TAPERED SLOT CPW-FED NOTCH BAND MIMO ANTENNA

Transcription

1 TAPERED SLOT CPW-FED NOTCH BAND MIMO ANTENNA M. L. S. N. S. Lakshmi, B. T. P. Madhav, Habibulla Khan, N. Sai Sri Vasanthi, Anuja Bamra, G. V. Krishna and N. Pavan Srikar Department of Electronics and Communication Engineering, K L University, AP, India btpmadhav@kluniversity.in ABSTRACT A coplanar waveguide fed notch band antenna is proposed in this paper to notch WLAN operating band. A tapered step ground with notched circular patch is used in the proposed antenna design to get notch band characteristics. Half wavelength slits are introduced inside the tapered slot ground and in the circular patch respectively. An FR4 substrate material is used to prototype the proposed model and measured the S-Parameters on ZNB 20 vector network analyser. The modified model is notching the band from 4GHz-7GHz in which WLAN operating band is there. The proposed antenna has lower cross polarisation with excellent impedance bandwidth in the operating band. Keywords: coplanar waveguide feeding (CPW), multiple input multiple output (MIMO), notch band antenna, tapered slot ground, ultra wideband (UWB). 1. INTRODUCTION As we know that UWB systems plays an important role in wired and wireless communications because of their significant characteristics like high data rate, low power dissipations and so on. In the recent times many UWB antennas are designed for single ended operation [1-4]. But attention has been paid towards the differential signal operations which are widely used in the radio frequency systems. Baluns which are used to transform these differential signals into single ended signals and it causes energy loss. Moreover, it decreases the efficiency of the system. Recently several differential UWB antennas have been reported [5-10], but none of them are neither single layer structure nor have notch-band characteristic. The operating bands of UWB ( GHz) systems have been overlapped by some existing wireless communication systems. Wireless local area network operates at GHz. It causes interference between the two systems. Hence the UWB antenna with notch band characteristics is needed. Several UWB antennas which have notch band which have single notch band [11], dual notch band [12], and triple notch band [14] have been proposed. However these antennas don t have sharp selectivity in the notch band except in [15-18] which have better notch-band characteristic. Moreover it was difficult not only to control the notch band but also none of the reported antennas are differentially fed [19-20]. 2. ANTENNA GEOMETRY Initially, a notch band MIMO antenna is designed to notch 5-6GHz operating band. The structure of the basic notch band antenna is shown in Figure-1. The basic model consisting of circular patch and a tapered slot ground on the same side of the substrate. A small square shaped part is cut from the circular patch to enhance the impedance matching. The overall dimension of the base antenna is around 30*35*1.6mm and it is simulated using commercial electromagnetic tool HFSS. In this model both the circular patches are connected with coplanar waveguide feeding, making up two differential parts of the differential antenna. Figure-1B shows the modified notch band antenna by introducing slits on the circular patch. The lengths of the slits are half of the wavelength of the notched frequencies of WLAN band. The dimensions of the proposed antenna are given in Table

2 Figure-1. MIMO Antenna, (a) Notched MIMO Antenna, (b) Modified notched MIMO Antenna. Table-1. Antenna parameters. Parameter L W g h Value(mm) Parameter Wm Wn Wa Lx Value(mm) Parameter A Ln s1 s2 Value(mm) Parameter Wf R Ws Ls Value(mm) The length of the slot is calculated using by L slot = Where c is the speed of the light in free space is the effective dielectric constant f is the resonant frequency of the half wavelength slot 3. RESULTS AND ANALYSIS Figure-2 shows the return loss of the notched MIMO antenna resonating between 3-15GHz with notching at 5-6GHz. The impedance bandwidth of the notched MIMO antenna at lower resonant band is around 75% ad at higher operating band is around 80%. Figure-3 shows the return loss curve for the modified notched MIMO antenna which is blocking the frequency between 4-7GHz. The proposed antenna is showing an impedance bandwidth of 100% in the higher operating band. Bothe these antennas are covering the communication band of the UWB systems. When using the antenna without slots we observed a bad selectivity in the notch band whereas by introducing slits on the structure the notch band is increased by almost 2GHz. As a result a notch band form 4-7GHz with very good selectivity is reached. 8350

