Sidelobe Level Research Articles

Polarization microwave correlation imaging method based on orthogonal complement space

AbstractCurrently, microwave correlation imaging (MCI) is regarded as an important method to address the forward‐looking imaging problem in radar. The key step of this method is to form a spatio‐temporal two‐dimensional random radiation field through various means. However, the current methods do not consider the polarization domain, which is an important dimension of electromagnetic signals. The existing research mainly focuses on using polarized antenna elements, without incorporating polarization information into the imaging system. To fill this gap, this letter proposes the polarization microwave correlation imaging (PMCI) based on the orthogonal complement space, which performs instantaneous polarization measurements (IPM) while correlating imaging of the target. Through simulation analysis, this method can further improve the quality and anti‐interference ability of MCI. Moreover, under the condition of low time‐frequency product, the peak sidelobe level (PSL) and isolation of this method are approximately 3.5 dB and 12.5 dB higher than those of traditional instantaneous polarization measurement methods (TIPM).

Designing of two-dimensional acoustic beamforming array using machine learning

Acoustic beamforming arrays are used for locating sound sources and their performance is measured by their directivity pattern. Designing an acoustic beamforming array to meet specific performance requirements can be challenging and requires numerical optimization of various factors such as array width, microphone positions, and the number of microphones. This study employed a Deep Neural Network (DNN) approach to predict the arrangement of a two-dimensional acoustic beamforming array giving the desired beam pattern. The DNN was trained on 90,000 microphone array designs and beam patterns of 1-kHz sound. The prediction accuracy was evaluated based on the mean absolute errors (MAE) of beam patterns, frequency-averaged main lobe width (MLW), and maximum sidelobe level (MSL). The results for commonly designed arrays datasets such as Brüel & Kjær style array had a 26.54% error in beam patterns, 2.34 degree/m error in MLW, and 4.21 dB error in MSL. However, for predicted arrays generated by the random array designs, the results were more accurate, with deviations of 22.08% in beam patterns, 1.82 degree/m error in MLW, and 5.07 dB in MSL.

Synthesis of Large Ultra-wideband Sparse Circular Planar Arrays Based on Rotationally Symmetric Structure

This article aims to improve the synthesis efficiency and radiation performance of large ultra-wideband (UWB) rotationally symmetric sparse circular planar arrays by using a modified differential evolution algorithm (MDEA). In the proposed MDEA, we adopt a new encoding mechanism in which an individual represents an element position expressed in polar coordinates. Importantly, such an encoding mechanism can facilitate the multiplication calculation for the array factor in the individual being updated while making it easier to meet the given minimum element spacing constraint. Moreover, to cater to the new encoding mechanism, some low-dimensional evolution operators are introduced to avoid the prematurity. In particular, the UWB rotationally symmetric sparse planar array synthesis problem is transformed into the sidelobe suppression problem of the array pattern at the highest frequency under the given array aperture, and the minimum spacing constraints is used to guarantee enough space to place physical UWB antenna elements. Two synthesis examples of UWB sparse planar arrays based on rotationally symmetric structures are presented. The results show that the peak sidelobe level (PSL) obtained by the proposed MDEA is significantly lower than the results obtained by some existing algorithms in an acceptable CPU time, which proves the effectiveness and superiority of the proposed MDEA.

