Design and Performance Analysis of Compact MIMO Antenna by Mutual Coupling Suppression between Elements

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2 Design and Pefomance Analysis of Compact MIMO Antenna by Mutual Coupling Suppession between Elements Jagadish M 1, T Ramya 2 Student 1, Assistant Pofesso (S.G) 2, Depatment of Electonics and Communication Engineeing SRM Univesity, Kattankulathu, Tamil Nadu, India Padeep A S 3 Assistant Pofesso, Depatment of Electonics and Communication Engineeing Govenment Engineeing College, Hoovinahadagali, Bellay Distict, Kanataka Abstact Moden wieless communication systems equie low pofile, light weight, high gain, and simple stuctue antennas to assue eliability, mobility, and high efficiency chaacteistics. Micostip antennas povide such equiements. This pape pesents a compact micostip antenna aay designed fo WLAN application. The designed antenna aay woks in the fequency ange of to GHz by using FR4 dielectic substate with pemittivity ε = 4.4 and height, h =1.588 mm. The small spacing between the aay elements esults in stong mutual coupling, which has been shown to affect the pefomance by changing the antenna patten and educing the antenna efficiency. To mitigate the afoesaid coupling effects, a novel Ring Resonato (RR) Stuctue was employed in the micostip antenna aay. The poposed stuctue educes mutual coupling by 10dB at /8 element spacing. The simulation has been pefomed by using HFSS simulato. The designed antenna aays wee fabicated and tested using National Instument s NI-PXIe-1075 Spectum Analyze. Keywods aay antenna, metamateials, micostip antenna, mutual coupling I. INTRODUCTION Pesent communication devices employ MIMO antennas to achieve high speed and high quality tansmission to tansmit lage use data. Also, moden wieless communication system equies low pofile, light weight, high gain and simple stuctue antennas to assue eliability, mobility, and high efficiency chaacteistics. Micostip antennas satisfy such equiements [1]. The advantages of micostip antenna ove othes is the ease of constuction, light weight, low cost and confomability to mounting suface which makes them suitable fo use in moden communication equipments. The design of compact MIMO antennas fo seveal applications was discussed in [2-5]. The majo issues addessed in these liteatues wee mutual coupling that aise due to small antenna sepaation. Techniques to educe the coupling between antennas include a dielectic slab EBG [6], inclusion of paasitic elements in the spacing [7], modified gound planes such as UC-PBG defects with diagonal slots on patch [8], concave ectangula patches [9]. Engineeed stuctues such as metamateials wee also used fo coupling eduction. The most popula among them ae the split ing esonatos (SRR) and thei vaiants [10-13]. The efeence [14] discusses a mathematical appoach to educe mutual coupling that includes impedance matching technique and [15] deive the expessions fo mutual coupling between the ectangula patch elements. The expession emphasizes the effect of element spacing on the mutual coupling. Also, an expession fo fa field adiation patten fo micostip antenna aays taking into account the mutual coupling was deived. In this pape, we investigate the design and pefomance of a micostip antenna aay with a novel Ring Resonato stuctue that is included between the antenna elements fo mutual coupling eduction. The effects of the inclusion of this stuctue on antenna pefomances ae also studied. The pape is oganized as follows: Section II gives antenna design; sections III and IV povide simulation esults and effects of mutual coupling on antenna pefomance. II. ANTENNA DESIGN A. Micostip Aay Design A ectangula patch antenna aay with two elements, as shown in Fig.1, is etched on a common gound plane with each element esonating at 5.5GHz. An FR4 substate with =4.4 used fo the simulations. Fig.1. Rectangula Patch Antenna aay simulated on FR4 substate using HFSS tool. (This wok is licensed unde a Ceative Commons Attibution 4.0 Intenational License.) 131

