Low Sidelobe Patterns Research Articles

Fast Low-Sidelobe Pattern Synthesis Using the Symmetry of Array Geometry.

Array pattern synthesis with low sidelobe levels is widely used in practice. An effective way to incorporate sensor patterns in the design procedure is to use numerical optimization methods. However, the dimension of the optimization variables is very high for large-scale arrays, leading to high computational complexity. Fortunately, sensor arrays used in practice usually have symmetric structures that can be utilized to accelerate the optimization algorithms. This paper studies a fast pattern synthesis method by using the symmetry of array geometry. In this method, the problem of amplitude weighting is formulated as a second-order cone programming (SOCP) problem, in which the dynamic range of the weighting coefficients can also be taken into account. Then, by utilizing the symmetric property of array geometry, the dimension of the optimization problem as well as the number of constraints can be reduced significantly. As a consequence, the computational efficiency is greatly improved. Numerical experiments show that, for a uniform rectangular array (URA) with 1024 sensors, the computational efficiency is improved by a factor of 158, while for a uniform hexagonal array (UHA) with 1261 sensors, the improvement factor is 284.

Mitigating Peak Sidelobe Levels in Pulse Compression Radar using Artificial Neural Networks

In this paper, Artificial Neural Networks (ANNs) are being considered to obtain low sidelobe pattern for binary codes and thereby to improve the performance of pulse compression radar. Pulse compression is a popular technique used for improving range resolution in the radar systems. This paper proposes a new approach for Pulse Compression using various types of ANN networks like Multi-Layer Perception (MLP), Recursive Neural Networks (RNN), Radial Basis Function (RBF) and Recurrent Radial Basis Function (RRBF) and a special class of Feed-Forward Wavelet Neural Network (WNN) with one input layer, one output layer and one hidden layer are being considered. Networks of 13-bit Barker code and extended binary Barker codes of 35, 55 and 75 length codes were used for the implementation and thereby to improve the performance of pulse compression radar. WNN-based networks using Morlet and Sigmoid activation function in hidden and output layers respectively, a special class of Artificial Neural Network is considered in this paper. The performance metrics used are Peak Sidelobe Ratio (PSLR), Integrated Sidelobe Ratio (ISLR) and Signal-to-Sidelobe Ratio (SSR). Further the performance in terms of range and Doppler resolution is also presented in this paper. Better performance in terms of sidelobe reduction can be achieved with ANNs compared to Autocorrelation Function (ACF) called as matched filter. If the sidelobe values are high there is possibility of masking weaker return signals and there by detection becomes difficult. From this paper it can be established that RRBF gives better result than other ANN networks. Further, WNN gives the best performance even compared with RRBF in terms of sidelobe reduction in pulse compression radar.

Design of Millimeter Wave Radar Antenna Array with Flat-top Pattern

In this paper, a planar millimeter wave radar array antenna with flat-top pattern is proposed for wide detection angle. Firstly, the Chebyshev synthesis method is used to design the linear array with high gain and low sidelobe pattern which works in the 24 GHz frequency band. The maximum gain of the linear array is roughly 15 dBi, and the main-sidelobe ratio is close to 20 dB. By setting the excitations and phases distribution of the planar array feeding network, a 5××4 antenna array with a flat-top pattern is obtained. The simulated and measured results show that the radar antenna array has a wide half-power beamwidth of 88 degrees, which can ensure that the automotive radar has a longer detection range and a larger monitoring angle.

Low-Sidelobe Pattern Synthesis for Spaceborne Array Antenna Based on Improved Whale Optimization Algorithm

For the purpose of fulfilling the low sidelobe level (SLL) requirements for spaceborne phased array antenna pattern synthesis, this paper proposes a new improved whale optimization algorithm (IWOA). As a type of new heuristic algorithm inspired by whale hunting behavior, WOA has the advantages of simple structure, few parameters, fast optimization speed, and high precision. In this paper, improvements are made in three aspects of adaptive weight, spiral coefficient optimization, and optimal neighborhood perturbation, and the proposed algorithm is successfully applied to the intelligent calculation of antenna synthesis. In light of the engineering requirements, the mathematical model of the optimization problem is established, and the desired antenna pattern with high gain and low sidelobe is obtained using IWOA under the constraint that the amplitude variation is within 20 dB. Simulation results demonstrate that IWOA is superior in maximum sidelobe level (MSLL) suppression and convergence. Consequently, EM simulations were conducted on a 64-element planar array, with the results consistent with the theoretical simulation, verifying the feasibility and effectiveness of the proposed algorithm.

