SQUARE SPLIT RING MIMO ANTENNA FOR WIMAX /WLAN APPLICATIONS WITH REDUCED ECC

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1 International Journal of Advanced Research in Engineering and Technology (IJARET) Volume 8, Issue 6, November - December 2017, pp , Article ID: IJARET_08_06_007 Available online at ISSN Print: and ISSN Online: IAEME Publication SQUARE SPLIT RING MIMO ANTENNA FOR WIMAX /WLAN APPLICATIONS WITH REDUCED ECC Rajeev Mathur Department of Electronics & Communications Engineering, School of Engineering & Technology, Suresh Gyan Vihar University, Jaipur, India Dr. K. C. Roy Kautilya Institute of Engineering & Technology, Jaipur, India Dr. Onkar Singh Lamba Department of Electronics & Communications Engineering School of Engg & Technology, Suresh Gyan Vihar University, Jaipur, India ABSTRACT A high gain 2-element MIMO antenna operating in GHz band is proposed in this paper. A Square Split Ring (SSR) antenna element is designed, simulated and fabricated on a conventional FR-4 substrate. Performance of an array of SSR antenna is investigated in terms of envelop correlation coefficient (ECC). For Square Split Ring Antenna element, Gain of 5.8 dbi is obtained along with the 810 MHz impedance bandwidth. Then ECC is calculated using scattering parameters and its value comes out to be with inter-element spacing of 0.25mm i.e. d= Normally value of ECC should range between 0.5 to 0.7 for the interelement spacing of We have reduced ECC to very low value inspite of very small inter-element spacing. Circular Polarization of SSR-MIMO Antenna makes this suitable for the use in various mobile applications. Key words: MIMO, ECC, WiMAX, WMAN, Split Ring. Cite this Article: Rajeev Mathur, Dr. K. C. Roy and Dr. Onkar Singh Lamba, Square Split Ring MIMO Antenna for WiMAX /WLANW Applications with Reduced ECC. International Journal of Advanced Research in Engineering and Technology, 8(6), 2017, pp INTRODUCTION Wireless communication traffic load increasing day by day due to growth of mobile/ cellular subscribers. Mobile data communication is expected to grow many-folds in future. This fact is constantly increasing the pressure on service providers to increase the capacity and coverage of mobile communication without much investment cost. Best solution for this problem is 65 editor@iaeme.com

2 Square Split Ring MIMO Antenna for WiMAX /WLANW Applications with Reduced ECC deployment of Multiple Input Multiple Output (MIMO) antenna technology & smart antenna system. Multiple Input Multiple-Output (MIMO) systems have two or more antennas as a single entity. By using MIMO antenna or multiple antennas, data throughput and range are increased compared to a single antenna using the same radio transmit power. Additionally MIMO antennas improve link reliability and experience less fading than a single antenna system. By transmitting multiple data streams at the same time, wireless capacity is increased. Separation between two antenna is such that multipath fading will not occur amongst antennas and mutual coupling effect will be reduced. The required separation must be at least 1/4 wavelength, preferably 1/2 to 1 wavelength [1]. The spacing between two antennas could be quantified by calculating Envelope Correlation Coefficient (ECC). Envelope Correlation Coefficient (ECC) ρ e is an important parameter to ensure performance of a MIMO antenna system. Since all the handheld devices are small in size, it is likely that two antennas should be closely spaced to each other without degrading the performance of the communication system [1]-[10]. One of the method of calculating ECC is based on scattering parameters obtained on the antenna elements. The procedure of calculating the correlation between antennas in a two antenna system using the scattering parameters is proposed in [10]. 2. DESIGN OF PROPOSED ANTENNA 2.1. Design Approach First we have designed a linearly polarized rectangular patch antenna and investigated its parameters, as shown in Figure 1. Since a patch antenna has limitations of small impedance bandwidth, gain, and directivity and radiation efficiency. To improvise performance, next we modified the structure to a Square Split Ring (SSR) antenna with proximity coupled feed. MIMO antenna system is than analyzed using two SSR antenna elements Designing of Rectangular Patch Antenna A rectangular patch is first designed on the commercially IE3D software. Parameters for designing the antenna are substrate thickness (h=1.588), relative permittivity ( r =4.4 ) and the resonant frequency (f r = 5.5GHz). For a rectangular patch, the width W and the length L is calculated using formulas as per [12]. Structure of conventional patch antenna is as shown in the Figure 1. Geometrical dimensions of antenna are calculated as in Table 1. Figure 1 Conventional Patch Antenna with L eff = 128.7mm & W= 56.3mm 66 editor@iaeme.com

