Array pattern synthesis with high radiation efficiency for transmission antenna arrays

This paper introduces an application of the dandelion optimization (DO) algorithm in antenna arrays. This is the first time that the DO algorithm has been used for optimizing antenna arrays. For antenna array optimization, sidelobe level (SLL) and deep nulls are key technical indicators. A lower SLL can improve the signal-to-noise ratio and reduce the impact of clutter signals outside the main beam. Deep nulls need to be aligned with the direction of interference to eliminate the influence of interference sources. The combination of the two can effectively improve the anti-interference ability of the entire system. Therefore, antenna arrays with ultra-low sidelobes and ultra-deep nulls are currently hot in the field of antenna array design and are also some of the key technologies needed to achieve modern high-performance radar systems. As a new type of evolutionary algorithm inspired by nature, the DO algorithm is inspired by the wind propagation behavior of dandelions in nature. This algorithm iteratively updates the population from three stages of ascent, descent, and landing, ultimately finding the optimal position. It has good optimization ability in solving complex problems such as those involving nonlinearity, discreteness, and non-convexity, and the antenna array pattern synthesis optimization problem belongs to multivariate nonlinear problems. Therefore, the DO algorithm can be effectively applied in the field of antenna array optimization. In this work, we use the following method to obtain an optimized pattern of a linear array with the lowest sidelobe level (SLL), null placement in particular directions, and a lower notch in particular directions: by controlling the antenna array’s element spacing and leaving the phase unchanged to optimize the current amplitudes and by controlling the excitation current and phase fixation of the antenna array and changing the element spacing. In the first and second examples, different algorithms are used to reduce the SLL of the antenna. In the first example, the DO algorithm reduces the SLL to −33.37 dB, which is 2.67 dB, 2.67 dB, 3.77 dB, 2.74 dB, and 2.52 dB lower than five other algorithms. In the second example, the SLL optimized by the DO algorithm is −42.56 dB, which is 5.04 dB and 1.48 dB lower than two other algorithms. In both examples, the DO algorithm reduces the SLL lower than other algorithms when the main lobe of the antenna is not significantly widened. Examples 3, 4, and 5 use the DO algorithm to optimize the amplitude of the current, generating deep nulls and deep notches in specific directions. In Example 3, the DO algorithm obtains a depth of nulls equal to −187.6 dB, which is 66.7 dB and 44.3 dB lower than that of the flower pollination algorithm (FPA) and the chaotic colony predation algorithm (CCPA), respectively. In Example 4, the deep null obtained by the DO algorithm is as low as −98.69 dB, which is 6.67 dB lower than the deep null obtained by the grey wolf optimization (GWO) algorithm. In Example 5, the deep notch obtained by the DO algorithm is as low as −63.1 dB, which is 6.4 dB and 1.9 dB lower than the spider monkey optimization (SMO) algorithm and the grasshopper optimization algorithm (GOA), respectively. The data prove that the DO algorithm produces deeper nulls and notches than other algorithms. The last two examples involve reducing sidelobe levels and generating deep nulls by optimizing the spacing between elements. In Example 5, the SLL obtained using the DO algorithm is −22.8766 dB, which is 0.1998 dB lower than the lowest SLL of −22.6768 dB among other algorithms. In Example 6, the SLL obtained using the DO algorithm is −20.1012 dB, and the null depth is −125.1 dB, which is 1.592 dB lower than the SLL obtained by the cat swarm optimization (CSO) algorithm and 19.1 dB lower than the deep null obtained by the GWO algorithm, respectively. In summary, the results of six simulation experiments indicate that the DO algorithm has better optimization ability in linear array optimization than other evolutionary algorithms.

