Azimuth Beam Research Articles

Controllable split polarization singularities for ultra-precise displacement sensing

The topic of optical precise displacement measurement has garnered significant attention and generated widespread interest recently. The use of optical singularity offers a potential solution for this purpose, although effectively manipulating the singularity in an ideal manner remains challenging. In this work, we propose a theoretical approach to achieve controllable position modulation of the C-point in the focal plane, whose spatial position can be easily modulated by adjusting the relative offset factor β and the offset angle α of an azimuthal polarization beam (APB), while the interval and orientation of the C-points can be flexibly regulated. Notably, the chiral polarization state undergoes a distinct reversal along the link-line connecting the two C-points, thereby providing a promising approach for accurate displacement sensing. To evaluate its sensing characteristics, the varying pattern of the scattered field intensity is monitored when sweeping a gold helix and nanoparticle along the link-line. The results of simulation quality index Q verify that the equilibrium factor of the scattering field possesses an obvious linear relationship with the displacement, signifying a precise sub-nanometric sensitivity. This research introduces new methods for the flexible control of polarization singularities in tightly focused fields, thereby enhancing the utilization of circular polarization properties near C-points for displacement sensing. These findings not only enrich the field of nanometer measurement technology but also pave the way for new avenues of research in this domain.

Compact-size Lightweight Beam-reconfigurable ESPAR Antenna with Parasitic Elements for UAV Applications

This paper presents a compact lightweight beam-reconfigurable antenna system for unmanned aerial vehicles (UAVs). The antenna system consists of a central active monopole element surrounded by eight parasitic elements, which can be controlled using PIN diodes to switch the beam across four elevation angles and eight azimuth beams. This beam-reconfigurable antenna system has several advantages over traditional UAV antennas, including light weight, efficiency, and compactness. The antenna system operates at 5.09 GHz and achieves a measured peak gain of 4.55 dBi, with a remarkably low weight of 9 g and a size of 1.00λ0×1.00λ0×0.22λ0.

Resonance of vector vortex beams in a triangular optical cavity

We experimentally demonstrate resonance of first-order vector vortex beams (VVB) with a triangular optical cavity. We also show that, due to their symmetry properties, the VVBs commonly known as radial and azimuthal beams do not resonate at the same cavity length, which could be explored to use the triangular resonator as a mode sorter. In addition, an intracavity Pancharatnam phase shifter (PPS) is implemented in order to compensate for any birefringent phase that the cavity mirrors may introduce.

Research on Azimuth DBF Method of HRWS SPC MAB SAR Imaging Mode with Non-Ideal Antenna Mode

Single-phase center multiple azimuth beam (SPC MAB) mode is an effective method for high-resolution wide-swath (HRWS) SAR imaging. The traditional azimuth spectrum reconstruction method for SPC MAB mode is based on the combination scheme from which fake targets along the azimuth direction arise because the inter-beam interference is not considered. When the real antenna mode is inconsistent with the ideal one, the disadvantages of the combination scheme become more serious. In this paper, based on the basic theory of the low-pass, band-limited, multiple-channel under-sampling and reconstruction, a novel digital beam-forming method is proposed for the SPC MAB imaging mode with ideal antenna mode first. The method analyzes the system functions of the sub-beams, based on which digital beam-forming filters are designed for all the sub-beams. The designed filters can reconstruct the correct wide-bandwidth azimuth spectrum and suppress the inter-beam interference simultaneously. Furthermore, the proposed method is extended to SPC MAB mode with the non-ideal antenna mode. The simulation experiments prove the validities of the proposed method both for azimuth spectral reconstruction and the inter-beams interfering suppressing, no matter that the SPC MAB’s antenna mode is ideal or non-ideal.

Azimuthal beam shaping in orbital angular momentum basis

Azimuthal beam shaping in orbital angular momentum basis

Using the Displaced Phase Center Azimuth Multiple Beams Technique with Spaceborne Synthetic Aperture Radar Systems for Multichannel Reconstruction of Accelerated Moving Targets

The displaced phase center multiple azimuth beams (DPCMAB) technique can help spaceborne synthetic aperture radar (SAR) systems obtain the high-resolution wide-swath (HRWS) imaging capacity, and azimuth multichannel reconstruction is usually required due to azimuth non-uniform sampling. Compared with stationary and moving targets, the range history and azimuth signal model of the moving target with an acceleration are obviously different. The azimuth multichannel signal model of an accelerated moving target is established, and the relationship between acceleration and Doppler parameters is analyzed. Furthermore, the impact of the acceleration on azimuth multichannel reconstruction and imaging results is simulated and analyzed. According to the azimuth multichannel signal model, an azimuth multichannel reconstruction approach for accelerated moving targets is proposed. The key point of the proposed reconstruction approach is the modified azimuth multichannel matrix, which is related not only to azimuth and slant velocities but also accelerations. The target’s velocities and accelerations are obtained using multiple Doppler parameter estimations. Compared with the conventional method of processing the raw data of accelerated moving targets, this proposed method could distinctly suppress image defocusing and pairs of false targets. Simulation results on point targets validate the proposed azimuth multichannel reconstruction approach.

Vector Beams with Only Transverse Intensity at Focus

In this work, the tight focusing of vector beams with azimuthal polarization and beams with a V-line of polarization singularity (sector azimuthal polarization) was simulated numerically using the Richards–Wolf formulas. It was demonstrated that in a tight focus for these beams, there is no longitudinal component of the electric field. Previously, a similar effect was demonstrated for azimuthally polarized light only. The longitudinal component of the spin angular momentum for these beams was calculated, and the possibility of creating sector azimuthally polarized beams (beams with V-line singularities) using vector waveplates was demonstrated.

