Sidelobe Region Research Articles

Do All Fast Radio Bursts Repeat? Constraints from CHIME/FRB Far Sidelobe FRBs

We report 10 fast radio bursts (FRBs) detected in the far sidelobe region (i.e., ≥5° off-meridian) of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) from August 28 2018 to August 31 2021. We localize the bursts by fitting their spectra with a model of the CHIME/FRB synthesized beam response. We find that the far sidelobe events have on average ∼500 times greater fluxes than events detected in CHIME’s main lobe. We show that the sidelobe sample is therefore statistically ∼20 times closer than the main lobe sample. We find promising host galaxy candidates (P cc < 1%) for two of the FRBs, 20190112B and 20210310B, at distances of 38 and 16 Mpc, respectively. CHIME/FRB did not observe repetition of similar brightness from the uniform sample of 10 sidelobe FRBs in a total exposure time of 35,580 hr. Under the assumption of Poisson-distributed bursts, we infer that the mean repetition interval above the detection threshold of the far sidelobe events is longer than 11,880 hr, which is at least 2380 times larger than the interval from known CHIME/FRB detected repeating sources, with some caveats, notably that very narrowband events could have been missed. Our results from these far sidelobe events suggest one of two scenarios: either (1) all FRBs repeat and the repetition intervals span a wide range, with high-rate repeaters being a rare sub-population, or (2) non-repeating FRBs are a distinct population different from known repeaters.

Marine predator’s algorithm-based linear and elliptical antenna array design for 5G communication

The highly efficient linear and elliptical antenna array design presented in this article is intended to synthesize far-field radiation patterns for 5G communication. The objective is to achieve the best possible radiation pattern, which includes a lower side lobe level (SLL) and a narrower half-power beam width (HPBW). A low SLL is crucial to minimize intervention in the entire side lobe region, whereas long-distance communication requires a low HPBW. The marine predator’s algorithm (MPA) is used here to determine the optimal feeding currents to each array element to reduce the SLL and HPBW values. Two linear antenna array (LAA) design examples and the three elliptical antenna array (EAA) design examples are discussed in this article which are achieved using the optimal current excitations to each array element. Two well-established evolutionary optimization techniques, namely the genetic algorithm (GA) and the differential evolution (DE) technique, are also employed for comparison to demonstrate the superiority of the MPA optimization-based technique. The results achieved utilizing the MPA show the improvement of SLL contraction compared to the uniform antenna array and the methods affirmed in the recently published article.

Defeating angle tracking: A comprehensive analysis of scan rate modulation jamming against sequential lobing radars

AbstractThe authors analyse the sequential lobing radar (SLR) resistance against the scan rate modulation (SRM) jamming technique. Unlike previous studies, the authors analyse SLRs with sinc antenna patterns, enabling investigation of the sidelobe region's vulnerability. By incorporating second‐order angular tracking loops (SOATLs), the first analysis of break‐lock probability for SLRs under SRM jamming is introduced. The analysis reveals the influence of SOATL parameters (damping ratio and natural frequency) on both angular root‐mean‐square‐error at low jamming‐to‐signal‐ratio (JSR) region and break‐lock probability at high JSR region. Additionally, the impact of squint angle on SLR resistance to SRM jamming is examined. Furthermore, the optimal duty cycle as a function of JSR, which maximises break‐lock probability is presented. Significantly, the theoretical results support the 20 dB JSR requirement for SRM effectiveness, often cited experimentally in literature, and extend the theoretical analysis of the SRM technique carried out for the main lobe region of SLRs. This finding bridges the gap between theoretical analysis and practical observations.

An optimal linear and elliptical antenna array design using black widow optimisation for 5G communication

SummaryThis research illustrates a precise linear and elliptical antenna array design for synthesising the optimal far‐field radiation pattern in the fifth‐generation (5G) communication spectrum using a meta‐heuristic optimisation technique known as black widow optimisation (BWO). 5G communication is an emerging technology with revolutionary changes in the wireless communication system with ultra‐high data rate, enhanced capacity, low latency and good quality of service. An accurate antenna array design for an ideal far‐field radiation pattern synthesis with a suppressed side lobe level (SLL) value and half power beam width (HPBW) is the most crucial aspect of 5G communications. A suppressed SLL is necessary to reduce interference in the entire side lobe region, whereas a low HPBW is required for long‐distance communication. Here, the BWO is employed to find the optimal feeding current to each array element to lower the SLL and the HPBW value. The BWO algorithm sustains impeccable equity between the exploration and exploitation stages to impact different potential regions of the search space and generate new solutions to attain the global optima by evading the trap of local optima. The design examples of the linear antenna array (LAA) and elliptical antenna array (EAA) are illustrated in this article by applying the optimal feeding currents to each array element. Compared to the uniform antenna array and methodologies described in the recently published literature, the results obtained utilising the BWO algorithm for designing the LAAs and EAAs demonstrate a substantial development in the reduction of SLL and HPBW.

