International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
ISSN 2319 - 4847
A Switched Multibeam Antenna Array using
Butler Matrix Feed Network
Ms. Priti S.GundPujari1, Prof. S.A.Annadate2
1
2
M.E.(EC) Department of Electronics & Telecommunication Engineering
Jawaharlal Nehru Engineering College, Aurangabad, India
Associate Professor in Department of Electronics & Telecommunication Engineering
Jawaharlal Nehru Engineering College, Aurangabad, India
Abstract
In this paper, Smart Antenna system of 4- element microstrip linear array antenna with Butler matrix beam forming network is
designed, analyzed and implemented using microstrip technology in completely planar structure. The performance of this smart
antenna system is analyzed and the beam forming features are monitored as function of geometrical antenna and Butler matrix
parameters at frequency 2.4 GHz.
Keywords: Beam forming network, Butler Matrix, Microstrip Antenna, Switched Beam
1. INTRODUCTION
Smart antennas have been characterized as one of the most prominent devices in wireless communication. Electronic
scanning of antennas is used in a variety of applications and can be accomplished using beam forming networks (BFNs).
Butler Matrix [1] is an NN passive microwave network that consists of ‘N’ input and ‘N’ output independent ports. It is
used as a feed to an array of antennas to generate a set of ‘N’ orthogonal beams, which scans the array generated beam.
Thus a Butler Matrix is considered to be a significant component of a (BFN) beamforming network [2] and widely used in
Smart antennas [6]. The matrix is easy to be implemented using micro strip with an advantage of ease in fabrication,
compactness and low cost.
A 44 Butler matrix is designed to form orthogonal beams and the switching is obtained at the end of the array of 4 patch
antennas. Basically a 44 matrix consists of four 90 degree hybrids, two 0 dB cross-overs and two 45 degree phase
shifters. The end four antenna elements are designed for optimum feed position, along with the element spacing, using
Method of Moment (MoM), to get a proper VSWR value, maintaining gain characteristics.
2. DESIGN AND ANALYSIS
A simple 44 Butler matrix is show
For simulation, though the data was considered for a range of 2 to 3 GHz frequency, but the individual component
designs were done at 2.4 GHz. The final design was done on FR4 board, with substrate height of 1.6mm, r = 4.4, tan =
0.0027, with all terminations offered at 50 . The 90 degree hybrid pull out at the port side thickness is 1.141 mm.
Along the major width-side arm (thickness 1.932mm), the tapering done at 45 degree gave a proper isolation at port 2.
Figure.1. Block diagram of 4 × 4 Butler matrix array
2.1 Zero dB cross-over coupler
Crossover coupler shown in Fig 2 was first designed by cascading two hybrids. But the branch increased thickness did
not give proper isolation at port 4; as well as zero degree phase was not obtained at port 3. All its arm thickness was then
redesigned at 1.414 mm, again with tapering at 45 degree along the port arm side.
Volume 2, Issue 10, October 2013
Page 33
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
ISSN 2319 - 4847
Figure 2 Zero dB cross-over coupler
Figure 3 Phase shifter
For the phase shifter [7] shown in fig 3, the phase shift is given by,  = (2 / g) l, where the wavelength is given by, o/
sqrt (eff).
Finally the single patch antenna [9] was designed, with an inset feed at a length of 33.33 % of the total length.
However when the array of four patches was placed together, it is observed that maximum radiated field obtained at normal to the structure surface. Hence to
take care of this new problem of the fringing fields along the width, the patch length is extended on both sides by additional length given by,
Leff = L + 2L
(1)
where,
L = 0.412h (reff + 0.3)(W/h + 0.264)
----------------------------------(reff - 0.258)(W/h + 0.8)
Leff = c/ 2fo sqrt (reff).
Figure 4 Quadrature (90○) Hybrid
Figure. 5 Patch Antenna
Quadrature hybrids are 3dB directional couplers with 90○ phase difference in in the outputs of the through and coupled
arms. This type of hybrid is often made in Microstrip or stripline and is also known as branch-line hybrid. With all ports
matched, power entering port 1 is evenly divided between ports 2 and 3, with a 90○ phase shift between these outputs. No
power is coupled to ports 4.
The Butler matrix connected to the patch array [11] shown in Fig 1. The VSWR graph is shown in Fig 5 is at a value of
1.67 at 2.4 GHz.
Figure.6. Current distribution of Microstrip Patch Antenna
Volume 2, Issue 10, October 2013
Figure. 7 VSWR of Patch Antenna
Page 34
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
ISSN 2319 - 4847
The current distribution on the patch surface is shown in Fig.6. The lowest current densities are located at the
patch corners and the strongest currents (in red) are around the end of the slot and slits. Therefore, the
surface current path is effectively lengthened by the slot and slits resulting in lower resonance frequency.
However the element spacing was kept constant throughout the four patch antennas [12].
Figure. 8.HFSS Butler Matrix Design
A 4 × 4 BM consists of four couplers, four phase shifters and two crossovers. The arrangement is shown in Fig.
8. The first four ports (Ports 1, 2, 3 and 4) are input ports, and the remaining ports are outputs. Consider
an array fed by the BM, with consecutive antenna elements separated by d. Four square patches, studied in
earlier section. by design of single patch, laid on the FR4 substrate are separated by distance d ≈43mm i.e.
λ/2 distance between centers of patch.
Figure.9. Measured Voltage standing wave ratio (VSWR)of Butler Matrix
Fig. 9. Shows measured VSWR at port 1, with marker m1 , m2 ,m3, m4,m5 and m6. Fig.6.48 Shows
Impedance using smithchart for port 1 ,with marker m1 , m2 ,m3, m4,m5 and m6.
