Proceedings of Asia-Pacific Microwave Conference 2007

Sutdy of A CPW-Fed Slot Dipole One-Sided
Directional Antenna for UWB Systems
H. Kanaya, T. Hashiguchi, R. K. Pokharel, and K. Yoshida
Graduate School of Information Science and Electrical Engineering
Kyushu University
744, Motooka, Fukuoka, 819-0395, JAPANkanaya@ed.kyushu-u.ac.jp

Keywords-Slot antenna, ultra wide band (UWB), coplanaer
waveguide.

I.

INTRODUCTION

Ultra wide band (UWB) technology has become the mostpromising solution for future short-range and high-speed
wireless data communication application such as home serverand cable less PC system [1].
In 2002, the Federal Communication Commission (FCC) in
United States officially released the regulation for UWBtechnology [2]. FCC regulated the emission limits for the
allocated 7.5 GHz band unlicensed use of commercial UWB
communication devices. However, because interference fromthe 5 GHz-band wireless LAN (IEEE 802.11a) systems
becomes a serious problem, this band is avoided and it
provides low band (3.4 GHz - 4.8 GHz) and High band (7.25
GHz - 10.25 GHz), respectively, in Japan.
For size reduction of the UWB devices, there are many
reports for planar UWB omni directional antennas, for example,
planar inverted cone antenna [3], tapered-slot-fed slot antenna[4], printed circular disc monopole antenna [5], and so on.
However, the characteristics of the omni directional antennas
are remarkably deteriorated if metal blocks like a ground planeof monolithic microwave integrated circuits (MMIC’s) or bodyof a car approach, because of the electro-magnetic interference.
So that, UWB antenna, which has one-sided directional isnecessary.
The coplanar waveguide (CPW) transmission lines havelower radiation leakage and less dispersion than microstrip
lines. Also, they are preferable for MMIC and RFIC (radio
frequency integrated circuit) since no via holes are required for
integration with devices [6, 7]. Slot antennas with groundplane are suitable for CPW-fed configuration and achieve onesided directional. In our previous works, we designed theCPW-fed slot dipole antenna whose length is one-wavelengthwith a bandpass filter using CPW lines, which acts as an
impedance matching circuit as well [8-10].
In this paper, we design the slot antennas with floating
metal layer on the bottom side, which have one-sided

directivity for UWB high band (7.25 GHz - 10.25 GHz)
application. By using the three resonances appeared from theslot and substrate, we can realize the wide band radiation. We
design and simulated by using the commercial electromagnetic (EM) field simulator (Ansoft; HFSS, ver.10). We
also carried out experiments on the UWB antenna by using
FR4 printed circuit board.
II. ANTENNA DESIGN
Fig. 1 shows the CPW-fed slot antenna with onewavelength center feed line. Cross section of the substrate isalso shown. This antenna has a conductor-baked configuration.
The substrate has dielectric constant εr=4.25 and tanδ = 0.015.
The thickness of the dielectric substrate and metal (Cu) layer,
which has conductivity = 5.8 x 107 S/m, is 1.6 mm and 18 μm,
respectively. Fig. 2 shows the simulated radiation patterns of
the slot antenna with a floating conductor and without floating
conductor, respectively. This floating conductor suppresses theradiation of the downward direction (-Z direction). Figs. 3(a)and 3(b) shows the input impedance (Zin=Rin+jXin) and returnloss of the standard slot dipole antenna. We can see theresonance of the slot antenna appears at 8.6 GHz, where input
impedance matches to 50Ω. However, this antenna doesn't
satisfy the bandwidth of the UWB high-band. Also, we can see
the parallel resonances at around 7.5 GHz and 10.5 GHz, butthey do not match to 50Ω (See point A and C in Fig. 3). If
these resonance points can be moved and input impedance
matches to 50 Ω, the wider bandwidth becomes possible.

This work was partly supported by a Grant-in-Aid for Scientific Research(C) from the Japan Society for the Promotion of Science (JSPS).

1-4244-0749-4/07/$20.00 @2007 IEEE.

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X=25 mm
Y=15 mm

Abstract—This paper presents the design method of the CPW-fed
slot dipole antenna for one-sided directional ultra wide band
(UWB) high band application. By using and controlling the threeresonances from the slot and antenna substrate, we can realize
the wide band radiation. The tested antenna size is 16 mm x 29
mm.

L
W

Y
Z

F
X

Cross section

copper

0.018mmfloating
layer

FR4

1.6mm

L=9.5 mm
W=1.0 mm
F=8.5 mmFigure 1. Layout of standard slot dipole antenna.

that this resonance is caused by the resonance of the slot
antenna with feed line. The input impedance moves to 50 Ω atresonant frequency when the value of W is adjusted to 1.0 mm.
Also, the frequency of point A and C hardly moves even if we
executed the above process.
X

X1
X1

Figure 2. Simulated radiation patterns of the slot antenna with a floating
conductor (a) and without a floating conductor (b).