Hybrid FSK–FDM Scheme for Data Rate Enhancement in Dual-Function Radar and Communication

In this paper, we present a hybrid frequency shift keying and frequency division multiplexing (i.e., FSK–FDM) approach for information embedding in dual-function radar and communication (DFRC) design to achieve an improved communication data rate. Since most of the existing works focus on merely two-bit transmission in each pulse repetition interval (PRI) using different amplitude modulation (AM)- and phased modulation (PM)-based techniques, this paper proposes a new technique that doubles the data rate by using a hybrid FSK–FDM technique. Note that the AM-based techniques are used when the communication receiver resides in the side lobe region of the radar. In contrast, the PM-based techniques perform better if the communication receiver is in the main lobe region. However, the proposed design facilitates the delivery of information bits to the communication receivers with an improved bit rate (BR) and bit error rate (BER) regardless of their locations in the radar’s main lobe or side lobe regions. That is, the proposed scheme enables information encoding according to the transmitted waveforms and frequencies using FSK modulation. Next, the modulated symbols are added together to achieve a double data rate using the FDM technique. Finally, each transmitted composite symbol contains multiple FSK-modulated symbols, resulting in an increased data rate for the communication receiver. Numerous simulation results are presented to validate the effectiveness of the proposed technique.

An effective beamformer for interference suppression without knowing the direction

&lt;span&gt;This paper proposes an effective beamformer for uniform linear arrays of half-wave dipole antennas based on binary bat algorithm (BBA) by controlling complex weights (both amplitudes and phases) excited at elements in an array. The proposed beamformer can impose adaptive nulls at interferences without knowing directions in the sidelobe region by minimizing the total output power of an array, whereas the main lobe and sidelobe levels are maintained. To demonstrate this capability, the proposal will be evaluated in several scenarios, compared to a beamformer based on binary particle swarm optimization (BPSO).&lt;/span&gt;

A Probability-Based Time-Modulated Array and Its Statistical Model

In this letter, a novel probability-based time-modulated array (TMA) for sideband radiation (SR) suppression is proposed. The elements of the TMA are activated with a probability related to the desired excitation amplitude as a way to obtain a desired radiation pattern. This minimizes the power spectral density of the SR signal and enhances its randomness. In doing so, the sideband signal behaves as an artificial additive white Gaussian noise. By analyzing the statistical model, the transmitted signal in the sidelobe region could be avoided from being received by eavesdropper, which has a great potential in the field of physical layer secure communication. The statistical properties can be used for measure the symbol error ratio metric. A set of full-wave simulations in conjunction with numerical analysis is performed to validate the theoretical predictions, proving the accuracy and reliability of the proposed system.

An Efficient Beamformer for Interference Suppression Using Rectangular Antenna Arrays

Over the past ten years, the development of fifth-generation cellular network technology opens the door to the deployment of huge sensors inside the Internet of Things (IoT), challenging the technologies of communications. IoT establishes wireless communication between numerous physical things to connect them over the Internet, as a result, these things may seriously pollute the environment for electromagnetic propagation. This paper proposes an efficient beamformer based on binary bat algorithm for interference suppression in wireless technology applications. The proposed beamformer utilizes the technique of controlling only the phase of excitation weights in uniform rectangular arrays. This beamformer can produce optimal patterns with minimal distortions in sidelobe regions while maintaining the main lobe and placing nulls in the direction of interfering signals. To demonstrate this ability, the proposed beamformer is evaluated through several scenarios and compared to a beamformer based on Binary Particle Swarm Optimization (BPSO). The results show that the proposed beamformer maintains the main lobe toward the desired user direction while imposing nulls in unwanted user directions (interferences) and that it surpassed BPSO-based beamformers in terms of convergence speed and interference suppression ability.

Window function design via fractional programming

The window functions formed from simple functions (e.g. trigonometric functions) have not utilized the degree of freedom (DOF) sufficiently, and thus they may not be optimal. In this paper, we derive two new window design algorithms via optimizing all window elements rather than the weighting coefficients of such simple functions, which are formulated as fractional programming models that only focus on minimizing the ratio of the maximum sidelobe level to the minimum level of the user-defined main energy region and that do not require masks or particular sidelobe level constraints. Especially, the first method is based on only the spectral mainlobe and sidelobe region information, whereas the second method is developed with only the range sidelobe region information from the view of pulse compression. Moreover, the solutions to the resultant nonlinear and nonconvex optimization problems are derived. Finally, simulation results show that proposed windows have advantages of enhanced spectral characteristics, better filtering performance, and improved range sidelobe suppression over their counterparts.

