yesThis paper presented a planar printed multiple-input-multiple-output (MIMO) antenna with a dimension of 100 x 45 mm2. It composed of two crescent shaped radiators placed symmetrically with respect to the ground plane. Neutralization line applied to suppress mutual coupling. The proposed antenna examined both theoretically and experimentally, which achieves an impedance bandwidth of 18.67% (over 2.04-2.46 GHz) with a reflection coefficient < -10 dB and mutual coupling minimization of < -20 dB. An evaluation of MIMO antennas is presented, with analysis of correlation coefficient, total active reflection coefficient (TARC) and capacity loss. These characteristics indicate that the proposed antenna suitable for some wireless applications

Abd-Alhameed, Raed A.

Abidin, M.N.Z.

Marzudi, W.N.N.W.

Muji, S.Z.M.

Yue, Ma

YesThis paper presented a planar printed multiple-input-multiple-output (MIMO) antenna with a dimension of 100 x 45 mm2. It composed of two crescent shaped radiators placed symmetrically with respect to the ground plane. Neutralization line applied to suppress mutual coupling. The proposed antenna examined both theoretically and experimentally, which achieves an impedance bandwidth of 18.67% (over 2.04-2.46 GHz) with a reflection coefficient < -10 dB and mutual coupling minimization of < -20 dB. An evaluation of MIMO antennas is presented, with analysis of correlation coefficient, total active reflection coefficient (TARC) and capacity loss. These characteristics indicate that the proposed antenna suitable for some wireless applications