Layout250

Imput Impedance [[Ω]
Ω]

200

(a)

Figure 4. Simulated electric field distribution on the UWB slot antenna at
7.75 GHz.

Re[Zin]Im [Z ]

150

in

100

50

Y1

0
-50
-100
-150
6.5
0

Return Loss [dB]

-5

A
7

7.5

B

C

8 8.5 9 9.5
Frequency [GHz]10 10.5

L(b)

Layout-10

Figure 5. Simulated electric field distribution on the UWB slot antenna at
9.75 GHz.

-15
-20
-25
-30
-35
6.5

7

7.5

8 8.5 9 9.5
Frequency [GHz]10 10.5

W

Figure 3. Input impedance (a) and return loss (b) of the standard slot dipole
antenna.

F

Fig. 4 shows the simulated electric field distribution on theslot antenna at 7.75 GHz (point A). This frequency moves
from 7.5 GHz to 7.75 GHz when the value of X is adjusted to29.0 mm. It is thought that this resonance is done by the width(X) of the antenna substrate. The input impedance moves to 50
Ω at resonant frequency when the length of the square slot
(X1) is adjusted to 5.0 mm.
Fig. 5 shows the electric field distribution on the slot
antenna at 9.75 GHz (point C). This frequency moves from10.5 GHz to 9.75 GHz when the value of Y1 is adjusted to 7.0
mm. It is thought that this resonant frequency is a resonancethat happens between the slot of the antenna and the front edgeof the substrate. The input impedance moves to 50 Ω atresonant frequency when the value of L is adjusted to 11.5 mm.
Also, the resonant frequency and input impedance of point A
hardly moves even if we adjust Y and L.
Fig. 6 shows the electric field distribution on the slot
antenna at 8.75 GHz (point B). The frequency moves to 8.75
GHz when the value of F is adjusted to 8.0 mm. It is thought

LayoutFigure 6. Simulated electric field distribution on the UWB slot antenna at
8.75 GHz.

III.

ANTENNA CHARACTERISTICS

Figs. 7(a) and 7(b) show the simulated input impedance andreturn loss of the UWB antenna, where Re[Zin] represents
radiation resistance and transmission loss, and Im[Zin] is thereactance of the antenna. The input impedance is almost 50 Ω,
and –10 dB bandwidth is almost satisfying the UWB high band.
Fig. 8 shows the simulated frequency dependence of the φ=0°
and φ=90° element of the electric field Eφ (See the direction in
Fig. 8). In each frequency, because the value of Eφ=0° is larger
than that of Eφ=90°, it can be said that the polarization of theelectric field is almost the same in the UWB high band.

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Fig. 9 shows the radiation pattern of the UWB slot antenna
at different frequencies. The directivity for upward direction islarger than that of lower direction.
Fig. 10 shows thefrequency dependence of the peak gain at θ=0 (upward) andpeak realized gain, respectively. The radiation efficiency is
70% or more in the UWB high band because of the conductor
and dielectric loss. We can see that this UWB antenna has apeak realized gain more than 5 dB in UWB high band.

Imput Impedance [Ω][Ω]8Gain [dB]

100

10

4

(a)

50

2

0

0

-50

Re [Zin]

-100
6.5

7

7.5

8 8.5 9 9.5
Frequency [GHz]

-10

IV.
(b)

-15
-20
-25
-30
6.5

7

7.5

8 8.5 9 9.5
Frequency [GHz]

7

7.5

8

8.5
9
9.5
Frequency [GHz]

10

10.5

10 10.50-5Peak Gain
Peak Realized Gain

Figure 10. Frequency dependence of the upward peak directivity and peakrealized gain.

Im [Zin]

Return Loss [dB]6

10 10.5

EXPERIMENTAL RESULTS AND DISCUSSIONSAn UWB antenna is fabricated on FR4 substrate by using
the print board making equipment (MITS; FP-21T model 40),
which has 100 mm-diameter milling cutter. Fig. 11 shows thephotographs of the antenna fabrication system, and the UWB
fabricated antenna, respectively. In the figure, the close up of
the high-frequency milling cutter is also shown. We measured
the S-parameters by using a GP-IB controlled vector network
analyzer (HP; HP8722C) through MMCX connector which has
characteristic impedance=50 Ω.

Figure 7. Input impedance (a) and return loss (b) of the UWB slot dipole
antenna.

θΕφ =0°

7.25GHzΕφ =90° 8.25GHz
Εφ =0° θX

φZ

9.25GHzΕφ =90°Y

Figure 8. Frequency dependence of the φ=0°and φ=90°element of theelectric field Eφ.
Figure 11. Photographs of the antenna fabrication system and UWB slot
antenna.

