Sidelobe Level Ratio Research Articles

Minimum peak sidelobe ratio filter for MIMO radar via convex optimization

Multiple input multiple output (MIMO) radar retains transmitting freedom by transmitting multiple waveforms simultaneously. However, due to the cross-correlation between waveforms, the performance of range sidelobes is degraded. So, low sidelobes techniques are especially demanded in MIMO radar. This article proposes a mismatched filtering method for minimizing MIMO radar’s peak sidelobe level ratio (PSLR). In this method, we formulate the problem as a convex optimization (CO) problem and thus ensure its solution is globally optimal. To apply mismatched filters to MIMO radar, we introduce the traditional strategy and propose a new one. Instead of attempting to minimize all auto-correlations and cross-correlations of all waveforms as in the traditional strategy, our proposed strategy directly optimizes the mismatched filter of the synthesis signal for each considered direction. To verify the effectiveness of our method, numerical simulations are carried out. Firstly, the PSLR effects of those two strategies are compared. The results indicate that our proposed strategy dramatically improves the PSLR performance of MIMO radar compared to the traditional one. Then, the influences of several parameters on the PLSR performance are revealed, which indicates that our method is flexible enough to make trade-offs between PSLR and other parameters.

Range and Velocity Resolution of Linear- Frequency-Modulated Signals on Subarray-Mimo Radar

The most important radar system performance is determining the range-velocity of the detected target. This performance is obtained from processing an ambiguity-function (AF) between signals from target reflections and radar radiation signals. Selection of the appropriate waveform transmitted by the radar is a key factor in supporting high resolution radar performance in the AF. There are many waveforms that have been studied in radar systems, especially for multi-antenna radars, i.e., subarray-MIMO (SMIMO) radar which can form phased array (PA) and MIMO radars simultaneously, in the form of linear-frequency-modulated (LFM) signals. In this paper, we examine the use of LFM waveforms combined with SMIMO radar to produce plots of three-dimensional AF as a function of time delay and Doppler shift. The results of the comparison with the Hadamard signal determine the effectiveness of the observed AF performance on parameters such as magnitude, range-velocity resolution, peak sidelobe level ratio, and integrated sidelobe ratio by taking into account the factors of the number of Tx antennas on the PA radar and the number of Tx subarrays on the MIMO radar. The evaluation results of the SMIMO radar configuration (M = 6) with the number of Tx-Rx antenna elements the being 8 provide the best mainlobe magnitude, sidelobe magnitude, range resolution, velocity resolution, PSLR, and ISLR of AF LFM signals compared to conventional radars are 235.2dB, 7.54dB, 37.5m, 75km/s, 29.89dB, and 29.8dB, respectively. Meanwhile, the LFM signal is far superior to the Hadamard signal which has PSLR and ISLR 1.16dB and -3.36dB, respectively.

Study of Correlation Properties of New Code Sequences Based on Persymmetric Quasi-Orthogonal Circulants

For radar and communication systems, the search for code sequences with good correlation properties remains one of important tasks. This work shows the results of the study of aperiodic autocorrelation functions of new code sequences based on persymmetric quasi-orthogonal circulants. The numerical values of the quality parameters such as: the maximum sidelobe level, integrated sidelobe level ratio, and merit factor are given. Applying new code sequences makes it possible to reduce the maximum sidelobe level of the aperiodic autocorrelation function, as well as to reduce the summary energy of the sidelobes, which makes it possible to conclude that their application is promising. The obtained results are aimed at stimulating scientific interest in new bases derived from quasi-orthogonal matrices, as a basis for the revision of signal coding algorithms.

Doppler Shift Tolerance of Typical Pseudorandom Binary Sequences in PMCW Radar.