Synthesis of Concentric Circular Antenna Array Employing Jaya Algorithm

In the present scenario, Sidelobe Level (SLL) is treated as the most important parameter of the antenna array as it assists in suppressing interference and adjacent noise in wireless communication systems. As the maximum SLL value examined higher power wastage in unwanted signal direction, a transmitter of the communication system encounters major hitches. In this article, the optimum design of four various groups of Concentric Circular Antenna Array (CCAA) of the array antenna has been to lower SLL as much as possible. Optimum beam pattern synthesis of the proposed array antenna has been carried out by optimizing the standardized current distribution of the array antenna elements, all elements placed with fixed inter-element spacing. The work proposed algorithm is the Jaya optimization algorithm, the main aim of this technique is to describe the credibility of a currently chosen human social behaviour-based optimization algorithm known as Jaya. This very easy algorithm with lower complexity to synthesize Concentric Circular Antenna Array (CCAA) which is thoroughly utilized in the present scenario communication systems. The obtained results of the Jaya algorithm compared with Particle Swarm Optimization (PSO) and previously published articles. The Jaya algorithm achieved an improved side lobe level reduction as correlated to the PSO algorithm, finally getting results to examine the improved ability of Jaya as the best suitable method and achieve better sidelobe level suppression.

Peak sidelobe level suppression via reconfigurable element pattern selection for beam scanning linear array antenna

Array antenna with reconfigurable elements can further suppress the peak sidelobe level (PSLL) by selecting reconfigurable element pattern (REP) combination according to the variation of the beam directions. However, the pattern selection for N array elements from K possible REPs is a typical non-deterministic polynomial-hard problem, resulting in the REP selection being intractable even with small N and K. To solve this REP selection problem effectively, this paper proposes an improved genetic algorithm to shrink the REP combinations that contain the suboptimal one. As a result, the proposed algorithm can adaptively select the best REP combination for different scanning beams by searching a relatively minor solution space. The alternating direction multiplier method is used to accelerate the computational speed of optimizing the array excitation. Array antennas with two-type REPs and three-type REPs, respectively, are simulated with high-frequency simulation software (HFSS) to validate the superiority of the proposed algorithm. Comparisons with the existing algorithms show that the proposed algorithm can select a superior REP combination to obtain 1 dB to 3 dB lower PSLL for different scanning beams.

Multipath Detection and Mitigation of Random Noise Signals Propagated through Naturally Lossy Dispersive Media for Radar Applications

This paper describes a methodological analysis of the Brillouin precursor formation to understand the impairments undergone by like-noise and random noise waveforms propagating through naturally dispersive media commonly found in radar applications. By means of a frequency-domain methodology based on considering the frequency response of the medium under study, the effect of these dispersive media on the evolution of an input signal can be seen as frequency filtering. The simulations were performed at a center frequency of 1.5 GHz and for a signal bandwidth of 3 GHz. Four random noise signals were considered: Barker codes, PRBS codes, Frank codes, Costas codes and additive white Gaussian noise. The experienced impairments were assessed in terms of cross-correlation function (CCF) degradation. The differences in the behavior of each type of phase and frequency coded signal to face the dispersive propagation have been demonstrated in terms of parameters used for information retrieval: peak amplitude decay, CCF secondary sidelobe level and multipath detectability. Finally, a frequency filtering approach is proposed to mitigate the impairments due to dispersive propagation under multipath conditions.

Towards phased array antenna operating in Ku-band for satellite communications

Satellite communication systems for mounting on vehicles are commonly based on phased array antennas with electronical beam steering. In this work we develop active metasurface-based receive-transmit antenna arrays for newly deployed satellite constellation system running in Ku-band. Both receive and transmit subarrays are based on patch-antenna elements driven in circular polarization using 90∘ hybrids. In both subarrays we optimized elements sizes and array period to have optimal ellipticity, gain, side lobe level. In electromagnetic simulations we achieved realized gain of 32.2 dBi for the Rx subarray and 33.4 dBi for the Tx subarray obtained in a broad scanning angle range from − 15∘ to + 45∘.

