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In this article, a gradient-based phase-only synthesis approach for solving the Q-N clustering problem of planar clustered phased arrays (CPAs) for sidelobe suppression is presented. Through establishing an appropriate parameterization scheme, the synthesis problem is transformed to an unconstrained continuous problem which is suitable for solving with the gradient-based algorithm. The synthesis is carried out through simultaneously optimizing the clustering variables and the phase variables, and the $Q$ - $N$ problem is addressed without reducing the feasible region of the problem. Typical examples are provided to validate the effectiveness of the proposed approach. In addition, by considering several steering angles in the proposed synthesis approach, the scanning issue in the clustering problem is clarified and discussed. [ABSTRACT FROM AUTHOR]

This article presents an electromagnetic inversion algorithm for the design of cascaded metasurfaces that enables the design process to begin from more practical output field specifications, such as a desired power pattern or far-field (FF) performance criteria. Thus, this method combines the greater field transformation support of multiple metasurfaces with the flexibility of the electromagnetic inverse source framework. To this end, two optimization problems are formed: one associated with the interior space between two metasurfaces and the other for the exterior space. The cost functionals corresponding to each of these two optimization problems are minimized using the nonlinear conjugate gradient (CG) algorithm with analytic expressions for the gradient operators. The numerical implementation of the developed design procedure is presented in detail, including a total variation (TV) regularizer that is incorporated into the optimization procedure to favor smooth field variations from one unit cell to the next. The capabilities of the method are demonstrated by converting the produced surface susceptibilities into three-layer admittance sheet models, which are simulated in several 2-D examples. [ABSTRACT FROM AUTHOR]

A gradient-based optimization algorithm that is capable of directly designing a metasurface at the circuit parameter level for a desired field (amplitude and phase) pattern or a desired power (phaseless) pattern on some region of interest (ROI) external to the metasurface boundary is presented. Specifically, the inversion algorithm designs the microwave admittance profile of each subwavelength element of the metasurface when a three-layer admittance model is assumed. To this end, a forward model that maps the admittance profile of each layer of the metasurface to the desired field on the ROI is developed. Then, for the inverse design problem, a data misfit cost functional is defined and minimized over the unknown admittance profile using analytically derived gradients and step lengths. The developed inversion algorithm is then utilized to design metasurfaces capable of beam forming in the far-field zone. [ABSTRACT FROM AUTHOR]

The generation process of difference beam is analyzed from the perspective of beam superposition. By analyzing the continuous linear source, a differential beam synthesis method, which can control the sidelobes level, is proposed with a simple form. The sidelobes level of the difference pattern is determined by controlling the direction of the subbeam and applying the traditional synthesis method, such as Chebyshev method and Taylor method. The proposed synthesis method is theoretical and explicit. Examples are presented for assessing the capabilities of the synthesis of difference patterns. The general distribution function is given. [ABSTRACT FROM AUTHOR]

This article presents an optimization method for pattern synthesis of sparse planar arrays considering mutual coupling and nonoverlapping constraint. The design optimization is carried out through simultaneously optimizing the rotation and position parameters of each array element within a given array aperture. To prevent the overlaps among multiple coupled array elements, a single level-set-based constraint is constructed, which can deal with the difficulty of large numbers of nonoverlapping constraints. In order to guarantee the design precision, the full-wave method of moments (MoM) simulation is well integrated in the optimization method for rigorously considering the mutual coupling among the coupled array elements. The design sensitivity of the optimization problem is analytically derived and the pattern synthesis is actualized by using gradient-based algorithm. Several examples are provided to demonstrate the validity and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, a systematic and generally applicable method to synthesize patterns for single antennas is proposed based on characteristic mode analysis (CMA). Both the theoretical analysis and real implementations are taken into consideration. To obtain a desired pattern, we first calculate the weighting coefficient of each mode using the correlation between the characteristic field and the desired pattern. Afterward, the synthesized current and the feeding vector are solved using CMA, providing feeding information, such as feeding numbers, locations, amplitude, and phase. The feeding vector is nonsparse, making practical feeding impossible. In this circumstance, the theory of compressed sensing is applied so that the number of ports can be greatly reduced, and the synthesized pattern is still highly correlated with the desired one. The method is applied to 2-D and 3-D structures, where a mobile handset and a scaled model of the shipboard are utilized as representatives. The prototype of the handset antenna was fabricated and measured, with the desired pattern achieved, having null in the boresight direction and being almost omni-directional on the plane of the chassis. The measured results agree well with the simulated ones. With the synthesized pattern, the handset antenna is robust to the user effects. The method can be generally applied to pattern synthesis for planar and 3-D antennas. [ABSTRACT FROM AUTHOR]

