310 ACES JOURNAL, Vol. 34, No.

2, February 2019

Wideband Dielectric Resonator Antenna Excited by a Closed Circular Loop

GCPW Slot for WLAN 5.5 GHz Applications

Wei-Chung Weng 1, Min-Chi Chang 1, and Min-Sian Chen 2

1
Department of Electrical Engineering
National Chi Nan University, 301, University Rd., Puli, Nantou 54561, Taiwan
wcweng@ncnu.edu.tw, s100323910@mail1.ncnu.edu.tw
2
R&D Department
Master Wave Technology Co., Ltd., Zhubei City, 302, Taiwan
minsian.chen@masterwave.com.tw

Abstract ─ A dielectric resonator antenna is designed for bottom layer of the substrate to block the backside
WLAN 5.5 GHz band applications in this study. The radiations. Also, the ground plane can create an extra
dielectric resonator antenna is fabricated on a cheap FR4 image radiator to improve the gain of the DRA.
substrate with grounded CPW (GCPW) structure. A new In this study, a wideband DRA excited by a GCPW
closed circular loop GCPW slot structure is employed to line with slot-CPW fed structure is proposed. The
obtain wideband impedance matching. Results of the designed DRA operates at the WLAN 5.5 GHz (5.15 –
designed dielectric resonator antenna show that good 5.85 GHz) band. The proposed DRA has characteristics
agreement between simulated and measured reflection of wideband, high gain, and wide beamwidth. Details of
coefficients, radiations, and antenna gains is observed. the proposed DRA design are described. Results of the
The measured -10 dB bandwidth of the dielectric prototype are presented and discussed as well.
resonator antenna is 1.6 GHz (28.5%, 4.8 – 6.4 GHz),
which covers the WLAN 5.5 GHz band.

Index Terms ─ Dielectric resonator, DRA, GCPW,

wideband, WLAN.

I. INTRODUCTION
Dielectric resonators [1-3] have the advantages of
no conductor loss, low quality factor, and high dielectric
constant; hence, they are widely used for designing
dielectric resonator antennas (DRAs). Theoretical analyses
for first few resonant modes in an isolated cylindrical
dielectric resonator have been done [4-6]. DRAs have
many advantages such as compact size, wideband, and
high efficiency. Different excitation mechanisms such
as coaxial probe [6, 7], slot-microstrip [8], microstrip
[9, 10] and slot-coplanar waveguide (CPW) can excite
the dielectric resonator [3]. Apparently, the excitation
(a)
mechanism of using slot-microstrip outperforms the
coaxial probe since coaxial probe fed are not easy to
adjust the optimal feeding position to obtain good
impedance matching. DRAs also can be fed by CPW
lines [11, 12]. However, CPW fed structure without a
ground plane on the backside has a drawback that
decreases the antenna gain and efficiency due to (b)
backside radiations. To overcome this drawback, a
grounded CPW (GCPW) structure can be used. The Fig. 1. The geometry of proposed wideband GCPW fed
GCPW structure has an additional ground plane on the DRA: (a) top view and (b) side view.

Submitted On: September 27, 2018

Accepted On: November 4, 2018 1054-4887 © ACES
WENG, CHANG, CHEN: WIDEBAND DIELECTRIC RESONATOR ANTENNA 311

