Sidelobe Reduction Research Articles

Vertical line arrays of vector sensors.

A vertical line array (VLA) of vector sensors has a multi-component vector sensor at each sensor position. Vector sensors consist of an omni-directional receiver (Omni), two orthogonal horizontal dipoles, and possibly a vertical dipole. VLA beamforming may be factored into azimuthal processing at each sensor by using a weighted sum of the sensor components and vertical beamforming that combines the vector sensor outputs. Alternative sensor weights, which may depend on vertical steering angle, including cardioids, limacons, and the optimal weights for azimuthally symmetric noise are compared. The vertical dipole's usefulness is limited to sidelobe and grating lobe reduction. For steep vertical steering angles, the optimal weight on the horizontal dipoles becomes large, resulting in an undesirable sensitivity to white noise and tolerance errors. The optimum weights that minimize beam noise subject to an inequality constraint on sensitivity to white noise are derived. For non-symmetric noise, optimal beamforming may cause the mainlobe to squint in azimuth away from the steering direction in pursuit of reduction in directional noise. A simplified optimization approach is introduced that requires a global peak in the steering direction and completely prevents undesirable squinting. The performance of tilted dipoles in azimuthally symmetric noise is compared with other configurations.

Quality Improvement Synthetic Aperture Radar (SAR) Images Using Compressive Sensing (CS) With Moore-Penrose Inverse (MPI) and Prior From Spatial Variant Apodization (SVA).

When the locations of non-zero samples are known, the Moore-Penrose inverse (MPI) can be used for the data recovery of compressive sensing (CS). First, the prior from the locations is used to shrink the measurement matrix in CS. Then the data can be recovered by using MPI with such shrinking matrix. We can also prove that the results of data recovery from the original CS and our MPI-based method are the same mathematically. Based on such finding, a novel sidelobe-reduction method for synthetic aperture radar (SAR) and Polarimetric SAR (POLSAR) images is studied. The aim of sidelobe reduction is to recover the samples within the mainlobes and suppress the ones within the sidelobes. In our study, prior from spatial variant apodization (SVA) is used to determine the locations of the mainlobes and the sidelobes, respectively. With CS, the mainlobe area can be well recovered. Samples within the sidelobe areas are also recovered using background fusion. Our method is suitable for acquired data with large sizes. The performance of the proposed algorithm is evaluated with acquired space-borne SAR and air-borne POLSAR data. In our experiments, we use the [Formula: see text] space-borne SAR data with the size of 10000 (samples) × 10000 (samples) and [Formula: see text] POLSAR data with the size of 10000 (samples) × 26000 (samples) for sidelobe suppression. Furthermore, We also verified that, our method does not affect the polarization signatures. The effectiveness for the sidelobe suppression is qualitatively examined, and results were satisfactory.

Optimal Design of Smart Antenna Arrays for Beamforming, Direction Finding, and Null Placement Using the Soft Computing Method

ABSTRACTThe urge of modern communication system is to design and development of the smart antennas with adaptive radiation characteristics. The multifold capabilities of fourth‐dimensional antenna arrays can cater that much needed adaptiveness if properly designed. Compared to the conventional arrays, the fourth‐dimensional arrays have one added advantage as the ‘Time’ of all the switched‐on antenna elements can be managed to generate the required amplitude and phase tapering without even using attenuators and phase shifters. However, one inherent limitation of fourth‐dimensional control parameter is the generation of harmonics or sidebands. This article proposes various means of radiation pattern synthesis in fourth‐dimensional linear antenna arrays with pulse shifting, pulse splitting, and a combination of both. First of all, the pulse splitting and shifting techniques are combinedly proposed by reducing the sidelobe levels and sideband levels of the beamforming antenna arrays to enhance directivities and efficiencies. Then, this mathematical proposition of the direction finding fourth‐dimensional arrays is developed. Finally, broad nulls over a specific angle of arrival region are created for jamming and interference mitigation. For all these cases, the sidelobe level and the unwanted higher‐order sideband levels are suppressed to reduce the unwanted interferences and power losses. The optimal time schemes for all the synthesized patterns are generated by proposing a chaos‐based soft computing algorithm. The radiofrequency signals at each radiating array element are processed by the optimal time schemes proposed for specific applications. The outcomes are validated and compared with other state‐of‐the‐art works of this domain to prove the competency of the proposed work. The qualitative and quantitative comparisons presented for beamforming array is aimed for a good improvement over other reported works by targeting ultralow (less than −40 dB) sidelobe and sideband levels. For direction‐finding array, the proposed idea has also targeted ultralow sidelobes for the main as well as steered beam patterns. Furthermore, the null placement over a region has been aimed to cover more area for jamming and sidelobe reduction for interference mitigation. Overall, the optimal designs proposed for these advanced applications are beneficial for cutting‐edge communication systems.

