Sidelobe Level Research Articles

Design and Analysis of Wideband Single-Layer Reflectarray Antenna for Remote Sensing and Environmental Monitoring

In this article, a wideband single-layer reflectarray antenna for Ku-band applications is presented. The proposed reflectarray antenna is suitable for applications such as fixed satellite service (FSS), broadcasting satellite service (BSS), earth exploration satellite service (EESS), remote sensing, and environmental monitoring. The developed single element of the proposed reflectarray antenna is made up of a horizontal strip, discrete vertical strips of varying sizes, and circular structures. The reflectarray antenna has 441 elements arranged on a square aperture made of Rogers 5880 substrate, measuring 21 cm × 21 cm. The maximum gain obtained is 26.31 dBi, with a bandwidth of 15.4% of 1 dB gain. The achieved aperture efficiency is 44.4%. The obtained cross-polarizations are less than −21.46 dB for the E-plane and −25.27 dB for the H-plane. The side lobe level is found below −15.06 dB in the E plane and −15.7 dB in the H plane. The side lobe level is minimal at 13.5 GHz, measuring less than −18.2 dB and −18.5 dB in the E and H planes, respectively. The reflectarray antenna designed has a fractional bandwidth of 40%. Hence, the developed antenna is suitable for wide Ku-band applications.

Hybrid phase-correction metasurfaces for accurate near-field manipulation

Although metasurface has attracted significant attention in recent years due to its ability to manipulate electromagnetic waves, discrepancies are often observed when comparing the designed and realized near-field performances. Among various contributing factors, one important issue is related to the fact that the elements arranged on a metasurface are typically designed under the assumption of normal incident excitation, whereas in practice they are actually excited at various oblique incidence angles depending on the element's relative position to the feed antenna. This introduces amplitude and phase errors in the reflection or transmission coefficients of the elements within the metasurface, thereby affecting its overall performance. In this paper, a hybrid phase-correction method is proposed to compensate for the effect of oblique incidence on metasurfaces. The actual oblique incidence angles are decomposed into elevation and azimuth directions: In the elevation direction, the element characteristics under oblique incidence replace those under normal incidence, while in the azimuth direction, element rotation is introduced to compensate for the local effects. Near-field focusing and holographic metasurfaces are designed to verify the proposed hybrid phase-correction method. Full-wave electromagnetic simulations show that the proposed metasurface has the advantage in sidelobe levels without significant costs in terms of the amount of element-level computations. Finally, the near-field focusing metasurfaces are fabricated, and the measured results further demonstrate the potential of the proposed design for accurate near-field manipulation.

Beam Scanning with Ultra-Low Sidelobes and In-Band Ultra-Low Scattering Characteristics Empowered by Single Space-Time-Coding Radiation-Scattering Metasurface.

The integrated modulation of radiation and scattering provides an unprecedented opportunity to reduce the number of electromagnetic (EM) apertures in the platform while simultaneously enhancing communication and stealth performance. Nevertheless, achieving full-polarization, arbitrary amplitude, and phase modulation of radiation scattering remains a challenge. In this paper, a strategy that realizes space-time coding of radiation scattering within the same frequency band, which enables the simultaneous and independent modulation of amplitude and phase, is proposed. To address the limitations of the high sideband levels (SBLs) of conventional space-time-coding metasurfaces, a strategy comprising nonuniform modulation periods and stochastic coding is proposed. Consequently, beam scanning with ultra-low sidelobe levels (SLLs) and suppressed SBLs is achieved in the radiation mode (RM). In scattering mode (SM), in-band low scattering characteristics are achieved within the same operating frequency band as RM. A prototype of a space-time-coding radiation-scattering metasurface (STCRSM) is fabricated and the aforementioned functionalities are validated by measurements. Furthermore, the proposed strategy does not necessitate the utilization of optimization algorithms and exhibits low SLLs and low SBLs, which will make it flourish in RF stealth applications, such as covert communication systems.

