Grating Lobe Suppression Research Articles

Improving the Performance of the Optical Antenna for Integrated LIDAR with Optical Phased Arrays through High Contrast Grating Structure on SOI Substrate

A novel optical antenna for integrated LIDAR with optical phased arrays is proposed and simulated. A HCG structure is used to achieve extremely efficient emission. The emission efficiency is as high as 93.94% at 1550 nm, which exceeds 50% in a range of wavelength from 1480 nm to 1620 nm. The antenna can achieve a perfect grating lobe suppression with background suppression of 28.4dB when the phase difference between adjacent waveguides is 0. A 16-wire optical phased arrays LIDAR can easily achieve a scan range of ±22.8°×20.2° with a beam width of 2.4°×2.5°, by employing the optical antenna proposed.

Transmissive/Reflective Frequency Selective Surface for Satellite Applications

A single-layered triband transmissive/reflective frequency selective surface (FSS) with incident angle up to 80° and polarization stability is designed, simulated, and measured. The periodic element includes a compact hexagonal arrangement of Y-slot and Y-patch, which can effectively reduce unit spacing to 0.16 $\lambda $ . Compared with the conventional hexagonal arrangement, compact arranged Y-unit has a larger band range from 1 to 40 GHz using grating lobes suppression. Controllable passband in X -band and reflectband in Ku -band and Ka -band are proposed. Transmission loss is less than 1 dB in 9.41 GHz in bandwidth of 5% when the incident angle is from 0° to 80°, while the return loss in bandwidth of 5% when 14.5 and 35 GHz is less than about 1 dB when incident angle range is from 0° to 80°/60° for dual polarization, respectively. Hyperboloid FSS is simulated, and performance of transmission and reflection is good. To the best of our knowledge, this is the first report of single-layered FSS that simultaneously operates for angle of incidence more than 60° in X/Ku/Ka -bands for dual polarization.

Enhanced Imaging of Building Interior for Portable MIMO Through-the-wall Radar

Portable multi-input multi-output (MIMO) radar system is able to imaging the building interior through aperture synthesis. However, significant grating lobes are invoked in the directly imaging results, which may deteriorate the imaging quality of other targets and influence the detail information extraction of imaging scene. In this paper, a two-stage coherence factor (CF) weighting method is proposed to enhance the imaging quality. After obtaining the sub-imaging results of each spatial sampling position using conventional CF approach, a window function is employed to calculate the proposed “enhanced CF” adaptive to the spatial variety effect behind the wall for the combination of these sub-images. The real data experiment illustrates the better performance of proposed method on grating lobes suppression and imaging quality enhancement compare to the traditional radar imaging approach.

Nested Array Sensor With Grating Lobe Suppression and Arbitrary Transmit–Receive Beampattern Synthesis

Sparse arrays have potential advantages over their regularly spaced counterparts, but they will generate undesired grating lobes. This paper investigates a sparse linear phased-array for grating lobe suppression and arbitrary transmit–receive beampattern synthesis. To achieve these aims, a modified two-level nested-array is developed, which provides increased degrees-of-freedom than a standard uniform linear array with the same number of elements via the difference co-array processing algorithm in the receiver. A least squares and iterative algorithm is also devised for linear array arbitrary transmit–receive beampattern design with minimum number of antenna elements. Moreover, the nested-array design is exploited for minimum variance distortionless response adaptive beamforming and direction finding. The effectiveness of the proposed approach is verified through extensive numerical results.

Grating lobes suppression by adding virtual receiving subaperture in synthetic aperture imaging

A method of suppression of grating lobes is presented, analyzed, and verified. The method is based on creating a Virtual Receiving Subaperture (VRS) by adding virtual transducer elements not existing in the physical layout of the receiver. The VRS channels are filled with data based on signals from real channels. The analytical model of the synthetic aperture imaging system’s impulse response is presented to describe the properties of the VRS. The model shows a reduction of the receiving grating lobes’ amplitude (with a comparison to the main lobe’s amplitude) by a magnitude equal to the number of receiving transducer elements. It is shown that effective properties of the entire system with a VRS are similar to a system with a pitch in the receiving aperture that is twice as small. The numerical calculations of the impulse response show a doubling of the signal to noise ratio, which results in a reduction of the receiving grating lobes. For experimental validation, the generalized Plane Wave Imaging with and without the VRS is compared with a basic synthetic transmit aperture (STA) imaging. The experiment confirmed that the use of a VRS allows for visualization of the objects in a medium in which they are not imaged without a VRS or are visualized with a lower contrast. The reduction of grating lobes attained using the proposed method is at the level of 15dB in the visualization of the superficial cyst.

A Robust Range Grating Lobe Suppression Method Based on Image Contrast for Stepped-Frequency SAR.