3 Figure-2. Return loss vs frequency of notched MIMO antenna. Figure-3. Return loss vs frequency of modified notched MIMO antenna. Figure-4 shows the radiation characteristics of notched MIMO antenna at 3.5GHz. Both polar and 3 dimensional plots are placed in this figure for better understanding of the radiation characteristics of the designed model. It is been observed that an omni directional radiation pattern with nulling towards y- direction is observed in the H-Plane. Figure-5 shows the radiation pattern of modified notch MIMO antenna at lower operating band 3.5GHz. In the H-Plane antenna is showing low cross polarisation with quasi omni radiation pattern in the E-Plane. Figure-6 shows the radiation characteristics of the proposed notched MIMO antenna at higher operating band 14.3 GHz. At higher operating band the radiation pattern is little bit disturbed with improper cross polarisation in the H-Plane. In the E-Plane antenna is showing directive radiation pattern with considerable gain. Figure-4. Radiation pattern of notched MIMO antenna at 3.5 GHz. 8351

4 Figure-5. Radiation pattern of modified notched MIMO antenna 3.5 GHz. Figure-6. Radiation pattern of modified notched MIMO antenna at 14.3 GHz. Figure-7 and Figure-8 shows the current distribution characteristics of the notched MIMO antenna and proposed antenna. For notched MIMO antenna at lower operating band current intensity is distributed over the boundary of the tapered slot ground. At higher frequency there is a discontinuity around the tapered slot ground with respect to current intensity. From Figure-8 we observed that current intensity is focussed on both patches at 3.5GHx but at 14.3 GHz most of the intensity is focussed around second circular patch. Figure-7. Current distribution of modified notched MIMO antenna 3.5 and 10.5 GHz. 8352

5 Figure-8. Current distribution of modified notched MIMO antenna at 3.5 and 14.3 GHz. Figure-9 shows the gain characteristics of the notch band antenna and proposed slits based modified notch band antenna. It is been observed that a maximum peak gain of 6.4dB is attained for the case of modified notch antenna whereas only 4.5dB is observed for the basic notch MIMO antenna. Figure-9. Frequency vs gain of the antenna models. Figure-10. Frequency vs directivity of the antenna models. Figure-10 shows the frequency versus directivity of the designed models. From this figure surprisingly we observed almost similar kind of pattern for both the antenna models. 8353

6 Figure-11. Fabricated antenna on FR4 substrate. Figure-12. Measured reflection coefficient on ZNB 20 VNA. Figure-11 shows the fabricated antenna on FR4 substrate with thickness 1.6 mm. Two ports are connected with SMA connectors of 50 ohms for RF measurements. Slot on the patch element can be observed clearly for notch band. Figure-12 shows the measured reflection coefficient of the antenna on ZNB 20 vector network analyzer. The lower band notching can be clearly observed from the above measured results. 4. CONCLUSIONS A CPW fed notch band antenna is designed and analyzed in this work to notch WLAN band of operation. The proposed model with MIMO structure is reducing the polarization diversity related issues when placed in the real time environment. The prototyped antenna measurement results on FR4 substrate are providing similar kind of results when compared with simulation of HFSS. The performance characteristics like gain of 6.4 db and peak directivity of 4.5 db are attained from the proposed notch band MIMO antenna. ACKNOWLEDGEMENTS Authors like to express their gratitude towards the department of ECE and management of K L University for their support and encouragement during this work. Further Madhav likes to express his gratitude to DST through FIST grant SR/FST/ETI-316/2012. REFERENCES [1] B.T.P. Madhav, D. Ujwala, Habibulla Khan, Atluri Lakshmi Tejaswani, Sriram Guntupalli and Atluri Bala Substrate Permittivity Effects on the Performance of Slotted Aperture Stacked Patch Antenna. International Journal of Applied Engineering Research, ISSN , 8(8): [2] B T P Madhav, Krishnam Naidu Yedla, G.S., Kumar, K.V.V., Rahul R Fractal aperture EBG ground structured dual band planar slot antenna. International Journal of Applied Engineering Research, ISSN , Volume 9, Number 5, January, pp [3] K.W. Xu et al A printed Single-layer UWB monopole antenna with extended ground plane stubs. IEEE Antennas Wireless Propag. Lett. 12: [4] B. Sadasivarao, B. T. P. Madhav Analysis of Hybrid Slot Antenna based on Substrate Permittivity., ISSN , 9(6): [5] L.Li et al Ultra-wideband differential wide-slot antenna with improved radiation patterns and gain. IEEE Trans. Antennas Propag. 60(12):