An ultrawideband monopulse feed with slant polarization for tracking radar systems

An ultrawideband slant-polarized monopulse feed is designed and fabricated for microwave applications. The proposed configuration features four end-launched diagonal horns allowing for the production of sum and difference channels in two principal planes. The key advantage of this proposed monopulse antenna over traditional monopulse feeds is its ability to combine the benefits of ultrawideband performance with slant polarization while maintaining acceptable side lobe level. The design is validated by fabricating a prototype of the proposed feed antenna. Measurement results are in a reasonable agreement with the simulations. The measured ratio bandwidth is 2.5:1 from 8 to 18 GHz with a peak gain of 17.92 dBi. The null depth in the difference patterns is approximately − 32 dB. Given these characteristics, the proposed monopulse feed is a suitable choice for use in commercial tracking radar systems that require wide bandwidth and slant polarization, such as those found in satellite-based applications.

Dual Function Radar and Communication Signal Design with Combined Waveform Selection and Pulse Repetition Interval Agility

The traditional probe–pass integration system embeds communication information into a radar waveform, which leads to a high level of waveform autocorrelation sidelobes and a poor false symbol rate at low signal-to-noise ratios. This article proposes a three-dimensional indexed modulation-based design method for probe–pass integration waveforms. This method realises communication information modulation and demodulation by simultaneously indexing orthogonal waveform selection, transmitting pulse PRI changes and carrier frequency changes in three dimensions, and applying compressed perception technology to solve the problems of PRI shortcuts and carrier frequency, resulting in a velocity term in the received waveform that cannot be accumulated by phase reference to realise velocity super-resolution. Finally, the radar detection performance and communication performance are simulated and analysed, and the simulation results reveal that the method proposed in this paper can not only satisfy the radar detection performance requirements but also achieve a lower unsigned rate on the basis of an improved communication rate.

Design of Microstrip Antenna Integrating 24 GHz and 77 GHz Compact High-Gain Arrays.

The swift advancement of contemporary communication technology, along with the development of radar systems, has raised the requirements for antenna systems. In this work, an integrated array antenna operating in the 24 GHz and 77 GHz frequency bands is proposed. The microstrip antenna array element uses a width reduction approach to reduce its volume by 39.82%. By using corner series feeding, a 3 × 3 planar array is created. The arrays operating at 77 GHz and 24 GHz can produce gains of 14.19 dBi and 15.34 dBi, respectively, with sidelobe levels of less than -9.14 dB and -12.85 dB and cross-polarization levels of -29.26 dB and -40.52 dB. This design reduces the volume of the array, eliminates the need for a complex feeding network, minimizes feeding losses, and enhances the antenna's gain, all while maintaining good sidelobe levels and cross-polarization performance. These improvements hold significant potential for broader application. Moreover, the simulation and measurement results are in close agreement.

High efficiency high gain low side lobe level and slant polarization monopulse antenna using cavity backed slot coupled patch antenna

In this paper, a multilayer monopulse antenna at Ku-Band with high efficiency, high power handling capability, high gain, 45° linear polarization and low sidelobe is presented. A new slot antenna is proposed as a radiating element based on a cavity-backed slot-coupled patch antenna. Using an enclosed cavity structure reduces coupling between antenna elements, thus increasing the antenna efficiency. The sub-array antenna has been designed to reduce the feed network complexity. A cavity power divider and feeding slots are inserted between the layers of the sub-array to compact it. An innovative feeding network has been designed with two-dimensional Chebyshev distribution. The simulated impedance bandwidth is 11%. The peak gain is 38.4 dBi and the sidelobe level of lower than 18 dB with a half-power beamwidth of approximately 2.4° for sum patterns at the center frequency and efficiency is more than 86% across the bandwidth. The maximum value of null depth for the difference patterns is − 38 dB. The radiation patterns have good symmetry in both E- and H-planes. The simulation results are compared with the results obtained from the built part of the antenna. the measurements results are in good agreement with the simulation.

Wideband Circularly Polarized Multimode Horn Array Antenna Using Single Layer E‐Plane Waveguide Sequential Feeding Network

ABSTRACTThis paper presents the design and fabrication of a 4×4 array antenna based on multi‐mode horn elements and sequential feeding network. The multi‐mode horn antenna is a structure that can suppress grating lobes and side lobe levels by excitation and combining different modes of electromagnetic wave radiation. The sequential feeding network is a technique that can generate circularly polarized radiation from linearly polarized elements by arranging them in a square array with 90° rotations and feeding them with 90° phase difference. The proposed array antenna achieves wideband impedance matching and axial ratio performance, as well as high gain and low complexity. The array antenna operates from 9.9 to 12.6 GHz, with a maximum gain of 24.5 dBi at 11 GHz. The array antenna is fabricated using CNC milling and measured in an anechoic chamber. The measured results agree well with the simulated ones, validating the effectiveness of the proposed design.