This paper presents a new scheme based on Weight vector ORthogonal Decomposition (WORD) to control the array response at a given direction and a novel WORD-based approach to pattern synthesis for arbitrary arrays. The central concept of the proposed methods stems from the adaptive array theory. More precisely, it is found that the inverse of the noise-plus-interference covariance matrix in adaptive beamforming can be regarded as a linear combination of two orthogonal projection matrices, and, accordingly, the optimal weight vector is a linear combination of two orthogonal vectors. With such an observation, the WORD scheme is developed to design the desired weight vector. It is shown that the array response at a given direction can be precisely adjusted to an arbitrary level, by simply determining appropriate combination coefficients for those two orthogonal vectors. Furthermore, a closed-form expression of the weight vector can be achieved by introducing a new cost function that measures pattern variation. By employing the WORD scheme successively, a novel approach to pattern synthesis for arbitrary arrays is devised. At each implementation step of this approach, the array pattern is adjusted in a point-by-point manner by successively modifying the weight vector. As such, both the sidelobe and mainlobe regions can be flexibly synthesized. Numerical examples are provided to demonstrate the effectiveness and flexibility of the WORD scheme in array response control at a single direction as well as pattern synthesis.

Multi-beam antenna is an important way to increase the channel capacity of cellular communications. It is available in two ways, one is based on optical methods, such as Luneberg lens and Rotman lens. However, the common problem with this method is that the lens size is too large or difficult to process. Another method is based on beam-forming network composed of coupler and phase shifter, such as Butler matrix. The Butler matrix has been studied for a long time, in the form of microstrip, stripline, or substrate-integrated waveguide. The substrate-integrated waveguide with low insertion loss is mainly used in the higher frequency such as millimeter wave band. The microstrip is mainly used in 4G/5G base stations, suitable for broadband design and process. Low side-lobe level, narrow beams are especially important for multi-beam base station antennas. The traditional Butler matrix is 4 × 4 Butler matrix for 4-beam base stations. However, the traditional Butler matrix can only output equal-amplitude power, with a side-lobe level higher than −13.4 dB. The beam width is too wide due to the few number of antenna. The 4 × 4 Butler Matrix with attenuator can reduce the side-lobe level, but it will increase the insertion loss of the beam-forming network. The 4 × 4 Butler matrix with phase shifter and power divider can form a 4 × 6 Butler matrix, which reduce the beam width beam and side-lobe level. However, for large-angle scanning, not only the side-lobe level, but also the grating-lobe problem caused by the wide-angle scanning and wide antenna spacing needs to be solved. The array with triangle arrangement can reduce the side-lobe and grating-lobe level. A wide-band 4-beam antenna array and beam-forming network for 4G base stations are presented in this paper. Adopting triangular arrangement, the number of antenna in sub-array is increased, and the antenna spacing is reduced, resulting in good side-lobe and grating-lobe level suppression. The output amplitude and phase errors are small over a wide band, with low insertion loss.

Planar Beam-forming Antenna Array for 60-GHz Broadband Communication

Optical traveling wave antennas offer unique opportunities to control and selectively guide light into a specific direction, which renders them excellent candidates for optical communication and sensing. These applications require state-of-the-art engineering to reach optimized functionalities such as high directivity and radiation efficiency, low sidelobe levels, broadband and tunable capabilities, and compact design. In this work, we report on the numerical optimization of the directivity of optical traveling wave antennas made from low-loss dielectric materials using full-wave numerical simulations in conjunction with the particle swarm optimization algorithm. The antennas are composed of a reflector and a director deposited on a glass substrate, and an emitter placed in the feed gap between them serves as an internal source of excitation. In particular, we analyze antennas with rectangular- and horn-shaped directors made of either hafnium dioxide or silicon. The optimized antennas produce highly directional emissions due to the presence of two dominant guided TE modes in the director in addition to leaky modes. These guided modes dominate the far-field emission pattern and govern the direction of the main lobe emission, which predominately originates from the end facet of the director. Our work also provides a comprehensive analysis of the modes, radiation patterns, parametric influences, and bandwidths of the antennas, which highlights their robust nature.

