Corner truncated inverted u slot triple band tunable rectangular microstrip antenna for wlan applications

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976

– 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 1, January- June (2012), © IAEME

1

CORNER TRUNCATED INVERTED U - SLOT TRIPLE BAND

TUNABLE RECTANGULAR MICROSTRIP ANTENNA FOR WLAN

APPLICATIONS

Nagraj Kulkarni1

and S. N. Mulgi2

Department of PG Studies and Research in Applied Electronics,

Gulbarga University, Gulbarga-585106, Karnataka, India

Email: [email protected]

2 [email protected]

ABSTRACT

This paper presents the design and development of simple corner truncated rectangular

microstrip antenna comprising inverted U-slot on the radiating patch for triple band and

tunable operation. The proposed antenna is excited through microstripline. The low cost

glass epoxy substrate material is used to fabricate the antenna. The antenna operates

between 4.74 to 9.59 GHz for three frequency bands and gives broadside radiation

characteristics. The tuning of secondary bands can be achieved by varying the width of

inverted U-slot. The experimental and simulated results are in good agreement with each

other. The proposed antenna may find applications in WLAN.

Key words: Corner truncated, microstrip antenna, triple band, tuning.

1. INTRODUCTION

Microstrip antennas are becoming increasingly popular because of their small size,

lightweight, low cost, easy to fabricate and compatible to microwave integrated circuits

[1-2]. However, the modern communication systems such as wireless local area networks

(WLAN) often require antennas possessing two or more discrete frequency bands, which

can avoid the use of multiple antennas. The multiband microstrip antennas are designed

by cutting slots of different geometries like bow-tie, rectangular, square ring, annular ring

etc. on the radiating patch [3-6]. The tuning of the bands is achieved by incorporating

shorting pins, open and closed stubs, shorting posts and use of active devices with

variable biasing voltages [7-12] etc. But the multiband operation and tuning of the

INTERNATIONAL JOURNAL OF ELECTRONICS AND

COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)

ISSN 0976 – 6464(Print) ISSN 0976 – 6472(Online)

Volume 3, Issue 1, January- June (2012), pp. 01-09

© IAEME: www.iaeme.com/ijecet.html

Journal Impact Factor (2011)- 0.8500 (Calculated by GISI)

www.jifactor.com

IJECET

© I A E M E



2

operating bands using planar corner truncated inverted U-slot rectangular microstrip

antenna is found to be rare in the literature.

2. DESIGNING OF ANTENNA

The conventional rectangular microstrip antenna (CRMSA) and corner truncated inverted

U-slot rectangular microstrip antenna (CTIUSRMSA) are fabricated on low cost glass

epoxy substrate material of thickness h = 1.6 mm and dielectric constant εr = 4.2. The

artwork of CRMSA and CTIUSRMSA is developed using computer software AUTO

CAD to achieve better accuracy. The antennas are etched by photolithography process.

The bottom surface of the substrate consists of a tight ground plane copper shielding.

Figure 1 shows the top view geometry of CRMSA. This antenna is designed for the

resonant frequency of 3.5 GHz using the equations available in the literature for the

design of rectangular microstrip antenna on the substrate area A x B [13]. This antenna

consists of a radiating patch of length L and width W. A quarter wave transformer of

length Lt and width Wt is incorporated to match the impedances between CP and

microstripline feed of length Lf and width Wf. A 50 Ω semi miniature-A (SMA)

connector is used at the tip of the microstripline to feed the microwave power.

Figure 2 shows the top view geometry CTIUSRMSA which is constructed from CRMSA.

Two diagonally opposite corners of CRMSA are truncated as Xd and Yd. The novel

inverted U slot is placed at the center of the rectangular radiating patch. Lh and Lv are

the lengths of horizontal and vertical arms of inverted U slot respectively. The

dimensions Lh and Lv are taken in terms of λ0, where λ0 is a free space wave length in cm

corresponding to the designed frequency of 3.5 GHz. Uw is the width of the horizontal

and vertical arms of inverted U slot. The inverted U-slot is placed at a distance of 0.305

cm from radiating (W) and 0.415 cm from non-radiating (L) edges of the rectangular

patch respectively. The various parameters of the proposed antennas are listed as in Table

1. Figure 3 (a) and (b) show the 3D view of CRMSA and CTIUSRMSA respectively.

3. EXPERIMENTAL RESULTS

The German make (Rohde and Schwarz, ZVK model 1127.8651) Vector Network

Analyzer is used to measure the experimental return loss of CRMSA and CTIUSRMSA.

