Sidelobe Suppression Method Research Articles

Sidelobe Suppression Method with Improved CLEAN Algorithm for Pulse Compression OTDR

Sidelobe Suppression Method with Improved CLEAN Algorithm for Pulse Compression OTDR

Coherence sidelobe suppression of laser diode by white-noise-current modulation and external cavity feedback.

A coherence sidelobe suppression method for a laser diode (LD) is proposed, based on the white-noise-current modulation and external cavity feedback. The theoretical model of the coherence of the white-noise-current-modulated external cavity laser (WECL) is established, which details the spectrum broadening mechanism and the coherence sidelobe suppression. At the noise current modulation, the coherence sidelobe induced by the internal cavity is lowered by the external cavity feedback, and the position of the coherence sidelobe induced by the external cavity is controlled with the cavity length, which can extend the coherence range without the sidelobes. The experimental results demonstrate that the 98.4% sidelobe suppression ratio (SLSR) of the WECL is achieved in dynamic interferometry, which is about 20% higher than that of the laser diode only with the white-noise-current modulation. This new, to the best of our knowledge, method can avoid the stray fringe cross talk caused by the multiple coherence sidelobes in the surface error measurements of parallel plates.

Through-the-Wall Radar Imaging Grating-Lobe and Sidelobe Suppression Method Based on Imaginary Sign Coherence Factor

Through-the-Wall Radar Imaging Grating-Lobe and Sidelobe Suppression Method Based on Imaginary Sign Coherence Factor

Sidelobe suppression in structured light sheet fluorescence microscopy by the superposition of two light sheets.

Light sheet microscopy has emerged as a powerful technique for three-dimensional and long-term vivo imaging within neuroscience and developmental biology. A light sheet illumination with structured light fields allows a better tradeoff between the field of view and axial resolution but suffers from strong side lobes. Here, we propose a method of producing structured light sheet illumination with suppressed side lobes by applying the superposition of two light sheets. The side lobe suppression results from the destructive interference between the side lobes and constructive interference between the main lobe of the two light sheets. In the proposed method, the incident light pattern in the rear pupil plane of the illumination objective is a combination of the incident light line beams required for the generation of the two interfering light sheets. We present a fast and simple calculation method to determine the incident light pattern in the rear pupil plane. Simulation results demonstrate the effectiveness of the proposed sidelobe suppression method for double-line light sheet, four-line light sheet, as well as line Bessel sheet. In particular, an 81% decrease in the relative side lobe energy can be achieved in case of double-line light sheet with an almost nonchanging propagation length. We show a way of using combined incident light patterns to generate structured light sheets with interference-resulted side lobe suppression, which is straightforward in design and with advantages of improved imaging performance.

A Sidelobe Suppression Method for Circular Ground-Based SAR 3D Imaging Based on Sparse Optimization of Radial Phase-Center Distribution

Circular ground-based SAR (GBSAR) is a new 3D imaging GBSAR with the potential of acquiring high-quality 3D SAR images and 3D deformation. However, its donut-shaped spectrum and short radius of antenna rotation cause high sidelobes on 3D curved surfaces, resulting in 3D SAR images with poor quality. The multi-phase-center circular GBSAR with full array can effectively suppress sidelobes by filling the donut-shaped spectrum to be the equivalent solid spectrum, but it requires a larger number of phase centers, increasing system cost and engineering difficulties. In this paper, a sidelobe suppression method for circular GBSAR 3D imaging based on sparse optimization of radial phase-center distribution is proposed to suppress high sidelobes at low cost. By deriving the point spread function (PSF) of multi-phase-center circular GBSAR and taking the peak sidelobe level (PSL) and integrated sidelobe level (ISL) of the derived PSF as multi-objective functions, we solve the multi-objective optimization problem to optimize the sparse distribution of radial phase centers. The advantage of the proposed method is that the solved optimal radial phase-center distribution can effectively suppress the 3D sidelobes of circular GBSAR with a limited number of phase centers. Finally, the sidelobe suppression effect of the proposed method is verified via 3D imaging simulations.

