Smart Antenna System using 4x4 Butler Matrix switched beam network for 2.4 GHz ISM band Prof. F I Shaikh 1, Mr. Sanjay Bansidhar Akhade 2 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 45 0 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 45 0 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
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 90 0 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 90 0 phase difference between each other. The fig shows the schematics of the Quadrature coupler. In fig.2 Z s and Z p 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 Z s = Z 0 / 2, Z p = Z 0 where Z 0 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 90 0 2.2 The crossover coupler Figure 2 Qudreture 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
2.3 45 0 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. 45 0 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
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
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