International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 3, March 2015
ISSN 2319 - 4847
Smart Antenna System using 4x4 Butler Matrix
switched beam network for 2.4 GHz ISM band
Prof. F I Shaikh1, Mr. Sanjay Bansidhar Akhade2
1
Electronics and Telecommunication department
J. N. E. C. Aurangabad
2
Electronic and Telecommunication department
Shri Tuljabhavani college of engg. Tuljapur
ABSTRACT
In recent years the researches on the beam forming networks is becoming very important. Recent trends in telecommunication
have shown the vital importance of the beam forming network in modern telecommunication system. In this paper, study and
analysis of one of the beam forming network (i.e. Butler matrix) is presented.Here 4x4 butler matrix beam forming network is
studied. Such a beam forming network can be used for multibeam base stations systems in mobile communication applications.
A switched beam array system can be implemented using butler matrix for telecommunication networks. Such a network is
capable of production of 4 orthogonal uniform beams when feed with electromagnetic signals. In 4x4 butler matrix 4 input
ports are used for the input signal connections. Four output ports can be connected to an array of four micro strip slot
antennas. Performance of the system can be analyzed and studied with the help of results beam forming patterns are also
studied. System can be designed and optimized on the basics of results and simulation done.
Keywords: butler matrix, beamformer, multibeam, microstrip antenna.
1. INTRODUCTION
The presence of co channel interferenceand fading in the communication system can be observed due to the multiple
users and multipath signal propagation. This phenomenon can cause inefficient system with degraded quality of
wireless communication. This degradation of quality of wireless communication can be avoided by using the concept of
pace discriminations of the multiple signals tries to propagate through same medium. This can be done with the help of
beam forming networks with an antenna array. Beam forming networks have the ability to form a beam of signals in
the direction of desired user location. Whereas other undesired locations will not have any beam of very small size
beam. That is only desired user can receive the signal and co-channel interference and fading can be avoided. Butler
matrix is one of the well-known beam forming network can be used in switched beam smart antenna system. Butler
matrix has N input and Noutput ports witch creates sophisticated NxN design. Array of N antennas can be connected to
the system to form a N beam forming network. This design if capable of forming N orthogonal uniform beams in N
different directions. That helps to avoid co-channel interference in communication. Butler matrix is composed of three
main components as 3dB quadrature coupler, cross over coupler and 450 phase shifter. The design and implementation
of the system is as studied follows.
2. BUTLER MATRIX
A Butler beam forming matrix for a four element array is as show in fig.1. By tracing the signal from the four input
ports to the array elements, here 4x4 butler matrix is considered for the paper. Here for construction of Butler matrix
four number of quadreture coupler, two number of cross over coupler and two number of 450 phase shifter. Brief design
and analysis is disused in next part of this paper.
Figure 1 Block digram of 4X4 butler matrix
The system should produce four separate beams ideally with different phase angles as show in table 1.
Volume 4, Issue 3, March 2015
Page 278
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 3, March 2015
ISSN 2319 - 4847
Table 1 ideal phase shift results between different ports of the butler matrix
2.1 Quadrature coupler or hybrid coupler
Hybrid coupler or 3dB quadrature coupler has ability to generate 900 out of phase signal at output ports. It consists of
main line that is coupled with a secondary line by two quarter wavelength long section spaced one quarter wavelength
apart, thus creating a square approximately one wavelength in circumference.When a signal is introduced at port-1, the
signals at the two output arms (2,3) are equal in amplitude but have a 900phase difference between each other. The fig
shows the schematics of the Quadrature coupler. In fig.2 Zs and Zp denote the characteristic impedance of the series and
shunt lines respectively. Similarly λgs and λgp denote the guided wavelengths of the series and shunt lines. S matrix
describing S parameter of the quadrature coupler is as below.
And Zs = Z0/√2 , Zp= Z0where Z0 is the characteristic impedance of the feeding system. From above equation it is also
clear that outputs of port 2 and 3 are equal in magnitude but are have phase different of 900
Figure 2 Qudreture coupler
2.2 The crossover coupler
Fig. shows the typical crossover coupler .in butler matrix the signal paths have to be physically crosses one other while
maintain high degree of isolation in remaining lines. This can be archive in micro strip technique using cross over
couplers. Crossover couplers are a symmetric four port network. Where tow ports are input ports and two ports are
output ports .in perfectly designed cross over coupler all adjacent ports of the coupler should be perfectly isolated from
each other. That is port 1 is feed with signal the output at ports 2 and 4 should be zero, similarly when port 4 is feed
with signal ports 1 and 3 should be zero.