Abd-Alhameed, Raed

Bradford Scholars

 The University of Bradford Institutional Repository http://bradscholars.brad.ac.uk This work is made available online in accordance with publisher policies. Please refer to the repository record for this item and our Policy Document available from the repository home page for further information. To see the final version of this work please visit the publisher’s website. Available access to the published online version may require a subscription. Link to publisher’s version: http://taeece2014.sdiwc.us/ Citation:   Marzudi WNNW, Abidin ZZ, Muji SZ, Yue M and Abd-Alhameed RA (2014) Mutual Coupling Reduction of Two Elements Antenna for Wireless Applications. Presented at: The Second International Conference on Technological Advances in Electrical, Electronics and Computer Engineering (TAEECE2014). Asia Pacific University of Technology and Innovation (APU), Kuala Lumpur, Malaysia; March 18-20, 2014. Copyright statement: © 2014 SDIWC. Reproduced with permission, in accordance with the publisher's self-archiving policy.    Mutual Coupling Reduction of Two Elements Antenna for Wireless Applications  W.N.N.W. Marzudi1, Z.Z. Abidin1, S.Z. Muji1, Ma Yue2 and Raed A. Abd-Alhameed3 1Research Center of Applied Electromagnetic, Universiti Tun Hussein Onn Malaysia, Johor, Malaysia. 2National  Astronomical Observatories (NAOC), Chinese Academy of Sciences. 3Mobile and Satellite Communications Research Centre, University of Bradford, United Kingdom wannoornajwa@gmail.com, zuhiria@uthm.edu.my   ABSTRACT  This paper presented a planar printed multiple-input-multiple-output (MIMO) antenna with a dimension of 100 x 45 mm2. It composed of two crescent shaped radiators placed symmetrically with respect to the ground plane. Neutralization line applied to suppress  mutual coupling. The proposed antenna examined both theoretically and experimentally, which achieves an impedance bandwidth of 18.67% (over 2.04-2.46 GHz) with a reflection coefficient < -10 dB and mutual coupling minimization of < -20 dB. An evaluation of MIMO antennas is presented, with analysis of correlation coefficient, total active reflection coefficient (TARC) and capacity loss.  These characteristics indicate that the proposed antenna suitable for some wireless applications. KEYWORDS  Multiple-Input-Multiple-Output (MIMO), impedance bandwidth, mutual coupling, neutralization line wireless applications.  1 INTRODUCTION  The potential for MIMO antenna systems to improve reliability and enhance channel capacity in wireless mobile communications has generated great interest[1]. A major consideration in MIMO antenna design is to reduce correlation between the multiple elements, and in particular the mutual-coupling electromagnetic interactions that exist between multiple elements are significant, because at the receiver end this effect could largely determine the performance of the system. Lower mutual coupling can result in higher antenna efficiencies and lower correlation coefficients[2]. Significant research efforts to reduce mutual coupling have been reported in [3-9]. For example, by connecting an additional non radiating folded shorting strip between antenna element and ground plane [3], port to port isolation lower than –28 dB achieved for lower WLAN band. It is also intresting to observed that by applying T-shape slot impedance transformer to both single and dual band PIFA’s, the isolation over 20 dB is obtained [4]. In [5], the authors proposed the method to obtained low mutual coupling by cutting two quarter wavelength slots into the ground plane. The use of planar soft surfaces proposed in [6] to reduce mutual coupling. Other methods to reduce mutual coupling and enhanced isolation of the MIMO antenna , such as inserting slits on ground plane [7], I-haped conductor in modified ground plane [8] and inserting neutralization line between antenna element[9] was also promising methods.       In this paper, two-element crescent shaped MIMO antenna presented for the purpose of wireless applications. The MIMO antenna consists of two crescent shaped radiators placed symmetrically with respect to ground plane with neutralization line (NL) connected in between of the two antennas. The total dimensions of this antenna are 100 x 45 x 1.6 mm3. Both simulated and measured result of the fabricated prototype details reported and discussed.  2 ANTENNA DESIGN CONCEPT  The proposed antenna geometry is illustrated in Fig.1. The antenna system comprises with two crescent shaped radiators that is similar to that in [10] deployed on an economically FR-4 substrate with relative permittivity of 4.4 and a thickness of 1.6 mm operating at 2.4 GHz. The radiators are  ISBN: 978-0-9891305-4-7 ©2014 SDIWC 131  separated by 0.147λ (18.36 mm) for the minimization of mutual coupling. While, 83 × 45 mm2 ground plane placed on the other side of the substrate as shown in Fig.1 (b). The overall dimensions of the proposed antenna are 100 × 45 × 1.6 mm3 which is suitable for wireless application such as a network card or mobile device.                          (a) Top View                         (b) Bottom View Figure 1.  