In the context of all-digital radar systems, phase-modulated continuous wave (PMCW) based on pseudorandom binary sequences (PRBSs) appears to be a prominent candidate modulation scheme for applications such as autonomous driving. Among the reasons for its candidacy are its simplified transmitter architecture and lower linearity requirements (e.g., compared to orthogonal-frequency division multiplexing radars), as well as its high velocity unambiguity and multiple-input multiple-output operation capability, all of which are characteristic of digital radars. For appropriate operation of a PMCW radar, choosing a PRBS whose periodic autocorrelation function (PACF) has low sidelobes and high robustness to Doppler shifts is paramount. In this sense, this article performs an analysis of Doppler shift tolerance of the PACFs of typically adopted PRBSs in PMCW radar systems supported by simulation and measurement results. To accurately measure the Doppler-shift-induced degradation of PACFs, peak power loss ratio (PPLR), peak sidelobe level ratio (PSLR), and integrated-sidelobe level ratio (ISLR) were used as metrics. Furthermore, to account for effects on targets whose ranges are not multiples of the range resolution, oversampled PACFs are analyzed.

Sum/Difference Pattern Synthesis With Dynamic Range Ratio Control for Arbitrary Arrays

This article proposes a method which generates a set of weights to synthesize sum or difference pattern with precisely controlled sidelobe level (SLL), null, and dynamic range ratio (DRR) for arbitrary arrays. Our pattern synthesis approach reduces mutual coupling (MC) between the neighboring elements and complexity of the feeding network design. However, the formulated optimization problem is nonconvex due to the nonconvex objective function and fractional DRR constraint. To tackle it, we first introduce two sets of auxiliary variables: one for DRR constraint and the other for sidelobe and null constraints. By doing so, we then decompose the original optimization problem into three sets of subproblems characterized by the auxiliary variables and weight variables. To facilitate the subproblem with weight variables reaching its optimum values, we derive an appropriate range of step size. Finally, we iteratively solve these subproblems to obtain the solution to the original problem. Extensive experiments employing non-equispaced linear and rectangular arrays, concentric ring array, and cylinder array, are implemented to demonstrate that the developed approach can accurately control SLLs, null and DRR for arbitrary arrays.

A Multicarrier Phase‐Coded Waveform Design Scheme for Joint Radar and Communication System

A Multicarrier phase-coded (MCPC) waveform design scheme with two steps for Joint radar and communication (JRC) system is developed. Firstly, an integrated MCPC waveform design method is addressed by simultaneously maximizing the Signal-to-clutter-to-noise ratio (SCNR) and the Shannon capacity, subject to both the Integrated sidelobe level ratio (ISLR) constraint and the energy constraint. This model is theoretically proved to be a convex optimization problem with respect to the absolute squares of the transmit weights corresponding to different subcarriers, of which the analytical result is also discussed. Subsequently, by further optimizing the phases of the transmit weights, minimizing the Peak to average power ratio (PAPR) for JRC system is recast as a Semidefinite programming (SDP) problem, which can be effectively solved with the Semidefinite relaxation (SDR) technique via Eigenvalue decomposition (EVD) or Complex Gaussian randomization (CGR). Numerical examples are provided to verify the effectiveness of the proposed scheme.

Enhanced target detection using a new combined sonar waveform design

In this paper, a method for combining wideband and narrowband waveforms is proposed to improve target detection in shallow water environments. In this regard, a sonar waveform design suitable for target speed has been proposed too. The method uses a wideband frequency-modulated waveform for high range resolution in a reverberation environment and the Doppler-sensitive (DS) waveform to improve the detection of moving targets. The proposed combined waveform is mathematically modeled, and the Calculating of ambiguity function (AF) is performed. The AF and autocorrelation function (ACF) of the designed waveform indicate both DS and fair range resolution features simultaneously exist. So the initial range resolution for target detection is preserved. The Peak to Sidelobe level (PSL) ratio of the proposed waveform is at least 25 dB more than the previous state of the art waveforms. Calculating the Q-function criterion for the designed waveform reveals the superior reverberation suppression and detection performance with respect to the state of the art waveforms. After calculating the reverberation channel model, waveform echo, and detection of the target, the probability of detection (Pd) versus signal-to-reverberation ratio (SRR) was simulated by the Monte Carlo method. It was shown that the proposed waveform improved the probability of target detection by 20 dB, comparing to the base waveforms.

