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									         INTERNATIONAL Communication OF ELECTRONICS AND
International Journal of Electronics and JOURNALEngineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 98-102 © IAEME
 COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)                                                      IJECET
Volume 5, Issue 2, February (2014), pp. 98-102
© IAEME: www.iaeme.com/ijecet.asp                                            ©IAEME
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   TWO ELEMENT U - SLOT LOADED CIRCULAR MICROSTRIP ARRAY
             ANTENNA FOR WLAN APPLICATIONS

                                   Dr. Nagraj K. Kulkarni
                      Government College, Gulbarga-585105, Karkataka, India



ABSTRACT

       This paper presents the two element U- slot loaded circular microstrip array antenna for dual
band operation. The antenna operates between 2.6 to 7.00 GHz. The antenna has been fabricated
with a volume of 9 X 5 X 0.16 cm3. The maximum bandwidth of 44.90% is achieved. With a peak
gain of 5.24 dB is obtained in primary band. The antenna exhibits a broadside and linear radiation
characteristics. The results are presented and discussed. This antenna may find its applications in
WLAN communication system.

 Keywords: Two Element, Circular, Microstrip Antenna, Size Reduction.

1. INTRODUCTION

         In today’s era microstrip antennas (MSAs) have become the attractive candidate for the
antenna designers because of their inherent features such as light weight, low profile, compatibility
with MMICs [1] etc. The patch antennas are receiving increasing interest in modern communication
systems such as WLAN, WiMAX, HIPERLAN/2 etc, because of their many advantages over
traditional microwave antennas in terms of achieving dual, triple and multiple bands which are
realized by using different techniques such as, cutting slots of different geometries like rectangular,
L- shape, E-shape, circular shape, square shape [2-7] etc. In many applications, the wide bandwidth
and gain are the essential needs to use the antenna for specific applications. During past years, many
efforts have been put forth to realize bandwidth widening techniques of microstrip antennas, which
include the use of impedance matching, multiple resonators and a thick substrate [8, 9] etc. But, the
two element array antenna having a U shaped slots on the circular radiating patch and plus shaped
slots on the ground plane is used for enhancing the bandwidth and gain. This kind of study is found
to be rare in the literature. The slot loading technique provides the freedom to design the required
slot irrespective of their size or shape and can be suitably loaded at the desired place on the geometry
of the antenna for broadening the bandwidth of the antenna [9]. Also, the array technique, gives the


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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 98-102 © IAEME

flexibility to design the required feed line between the array elements to energize, which helps in
enhancing the gain of the antenna [10].

2. DESIGN AND EXPERIMENTAL RESULTS

      The antenna is fabricated using low-cost glass epoxy substrate material of thickness h = 1.6
mm and dielectric constant εr = 4.2. Artwork of the antenna is sketched using computer software
Auto-CAD 2006 to achieve better accuracy. The antenna is etched using photolithography process.




                             Fig. 1: Top view Geometry of TUCMAA

        Figure 1 shows the top view geometry of the two element, U-slot loaded circular microstrip
array antenna(TUCMAA). The antenna has two circular patches of radius R are designed for the
resonant frequency of 3.5 GHz, using the basic equations available in the literature. The U shaped
slot of horizontal and vertical arm lengths h and v are placed on the two circular patches.




                           Fig. 2: Bottom view Geometry of TUCMAA

        Fig. 2 shows the bottom view geometry of TUCMAA. The two plus shaped slots which are D
mm apart and each having a width 2 mm are incorporated on the ground plane such that the mid-
point of these slots lie exactly below the center of the each radiating patch. The L and H are the
horizontal and vertical arm lengths of the plus shaped slots. The dimensions D, R h, v, L and H are
taken in terms of λ0, where λ0 is the free space wavelength in millimeter corresponding to the
designed frequency of 3.5 GHz. The parallel feed arrangement is used in the present study, because
it has the advantage over series fed arrangement, that is, its wideband performance. The feed
arrangement shown in this figure is a contact feed and has the advantage that it can be etched
simultaneously along with the antenna elements. The microstripline feed arrangement is designed
using the relations available in the literature [12]. A 50 feed line of length L50 and width W50 is
connected to 100 line of length L100 and width W100 to form a two way power divider. A quarter
wave transformer of length Ltr and width Wtr is connected between 100 feed line and midpoint of
the radiating elements to establish perfect impedance matching. A 50 semi miniature–A connector

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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 98-102 © IAEME

is used at the tip of the 50   feed line. The various parameters of the proposed antenna are enlisted
in Table 1.