A novel antenna integrated the advantages of the Yagi–Uda and the dielectric rod antenna (DRA) is presented in this communication. The antenna mainly consists of a tapered printed Yagi–Uda, a tapered dielectric cover, and a periodic dielectric rod. First, a tapered printed Yagi is designed as the primary feeder and embedded inside a tapered dielectric rod to improve the directive gain, radiation efficiency, and sidelobe levels. The influence of the dielectric cover to the Yagi is discussed. Then, a dielectric rod with triangular periodic surface is also loaded to the end of the dielectric cover to obtain higher gain and better front-to-back ratio. Finally, a sample of the antenna working at 8.5–9.7 GHz with 18 dBi maximum gain and −23.37 dB sidelobe level is designed. A prototype is fabricated and tested; the measured results match well with the simulated. Compared with the traditional Yagi–Uda antenna and DRA with the same length, the presented integrated antenna has higher gain with lower sidelobe level.

An efficient method based on the sequential quadratic programming (SQP) algorithm for the linear antenna arrays pattern synthesis with prescribed nulls in the interference direction and minimum side lobe levels by the complex weights of each array element is presented. In general, the pattern synthesis technique that generates a desired pattern is a greatly nonlinear optimization problem. SQP method is a versatile method to solve the general nonlinear constrained optimization problems and is much simpler to implement. It transforms the nonlinear minimization problem to a sequence of quadratic subproblem that is easier to solve, based on a quadratic approximation of the Lagrangian function. Several numerical results of Chebyshev pattern with the imposed single, multiple, and broad nulls sectors are provided and compared with published results to illustrate the performance of the proposed method. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.

In this paper, an improved multi-objective artificial bee colony algorithm (IMOABC) is presented to synthesis the beam pattern of conformal arrays. The upper bound of conformal array efficiency (AE) is derived and the relative array efficiency is defined for the optimization object as well as the maximum side lobe level (SLL) of array beam pattern. Modified neighborhood search strategy and redefined crowding distance are adopted to improve the performance of the algorithm. Optimal solution set can be obtained by an iterative process and proper weight vector can be selected according to the actual demand. The final experiments demonstrate the effectiveness of the proposed method.

The pattern synthesis technique of antenna arrays has a wide range of applications in radar and communication systems, which is an important research direction in the field of smart antennas. In order to improve the optimization performance of pattern synthesis of linear antenna arrays, an optimization method based on the Modified RIME Optimization Algorithm (MRIME) is proposed. RIME is a new heuristic algorithm inspired by the condensation process of frost ice in nature, which has a unique update mechanism with strong convergence as well as randomization. In the present work, MRIME is used for optimal pattern synthesis of a linear antenna array (LAA). One part of the present study is to optimize the side lobe level by optimizing the antenna current amplitude while maintaining a uniform spacing; the other part is to optimize the antenna position while assuming a uniform excitation in the synthesis of a sparse LAA, where constraints are imposed on the spacing of the array elements and aperture length, and suppression of the side lobe level with the position of the zeros in the specified direction is also achieved. In this article, simulation experiments for uniform linear arrays as well as sparse linear arrays are presented in detail, and the results show that the MRIME optimization algorithm outperforms most of the existing evolutionary classes of optimization algorithms in optimizing the side lobe level. This illustrates the potential of utilizing the MRIME optimization algorithm for antenna arrays and various other electromagnetism-related challenges.

An efficient search technique based on a touring ant colony optimization algorithm is presented for the shaped-beam pattern synthesis of a linear antenna array. The element excitations of equally spaced array and the element positions of uniformly excited array are determined to closely approximate the desired pattern. In the touring ant colony optimization algorithm, the frequency memory feature of tabu search is used. Illustrative examples of cosecant, flat-topped and pencil beam patterns are given to verify the validity and accuracy of the technique.