3 Rajeev Mathur, Dr. K. C. Roy and Dr. Onkar Singh Lamba 2.3. Designing of Square Split Ring (SSR) Antenna An antenna with proximity coupled feed is designed with same overall L eff & W dimension. The ground plane of the proposed structure is modified into eight Square Split Ring (SSR) with dimension as shown in the Table 1. Patch antenna is modified with H shaped structure. SSR give two advantages, one antenna becomes circularly polarized and secondly mutual coupling is reduced. Each Square Split Ring SSR structure of dimension 25 mm X 25 mm and arranged in the form of array with inter-element spacing of about 0.1λ to 0.25λ as shown in Figure 2. CPW feed strip line is used to excite this antenna. Figure 2 SSR Antenna structure. Figure 3 2-e SSR-MIMO Antenna with inter-element spacing of 0.25mm (λ/200) Designing of Two element Square Split Ring (SSR) MIMO Antenna Further, a two element (2-e) SSR - MIMO Antenna is designed with the inter-element spacing of 0.25 mm i.e. λ/200 to observe MIMO specific application for WLAN/WiMAX applications in MIMO system as per Figure 3. Structure Table 1 Dimension of Patch Antenna and SSR Antenna Length Width Outer ring Dimension S Inner Ring Dimension S1 L eff W g Patch SSR Antenna Gap 67 editor@iaeme.com

4 Square Split Ring MIMO Antenna for WiMAX /WLANW Applications with Reduced ECC 3. RESULTS ANALYSIS AND DISCUSSIONS The patch antenna, SSR antenna and SSR-MIMO Antenna are simulated in Modua simulation engine and results are obtained. Scattering parameters are then used to calculate ECC to check suitability of SSR-MIMO Antenna in MIMO systems Return Loss of Conventional Rectangular Patch Antenna Return Loss of Patch antenna is found well below -10 db for frequency of 5 and 5.6 GHz (-40 db & -38dB respectively) as shown in Figure 4. However, as per the property of the Patch antenna, the impedance bandwidth found is very less. Figure 4 Return loss of Conventional Patch Antenna Return Loss & Gain of SSR Antenna Return loss of SSR Antenna structure of Figure 2 is simulated, S 11 parameter is observed to be -25 db at the frequency on interest 5.48 GHz. Return loss is below -10 db for the frequency range of 5.03 to 5.84 GHz. as shown in Figure 5. The Impedance bandwidth of 800 MHz is obtained for SSR antenna, which is many fold that of patch antenna. It is investigated that in terms of gain, SSR Antenna has good performance since gain is fairly constant in the desired frequency range of 5 to 6 GHz i.e. 5.8 dbi. Gain Frequency plot is as shown in Figure 6. Figure 5 Return Loss of SSR Antenna editor@iaeme.com

5 Rajeev Mathur, Dr. K. C. Roy and Dr. Onkar Singh Lamba Figure 6 Comparison of Gain between Patch Antenna & SSR Antenna Table 2 Comparison of parameters of Patch, SSR and SSR-MIMO antenna Parameters Patch Antenna SSR Antenna SSR Antenna in MIMO System Frequency (GHz) Gain (dbi) Bandwidth (MHz) Return loss and Gain SSR-MIMO Antenna Return loss of the SSR-MIMO antenna as shown in Figure 7. It is observed that return loss is below -10dB for frequency range of 5.05 to Return loss is measured using Agilent E5071C vector network analyzer (VNA) in the laboratory as shown in the Figure 8 and have good agreement with simulated results. The experimental set-up for measurements is as shown in Figure 8. Figure 7 Return loss of SSR-MIMO Antenna -22dB at frequency 5.44GHz editor@iaeme.com