II. ANTENNA DESIGN magnetic fields are more concentrated at the center of the
Figure 1 shows the geometry of the proposed cylindrical dielectric resonator. The directions of electric
wideband DRA. The full-wave EM simulator, HFSS fields and magnetic fields are orthogonal each other,
[13] is used to analyze the prototype of the DRA. The which demonstrate the dielectric resonator operating
proposed antenna is to be fabricated on an FR4 substrate at the dominate HEM11 mode. Here, HEM11 is the
with a thickness (h) of 0.8 mm, dielectric constant of 4.4, lowest resonant frequency.
and loss tangent of 0.02. The square size of the DRA is
60.0 mm (W) by 60.0 mm. The shorting walls are applied
in the y-direction to block surface waves in the substrate.
Wf is the width of the central fed line. g is the gap
between the edge of the central fed line and the edge of
the ground plane on the top layer of the FR4 substrate.
The GCPW fed line becomes a closed circular loop line
at the end. The closed circular loop GCPW slot line
consists of a circular patch and a circular slot. They are
concentric. The radii of the outer and inner edge of the
circular slot are R1 and R2, respectively. The distance
from the center of the cylindrical dielectric resonator to
the center of the circular patch is d. This closed circular
loop GCPW slot excites a ring of magnetic current. The
magnetic current M can be determined by:
M  nˆ  E , (1)
where E is the electric fields between the edges of the
slot and n̂ is the direction normal to the plane of the fed Fig. 2. The magnetic currents flow along the closed
line. Figure 2 demonstrates the magnetic currents flow circular loop GCPW slot line. The magnetic currents are
along the closed circular loop GCPW slot. The magnetic obtained by HFSS EM simulator at 5.7 GHz.
currents are obtained by HFSS at 5.7 GHz. The circular
loop magnetic current is equivalent an electric dipole Parametric study is performed to reveal the influence
source, which then excites the cylindrical dielectric of the magnitude of reflection coefficients (|S11|) by key
resonator [2]. By properly adjusting the orientation of the parameters, R1, R2, and d. Other dimensions are fixed
cylindrical dielectric resonator and dimensions of the at values as shown in Table 1 when the parameter is
closed circular loop GCPW slot structure, the desired investigated. In Fig. 4 and Fig. 5, |S11| is much sensitive
hybrid HEM11 mode can be excited. Meanwhile, in the variation of R2 than that of R1 and d. The variation
wideband impedance matching of the DRA can be of d slightly affects the |S11| as can be seen in Fig. 6.
obtained [3]. The resonant frequency of dominant hybrid Based on the results, when designing the proposed DRA,
HEM11 mode can be determined by [14]: we suggest firstly adjust the value of R2 to obtain
wideband impedance matching at the desired band. The
c 6.324  Rd Rd 2 
fr  0.27  0.36( )  0.02( ) , next step is to slightly adjust R1 and d to achieve better
2 Rd  r  2  2Hd 2Hd  |S11| performance of the DRA.
(2) Detailed dimensions of the designed wideband DRA
where c is light speed in free space and  r is the are listed in Table 1 as well. A prototype has been
physically realized. Figure 7 shows the pictures of the
dielectric constant of resonator. To achieve wider
designed wideband DRA without and with the cylindrical
bandwidth,  r of resonator should be kept low. Hence,
dielectric resonator.
we choose an available cylindrical dielectric resonator
with a height (Hd) of 4.2 mm, a radius (Rd) of 14.9 mm, Table 1: Dimensions of the proposed dielectric resonator
 r of 9.8, and loss tangent of 0.01 applied in this antenna antenna (Unit: mm)
design. The resonant frequency f r of dominant HEM11 Parameter Size Parameter Size
mode determined by (2) is 5.73 GHz, which is closed W 60.0 R1 10.0
to the center of the operating band. Simulated electric Wf  R2 6.5
and magnetic fields at 5.7 GHz are shown in Fig. 3. The g  d 4.0
electric fields are more concentrated on the surface close h 0.8 Rd 14.9
to the top of the cylindrical dielectric resonator while the Hd  Ws 12.0
312 ACES JOURNAL, Vol. 34, No. 2, February 2019

(a)

Fig. 5. Simulated reflection coefficients of the proposed

DRA with varying of R1.

(b)

Fig. 3. Simulated top view field distributions at 5.7 GHz.

(a) E-Fields close to the top surface of the dielectric
resonator, and (b) H-Fields on the cross section at the
center of the dielectric resonator.

Fig. 6. Simulated reflection coefficients of the proposed

DRA with varying of d.

(a) (b)

Fig. 7. The pictures of the proposed wideband DRA: (a)

Fig. 4. Simulated reflection coefficients of the proposed without the cylindrical dielectric resonator, and (b) with
DRA with varying of R2. the cylindrical dielectric resonator.
WENG, CHANG, CHEN: WIDEBAND DIELECTRIC RESONATOR ANTENNA 313

more than 20 dB isolation from the peak. It indicates

excellent linearly polarized radiation along the broadside
direction. Figure 11 shows the peak gains of the proposed
DRA. The measured peak gain is 3.64 dBi at 5.5 GHz
and 4.77 dBi at 5.9 GHz. Measured radiation properties
of the proposed DRA at 5.15, 5.5, and 5.85 GHz are
summarized in Table 2. The DRA has high gain, wide
beamwidth, and good front-to-back (F/B) ratio. Based
on the results of reflection coefficients and radiation
properties, the designed DRA has good performance and
is suitable for operating at the WLAN 5.5 GHz band.

Fig. 8. The reflection coefficients of the proposed DRA.

