Sidelobe Performance Research Articles

Optimization of Sparse Frequency Diverse Array With Time-Invariant Spatial-Focusing Beampattern

The optimization of the sparse time-modulated optimized frequency offset frequency diverse array (S-TMOFO-FDA) with time-invariant spatial-focusing beampattern is presented. The minimum array with smallest number of elements is obtained through iterative optimization. From numerical results, the S-TMOFO-FDA can provide above 70% reduction in the element amount while displaying superior sidelobe performance than the same aperture-sized full uniform time-modulated logarithmically increasing frequency offset frequency diverse arrays. Furthermore, the scanning performance of the optimized array is also investigated. The S-TMOFO-FDAs of different array length are optimized.

Unified coprime array with multi-period subarrays for direction-of-arrival estimation

The original coprime array is a sparse geometry with a pair of one-period subarrays, where the interelement spacing and number of sensors are coprime so that no elements overlap except at the zeroth position. In this paper, we unify the coprime array by extending two subarrays from one period to multiple periods. Each subarray can have an arbitrary number of periods and therefore more than one element of the unified structure coincide. The resulting configuration treats the nested array as well as the existing coprime structures, such as the original coprime array, the extended one and the coprime array with compressed inter-element spacing (CACIS) as its special cases. The new coprime array has a lower peak side-lobe level than the nested array and the CACIS. An improved structure based on the multi-period coprime array is further proposed to improve the degrees-of-freedom (DOF) of the unified geometry with one of the subarrays displaced by a certain number of spacings. Although the improved configuration does not reach the same DOF as the CACIS and the coprime array with displaced subarrays (CADiS), it can acquire a low peak side-lobe level with the DOF not being decreased too much. Different from CADiS, we focus on the analysis and proper choice of the displacement to acquire more consecutive lags. The properties of coarray of the proposed array design strategy are provided as well. Finally, the direction-of-arrival estimation, physical aperture and peak side-lobe level performance of the unified structures are examined through numerical simulations.

Application of Computer Identification and Location Algorithm in Small far Infrared Target Recognition of Ship Under Surge Interference

Abstract The small far infrared target of ship in surge interference is easy to have visual deviation causing the low accuracy of target positioning and the bad target identification performance. In order to improve the accuracy of far small infrared targets recognition of ship under surge interference, this paper proposed far small infrared target recognition algorithm of ship based on distributed target position estimation and DOA location in computer vision model for constructing coherent distributed source array model of far small infrared target distribution of ship. This algorithm used MUSIC algorithm for the beamforming processing of far small infrared target echo model of ship. Combined with the adaptive filtering algorithm we carried out the surge interference suppression and the estimation of central direction of arrival and angle spread of far small infrared target of ship through multidimensional spectrum peak searching algorithm, realizing the joint estimation of distance of ship target, DOA and frequency parameters, so as to realize the accurate positioning and recognition of targets. Simulation results show that using this method for the far small infrared target recognition of ship under surge interference, the spectral peak sharpness of spectral peak search of target position is high, side-lobe suppression performance is good, which shows the high accuracy of target position estimation and location, the accuracy and anti-interference performance of far small infrared target recognition of ship is good, and has superior performance.

Four harmonic analysis and energy metering algorithms based on a new cosine window function

In order to further improve the calculation accuracy of the windowed fast fourier transform (FFT) interpolation algorithm, this study proposes a four-order Hanning self-multiplication window, and based on this new window function, four kinds of windowed FFT interpolation algorithms for harmonic analysis have been derived, include single-spectrum-line interpolation, double-spectrum-line interpolation, triple-spectrum-line interpolation and four-spectrum-line interpolation. Using these four harmonic analysis algorithms, the amplitude, phase and frequency of the fundamental and harmonic in the measured voltage and current signal can be obtained, and then the fundamental and harmonic energy can be calculated accurately by using the energy metering equation. The simulation results show that the window function has better main lobe and side lobe performance, which can effectively suppress the influence of spectrum leakage and fence effect, so based on this window function, the four harmonic analysis and energy metering algorithms can inhibit the effect of fundamental frequency fluctuation, and with the number of spectrum lines increasing, the computing accuracy of the algorithm is improved.

