a compact cpw-fed slotted patch antenna for dual-band operation-evm

110 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 9, 2010

A Compact CPW-Fed Slotted Patch Antennafor Dual-Band Operation

Wen-Chung Liu, Senior Member, IEEE, Chao-Ming Wu, and Nien-Chang Chu

Abstract—A compact coplanar waveguide (CPW)-fed patchantenna designed by simply embedding two types of shaped slotsinto a rectangular patch for achieving dual-band operation ispresented. The use of embedded slots can effectively excite mul-tiresonant modes together with good dual-impedance bandwidths,especially ultrawide for the upper bandwidth. By fabricatingand measuring the prototype of the proposed optimal antenna,dual operating bands with 10-dB return-loss bandwidths of about230 MHz centered at 2.42 GHz and of about 73% ranging from 4.8to 9.62 GHz covering the required bandwidths of 2.4/5.2/5.8 GHzWLAN standards and the C-band satellite communication wereobtained. Also, a stable monopole-like radiation pattern and anaverage antenna gain of 1.4 and 5.1 dBi, respectively, across thedual operating bands have been measured.

Index Terms—Coplanar waveguide (CPW), dual-band, patchantenna, ultrawideband, WLAN.

I. INTRODUCTION

RECENTLY, the ability to integrate more than one com-

munication standard into a single system has become an

increasing demand for a modern portable wireless communi-

cation device. However, it is difficult to simultaneously set the

dual or multiple antennas and a diplexer into such a device due

to the device’s limited space. This indicates that a modern an-

tenna requires not only the function of providing a dual- or

multiband operation, but also a simple structure, compact size,

and easy integration with the system circuit. For this, many

promising dual- or multiband planar antenna designs such as

the microstrip-line-fed antennas [1]–[3], the probe-fed antennas

[4]–[6], the planar inverted-F antennas (PIFAs) [7]–[9], the di-

electric resonator antennas [10], [11], and the coplanar wave-

guide (CPW)-fed antennas [12]–[14] have been reported. How-

ever, most of them have either a large overall size or a compli-

cated structure to reduce the antenna’s application. Considering

that the planar slot antenna has a low Q-factor that can thus pro-

vide a wide impedance bandwidth and is easy to generate mul-

tiresonance by simply varying the slot width and shape, it has

received much attention recently [15], [16]. Meanwhile, for the

known attractive features of the CPW-fed antenna such as low

profile, light weight, a single metallic layer, easy realization, and

Manuscript received December 16, 2009; manuscript revised January 28,2010. Date of publication February 25, 2010; date of current version March16, 2010. This work was supported by the National Science Council of theRepublic of China (on Taiwan) under Grant NSC 98-2221-E-150-045.

W.-C. Liu and C.-M. Wu are with the Department of AeronauticalEngineering, National Formosa University, Yunlin 632, Taiwan (e-mail:[email protected]).

N.-C. Chu is with the Institute of Electro-Optical and Materials Science, Na-tional Formosa University, Yunlin 632, Taiwan.

Digital Object Identifier 10.1109/LAWP.2010.2044135

Fig. 1. Configuration of the proposed CPW-fed slotted patch antenna for dual-band operation.

integration with system circuits, it is therefore feasible for de-

signing a simple and compact dual- or multiband antenna by

composing both the slot structure and the CPW-feeder.

In this letter, a simple dual-band design of a CPW-fed

monopole antenna consisting of a compact rectangular

patch and a couple of twin embedded slots is presented.

By properly selecting shapes and dimensions of these

embedded slots, good dual-band impedance bandwidths

as well as suitable radiation characteristics for use in

2.4 (2.4-2.484)/5.2 (5.15-5.35)/5.8 (5.725-5.825) GHz WLAN

and C-band (4–8 GHz) satellite operations can be achieved. The

effects of the embedded slots to the resonance were studied,

and an experimental prototype of the proposed antenna design

working at these frequencies was fabricated and measured,

verifying the design concept.

