A Dual Band Planar Monopole Antenna with Inverted-M Parasitic Plane

H.M.R Nurul

1, P.J Soh

1, A.A.H Azremi

1, N.A Saidatul

1, S.R Norra

1, M.I Ibrahim

2, R.B Ahmad

1

1School of Computer and Communication Engineering.

Universiti Malaysia Perlis (UniMAP), Kangar, Perlis, MALAYSIA

2Faculty of Electronics and Computer Engineering.

Universiti Teknikal Malaysia Melaka (UTeM),

Ayer Keroh, Melaka, MALAYSIA

nh_husna@yahoo.com, pjsoh@unimap.edu.my, azremi@unimap.edu.my, buffy_0510@yahoo.com, gurlz_emerald@yahoo.com,

imranibrahim@utem.edu.my, badli@unimap.edu.my

Abstract - Introduction of parasitic plane as additional

radiator helps to produce desired resonant frequencies,

while helping to minimize the size of the antenna. A

dual-band monopole antenna with parasitic plane is

designed to satisfy dual-band applications, namely

UMTS and WLAN 802.11. This work is an effort to

investigate the effect of employing an inverted M-

shaped parasitic plane, which introduces double slits in

the monopole structure. The antenna parametric

analysis of the antenna configuration was performed

using experimental method. Results simulated and

measured shows good correlation and the antenna is

verified to be working in a dual band mode.

Keywords: monopole antennas, microstrip antennas, dual-

band antennas, parasitic plane

1. Introduction

The rapid progress in mobile handsets and

computer communication systems requires a single RF

device such as an antenna to operate in dual band or

multi band scheme [1]. Current consumer electronic

devices, especially PDAs and smart phones, provide

wireless interconnectivity through various means

simultaneously, for example having the choice to

access wireless networks through WLAN or UMTS.

This has prompted a need for a miniaturized and

multiple resonating antennas.

A monopole antenna is very simple and an

efficient radiating element [1]. However, these

antennas suffer from the problem of limited bandwidth

and distortion radiation characteristics. Recently, it has

been demonstrated that monopole antennas are

promising to be used for dual-band or multi band

mobile services [1 – 3], especially when its size can be

significantly reduced, and bandwidth enhanced using

the a parasitic plane. In circularly-polarized antennas,

axial ratio’s 2-dB bandwidth has also been shown to

have significant improvements [4, 5]. Various shapes

and structures of parasitic planes for different

applications have been proposed,

Figure 1: Layout of the planar monopole.

as can be seen in [6 - 8].

In this work, a dual band monopole antenna with

parasitic plane was designed to satisfy system

requirements for Universal Mobile

Telecommunication System (UMTS) and Wireless

Local Area Network (WLAN) at the same time. The

introduction of parasitic plane as an additional radiator

helps to produce desired resonant frequencies.

2. Antenna Design

Figure 1 shows the dimension of the designed

antenna. The top layer design consists of a rectangular

patch antenna, sized at 30 mm x 23 mm. The initial

size of the patch is determined by a lower limit of the

operating frequency band, and can be calculated using

the procedure described in [9]. It has an I-slit and an

inverted L-slit structure fed using an inset feed. Slits

are added in order to achieve a multiple band feature.

The parametric analysis of the antenna configuration is

performed using the experimental method.

1-4244-1435-0/07/$25.00©2007 IEEE

Figure 2: The fabricated monopole antenna (a) Top view;

(b) bottom view

Figure 3: The simulated and measured S11 for the

monopole antenna

At the bottom layer, a parasitic plane is added to

act as an additional radiator. Its size settings enabled

the antenna to be tuned to the higher desired frequency,

while at the same time, helped to keep the size of the

antenna as minimal as possible. Operation bandwidth

is also enhanced by implementing this structure [4].

The antenna is fabricated on a FR-4 substrate with a

thickness of 1.6 mm and relative permittivity, εr, of

4.7. The analogous feed width calculated using a 50 Ω

impedance at 2 GHz and 2.45 GHz aggravated a fixed

width of 3 mm.