Spatial- and Range- ISLR Trade-Off in MIMO Radar Via Waveform Correlation Optimization

This paper aims to design a set of transmitting waveforms in cognitive colocated Multi-Input Multi-Output (MIMO) radar systems considering the simultaneous minimization of spatial- and the range- Integrated Sidelobe Level Ratio (ISLR). The design problem is formulated as a bi-objective Pareto optimization under practical constraints on the waveforms, namely total transmit power, peak-to-average-power ratio (PAR), constant modulus, and discrete phase alphabet. A Coordinate Descent (CD) based approach is proposed, in which at every single variable update of the algorithm we obtain the solution of the uni-variable optimization problems. The novelty of the paper comes from deriving a flexible waveform design problem applicable for 4D imaging MIMO radars which is optimized directly over the different constraint sets. The simultaneous optimization leads to a trade-off between the two ISLRs and the simulation results illustrate significantly improved trade-off offered by the proposed methodologies.

Design procedure for planar slotted waveguide antenna arrays with controllable sidelobe level ratio for high power microwave applications

SummaryThis article presents a complete design procedure for planar slotted waveguide antennas (SWA). For a desired sidelobe level ratio (SLR), the proposed method provides a pencil shape pattern with a narrow half power beamwidth, which makes the proposed system suitable for high power microwave applications. The proposed planar SWA is composed of only two layers, and uses longitudinal coupling slots rather than the conventional inclined coupling slots. For a desired SLR, the slots excitation in the radiating and feeder SWAs are calculated based on a specified distribution. Simplified closed‐form equations are then used to determine the slots nonuniform displacements, for both the radiating and feeder SWAs, without the need to use optimization algorithms. Using simplified equations, the slots lengths, widths, and their distribution along the length of the radiating and feeder SWAs can be found. The feeder dimensions and slots positions are deduced from the dimensions and total number of the radiating SWAs. An 8 × 8 planar SWA has been designed and tested to show the validity of the proposed method. The obtained measured and simulated results are in accordance with the design objectives.

Dual-Use Signal Design for Radar and Communication via Ambiguity Function Sidelobe Control

This article considers the dual-use unimodular signal design for a novel dual-functional radar-communication (DFRC) architecture. The information of downlink communication is modulated via the ambiguity function (AF) sidelobe nulling in the prescribed range-Doppler cells. At the same time, the sidelobe around the AF mainlobe is suppressed to ensure the radar detection performance. User equipment (UE) computes the AF of the received signal to make a judgment of the position of nulling for achieving demodulation. To this end, an objective function to evaluate the depth of nulling in AF is developed as figure of merit accounting for the worst-case sidelobe level ratio over the range-Doppler cells of interest. The resultant design is very challenging to solve due to the non-convex and non-smooth quartic fractional objective function and the NP-hard constant modulus constraint. Herein, we develop a fractional-alternating direction penalty method (FADPM) algorithm that invokes the fractional program theory and the ADPM framework. Specifically, we formulate a new ADPM form through introducing an auxiliary variable and resorting to the Dinkelbach's procedure. In each iteration, we transform the original quartic fractional program into two quadratic optimization subproblems both of which are approximated successively through a series of convex subproblems. We also provide the analytical convergence guarantee of the proposed FADPM algorithm. The simulation results verify the performance of the proposed algorithm and exhibit the effectiveness of the DFRC framework in modulation and demodulation process guaranteeing that a high data rate is achievable.

Convolutional Windows for Side Lobe Reduction

A lot of applications in radar systems necessitate low range side-lobe performance which is achieved by pulse compression processing. Linear Frequency Modulation (LFM) signal is mainly used chirp signal for this processing. The paramount drawback in LFM is the first side-lobe level of -13dB at the receiver side. In this paper, LFM signal is modified by using simple two-stage piece wise linear frequency modulation (PWLFM) functions. The autocorrelation function of this PWLFM signal exhibited low peak sidelobe level ratio (PSLR) value compared to its counterpart LFM signal. An attempt is made to further reduce the side lobe values by using novel Convolutional windows. The simulation results confirm a significant side lobe reduction by the LFM signal designed using PWLFM functions when a more flexible Power of Cosine window function is applied compared to all other window functions.