A planar angled-dipole antenna is investigated in this communication. The angled dipole has an intersection angle of 60°, radiating quasi-isotropic pattern with a gain difference of about 6.4 dB over the entire spherical radiating surface. To improve the isotropy of the antenna, two near-field parasitic elements (NFPEs) are further introduced. The NFPEs function as supplementary radiators and they help to enhance the radiation in the weak region, decreasing the gain difference significantly to 1.57 dB. For demonstration, a prototype operating at 2.4 GHz is fabricated and measured. The prototype shows a high efficiency of 90%, and the roundness is less than 2.59 dB across the entire impedance passband (2376–2526 MHz). [ABSTRACT FROM AUTHOR]

Reconfigurable array radiates multiple patterns with only a single array via designing multiple excitation vectors with common magnitudes for the same element-index excitation elements, so as to guarantee phase-only control. To tackle this problem, this article proposes a new reconfigurable array beampattern synthesis method. First, we borrow the concept of sensor network consensus computation and model the synthesis problem as a sensor network computation problem via imitating a virtual (conceptual) multinode sensor network, where each “node” corresponds to an individual beampattern synthesis task. More specifically, these “nodes” with the same number as those of radiated patterns share a set of common excitation magnitudes, which results in a special magnitude-consensus computation problem in the imitated sensor network. Then, via locally computing the excitation in each “node” and exchanging current computation results with neighboring “nodes,” all “nodes” obtain the magnitude-consensus excitations after the “network” is stable. Numerical examples are provided to demonstrate the validity and faster convergence speed of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a synthesis method for a shaped-beam pattern of the 2-D array antenna is proposed. The method is based on the array scanning principle and the superposition principle. The method can limit the ripple of the main beam by adjusting the sampling point interval and can easily achieve low sidelobe level (SLL). Compared to the stochastic optimization methods, this method has obvious time advantage when it is used to synthesize a large array antenna. The factors that affect the SLL, ripple, and dynamic range ratio (DRR) are discussed. Sparse array is used to reduce DRR. [ABSTRACT FROM AUTHOR]

An efficient pattern synthesis approach is proposed for the synthesis of large-scale 4-D antenna arrays in this paper. A 4-D antenna array is separated into two dependent “conventional arrays” with identical array structures, whose far-field radiation patterns correspond to the patterns at the center frequency and the sidebands, respectively. It is demonstrated that the problem can be formulated as a nonconvex programming problem. Mathematical transformation is then applied to change the nonconvexity with respect to the excitation coefficients. Therefore, the programming problem can be reduced to two dependent convex optimization problems, and convex optimization can be efficiently used to optimize the two problems. Owing to the introduction of the convex optimization, the proposed method is much more efficient than conventional approaches using brute-force evolutionary optimizations. Numerical examples of 4-D linear/planar arrays (≥1000 elements for each) are presented to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A novel approach, named multiple time modulation frequency, is proposed for the effective suppression of the sideband radiations in 4-D antenna arrays. The time modulation frequency, different for each array element, is exploited as additional design parameter to avoid the superposition of the sideband frequencies generated by the array elements. A customized optimization strategy including the analysis of the mutual coupling effects among the array elements is proposed for the 4-D array synthesis. Selected numerical and experimental results are provided to show that the sideband level of a 4-D antenna array can be significantly reduced by properly designing the switch-on time intervals of each element, even with uniform amplitude excitations. [ABSTRACT FROM PUBLISHER]

A technique for the synthesis of shaped beam radiation patterns is proposed. The new synthesis method is based on superposition principle and Taylor method. The method may control the sidelobe level of the shaped beam. The approach includes four steps: 1) get the distribution of pencil beam array with low sidelobe by Taylor method; 2) let the beams scan as a phased array to the specific angles according to the requirement of the shaped beam, The sum pattern is close to the shaping beam; 3) determine the value of angles and weights; and 4) count the distribution of the shaped beam array according to the new array factor function. Numerical results are provided to assess the capabilities of the proposed design method. The method develops an effective approach for the synthesis of shaped beams via uniform linear arrays. Both the ripple and sidelobe level of shaped beam may be controlled by the new synthesis method. [ABSTRACT FROM AUTHOR]