A dual beam adaptive beamforming algorithm with sidelobe suppression

A new adaptive beamforming algorithm is developed not only to provide distortionless responses towards the two desired signals in the presence of interferences and noise but also to control the sidelobe level (SLL). The conventional standard Capon beamformer (SCB) deals with only one desired signal at a time and also offers much high SLL which can enhance unanticipated interferences. So, the conventional SCB is modified for incorporating two signals of interest (SOI) and a limited number of constraints are introduced for suppressing the SLL. Unity gain is maintained towards the second desired signal by employing an additional constraint in the conventional SCB. To control the SLL, a limited number of angles are sampled in the sidelobe region and the powers that correspond to these sampled angles are constrained to a specified level. The sampled angles are chosen from the particular sidelobe regions around the main beams and an empirical formula is given for determining the number of constraints. The resulting optimization problem is convex and solved by the CVX solver of Matlab to obtain the optimum weight vector. Finally, simulations are performed for various scenarios to evaluate the performance of the proposed algorithm. Simulation results illustrate that the proposed algorithm can receive two desired signals simultaneously and also becomes less vulnerable to unpredicted interferences in the vicinity of main beams as the SLL is minimized. The proposed algorithm achieves the maximum improvements of 20 dB and 16 dB in the SLL for two different scenarios as compared to the conventional algorithm. Moreover, the proposed algorithm preserves the SINR as that of SCB dual beam algorithm. In addition, the proposed algorithm can be used in medical imaging to resolve dual targets using two beams.

LssDet: A Lightweight Deep Learning Detector for SAR Ship Detection in High-Resolution SAR Images

Synthetic aperture radar (SAR) ship detection has been the focus of many previous studies. Traditional SAR ship detectors face challenges in complex environments due to the limitations of manual feature extraction. With the rise of deep learning (DL) techniques, SAR ship detection based on convolutional neural networks (CNNs) has achieved significant achievements. However, research on CNN-based SAR ship detection has mainly focused on improving detection accuracy, and relatively little research has been conducted on reducing computational complexity. Therefore, this paper proposes a lightweight detector, LssDet, for SAR ship detection. LssDet uses Shufflenet v2, YOLOX PAFPN and YOLOX Decopuled Head as the baseline networks, improving based on the cross sidelobe attention (CSAT) module, the lightweight path aggregation feature pyramid network (L-PAFPN) module and the Focus module. Specifically, the CSAT module is an attention mechanism that enhances the model’s attention to the cross sidelobe region and models the long-range dependence between the channel and spatial information. The L-PAFPN module is a lightweight feature fusion network that achieves excellent performance with little computational effort and a low parametric count. The Focus module is a low-loss feature extraction structure. Experiments showed that on the Sar ship detection dataset(SSDD), LssDet’s computational cost was 2.60 GFlops, the model’s volume was 2.25 M and AP@[0.5:0.95] was 68.1%. On the Large-scale SAR ship detection dataset-v1.0 (LS-SSDD-v1.0), LssDet’s computational cost was 4.49 GFlops, the model’s volume was 2.25 M and AP@[0.5:0.95] was 27.8%. Compared to the baseline network, LssDet had a 3.6% improvement in AP@[0.5:0.95] on the SSDD, and LssDet had a 1.5% improvement in AP@[0.5:0.95] on the LS-SSDD-v1.0. At the same time, LssDet reduced Floating-point operations per second (Flops) by 7.1% and Paraments (Params) by 23.2%. Extensive experiments showed that LssDet achieves excellent detection results with minimal computational complexity. Furthermore, we investigated the effectiveness of the proposed module through ablation experiments.

Spatial Delay Line Canceler-Based Sidelobe Blanking for Low Radar-Cross-Section Target

This study proposes a sidelobe blanking (SLB) system with a spatial delay line canceler (DLC) and non-coherent integrator in a uniform linear array. After the equations for the target and noise power in the SLB system were established, SLB-ratio functions for the proposed and conventional SLB channels were developed. Using these ratio functions, the optimal SLB thresholds for the general detectable target and low radar-cross-section (RCS) target were estimated. The results of the SLB thresholds were confirmed by the Monte Carlo simulation, which indicated that the proposed SLB channel provides reliable performance without false SLB decisions in the sidelobe region. Using the estimated optimal threshold, the proposed SLB channel provides reliable performance, particularly for low-RCS targets. In contrast, the conventional SLB channel produces numerous false SLB decisions in the sidelobe region. The proposed synthesis is a simple but powerful method for obtaining the reliable SLB ratio. The SLB channel in various array antenna systems can be developed based on this method.