Improved subarray coherence factor beamformer for ultrasound plane-wave imaging

Abstract Coherent plane-wave compounding (CPWC) has gained significant traction in medical ultrasound imaging. The coherence factor (CF) weighting algorithm, a classical adaptive beamforming strategy, aims to enhance the CPWC imaging lateral resolution, but it also noticeably compromises the speckle patterns, particularly.at a low signal-to-noise ratio (SNR). Delay multiply and sum (DMAS) has been proposed to reduce side lobes. However, the reconstructed image quality with DMAS is limited in terms of resolution and speckle level. In the present study, an improved subarray coherence factor (ISCF) algorithm is introduced by combining CF with DMAS strategies, aiming to improve the contrast and resolution while preserving the speckle level. The performance of the proposed algorithm is evaluated using simulation and phantom datasets. Results indicate that the resolution and the contrast of ISCF can be improved by 41.6% and 79.4%, respectively; compared with delay and sum (DAS) algorithm. Additionally, the resolution and the speckle level of ISCF can be improved by 10.6% and 35.7% compared with CF algorithm, respectively. The proposed ISCF algorithm outperforms CF in terms of resolution, contrast, and speckle preservation.

Unequally-spaced slot strategy for radiation null reduction in single SIW-embedded antenna element

The incorporation of higher-order modes (HOMs) can substantially augment the antenna gain and bandwidth, but this improvement is typically accompanied by compromised radiation performance including radiation nulls and higher side lobe levels. In this study, an inventive strategy is introduced to reduce the radiation nulls and the side lobe levels of a single antenna element by positioning multiple slots of the radiating element at unequal spacing. Dual hybrid HOMs are analyzed inside a substrate integrated waveguide-based cavity to design a wide band, enhanced gain dual-polarized antenna. The radiating element of the antenna is designed with multiple slots positioned at unequal spacing but symmetrical along the origin. This methodology provides three-fold advantages: a reduction of side lobes, an adjustment of phase center, and a significant reduction of radiation nulls. The antenna has been fabricated, and experimentally validated. The antenna exhibits a reduction in radiation null to − 0.5 dB, a phase adjustment of the main lobe to 0°, and a reduction in side lobe level from − 14.4 dB (N = 2, equal spacing) and − 15.5 dB (N = 4, equal spacing) a maximum of − 19.7 dB (N = 4, unequal spacing) at 12.35 GHz in the phi-0 plane. Excellent agreement between measured and simulated results corroborates the efficacy of the proposed approach. The significant improvement in the radiation performance of the single-element antenna design sets the antenna design apart from the state-of-the-art solutions.