Spatially Variant Sidelobe Suppression for Linear Array MIMO SAR 3-D Imaging

Linear array (LA) multiple-input–multiple-output (MIMO) synthetic aperture radar (SAR) has the capacity of achieving 3-D images in a single pass. If processed by matched filtering-based linear 3-D imaging, sidelobe suppression is often required for image quality enhancement. However, in the case of imaging a large target in a short range, sidelobes of the target will become spatially variant and curved, and traditional sidelobe suppression methods will fail. This article proposes a new spatially variant curved sidelobe suppression method for LA MIMO SAR short-range 3-D imaging. The key technique is the employment of a new pseudopolar coordinate system where both the spatial variance and the curvature of 3-D sidelobes can be removed. Specifically, a new 3-D spatially variant apodization (SVA) kernel is applied for sidelobe suppression to maintain the resolution performance. The validity of the presented approach has been demonstrated via computer simulations, the tower crane experiment, and the unmanned ground vehicle experiment.

Spatially Variant Apodization for Grating and Sidelobe Suppression in Near-Range MIMO Array Imaging

In this article, a grating and sidelobe suppression method for near-range multiple-input multiple-output (MIMO) array imaging is proposed, which achieves grating and sidelobe suppression by reducing the sidelobes of the transmitting and receiving array. The method first utilizes the generalized matched filtering (GMF) for imaging to obtain the imaging results which are separable along the transmitting and receiving array. Then, an image domain phase compensation term is derived to eliminate the spatially variant characteristic of the wavenumber spectrum, and a spatially variant weighting scheme with the adaptive weighting range is proposed to reduce the sidelobes of the transmitting and receiving array, respectively. The proposed method can effectively suppress the grating and sidelobes while maintaining the width of the mainlobe. Both simulated and experimental data verify its effectiveness.

Correlation Processor Based Sidelobe Suppression for Polyphase Codes in Radar Systems

Peak sidelobe level (PSL), integrated sidelobe level (ISL) and signal to noise ratio (SNR) are the main performance indices in pulse compression radar. Pulse compression is useful in providing two contradicting requirements, namely, higher transmitted power required for longer pulse transmission, and smaller range resolution which is a desirable characteristic of smaller pulse transmission. The sidelobe suppression method proposed in this paper is based on the correlation processor that uses the P4 polyphase codes. P4 codes are known for their better Doppler tolerant property. Sidelobes are undesirable as jammers or noise present in sidelobes may interfere with the desired target. The proposed method has been implemented with six different windows namely Hamming, Hanning, Blackman, Nuttall, Blackman–Nuttall, and Blackman–Harris and results show that PSL value of − 275.6 dB and ISL value of − 152.98 dB are achieved without much degradation in SNR value. Ambiguity function is derived for the designed sequence and the results are compared with the Frank, Barker and P4 code in the delay-Doppler plane. Results show that the proposed method provides significant performance improvement compared to existing sidelobe suppression methods.

A Novel SAR Sidelobe Suppression Method Based on CNN

Sidelobe suppression is a basic but important task for synthetic aperture radar (SAR) images, since the existing sidelobes can reduce the image quality and complicate image interpretation. The main task of sidelobe suppression is to suppress the sidelobes effectively while maintaining high image resolution and the mainlobe's energy. However, the most effective method, robust spatially variant apodization (RSVA), still faces the problem of energy loss on cluttered targets caused by phase factors. This letter proposes an SAR sidelobe suppression method based on the convolutional neural network (CNN) to compensate for the energy loss in RSVA. The experiments on the SAR images show better performance on both sidelobe suppression evaluation metrics and signal-to-noise ratio (SNR) preservation compared with conventional methods.

Multi-Phase-Center Sidelobe Suppression Method for Circular GBSAR Based on Sparse Spectrum

Circular ground-based synthetic aperture radar (GBSAR) is a new type of GBSAR with three-dimensional (3D) imaging capability. Its relatively low bandwidth-to-frequency ratio and donut shaped spectrum cause high sidelobes problem, which seriously affects the quality of SAR images. To solve this problem, a multi-phase-center sidelobe suppression method for circular GBSAR based on sparse spectrum is proposed in this paper. This method optimizes the sparse spectrum distribution of multi-phase-center circular GBSAR to suppress the originally high sidelobes. In this paper, the signal model of multi-phase-center circular GBSAR is established, the point spread function (PSF) is derived, and the relationship between the sparse spectrum distribution and the sidelobe level is also analyzed. Moreover, we provide the optimal distribution of the sparse spectrum, thus the optimal distribution of multiple phase centers can be calculated with given imaging geometry, providing the best sidelobe performance. The proposed method is verified via simulation experiments.