The magnitude error and phase error (MEPE) in the transfer function of a stepped-frequency synthetic aperture radar (SAR) system results in a periodic MEPE in the synthesized wideband waveform (SWW), which induces the grating lobes in the high-resolution range profile (HRRP). In this paper, a robust data-driven grating lobe suppression (GLS) method is proposed. Based on a contrast-based error estimation method and the grating lobes of the brightest scatterers in the SAR image, the periodic MEPE can be robustly estimated using the proposed method. By compensating the estimated periodic MEPE, the range grating lobes can be suppressed to the background level of the SAR image. Simulation results and real data processing have demonstrated the superiority of the proposed method.

A Range Grating Lobes Suppression Method for Stepped-Frequency SAR Imagery

Stepped-frequency synthetic aperture radar (SAR) system errors induce the periodic magnitude error and phase error (MEPE) in the synthesized wideband spectrum. The periodic MEPE results in periodic grating lobes in the high range resolution profile, which degrade the SAR image quality seriously. This paper presents a data-driven grating lobes suppression (GLS) method, named MEPE-GLS, to suppress grating lobes by estimating and compensating the periodic MEPE. Based on the dominant targets' image domain data, MEPE-GLS estimates the phase error and magnitude error by the weighted maximum-likelihood estimation and weighted least-squares estimation, respectively. In order to improve the signal-to-clutter-and-noise ratio (SCNR) of the data employed in the MEPE estimation, MEPE-GLS applies the discrete windows to selected targets to remove clutters between two adjacent grating lobes. Compared with conventional GLS methods, MEPE-GLS removes grating lobes effectively while at the same time preserves the original image information, and has no restriction on hardware, scenes, and spectrum reconstruction methods. Simulation and real data experiments validate the effectiveness and robustness of MEPE-GLS.

Wideband distributed coherent aperture radar based on stepped frequency signal: theory and experimental results

As the next generation radar, although the distributed coherent aperture radar (DCAR) has been proposed and some basic works have been developed in recent years, this new radar technology has not been researched systematically. In this study, the concept and closed-loop workflow of DCAR are described in detail first. Then, the coherent parameters (CPs), which play an important role to realise full coherence in DCAR, are estimated based on orthogonal signal and coherent signal. To investigate the limits of estimation accuracy of CPs, the Cramer–Rao lower bounds are derived. The estimation values of CPs are filtered using Kalman filter to improve the estimation accuracy. In the following, the wideband full coherence technology based on stepped frequency signal is proposed to improve system robustness to time synchronisation error, which makes the DCAR technology more realisable in engineering. Furthermore, a grating lobe suppression method based on modified genetic algorithm in synthetic array pattern of DCAR is presented. Ultimately, the experiments are carried out using test system to verify the theory of wideband DCAR.

Waveguide Slot Array Antenna with a Hybrid-Phase Feed for Grating Lobe Reduction

The design of a 112-element millimeter-wave waveguide slot array antenna to reduce the grating lobe level is presented. A hybrid-phase feeding technique combining a cophase feed and an alternating-phase feed is applied to facilitate the suppression of grating lobes. In addition, a stepped feed waveguide and offset coupling slots aligned in a line are employed to realize a tapered aperture distribution. As a result, grating lobe suppression of 8.1 dB was achieved on the diagonal planes compared to a conventional alternating-phase-fed waveguide slot array antenna. A prototype of the proposed antenna was fabricated and measured. The measured results show that the proposed antenna exhibits a −15 dB reflection bandwidth of 3.4%and an average realized gain of 26.72 dBi within the measured frequency range. Good agreement between the simulated and measured radiation patterns is also observed.

Wideband Grating-Lobe Suppression by Rotation of the Phased Array Stations in the SKA Low-Frequency Sparse Aperture Array

A simple cost-effective technique of wideband grating-lobe (GL) suppression by rotation of the phased array antennas is developed for application in a system of low-frequency sparse aperture array (LF-SAA) antennas of the square kilometer array (SKA) radio-telescope. The technique implies using of equal sparse planar circular antennas with the well-tried square lattice (SqL) distribution of the station antenna array sensors, which is known as the best in terms of production costs and maintenance charges. The peak levels of residual GLs in the fringe pattern of most pairs of the rotated antenna array stations do not exceed value of -17 dB over frequencies ranged from 70 to 450 MHz in the case of uniform antenna array element weighting, whereas the maximum levels of residual GLs are reduced to -25 dB when the Hamming weight tapering is applied.