A Review on Multi-Geometrical Antenna Reflector

Parabolic antennas are among the most important devices for long-distance communications because of their significant advantages in terms of directivity, gain, and power handling capabilities. Hat feeds are frequently used as feeders for parabolic antennas because they exhibit low levels of cross-polarisation, low sidelobes, and low reflection coefficients. However, hat feeds possess a limited impedance bandwidth (IBW) range of just 30% and are not suitable for use in wideband applications. More work is being done with the objective of increasing the hat feed’s bandwidth capacity. The fundamental structure of a hat feed comprises a hat sub-reflector, circular waveguide, and dielectric material to provide structural support. The hat feeder had a bandwidth capacity of 10% at first. Later, the Chinese hat feed was introduced and used, resulting in a notable enhancement of the bandwidth, with an increase of 18%. The hat feed's geometric structure is redesigned with the help of a generic algorithm optimisation to further enhance the bandwidth, resulting in a 33% improvement.

A high-gain gap waveguide-based 16 × 16 slot antenna array with low sidelobe level for mmwave applications

This study presents the design of a high-gain 16 × 16-slot antenna array with a low sidelobe level (SLL) using a tapered ridge gap waveguide feeding network for Ka-band applications. The proposed antenna element includes four cavity-backed slot antennas. A tapered feeding network is designed and utilized for unequal feeding of the radiating elements. Ridge gap waveguide technology is used to reduce the feeding network loss and achieve a low-loss array antenna. The feed layer of the proposed antenna is coupled to a standard rectangular waveguide (WR-28) using a proper transition. The measured results show an impedance bandwidth of more than 17% over the frequency range of 27.5–32.6 GHz covering one of the standard vehicle-to-satellite band (29.4–31.0 GHz) and 5G mmWave N261 band (27.5–28.35 GHz), a maximum gain of 28.9 dBi, and SLL lower than − 20 dB. Thanks to its high performance and desirable features, the proposed antenna shows potential for use in vehicular radar systems and high data rate mmWave communications.

Synthesis of the Large-Scaled 64 × 64 Thinned Array Using the Branch and Bound Technique with Convex Optimization for Satellite Communication

This paper presents the synthesis of a 64 × 64 thinned array, using the branch and bound technique with convex optimization and a low sidelobe level for satellite communication. The branch and bound technology decomposes optimization into several subproblems. The convex optimization transforms the optimized variable binary [0, 1] of the thinned array into a continuous variable, i.e., from 0 to 1. Based on the branch and bound technique with convex optimization, the fast and accurate convergence of the synthesis of large-scale thinned array was achieved, and 2400 elements were selected for a full 64 × 64 array with a sidelobe level that satisfies the system requirements. The proposed thinned array with 2400 elements was simulated via full-wave 3D simulation. A prototype of the proposed thinned array was fabricated and measured. The simulated and measured results verified the effectiveness of the branch and bound technique with convex optimization.

Design of TMLAA for the Utilization of Radiated Harmonic Beam Over Digital Modulation Schemes

ABSTRACTThis work presents the effective steering of multi‐harmonic beams of a time‐modulated linear antenna array (TMLAA) for multi‐channel communication. A classroom learning‐inspired Teaching Learning Based Optimization (TLBO) is utilized for active duration optimization of the 16‐element TMLAA for harmonic steering. The simulation study employing the optimization technique effectively steered the first two harmonic beams with enhanced radiated power and considerable Sidelobe level (SLL) below . Further, for practical validation, the measurement of the fabricated prototype is presented for one scenario. Finally, the use of harmonic beams for the communication links is validated by measuring the bit error rate (BER) of the considered digitally modulated scheme.

Guided and Space Waves Multiplexed Metasurface for Advanced Electromagnetic Functionalities in Microwave Region.