II. ANTENNA DESIGN AND DISCUSSIONS

The configuration of the proposed dual-band CPW-fed

slotted patch antenna is shown in Fig. 1. The antenna was

etched on a 1.6-mm-thick FR4 substrate with relative per-

mittivity 4.4. The basis of this antenna structure is a

rectangular patch with dimensions of mm or

about with respect to the desired lower resonant

frequency 2.4 GHz. This incidentally makes the patch be the

quarter-wavelength antenna candidate. A couple of twin slots

including dual folded slots and dual inverted-L-shaped slots

were embedded into the patch to form the antenna as a CPW-fed

rectangular patch monopole with four protruded strips, which

include dual side strips and dual short strips. However, dif-

ferent from a conventional CPW-fed patch antenna, each of

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LIU et al.: COMPACT CPW-FED SLOTTED PATCH ANTENNA FOR DUAL-BAND OPERATION 111

Fig. 2. Simulated return loss against frequency for the proposed antenna withdifferent embedded slots.

TABLE IOPTIMAL GEOMETRICAL PARAMETERS OF THE PROPOSED CPW-FED

DUAL-BAND SLOTTED PATCH ANTENNA

the two side strips was shorted to the ground. Such a design

skill was found to be helpful for improving the antenna’s

impedance matching. In examining the performance of the

proposed antenna configurations in terms of enhancing the dual

bandwidths, the commercially available moment method code

IE3D was used for required numerical analysis. Via iterative

design process, the proper parameters for optimal dual-band

operation of the proposed antenna were finally obtained and are

listed in Table I. Note that in this design, the width of all slots

was selected as 0.5 mm.

Fig. 2 shows the simulated frequency response of return loss

for the proposed antenna, denoted as ant 1. It is clearly seen that

dual impedance bandwidths (10 dB return loss) of 210 MHz

(2.34–2.55 GHz) and 5.05 GHz (4.8–9.85 GHz) with two dom-

inant resonant modes excited at 2.42 and 5.21 GHz were ob-

tained. Particularly, an ultrawide bandwidth for the upper oper-

ating band was produced as two more resonances at 6.86 and

9.5 GHz were excited to thus form an ultrawide continuous

bandwidth. The bandwidths clearly cover the required band-

widths of the WLAN 2.4/5.2/5.8 GHz standards and the C-band

satellite communication. Meanwhile, to examine the effects of

the embedded slots to the antenna’s matching condition, the

simulated results of return loss for the proposed antenna without

part of the embedded slots were also studied and plotted in

Fig. 2. Obviously, for the case without the upper portion for

each folded slot (denoted as ant 2), only a worse resonance was

excited at the lower band of about 2.45 GHz, which is mainly

due to the fundamental mode of the rectangular patch. However,

for the case of the proposed antenna without the two inverted-L-

shaped slots (denoted as ant 3), multiresonant modes with worse

and good impedance matching for the lower (3.1 GHz) and

upper (5.45 GHz) bands, respectively, were excited.

Fig. 3. Simulated return loss against frequency for the proposed dual-bandslotted patch antenna with different slot embedment. All dimensions are thesame as listed in Table I.

Fig. 4. Simulated return loss against frequency for the proposed dual-bandslotted patch antenna with various � . Other parameters are the same as listedin Table I.

To further investigate the effect of each slot to the proposed

antenna’s bandwidth characteristic, the frequency response of

return loss for the proposed antenna with different slot embed-

ment was also analyzed and is shown in Fig. 3. Obviously, for

the case with the folded strip (ant 4, 6, 7, 8, and 9), the upper-

band resonance was effectively excited, and especially, good

ultrawideband impedance matching was achieved as the dual

folded strips were simultaneously embedded. Similarly, better

lower-band matching condition was obtained when inserting the

dual inverted-L-shaped slots into the patch. These results clearly

indicate that existence of the inverted-L-shaped slots can signif-

icantly affect impedance matching to the lower band, whereas

the upper portions of the two folded slots will seriously change

the excitation of the upper-band resonant modes.