θ
φ =0°7.25GHzφ =90°

8.25GHz

9.25GHz

Figure 9. Simulated radiation pattern of the UWB slot dipole antenna withground plane.

Fig. 12 and Fig. 13 show the experimental results of the
input impedance and return loss of the one-sided directional
UWB antenna, respectively. In Fig. 13, broken line shows thereturn loss of the EM simulated result. It seems that the
bandwidth slightly decreases, however, three-designed
frequencies appear and match to almost 50 Ω. Also, the realpart of input impedance is larger in low frequency region thanthat of EM simulated results (see Fig. 7). The observed

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experimental results are caused by an error in edge part of theslot antenna for milling process, an error of the dielectric
constant of the FR4 substrate and residual loss of theconnection between the MMCX connector and antenna.
However, this design method and the experimental results may
be comparatively corresponding.
200

Imput Impedance [Ω]

150
100
50

REFERENCES[1]

Z. N. Chen, X. H. Wu, H. F. Li, N. Yang, and Y. W. Chia,“Consideration for Source Pulses and Antennas in UWB Ratio System,”IEEE Trans. Antennas Propagat., vol. 52, no. 7, pp. 1739-1748, July
2004.
[2] “First Report and Order, Revision of Part 15 of the Commission’s Rule
Regarding Ultra Wideband Transmission Systems,” Fed. Commun.
Comm., FCC 02-48, April 2002.
[3] S. Y. Suh, W. K. Stutzman, and W. A. Davis, “A New Ultrawideband
Printed Monopole Antenna: The Planar Inverted Cone Antenna (PICA),”IEEE Trans. Antennas Propagat., vol. 52, no. 5, pp. 1361-1365, May
2004.
[4] T. G. Ma, and S. K. Jeng, “Planar Miniature Tapered-Slot-Fed Annular
Slot Antennas for Ultrawide-Band Radios,” IEEE Trans. Antennas
Propagat., vol. 53, no. 3, pp. 1194-1202, March 2005.
[5] J. Liang, C. C. Chiau, X. Chen, and C. G. Parini, “Study of a Printed
Circular Disc Monopole Antenna for UWB Systems,” IEEE Trans.
Antennas Propagat., vol. 53, no. 11, pp. 3500-3504, November 2005.
[6] B.K. Kormanyos, W. Harokopus, L. Katehi, and G. Rebeiz, “CPW-fed
active slot antennas”, IEEE Trans. Microwave Theory & Thech., vol. 42,
pp.541-545, April, 1994.
[7] S. S. Garcia, and J. J. Laurin, “ Study of a CPW Inductively coupled slot
antenna”, IEEE Trans. Antennas Propagat., vol. 47, no. 1, pp. 58-64,
January 1999.
[8] K. Yoshida, T. Takahashi, H. Kanaya, T. Uchiyama, and Z. Wang,“Superconducting slot antenna with broadband impedance matchingcircuit,” IEEE Trans. Appl. Supercond., vol. 11, pp. 103-106, March
2001.
[9] H. Kanaya, Y. Koga, G. Urakawa, and K. Yoshida, “Design of HTS
Coplanar Waveguide Matching Circuit for Low Noise CMOS-HTS
Receiver,” IEEE Trans. on Appl. Supercond., vol. 13, no. 2, pp. 10311034, June 2003.
[10] K. Yoshida, Y. Tsutsumi, and H. Kanaya “Electrically Small Antennas
with Miniaturized Impedance Matching Circuits for Semiconductor
Amplifiers,” IEICE Trans. Electron., vol. E88-C, pp1368-1374, no. 7,
July 2005.

0
Re[Z ]-50

in

Im[Z ]
-100
6.5

in

7

7.5

8 8.5 9 9.5
Frequency [GHz]10 10.5

Figure 12. Measured input impedance of the UWB slot antenna.

0
Exp.

-5
Return Loss [dB]high band application. For realize the one-sided directional, weapplied the floating metal layer on the bottom of the antenna
substrate. By using and controlling the three resonances fromthe slot and substrate, we can realize the wide band radiationand impedance matching. The commercial three-dimensional
EM simulator simulates RF characteristics. Moreover, thisUWB antenna was fabricated and tested, thereby wedemonstrated frequency characteristics as expected. The tested
antenna size is 16 mm x 29 mm.
Now, we measure the communication distance of the UWB
test signal by implementing this antenna into commercial
system, and this antenna is shown to transmit the UWB pulse.
This result will be published elsewhere.

-10
-15
-20
-25
Sim.

-30
-35
6.5

7

7.5

8 8.5 9 9.5
Frequency [GHz]10 10.5

Figure 13. Measured return loss of the UWB slot antenna.

V.

CONCLUSIONS

We studied the design method of the CPW-fed slot dipole
antenna with one-sided directional for ultra wide band (UWB)

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