6 Square Split Ring MIMO Antenna for WiMAX /WLANW Applications with Reduced ECC Figure 8 Experimental set-up for measurements of return loss. Gain of the SSR-MIMO antenna is found to be constant over the frequency range of 5 to 7 GHz. Gain is 6.1 dbi for frequency of interest 5.5GHz as shown in Figure 9. Radiation pattern of SSR-MIMO antenna is as shown in Figure 10. SSR-MIMO Antenna has two beams in the direction 60 & 120 degrees. Figure 9 Gain of SSR-MIMO Antenna. Figure 10 2-D Radiation pattern of SSR-MIMO Antenna. Table 2 shows the comparison of all the parameters of above antennas editor@iaeme.com

7 Rajeev Mathur, Dr. K. C. Roy and Dr. Onkar Singh Lamba 3.4. ECC Calculations Envelop correlation coefficient is calculated for proposed SSR-MIMO antenna for the interelement spacing to be λ/200 (0.25mm), ECC obtained is Thus proposed SSR Antenna element is best suited for MIMO antenna system. 4. CONCLUSIONS A high gain 2-element SSR-MIMO Antenna is specifically designed to conform to the IEEE ac wireless standard for WLAN/WiMAX operating in GHz band. Gain of this antenna is 6.1dBi. Normally the inter-element spacing in MIMO antenna should be to λ/2 to λ/4 to avoid mutual coupling. For MIMO specific communication systems envelop correlation coefficient (ECC) should be lower than In proposed SSR-MIMO antenna we have kept interelement spacing to be λ/200 (0.25mm) and envelop correlation coefficient obtained is There is a significant reduction in ECC of the proposed SSR-MIMO Antenna, thus it is best suited in fading environment or in MIMO system. Further Circular Polarization of SSR- MIMO Antenna makes this suitable for the use in various mobile applications also. Radiation pattern of this antenna indicates two beams in 60 and 120 direction. Hence, we deduce that smart antenna technology of multiple beamforming could be implemented in this SSR-MIMO antenna. Generated beams have 3 db beamwidth of 26 degrees. These beam obtained could be controlled with the support of sophisticated signal processing units, to give better results in MIMO system for wireless communication to increase the coverage. REFERENCES [1] G. Foschini and M. Gans, On Limits of Wireless Communications in a Fading Environment when Using Multiple Antennas, Wireless & Personal Communications, vol. 6, pp , March [2] J. Blanch, J. Romeu and I. Cordella, Exact Representation of Antenna System Diversity Performance from In-put Parameter Description, Electronics Letters, Vol. 39, 2003, pp [3] K. Boyle, Radiation Pattern and Correlation of Closely Spaces Linear Antennas, IEEE Transactions on Antenna Propagation, Vol. 50, 2002, pp [4] S. M. Ali and J. Warden, Controlling coupling between two transmitting antennas for MIMO handset applications, Personal Indoor and Mobile Radio Communications (PIMRC), pp , [5] H. Arun, A. K. Sarma, M. Kanagasabai, S. Velan, C. Raviteja, and M. G. N. Alsath, Deployment of modified serpentine structure for mutual coupling reduction in MIMO antennas, Antennas and Wireless Propagation Letters, vol.13, pp , [6] S. Zhang, A. A. Glazunov, Z. Ying, and S. He, Reduction of the envelope correlation coefficient with improved total efficiency for mobile LTE MIMO antenna arrays: Mutual scattering mode, Antennas and wireless Propagation letter, June 2013.,vol. 61, no. 6, pp [7] Q. Wang, D. Plettemeier, H. Zhang, K. Wolf, and E. Ohlmer, A Diversity performance of an optimized meander PIFA array for MIMO handsets, Antennas and Wireless Propagation Letters, 2012, vol. 11, pp [8] Mathur R, Joshi S, Roy K C, A novel multiband Koch loop antenna using fractal geometry for wireless communication, International journal of wireless and mobile networks (IJWMN), vol. 3, no. 5, October pp DOI : /ijwmn editor@iaeme.com

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