Synthesis of Scan- and Frequency-Invariant Low-Sidelobe Tapers for Planar Array Antennas

The impact of the array factor (AF) on the synthesis of a low-sidelobe taper for planar array antennas with a periodic element grid is investigated. A low-sidelobe taper that is synthesized for those far-field directions of the AF belonging to only visible direction, cosine $u$ - $v$ space, can seriously deteriorate with respect to peak sidelobe level (PSLL) when the main beam is scanned or the operating frequency is raised. In order to get a scan- and frequency-invariant taper, its synthesis must comprise all far-field directions of the AF including those of invisible $u$ - $v$ space. This communication describes the Fourier properties responsible for the degradation of taper sidelobe level performance when the taper synthesis excludes the invisible space region of the AF. Examples are presented for a circular array antenna to illustrate the impact of the invisible region of the AF on sidelobe performance. The presented results refer to phase-only and amplitude-only sidelobe tapers. The requirements to realize for aperiodic planar array antennas’ scan and frequency proof patterns with invariant PSLL are shortly addressed.

Perfect orthogonal waveform scheme used for high-resolution multiple-input multiple-output synthetic aperture radar system

We investigate multiple-input multiple-output (MIMO) synthetic aperture radar (SAR) scheme with an ultra-low side-lobe ratio performance for using complete complementary sequences (CCS) waveform. It is shown that the CCS can be applied in a MIMO SAR system to obtain high resolution in range direction. In addition, the azimuth channel scheme with the multiple subsequences of CCS is also considered. First, we introduce the concept of CCS and establish the transmitter model based on CCS in MIMO SAR system. Then, we propose the corresponding imaging algorithm for employing the CCS to accurately focus the raw data of the MIMO SAR system and derive the range cell migration correction. Considering the signal complexity, we make use of the CCS pairs to analyze the MIMO SAR imaging algorithm. Finally, simulation results demonstrate the validity and feasibility of the proposed MIMO SAR scheme and the potential advantage of CCS.

Prototype filter design for QAM-based filter bank multicarrier system

In this paper, we provide conditions for a prototype filter design of filter bank multicarrier (FBMC) based on quadrature amplitude modulation (QAM). The conditions consist of a generalized Nyquist criterion (GNC) for nearly perfect reconstruction (NPR) and meeting the stopband condition for a small side-lobe. In a practical environment, a small side-lobe is a key aspect of achieving high spectral efficiency, which becomes an important factor in reducing the size of the guard band among channels. In addition, because the conventional GNC is derived under the assumption of an ideal channel, which can be easily broken over a practical multipath channel, we propose a relaxed NPR that considers the multipath delay using a 2L-oversampled discrete Fourier transform (DFT) in the frequency domain. Based on the relaxation of the GNC depending on a multipath channel, we formulate an optimization problem for a QAM-FBMC prototype filter design and propose a prototype filter with a small side-lobe and reliable BER performance. Simulation results show that the proposed prototype filter remarkably reduces the side-lobe compared to conventional QAM-FBMC based on two types of prototype filters and orthogonal frequency division multiplexing (OFDM) via the trade-off between GNC and side-lobe performance. The benefit of the side-lobe condition allows the proposed prototype filter, the Relaxed-NPR-F, to improve spectral efficiency by reducing the guard band in the frequency domain.

Compact Corrugated Feedhorns With High Gaussian Coupling Efficiency and <inline-formula> <tex-math notation="LaTeX">$-60\;\text{dB}$</tex-math> </inline-formula> Sidelobes

We demonstrate that very high performance, extremely compact, scalar corrugated feedhorns can be designed and constructed by optimizing the excitation and phasing of the ${\rm HE}_{11}$ , ${\rm HE}_{12}$ , and ${\rm HE}_{13}$ modes near the throat of the horn while limiting excitation of higher order modes. We present the design and measurement of two families of dual-profiled horn, both with a directivity of 20 dBi that couple with very high efficiency to a fundamental Gaussian mode. The first was optimized for sidelobe performance and features sidelobes approaching $-$ 60 dB for a horn length of only 15.6 ${\lambda}$ . The second was designed to minimize horn length and to achieve sidelobe levels below $-35\;\text{dB}$ for a horn that is only 4.8 ${\lambda}$ long. The horns exhibit excellent coupling to the fundamental free-space Gaussian mode, with ${\rm LG}_{00}$ power coupling of 99.92% and 99.75%, respectively. We demonstrate excellent agreement between simulation and experiment at 94 GHz and simulate the performance over a 20% bandwidth. High-performance compact scalar horns are of interest because they reduce manufacturing risk at high frequencies, and reduce size and weight at lower frequencies, which can be important in horn arrays and space applications, where horn arrays often have serious weight and size restrictions.