Nowadays, metasurfaces have attracted considerable attention due to their promising and advanced control of electromagnetic (EM) waves. However, it is still challenging to shape guided waves into desired free-space mode, while simultaneously manipulating spatial incident waves using a single metasurface. Herein, a class of metasurfaces capable of multiplexing guided and space waves is proposed to achieve advanced EM functionalities in microwave regions, which can find great application potentials in radar systems, wireless communications, and wireless power transfer (WPT). The proposed metasurface, composed of specially designed meta-atoms with polarization-dependent radiation and reflection properties, provides the capability to fully manipulate complex amplitude of guided waves and reflection phase of space incident wave independently and simultaneously, thus enabling arbitrary radiation and reflection functionalities without encountering crosstalk issues. As examples of potential applications, three advanced EM functionalities operating in both far-field and near-field regions are presented: low-sidelobe microwave antenna with reduced radar cross section (RCS), multifunctional WPT, and feed multiplexed holograms, respectively. The far-field characteristics of the low sidelobe level antennas showing radiated beams at ±30° together with RCS reduction under arbitrarily polarized incidences are validated by both simulations and measurements. A good agreement between experiments and simulations is also observed for the near-field intensity distribution of the hologram, which further validates the feasibility of near-field shaping. The findings significantly expand the capabilities of metasurfaces in manipulating EM waves and stimulate advanced multifunctional metadevices facing more challenging and diversified application demands.

Pulse splitting technique for low sidelobe time-modulated antenna array synthesis with harmonic suppression

Abstract In this paper, pulse splitting approach is proposed to simultaneously reduce the sidelobe level (SLL) of fundamental signal and maximum sideband levels (SBLs) of harmonic signals for time-modulated linear array (TMLA). This is achieved by controlling only the periodic switching time sequence of each element of the TMLA. In pulse splitting, the on–off switching sequence of each radiating element is characterized by multiple rectangular sub-pulses within the modulation period which increase the degrees of freedom in order to better synthesize the desired fundamental pattern with simultaneous suppression of harmonic or sideband radiation. A genetic algorithm is employed to optimize the switch-on and switch-off instants of each sub-pulse for each element for 16-element uniform amplitude, phase, and space linear antenna array. The simulation results reveal that the proposed method can achieve the desired patterns with very low SLL and SBLs compared with previous published results.

Simultaneous Multibeam Clustered Phased Arrays Analysis Using Mixed and Multiple Antenna Element Factors.

A novel design strategy for improving the radiative performance of simultaneous multibeam (SMB) phased arrays is addressed. The proposed scheme relies on the adoption of mixed and multiple antenna element factors with a dynamic selection of their radiation patterns whose choice depends on the desired SMB pointing directions. In addition, a Penrose-inspired clustering technique is also employed for reducing the array feed points. Compared with traditional phased arrays based on a single antenna element factor, the novel array architecture allows the scan angle range to be widened by improving the minimum array gain as well as reducing the peak side lobe level (PSLL). The superior radiative performance of the proposed approach with respect to the clustered phased arrays with a single-mode element factor is assessed in SMB scenarios comprising two and three main lobe peaks. The notable SMB radiative improvement has been also confirmed from a statistical point of view by considering up to four and five concurrent main lobes. The remarkable radiative improvements confirm the effectiveness of the proposed solution, which also represents an appealing candidate for its exploitation in multiuser and multibeam communications.

Ultrasonic nonlinear frequency diverse array: principle and applications

In ultrasonic testing, omnidirectional wave propagation presents challenges of nonfocus energy loss and interface interference. Traditional phased array (PA) methods, despite their focusing capabilities, suffer from limitations in energy utilization and target detection accuracy. Frequency diverse array (FDA) technology, initially developed for radar, has demonstrated potential for improved range-angle-dependent ultrasonic beampatterns but still exhibits limitations due to S-shaped coupling. This study proposes an ultrasonic nonlinear frequency diverse array (ultrasonic-NFDA) with nonuniform frequency offsets to address these issues. The ultrasonic-NFDA employs modulated frequency offsets by introducing nonlinear carrying functions and incorporating additional parameters to manipulate beamforming and enhances energy concentration at focal points. Furthermore, the multi-objective differential evolution algorithm is used for parameter optimization. The proposed method decouples the range-angle beampattern and improves the signal-to-interference-plus-noise ratio. Numerical evaluations and simulations demonstrate that ultrasonic-NFDA outperforms the ultrasonic linear FDA and PA series, achieving better peak sidelobe level and half-power beam width. Experimental validations confirm the effectiveness of ultrasonic-NFDA in practical ultrasonic testing scenarios, showing significant improvements in defect detection and imaging clarity. The optimized beampatterns effectively reduce artifacts and enhance the precision of defect localization. The proposed integration of nonlinear frequency offsets and parameter optimization in array testing offers a robust solution for more accurate and efficient ultrasonic inspection methodologies.