3 The antenna aay dimensions, mateial popeties and opeating fequency details ae shown in Table.1. TABLE 1: ANTENNA ARRAY SPECIFICATIONS Paametes Specifications Fequency of Opeation 5.31 GHz to 5.62 GHz Resonant Fequency 5.5GHz Substate Height of the Substate Length of the Patches Widht of the Patches Dielectic constant 4.4 Distance between antennas FR4 epoxy 1.58mm mm mm 30mm B. Ring Resonato and its Design The developments in wieless devices inceased the need fo moe compact antenna designs. But this compactness leads to sevee degadation in gain and diectivity due to nea field inteactions and stong mutual coupling between the antenna elements. Theefoe, suppessing this coupling in the aay is essential fo bette pefomance in MIMO systems. Ring esonatos wee used fo the pupose of educing the mutual coupling between antenna elements. Fou ings employed between the antennas with / 2 spacing between them ae shown in Fig.3. Each ing is of 1.7mm width and 0.1 mm height with spacing between the ings equal to 0.8 mm in x-diection and 1.3mm in y-diection. The ings ae made of low cost coppe mateial with elative pemittivity =1. The ings ae suppoted by FR4 substate with =4.4. The width of the adiating edge is pedicted by the following fomula [1] V w 2 0 f 2 1 (1) Whee, f is the esonant fequency (5.5GHz), is the dielectic constant of the substate and V o is the velocity of light in fee space = 3e8 m/s. The width obtained fom (1) is mm. A sepaation of 30 mm was maintained between the antennas. The photogaph of the fabicated antennas is shown in Fig.2. Fig.3. Ring Resonato Stuctue employed between antenna elements with /2 spacings between them The ing dimension and spacing ae optimized to get lowest mutual coupling. The suface cuent plot of the RR based aay designed using HFSS tool is shown in Fig.4. Fig.2. Photogaph of the Fabicated Antennas Fig.4. Suface Cuent Plot fo Antenna Aay with RR fo mutual coupling eduction between elements simulated using HFSS. (This wok is licensed unde a Ceative Commons Attibution 4.0 Intenational License.) 132

4 s(2,1) in db The RR localizes the cuents within the antenna (geen colou) and theeby contibutes in the eduction of mutual coupling. III. SIMULATION RESULTS AND TESTING The mutual coupling between the antennas was analyzed in tems of electical isolation (S 21 ) between the two pots fo diffeent element spacing in wavelengths. The esult of this analysis is shown in Table.2. TABLE 2: MUTUAL COUPLING AND ARRAY SIZE FOR DIFFERENT SPACINGS Distance Between Antennas In Wavelengths BETWEEN ANTENNA ELEMENTS Aay Size Mutual In mm Coupling Without Ring Stuctue In db Mutual Coupling With Ring Stuctue In db λ/ x Fig.6. Expeimental set-up with spectum analyze λ/ x λ/ x It can be obseved that thee is aound 10 db mutual coupling eduction in all the cases and aay expeiences 59% eduction in size to obtain same amount of mutual coupling as obtained in λ/2 without Ring Stuctue. The HFSS plot fo mutual coupling eduction in λ/8 case is shown in Fig.5. Ansoft LLC HFSSDesign1 Name X Y m m MUTUAL COUPLING PLOT Black Line - MC without Ring Stuctue Red Line - MC with Ring Stuctue Feq [GHz] m1 m2 ANSOFT Cuve Info db(s(1,2)) Setup1 : Sweep db(s(1,2))_1 Impoted Fig.5. Mutual Coupling Plot fo λ/8 element spacing between antennas The fabicated antennas wee tested using National Instument s Spectum Analyze, NI-PXIe The Antenna Unde Test (AUT) is connected to RF cable with the help of SMA connecto on the eceiving side. The expeimental setup is shown in Fig.6. Fig.7. Spectum Analyze output fo Patch Antenna The spectum analyze output fo single patch is shown in Fig.7. It shows that the peak eceived powe is -62.5dBm at 5.53GHz indicating that it is the esonant fequency. The bandwidth obtained is 342MHz. The antenna is having an attenuation of 30dB. The distotions ae a function of amount of metal used and location of soldeing. TABLE 3: COMPARISON OF SIMULATED AND MEASURED PATCH ANTENNA Paametes Simulation Results P1 RESULTS Testing/Measued P2 Pecentage Deviation fom simulation (P1~P2)/P1 % Resonant fequency 5.5GHz 5.53GHz 5.4 (300MHz) Bandwidth 300MHz 342MHz 14 (42MHz) Resonant fequency 5.5GHz 5.53GHz 5.4 (300MHz) (This wok is licensed unde a Ceative Commons Attibution 4.0 Intenational License.) 133

5 Compaison between simulated and measued patch antenna esult is shown in Table 3. Thee is a 300MHz shift in esonant fequency of AUT compaed to the simulated one. This shift will not ceate a poblem as the AUT s esonating fequency is within the fequency ange ( GHz) fo which the antenna was designed. Thee is an incease in the bandwidth of AUT by 42 MHz compaed to simulated one which is 14% shift. Both the paametes measued deviate by less than 15% compaed to simulation owing to the accuacy of simulato. The deviation of measued patch antenna pefomance fom the simulated esults can be accounted fo fabication and human eos (setup aangement /vaiation) duing antenna testing. Fom Fig.9 we see that the diectivity in with RR case is moe than without RR case by 3dB. The diectivities ae measued at Phi=0 deg. The ing esonato educes the adiation of the antenna in undesied diection and inceases the adiation only in the desied diection. IV. EFFECT OF MUTUAL COUPLING ON ANTENNA PERFORMANCE OF /8 ELEMENT SPACINGS BETWEEN THE ANTENNAS The analysis on the impact of mutual coupling is made fo λ/8 element spacing between the elements and assumes simila effects on othe element spacing. Fig.10. VSWR Plot fo λ/8 Element Spacing Between the Elements Fig.8. Retun Loss Plot in db fo λ/8 Element Spacing Between the Elements Fom Fig.8 we see that almost the same bandwidth is achieved in with and without RR cases. (0.3GHz). Retun loss in with RR case is moe compaed to without RR case but is slightly shifted in esonant fequency which can be ovecome by adjusting antenna dimensions. The VSWR with RR is 1.7 and without RR it is In both the cases VSWR is maintained below 2. The VSWR in RR case is moe because of cuent flowing between the antenna elements esulting in standing wave patten. V. CONCLUSION In this pape, bulkiness of the designed antenna aay system was teated fo miniatuization by educing the mutual coupling between the elements. The poposed ing esonato stuctue educes mutual coupling by 16dB at λ/2 element spacing, and 10dB at λ/8 element spacing. Also the aay size was educed to 59% to obtain same amount of mutual coupling as obtained in λ/2 without Ring Resonato Stuctue. The simulation has been pefomed by using HFSS simulato which is a commecially available antenna simulato. The designed antenna aays wee fabicated and tested using National Instument s NI-PXIe-1075 Spectum Analyze. The simulated and measued patch antenna pefomances such as Bandwidth and Resonant Fequency showed less than 15% deviation which also depicts the efficiency of the simulato. ACKNOWLEDGEMENT This wok was caied using infastuctue unde DST- FIST, ADS tool and Signal Analyze, Depatment of Electonics and Communication Engineeing, SRM Univesity. Fig.9. Diectivity Plot db fo λ/8 Element Spacing Between the Elements (This wok is licensed unde a Ceative Commons Attibution 4.0 Intenational License.) 134