Fig. 4 presents the tuning effect of the length for the dual

inverted-L-shaped slots with selected values from 3 to 7 mm


112 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 9, 2010

Fig. 5. Simulated return loss against frequency for the proposed dual-bandslotted patch antenna with various � . Other parameters are the same as listedin Table I.

on return-loss response. As predicted, the lower-band resonance

is significantly affected by this parameter. The lower opera-

tion band is moved toward the lower frequency when in-

creases, whereas that of the upper band is almost unchanged.

Such a band-tunable function for the lower band is very helpful

when this antenna is expected to also be used for communication

standards operating at around 2 GHz, such as the GSM-1900,

UMTS, and IMT-2000, etc.

Fig. 5 illustrates the effect of length for each folded slot

with varying dimensions of 1, 2, 3, 5, and 7 mm on the frequency

response of the return loss for the proposed antenna. Note that

the case of mm is the proposed optimal design. The re-

sults show that the upper operation band is shifted toward the

higher frequency and has a narrower bandwidth when de-

creases, whereas the lower resonant mode is almost unaffected.

The main reason for and to significantly affect the lower

and upper operating bands, respectively, is due to the lengths of

the dual side strips and the dual short strips, which appropriately

provide the electric current paths for the lower and upper reso-

nances and are changed by varying and . The larger the

, the longer the side strip (short strip) to thus shift the

lower (upper) operating band toward the lower frequency, and

vice versa. The above study is very vital for the designer to have

information in achieving the desired operating band for various

applications based on this antenna prototype.

III. EXPERIMENTAL RESULTS

The prototype of the proposed antenna, denoted as ant 1

in Fig. 2, was constructed and experimentally investigated.

Fig. 6 presents the measured return loss against the frequency

for this antenna. Obviously, dual-band operations, especially

an ultrawide bandwidth for the upper operating band, were

obtained. The lower-band resonance was excited at 2.42 GHz

with impedance bandwidth of 210 MHz (2.34–2.55 GHz),

whereas the upper-band resonances occurred at 5.12, 6.61, and

Fig. 6. Measured and simulated return loss against frequency for the proposeddual-band slotted patch antenna.

Fig. 7. Measured far-field radiation patterns of the proposed antenna at dif-ferent frequencies �� —�� . (a) 2.42, (b) 5.21, and (c) 6.61 GHz.

9.35 GHz accompanying an ultrawide bandwidth of 4.82 GHz

(4.8–9.62 GHz). Agreement between simulation and measure-

ment seems very good, allowing for a bandwidth discrepancy

(230 MHz) of % at the upper operating band.

The far-field radiation characteristics at frequencies of 4.42,

5.21, and 6.61 GHz for the proposed antenna have also been

measured and are shown in Fig. 7. The results, in general, show

this antenna has a stable monopole-like radiation pattern with

conical radiations in the elevation planes (xz and yz planes) and

a nearly omnidirectional pattern in the azimuth plane (xy plane).


LIU et al.: COMPACT CPW-FED SLOTTED PATCH ANTENNA FOR DUAL-BAND OPERATION 113

Fig. 8. Measured peak antenna gains across the lower and upper bands for theproposed antenna.

However, the omnidirectional property is degraded when oper-

ating frequency increases. This may due to the difference of ver-

tical and horizontal current distributions on the slotted patch in-

creasing when operating frequency increases. Finally, the peak

antenna gains against frequency for the proposed antenna across

the dual operating bands were measured and are shown in Fig. 8.

It should be noted that the gain across the upper band was only

measured up to 8.2 GHz due to the equipment limitation in our

laboratory. We obtained an average gain of 1.4 (1–1.6 dBi) and

5.1 dBi (3.8–6.6 dBi) for the lower and higher measured bands,

respectively.

IV. CONCLUSION

A single-layer CPW-fed monopole antenna designed from

simply embedding slots into a rectangular patch has been pre-

sented. With an antenna size of only 30 25 mm , including

the ground plane, multiresonance having dual continuous oper-

ating band and suitable radiation performance to cater for the

WLAN 2.4/5.2/5.8 GHz and the C-band satellite applications

are achieved. Also, the prototype has been constructed and mea-

sured to show a good agreement with the simulated results.

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a compact cpw-fed slotted patch antenna for dual-band operation-evm

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