The simulation of the CRMSA and CTIUSRMSA is carried out using High Frequency

Structure Simulator (HFSS) software.

Figure 4 shows the variation of return loss versus frequency of CRMSA. From this figure

it is clear that, the CRMSA resonates at 3.39 GHz of frequency which is close to the

designed frequency of 3.5 GHz. The experimental impedance bandwidth over return loss

less than -10dB is calculated using the formula,

2 1

c

( ) = ×100 %Impedance Bandwidth (%)

−

f f

f



3

where, f2 and f1 are the upper and lower cut off frequencies of the resonating band when

its return loss reaches -10 dB and fc is a centre frequency between f1 and f2. The

impedance bandwidth of CRMSA is found to be 3.27 %. The simulated result of CRMSA

is also shown in Fig. 4.

Figure 5 shows the variation of return loss versus frequency of CTIUSRMSA. It is clear

from this figure that, the antenna operates for three bands BW1 (4.67-4.82 GHz), BW2

(5.74-6.01 GHz) and BW3 (8.79-9.74 GHz) for the resonating modes of f1, f2 and f3

respectively, when Uw = 0.2 cm. The three bands BW1, BW2 and BW3 are due to the

independent resonance of patch, corner truncated slots and inverted U-slot of

CTIUSRMSA. The BW1 is considered as primary band because its resonating mode f1

remains close to fr of CRMSA. The BW2 and BW3 are considered as secondary bands. It

is observed from Fig. 5 that, the construction of CTIUSRMSA does not affect much the

resonant mode of primary band i.e. f1, but two additional resonating modes appear at f2

and f3. The simulated result of CTIUSRMSA is also shown in Fig. 5 which is in good

agreement with the experimental results. The magnitude of impedance bandwidth of

BW1, BW2 and BW3 are found to be 3.16%, 4.5% and 10.2% respectively. The

frequency ratio f2/f1 of CTIUSRMSA is found to be 1.242.

Figure 6 shows the variation of return loss versus frequency of CTIUSRMSA. It is seen

from this figure that, the antenna operates for three bands BW4 (4.73-4.91 GHz), BW5

(7.48-7.92 GHz) and BW6 (8.93-10.24 GHz) for the resonating modes of f4, f5 and f6

respectively, when Uw is increased from 0.2 to 0.3 cm. It is clear from this figure that,

the resonating modes f5 and f6 are shifted towards higher frequency side when compared

to f2 and f3 respectively, without much shift in the primary resonant mode i.e. f1. This

change in the resonating modes of antenna is due to the increase of Uw from 0.2 to 0.3

cm. The simulated result of CTIUSRMSA is also shown in Fig. 6 which is in good

agreement with the experimental results. The magnitude of impedance bandwidth of

BW4, BW5 and BW6 are found to be 3.73%, 5.71% and 13.55% respectively. The

frequency ratio f5/f4 of CTIUSRMSA is found to be 1.59 indicates shifting of secondary

resonant mode f5 with respect to primary resonant mode f4 .

The gain of the proposed antennas is measured by absolute gain method. The

power transmitted ‘Pt’ by pyramidal horn antenna and power received ‘Pr’ by antenna

under test (AUT) are measured independently. With the help of these experimental data,

the gain (G) dB of AUT is calculated by using the equation,

λP 0r(G) dB=10 log - (G ) dB - 20log dBt

P 4πRt

where, Gt is the gain of the pyramidal horn antenna and R is the distance between the

transmitting antenna and the AUT. The maximum gain CTIUSRMSA measured in BW1

and BW4 are found to be 1.21dB, 1.64 dB respectively.

Figure 7-9 show the co-polar and cross-polar radiation pattern of CRMSA and

CTIUSRMSA measured in their operating bands. From these figures it is clear that, the

patterns are broadsided and linearly polarized.



4

4. CONCLUSION

From the detailed experimental study, it is concluded that, the CRMSA can be

made to operate at three frequency bands between 4.74 to 9.59 GHz by loading inverted

U-slot on the radiating patch. The secondary bands of CTIUSRMSA can be tuned to

higher side of the frequency spectrum by increasing the width of horizontal and vertical

arms of inverted U-slot without affecting much the primary band. Tuning of triple bands

does not affect the nature of broadside radiation characteristics. The proposed antennas

are simple in their geometry and are fabricated using low cost glass epoxy substrate

material. The CTIUSRMSA may find applications in wireless local area

network(WLAN).