S matrix of the cross over coupler describing s parameters is as follows
And Zs=Zp=Z0 where Zs and Zp are the characteristic impedance of the series and shunt arms
Figure 3 Cross over coupler
Volume 4, Issue 3, March 2015
Page 279
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 3, March 2015
ISSN 2319 - 4847
2.3 450 Phase shifter
Phase shifter is use to provide phase shift to the signal. Here phase shifter is provided 90degree phase shift. We know
that whenever a transmission line of length l is faded with signal, it introduces a phase shift in signal given by
following equation.
Where g is the guide wavelength in the substrate so
Figure 4. 450 Phase shifter
2.4 Microstrip patch antenna
Microstrip patch antenna design typically is of a rectangular (or of any shape, but rectangular shape is preferred as it
can be easy in fabrication and analysis) patch of metal ( like copper ) on a dielectric ground plane like FR4 material .
the thickness of the metallic strip patch is generally taken t << λ . And height of ground plan is also given as h << λ.
Fig 5 shows the typical patch design.
Figure 5 The designed micro stripe patch antenna
Figure. 6. VSWR and Directivity of micro stripe patch antenna
3. IMPLEMENTATION OF 4X4 BUTLER MATRIX WITH MICRO STRIPE PATCH ANTENNA ARRAY
The figure 7. shows the 4x4 butler matrix microstrip patch smart antenna system. Here patch antennas are connected to
the output ports of the butler matrix. Patch antennas are the beam forming devices and butler matrix is a beam forming
network. So the characteristics of 4x4 butler matrix with 4 microstrip patch smart antenna system are analyzed with
HFSS 13. Fig 8, 9, and 10 shows radiation pattern, returning losses, and VSWR respectively when port 1 is exited .
Volume 4, Issue 3, March 2015
Page 280
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 3, March 2015
ISSN 2319 - 4847
Figure 7. 4X4 butler matrix implemented
Figure 8 Measured beam patterns at 2.45 GHz when a. port 1R is fed, b. port 2L is fed, c. port 2R is fed, and d. port 1L
is fed.
Figure 9 returning losses when port 1 is exited
Volume 4, Issue 3, March 2015
Page 281
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 3, March 2015
ISSN 2319 - 4847
Figure 10 VSWR when port 1 is exited
4. CONCLUSION
All elements of the butler matrix like microstrip patch antenna, quadreture couple, crossover coupler and 450 phase
shifter are designed and analyzed using HFSS vs 13. Also simulated resulted are studied. Finally on the analysis it is
observed that by using butler matrix, on excitation of each input port all output ports will give same signal at each
output with different phase angle as shown in table
Table 2 actual phase shift results between different ports of the butler matrix
And finally butler matrix beam forming smart antenna is studied and analyzed with the help of above results achived
using HFSS 13. Also smart antenna parameters like efficiency, directivity and maximum scan angel are improved. But
actual size of the antenna is minimized.
REFERENCES
[1] A. M. El-Tager and M. A. Eleiwa, Design and Implementation of a Smart Antenna Using Butler Matrix for ISMband, Progress In Electromagnetics Research Symposium, Beijing, China, March 23{27, 2009
[2] Jesse Butler, Ralph Lowe, “Beam-Forming Matrix Simplifies Design of Electronically Scanned Antennas”,
Electronic Design, volume 9, pp. 170-173, April 12, 1961.
[3] Ching-Wen Tang, Ming-Guang Chen, “Synthesizing Microstrip Branch-Line Couplers with Predetermined
Compact Size and Bandwidth,” in IEEE Transactions on Microwave Theory and Techniques, VOL.55 ,NO.9,
SEPTEMBER2007.
[4] M. F. Abd Kadir, M. R. Che Rose, M. S. R. Mohd Shah, D. Misman, M.K. Suaidi, M. Z. A. Abd Aziz, “4x4 Butler
Matrix Design by Using Circular Ben”Asia pacific conference on applied electromagnetic proceedings, December,
2007.
[5] Constantine A. Balanis, Antenna Theory, analysis and design, Harper and ROW publishers, New York, 1981
[6] David M. Pozar, Microwave Engineering, 2nd Edition, John Wiely
[7] Hayashi, H., D. A. Hitko, and C. G. Sodini, \Four-element planar Butler matrix using half-wavelength open stubs,"
IEEE Microwave and Wireless Component Letters, Vol. 12, No. 3,73,75, March 2002.
AUTHORS
Prof. F. I. Shaikh Electronics and Telecommunication department J. N. E. C. Aurangabad
Mr. Sanjay Bansidhar Akhade Electronic and Telecommunication department Shri Tuljabhavani
college of engg. Tuljapur
Volume 4, Issue 3, March 2015
Page 282