broadband bow-tie antenna with tapered balun...addition, a reflector is used to increase the antenna...

Broadband Bow-Tie Antenna with Tapered Balun

Hussein Mohammed AL-Dahhan,

Department of electrical and electronic engineering

Eastern Mediterranean University

Gazimağusa, North Cyprus

[email protected]

Bashar B. Qas Elias

Department of electrical and electronic engineering

Eastern Mediterranean University

Gazimağusa, North Cyprus

[email protected]

Abstract— This letter presents a new broadband Bow Tie

Antenna with high performance characteristics, such as high gain

and wideband to cover wireless applications at 2.4 GHz (ISM)

band. Tee-Junction Balun technique is used to reduce the power

loss due to the radiation which occurs on feed excitation of the

antenna. Tapering technique is used on the Balun to reduce the

effect of discontinuity on the power flow. From the simulation

results of a Bow Tie Antenna we can conclude that our proposed

antenna has met the desired specifications; antenna bandwidth

1.89-3.25 GHz and 3.5-3.67 GHz for operating frequency 2.45

GHZ. Maximum gain achieved at 2 GHz is 4.8 dB and the gain

for 2.5 GHz, 3 GHz and 3.5 GHz are 4.8 dB, 4.1 dB and 3.8 dB

respectively.

Index Terms—Broadband, Bow-Tie, ISM, Balun, Taper.

I. INTRODUCTION

Bow-Tie Antennas (BTA) are made of bi-triangular sheet

of metals feed at the vertex [1]. They are widely used in

wireless communication [2] and ultra wide band (UWB)

applications [3]-[5]. A bow-tie antenna can be printed on a

substrate in different configurations such as double side bow-

tie antenna where one arm may be placed on the upper and the

other one on the lower surface of the substrate. The feeding of

such a structure is done by designing microstrip line feed, connected to a coaxial cable feed.

Different studies have been carried out on Bow-Tie

Antennas to improve the band characteristics. In [6], a Dipole

Bow Tie Antenna (D-BTA) for wireless application at 2.45

GHz is presented. The frequency band of 2.45 GHz was

approved by the international Telecommunication Conference

of ITU in Atlantic City. In [7], a broadband bow-tie antenna

with broadside feed and reflector ground plane is designed to

reach the UHF band applications. This antenna design is

composed of double side antenna feed by double strip line. In

addition, a reflector is used to increase the antenna gain. In [8]

a double side bow-tie antenna designed in ISM band with

different forms of slots is recorded, to produce multiband

frequency. An asymmetric bow-tie antenna, with overlapping

arms together with the tapered ground plane is designed for

GSM/CDMA and 3G/WLAN applications [9].

In this study, a Bow Tie Antenna placed on the same side

of the substrate is proposed. The operating frequency of this

antenna is 2.45GHz to cover wireless application of ISM band

and fed by two different broadband microstrip-to-coplanar

stripline (MSL-to-CPS) Balun transitions. The return loss,

VSWR and far-field characteristics are examined by the FEKO

5.5 simulator and the results are presented.

II. BALUN DESIGN FOR MLS-TO-CPS TRANSITIONS

In this study, multi-sections for impedance transformations

are replaced by exponential tapering to improve the transition characteristics for the balun.

A. Multi-Sections Balun

This balun provides a microstrip to CPS transition. The idea

of the transition is to get an 180ο current distribution phase shift

between each branch of the balun as illustrated in Fig. 1. This

was achieved by adjusting the lengths so that l2-l3=λg/4 where,

λg is the guide wave length, l2 is the left side length and l3 is the

right side length as indicated in Fig.2

Bashar B Qas Elais et al, Int.J.Computer Technology & Applications,Vol 6 (1),76-80

IJCTA | Jan-Feb 2015 Available [email protected]

76

ISSN:2229-6093

Fig. 1 Current distribution between balun’s branches

Fig. 2 (MSL-to-CPS) Balun Transition Configuration

The balun dimensions are given by Table 1.

TABLE I

Balun Dimensions

Balun Element Dimensions (mm)

W1 2.33

L1 11.3

W2 4.48

L2 5.66

W3 16.32

L3 2.33

Lh 10.8

L5 5.66

S 0.9

X 2

Y 2.5

The proposed balun is design and simulated by using FEKO

5.5 full wave simulator software. The balun is placed on the

RT-Duroid 6010 substrate layer, with relative permittivity of

10.2 with the thickness of 2.5mm. Quarter wavelength 35.5Ω

impedance transition is employed for matching between MSL

feed and T-junction (divider/ combination) TL. For this reason,

it is named as multi-sections balun. The following equations

are used to determine the width of the MSL, in terms of the

thickness of substrate, dielectric constant and characteristic

impedance of TL [1].

2

8, 2

2

12 0.621 ln 2 1 ln 1 0.39 , 2

2

(1)

A

A

r

r r

e wfor

e dw

wdB B B for

d

1 1 0.11(0.23 )

60 2 1

r r

r r

ZA

(2)

377

(3)2 r

BZ

B. Exponential Tapered Balun Technique

This section is about multi-sections for impedance

matching. Here, multi-section transformations are replaced

by a new exponential tapering and 53% improvement has

been achieved in the reflection, compared to the multi-

section technique.

In this tapering technique, the width of the exponential taper is calculated by using the following equations [10]:

0(Z( )) (Z )e 4 aW W zz

Where constant a is defined as:

0

W(Z )1ln( ) 5

(Z )

Lal W

Note that, 0Z is the characteristics impedance of MSL and ZL

is the load side impedance.