Effect of Beam-Steering Angle, Operation Wavelength and Mean Inter-Element Distance on the Side-Lobe Levels of Integrated Optical Phased Arrays under Beam-Steering Operation

Integrated optical phased arrays (OPAs) play an important role in a broad range of applications. Fabrication constraints, however, pose a limit to the minimum inter-element separation that further results in high-intensity side lobes. The intensity of these secondary lobes can be reduced by arranging the antenna elements with non-uniform separation distance, which has been addressed by different methods. In this paper we employ one of the already proven optimization algorithms, i.e., differential evolution, to optimize the element positions of linear arrays with different configurations operating under beam-steering operation and considering a minimum inter-element distance. These optimizations allowed us to derive some design guidelines that can assist in reducing the side-lobe level (SLL) of integrated linear OPAs. In particular, we found that it is necessary to optimize the positions for the broadest beam-steering angle and the shortest operation wavelength. Additionally, optimizations of different configurations reveal that, when imposing a minimum inter-element distance, there is an optimum mean distance that minimizes the SLL of the array.

Utilizing gammatone filter coefficient to improve human mouth-click signal detection using a multi-phase correlation process

This study introduces an enhanced structured signal processing scheme for detecting the “transmit-echo” of mouth-click signals used by blind individuals for echolocation. The processing scheme is based on coexisting work on the detection of the mouth-click signal, with an additional band-pass filter process introduced before synthesis, multi-phase correlation, and summation. The level of side lobes at the output was improved by more than −19 dB, and the number of local maxima was minimized by using a band-pass filter. The detection of “transmit-echo” results using artificial mouth-click signal data was validated and achieved a 100% success rate in detecting obstacles at 60 cm, 80 cm, and 100 cm. Nonetheless, the detection scheme discussed in this investigation is thought to be intuitive, having been learned from the human hearing process. The emerging concepts in this research are expected to benefit radar and sonar system applications in the near future.

LMS and RLS beamforming algorithms based linear antenna array with known mutual coupling

This study explores the application of LMS and RLS algorithms in adaptive beamforming for a linear array of half wavelength dipole (HWD) antennas with known mutual coupling. The research initiates by deriving analytical expressions for the covariance matrix of signal impinging on an HWD antenna array, accounting for mutual coupling effects. Leveraging these expressions, we calculate the weights for both LMS and RLS algorithms, enabling the evaluation of the overall far-field radiation patterns of the HWD antenna array. The results demonstrate that these algorithms effectively steer the main lobe of the radiation pattern towards the desired user while creating nulls in the direction of undesired users. Notably, simulations indicate that the proposed compensation method enhances the performance of beamforming algorithms, particularly when considering mutual coupling effects. Specifically, the LMS algorithm outperforms the RLS algorithm in reducing interference, resulting in lower side lobe levels (SLL) in the radiation pattern.

Broadband Continuous Transverse Stub (CTS) Array Antenna for High-Power Applications.

A continuous transverse stub (CTS) array antenna with broad bandwidth and high-power handling capacity is proposed in this paper. The technologies of multi-step impedance matching and T-shaped electromagnetic band-gap (EBG) loading are utilized, which improved the antenna operating frequency bandwidth. An H-plane lens horn is used to feed the CTS array. As a result, a good bandwidth capability of more than 32% is achieved, with a gain variation less than 3.0 dB. The measured sidelobe level (SLL) is below -18 dB in the entire frequency range. Moreover, the power handling capacity of the antenna is more than 80 MW and can reach the GW level after arraying, which indicates that this antenna has application potential in the high-power microwave (HPM) field.

Tapered-slot radiation-traveling wave mechanism inspired extreme wideband efficient antenna with ultra-low SLL

ABSTRACTThe manuscript proposes a radiation-inspired tapered-slot-traveling wave mechanism rooted in the combined profile of an efficient extreme wideband (EWB) antenna with ultra-low side-lobe level (SLL), operating in 1–50 GHz. The proposed antenna design, proximity coupled by a transmission line section (50 Ω) followed by differential dual-stub (stethoscope kind), uses two broad banding techniques – The first part of the profile is designed according to the radiation profile of a tapered slot and the second profile section comprises a tapered director (funnel kind) along with an array of reflectors on either side of the flared throat. A comprehensive mathematical analysis of both tapered profiles along with the relationship of different dimensional parameters of the geometry to arrive at an optimized compact and efficient design is narrated. Further, the gain is improved from 8 dB to 12.5 dB by introducing the director and the reflectors. The measured result of the antenna is extreme wideband with high peak gain, ultra-low SLL (Max. −51.0 dB), radiation efficiency (89−94%), improved XPD (−33 dB and below), and good transient response when compared to other state-of-art EWB tapered antenna designs. The proposed antenna is a potential sensor for high resolution/precision, imaging/positioning, and energy harvesting applications.