A Novel Range Grating Lobe Suppression Method Based on the Stepped-Frequency SAR Image

The magnitude error and phase error (MEPE) in the transfer function of a stepped-frequency synthetic aperture radar (SAR) system results in a periodic MEPE in the synthesized wideband waveform, which induces the grating lobes in the high-resolution range profile. In this letter, a novel grating lobe suppression method based on the SAR image is proposed. In the paired-echo theory, a single sinusoidal term of the periodic MEPE in the frequency domain induces a pair of grating lobes in the time domain. Based on the magnitudes and phases of a strong scatterer and its grating lobes in the SAR image, the sinusoidal terms in the periodic MEPE can be estimated using the proposed method. By compensating for the estimated sinusoidal terms in the spectrum reconstruction, the corresponding grating lobes can be suppressed to the background level of the SAR image. The validity of the proposed method has been demonstrated using computer simulations and experiments based on real data.

Grating Lobe Suppression in Aperiodic Phased Array Antennas Composed of Periodic Subarrays with Large Element Spacing

The techniques of grating lobe (GL) suppression in planar phased array antennas composed of periodic subarrays with rectangular or triangular grids with large element spacing are considered. GL suppression is achieved using an aperiodic arrangement of subarrays. This approach provides a means to decrease GLs without a significant increase in structural complexity relative to periodic arrays; moreover, other antenna parameters do not essentially change compared with periodic arrays. Estimations of maximum GL suppression are presented. Antenna characteristics such as sidelobe level, beam efficiency, and aperture efficiency are also considered. The influences of element radiation pattern and amplitude tapering are analyzed. Examples of radiation patterns of such phased arrays are given.

Grating Lobe Suppression with Element Count Optimization in Planar Antenna Array

The novel approach of this paper describes the suppression of grating lobe level with the element count optimization in planar antenna array. Rectangular lattice (RL) and triangular lattice (TL) structures are chosen for determining the achievable array element patterns (EP) and further suppressing the grating lobe level. The element spacing and number of elements (10 × 20 array) are taken into account for particular lattice. Grating lobe peaks are observed for the 200-element planar array at maximum scan angle (θ) with the set frequency of 3 GHz. Further, it is found that 14°; bore sight elevation of rectangular lattice produces a transformed field of view, which permits a reduction in element count of 20.39% compared with 10° bore sight elevation. Finally, the typical values of elevation, element count and array size (25 cm2) are trained using artificial neural network (ANN) algorithm and element count is predicted after testing the network. The network shows a high success rate.

Grating lobes suppression method for stepped frequency GB-SAR system

A grating lobes suppression method for chirp-subpulse stepped frequency (CSSF) signals is proposed, which is applied to deformation monitoring using the ground based synthetic aperture radar (GB-SAR) system. This method is based on accurate estimation and correction of the phase and amplitude error along two dimensions (range and azimuth), i.e., the error estimation inside the subpulse (in-subpulse error) and across the stepped frequency subpulses (cross-subpulse error) of transmitted CSSF signals. Validated both with simulated data and experimental data recorded in the deformation monitoring campaign, it can be seen that the method as well as the relative conclusions can be fully and effectively applied to most of the stepped frequency systems.

HIGH POWER 12-ELEMENT TRIANGULAR-GRID RECTANGULAR RADIAL LINE HELICAL ARRAY ANTENNA

A 12-element triangular-grid rectangular radial line helical array antenna is proposed and investigated. The major characteristic of this antenna is that its radiation elements are arranged in triangular-grid, which is helpful to reducing the number of elements demanded for a certain antenna aperture and grating lobe suppression capacity. The radiation element is optimized to facilitate the manufacture. The feed system with six different groups of output ports is designed to obtain equal- amplitude output using three kinds of probes. An antenna prototype with the center frequency of 2.856 GHz is simulated and measured. In the range of 2.75-2.95 GHz, the experimental result shows an antenna VSWR below 1.2, an antenna gain over 16.3 dB, and an aperture efficiency more than 80%. The field distributions of this antenna are analyzed through simulation, which prove its advantage of high power-handling capacity. Its ability to be used as a sub-array is also demonstrated by forming a 48-element array antenna.

Experimental verification of pulse-probing technique for improving phase coherence grating lobe suppression.

Fabrication of high-frequency phased-array ultrasound transducers is challenging because of the small element- to-element pitch required to avoid large grating lobes appearing in the field-of-view. Phase coherence imaging (PCI) was recently proposed as a highly effective technique to suppress grating lobes in large-pitch arrays for synthetic aperture beamforming. Our previous work proposed and theoretically validated a technique called pulse probing for improving grating lobe suppression when transmit beamforming is used with PCI. The present work reports the experimental verification of the proposed technique, in which the data was collected using a high-frequency ultrasound system and the processing was done offline. The data was collected with a 50-MHz, 256-element, 1.26 λ-pitch linear array, for which only the central 64-elements were used as the full aperture while the beam was steered to various angles. By sending a defocused pulse, the PCI weighting factors could be calculated, and were subsequently applied to the conventional transmit-receive beamforming. The experimental two-way radiation patterns showed that the grating lobe level was suppressed approximately 40 dB using the proposed technique, consistent with the theory. The suppression of overlapping grating lobes in reconstructed phased array images from multiple wire-phantoms in a water bath and tissue phantoms further validated the effectiveness of the proposed technique. The application of pulse probing along with PCI should simplify the fabrication of large-pitch phased arrays at high frequencies.