Robust Near-field Circular Beamformer with Artificial Intelligence Based Side-lobe Reduction Technique

Robust Near-field Circular Beamformer with Artificial Intelligence Based Side-lobe Reduction Technique

On cyclic frequency sidelobe and range sidelobe reduction for LPI radar waveform

On cyclic frequency sidelobe and range sidelobe reduction for LPI radar waveform

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

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

Synthesis of a steerable frequency-invariant radiation pattern for broadband scalable antenna arrays

This paper discusses the synthesis of a steerable frequency-invariant radiation pattern for broadband scalable antenna arrays (SAAs). The proposed method allows to achieve constant beamwidth and beam direction over a 3:1 bandwidth and is based on an appropriate radiating elements’ placement in the SAA and a proper amplitude and phase excitation of the array. Both amplitudes and phases of signals exciting the radiating elements are varied with frequency to ensure the radiation pattern invariance. Additionally, the paper proposes solutions to problems occurring in SAAs i.e., the problem of overlapping radiating elements and the problems of sidelobe and grating lobe reduction. To verify the proposed synthesis method, a set of radiating elements, which operate over a 3−9 GHz frequency range, has been manufactured and measured. The overall radiation pattern of the antenna array has been obtained by a summation of the radiation patterns produced by each of the radiating elements.

PAPR and Sidelobe Reduction Using Tone Reservation in OFDM RadCom Systems

PAPR and Sidelobe Reduction Using Tone Reservation in OFDM RadCom Systems

Retracted: Sidelobe Reduction in NC-OFDM-Based CRNs Using Differential Evolution-Assisted Generalized Sidelobe Canceller

Retracted: Sidelobe Reduction in NC-OFDM-Based CRNs Using Differential Evolution-Assisted Generalized Sidelobe Canceller

Sidelobes Reduction Technique for Binary Codes

Pulse compression techniques enable the radar designers to transmit long duration pulse to cater the need of high power at the transmitter and achieve the range resolution of short duration pulse at the radar receiver simultaneously. Due to easy generation and processing, binary codes are widely used as pulse compression codes in radars, sonars and spread-spectrum communication systems. But binary codes have high unwanted pulse compression sidelobes at the output of pulse compression receivers. In this paper, optimum binary codes reported in the literatures are overlaid on Discrete frequency sequences to reduce unwanted peaks sidelobes of optimum binary codes. The proposed approach not only reduced peak sidelobes of optimum binary codes but also increased the pulse compression ratio. In this paper, optimum discrete frequency sequences for overlaying with binary codes are optimized using the Modified Simulated Annealing Algorithm (MSAA). A Discrete Frequency Coded binary signal has a complex signal structure which will be difficult to detect and analyze by enemy Electronics Support Measures (ESM). In this paper, a unified adaptive radar model is also proposed to cater the needs of today's radar signal design requirements. The proposed model will help to improve range resolution, the detection capability of radar, reduce the peak sidelobes significantly, and also improve the ESM capability of radar systems.

Thinned Smart Antenna of a Semi-circular Dipole Array for Massive MIMO Systems

Massive MIMO (multiple-input multiple-output) is a multi-user MIMO technology that can provide high-speed multimedia services in 5G wireless networks using sub-6 GHz and millimeter wave bands. The massive MIMO (MMIMO) installs array antennas in the base stations, using hundreds of transceivers with other RF modules. One of the drawbacks of the MMIMO system is its huge power consumption, and the beamforming network with RF modules for a large number of antennas is the main contributor to the power consumption. In this paper, a novel beamforming method is proposed for the low power consumption of an MMIMO system. The proposed thinned smart antenna (TSA) of a semi-circular array produces a secure beam toward the user’s terminal with reduced interference. By thinning the antenna array, some of the antenna elements are kept off, resulting in less power consumption, while the array pattern remains the same as a fully populated array with a reduced side lobe level (SLL). The sub-6 GHz band of 5 GHz is used for the design of thinned array antennas. The genetic algorithm (GA) is used to determine the array sequence in thinning, and the adaptive signal processing algorithms least mean square (LMS), recursive least square (RLS), and sample matrix inversion (SMI) are used for the beamforming of the TSA, and the corresponding algorithms are GA-LMS, GA-RLS, and GA-SMI. The power saving of 40% to 55% is achieved using TSA. The maximum SLL reductions of 13 dB, 12 dB, and 14 dB are achieved for TSA using GA-LMS, GA-RLS, and GA-SMI algorithms, respectively.