ACKNOWLEDGMENTS

The authors would like to thank the authorities of Dept. of Science. &

Technology. (DST), Govt. of India, New Delhi, for sanctioning the Vector Network

Analyzer under the FIST project to the Department of Applied Electronics, Gulbarga

University, Gulbarga.

REFRENCES

1. Kin-Lu Wong, Compact and Broad band microstrip Antennas, A Wiley-Inter

Science Publication, John Wiley & Sons. Inc.

2. Garg Ramesh , Bhatia Prakesh, Bahl Inder and Boon Apisakittir (2001),

Microstrip Antennas Design Hand Book, Artech House Inc.

3. Behera. S and Vinoy. K. J, “Microstrip square ring antenna for dual band

operation,” Progress In Electromagnetics Research, PIER 93, 41–56, 2009.

4. Roy . J. S, Chattoraj, and N. Swain, “ short circuited microstrip antenna for

multi-band wireless communications,” Microwave and Optical Technology

Letters, Vol .48, 2372-2375, 2006.

5. Sadat, S , M. Fardis F. Geran, and G. Dadashzadeh,” A compact microstrip

square-ring slot antenna for UWB applications,” Progress In Electromagnetic

Research PIER 67, 173-179, 2007.

6. Shams. K. M Z , M. Ali, and H. S. Hwang, “A planar inductively coupled

bow-tie slot antenna for WLAN application,” Journal of Electromagnetic

Waves and Applications, Vol.20, 86-871, 2006.

7. Kuo, J. S and K. L. Wong, “A compact microstrip antenna with

meandered slots in the ground plane,” Microwave and Optical Technology

Letters, Vol. 29, 95-97, April 2001.

8. Sharma A. and G. Singh, “Design of single pin shorted Three – dielectric

layered substrates rectangular patch microstrip antenna for communication

system,” Progress In Electromagnetic Research PIER 2. 157 – 165, 2008.

9. Ang. B. K and B.K Chung,“A wideband microstrip patch antenna for 5-6 GHz

Wireless communication,” Progress In Electromagnetic Research PIER 75,

397-407, 2007.



5

10. Eldek .A. A, A .Z. Elsherbeni and C.E. Smith, “Characteristics of bow-tie slot

antenna with tapered tuning stubs for wideband operation,” Progress In

Electromagnetic Research PIER 49, 53 – 69, 2004.

11. Waterhouse R.B, “Broadband stacked shorted patch” Electronic Letters, Vol.35,

98-100, Jan. 1999.

12. Ge,Y, K. P. Esselle and T. S. Bird, “A broadband E-shaped patch antenna

with a microstrip compatible feed,” Microwave and Optical Technology

Letters, Vol .42, No. 2, July 2004.

13. Bahl, I. J and P. Bhartia, Microstrip Antennas, Artech house, New Delhi, 1980.

Table 1 Design Parameters of CRMSA and CTIUSRMSA

Antenna

Parameters

Dimensions

in cm

Antenna

Parameters

Dimensions

in cm

W 2.66 Lh λ0/85

Wf 0.32 Lv λ0/42

Wt 0.06 Xd 0.8

L 2.04 Yd 0.2

Lf 2.18 A 5

Lt 1.09 B 8



6

Figure 1 Top view geometry of CRMSA

Figure 2 Top view geometry of CTIUSRMSA



7

Figure 3(a) 3d view of CRMSA

Figure 3(b) 3D view of CTIUSRMSA

Figure 4 Variation of return loss versus frequency of CRMSA



8

Figure 5 Variation of return loss versus frequency of CTIUSRMSA when Uw = 0.2 cm

Figure 6 Variation of return loss versus frequency of CTIUSRMSA when Uw = 0.3 cm

Figure 7 Radiation pattern of CRMSA measured at 3.39 GHz



9

Figure 8 Radiation pattern of CTIUSRMSA when Uw = 0.2 cm measured at 4.74 GHz

Figure 9 Radiation pattern of CTIUSRMSA when Uw = 0.3 cm measured at 4.82GHz

Documents

Corner truncated inverted u slot triple band tunable rectangular microstrip antenna for wlan applications