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					International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING &
ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 01-04 © IAEME
                                TECHNOLOGY (IJEET)

ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
                                                                                IJEET
Volume 5, Issue 3, March (2014), pp. 01-04
© IAEME: www.iaeme.com/ijeet.asp                                              ©IAEME
Journal Impact Factor (2014): 6.8310 (Calculated by GISI)
www.jifactor.com




EFFECT OF FEEDLINE ON RESONANT MODE OF SQUARE MICROSTRIP
                         ANTENNA

                                        Dr. Nagraj Kulkarni
                                  Department of Electronics,
                      Government College, Gulbarga-585105,Karkataka, India




ABSTRACT

       In this paper the effect of microstripline feed on resonant mode of the square microstrip
antenna is studied. The antenna is constructed with its structure of dimension 8 X 5 X 0.16 cm3. The
microstripline feed arrangement along with quarter wave transformer is used to excite the proposed
antenna. The antennas exhibits a broadside and linear radiation characteristics. The results are
presented and discussed. This antenna may find its applications in S-band communication system.

Key words: Square Microstrip Antenna, Feedline, Resonance.

 1. INTRODUCTION

        In the recent years the microstrip antennas (MSAs) have gained popular position in
communication system because of their inherent attractive features like light weight, planar in
structure, ruggedness, different geometries and shapes, easy installation, low fabrication cost [1] etc.
In this paper the effect of microstrip feedline on the resonant modes of the antenna is presented. This
study may be useful for switching of bands applications. This kind of study is found to be rare in the
literature.

2. DESIGNING

        The low cost glass epoxy substrate material of area A × B, thickness h = 0.16 cm and
dielectric constant εr = 4.2 is used to fabricate the proposed antenna. The artwork of the antenna is
sketched using computer software Auto CAD to achieve better accuracy. Photolithography process is
used to fabricate the antenna.


                                                   1
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 01-04 © IAEME




                              Figure 1: Top view geometry SMSA-1

        Figure 1 shows the top view geometry of square microstrip antenna (SMSA-1), which is
designed for the resonant frequency of 3.5 GHz using the equations available in the literature for the
design of square microstrip antenna [2]. The SMSA-1 consists of a square radiating patch of equal
length (L) and width (W). The Lf and Wf are the length and width of the microstripline used to
excite the patch. The SMSA-1 has Lf equal to λ0/4. A semi miniature-A (SMA) connector of 50
impedance is used at the tip of the microstripline to feed the microwave power. A quarter wave
transformer of length Lt and width Wt is used to match the impedances between lower radiating edge
of the patch and microstripline feed.




                             Figure 2: The top view geometry SMSA-2

       Figure 2 shows the geometry of modified square microstrip antenna (SMSA-2). The SMSA-2
has the entire dimension same as that of SMSA-1, the modification is made in microstrip feedline
length of SMSA-2, which is reduced to λ0/6. Table 1 gives the design parameters of SMSA and
SMSA-2.

                        Table 1: Design parameters of SMSA and DOSMSA ( cm )
          Antenna       L      W       Lf    L ’f     Wf    Lt     Wt    A               B
          SMSA-1       2.04   2.04    2.18    -      0.32  1.09   0.06   5               8
          SMSA-2       2.04   2.04      -   1.416 0.32     1.09   0.06   5               8

                                                  2
                                                               (IJEET),
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 01-04 © IAEME

3. EXPERIMENTAL RESULTS

                                                                    ),
        The Agilent Technologies make (Agilent N5230A: A.06.04.32), Vector Network Analyzer
is used to measure the experimental return loss of SMSA and SMSA-2.




            Figure 3: Variation of return loss versus frequency of SMSA-1 and SMSA
                                   retur                                      SMSA-2

        Figure 3 shows the variation of return loss versus frequency of SMSA-1 and SMSA-2. From
                                               lo                                  nd
                                 SMSA
this figure it is seen that, the SMSA-1 resonates at 3.43 GHz of frequency which is nearer to the
                                        SMSA-2
designed frequency of 3.5 GHz, while SMSA resonates at 2.64 GHz. This shift of resonant mode
toward lower frequency side is due to the reduction in length of the microstrip feedline. This shift of
resonant mode helps in switching action of band applications. The bandwidth BW1 and BW2 of
SMSA-1 and SMSA-2 are 3.61% and 2.94% respectively.




                    Figure 4: Radiation pattern of SMSA measured at 3.43 GHz




                   Figure 5: Radiation pattern of SMSA-2 measured at 2.20 GHz

       Fig 4 and 5 show the radiation patterns of SMSA-1 and SMSA-2 respectively. It can be noted
                                                                                cross polar
from these figures that, the patterns are broadside and linearly polarized. The cross-polar power level
                                         co polar
is much lower when compared to the co-polar power level indicates the broad nature of radiation.
The gain of SMSA-1 and SMSA-2 is calculated using the absolute gain method given by the relation,



                                                  3
                                                               (IJEET),
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 01-04 © IAEME

                                    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’ is measured independently. The gain
                                                                         SMSA-2
measured for SMSA-1 is found to be 0.8 dB maximum and the peak gain of SMSA is found to be
0.92 dB.

4. CONCLUSION

                                                                            SMSA-2
        From this detailed study, it is concluded that the resonant mode of SMSA shifts towards
lower frequency side when length of the microstrip feedline is reduced keeping all other dimensions
same as that of SMSA-1. The radiation characteristics of SMSA-1 and SMSA-2 are broadside and
                                              a
linearly polarized. This antenna may find its applications in S-band communication system.

REFERENCES

                                                                 MA:
 1. G. Kumar and K. P. Ray, Broadband Microstrip Antennas, MA: Artech House, Norwood,
    (2003).
                            :
 2. Antennas: John D Kraus: MacGraw Hill Pub Co.Ltd.
                                            Mulgi                  Symmetric
 3. Kishan Singh and Shivasharanappa N Mulgi, “Complementary-Symmetric Corner Truncated
                                                                     ”,
    Compact Square Microstrip Antenna for Wide Band Operation”, International Journal of
    Electronics and Communication Engineering & Technology (IJECET), Volume 1, Issue 1,
                      ,             0976
    2010, pp. 99 - 106, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.


BIO-DATA


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




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