                             Table 1: Various parameters of TUCMAA
                        Antenna     Dimensions     Antenna     Dimensions
                       Parameters     in (mm)     Parameters    in (mm)
                            R            26.6          v          λ0/10
                           L50          21.84         WTr         0.15
                          W50            3.2           D         λ0/1.96
                          L100          21.88         ASub         90
                          W100           0.74         BSub         50
                           LTr          10.92          H         λ0/9.96
                            h           λ0/10          L         λ0/8.32


        The Vector Network Analyzer (Germany make, Rohde and Schwarz, ZVK model 1127.8651)
is used to measure experimental return loss of TUCMAA. The experimental impedance bandwidth
over return loss less than -10 dB is calculated using the formula,

                                                       f 2− f1
                                  Bandwidth (%) =              × 100 %
                                                          fC

       where, f2 and f1 are the upper and lower cut off frequencies of the resonating bands
when their return loss reaches -10 dB and fC is a centre frequency of f2 and f1.




                    Fig. 3: Variation of return loss versus frequency of TUCMAA

        Figure 3 shows the return loss versus frequency of TUCMAA. It is clear from this figure that,
the antenna resonates for dual bands with their respective bandwidths are BW1= 6.45% (3.0-3.2
GHz) and BW2= 44.90 % (4.37-6.9 GHz). The resonating bands BW1 and BW2 are due to the
fundamental resonance of the patches and the currents along the edges of the U- slots. This increase
in the bandwidth is due to the combined effect of the plus shaped slots present on the ground plane
that help in widening the bandwidth of the antenna. Also, these slots in addition cause the first band
BW1 to resonate at 3.1 GHz, which is less than the designed frequency i.e. 3.5 GHz, shows the
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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 98-102 © IAEME

virtual size reduction of about 6.01 %. Furthermore, the bandwidth of the second band BW2 is
enhanced to a maximum of 44.90%.




                               Fig. 4: Radiation pattern of TUCMAA

        The co-polar and cross-polar radiation pattern of TUCMAA measured in its operating bands
is as shown in Figures 4. From this figure, it can be observed that, the pattern is broadside and
linearly polarized, the cross polar level is maximum -15 dB down when compared to its co–polar
power level indicates the directional nature of radiation.
        The gain of TUCMAA is calculated using the absolute gain method given by the relation,

                                      Pr                      λ0 
                      (G )dB = 10 log     - (Gt )dB - 20 log        dB      (2)
                                      Pt                      4π R 

       where, Gt is the gain of the pyramidal horn antenna and R is the distance between the
transmitting antenna and the antenna under test (AUT). The power received by AUT, ‘Pr’ and the
power transmitted by standard pyramidal horn antenna ‘Pt’ are measured independently. The
TUCMAA gives a peak gain of about 5.24 dB in its operating band.

3. CONCLUSION

       From the detailed study, it is found that, the TUCMAA can be made to operate between 2.6
to 7.00 GHz by loading two U- slots on the radiating patch and plus shaped slots on the ground
plane. The maximum bandwidth of 44.90% is achieved by this antenna. The TUCMAA gives a peak
gain of 5.24 dB with a virtual size reduction of 6.01 % with broadside radiation characteristics. The
proposed antenna is simple in its geometry and is fabricated using low cost glass epoxy substrate
material. This antenna may find applications in this antenna may find its applications in WLAN
communication system.

ACKNOWLEDGEMENTS

     The authors would like to thank the Dept. of Science & Technology (DST), Govt. of India,
New Delhi, for sanctioning Vector Network Analyzer to this Department under FIST project.

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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 98-102 © IAEME

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BIO-DATA

                Dr. Nagraj K. Kulkarni received his M.Sc, M.Phil and Ph. D degree in Applied
                Electronics from Gulbarga University Gulbarga in the year 1995, 1996 and 2014
                                                  Assistant
                respectively. He is working as an Assistant professor and Head, in the Department of
                                         Degree
                Electronics Government Degree College Gulbarga. He is an active researcher in the
                field of Microwave Electronics.




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