WCA-Based Low-PSLL and Wide-Nulling Beampattern Synthesis for Radar Applications

There are many unavoidable array errors in practical scenarios, which would drastically increase the sidelobe level (SLL) and distort the performance of radar systems accordingly. In this paper, an effective beampattern synthesis approach is proposed to realize a low peak sidelobe level (PSLL) and wide-nulling in the presence of array errors, thus improving the consequent performance of the radar. In particular, the covariance matrix of the sidelobe region (CMSR) is incorporated into the optimization. Considering the randomness of array errors, the statistical mean method is adopted to obtain a more accurate calculation of the CMSR in the presence of array errors based on a Monte Carlo trial. To efficiently and effectively solve the optimization problem, an advanced metaheuristic algorithm, i.e., the water cycle algorithm (WCA), is adopted when seeking the corresponding optimal weight vectors. Numerical results are provided and discussed to demonstrate the effectiveness of the proposed approach including the results based on a wideband linearly spaced magneto-electric (ME) dipole array.

Discrete interferences optimum beamformer in correlated signal and interfering noise

This paper introduces a significant special situation where the noise is a collection of D-plane interference signals and the correlated noise of D+1 is less than the number of array components. An optimal beamforming processor based on the minimum variance distortionless response (MVDR) generates and combines appropriate statistics for the D+1 model. Instead of the original space of the N-dimensional problem, the interference signal subspace is reduced to D+1. Typical antenna arrays in many modern communication networks absorb waves generated from multiple point sources. An analytical formula was derived to improve the signal to interference and noise ratio (SINR) obtained from the steering errors of the two beamformers. The proposed MVDR processor-based beamforming does not enforce general constraints. Therefore, it can also be used in systems where the steering vector is compromised by gain. Simulation results show that the output of the proposed beamformer based on the MVDR processor is usually close to the ideal state within a wide range of signal-to-noise ratio and signal-to-interference ratio. The MVDR processor-based beamformer has been experimentally evaluated. The proposed processor-based MVDR system significantly improves performance for large interference white noise ratio (INR) in the sidelobe region and provide an appropriate beam pattern.

MIMO Radar Waveform Design for Simultaneous Space–Time–Doppler Domain Optimization: Framework and Implementation

Waveform design has become an attractive topic in the field of colocated multiple-input multiple-output (MIMO) radar that allows antennas to transmit different waveforms. Waveform properties of MIMO radar in space, time and Doppler domains determine the performances of resource utilization, interference suppression, and moving target detection. Therefore, simultaneous optimization of multi-domain properties through waveform design is significant to improve the performance of MIMO radar. In this paper, a novel MIMO radar waveform design framework that constrains the beampattern while maximizing the similarity between the designed and desired waveforms is proposed for simultaneous space-time-Doppler domain optimization. To solve the resulting multi-constraint non-convex problem, an efficient beampattern control and similarity maximization (BCSM) algorithm is developed and its convergence is demonstrated. Especially, the coupling problem due to the similarity constraint is handled by transforming the number domain and introducing the proximal algorithm. While reducing the target distortion in mainlobe region and interference in sidelobe region, the proposed method can also maximize the similarity of MIMO transmit waveforms. Numerical simulation results, apart from verifying that the proposed method outperforms existing methods in space-time-Doppler domain, also illustrate the robustness of proposed method in terms of mainlobe width and desired peak sidelobe level (PSL).

BA-Based Low-PSLL Beampattern Synthesis in the Presence of Array Errors

In practical scenarios, there are always array errors, which would increase the sidelobe level (SLL) of the array and distort the performance of the electronic devices consequently. Nevertheless, most of the reported works do not take these unavoidable errors into consideration when implementing array beampattern synthesis. To remedy this problem, a low sidelobe beampattern synthesis approach is proposed in the presence of array errors based on the bat algorithm (BA). In particular, the covariance matrix of the sidelobe region in the presence of array errors is incorporated into the optimization problem. Generally, there are many factors that would contribute to array errors in practical scenarios. Therefore, to reduce the influence of the uncertainty characteristic of the errors on the low-SLL beampattern synthesis, the statistical mean method is utilized to obtain a robust calculation of the covariance matrix in the presence of array errors. Theoretical analysis using signal processing technique and electromagnetic simulation using Ansoft HFSS workbench are combined to testify the effectiveness of the proposed approach. Numerical results show that peak SLLs (PSLLs) of around −22dB and −20dB can be respectively achieved in the above two simulation situations with the obtained weight vectors.