3. Results and Discussion

S11 measurements are done by connecting a 50 Ω

SMA end launch to the monopole antenna, and an

Agilent E5062A network analyzer. The measured

versus simulated results are shown in Figure 3. It has a

measured first resonance bandwidth of 2.110 – 2.130

GHz, which is suitable for UMTS applications. The

second measured resonance occurred at the frequency

starting from 2.450 till 2.500 GHz. This implies that

this antenna fall short of having enough bandwidth for

the WLAN 802.11(b) requirement.

This differs from the simulated results, where it is

seen that the first simulated resonance transpired from

a frequency of 2.010 GHz till 2.050 GHz for UMTS,

while sufficient bandwidth is observed at the WLAN

domain, which is shown from 2.359 – 2.556 GHz.

Figure 4: The simulated radiation pattern for the

monopole antenna (a) E-plane at 2.030 GHz (b) H-plane

at 2.030 GHz, (c) H-plane at 2.465 GHz and (d) H plane

at 2.465 GHz

Table 1: Simulated and measured HPBW and isolation

HPBW (θ0) Isolation (dB) Frequency

(GHz) E Plane H Plane E Plane H Plane

2.030 168 90 7.64 7.53

2.465 87 99 8.47 11.54

It is already showed that frequency shifting is a

normal occurrence from [10, 11], and perhaps a lower

design frequency should be taken into consideration in

the first place. Anyhow, this known inconsistency is

hard to predict as inaccuracies in the fabrication

process and varying dielectric constant are some of the

factors contributing to this cause [12 – 14]. Moreover,

during the design stage, enough allowance and a guard

band of nearly 150 MHz is already allocated but still

failed to decipher this glitch.

Only the center frequency seems to be accurate

enough in this domain, with a difference as little as 10

MHz only when comparing simulation and

measurement results. However, a contradicting

scenario can be seen in the lower UMTS frequency

realm. It produced a difference of almost 90 MHz

between center frequencies of simulation and

measurement results.

Figure 4 shows the simulated radiation pattern for

the designed antenna in terms of co-polarization and

cross-polarization in the E- and H-planes for both

WLAN and UMTS center frequencies. Table 1

summarizes the radiation characteristics.

The simulated radiation characteristics shows a

symmetrical azimuth, but not necessarily centered at θ

= 0o. E-plane radiation at WLAN frequency indicated a

minor skewed response towards the left, as can be

observed in Figure 4(c). H-plane showed a more

directive radiation on both WLAN and UMTS

frequencies, as indicated in the table. Both readings in

the H-planes are also almost consistent, with a

difference of only 9o.

The E-plane, on the other hand, exhibits a larger

difference in different frequencies. The E-plane

beamwidth is found to have almost twice the size when

the antenna is operating in the UMTS frequency,

compared to WLAN operation. This is beneficial to

both applications as a UMTS receiver requires an

omni-directional pattern.

While on the other hand, WLAN Access Points

(APs) are normally placed at higher position inside a

building, against the wall, thus the need for a more

directional pattern, instead of the former. Such pattern

of this antenna is also convenient for indoor multipath

communications where the angle of arrival is

statistically uniformly distributed [15]. Thus, this

antenna will be almost ideal when applied to both

cases, considering the different radiation properties

that the antennas exhibit at the different frequencies.

4. Conclusion

A dual band monopole antenna with an inverted-

M parasitic plane is designed and presented. The

designed antenna exhibited acceptable reflection and

radiation characteristics in both target design bands.

Considerable size reduction had been achieved using

the M-shaped parasitic plane, while additional

resonance and matching for both resonances have been

improved using the L- and I-shaped slits, without

compromising the size of the antenna.

References

[1] E.A Altshuler, “A Monopole Antenna Loaded

with a Modified Folded Dipole” Antennas and

Propagation, IEEE Transactions on,

vol. 41, Issue 7, pp. 871 – 876, July 1993

[2] K.M Seol, J.H Jung, H. Park, S.G Jeon, U.S Kim,

J.H Choi, “Multi Band Monopole Antenna with an

Inverted U-Shaped Parasitic Plane”, Electronics

Letters, Vol. 42, Issue 15, pp. 844 – 845, July

2006

[3] B. Schaer, K. Rambabu, J. Bornemann, R.