(a) (b)

(a) (b) (c)

Fig. 9. Simulated 3-D radiation gain patterns of the

proposed DRA at frequencies of: (a) 5.15 GHz, (b) 5.5
GHz, and (c) 5.85 GHz.
(c) (d)
III. RESULTS AND DISCUSSIONS
The prototype of the proposed wideband DRA
is measured by an Agilent’s N5230A vector network
analyzer (VNA) to obtain measured |S11|. The simulated
and measured |S11| of the proposed DRA are shown
together in Fig. 8. The simulated |S11| agrees with
the measured one. The measured -10 dB impedance
bandwidth is 1.6 GHz (28.57%, 4.8-6.4 GHz), which (e) (f)
covers the WLAN 5.5 GHz band and can be considered
a wideband impedance matching. Figure 9 shows
simulated 3-D radiation gain patterns of the proposed
DRA at frequencies of 5.15 GHz, 5.5 GHz, and 5.85
GHz. The gain patterns reveal broadside radiations. Gain
patterns are similar each other at the three frequencies
and near omnidirectional in the +z direction with small
back lobe levels. Measured radiation properties of the
proposed DRA are obtained by an MVG SG-24 antenna (g) (h)
measurement system. Figure 10 shows the normalized
far-field radiation patterns of the DRA in the y-z and
x-z planes at 5.15 GHz, 5.5 GHz, and 5.85 GHz,
respectively. The DRA has broadside radiations with
wide beamwidths. Good agreement between simulated
and measured radiation patterns is observed. It shows
the validity of the simulation. The measured 3 dB
beamwidths in the y-z plane are larger than those in the (i) (j)
x-z plane. The beamwidth is around 84 degrees in the
x-z plane at 5.5 GHz. Cross-polarized patterns show
314 ACES JOURNAL, Vol. 34, No. 2, February 2019

ACKNOWLEDGMENT
This work was supported in part by the MOST under
Grant 106-2918-I-260-002.

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VI. CONCLUSION Hawatmeh, “Design and measurements of rect-
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WENG, CHANG, CHEN: WIDEBAND DIELECTRIC RESONATOR ANTENNA 315

Letters, vol. 10, pp. 544-547, May 2011. Min-Chi Chang Min-Chi Chang was
[13] Ansoft High Frequency Structure Simulation born in Yunlin, Taiwan. He received
(HFSS), ver. 10, Ansoft Corporation, Pittsburgh, the B.S. degree in Electrical Engin-
PA, 2005. eering from National United Univ-
[14] R. K. Mongia and P. Bhartia, “Dielectric resonator ersity, Miaoli, Taiwan, in 2009. He
antennas—A review and general design relations is currently working toward the
for resonant frequency and bandwidth,” Int. J. Ph.D. degree in the Department of
Microw. Millimeter-Wave Comput.-Aided Eng., vol. Electrical Engineering, National
4, no. 3, pp. 230-247, 1994. Chi Nan University, Puli, Taiwan. His research interests
focus on antenna design, computational electromag-
netics, and optimization techniques in electromagnetics.

Min-Sian Chen was born in Miaoli,

Wei-Chung Weng received the B.S. Taiwan. He received the M.S.
degree in Electronic Engineering degrees in Electrical Engineering
from National Changhua University from National Chi-Nan University,
of Education, Changhua, Taiwan, in Nantou, Taiwan, in 2015. Since
1993, the M.S. degree in Electrical October 2016, he has been an
Engineering from I-Shou Univer- Antenna Design Engineer in the
sity, Kaohsiung, Taiwan, in 2001, R&D Department of Masterwave
and the Ph.D. degree in Electrical Technology Co., Zhubei, Taiwan. His research interests
Engineering from The University of Mississippi, MS, include designing, fabricating, and testing for WiFi and
USA, in 2007. LTE antennas for wireless products, as well as high-gain
In 2008, he joined the Department of Electrical antenna arrays for 5G communication systems and
Engineering, National Chi Nan University, Puli, Taiwan, outdoor applications.
where he is currently an Associate Professor. From 2017
to 2018, he was a Visiting Scholar at the Department
of Electrical Engineering, Colorado School of Mines,
Golden, CO, USA. From 2004 to 2007, he was a
Graduate Research Assistant in the Department of
Electrical Engineering, The University of Mississippi.
From 1993 to 2004 and 2007 to 2008, he was a Teacher
in the Department of Computer Engineering, Kaohsiung
Vocational Technical School, Kaohsiung City, Taiwan.
He has authored over 50 journal articles and conference
papers and a book entitled Electromagnetics and
Antenna Optimization Using Taguchi’s Method (Morgan
& Claypool, 2007). His research interests include
antennas and microwave circuits design, computational
electromagnetics, electromagnetic compatibility, and
optimization techniques in electromagnetics.
Weng has served many journals as a Reviewer for
years. He is a Member of the Applied Computational
Electromagnetic Society, a Senior Member of IEEE, and
a Life Member of the Institute of Antenna Engineers of
Taiwan (IAET). He was the recipient of Outstanding
Teaching Award of National Chi Nan University in 2013
and 2016, respectively.