Synthesis of Low Sidelobe Pattern with Enhanced Axial Radiation for Sparse Conformal Arrays Based on MCDE Algorithm

A hybrid optimization method for the synthesis of a sparse conformal array with the verification of a truncated cone antenna array is proposed in this manuscript. This array synthesis is studied aiming at enhancing axial radiation and reducing the peak sidelobe level (PSLL) by figuring out the optimal antenna element arrangement and corresponding feeding scheme. A multi-agent composite differential evolution (MCDE) algorithm is established by integrating a multi-agent system (MAS) with a differential evolution (DE) algorithm. In addition, a hybrid strategy method and a time-varying weighting factor are added to the mutation operator to accelerate convergence. Two examples of 64-element and 900-element truncated cone antenna arrays were synthesized. After forming a sparse antenna array out of the original full array, the number of antennas was decreased to 80% and 56.8%, respectively. The results show that the main beam of the sparse conformal antenna array is accurately fixed to the axial direction with the PSLL less than −20 dB at both the φ = 0° and φ = 90° planes, which proves the effectiveness of this method in conformal sparse array synthesis.

Design of Ka band substrate integrated waveguide slot traveling wave array antenna

Aiming at the requirements of Missile Radio Fuze Antenna with low sidelobe, narrow beam and specific directional pattern, a design method of Ka band substrate integrated waveguide (SIW) slot traveling wave array antenna is proposed. Based on the slot theory of SIW, the slot parameters and the excitation amplitude of Taylor linear array elements are calculated by MATLAB, and then the slot parameters and the excitation amplitude of array elements are optimized by Ansoft HFSS electromagnetic simulation software to realize the design of Ka band SIW slot traveling wave array antenna. The simulation results show that the Ka band SIW slot quasi traveling wave array antenna has a working frequency of 34.5 GHz, a gain of 14.2 dB, an E-plane beam width of 8° and a beam inclination of 20°, which can meet the requirements of missile radio fuze.

A Method for Designing Unequal Power Divider for Implementing Antenna Array Excitations

In this paper, a method for designing a feeding network to obtain a low peak sidelobe pattern of an 8*1 linear antenna array is proposed. The optimized element weights were first obtained using genetic algorithm. Then two different networks based on equal and unequal power dividers are designed for the linear antenna arrays. In an equal power divider structure, the power is divided equally into all branches of the network to reach the final ports, while in the unequal structure; the division is only made equal in some branches and unequal in other branches to build an unequal power divider. In the two methods, the design process is based on two stages, the first stage uses a T-junction power divider, and the second stage a Wilkinson power divider is used. In an equal power divider, T-junction and Wilkinson divide the power equally, while in the case of an unequal power divider the T-junction divider is only unequal. In the two designs, the feeding network is designed according to the following specifications: the substrate (FR-4 with ϵr =4.3) and ground dimensions are 440.4mm × 103.8mm ×1.6 mm and 440.4mm × 103.8mm × 0.035mm respectively, and at a resonant frequency of 2.36 GHz. The simulation results showed the effectiveness of the designed power dividers that to be used as a feeding network in the linear antenna arrays.

Technique for spatial interference reduction and its application in monopulse radar with active phased array antenna

The paper describes monopulse radar with sidelobe-blanking system. The antenna of the sidelobe-blanking system is one subarray of the radar’s active phased array antenna. The elements of the subarray is also used for sum and difference pattern generation. It is shown that if aperture distribution required to produce low-sidelobe sum pattern is used, the pattern of one subarray will satisfy the requrements for antenna of the sidelobe-blanking system. An example of designing the monopulse radar with sidelobe-blanking system is presented. Sum pattern of the radar anettena is produced with different low-sidelobe pattern synthesis procedures. The analysis of monopulse radar parameters and sidelobe-blanking system performance is done.