A sidelobe level control algorithm for wide-beam power gain pattern synthesis via array antenna

The paper tries to maximize the minimum power gain in a wide-beam mainlobe with a controllable peak sidelobe level (PSLL) by solving the power gain pattern synthesis (PGPS) problem. Since the PGPS problem is nonconvex, it cannot be solved effectively in polynomial time. In this paper, the nonconvex PGPS problem is simplified by converting it into two nonconvex subproblems. The first subproblem's solution space is divided into a finite set of smaller spaces in which the solution has a closed-form, resulting in the subproblem being pseudo-analytically solvable. The second subproblem's solution can be rapidly obtained with a bisection searching strategy. In such a way, the original problem can be solved effectively by iteratively solving these two subproblems. Another advantage of the proposed algorithm is that its convergence is theoretically guaranteed and the PSLL is strictly controllable. Numerical examples with both isotropic element pattern (IEP) array and active element pattern (AEP) array are simulated to validate the effectiveness and superiority of the proposed algorithm by comparing it with the existing algorithms.

Enhanced Phase Coherence in Series‐Fed Patch Array Antenna: A Design Method for Uniform Element Spacing With Low Sidelobe Levels

ABSTRACTMicrostrip series‐fed patch array antenna (SFPA) is increasingly prominent in millimeter‐wave radar systems. Especially, SFPA with tapered amplitude using Dolph–Chebyshev, Taylor, and Binomial distribution has been developed to reduce a sidelobe level (SLL), which is critical to radar resolution. Even though reported designs of SFPA have achieved notable reductions in SLLs, the patch element and inter‐element spacing optimized by simulation over the entire array design can't guarantee perfect in‐phase radiation. Consequently, for nonuniform SFPA designs, achieving precise in‐phase radiation necessitates a theoretical approach and a thorough phase analysis of each element. In this article, we present a noniterative design method to ensure in‐phase feeding to each patch element by accurately compensating for the phase difference encountered in nonuniform SFPA. This approach begins with designing the electrical length of each patch element to be equal to 35 GHz. Subsequently, delay lines are then designed to provide in‐phase feeding across the array while maintaining uniform spacing between elements. Consequently, we fabricated three 8‐element SFPAs operating at 35 GHz and compared their performance, and the proposed design shows an SLL of –20.7 dB with a radiation angle of .

High Gain Radial Line Slot Array Antenna (RLSA) Integrated with Frequency Selective Surface (FSS) for mm-wave 5G Applications

Abstract The proposed RLSA antenna incorporates a new metamaterial designed at 26 GHz resonance frequency, utilizing a Rogers 5880 substrate layer that has a 1.575 mm thickness. The diameter of the RLSA antenna in Free-space wavelength is 17.34λ0. This RLSA antenna, equipped with a frequency selective substrate (FSS) metamaterial reflector, operates within the frequency range of 22.5 to 30.5 GHz, obtaining a 24.58 dBi realized gain. This development is capable of enhancing the gain and reducing the side lobe level, making it compatible with 5G millimeter-wave applications.

Design of Nonstandard Waveguide Slot Array Antenna for High‐Power Applications

ABSTRACTWaveguide slot array antennas are extensively used in radar systems, satellite communications, and wireless networks due to their high gain, low side lobe levels, and good impedance matching. Conversely, designing these antennas for high‐power scenarios with non‐standard configurations presents challenges. This paper proposes a novel Mode Matching Based Deep Neural Method (MMbDNM) to optimize the design and performance of waveguide slot array antennas. By integrating deep learning with mode‐matching techniques, the method streamlines antenna design, reducing development time and cost while maintaining high performance across multiple frequency bands. The proposed (MMbDNM) method achieves a frequency of 10.4 GHz; the antenna achieves a high coupling coefficient of 0.99, indicating efficient energy transfer between slots. The power handling capability of 0.99 W ensures robust performance under high‐power conditions, while the radiation pattern with a gain of 0.95 dB suggests effective signal propagation. Additionally, a bandwidth of 1.1 GHz allows for versatile application across a range of frequencies, contributing to the antenna's overall efficiency and adaptability. The results demonstrate improved antenna efficiency and adaptability, making it ideal for waveguide junctions used in complex electromagnetic systems.