A novel design of the passive license plate radio frequency identification tag antenna in UHF band based on the characteristic mode theory (CMT) is proposed in this paper. The license plate is operated as a tag antenna since it is conductor (made of aluminum). A desired up-tilted pattern beam is achieved successfully by using a direct CMT-based radiation pattern synthesis procedure. The pattern can be expanded as a superposition of some specific characteristic modes pattern, which is identified according to characteristic mode analysis of the plate. Four coupling slots are exploited to excite the selected modes current distribution. The mode weighting coefficients can be tuned to form the desired pattern beam by changing the relative phase between the coupling slots. The feed structure is carefully designed without damaging the layout of characters and numbers on the license plate. The synthesized radiation pattern corresponds with the pattern simulated by HFSS. The measured radiation pattern proves that the proposed design is reliable and applicable. The measured read range is about 20 m, which can satisfy the actual requirements. [ABSTRACT FROM PUBLISHER]

An innovative technique based on the enhanced unitary matrix pencil (MP) method is presented for the design of sparse multiple-pattern linear arrays. By virtue of the equivalent MP obtained with a unitary transformation, the relation between the element positions and the generalized eigenvalues is achieved in this method, which contributes to the real solutions of the common element positions for all multiple patterns. Owing to the utilization of a unitary transformation that can convert a complex matrix to a real one, the computational complexity can be significantly reduced since only the real computations are involved in the singular value decomposition and eigenvalue decomposition procedures. Consequently, by only varying the obtained excitation distributions, different patterns are generated with a higher matching accuracy. Representative experiments are provided to validate the effectiveness and advantages of the proposed method. [ABSTRACT FROM PUBLISHER]

Nonuniform leaky-wave antennas (LWAs) are analyzed and synthesized using a lossy transmission line model. The analysis is based on a general waveguide circuit theory. Compared to the classical approach, the model yields a higher accuracy in the computation of both aperture field distribution and radiation patterns. The proposed analysis is also able to provide scattering parameters of the whole structure in a fraction of a second, which is valuable for antenna optimization. Based on the analysis, a general method for far-field pattern synthesis utilizing global optimization is presented. As an application demonstration, the half-mode substrate-integrated waveguide (HMSIW), or half-width microstrip line, has been selected as basis structure for the LWA designs. Two antennas have been optimized targeting different specifications, i.e., a low-sidelobe level and a wide null in the radiation pattern. Experimental results are provided for these selected examples of nonuniform LWAs, which ultimately validate the proposed technique as an improvement over the classical approach. [ABSTRACT FROM PUBLISHER]

This paper presents a study on linear frequency modulation (LFM) pulsed signal transmission by four-dimensional (4-D) antenna arrays. LFM pulse is used as the input of 4-D antenna arrays and the influence brought by the periodic time modulation is analyzed. The relationship among pulse duration, chirp rate, sample frequency, time-modulation frequency, and propagation direction is analyzed and the restrictions to these parameters are highlighted. The transmitting and receiving structures are introduced and relevant signal processing steps are described. Numerical examples with several different time schemes, including the pulse shifting (PS) scheme and binary phase center motion (BPCM) scheme, are presented to demonstrate the effectiveness of the LFM signal transmission by 4-D arrays. Simulation results validate that original chirp signal can be correctly recovered and low sidelobe power patterns can be simultaneously achieved by 4-D antenna arrays, as long as the proposed limitations are satisfied. [ABSTRACT FROM PUBLISHER]

A six-beam switched beam antenna (SBA), whose beam patterns are shaped in the azimuth plane, is designed and fabricated. A synthesis method, which is based on a four-elements array and can generate a flat-top beam pattern with 46° flat gain region (gain fluctuation within \pm \mathbf0.5\,\mathbfdB), 60° 3-dB beam width, and less than - \mathbf20.1\,\mathbfdB side lobe level (SSL), is proposed. By combining six of those beams together, the proposed SBA can provide near consistent gain and good interference rejection in the azimuth plane. Meanwhile, an interleaving array architecture, which minimizes the size of the proposed array, is also implemented. To extend the beam coverage, a series-fed in-phase array with tapered amplitude distribution is introduced in the elevation plane. The peak gain of the beam reaches 16.6 dB, and the SLL is controlled under - 23.2\,\mathbfdB in this plane. [ABSTRACT FROM PUBLISHER]