A Combined Electronic Position- and Partial Amplitude-Control Synthesis Technique for Sidelobe Reductions in Linear Array Antennas

A Combined Electronic Position- and Partial Amplitude-Control Synthesis Technique for Sidelobe Reductions in Linear Array Antennas

Effective reduction of sidelobes in pulse compression radars using NLFM signal processing approaches

Pulse compression techniques are widely used in modern radar systems to enhance range resolution and detection capability. As signal design is one of the basic factors of an efficient radar system, the problem of designing a radar signal with good characteristics using pulse compression is addressed in this paper. A linear frequency modulated (LFM) waveform has been widely used for conventional radars. However, it has a higher sidelobe level which makes the detection of weak targets very difficult in presence of strong targets returns and as a result the problem of masking occurs. In order to get suppressed sidelobes of radar matched filter output as well as preserve the main lobe resolution and level to overcome the problem of masking, nonlinear frequency modulated (NLFM) signals are used in modern radars. In this paper, we will introduce two different approaches to design an optimized NLFM signal which is characterized by optimized sidelobe level (SLL). The first is the exponential piecewise linear function (EPWL) which is the modification of piecewise linear (PWL) functions relying on an exponential predistortioning function. The second is the odd-term polynomial approximation (OTPA) in which the generation of NLFM signal depends only on odd-powered terms of the polynomial function. Furthermore, the simulation results of autocorrelation functions (ACF) of the proposed signals show its superiority over the traditional LFM signals and significantly enhancement compared to the recent background work. The Doppler sensitivity of the designed signals has been evaluated, revealing that the first approach offers Doppler tolerance and is suitable for surveillance radar systems, while the second approach with a lower sidelobe level is used in applications such as Synthetic Aperture Radar (SAR). Finally, the ambiguity function of the designed signals has been measured to illustrate the effect of the Doppler effect relative to different velocities.

An Efficient Multi-Beam Generation Method for Millimeter-Wave Reconfigurable Intelligent Surface: Simulation and Measurement

Reconfigurable intelligent surface (RIS) is a promising technology for controlling wireless signals. In particular, it has the potential to provide remarkable performance improvements for wireless links, which is especially appealing for millimeter-wave (mmWave) communications. With this purpose, a proper design of the RIS's reflection beam patterns is highly required. In this paper, a direct method is firstly introduced for multi-beam generations based on RIS. Then, equipped with the artificial bee colony (ABC) algorithm, an efficient multi-beam generation method is proposed to configure RIS for high-performance multi-beam patterns on top of the direct method as the initial design. Finally, by employing a fabricated mmWave RIS, we conduct numerical simulations and experimental measurements, and the measured results validate that the proposed method can obtain higher-quality RIS-based multi-beam patterns with an average 7.96 dB side-lobe level reduction, which may provide an efficient way to enhance the capacity of mmWave communications.

Position‐only planar hexagonal array antenna pattern nulling with simultaneous side lobe reduction at multiple azimuth planes

SummaryThis article presents a study on the placement of multiple nulls as well as minimization of side lobe level in the radiation pattern using a planar hexagonal antenna array structure in two different vertical planes. The desired null depth is achieved to suppress the interference signal by the position‐only control of the uniformly excited isotropic antennas in the array structure. The immediate solution to the mentioned computational problem is reached by various meta‐heuristic optimization algorithms such as teaching learning‐based optimization (TLBO), symbiotic organism search (SOS), and moth fly optimization (MFO) within a considerably reduced processing time with a control over the design constrains. Various examples for diversified scenarios are demonstrated to place multiple deep nulls in the radiation pattern without compromising the pattern constraints and all other radiation pattern characteristics. This experiment sought to illustrate and quantify the unique benefits and limitations of proposed technique using three considered meta‐heuristic optimization algorithm.