Single-Variable-Input Active Sidelobe Suppression Method for Synthesized Magnetic Field Focusing Technology and Its Optimization

In this article, a novel method to calculate the current distribution, which enables the active sidelobe suppression of the magnetic flux density in an synthesized magnetic field focusing (SMF) system, is proposed for the first time. The proposed method calculates the current distribution, which enables further sidelobe suppression and keeping the resolution at the same time, by changing the target magnetic flux density distribution with only one varying parameter. The proposed calculation method is very intuitive and time-efficient compared with the other calculation methods, as it only changes one variable to control the sidelobe with one step of matrix multiplication. With the finite element method simulation, it is verified that the proposed method can suppress the sidelobe with any target Rx point when the SMF system has 14 coils with size of 10 cm × 10 cm, and the synthesis distance is 30 cm. When the field is synthesized at the center, over 90% of the sidelobe is suppressed for maximum case. An figure-of-merit (FoM) is constructed to optimize the system between the resolution increment and the sidelobe suppression, and 79% of the sidelobe is suppressed for the optimized case while keeping the resolution increment ratio below 30%. In addition, it is verified that the method can also be applied to the two-dimensional (2-D) SMF systems. The experimental results were in good agreement with the simulated results when the experimental prototype of the same condition with simulation was utilized, including a case in which the magnetic field is focused at the Rx point other than the center.

Range sidelobe suppression for OFDM‐integrated radar and communication signal

To improve the RadCom system of performing both data transmission and radar-sensing functions, here a waveform design method for orthogonal frequency division multiplexing (OFDM) signal is proposed to solve the problem of high range sidelobe level in radar detection process while maintaining a reasonable channel capacity. The method only transmits data in the sub-channels with preferable channel quality. Then, calculate the weight of the chosen subcarriers through the convex optimisation method to traditionally minimise the peak-to-sidelobe (PSL) ratio. Simulation results prove that, compared with traditional range sidelobe suppression method, this algorithm is more suitable for RadCom system.

A method of sidelobe suppression in the specified location based on window function

Dechirp technology for LFM (liner frequency modulation) echo signal will cause sidelobe. The sidelobe of a strong scattering object may mask weak scattering targets nearby. By suppressing the sidelobe in the specified location with a calculated window function, the sidelobe masking can be eliminated. The mainlobe level and the sidelobe level in the specified location are used to construct the objective function. By iterating, we can suppress the sidelobe in the specified location without mainlobe attenuation. The numerical simulations and the actual measurements demonstrate that the proposed method can suppress sidelobe successfully and eliminate the sidelobe masking effectively without mainlobe attenuatio.

Sidelobe Suppression with Resolution Maintenance for SAR Images via Sparse Representation.

Severe sidelobe interference is one of the major problems with traditional Synthetic Aperture Radar (SAR) imaging. In the observation scene of sea areas, the number of targets in the observation scene is so small that targets can be regarded as sparse. Taking this into account, a method of sidelobe suppression, on the basis of sparsity constraint regularization, is proposed to reduce sidelobes of Gaofen-3 (GF-3) images in sea areas of the image domain. This proposed method has a prominent sidelobe suppression effect with resolution maintenance and without destruction of amplitude and phase information. This method can also be applied to SAR images of other satellites. In addition to the employment of peak sidelobe ratio (PSLR) and integrated sidelobe ratio (ISLR) in evaluating sidelobe suppression level, AE (amplitude error) and PE (phase error) are firstly defined for the evaluation of amplitude and phase-preserving quality, respectively. Through the proposed method, AE and PE values are nearly unchanged and the PSLR and ISLR are significantly reduced. The method, as an important part of the quality-improvement project of GF-3, has been successfully applied to the sidelobe suppression of GF-3 data.