Investigation of Scattering Properties of Large-Scale Aperiodic Tilings Using a Combination of the Characteristic Basis Function and Adaptive Integral Methods

This paper presents a hybrid approach for efficient analysis of electromagnetic (EM) scattering from large-scale aperiodic structures (e.g., aperiodic Penrose and Danzer tilings), which integrates the characteristic basis function method (CBFM) and the adaptive integral method (AIM). By performing a domain decomposition, a series of characteristic basis functions (CBFs) that are defined on a macro block and comprised of a relatively large number of sub-domain basis functions facilitate a substantial reduction in the method of moments (MoM) matrix size, enabling the use of a direct solver for large problems. The AIM is applied to accelerate the calculation of CBFM-reduced MoM matrices, significantly decreasing the CPU time and memory required for solving large-scale problems. As the size of one block becomes electrically large, the original CBFM combined with the AIM is employed to generate the initial CBFs by solving a large problem with multiple excitations, which results in efficiently constructing the final CBFs afforded by the singular value decomposition (SVD) procedure. This methodology produces a two-level “CBFM + AIM” hybrid algorithm for efficiently characterizing large-scale objects. The numerical results presented demonstrate the accuracy and efficiency of the proposed hybrid algorithm. Then, the developed solver is applied to investigate EM scattering properties of large-scale aperiodic tilings. The numerical results show that Penrose/Danzer tilings exhibit significantly improved grating lobe suppression as compared to their periodic counterparts.

Reflectarray Antenna at Terahertz Using Graphene

The use of graphene for fixed-beam reflectarray antennas at Terahertz (THz) is proposed. Graphene's unique electronic band structure leads to a complex surface conductivity at THz frequencies, which allows the propagation of very slow plasmonic modes. This leads to a drastic reduction of the electrical size of the array unit cell and thereby good array performance. The proposed reflectarray has been designed at 1.3 THz and comprises more than 25000 elements of size about λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /16. The array reflective unit cell is analyzed using a full vectorial approach, taking into account the variation of the angle of incidence and assuming local periodicity. Good performance is obtained in terms of bandwidth, cross-polar, and grating lobes suppression, proving the feasibility of graphene-based reflectarrays and other similar spatially fed structures at Terahertz frequencies. This result is also a first important step toward reconfigurable THz reflectarrays using graphene electric field effect.

Subarray Design Diagnostics for the Suppression of Undesirable Grating Lobes

This paper investigates various subarray pattern distortions that can cause the appearance of grating lobes with the aim to provide an insightful and valuable first-order diagnostic tool for antenna array designers. In typical subarray configurations, the emergence of undesirable grating lobes is a possibility due to distortions in the subarray array factor which can be caused by feeding errors, mutual coupling between elements and/or feed lines, or other discrepancies. This paper will focus on systematic errors that can arise in subarray designs that feature common element excitation schemes. Distortions will be categorized by amplitude and phase errors separately, demonstrating their distinct manifestations in each excitation scheme. Recognition of these manifestations can lead to better subarray designs and save significant time in the development of large array antennas. The concepts introduced here will be supported by analytical array factor calculations for 1 × N linear subarrays, full-wave simulations of a 1 × 4 subarray and 1 × 16 array, and representative measurements of two 1 × 16 arrays at Ku-band.

Adaptive Grating Lobe Suppression in Ultrasound Imaging

Adaptive grating lobe suppression is provided. Received ultrasound data is measured, compared or otherwise processed to determine the presence of grating lobe energy. A further process is then altered as a function of the level of grating lobe energy. In one embodiment, the adaptive grating lobe suppression is implemented in the receive beamformer. Data representing a virtual element is formed as a normalized sum of data from adjacent sparse elements. The data from the adjacent elements is correlated to determine the presence of grating lobe energy as a function of the amount of shift associated with the peak correlation. A phase shift is applied to the data representing the virtual element where sufficient grating lobe energy is determined. In another embodiment, an amount of grating lobe energy is measured by comparing data from prior to a filter with filtered data. The filter is selected to isolate main lobe energy from grating lobe energy. A gain is modulated as a function of any detected grating lobe energy or filtered or unfiltered data is selected for further processing.