Sparse frequency waveform analysis and design based on ambiguity function theory

This study presents new insights into sparse frequency waveform analysis and new waveform design methods. For a general radar waveform, the total ambiguity in its auto-correlation function (ACF) is equal to the total energy in its power spectral density (PSD) in the frequency domain. With this relationship, the total ambiguity in an ACF is found to be minimised when the corresponding PSD is uniformly distributed. This property is extended to the sparse frequency waveform by establishing the relationship between the optimal PSD and the minimum ambiguity in ACF. Based on this analysis, a new method of designing sparse frequency waveform with sidelobe constraint is proposed. The new method simultaneously optimises the sidelobe performance and the PSD performance through constrained non-linear optimisation. This is different from existing methods that compromise the performance of sidelobe to the performance of PSD in an ad-hoc manner by minimising the weighted sum of the total power in the stopbands and the total power in the sidelobe. The analysis and the design method have been extended to the case of multiple sparse frequency waveforms. Simulation studies are provided to demonstrate the effectiveness of the proposed new design methods.

Improvement in side-lobe performance of prime focal reflector antenna

This paper presents a simple and elegant solution to improve the degradation of side lobe level (SLL) caused by strut and feed system blockage in prime focal reflector antenna system. This is accomplished by numerical optimization of reflecting wedges, which may be integrated with conventional rectangular cross-sectional struts. Design, optimization and analysis of metallic sheet feed cover have been carried out to reduce diffraction caused by the feed system. Quadrilateral meshing is used to analyze non-standard scatterers. Comprehensive analysis results showing frequency response of SLL of antenna system have been discussed, for different antenna component assemblies. A novel method has been implemented to understand the effect of wedged struts and feed cover for SLL improvement. Experimental data have also been presented to validate the simulated antenna parameters. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1304–1311, 2016

Low Side-Lobe Substrate-Integrated-Waveguide Antenna Array Using Broadband Unequal Feeding Network for Millimeter-Wave Handset Device

A low side-lobe substrate-integrated-waveguide (SIW) antenna array is presented at the 28-GHz band using broadband unequal feeding network for millimeter-wave (mm-wave) handset devices. The ground-plane size of the proposed antenna is fixed to half of the size of the Samsung Galaxy Note 4. The antenna array has been implemented with a multilayer structure created by stacking three substrates and a copper plate. An 8-way SIW feeding network with broadband 4-stage T-junction dividers and a cavity-backed antenna are investigated to obtain broadband performance. The proposed unequal T-junction dividers with phase compensation are introduced and designed for various output ratios. Applying Taylor beam-pattern synthesis in the 8-way SIW feeding network, low side-lobe performance is achieved. The measured result of the fabricated antenna has 2.3 GHz bandwidth within $\text{S}_11\,{ . The fabricated antenna can be performed with a gain up to 13.97 dBi with a low cross-polarization and symmetrical fan beam radiation patterns with low side-lobe levels. Most of the measured results are validated with the simulated results. The proposed antenna array provides low cost, broadband performance, and good radiation performances with low side-lobe levels for mm-wave handset devices.

CPW-Fed Printed Antenna Array With Conical Beam

A printed antenna array with conical beam is presented. Coplanar waveguide (CPW) is used to feed the antenna. Loop slots with finite width of ground plane, which play the role of radiating elements are arranged collinearly to form a traveling wave antenna array. The widths of the loop slots are adjusted to achieve low sidelobe performance. The design procedures are proposed and a 16-element array with beam-pointing angle of 77° is fabricated and measured to verify the design. The measured 15-dB return loss bandwidth is 11.4% at central frequency of 10.5 GHz. The measured gain and the sidelobe level are 10.3 dBi and $-20\;\text{dB}$ , respectively. The agreement between the measured and the simulated results is acceptable.