Photonic generation of Barker encoded dual-nonlinear frequency modulated RADAR waveforms

Photonics enables the development of versatile waveform generators with carrier frequency tunability and broad bandwidths, allowing for high-range resolution for modern radar systems. Linear frequency-modulated waveforms are widely employed in various radar applications due to their large time-bandwidth products but are limited in functionality due to high sidelobe levels, resulting in a poor signal-to-noise ratio (SNR). On the other hand, non-linear frequency-modulated waveforms (NLFM) have a faster sweep rate at the edges than at the center, resulting in high SNRs, which can be boosted further through encoding techniques. A photonic approach for generating Barker-encoded dual-NLFM waveforms through a dual-drive Mach Zehnder modulator is proposed with improved range resolution, pulse compression ratio, and peak-to-sidelobe ratio. A theoretical analysis is performed, which is then modeled, and experimentally confirmed. Barker-encoded dual-NLFM waveforms are generated at 6 GHz with 500 MHz chirp bandwidth showing a maximum range resolution of 19.89 cm with PCR of 9803.

Directive Millimeter-Wave End-Fire Diplexing Antenna for IoT Applications

Millions of passengers use High-speed trains (HSTs) daily, in the world. The roofs of HSTs can be equipped with a variety of transmitting and receiving antennas to accommodate high-data-rate Internet services with reliable radio access for passengers. The design of commercial antenna systems is a compromise between cost, size, manufacturability, and performance. This paper proposes a new, compact and low-cost two-port millimeter-wave diplexing directive end-fire antenna, which is designed, fabricated and tested. The proposed antenna is made of a tapered slot antenna and a diplexing structure based on transitions in stacked Printed Circuit Boards (PCBs). The ports of the antenna cover the frequency band 25.9-32.4 GHz (6.5 GHz) and 34.6-37.1 GHz (2.5 GHz). In all operating frequency bands, measured isolation between input ports exceeds 24 dB. Furthermore, symmetric directive end-fire radiation patterns are obtained experimentally, with low side lobe level and low front-to-back ratio. All these features make the proposed diplexing antenna suitable for high-speed railway wireless networks.

Antipodal Vivaldi Antenna with Star Trek insignia-based side slot edge for ultra-wideband applications

This article presents a Vivaldi Antipodal Antenna (AVA) with lens and radiating side cavities based on the Star Trek insignia, called Star Trek Side Edge Radiation (STSER-AVA). The objective was to improve parameters to make the radiation of the proposed antenna more directive. To this aim, the development is focused on reducing the squint of the central radiation beam and the side lobe level (SLL), as well as increasing the gain compared to a Conventional AVA. To achieve the objective, using an optimized design. The proposed antenna with or without a lens reached the target with a squint of -2.0 degrees, at 3.90 GHz the antenna with a lens achieved better gain (9.42 dB), but with a greater reduction in SLL of -10.73 dB compared to the lens less antenna. The results were obtained with computational electromagnetic simulations and experimental measurements.