Phased Sub-arrays Pattern Synthesis Method with Deep Sidelobe Reduction and Narrow Beam Width

ABSTRACT Antenna arrays with low sidelobe patterns and high directivities are very desirable in practice and represent a key success for many communication systems such as radio telescopes, satellites, fifth-generation (5G) wireless communication systems, and high detection radars. To meet these features, a new array pattern synthesis method based on two uniformly sub-arrays controlled by a pre-specified power factor is presented. The proposed method includes the following steps: first, the outputs of those two scanned sub-arrays are added and subtracted to generate the sum and difference patterns, respectively. The sidelobe structures of these two generated patterns are nearly identical, then, an array pattern with greatly reduced sidelobes and narrowed beam width can be obtained by simply subtracting the difference pattern from the sum pattern. Simulation results show that the proposed array pattern with power factor, e = 0.5, can provide a sidelobe level about −32 dB (i.e. an improvement about −19 dB with compared to that of the corresponding fully uniform array). Moreover, the beam width of the proposed array has been greatly narrowed. Better results can be also obtained by controlling the scanned angles of the two sub-arrays.

Affine transformation for synthesis of low sidelobe patterns in planar array antennas with a triangular element grid using the IFT method

This study deals with the affine transformation that is used to convert the triangular element grid of a planar phased array antenna into a square one. By means of this kind of transformation, it is possible to apply the iterative Fourier transform (IFT) method to synthesise low sidelobe tapers for array antennas featuring a triangular grid. Combination of the IFT method with an affine transformation allows the synthesis of low sidelobe tapers of which the peak sidelobe level does not vary with changing frequency and/or altering main beam position. The considered affine transformation was already briefly addressed in earlier publications of this author. In this study detailed information is given on its use in combination with the IFT method. Examples to demonstrate the effectiveness of the combination affine transformation and the IFT method for triangular grid array antennas are given. It will be shown that the peak sidelobe levels of the obtained tapers are invariant with frequency and scan angle when all far-field directions of the array factor are involved in the low sidelobe taper synthesis.

Synthesis of Low-Sidelobe 4-D Heterogeneous Antenna Arrays Including Mutual Coupling Using Iterative Convex Optimization

A novel iterative convex optimization approach is proposed for the synthesis of low-sidelobe 4-D heterogeneous arrays in the presence of mutual coupling effect. To realize wide bandwidth and wide-angle scanning, a tightly coupled dipole element (TCDE) is selected as the basic element. Due to the strong coupling between antenna elements, the active element pattern (AEP) and active reflection coefficient (ARC) are included in the proposed approach in order to evaluate the overall mutual coupling and port matching. Specifically, a nonconvex programming problem in terms of the given maximum sidelobe level (SLL), the ARC or reflected power at the center frequency, and the given maximum sideband level (SBL) at sidebands is established. After the application of some mathematical transformations, the nonconvex programming problem is decomposed into a convex optimization problem at the center frequency and an iterative convex problem (ICP) at sidebands. Owing to the efficiency of the convex optimization, the two problems can be efficiently solved. The proposed approach is applied to synthesize low-sidelobe patterns while minimizing the SBL in a 32-element cone-shaped 4-D heterogeneous array. The simulated and measured results verify the effectiveness of the proposed approach and show the advantages (improved gain) of the heterogeneous array.

Traveling-Wave Series-Fed Patch Array Antenna Using Novel Reflection-Canceling Elements for Flexible Beam

The methodology of designing traveling-wave series-fed patch array antennas (TSPAAs) based on reflection-canceling elements for flexible radiation pattern has been proposed. By introducing a quarter-wave transformer as the reflection-canceling structure, the cascaded patch antenna with tapered width can be used as the reflection-canceling element for a nonuniformly spaced TSPAA. Because of its simple structure, the parameters of the transformer can be determined directly by the corresponding equivalent circuit. To achieve a flexible radiation pattern, the array aperture distribution can be controlled by changing the element width (for amplitude distribution) and the element spacing (for phase distribution). In this method, the initial array is synthesized through a genetic algorithm approach, and a simulation-based iterative process considering the accurate mutual coupling is developed to optimize the initial array. To evaluate the proposed method, two different types of 14-element linear arrays operating at ISM 24GHz are implemented for a low sidelobe pattern and shaped-beam pattern, respectively. The two arrays are both simulated, fabricated and measured, the measured results show reasonable agreement with the simulation results, which verifies the effectiveness and correctness of the proposed method in this paper.