A simple and flexible genetic algorithm (GA) for pattern synthesis of antenna array with arbitrary geometric configuration is presented. Unlike conventional GA using binary coding and binary crossover, this approach directly represents the array excitation weighting vectors as complex number chromosomes and uses decimal linear crossover without a crossover site. Compared with conventional GAs, this approach has a few advantages: giving a clearer and simpler representation of the problem, simplifying chromosome construction, and totally avoiding binary encoding and decoding so as to simplify software programming and to reduce CPU time. This method also allows us to impose constraints on phases and magnitudes of complex excitation coefficients for preferable implementation in practice using digital phase shifters and digital attenuators. Successful applications show that the approach can be used as a general tool for pattern synthesis of arbitrary arrays.

In this letter, a substrate integrated waveguide (SIW) based leaky-wave antenna with high radiation efficiency is presented. The radiating unit of the proposed LWA consists of a pair of meandering slots with different lengths. The combination of slots with different lengths effectively improves the leakage factor of leaky-wave antenna and thus improves the radiation efficiency of the antenna. The proposed antenna can scan from -46° to -9°, and the radiation efficiency of the antenna is 87.55%-97.6%. The leaky wave antenna is fabricated and measured. The measured results show good agreement with the simulation ones.

The ultra high frequency (UHF) band spectrum will likely be congested in near future since the next generation wireless as well as Radio Frequency Identification (RFID) system users will witness the use of UHF band technology with increased demand of bandwidth, bit rate, frequency spectrum and power consumption. The alternate solution is the use of millimeter-wave band technology. It is possible to improve data throughput, range resolution and multi-user capability in mm-wave band RFID system. ‘Higher power reception efficiency and lower side lobe level (SLL) of radiation pattern’ is required for RFID system that will increase the tag range and transmission bit rate. At the same time lower SLL will minimize the interference level. Beam pointing error is another problem of UHF band antenna which reduces the tag range and bit rate. These problems can be minimized by using large number of antenna elements. But with UHF band signal it is practically difficult to construct large array antenna; since the array size becomes tremendously larger with the increase of antenna elements. ‘Higher power reception efficiency and lower SLL’ can practically be obtained by using non-uniform power distribution of large number of antenna elements in millimeter wave band. A new and technically better method of beam forming by implementing the concept of staircase power distribution (SPD) of antenna elements at 60 GHz has been investigated and presented in the paper. The SPD method is compared with Gaussian edge tapering method. It was found that the maximum SLL (MSLL) is the lowest in case of SPD. The beam efficiency of SPD is also equivalent to that of Gaussian edge tapering method. It is easier to fabricate a larger number of antenna elements within smaller area with SPD at 60 GHz system; since the antenna size is smaller and the number of different power distribution in SPD case is less and stepwise uniform. Uniform and less number of different power distribution of SPD also minimizes other technical errors.

The construction of signals with a low level of side lobes of the impulse autocorrelation function is of great importance in the development of radar systems, and especially of synthetic aperture radars, where a bright point target can overlap a part of the radar image due to insufficiently low sidelobe levels. This paper presents an algorithm for constructing multiphase sequences of long lengths with a low level of side lobes of the impulse autocorrelation function. Using the proposed algorithm for lengths 680, 1024, 2048, 2730, 4096, polyphase pulse sequences were synthesized with the lowest known sidelobe levels.

Array Antennas used in some applications such as RFID systems, WiMAX, and collision avoidance radar, must have very low side lobes. Antenna with higher beam efficiency (BE) and lower side lobe level (SLL) can increase the coverage area of RFID systems, transmission bit rate and at the same time decrease the energy consumption and interference levels. The application of RFID system at 860–960 MHz frequency band will likely be witnessed in different emerging wireless applications as well as associated increase in energy consumption will also be witnessed in the near future. It is possible to achieve higher BE and lower SLL by implementing different amplitude or phase distribution technique in the array antenna. This paper describes a new method of SLL reduction and increase of BE by adopting staircase concept of power distribution of array antenna. The new beam forming technique optimizes between SLLs and BE.