Design of half circular wideband antenna for ship radar

The research aims to design a wideband antenna for the ship's radar. The ship's radar works on the S-Band range whose wavelengths range from 8 to 15 cm with a frequency of 2-4 GHz, This antenna design uses a new approach involving the use of Defected Ground Structure (DGS) and Defected Microstrip Structure (DMS), which builds on the initial theory. The results of the study obtained a bandwidth value of 1.6 GHz, an impedance antenna value of 49.7 ohms, with a total efficiency of -0.3356 a working frequency range ranging from 1.74 GHz to 3.3 GHz. The radiation pattern obtained the main lobe magnitude value of 3.85 dBi, Main lobe direction of 162.0 deg, angular width (3dB) of 76.7 deg, and side lobe level of -1.1 dB. From the results of working frequency, it is found that the antenna can be used for airborne warning & control (AWACS), remote sensing, WiFi, Bluetooth, mobile communication, XM radio, airport surveillance radar (ASR), radioastronomy, wireless LAN, ZigBee, missile guidance.

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.

Synthesis of flat‐top beampatterns based on simple polynomial transforms of Gaussian excitations

AbstractIn the design of antenna arrays which require fast and robust flat‐top beam synthesis, computationally efficient methods are preferred. This feature is usually met by analytical techniques or simple optimisation procedures. On the other hand, in the flat‐top beam synthesis, a common requirement is the ability to control beamwidth or sidelobe level. However, this can result in a high dynamic range ratio (DRR) of array's excitation coefficients. In this paper, a straightforward method for the design of symmetrical flat‐top arrays with controllable sidelobe level or DRR is proposed. The method is based on quadratic and cubic transforms of Gaussian excitations. In addition, the method utilises zero coefficients whose positions are used to control the DRR, including the ability to achieve its minimum. Compared to other flat‐top arrays with analytically shaped beams, the proposed arrays have lower DRRs for the same sidelobe level.

Multi-objective sparse synthesis optimization of concentric circular antenna array via hybrid evolutionary computation approach

Sparse synthesis can reduce the maximum sidelobe level (SLL) and overhead of the concentric circular antenna array (CCAA) by switching off partial array elements. However, previous works have not considered finding a balance between the number of switched-on elements of CCAA and reducing the maximum SLL, or jointly optimizing the excitation current weights of array elements to further suppress the maximum SLL. In this work, we address these challenges by formulating a hybrid multi-objective optimization problem (MOP) with discrete and continuous solutions. To solve this hybrid NP-hard problem, we consider two approaches: the two-step and one-step methods. In the two-step method, we convert the original MOP into two subproblems and propose an enhanced non-dominated sorting genetic algorithm-II (ENSGA-II) and an improved genetic algorithm with new mutation and attraction (IGAnMA) to solve these two subproblems. ENSGA-II and IGAnMA involve the hierarchy mechanism and attraction operator to enhance the solving abilities, respectively. In the one-step method, we propose an improved hybrid non-dominated sorting genetic algorithm-II (IHNSGA-II) with global search and hybrid solution update methods to solve the MOP in one step. Numerical simulation results show that the proposed methods are effective and stable for the sparse synthesis of CCAA. Additionally, electromagnetic simulation results demonstrate the validity of the proposed approaches in a more practical environment.

Angle-dependent phononic dynamics for data-driven source localization

The source angle localization problem is studied based on scattering of elastic waves in two dimensions by a phononic array and the exceptional points of its band structure. Exceptional points are complex singularities of a parameterized eigen-spectrum, where two modes coalesce with identical mode shapes. These special points mark the qualitative transitions in the system behavior and have been proposed for sensing applications. The equi-frequency band structures are analyzed with focus on the angle-dependent modal behaviors. At the exceptional points and critical angles, the eigen-modes switch their energy characteristics and symmetry, leading to enhanced sensitivity as the scattering response of the medium is inherently angle-dependent. An artificial neural network is trained with randomly weighted and superposed eigen-modes to achieve deep learning of the angle-dependent dynamics. The trained algorithm can accurately classify the incident angle of an unknown scattering signal, with minimal sidelobe levels and suppressed main lobewidth. The neural network approach shows superior localization performance compared with standard delay-and-sum technique. The proposed application of the phononic array highlights the physical relevance of band topology and eigen-modes to a technological application, adds extra strength to the existing localization methods, and can be easily enhanced with the fast-growing data-driven techniques.