7 [6] D S Ramkiran, B T P Madhav, Nimmagadda Haritha, R Sree Ramya, Kalyani M. Vindhya, Sai P Abhishek Design and analysis of microstrip slot array antenna configuration for bandwidth enhancement. Leonardo Electronic Journal of Practices and Technologies, ISSN , (25): [7] M S S S Srinivas, T V Ramakrishna, B T P Madhav, N Bhagyalakshmi, S Madhavi, K Venkateswarulu A Novel Compact CPW Fed Slot Antenna with EBG Structure. ARPN Journal of Engineering and Applied Sciences, ISSN , 10(2): [8] P Syam Sundar, Sarat K Kotamraju, T V Ramakrishna, B T P Madhav, T Sravya Sruthi, P Vivek, J Jaswanth Kumar, M Dileep Novel Miniatured Wide Band Annular Slot Monopole Antenna. Far East Journal of Electronics and Communications, ISSN: , 14(2): [9] M Ajay babu, B T P Madhav, D Naga Vaishnavi, P Radhakrishna, N Bharath, K Madhuri, K Bhavani Prasad, K Harish Flared V-Shape Slotted Monopole Multiband Antenna with Metamateril Loading. International Journal of communications Antenna propagation, ISSN: , 5(2): [10] T V Ramakrishna, B T P Madhav, G Manmohan, M Pavithra. Triple Band linearly polarized Square Slotted Micro strip Antenna for X - Band Applications. Far East Journal of Electronics and Communications, ISSN: , 15(2): [11] M. L. S. N. S. Lakshmi, B. T. P. Madhav Analytical Study on Folded-Slot Koch Fractal Antenna. Indian Journal of Science and Technology, ISSN , 8(17): [12] K V L Bhavani, Habibulla Khan, B T P Madhav Multiband Slotted Aperture Antenna with Defected Ground Structure for C and X-Band Communication Applications. Journal of Theoretical and Applied Information Technology, ISSN: , 82(3): [15] B T P Madhav, A Manikanta Prasanth, Sreeramineni Prasanth, Batchu Mohan Sai Krishna, Devani Manikantha, Usirika Sharmila NagaSai Analysis of Defected Ground Structure Notched Monopole Antenna. ARPN Journal of Engineering and Applied Sciences, ISSN , 10(2): [16] B T P Madhav, Harish Kaza, Thanneru Kartheek, Vidyullatha Lakshmi Kaza, Sreeramineni Prasanth, K S Sanjay Chandra Sikakollu, Maneesh Thammishetti, Aluvala Srinivas, K V L Bhavani Novel Printed Monopole Trapezoidal Notch Antenna with S- Band Rejection. Journal of Theoretical and Applied Information Technology, ISSN: , 76(1): [17] P. Lakshmikanth, Kh Takeshore, B T P Madhav Printed Log Periodic dipole antenna with Notched filter at 2.45 GHz Frequency for wireless communication applications. Journal of Engineering and Applied Sciences, ISSN: X, 10(3): DOI: /jeasci [18] D S Ram Kiran, B T P Madhav Novel compact asymmetrical fractal aperture Notch band antenna. Leonardo Electronic Journal of Practices and Technologies, ISSN , 27(2): [19] M L S N S Lakshmi, Habibulla Khan and B T P Madhav Novel Sequential Rotated 2x2 Array Notched Circular Patch Antenna. Journal of Engineering Science and Technology Review, ISSN: , 8(4): [20] P. Lotfi, M. Azarmanesh and S. Soltani Rotatable dual band-notched UWB/triple-band WLAN reconfigurable antenna. IEEE Antennas Wireless Propag. Lett. 12: [13] B. T. P. Madhav, Habibulla Khan, Sarat K. Kotamraju Circularly Polarized Slotted Aperture Antenna With Coplanar Waveguide Fed for Broadband Applications. Journal of Engineering Science and Technology, ISSN: , 11(2): [14] B T P Madhav, D Lakshmi Kranthi, Ch Kusumanjali Devi. A Multiband MIMO Antenna for S and C-Band Communication Applications. ARPN Journal of Engineering and Applied Sciences, ISSN: , 10(14):