77

ISSN:2229-6093

Fig. 3 Return loss S11 and insertion loss S21 of Multi-sections

Balun

Fig. 4 Exponential tapered balun geometry

III. BROADBAND BOW-TIE ANTENNA DESIGN

In this section, broadband bow- tie antenna designed with

tapered balun configurations is presented. Two kinds of balun

multi-section and exponential baluns are used as feed

transmission line to the antenna proposed. The antenna and

baluns are puts on the substrate layer with εr=10.2 and height

2.5mm. Below the substrate there is a truncated ground plane

which was employed as a reflector to the antenna. The

dimensions of the proposed antenna are: Lbt, W and Lcps are

23.5, 19.3 and 15.92 mm respectively. The approximated

dimensions of bow-tie can be calculated by using the following

equations:

1

2 2 22

( )3 r r

cx m mn n

f

(6)

0.5( )e rx x t (7)

x= side length of bowtie antenna

xe= effective side length of antenna

fr= operating frequency

εr= relative permittivity

Fig. 5 Antenna layout with Multi-sections balun

Fig. 6 Bowtie antenna with exponential taper

IV. RESULT AND DUSCUSSIONS



78

ISSN:2229-6093

In this section the return loss, radiation pattern and gain of

two different antenna designs are presented.The results for

return loss, by Fig. 8, shows that the bow-tie antenna with

eponential tapered balun have a broad bandwith 1.89-3.25 GHz

and the yagi antenna with mult-isection balun [11] have a

bandwidth 2.1-2.79 GHz , while the bow-tie antenna with

muli-sections taper has narrower bandwidth compared with

others which is 1.98-2.4 GHz. The return loss is improve by

24% of the bow- tie antenna with multi- sections balun

compared with bow-tie antenna for exponential tapered

technique and 18% for yagi antenna with multi section balun as

shown in Fig. 8.

Fig. 7 VSWR versus the frequency range

Fig. 8 Simulation reflection cofficient versus

Fig. 9 BTA with Multi-Sections Technique

Fig. 10 BTA with Exponential Taper Technique

The simulated gain of BTA with Multi-sections is 3 dB

(Fig. 10) at the resonant frequency and it is very close to the

BTA with Exponential tapered balun which is equal 3.1 dB.

For the gain of BTA with triangular tapered balun (Fig. 12).

Maximum gain gives for bith case at 2 GHz which equals 4.8

dB.

V. CONCLUSION

A new MSL-to-CPS transitions balun for Bow-Tie Antenna

has been proposed and simulated by FEKO 5.5 software, full

wave simulator. The proposed antenna is in the ISM band



79

ISSN:2229-6093

which is especially suitable for wireless communication

systems having a band from 1.89 GHz to 3.25 GHz (80%)

bandwidth. The antenna radiation gain has been obtained up to

4.8 dB and 3 dB at the resonant operating frequency (2.45GHz).

REFERANCES

[1] Constantine A. Balanis, Antenna Theory, 3rd ed. New Jersey,

Canada: John Wiley, 2005.

[2] María Elena de Cos Gomez R. C. Hadarig, "Novel Bow-tie–

AMC Combination for 5.8-GHz RFID Tags Usable With

Metallic Objects," IEEE Antenna and Wirless Prop. Let., vol. 9, pp. 1217-1220, 2010.

[3] Katsuki K., Akimasa H. " Double –Sided Printed Bow-Tie Antenna for UWB communications, " IEEE Antenna and

Wirless Prop. Let., vol. 3, pp. 152-156, 2004.

[4] Abdalnasser A., Atef Z. " Wideband Microstrip- Fed Printed

Bow-Tie Antenna for Phased Array System," Microwave and

Optical Tech. Letter., vol. 43, No. 2, pp. 123-126, oct. 2004

[5] Katsuki K., Akimasa H." Double –Sided Rounded Bow-Tie

Antenna (DSRBA) for UWB communication, " IEEE Antenna

and Wirless Prop. Let., vol. 5, pp. 446-449, 2006.

[6] K. R. Mahmoud, "Design Optimization of A Bowtie Antenna

for 2.45 GHz RFID Readers Using A HYBRID BSO-NM

Methods," in Progress In Electromagnetics Research, 2010, pp. 105-117

[7] Linyan Guo, Minhua Li, Helin Yang Boxun Xiao, "A Broadband Bow-tie Antenna Used in UHF with Metalic

Reflection Plane," in Yangtze University, Chaia, 2013, pp. 148-

150.

[8] K. Y. Kabalan, A. El-Hajj, C. G. Christodoulou, Y. Tawk, "A

Simple Multiband Printed Bowtie Antenna," IEEE Antenna and

Wireless Prop. Let., vol. 7, no. 3, pp. 557-560, May 22 2008.

[9] H. Wang, J. Liu, G. Wang " Asymmetric bow-tie antenna for

GSM/CDMA and 3G/WLAN," Electronic Let., vol. 43, no. 23, Nov. 2008.

[10] David M. Pozar, Microwave Engineering, 3rd ed., Bill Zobrist, Ed. Massachusetts, United State: Wiley, 2005.

[11] Sergio E. Melais and Thomas M. Weller, "A Quasi Yagi

Antenna Backed by a Metal Reflector," IEEE Trans. on Antenna and Prop., vol. 56, no. 12, pp. 3868-3872, Dec. 2008.

[12] X. Gang, On the resonat frequencies of the microstrip antennas,” IEEE Trans. of Antennas and Propagt., vol. 37, no. 2, pp. 245-

247, 1989.



80

ISSN:2229-6093

broadband bow-tie antenna with tapered balun...addition, a reflector is used to increase the antenna...

Documents