Range-angle-dependent beamforming with FDA using four-dimensional arrays

By virtue of its low sidelobe and multibeam pattern characteristic, four-dimensional time-modulated array (TMA) has been attracting considerable attention. Recently, a novel frequency diverse array (FDA), with flexible beam scanning characteristic, has been proposed. So far, TMAs and FDAs are investigated separately, but their integration which may possess both advantages has rarely been reported in the literature. In this paper, a new range-angle-dependent time-modulated frequency diverse array (TMFDA) is proposed. By introducing time-modulated radio frequency switches into the beamfoming network of an FDA, TMFDA can achieve range-angle-dependent patterns, both at the carrier frequency and at the sidebands. Additionally, TMFDA has a unique advantage in that its beam direction of the sidebands can be tuned by the pulse duration, switch-on instant and frequency shift, which offers greater design freedom, enabling better performance and a reduction of hardware requirements over FDA. Moreover, the TMFDA has low sidelobe and multibeam pattern characteristic in the joint range and angle domains. Numerical results are presented to validate the superiority of TMFDA characteristics in terms of achieving low sidelobe level, low sideband level and multibeam beamforming.

Radiation Performance Characteristic Optimization of Time-Modulated Circular Antenna Arrays

ABSTRACTIn this paper, memetic flower pollination algorithm (MFPA) is proposed for solving the optimal synthesis of time-modulated half symmetric circular antenna array (TMHSCAA) and time-modulated asymmetric circular antenna array (TMASCAA) by controlling the switching time sequence and the excitation phase of each element time intervals and phases. Current excitation and inter-element spacing of each element are kept uniform. A unique cost function has been formulated for both the case studies. Several low-side lobe patterns synthesized from TMHSCAA and TMASCAA have been compared with those of the conventional circular array. A 20- and 36-element TMHSCAA and TMASCAA have been taken as examples. Furthermore, a novel six-ring time-modulated concentric hexagonal antenna array (TMCHAA) design has been considered to check superiority of the MFPA. The cost function has been designed for the concurrent improvement of side lobe level (SLL) and directivity in the new geometry of TMCHAA by an appropriate fine-tuning of the switching time succession and the inter-element separation of the hexagonal ring. Numerical results show that TMHSCAA, TMASCAA, and TMCHAA can be successfully used for the synthesis of low SLLs even if the amplitude excitations and inter-element spacing are uniform. Statistical analysis is also carried out to ensure that the results are significant in terms of the statistics. The results show that MFPA can exhibit a better performance than the other algorithms like real-coded genetic algorithm, particle swarm optimization, and differential evolution for the antenna array synthesis examples.

A New Low-Sidelobe Pattern Synthesis Technique for Equally Spaced Linear Arrays

A class of nonuniformly excited, equally spaced linear arrays (ESLAs) that can meet design requirements for half-power beamwidth and sidelobe level (SLL) without any limitation is introduced. These arrays are constructed using the patterns of uniformly excited arrays as building blocks, thus lending themselves to simple analytical descriptions and analysis. A design procedure is presented, which can be used to determine the required number of elements and the excitation currents to achieve the specified radiation properties. For these arrays, the element currents always decrease monotonically from a maximum at the array center to a minimum value at edge elements. This property can be exploited to limit the current taper ratio (CTR) when the number of elements is very large. Simulation results indicate that these arrays can provide half-power beamwidths, directivities, and SLLs comparable to those of other desirable array choices, such as Chebyshev arrays, with the same number of elements and interelement spacings. It is shown that, in fact, when the number of elements is sufficiently large, the array introduced here outperforms the Chebyshev array by providing larger directivity and allowing a smaller CTR to be achieved. Numerical results for broadside and endfire arrays are given.