Linearly Polarized Shaped Power Pattern Synthesis With Dynamic Range Ratio Control for Arbitrary Antenna Arrays

This paper extends the semidefinite relaxation (SDR) method to be capable of synthesizing linearly polarized shaped patterns with accurate control of sidelobe level (SLL), cross-polarization level (XPL), and dynamic range ratio (DRR) of the excitation distribution for arbitrary antenna arrays. In addition, by using the vectorial active element patterns, mutual coupling and platform effect can be also incorporated into the proposed vectorial shaped pattern synthesis. Three examples for synthesizing linearly polarized patterns with different pattern shape requirements and different antenna array geometries have been conducted to check the effectiveness and robustness of the proposed method. Compared to the original vectorial shaped pattern synthesis without DRR control, the proposed method with the DRR control can significantly reduce the obtained DRR which is very useful in many antenna array applications.

Passive Compressive Device in an MIMO Configuration at Millimeter Waves

A passive compressive device (PCD), which works at millimeter waves, is proposed in this paper. In a passive manner, the device allows to compress the signals from multiple separate channels into a single or a reduced number of channels. This permits a simplification of the transmitter or receiver chains for radar imaging applications. The PCD is a 3-D cavity that ensures each channel to be decorrelated with each other. If the transfer functions are known, the compressed signals are decompressed in postprocessing. This paper proposes a suitable method to estimate simultaneously the transfer functions of the PCD. This is validated by measurements in a multiple-input-multiple-output (MIMO) configuration to produce a complex synthetic aperture radar image. Measurements revealed that the point spread function generated by the MIMO configuration with the use of the PCD leads to almost similar results, in terms of spatial resolution and sidelobe level ratio, as those of a single-input-multiple-output configuration (uniform amplitude), with a fewer receiving elements.

A Hybrid Nonlinear Method for Array Thinning

A nonlinear method for array thinning is proposed. The method is based on hybrid usage of genetic algorithm (GA) and nonlinear apodization. The method proposes a special layout, which consists of two subarrays. Layout and weights for the subarray having larger aperture are designed by GA. Layout and weights for the second subarray are determined according to results of the aforementioned design. Dual apodization is applied to the outputs of the subarrays to obtain the output. Results show that there is an improvement in peak side-lobe level, beam width, and current taper ratio for particular test problems in the literature.

Broadband target detection algorithm in FM‐based passive bistatic radar systems

In this study, the authors propose a new broadband target detection algorithm for FM-based passive bistatic radar systems, which simultaneously exploits multiple FM radio channels transmitted by the same transmitting station. It is shown that the joint exploitation of the signals of opportunity received at multiple carrier frequencies improves target detection capability as well as the target range resolution. In addition, the proposed detection algorithm exploits all available information making the detection performance robust against time-varying program content broadcast by the individual FM radio channels. Therefore, after formulating the broadband target detection problem as a composite hypothesis test, they derive a broadband uniformly most powerful invariant (B-UMPI) test, together with a closed-form expression for a statistical threshold that allows for automatic detection. To get a better insight into the detection performance of the proposed detector, a close-form expression for the probability of detection is also derived. In addition, they analytically show that how the range resolution of the proposed broadband target detection algorithm improves. They also analytically obtain an integrated sidelobe level ratio at the output of the B-UMPI statistics to show an improvement in the target detection quality. Finally, they provide some simulation examples to validate the authors’ theoretical analysis as well as to show the improvement in the target detection capability and the target range resolution in the broadband FM-based passive bistatic radar systems.