Geometry of the proposed antenna (in mm) (a) top view, and (b) Bottom view.   2 ANTENNA DESIGN CONCEPT  The proposed antenna geometry is illustrated in Fig.1. The antenna system comprises with two crescent shaped radiators that is similar to that in [10] deployed on an economically FR-4 substrate with relative permittivity of 4.4 and a thickness of 1.6 mm operating at 2.4 GHz. The radiators are separated by 0.147λ (18.36 mm) for the minimization of mutual coupling. While, 83 × 45 mm2 ground plane placed on the other side of the substrate as shown in Fig.1 (b). The overall dimensions of the proposed antenna are 100 × 45 × 1.6 mm3 which is suitable for wireless application such as a network card or mobile device.     4 PARAMETRIC STUDY  To clarify the effectiveness of the neutralization line (NL) of the proposed antenna, the parametric study of the location of the neutralization line, NLd was carried out with the width of the NL is kept at 0.5 mm.. From Fig. 2, it can be observed that the optimal distance of NLd is at 9.79 mm which gives the lowest mutual coupling at 2.4 GHz.  Figure 2. Simulated transmission coefficient, S21 of  the various distance location of neutralization line.   5 SIMULATED AND MEASURED PERFORMANCE  Fig.3 and Fig.4 show the simulated and measured s-parameters output for the proposed antenna with and without neutralization line, respectively. As can been observed, the measured return loss, |S11| and mutual coupling, |S21|  for both figures (Fig. 3 and Fig. 4) are reasonably good agreement with the simulated results. The resonance frequency is slightly shifted between the simulated and measured results and this is probably due to the discrepancy of SMA connector and fabrication tolerance. It is apparently seen that by implementing the neutralization lines, the mutual coupling, |S21| of the proposed antenna can be improved.       ISBN: 978-0-9891305-4-7 ©2014 SDIWC 132  Figure 3. Comparative plot of s-parameters output for simulated and measured results for the proposed antenna without neutralization line. Figure 4. Comparative plot of s-parameters output for simulated and measured results for the proposed antenna with neutralization line. To validate the simulated results, the physical prototypes of the proposed antenna with and without the neutralization line were fabricated and tested, as shown in Fig.5. The S-parameters of the antenna were measured by Vector Network Analyser 8722ET (VNA). The measured return loss |S11| and mutual coupling |S21| are plotted in Fig.6. As can be seen, when the neutralization line was inserted, the mutual coupling has been reduced around 7.14 dB (from -14.63 dB to -21.77 dB) with an impedance bandwidth of 18.67% (over 2.04-2.46 GHz). The bandwidth achieved fully covered the wireless application such as network card at 2.4 GHz.              (a)                                               (b) Figure 5. Practical prototype of the proposed antenna (a) with neutralization line (b) without the neutralization line. Figure 6.  Measured S-parameters of the proposed antenna with and without the neutralization line.  The simulated radiation patterns of the proposed antenna in the x-z plane (E-plane) and y-z plane (H-plane) with port 1 excited while port 2 terminated with 50Ω load plotted in Fig.7. The antenna shows a stable omnidirectional pattern in the E-plane and H-plane over the operating frequency of 2.4 GHz.       ISBN: 978-0-9891305-4-7 ©2014 SDIWC 133             Figure 7. Simulated radiation patterns for the proposed antenna for two planes at 2.4 GHz; (a) X-Z plane. “xxxx” (blue) simulated cross-polarization, “oooo” (red) simulated co -polarization. (b) Y-Z plane. “xxxx” (blue) simulated co-polarization, “oooo” (red) simulated cross-polarization Port 1(left) excited and port 2(right) terminated in 50Ω. 6 DIVERSITY PERFORMANCE  To evaluate the capabilities of MIMO/diversity antenna, the envelope correlation coefficient (ECC) is an important criterion to be presented. Basically, envelope correlation can be computed by using S-parameters or radiation pattern of the antenna. The envelope correlation of the MIMO antenna system can be expressed by using the following expression[11]:                    e = |  11 1     1   | ( 1-| 11| -|  1| )( 1-|   | -| 1 | )       (1)                                      The simulated envelope correlation coefficient of the proposed antenna with and without neutralization showed in Fig.7. An improvement of the ECC can be seen after the neutralization line was inserted and it fulfils the characteristic of diversity pe < 0.5 [7]. Therefore, the proposed antenna is suitable candidate for MIMO application.  Figure 8.  Simulated envelope correlation coefficient for the proposed antenna with and without neutralization line.  The simplified channel capacity loss of a 2 x 2 MIMO system can be evaluated by using the following equation, given in [9, 12]:                                   =                            (2) Where    is the receiving antenna correlation matrix :                                  [            ]                     (3)                         with     (  (|   |  |   | )) and                        for  i,j = 1 or 2. The simulated capacity losses of the proposed antenna with and without neutralization line shown in Fig.9. It can be seen that the capacity loss after inserting neutralization line neither exceeds 0.6 bps/Hz at 2.4 GHz. Figure  9.  