniaturization of planar monopole

antenna for ultrawideband radios,IEEE Trans. Antennas Propag., vol.

58, no. 7, pp. 24202425, Jul. 2010.