Optimal pulse shifting in timed antenna array for the reduction of sidelobe and sideband using improved harmony search algorithm (IHSA) dealt in this paper. The essence of 'Time-modulation' lies in the fact that 'Time' can be used as an additional control parameter in antenna array synthesis. The proposed approach demonstrates the controlling nature of periodic time sequences through pulse shifting. The undesired sideband radiations (SRs) generated in time modulated linear array (TMLA) is controlled by minimizing the sideband levels (SBLs) with an optimal pulse shifting scheme applied to the outer elements of the array. Evolutionary algorithm-based design is considered to optimize the time sequences and the excitation coefficients of the array along with the inter-element spacing between the array elements for sidelobe level (SLL) reduction at the fundamental frequency. Pulse shifting with optimized switch-ON instants and switch-ON time intervals of outer elements is responsible for the minimization of SBL only, as the fundamental pattern does not depend on pulse shifting. Thus, a combined approach is developed with optimized excitation coefficients and controlled pulse switching to reduce the SLL and SBL of TMLA simultaneously. 16 and 30 isotropic elements of TMLA structures are considered with a music-inspired IHSA to get the optimal solution. IHSA based numerical results are compared with the results obtained from other applied algorithms such as harmony search algorithm (HSA), particle swarm optimization (PSO), and real-coded genetic algorithm (RGA) with the proposed pulse shifting scheme. The obtained numerical results are also compared with previously published literature results to show the superior performance achieved by the proposed approach.
This article deals with the synthesis of multibeam steerable patterns in time‐modulated arrays (TMAs) for electronic scanning. The simultaneous generation of multiple beams in TMAs can be achieved through the exploitation of undesired harmonic radiations emitted at the multiples of modulating frequency due to the periodic switching. The direction‐dependent harmonic beams are capable of producing independent information channels with different spatial distributions beneficial for electronic beam steering. Multibeam patterns associated with harmonic frequencies along with the fundamental pattern can be synthesized with suitably designed switching schemes. The potentialities of linear TMAs are explored in this article to generate a simultaneous sum and difference pattern useful for monopulse tracking systems. Further assessment of multipattern operations with linear TMAs are proposed with beam steering at lower‐order harmonics. Steered double sum pattern with controlled harmonic radiations are also generated to achieve a steered multibeam with simplified beamforming network. Towards this aim, both the analytical and the optimized solutions of periodic switching sequences for different multibeam patterns are developed. Modified differential evolution with a wavelet‐based mutation strategy (DEWM) is employed for the optimal solution. Representative results are assessed and compared with other published literature results to show the effectiveness of the proposed methods.
SummaryThe pattern synthesis of timed antenna array with the exploitation and suppression of harmonic radiation is proposed in this paper. Timed arrays are the time‐domain alternatives of conventional antenna arrays, where an additional control parameter “time” is used to generate the desired time‐averaged radiation pattern. This additional control also comes with the inherent hindrance of harmonic radiation, generally considered as an undesired effect of time modulation. In this work, this hindrance is overcome with different objectives considering the exploitation and suppression of harmonic radiation of timed arrays. To demonstrate the exploitation of harmonic radiation, a simultaneous sum and difference pattern with reduced sidelobe suitable for monopulse tracking radar systems is obtained at the fundamental and the first harmonic frequency by an optimal subarrayed pulse splitting and shifting approach. Two separate cases, considering uniform and optimized static excitations along with the proposed subarrayed pulse sequence, are presented for the exhaustive analysis of the simultaneous multibeam pattern. To address the suppression of harmonic radiation, the sidelobe level (SLL) at the fundamental frequency and the sideband levels (SBLs) of higher‐order harmonic frequencies are simultaneously reduced. In this regard, a unique pulse shifting approach for the edge elements of the array, along with an optimal set of static excitations, is proposed to enhance the efficiency of the antenna system by reducing SLL and SBLs at the same time. Two uniquely defined cost functions are chosen to address the above‐mentioned objectives by exploiting and suppressing the harmonic radiation of timed arrays, which further increases the adaptability and reconfigurability of the array. A set of 16‐element “time‐modulated” linear array (TMLA) is considered for optimization, and a wavelet mutation‐based differential evolution (DEWM) algorithm is employed to obtain the optimal solutions. Obtained numerical results are reported and also compared with previously published works to show the proposed approach's potentialities.
An efficient analysis of time-modulated array (TMA) toward realizing less-attenuating radiation patterns with simultaneously suppressed sidelobe and sidebands is presented in this paper. In this framework, an optimal outer element-controlled time sequence is derived. The proposed time scheme, along with optimized array excitations, is profitably applied for the desired solution. TMAs are considered unconventional alternatives to the phased arrays. The desired array radiation features can be attained by periodically enabling and disabling the array elements through high-speed switches. Despite the advantages of architectural simplicity and real-time reconfigurability of periodic time sequences, time-domain antenna arrays inherently generate unavoidable sideband radiations (SRs). The undesired SRs obtained at multiple harmonics around the carrier frequency of the array resembles power loss in unintended directions. This paper aims to minimize the SRs as well as the sidelobe level (SLL) for an efficient analysis of time-modulated linear array (TMLA) with high-directive radiation patterns. The starting instants and the period of on-times are optimized to generate a unique shifted time scheme for the edge elements of the TMLA to reduce the sideband levels (SBLs). The array excitations and the uniform spacing between the elements are also optimized together with the shifted time scheme for the coveted solution. Other methods of suppressing SLLs and SBLs with shifted pulse schemes and sub-sectioned pulse schemes are also presented for a fair comparison. Modified versions of the particle swarm optimization algorithm (PSO) are applied for the desired solutions. The optimal results attained by wavelet mutation-based novel PSO is compared with the conventional PSO and the modified novel PSO-based results. The representative results are reported, and the superior performance abilities of the proposed method compared to other published studies are assessed.
Summary Steering the radiation pattern of an antenna array towards the desired spatial angle is beneficial for modern‐age communication systems. The generation of multiple steered patterns by enhancing the first‐order harmonics of a time‐modulated antenna array (TMAA) with controlled radiation features is proposed in this paper. Suitable switching sequences are designed to realize an efficient electronic beam steering with these simultaneously generated narrow directional beam patterns. TMAAs are considered the time‐domain counterparts of phased arrays where high‐speed switches are used to achieve a weighted response by periodically modulating the array elements instead of attenuators or phase shifters. This periodic modulation inherently produces spurious harmonic patterns generally considered as power loss in unintended directions. The beam steering aimed in this paper is accomplished by exploiting the first‐order harmonic patterns in some specific directions keeping the fundamental pattern unaltered. The intended first positive and first negative harmonic components of the TMAA are utilized as steered multibeam patterns, whereas all the remaining harmonic components are suppressed to improve the efficiency of the array. To achieve this, suitable switching sequences are designed by optimizing the ON‐time duration and switching intervals of the elements with a wavelet mutation‐based particle swarm optimization (PSOWM). 16‐element linear TMAA is used to generate the desired patterns with low sidelobe levels (SLLs) for enhanced performance. Numerical results obtained for spatially independent steered patterns are presented and compared with the state‐of‐the‐art literature results.
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