Simulated capacity loss of the proposed antenna with and without neutralization line. (b) (a) ISBN: 978-0-9891305-4-7 ©2014 SDIWC 134  Total active reflection coefficient or known as TARC can be defined as the return loss of the whole MIMO proposed antenna. Fig.10 shown the simulated total active reflection coefficient of the proposed antenna with and without neutralization line. The better performance of TARC obtained with neutralization line inserted. Figure 10. Simulated total active reflection coefficient of the proposed antenna with and without neutralization line.   Table 1. Simulated results for correlation coefficient, TARC and capacity loss at 2.4 GHz Parameter Proposed Antenna without Neutralization Line Proposed Antenna with Neutralization Line  Correlation Coefficient (dB) 0.091 0.0017 Capacity Loss (bits/s/Hz) -12.29 -17.02 TARC (dB) 0.9089 0.6854     The correlation coefficient, TARC and capacity loss summarized in Table 1. This shows that the proposed antenna with neutralization line have lower loss of capacity and better performance for TARC and envelope correlation coefficient compared to the proposed antenna without neutralization line.       7 CONCLUSION  A two-elements crescent shaped printed MIMO antenna for covering 2.4 GHz wireless applications presented. Neutralization line applied to meet the requirement of MIMO in term of low mutual coupling parameter. Simulated and measured results show that the antenna achieves an impedance bandwidth of 18.67% (over 2.04-2.46 GHz) with a reflection coefficient < -10 dB and mutual coupling minimization of < -20 dB. Further, the correlation coefficient, TARC, and capacity loss have been analyzed for antenna with and without neutralization line. It has been shown that the proposed antenna has met the requirements of MIMO practical antenna.  7 ACKNOWLEDGEMENT  The authors of this paper wish to acknowledge the funding of this project by Universiti Tun Hussein Onn Malaysia under short term grant Vot 0992.   8 REFERENCES  [1] G. J. Foschini and M. J. Gans, "On limits of wireless communications in a fading environment when using multiple antennas," Wireless personal communications, vol. 6, pp. 311-335, 1998. [2] J. Thaysen and K. B. Jakobsen, "Design considerations for low antenna correlation and mutual coupling reduction in multi antenna terminals," European transactions on telecommunications, vol. 18, pp. 319-326, 2007. [3] H. S. Singh, B. Meruva, G. K. Pandey, P. K. Bharti, and M. K. Meshram, "Low Mutual Coupling Between Mimo Antennas By Using Two Folded Shorting Strips," Progress In Electromagnetics Research B, vol. 53, 2013. [4] S. Zhang, B. K. Lau, Y. Tan, Z. Ying, and S. He, "Mutual coupling reduction of two PIFAs with a T-shape slot impedance transformer for MIMO mobile terminals," Antennas and Propagation, IEEE Transactions on, vol. 60, pp. 1521-1531, 2012. [5] S. Zuo, Y.-Z. Yin, W.-J. Wu, Z.-Y. Zhang, and J. Ma, "Investigations of reduction of mutual coupling between two planar monopoles using two λ/4 slots," Progress In Electromagnetics Research Letters, vol. 19, pp. 9-18, 2010. [6] O. Quevedo-Teruel, L. Inclan-Sanchez, and E. Rajo-Iglesias, "Soft surfaces for reducing mutual coupling between loaded pifa antennas," Antennas ISBN: 978-0-9891305-4-7 ©2014 SDIWC 135  and Wireless Propagation Letters, IEEE, vol. 9, pp. 91-94, 2010. [7] J.-F. Li, Q.-X. Chu, and T.-G. Huang, "A compact wideband MIMO antenna with two novel bent slits," Antennas and Propagation, IEEE Transactions on, vol. 60, pp. 482-489, 2012. [8] C. See, R. Abd‐Alhameed, N. McEwan, S. Jones, R. Asif, and P. Excell, "Design of a printed MIMO/diversity monopole antenna for future generation handheld devices," International Journal of RF and Microwave Computer‐Aided Engineering, 2013. [9] C. H. See, R. A. Abd-Alhameed, Z. Z. Abidin, N. J. McEwan, and P. S. Excell, "Wideband printed MIMO/diversity monopole antenna for WiFi/WiMAX applications," Antennas and Propagation, IEEE Transactions on, vol. 60, pp. 2028-2035, 2012. [10] C. H. See, R. A. Abd-Alhameed, D. Zhou, T. H. Lee, and P. S. Excell, "A crescent-shaped multiband planar monopole antenna for mobile wireless applications," Antennas and Wireless Propagation Letters, IEEE, vol. 9, pp. 152-155, 2010. [11] L. Xiong and P. Gao, "Compact Dual-Band Printed Diversity Antenna for Wimax/WLAN Applications," Progress In Electromagnetics Research C, vol. 32, pp. 151-165, 2012. [12] S.-W. Su, C.-T. Lee, and F.-S. Chang, "Printed MIMO-antenna system using neutralization-line technique for wireless USB-dongle applications," Antennas and Propagation, IEEE Transactions on, vol. 60, pp. 456-463, 2012.  ISBN: 978-0-9891305-4-7 ©2014 SDIWC 136

Mutual Coupling Reduction of Two Elements Antenna for Wireless Applications

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