Robust Capon beamforming with weighted sparse constraint

Adaptive beamforming is widely used in the fields such as radar, sonar, wireless communication to estimate the parameters of the signal of interest (SOI) at the output of a sensor array by data-adaptive spatial filtering and interference suppression. The standard Capon beamformer (SCB) is a typical adaptive beamforming approach which provides a superior performance by minimizing the array output power while simultaneously maintaining the array response under the assumption of distortionless direction of arrival (DOA). However, the advantages in performance of SCB are obtainable only when the number of snapshots available for the sample covariance matrix estimation is large enough and the direction of the SOI is known accurately. When applied to practical situations where the aforementioned two requirements are not satisfied, SCB will suffer high sidelobe levels and performance degradation in the parameter estimates due to lack of measurements and mismatch in the steering vector.A sparsity-constrained Capon beamformer (SCCB) arises to alleviate these problems. Unlike SCB, the constraint in SCCB is composed of two parts: the original array output power constraint part and the sparse constraint part (?1 norm constraint, encouraging sparse distribution in the array responses). However, if the sparse constraint in SCCB is set too large compared with the array output power constraint part, the responses in the directions of interferences will be influenced, and a tradeoff between the ability to reduce the sidelobe levels and the ability to reject the interferences must be made. Thus, based on the SCCB, a new robust Capon beamformer utilizing a weighted sparse constraint is proposed in this paper. In the proposed method, the sparse constraint part is replaced by a weighted sparse constraint, which is applied only to the sidelobe regions of the beampattern. By doing so, the number of the non-zero elements in the sidelobe response is minimized, resulting in an enhanced mainlobe region and suppressed sidelobe ones.In sparse recovery, the sparse constraint (the l1 norm constraint) does not necessarily enforce democratic penalization, which means that larger coefficients are penalized more heavily than smaller coefficients. Based on such a consideration, a weighting matrix can be constructed to put larger weights in the interferences directions to discourage their responses, and put smaller weights to maintain the responses in the remaining parts of the sidelobe regions. In this paper, the weighting matrix is obtained by utilizing the orthogonality between the signal subspace and the noise subspace. Since the steering vectors corresponding to the interferences and the SOI span the same space as the signal subspace, the inner products between the steering vectors in the interference directions and the noise subspace will produce zeroes ideally. By taking the reciprocals of these inner products, large values will yield in the interference directions while small values are obtained in other directions in the sidelobe regions. Using these values as the weights to the sparse constraint, a beampattern with deeper nulls, lower sidelobes, and better robustness to steering vector mismatch is obtainable as compared with SCB and SCCB. Besides, the output SINR is also effectively improved. Numerical simulations and a water-tank experiment are conducted to demonstrate the effectiveness of the proposed method.

Design of ultralow sidelobe chaotic radar signal by modulating group delay method

This paper proposes a method for chaotic radar signal (CRS) design with ultralow sidelobe performance. We first modulate the group delay (MGD) of a radar signal using a chaotic mapping sequence in the frequency domain, and then we transform the radar signal to its time domain form by inverse Fourier transformation. The designed CRS has ultralow sidelobe owing to its flat power spectrum density (PSD). Meanwhile, its ambiguity function is thumbtack, and the amplitudes of both in-phase and quadrature components are close to Gaussian noise. Both numerical simulation and experimental results demonstrate the ultralow sidelobe performance of the designed CRS.

Two-Way Pattern Grating Lobe Control for Distributed Digital Subarray Antennas

An approach to controlling the two-way pattern (i.e., the product of the transmitting and receiving antenna patterns) for a distributed digital subarray antenna (DDSA) is presented. Collectively combining periodic widely separated subarrays results in grating lobes (GLs), and they are unwanted because of the ambiguities that accompany them. The approach to GL control presented here involves a combination of conventional suppression methods on the transmitting side and in the digital beamforming on the receiving side, filling the gaps between the subarrays with “virtual” elements, thus forming a contiguous array. Individually, the transmitting and receiving antenna patterns may not have adequate performance, but it is demonstrated that if designed to complement each other, the two-way pattern can achieve ultralow sidelobe performance. The effects of receiving element signal-to-noise ratio (SNR) and errors in calibration are also addressed.

Directivity maximization and optimal far-field pattern of time modulated linear antenna arrays using evolutionary algorithms

In this paper evolutionary algorithm based design of time modulated 16-element linear antenna array with improved directivity and side lobe level (SLL) with low radiated power at sideband harmonics has been dealt with. In time modulated linear antenna array time is used as fourth dimensional parameter. The comparative study has been made with all the possible combinations of control parameters like constant excitation amplitude, inter-element spacing, and “time” as the fourth dimension. The same array radiates at various harmonic frequencies. In this paper the authors have considered only two harmonic frequencies; first sideband frequency and second side band frequency. Various simulation results are presented showing better side lobe performance, better side band performance and improved directivity with respect to the uniform case. The statistical analysis and t-test have been done to prove the superior performance of differential evolution with wavelet mutation (DEWM) better than real coded genetic algorithm (RGA), particle swarm optimization (PSO), and differential evolution (DE).

Density-tapered spiral arrays for ultrasound 3-D imaging.