Identifying and Compensating for Phase Center Errors in Wing-Mounted Phased Arrays for Ice Sheet Sounding

Highly crevassed ice surfaces at ice-sheet margins and fast-flowing glaciers significantly scatter radar signals. The scattered signals, often known as surface clutter, mask weak echoes from the ice-bed interface. Large wing-mounted antenna arrays are essential to synthesizing low-sidelobe patterns to reduce surface clutter. However, wing-mounted arrays are susceptible to structural flexure, which causes amplitude and phase errors that result in shifting and filling of desired array pattern nulls. In this communication, we characterize the effects of wing flexure on array beamformation using a scaled array model, and we present a compensation method to mitigate phase center errors caused by wing flexure. The compensation greatly improves clutter suppression through improved null formation. Experimental results show that we obtain an average of 7.5 dB improvement in the signal-to-interference noise ratio.

Cluster Analysis for the Synthesis of Subarrayed Monopulse Antennas

The design of monopulse radar systems requires the synthesis of both a sum pattern and a difference pattern, which is quite flexible and hard to be optimized for subarrayed antennas. In this study, innovative approaches to synthesize the optimal sum and difference patterns independently for subarrayed monopulse arrays are presented. By exploiting the relationship of the subarray partition and optimal excitations, the synthesis problem is formulated as the clustering of a set induced by the optimal excitations. Thus, the optimal subarray partition is transformed to a clustering problem. A clustering method is presented to solve the array synthesis with uniform excitation at element level. Furthermore, an improved approach is proposed to synthesize low sidelobe patterns. When compared with several classical approaches, various numerical experiments validate the effectiveness and potentiality of the proposed methods.

Comparison of Correction Techniques and Analysis of Errors for Digital Beamforming Antenna Array With Single RF Receiver

A new correction method is proposed for the single RF channel digital beamforming (DBF) antenna array. In this array, each array element is followed by a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$0/\pi$</tex></formula> phase shifter, and the element outputs can be recovered by the single channel through the time sequence phase weighting (TSPW) technique. The outputs can be used to form desired beams through DBF. The performance of the DBF is influenced by the imperfection of the phase shifters. To obtain the errors in each phase shifter, the online test method based on a single known plane wave is introduced. The online test results are used to correct the element outputs using the relationship between the actual and the incorrect outputs. Compared with another previously proposed correction method, the new method is simpler and more suitable for real time correction. The factors that may influence the capability of the correction are analyzed. To validate the proposed method, an eight-element prototype is measured, and the data are used to synthesize low sidelobe patterns. Results show that the sidelobe level and gain improvements after correction are 11.1 and 2.6 dB, respectively.

Hybrid alternate projection algorithm and its application for practical conformal array pattern synthesis

Based on the fabricated 12-element cavity-backed microstrip sector cylinder array, a novel hybrid alternate projection algorithm (HAPA), which combines analytical method with numerical techniques effectively, is proposed for synthesizing the pattern of practical conformal array. The algorithm applies the variable direction aperture projection method with mutual coupling correction techniques to provide the good initial excitations of elements to the enhanced alternate projection algorithm (EAPA). In order to do further optimization, which improves the convergent speed of the algorithm significantly. Finally, the HAPA has been applied to the fabricated sector cylinder array with mutual coupling considered. The results of synthesized patterns, such as low sidelobe with null points formed pattern, beam scanning with low sidelobe pattern and the shaped beam pattern are presented. It demonstrates the validity of HAPA in practical conformal array synthesis.

Sideband level suppression in time-modulated linear arrays using modified switching sequences and fixed bandwidth elements

A new technique for suppressing the sideband levels in time-modulated linear arrays (TMLAs) is presented. The technique utilises the fixed bandwidth of the radiating elements of the array to act as bandpass filters to suppress the out-of-band harmonics generated by the time-modulation process. The approach is combined with a new element switching sequence that can be designed to redistribute the dominant harmonic components of the TMLA to predetermined frequencies that are outside the bandwidth of the array elements. The proposed technique does not require the use of complicated optimisation procedures to generate the TMLA switching sequences and is applicable to a TMLA configured to synthesise arbitrary low sidelobe patterns. Numerical results are presented to illustrate the proposed approach by considering a 16-element array of patch antenna elements designed to provide a -30 dB Chebyshev sidelobe level radiation pattern.