Optimization of Matched and Mismatched Filters in Short Range Pulse Radars using Genetic Algorithm

Matched and mismatched filters are considered important parts of a radar signal processing unit. In this paper, we present an approach to optimize the matched filters and mismatched filters in short range pulse radars. For radar, the matched filter coefficients are the complex conjugates of transmitted code. We used binary phase codes as transmitted pulse. The disadvantage of binary phase codes is having high sidelobe levels in the output of correlation function. Thus, we decided to use optimization algorithms for finding binary phase codes with minimum peak sidelobe levels (MPS). After that, we succeeded in producing mismatched filter coefficients (Mis-co) for each code using floating point genetic algorithm (FGA) and we could generate and test the filter coefficients with maximum peak to sidelobe level ratio (PSR). For testing the filter, we plotted ambiguity function for each set of coefficients and tested the filter with Doppler shift.

Multiple input and multiple output synthetic aperture radar multiple waveform separation based on oblique projection in same frequency coverage

In multiple input and multiple output synthetic aperture radar (MIMO-SAR) the unwanted cross-correlation output sexist inevitably in the superposed echoes of multiple transmitted orthogonal waveforms in the same frequency coverage, which may deteriorate the quality of the reconstructed SAR image because of the high synthetic integrated sidelobe level (SISL). In this study, a novel signal decomposition based on oblique projection (SDOP) method is proposed to suppress the cross-correlation outputs. At first, the superposed echo of each receiver is modelled as a linear-combined vector of transmitted multiple waveforms. Then, the echo of each transmitted waveform is obtained by signal decomposition on the combined vector via SDOP, respectively. Besides, two new metrics, that is, synthetics integrated sidelobe level ratio improved factor and integrated sidelobe level ratio loss factor, are also proposed to assess the separation performance. It is found that the cross-correlation can be effectively suppressed among multiple waveforms via low-complexity projection operators and the output signal noise ratio can be remarkably improved, accordingly. Finally, the numerical experiments are also provided to demonstrate the effectiveness of the proposed method.

Design and performance analysis of orthogonal coding signal in MIMO-SAR

Multi-input multi-output (MIMO) radar which has evident advantages in many applications is a new radar system. Applying the MIMO technique to the earth observing synthetic aperture radar (SAR) system offers effective ways for the improvement of high resolution and wide swath imaging and ground moving target indication (GMTI) systems. Designing the optimal orthogonal waveform is a crucial problem in the research on MIMO radar. First, the index definition of synthetic integrated side-lobe level ratio (ISLR) is proposed by focusing on the SAR application and considering the cross-correlation energy influences between orthogonal coding signals with the same frequency band. Second, it is theoretically demonstrated that the performance of synthetic ISLR of orthogonal coding signals with the same frequency band cannot meet the demands of SAR imaging, which has been proved by one-dimensional numerical simulation. Third, it has been shown through numerical simulation that the performance of synthetic ISLR of orthogonal coding signals still cannot be improved by dealing with the mismatched filtering. Finally, a set of orthogonal phase coding signals are designed for multiple MIMO-SAR antennas. The conclusions are verified through MIMO-SAR imaging and InSAR simulation experiments.

Low-Distortion Optical Null-Steering Beamformer for Radio-Over-Fiber OFDM Systems

In this paper, we report a novel optical beamformer based on fiber Bragg grating technology capable of adjusting not only main beam direction, but also side-lobe level ratio (SLR) and null positions in the array radiation pattern. This beamformer is compatible with dense wavelength-division multiplexing (DWDM) configurations, and consists of two chains of cascaded gratings that can independently control both the phase and the amplitude of the signals, feeding each array element for 2pi and 10 dB, respectively. We characterized the effect of this beamformer on signal quality in an experimental radio-over-fiber (ROF) link by externally modulating and transmitting an IEEE 802.11a compliant signal over the beamformer. The measured error vector magnitude of the received signal confirmed that there was no additive distortion or noise, and consequently, we achieved error-free transmission for the highest possible bit rate. Finally, we demonstrated the capability of this beamformer in beam-/null-steering and SLR reductions by measuring the radiation pattern of the array antenna of an optimized DWDM-ROF link. The measurements are compared to simulations for several examples of radiation patterns.