The current high interest in 3-D ultrasound imaging is pushing the development of 2-D probes with a challenging number of active elements. The most popular approach to limit this number is the sparse array technique, which designs the array layout by means of complex optimization algorithms. These algorithms are typically constrained by a few steering conditions, and, as such, cannot guarantee uniform side-lobe performance at all angles. The performance may be improved by the ungridded extensions of the sparse array technique, but this result is achieved at the expense of a further complication of the optimization process. In this paper, a method to design the layout of large circular arrays with a limited number of elements according to Fermat's spiral seeds and spatial density modulation is proposed and shown to be suitable for application to 3-D ultrasound imaging. This deterministic, aperiodic, and balanced positioning procedure attempts to guarantee uniform performance over a wide range of steering angles. The capabilities of the method are demonstrated by simulating and comparing the performance of spiral and dense arrays. A good trade-off for small vessel imaging is found, e.g., in the 60λ spiral array with 1.0λ elements and Blackman density tapering window. Here, the grating lobe level is -16 dB, the lateral resolution is lower than 6λ the depth of field is 120λ and, the average contrast is 10.3 dB, while the sensitivity remains in a 5 dB range for a wide selection of steering angles. The simulation results may represent a reference guide to the design of spiral sparse array probes for different application fields.

Simultaneous Improvement of array factor directivity and side lobe level of time‐modulated linear antenna arrays using opposition‐based harmony search algorithm

SummaryIn this paper, simultaneous improvement of array factor directivity and side lobe level of time‐modulated linear antenna arrays using opposition‐based harmony search algorithm has been dealt with. Because of the periodic function of switching time, the same antenna array will radiate at fundamental (center) frequency as well as its harmonic frequencies. The first two harmonic frequencies are (f0 + Fp) and (f0 + 2Fp), where f0 and Fp are operating frequency and pulse repetition frequency, respectively. Four case studies have been adapted; Case‐1: optimal switching time sequence of each element; Case‐2: optimal switching time sequence of each element and optimal non‐uniform inter‐element spacing; Case‐3: optimal switching time sequence of each element, optimal excitation phase of each element, and optimal uniform inter‐element spacing; Case‐4 refers to optimal switching time sequence of each element and optimal uniform inter‐element spacing. Simulation results reflect that Case‐4 outperforms Case‐1, Case‐2, and Case‐3. The objective function was judiciously chosen in such a way that it can simultaneously improve the array factor directivity as well as side lobe level. Considered for the analysis was 16‐element linear antenna array. Various simulation results are presented showing better side lobe performance, better side band performance, and improved array factor directivity with respect to the uniform array having the same number of elements. The numerical results show the power radiated by any harmonic frequency is less as compared with the power radiated at the center frequency called the fundamental frequency. It has also been observed that as the harmonic frequency increases, sideband level and power radiated by the antenna at its harmonic frequency decrease. Copyright © 2015 John Wiley & Sons, Ltd.

A new hybridized backtracking search optimization algorithm with differential evolution for sidelobe suppression of uniformly excited concentric circular antenna arrays

In this work, a hybridized combination of backtracking search algorithm (BSA) with differential evolution (DE) is proposed and applied on sidelobe suppression problem of uniformly excited concentric circular antenna arrays (CCAA). Each array is assumed to have isotropic elements and be placed on x-y plane and has one center element. A search for optimal setting of ring radius and number of elements in each ring is carried out so as to achieve low sidelobe performance on overall azimuth plane. Care has been taken so that directivity does not get degraded as far as possible. Before applying this algorithm to CCAA design problem, BSA and the hybridized algorithm BSA-DE are tested on five complex benchmark functions. Based on 30-independent runs for each benchmark function, Wilcoxon's pairwise signed ranks test is utilized to judge the relative search performance of these two algorithms. The hybridized algorithm proves its superiority on almost all the considered benchmark functions. For the CCAA design problem dealt with in this work, BSA-DE shows its superiority on one or both pattern parameters as well as structural parameters. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:262–268, 2015.

All-Pass Filter-Based 2-D IIR Filter-Enhanced Beamformers for AESA Receivers

An active electronically scanned array (AESA) beamforming method that provides enhanced selectivity (interference rejection) for the same number of antennas compared to conventional delay-and-sum (DAS) beamforming is proposed. Conventional DAS 2-D transfer function is modified by introducing complex pole-manifolds based on recently proposed 2-D infinite impulse response (IIR) beam filters, at guaranteed stability. A continuous-time domain signal flow graph is proposed based on first order all-pass filters that eliminate the need of transmission line-based delays used in conventional DAS beamformers. Improved interference rejection is verified using closed-form signal processing models. For an array of 64 antennas, with desired signal direction of arrival (DOA) 10 ° and interference DOA -60° from array broadside, the proposed scheme shows an improvement in the signal-to-interference ratio (SIR) around 7 dB for the same number of antennas, compared to DAS beamforming. The improvement in interference rejection is observed for both uniform and non-uniform aperture weights in terms of side lobe performance. A feasibility study is presented on potential CMOS circuit implementation of the proposed AESA for a linear array of eight antennas and maximum operational frequency of 1 GHz.