Pattern synthesis of nonuniform antenna arrays has drawn significant attention because of its wide applications. With the aim of reducing the number of elements in linear and planar arrays, this paper introduces a novel non-iterative method based on the filter diagonalization method (FDM), which was originally applied in the problem of identifying and quantifying chemical molecules with nuclear magnetic resonance (NMR) in quantum mechanical formalism. The proposed method samples the data set from the desired discrete pattern and associates the sample data with a time autocorrelation function of a fictitious dynamical system, which is described by an effective “Hamiltonian” operator that contains the array element information. The “Hamiltonian” operator can be decomposed by a set of orthonormal eigenvectors. Therefore, the original pattern synthesis is converted into solving the general eigenvalue decomposition with Krylov bases. The number of nonuniform array elements depends on the number of the Krylov bases and the sample data. The proposed method can obtain an optimized antenna array to reconstruct the desired radiation pattern with a high accuracy. Numerical examples show that proposed FDM pattern synthesis can use less prior knowledge to achieve the desired pattern with highly sparse antenna arrays. [ABSTRACT FROM PUBLISHER]

Time-modulated arrays (TMAs) are studied in the time domain and frequency domain in this paper. The studies are based on the “instantaneous” array factor as a function of time and “average” array factor as a function of frequency, respectively. The two analysis approaches are shown to be unified and complementary through the Fourier transform. Antenna parameters including pattern, directivity, and gain are all addressed. Moreover, an experimental setup for the study of signal transmission is built and measured. Experimental results are in good agreement with the theoretical study. Finally, the bandwidth of TMAs is taken into account, and amplitude modulation (AM) signal transmission through the TMA is studied experimentally. The results presented in this paper can be used to explain the fundamental working principle of TMAs in a clear and comprehensive way. [ABSTRACT FROM PUBLISHER]

An accurate and efficient direct optimization technique for the design of contoured beam reflectarrays is presented. It is based on the spectral domain method of moments assuming local periodicity and minimax optimization. Contrary to the conventional phase-only optimization techniques, the geometrical parameters of the array elements are directly optimized to fulfill the contoured beam requirements, thus maintaining a direct relation between optimization goals and optimization variables, and hence resulting in more optimal designs. Both co- and cross-polar radiation patterns of the reflectarray can be optimized for multiple frequencies, polarizations, and feed illuminations. Several contoured beam reflectarrays, that radiate a high-gain beam on a European coverage, have been designed and compared to similar designs obtained using the phase-only optimization technique. The comparisons show that the designs obtained using the proposed direct optimization technique are superior in performance, both for multi-frequency and dual-polarization designs. A reflectarray breadboard has been manufactured and measured at the DTU-ESA Spherical Near-Field Antenna Test Facility to validate the proposed technique. An excellent agreement of the simulated and measured patterns is obtained. [ABSTRACT FROM AUTHOR]

This communication introduces a hybrid invasive weed optimization and particle swarm optimization (IWO/PSO) algorithm dedicated to pattern synthesis of conformal arrays. A 3\, \times \,9 cylindrical conformal microstrip array is studied to demonstrate the proposed algorithm. The active element pattern of each element in the conformal array is extracted and the phase and amplitude of each excited voltage are optimized to achieve the required goals using the hybrid IWO/PSO algorithm. The results indicate that, compared with standard IWO and PSO algorithms, the introduced hybrid algorithm maintains the respective advantages of the IWO and PSO algorithms while excluding their respective deficiencies. Moreover, the hybrid algorithm is very reliable in achieving global optimality. [ABSTRACT FROM AUTHOR]

This communication presents results for the low sidelobe synthesis using amplitude-only tapering applied on the turned ON elements of large circular thinned arrays. The low sidelobe synthesis was carried out with the same iterative Fourier transform method that was developed earlier to restore the original sidelobe performance in case of defective array elements. The presented low sidelobe results refer to highly thinned circular arrays with diameters ranging from 25 to 133.3 wavelengths and involved both sum and difference patterns. In addition, sector nulling in combination with low sidelobes was numerical investigated. [ABSTRACT FROM PUBLISHER]