Vahldieck, “Design of Reactive Parasitic

Elements in Electronic Beam Steering Arrays”,

Antennas and Propagation, IEEE Transactions

on, vol. 53, Issue 6, pp. 1998 – 2003, June 2005

[4] G. DeJean, R.L Li, J. Laskar, M.M Tentzeris,

“Circularly Polarized Loop Antennas with

Parasitic Elements for Bandwidth Enhancement”,

IEEE Antenna and Propagation Society

International Symposium, Proceedings of the, vol.

1B, 2005, pp. 401 – 404

[5] R.L Li, G. DeJean, J. Laskar, M.M Tentzeris,

“Investigation of Circularly Polarized Loop

Antennas with a Parasitic Element for Bandwidth

Enhancement”, Antennas and Propagation, IEEE

Transactions on, vol. 53, Issue 12, pp. 3930 –

3939, Dec. 2005

[6] P.M Lepeltier, J. Citerne, J.M Floch, “On the

EMC Dipole Feed-line Parasitic Radiation”,

Antennas and Propagation, IEEE Transactions

on, vol. 38, Issue 6, pp. 878 – 882, June 1990

[7] Y.J Cho, S.H Hwang, S.O Park, “A Dual Band

Internal Antenna with a Parasitic Plane for Mobile

Handsets and the Consideration of the Handset

Case and Battery”, Antenna and Wireless

Propagation Letters, pp. 429 – 432, vol. 4, 2005

[8] K.H Kim, Y.J Cho, S.H Hwang, S.O Park, “Band-

notched UWB Planar Monopole Antennas with

Two Parasitic Patches”, Electronics Letters, vol.

41, Issue 14, pp. 783 – 785, July 2005

[9] P.J Soh. M.K.A Rahim, A. Asrokin, M.Z.A Abdul

Aziz, “Comparative Studies on Performance of

Different Feeding Techniques Using Circuit

Model for a Microstrip Patch Antenna”, IEEE

Asia Pacific Conference on Applied

Electromagnetics (APACE‘05), Proceedings of

the, Dec 2005.

[10] P.J Soh, M.K.A Rahim, A. Asrokin, M.Z.A Abdul

Aziz, “Modeling of Different Feeding Techniques

for a Microstrip Patch Antenna”, MMU

International Symposium on Information and

Communications Technologies (M2USIC‘05),

Proceedings of the, Nov 2005, TS05 p.p9-13

[11] P.J Soh, M.K.A Rahim, A. Asrokin, “Design,

Modeling and Comparison of Non-Contacting

Feeds for a Microstrip Patch Antenna”, IEEE

International Conference on Computer &

Communication Engineering (ICCCE ‘06), vol. 2,

May 2006, pp. 694 – 699

[12] W. J Lui, C.H Cheng, H.B Zhu, “Frequency

Notched Printed Slot Antennas with Parasitic

Open-circuit Stub”, Electronics Letters, vol. 41,

Issue 20, pp. 1094 – 1095, Sept 2005

[13] A. Moleiro, J. Rosa, R Nunes, C. Peixeiro, “Dual

Band Microstrip Patch Antenna Element with

Parasitic for GSM”, IEEE Antennas and

Propagation Symposium, Proceedings of the, vol.

4, 16 – 21 July 2000, pp. 2188 – 2191

[14] R. Garg, P. Bhartia, I. Bahl, and A. Ittipiboon,

Microstrip Antenna Design Handbook, London:

Artech House, 2001

[15] A. Kaleghi, A.Azoulay, J.C Bolomey, “A Dual

Band Back Coupled Meanderline Antenna for

Wireless LAN Applications”, IEEE 61st Vehicular

Technology Conference 2005 (VTC 2005),

Proceedings of the, vol. 1, June 2005, pp. 226 –

229