光波导光学相控阵边瓣压缩方法研究

光波导光学相控阵边瓣压缩方法研究

A Side-Lobe Suppression Method Based on Coherence Factor for Terahertz Array Imaging

Terahertz (THz) arrays can be used to improve the data acquisition speed considerably in real-time imaging applications. However, the THz array imaging usually suffers from the side-lobe artifacts, which leads to a severe decline in the image quality. In this paper, a side-lobe suppression method based on coherence factor is proposed to improve the image quality. The influences of signal-to-noise ratio on the imaging results are analyzed by simulation. Furthermore, the results based on the real-world data validate the effectiveness of the proposed method, which indicates that the side-lobe is suppressed by 29 dB. This paper can benefit the development of THz imaging technique and its applications in real-time imaging realms.

Side Lobe Suppression in NC-OFDM Systems Using Variable Cancellation Basis Function

In non-continuous orthogonal frequency division multiplexing (NC-OFDM)-based cognitive radio system, the sidelobe suppression methods use the fixed length rectangular windowing functions for canceling carriers (CCs) like the extended active interference cancellation (EAIC) and active interference cancellation (AIC) methods. The AIC and its EAIC methods reduce the interference a lot, but the CCs in different frequency have a non-uniform assignment for sidelobe suppression. To overcome this problem a novel variable basis function proposed in which the CCs are grouped by frequency positions and modeled with different waveforms of different length to suppress NC-OFDM side lobes effectively while reducing inter carrier interference (ICI) at the same time. Simulation results show that using variable basis functions of the proposed method, −60-dB sidelobe suppression depth is reached even with higher order 64-QAM symbol mapping and the ICI caused by the subcarriers is almost negligible.

Pseudo-Random Coding Side-Lobe Suppression Method Based on CLEAN Algorithm

A pseudo-random coding side-lobe suppression method based on CLEAN algorithm is introduced. The CLEAN algorithm mainly processes pulse compression results of a pseudo-random coding, and estimates a target's distance by a method named interpolation method, so that we can get an ideal pulse compression result of the target, and then use the adjusted ideal pulse compression side-lobe to cut the actual pulse compression result, so as to achieve the remarkable performance of side-lobe suppression for large targets, and let the adjacent small targets appear. The computer simulations by MATLAB with this method analyze the effect of side-lobe suppression in an ideal or noisy environment. It is proved that this method can effectively solve the problem due to the side-lobe of pseudo-random coding being too high, and can enhance the radar's multi-target detection ability.

Sidelobes suppression in angular filtering with volume Bragg gratings combination

A method for beam diffraction sidelobe suppression based on the combination of volume Bragg gratings (VBGs) with different thicknesses or periods for angular filtering is proposed and performed. Simulated and experimental results show that the beam diffraction sidelobe is reduced from 12% to less than 1% with the non-sidelobe angular filter. The non-sidelobe angular filtering based on VBGs with thicknesses of 2.5 and 2.9 mm is simulated and demonstrated. The near-field distribution of filtered beams through the non-sidelobe angular filter is obviously smoother than that of the single VBG. The near-field modulation and contrast ratio (C) of filtered beams are found to be improved 1.17 and 1.66 times that of the single VBG. The far-field C of the filtered beam is improved to about 100∶1 and the power spectral density analysis shows that the cutoff frequency of the angular filter is greatly optimized with the VBG combination.

Thinning and Weighting of Planar/Conformal Arrays Considering Mutual Coupling Effects

Based on an improved active element pattern (AEP) technique, a novel effective method for sidelobe suppression considering mutual coupling (MC) in planar and conformal sparse arrays is proposed in this paper. A thinning and weighting process that includes the thinning module, optimization module, and far-field calculation module is presented, and three key points, namely, the modified AEP modeling, far-field calculation of planar and conformal thinned arrays, and modified thinning strategy, are highlighted. As an effective optimization algorithm, the differential evolution algorithm (DEA) is adopted in order to achieve low sidelobe. Several numerical examples are shown to validate the consistency and effectiveness of the proposed synthesis approach. With the first use of the AEP technique for the synthesis of sparse arrays, the planar and conformal microstrip arrays with the desired array filling factor are studied to obtain the expected sidelobe level (SLL).