Recently, the iterative Fourier transform (IFT) method has been introduced for the synthesis of low sidelobe patterns for array antennas with periodic element arrangement. The IFT method makes use of the property that for an array with periodic element spacing, an inverse Fourier transform relationship exists between the array factor and the element excitations. This property is used in an iterative way to derive the array element excitations from the prescribed array factor using a direct Fourier transform. With some simple additions, the same IFT technique is also applicable to mitigate the degradation of sidelobe performance of array antenna caused by quantization of its taper across the array when using discrete control devices. Numerical examples of low sidelobe pattern synthesis applying compensation for taper quantization errors are presented. The results refer to both phase as well as amplitude tapering of linear arrays of various sizes. [ABSTRACT FROM AUTHOR]

We present the design and realization of a microstrip patch array antenna, which is operated at 24 GHz band, and can be used in the applications of vital-sign detection with a higher resolution. The design uses the steepest descent method (SDM) to synthesize the excitation phases of the array such that the radiation has an optimum near-field pattern in the desired area. Both theoretical development of SDM formulations and experimental validations over the antenna prototype are presented. [ABSTRACT FROM AUTHOR]

We present an efficient procedure for the synthesis of planar array antennas to radiate contoured patterns in the near zone of array aperture, as desired in RFID applications. It first grids the target area, and then utilizes a global basis set to span the array's excitations. Each basis's excitation of the array radiates a focused spot beam in the near zone and serves as a local basis function for representing the radiation field. The unknown coefficients of the array's basis set are then found via a minimum least square error (MLSE) technique. It is found that only a small number of basis functions are sufficient to synthesize the radiation pattern, and make the present approach very fast. [ABSTRACT FROM AUTHOR]

A novel embedded element pattern decomposition method is proposed to synthesize conformal phased antenna arrays. This method decomposes the embedded element patterns as a product of a characteristic matrix and a Vandermonde structured matrix. This Vandermonde matrix is composed of modes in the modal space at the sampling angles. Because the fast Fourier transform (FFT) algorithm can be used in the Vandermonde structure, the computational cost can be reduced tremendously. In addition to its computational efficiency, the proposed method is also applicable to the synthesis of a pattern with any mainlobe direction and optimized polarization. A modified particle swarm optimization (PSO) method is applied to optimize the weights of the modes. This method is demonstrated through a simulation of a 9-element conformal array. The results show the advantages of the new method in achieving a low peak side lobe, accurate mainlobe scanning, and low cross-polarization. [ABSTRACT FROM AUTHOR]

The minimization of the power losses in time-modulated arrays is addressed by means of a suitable strategy based on particle swarm optimization. By properly modifying the modulation sequence, the method is aimed at reducing the amount of wasted power, analytically computed through a very effective closed-form relationship, while constraining the radiation pattern at the carrier frequency below a fixed sidelobe level. Representative results are reported and compared with previously published solutions to assess the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

A high convergence rate and a robust exploration ability constitute a contradiction in modern heuristic optimization techniques. This paper describes a modified differential evolution strategy (MDES) that builds up a balanced relationship between the two contradictive elements by introducing several modifications into the conventional differential evolution strategy (DES). The novel MDES opens up an effective and robust approach for global optimization problems. Several representative mathematical functions are minimized using various optimization methods and the convergence rates are compared to evaluate the performance of MDES. Moreover, array synthesis examples which can be formulated as non-convex problems are presented, including the optimal synthesis of sum and difference patterns and the synthesis of unequally spaced arrays. Numerical results demonstrate that the proposed approach improves the performance of the algorithm significantly, in terms of both the convergence rate and the exploration ability. [ABSTRACT FROM PUBLISHER]

Given an antenna array of N elements, we deal with the problem of finding an array pattern that approximates a desired pattern, while: a) null constraints are imposed in M(≤ N- 2) assigned directions; b) an upper bound D is imposed on the dynamic range ratio (DRR) of the excitations. At first we show that the system of constraint equations has solutions if and only if D ≥ D0, where D0 is a parameter depending on the null directions, and describe a method to evaluate D0. Then we propose two simple and fast algorithms to solve the synthesis problem and show their effectiveness by numerical examples. Statistical results show that usually D0 = 1 when M is small compared to N, thus exact nulls can be formed for any D 0≥1. This result provides an insight into the numerical results. [ABSTRACT FROM AUTHOR]