Reducing the Sidelobes in Doppler-Range Beam Pattern and Controlling the Frequency Channel in SIAR

Synthetic impulse and aperture radar (SIAR) is a multi-input multi-output orthogonal multicarrier frequency radar, kind of frequency diverse array (FDA). This radar has omnidirectional emission in the transmitter and each receiver or receiving array can form a beam. The 4D matched filter of this radar’s circular arrays can reveal the range, elevation angle, azimuth angle, and Doppler. The existence of a high sidelobe in the range-Doppler is one of the significant challenges of this radar, and pulse-to-pulse frequency code non-agile (PPFCNA) and pulse-to-pulse frequency code agile (PPFCA) are often used to reduce it. Weighting is one of the available methods for reducing sidelobes in array radars, but weighting in the matched filter is more effective in SIAR radars due to their ability to transmit signals with different and orthogonal frequencies. This paper proposes the use of amplitude weighting in the submatched filter, which is made possible by increasing the degree of freedom in the SIAR process. In this method, each receiver’s signal is independently processed and weighted with a submatched filter. Then, a synthetic pulse is formed by combining the data from multiple channels. The output of the simulation with weighting in the matched filter for the PPFCNA indicates an 8.7908 dB reduction in sidelobes, while the output for the PPFCA indicates a 3.3779 dB reduction in sidelobes.

Detection of microcalcifications using nonlinear beamforming techniques.

Abundant research demonstrates that early detection of cancer leads to improved patient prognoses. By detecting cancer earlier, when tumors are in their primary stages, treatment can be applied before metastases have occurred. The presence of microcalcifications (MCs) is indicative of malignancy in the breast, i.e., 30-50% of all nonpalpable breast cancers detected using mammograms are based on identifying the presence of MCs. Therefore, improving the ability to detect MCs with modern imaging technology remains an important goal. Specifically, improving the sensitivity of ultrasound imaging techniques to detect MCs in the breast will provide an important role for the early detection and diagnosis of breast cancer. In this work, a novel nonlinear beamforming technology for ultrasonic arrays is investigated for its ability to detect MCs. The beamforming technique, called null subtraction imaging (NSI), utilizes nulls in the beam pattern to create images using ultrasound. NSI provides improved lateral resolution, a reduction in side lobes, and an accentuation of bright singular targets. Therefore, it was hypothesized that the use of NSI would result in identification of more MCs in rat tumors having a speckle background. To test this hypothesis, rats with tumors were injected with Hydroxyapatite (HA) particles to mimic MCs. Ultrasound was used to scan the rat tumors and images were constructed using conventional delay and sum and using NSI beamforming. Three readers with experience in diagnostic ultrasound imaging examined the 1,344 images and scored the presence or absence of MCs. In all, 336 different tumor image slices were recorded and each reconstructed using NSI or conventional delay and sum with Hann apodization. In every image where one or MCs were detected in the Hann reconstructions, MCs were detected in the NSI images. In nine rat tumor images, one or more MCs were detected in the NSI images but not in the Hann images. Statistically, the results did support the hypothesis that NSI would increase the number of MCs detected in the rat tumors.

For 5G applications, high-gain patch antenna in Ka-Band

<span>The fifth generation (5G) of telecommunications is an attractive application for many researchers during the last years. The 5G requires high date rate with low latency communication medium and patch antenna was used recently for this application. In this article a patch antenna for 5G at 38 GHz was proposed. This article worked on enhancing the gain of patch antenna at Ka-Band and reducing side lobes level (SLL) in radiation pattern. The gain of the patch antenna was improved using a reflector layer located under antenna’s ground with free space air gap separating between two layers. Moreover, the SLL were reduced to satisfy low latency condition for 5G communications. The proposed antenna shows high gain around 8.10 dB with high front-to-back (F/B) ratio of 16.24 dB and wide operating bandwidth around 1.4 GHz for high data rate requirements as well as having reduced overall size antenna. The article based on analytical calculations for patch dimensions and optimization procedure to achieve the desired performance of antenna. Computer simulation technology (CST) had been used as an environment for simulation.</span>