Department of ECE, K L University, Vaddeswaram, Guntur, Andhra Pradesh, India. 1.

Transcription

1 Volume 115 No , ISSN: (printed version); ISSN: (on-line version) url: REDUCTION OF MUTUAL COUPLING IN ANTENNA ARRAYS BY SPARSE ANTENNA ijpam.eu M. Venkata Narayana 1,Govardhani.Immadi 2, Dr.Habibulla Khan 3 N. Suryateja 4, D. Manasa 4 1,2,3,4 Department of ECE, K L University, Vaddeswaram, Guntur, Andhra Pradesh, India. 1 mvn@kluniversity.in Abstract: This paper describes the reduction of the mutual coupling in antenna array by Sparse antenna. Sparse Antenna is the synthesis of the antenna array to achieve the desired radiation pattern by minimization of the antenna element. Mutual Coupling is reduced by using different techniques. Sparse antenna is applied to a uniformly excited linear array. But the radiation of the array is with smaller half power beam width and Directivity. In order to improve directivity we go for Non-uniform array. Binomial array is non-uniform amplitude with successive binomial coefficients. After the Sparsification of the antenna array, central element has the maximum radiation pattern. As the antenna array is symmetrical along Y-axis. First and last and successive the radiation pattern will be same. It has many application related to radar, army, radio station and e. t. c. In radar application it is used to detect the targets within the range of propagation [8]. Index Terms: Antenna array, sparse antenna, Mutual coupling, and Non-uniform array. 1. Introduction The antenna is an electrical device which acts as a transducer that emits electromagnetic energy into free space. As single antenna does not have sufficient gain to transmit for longer distances. To have high gain and directivity, we go for the antenna array. The array antenna is simply defined as a set of several antennas which work together as a single antenna so spaced and phased that their individual electromagnetic signals combine and superimpose to improve the radiation pattern in the desired direction and canceled in other direction. To obtain radiation pattern normal and parallel to the surface of the plane, we go for broadside array and end fire array respectively. These arrays have the side lobe levels of approximately db [6] which is very high and generally not applicable for many applications. To minimize the side lobe levels of an array, the technique used is Tapering, which means the excitation given to the array is non-uniform. Nonuniform array considered here is the binomial array. One of the drawbacks of using array antenna is mutual coupling. Mutual coupling in array antenna degrades not just the antenna efficiency, but it can alter the antenna s radiation pattern. In order to reduce mutual coupling, we have use phased array [5]. Phased array can be with same or with different amplitude, but it gives the possibility of steering of the beam it indirectly reduces mutual coupling. In this project, we consider a periodic antenna array in which some elements are active and remaining radiating elements will be deemed inactive to have the same radiation pattern as that of initial configuration, which is called Sparsification [1]. Sparse antenna array is unequally spaced antenna array and it reduces the side lobe levels compared to the equip-spaced array with the same number of elements. By sparse antenna array, the performance of full antenna array has been approximately achieved by the 40% fewer elements. 2. Description The array antenna drawback can be described as follows. Consider a Uniform Linear Array (ULA) of N identical sensor elements. The origin of the local coordinate system is the phase centre of array. The positive x-axis is the direction normal to the array and the elements of the array are located symmetrical distributed along the y-axis [2]. Array factor is a summation of single element radiation which is used to produce a radiation pattern that could not be achieved by single antenna. AF= Where W i is weights of i th sensor element of spacing d i, k is the wave number in the free space K=2Π/λ Linear uniform Array along Y -axis of equally Spaced Initially, we implemented the sparsification by using array factor.and weights of feed to the array factor are varied in according to our application. And observed the radiation pattern of array. In order to improve the 465

2 performance of the array, a non-uniform array i.e.; binomial array is used and simulated the results for sparsification. By using different types of the mat lab commands for the creation of the antenna array it improves the radiation pattern of both uniform and nonuniform antenna array. 3. Design Design is based on both uniform and non-uniform array antenna which is symmetrically along Y-axis. Initially a uniform antenna array of uniform excitation with and without phase as shown in Fig.a,Fig.b. And non-uniform array of excitation with and without phase as shown in Fig.c. And the Sparsification process is done in both uniform and non-uniform array as shown in Figures d to f. Sparsification is done by making second and fourth elements zero in an array as shown in the figure. Figure 3.A=[ ] with phase of π/2 and Figure 4.A=[ ] without phase Figure 1.A=[ ] without phase and Figure 2. A=[ ] with phase of π/2 466