Figure 10. Measured Smith chart results for Impedance
The simulated total gain in 3D pattern is shown figure.11. which is 5.112 dBi along the bore-sight direction.
The radiation patterns of gain and directivity have a very similar shape. This is due to the loss on the
substrate. The highest gain shown along the z-direction with red colour at the peak.
Volume 2, Issue 10, October 2013
Page 35
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
ISSN 2319 - 4847
Figure.11. Gain of
Patch Antenna
Figure.12. radiation pattern when all four input ports are excited
Figure 12 shows simulated radition pattern in the form of gain when all ports are excited by the antenna
array.The radiation pattern by taken keeping φ = 900 at resonant frquency 2.4Ghz.
Figure. 13. Four beam switching
The total beam steering of the four individual beams is shown in Fig 7. It is observed that the beam has switched at
18degree (shown in different colors). However during the appearance of the forth beam, there is a side lobe formation,
due to which its gain has reduced
The beam positions as per the progressive phase shifting at the feed end could be realized. Due to paper size constraints,
the figures cannot be discussed at length.
Figure.14. Smith Chart
Figure 15 Shows Simulated Return Loss of Intgrated Patch antenna with Butler Matrix for port 1 and port 2,with
marker m1 nad m2 showing the RL below −15dB.In the same manner Figure 16 shows Return Loss (RL) for port
3 and port 4 with marker m1 and m2.
The design consists of a uniformly spaced linear array of four square patch antenna, and a feed network consisting
of a 4 × 4.BM. A basic requirement for a good function of the circuit is to avoid coupling loss. It also has very
good Isolation between input ports.
Volume 2, Issue 10, October 2013
Page 36
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
ISSN 2319 - 4847
Figure.15. Simulated Return loss at port 1 and 2 of Anenna array fed by BM
This proves that the logical flow of the design process is correct. Return loss of all ports is greater than −10dB
which is the achievement for this design. The butler matrix without patch shows simulated results at 2.2 GHz
due to small mismatch in interconnection of butler elements. But in case of integrated patch with butler it gives
Figure.16. Simulated Return loss at port 3 and 4 of Anenna array fed by BM
3. CONCLUSION
A 4×4 Butler matrix has been designed for the excitation of microstrip array antenna to steer the beams in different
desired directions. Most important thing about the simulated structure is that it can be easily implemented using simple
material for construction with minimum cost. The planar design, simulation and implementation of a smart antenna
system using microstrip antenna array with Butler Matrix beamforming network for wireless applications in the
ISM-band at 2.45 GHz is done.The Butler matrix is also fabricated together with the patch antenna array to study
about the radiation patterns over the frequency band of 2.45 GHz.
The Beamforming/feeder network is designed using a 4 × 4
Butler matrix, and realized using 4 quadrature
hybrids, 2 phase shifters and 2 crossover circuits. To verify modeling and simulation procedures, the main basic
elements such as patch antenna, directional coupler, and cross coupler are fabricated and measured. Good
agreement between measurements and simulations is obtained which validates the design.
References
[1] Diu Chang, Shin Hue Jou, “The study of Butler Matrix BFN for four beams antenna system”, IEEE A & P Society
Symposium, June 22-27,2003, pp 176-179.
[2] Phan N. T., Gye Lee,”Microstrip antenna array with BFN for WLAN”, A & P Society Symposium, July 3-8,2005, pp
299-302.
[3] Tayeb A. Denidni, T. E. Libar, “Wideband four port Butler Matrix for switched multibeam antenna array”, 14th IEEE
International Symposium, September 7, 2003, pp 2461-2464.
[4] T. M. Macnamara,” Simplified design procedures for Butler Matrix incorporation 90 degree hybrids”, IEEE
Proceedings, Microwaves, A & P, 1987, Vol 134, pp 50-54.
[5] F. Cladwell, Kenney J. S., “Design and implementation of a switched beam Smart antenna”, Radio & Wireless
Conference, August 11-14, 2002, pp55-58
[6] S. H. Chu, H.P. Lin, “Performance enhancement by using switched beam smart antenna”, Wireless Communications
and Applied Computational EM Conference, April 3-7,2005, pp 1001-1005.
Volume 2, Issue 10, October 2013
Page 37
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
ISSN 2319 - 4847
[7] T. K. Kwang, Gary, “44 Butler Matrix beam-forming network using novel reduced size branch line coupler”, IEEE
European Microwave Conference, October 31,2001, pp1-4.
[8] S. R. Ahmad, F. C. Seman, “Four port Butler Matrix for switched multibeam antenna array”, IEEE Asia Pacific
Conference on Applied Eletromagnetics, December 20-21,2005, pp 69-73.
[9] Esin Chang, S. A. Long, “ An experimental investigation of electrically thick rectangular micro strip antenna”, IEEE
Transaction A & P, 1986, Vol 34, No 6, pp 767.
[10] J. P. Berenger,” A perfectly matched layer for the absorption of EM waves”, Journal Computational Physics, 1994,
Vol 114, pp1852.
[11] R. B. Waterhouse, s. D. Targonski,” Design and performance of small printed antennas”, IEEE Transaction on A &
P, November 1998, Vol 46, Issue 11, pp 1629-1633.
[12] M. Sanad, “ Micro strip antenna on very small ground plane for portable Communication systems”, A& P Society
Symposium, 1994, Vol 12, pp 810-813.
[13] I. J. Bahl, P. Bhartia, “Micro strip Antenna”, Artech House, 1980.
[14] C. A. Balanis, “Antenna Theory, analysis and Design”, John Wiley & Sons, 1982.
[15] D. M. Pozar, “Wide Band aperture coupled stacked patch antenna using thick substrates”, Electronic Letters, 1996,
Vol 32, No 21, pp 1941-1942.
Volume 2, Issue 10, October 2013
Page 38