Precise array response control for beampattern synthesis with minimum pattern distortion

This paper presents a precise array response control with minimum pattern distortion (PARC-MPD) algorithm to synthesize beampatterns efficiently. Specifically, the magnitude and phase responses are considered to establish the minimum pattern distortion (MPD) criterion, and the geometric interpretation of response adjustment is given to understand the MPD criterion intuitively. The MPD solution is rigorously derived to realize precise magnitude response control at one intended direction and minimize the pattern distortion at any other direction simultaneously. Moreover, a novel pattern synthesis scheme based on the PARC-MPD algorithm is proposed to realize array response control in the mainlobe and sidelobe regions, and a brief comparison of the recently proposed array response control algorithms is provided to reveal their unified principle to beampattern synthesis. Simulation results under the linear and planar arrays are carried out to show the superiority of the PARC-MPD algorithm.

Multi-user transmission for the joint radar communication systems based on amplitude phase shift keying modulation and waveform diversity

Abstract In this paper, an efficient dual function radar-communication system is proposed to improve the system's resource utilization. In this work, we considered a scenario where the location of the communication receiver is known prior but the radar target is moving and its location is changing with time. Therefore, we proposed a closed-loop design that allows an adaptive selection of appropriate information embedding strategies during tracking operations. We used two strategies that utilize the amplitudes and/or phases of the transmitted radar waveforms toward the communication direction according to the position of the communication receiver during each scan. Hence, during each radar illumination, the system carries out a target-tracking task and simultaneously maintains the communication symbols transmission toward the intended communication direction. The simulation results verify the effective performance of the proposed approach in terms of target detection and tracking performance and angular bit error rate (BER). Furthermore, the proposed amplitude phase-shift keying signaling strategy can transmit different communication symbols to different users located within the sidelobe region and also provides a significant improvement in data rate transmission and BER performance compared with the existing sidelobe-based communication strategies.

Transmit beampattern synthesis for MIMO radar with one-bit digital-to-analog converters

This paper considers the problem of transmit beampattern synthesis (i.e., transmit beamforming) in multiple-input multiple-output (MIMO) radar which deploys one-bit digital-to-analog converts (DACs). By appropriately designing the transmitted signal waveforms quantized by one-bit DACs, the majority of radiated energy can be focused into the mainlobe(s) region to enhance the intensity of backscattered signals from targets. Meanwhile, the amount of energy inevitably leaked into the sidelobe region is minimized to suppress the interferences. More specifically, the essence of the proposed design can be regarded as optimizing the one-bit signal waveforms such that the synthesized transmit beampattern has a minimum integrated-sidelobe-to-mainlobe ratio (ISMR). In order to tackle the nonconvex discrete constraint in the resulting optimization problem, we propose to introduce auxiliary variables to reformulate the discrete constraint into continuous constraints. On this basis, the alternating direction multiplier method (ADMM) framework is applied to deal with the reformulated problem. The proposed method can approximately solve the sub-problems with closed-form solutions in each iteration, and hence, it is computationally efficient. Simulation results indicate that the proposed method is able to provide promising performance.

Improved Sidelobe Recognition Method Using Boresight Error in a Uniform Circular Array for Wideband Direction Finding System

A strong signal through the antenna sidelobes can be interpreted as a main lobe signal and may cause a major angle error in the direction finding system. An auxiliary antenna channel in the Maisel’s sidelobe blanking system increases the cost, and the method using each boresight error (BSE) of the monopulse and interferometer causes many errors in the real antenna. In this paper, a sidelobe recognition method applicable to a wideband uniform circular array without auxiliary antenna channel is proposed. Four boresight errors are obtained from monopulse and interferometer in the circular array and then the maximum value of differences between boresight errors is taken and is compared to the optimal threshold value. The results have the effect of reducing errors occurring in the sidelobe region while maintaining the performance in the main lobe region. To validate the proposed method, a circular array antenna with eight wideband microstrip antennas is designed and manufactured. As a result, there is a significant improvement in the error rate compared to the existing method. It is confirmed that there is no error when the threshold value is from 0.5 ° to 0.7 ° at 6, 9, and 12 GHz, and the error rate is less than about 1 % when the threshold value is between 0.4 ° and 1.0 °.