6 REFERENCES [1] Jagadish M, T Ramya, Design and Paametic Analysis of Micostip Antenna Aay fo Inceased Gain, Poc IEEE Intenational Confeence on Communication and Signal Pocessing (ICCSP2014),page , Apil 3-5, 2014,Tamil Nadu,India [2] Ahmad A. Gheethan, Paul A. Hezig, Gokhan Mumcu, Compact 2x 2 Coupled Double Loop GPS Antenna Aay Loaded With Boadside Coupled Split Ring Resonatos, IEEE Tansactions On Antennas And Popagation, Vol. 61, No. 6, June 2013 [3] Chistos Masouos, Mathini Sellathuai, Tham Ratnaajah, Lage- Scale MIMO Tansmittes in Fixed Physical Spaces: The Effect of Tansmit Coelation and Mutual Coupling, IEEE Tansactions On Communications, 2013 [4] Dong-Jin Kim, Kyeong-Sik Min, Young-Min Moon and Young-Eil Kim, Compact 2-channel MIMO Antenna fo WiBo Handy Teminal Application, Poceedings of Asia-Pacific Micowave Confeence [5] Jae-Young Chung, Taesik Yang, Juhyung Lee, and Joongho Jeong, Low Coelation MIMO Antenna fo LTE 700MHz Band, Antennas & Popagation (APSURSI), IEEE Intenational Symposium, [6] Yoonjae Lee, Yang Hao, and Clive Paini, Applications of Electomagnetic Bandgap (EBG) Stuctues fo Novel Communication Antenna Designs, Poceedings of the 36th Euopean Micowave Confeence, Mancheste UK, Septembe 2006 [7] Kyeong-Sik Min, Dong-Jin Kim and Young-Min Moon, Impoved MIMO Antenna by Mutual Coupling Suppession between Elements, The Euopean Confeence on Wieless Technology, [8] Taha A. Elwi, Hussain M. Al-Rizzo, Yahiea Al-Naiemy, and Haide R. Khaleel, Miniatuized Micostip Antenna Aay with Ulta Mutual Coupling Reduction fo Weaable MIMO Systems, Antennas & Popagation (APSURSI), IEEE Intenational Symposium, [9] Ali Faahbakhsh, Shaham Mohanna and Saeed Tavakoli, Reduction of mutual coupling in micostip aay antennas using concave ectangula patches, 2009 Intenational Symposium on Antennas and Popagation (ISAP 2009), Bangkok, THAILAND, Octobe 20-23, 2009 [10] Xin Mi Yang, Xue Guan Liu, Xiao Yang Zhou, and Tie Jun Cui, Reduction of Mutual Coupling Between Closely Packed Patch Antennas Using Waveguided Metamateials, IEEE Antennas And Wieless Popagation Lettes, Vol. 11, 2012 [11] He-Xiu Xu, Guang-Ming Wang, and Mei-Qing Qi, Hilbet-Shaped Magnetic Waveguided Metamateials fo Electomagnetic Coupling Reduction of Micostip Antenna Aay, IEEE Tansactions On Magnetics, Vol. 49, No. 4, Apil 2013 [12] Pathaban Mookiah and Kapil R. Dandeka, Pefomance Analysis of Metamateial Substate Based MIMO Antenna Aays, IEEE Global Telecommunications Confeence, [13] Haide R. Khaleel, Hussain M. Al-Rizzo, Daniel G. Rucke, Yasi A. Rahmatallah, and Seshadi Mohan, Mutual Coupling Reduction of Dual-band Pinted Monopoles Using MNG Metamateial, Antennas & Popagation (APSURSI), IEEE Intenational Symposium, 2011 [14] Buon Kiong Lau, Jøgen Bach Andesen, Diection-of-Aival Estimation fo Closely Coupled Aays with Impedance Matching, IEEE Tansaction on Antennas and Popagation, vol. 54, pp ,2006 [15] Mahmoud M. Dawoud and Meeja K. Amjad, Analytical Solution Fo Mutual Coupling In Micostip Patch Antenna Aays, The Aabian Jounal fo Science and Engineeing, Volume 31, Numbe 1 B Apil (This wok is licensed unde a Ceative Commons Attibution 4.0 Intenational License.) 135