IOSR Journal of Electronics and Communication Engineering (IOSR-JECE) e-ISSN: 2278-2834,p- ISSN: 2278-8735. Volume 7, Issue 3 (Sep. - Oct. 2013), PP 13-18 www.iosrjournals.org www.iosrjournals.org 13 | Page Synthesis of Optimized Asymmetrical Sum Patterns Using Conventional Method M. Satya Anuradha, 1 Dr P. V.Sridevi 2 , Prof G. S. N.Raju 3 1 (Sr Assistant Professor, ECE dept, AUCE (A), Andhra University, INDIA) 2 (Associate Professor, Andhra University, INDIA) 3 (Vice Chancellor, Andhra University, INDIA) Abstract: Sum patterns find applications in Radar for searching and ranging of the targets. A sum pattern with low sidelobe level is a desirable feature in these applications, in order to reduce EMI problems. Sum patterns with Asymmetrical sidelobe topography are considered, in applications where only certain angular regions of pattern are required to have low sidelobe level. Asymmetrical pattern characteristics can have lower beam widths for given design specifications as compared to symmetrical patterns. In view of this, a conventional method of synthesis is carried out in this paper, to produce asymmetrical sidelobe level patterns using discrete arrays. The effect of beam scanning on the pattern behavior is also analyzed for the above synthesized patterns. Keywords: sum pattern, asymmetrical sidelobe level, beam width, complex excitation weights, and discrete array. I. Introduction A common pattern requirement is high directivity and low sidelobe level for Radar, communication and mapping applications. The main beam may be fixed at broad side or at some angle. Usually the radiation pattern of a single element is relatively wide and provides a very low value of directivity. In many applications it is necessary to design antennas with very directive characteristics to meet the demands of long distance communication. This can only be accomplished by increasing the electrical size of the antenna. Enlarging the dimensions of single element leads to more directive characteristics, which sometimes increases the system complexity. Another way to increase the directivity without necessarily increasing the size of the element is to form an assembly of radiating elements in electrical and geometrical configuration [1]. There are at least five controls that can be used to control the overall pattern of the antenna. They are number of elements in the array, the geometrical configuration of the overall array, the excitation of the individual elements, relative displacement and the radiation patterns of the individual elements. A linear array consists of equally spaced elemental radiators [2], laid out in a straight line, the sum pattern is characterized by a single narrow main lobe and a set of side lobes. For most of the applications the sum pattern should possess narrow mainlobe and very low sidelobes. In Radar and Communication applications, sum patterns with low side lobe levels are useful in order to have low beam widths. In some radar applications sum patterns with asymmetrical side lobes provide a system advantage [2]. The sum patterns with arbitrary side lobe topology are useful in applications where undesired signals are coming from a limited region of space, permitting the sidelobes to be higher elsewhere, results in a narrow main beam and more directivity from the same aperture [3]. Frequently antennas operate in an environment with several targets or interfering objects present. This may lead to ambiguous or false system response. A rather substantial error in the system response may be due to the contributions from the pattern sidelobes. Therefore it is desirable to keep the sidelobe level as low as possible. There exist several methods for designing line sources and uniformly spaced arrays which have lower sidelobe and narrow beam widths. However there is only specific angular region over which the antenna response must be very low. Reduction of all sidelobes to some very low level is possible in theory, but leads to wider main beam width and may be difficult to realize in practice. It is therefore important to be able to synthesize patterns with very low side lobes over one or more specified sectors of the pattern. Hyneman prescribed one method for achieving control over the near in sidelobe envelope function for line sources. Sum patterns can be generated with standard distributions and designed distributions. Instead of equal currents and equal phases, symmetrical taper distributions can be utilized, but the tapered distribution suffers the penalty of some increase in beam width to the first null. However, this sacrifice is benefited by a compensatory advantage of secondary minimum or first sidelobe lower than it was in the case of the uniform current distribution. The important conclusion is that the SLL can be controlled by tapering the array excitations, at some cost in beamwidth. The angular excitation of the main beam in a sum pattern is inversely related to the length of the array and for a given array length the main beam broadens as the sidelobe level is lowered. The