3 Figure 5. A=[ ] with phase of π/2 and Figure 6. A=[ ] without phase elements Active Element Inactive is symmetrical Fig.f along y-axis, radiation pattern of the first and last element are same and second and last but one are same and maximum radiation is for the central element of the array[7]. And it is used for the application to detect the more number of the target within the range of the radar. 4. Results A) Uniform Excitation Without Phase Consider a uniform linear array (ULA) with equal excitation and without phase of 5 elements, gives the majority of radiation along the direction of side lobes, which shows that side lobe levels increases[4]. D) Non-Uniform Array (Binomial Array) Of 5 Elements Without Phase Uniform linear array will have smaller half power beam width and possess larger directivity which indirectly specifies that side lobes levels are to be maintained at desired levels [4]. The side lobe levels can be trimmed down by giving non uniform excitation. The binomial array is a one of the non-uniform arrays. By Sparsification at central element, maximum radiation will be obtained. B) Uniform Excitation With Phase A ULA of 5 elements with phase of π/2. Here, the beam is shifted with a phase of π/2, which overcomes the drawback of (a). i.e., side lobe level is decreased which indirectly increases the directivity and gain. C) Non-Uniform Array (Binomial Array) Of 5 Elements With Phase Non-uniform array is used to increase the directivity and half power beam width. And the radiation of the 5 element binomial array is observed in this project. As it E) Sparsification Of Uniform Linear Array Of 5 Elements Consider 5 elements of uniform linear array placed symmetrically along Y-axis. Sparsification of the array is in the form of step pattern, i.e., alternately making elements zeros in the array. The radiation pattern of the array is more when central element is inactive when compare to the other elements are zeros. And by making central element zero, the side lobes are decreased which indirectly has increased in directivity and gain. Due to symmetrical property, first and last will have same radiation pattern, next first and next to last will have same radiation pattern with reduced side lobe level, similarly it continues for every element pattern. 467

4 [4] G. Oliveri, M. Donelli, and A. Massa, "Linear array thinning exploiting almost difference sets," IEEE Trans. Antennas Propag., vol. 57,no. 12,pp , Dec [5] R. L. Haupt, "Thinned arrays using genetic algorithms," IEEE Trans. Antenna Propag., vol. 42, no. 7, pp , Jul [6] G. Oliveri, F. Caramanica, and A. Massa, "Hybrid ads-based techniques for radio astronomy array design," IEEE Trans Antenna Propag., vol. 59, no. 6, pp , jun Conclusion In this project a sparse antenna is designed with random elements zeroed at different position with uniform and non-uniform spacing. Sparsification is done both the uniform and non-uniform antenna array. Sparsification of antenna array has for uniform linear array has lower directivity and smaller half power beam width. In non-uniform array i.e.; Binomial array which overcomes the drawbacks of linear array and it is best used for sparse antenna. 6. Future Scope It is used in the radar technology to detect wide range of the targets within the ranging by taking other non-uniform array which has maximum directivity and half power beamwidth. [7] T.Padmapriya and V.Saminadan, Utility based Vertical Handoff Decision Model for LTE-A networks, International Journal of Computer Science and Information Security, ISSN , vol.14, no.11, November [8] L. Cen, Z. L. Yu, and W. Ser, "Antenna array synthesis in presence of mutual coupling effect for low cost implementation," in Proc. ISIC, 2009, pp [9] G. Oliveri, F. Caramanica, and A. Massa, "On the impact of mutual coupling effect on the psll performances of ads thinned array," Prog. Electromagn. Res. B, vol. 17, pp , [10] O. Bucci, S. Perna, and D. Pinchera, "Advances in the deterministic synthesis of uniform amplitude pencil beam concentric ring array," IEEE Trans. Antenna Propag., vol. 60, no. 7, pp , Jul Acknowledgement The authors especially thank the management of KL University for supporting and encouraging this work by providing the required facilities in Centre for Applied Research in Electromagnetics (CARE) of ECE dept. References [1] Y. Liu, Z. Nie, and Q.-H. Liu, "Reducing the number of elements in a linear antenna array by the matrix pencil method," IEEE Trans. Antenna Propag., vol. 56, no. 9,pp ,sep [2] H. Unz, "Linear arrays with arbitrarily distributed elements," IRE Trans. Antennas Propag., vol. AP-8, no. 2,pp ,Mae [3] G. Toso and P. Angelletti, "Method of designing and manufacturing an array antenna, "US USO , Feb. 21,

5 469

6 470