Generation of highly azimuthal symmetric conical beam using the planar uniform circular array antenna for vehicular communication

Generation of highly azimuthal symmetric conical beam using the planar uniform circular array antenna for vehicular communication

System Design and Echo Preprocessing of Spaceborne Squinted Two-Dimensional Beam Scanning Synthetic Aperture Radar.

Conventional squinted sliding spotlight synthetic aperture radar (SAR) imaging suffers from substantial swath width reduction and complex processing requirements due to the continuous variation in the squint angle and the large range cell migration (RCM) throughout the data acquisition interval. A novel two-dimensional (2D) beam scanning mode for high-resolution wide swath (HRWS) imaging is proposed. The key to the novel imaging mode lies in the synchronous scanning of azimuth and range beams, allowing for a broader and more flexible imaging swath with a high geometric resolution. Azimuth beam scanning from fore to aft was used to improve the azimuth resolution, while range beam scanning was adopted to illuminate the oblique wide swath to avoid the large RCM and the serious swath width reduction. Compared with the conventional sliding spotlight mode, both the swath width and swath length could be extended. According to the echo model of this imaging mode, an echo signal preprocessing approach is proposed. The key points of this approach are range data extension and azimuth data upsampling. A designed system example with a resolution of 0.5 m, swath width of 60 km, and azimuth coverage length of 134 km is presented. Furthermore, a simulation experiment on point targets was carried out. Both the presented system example and imaging results of point targets validated the proposed imaging mode.

Series-feed UCA antenna for generating highly azimuthal symmetric OAM Beam for unmanned aerial vehicles

This paper presents a new approach to producing a conical beam (CB) with highly azimuthal symmetry through a series-feed uniform circular array (UCA) antenna using circularly polarized (CP) elements and the orbital angular momentum (OAM) technique. Most previously proposed antenna designs for generating CB radiation patterns using mode-combining techniques have complex structures and high costs. The proposed antenna utilizes the inherent properties of OAM waves to generate a conical-shaped beam with simplicity and compactness. The UCA antenna utilizes CP elements, which are rotated to provide the desired far-field phase for generating the OAM beam. This design achieves extensive signal coverage and is highly efficient, with minimal spurious radiation and low insertion losses. The experimental measurements validate that the OAM beam produced by the UCA antenna has high azimuthal symmetry at 6GHz. The OAM beam generated exhibits high mode purity and a peak gain of 10dBi, with a divergence angle of ± 22°.

Energy-Efficient Ground Base Station Antenna Array System for Wireless Back-Hauling and Two State Charging of Drone Base Stations

A ground base station (GBS) antenna array system (AAS) geometry and feed technique are proposed for 360 degree azimuth beam scan, elevation beam scan, azimuth beam-width control, elevation beam-width control, and in existing AASs these four capabilities do not coexist. Firstly, the results confirm that the number of active radio-frequency (RF) switches in the proposed AAS feed network is reduced by more than 99 %, and the AAS achieves a power consumption reduction of up to 50 % without fully connected (FC) architecture and 35 % with FC architecture compared to the existing AAS. Also, an independent GBS AAS azimuth and elevation plane beam-width control can be achieved from 65 to 0.01 degrees which makes it suitable for GBS-assisted wireless back-hauling plus wireless charging of unmanned aerial vehicle base stations (UAV-BSs), dynamic GBS sectorisation order control, and millimeter wave beam tracking. Also, a parallel concurrent UAV-BS battery charging configuration with power source swap capability is proposed to charge UAV-BS using the GBS back-haul and onboard power amplifier (PA) system as the power sources. The results show that the proposed charging configuration improves hovering time by 180.7 % compared to the existing onboard PA system configuration for battery charging. Furthermore, the proposed charging configuration can recharge the battery of the inactive state UAV-BS to increase the state of charge of two 16 Ampere hour batteries to 80 % in 180.13 minutes, and UAV-BS’s inactive state charging was not proposed in the existing onboard PA system configuration for UAV-BS’s battery charging.

An Improved UAV Bi-SAR Imaging Algorithm with Two-Dimensional Spatial Variant Range Cell Migration Correction and Azimuth Non-Linear Phase Equalization

The transmitter and receiver of unmanned aerial vehicle (UAV) bistatic synthetic aperture radar (Bi-SAR) are respectively carried on different UAV platforms, which has the advantages of flexible movement and strong concealment, and has broad application prospects in remote sensing fields. However, the range cell migration (RCM) and azimuth non-linear phase (ANP) of UAV Bi-SAR are seriously spatially variant along the range and azimuth directions, while the UAV Bi-SAR has a short operating range, complex trajectory and wide azimuth beam. Aiming at the problem that the RCM and ANP of UAV Bi-SAR in spotlight mode are difficult to correct and equalize due to the severe two-dimensional (2D) spatial variation, an RCM correction (RCMC) and ANP equalization (ANPE) method based on Doppler domain blocking is proposed. First, the azimuth spatial variance of RCM is eliminated by Doppler blocking, and the range spatial variant RCMC is realized by RNCS. Second, by combining Doppler blocking with azimuth nonlinear chirp scaling (ANCS), this method can adapt to ANPE with larger width and more severe spatial variation. At last, the criteria of Doppler blocking are given in detail, and the effectiveness of the proposed method is verified by UAV Bi-SAR real data and computer simulation.

System Design and Signal Processing in Spaceborne Squint Sliding Spotlight SAR with Sub-Aperture Block-Varying PRF

To tackle the problems of Doppler spectrum, aliasing caused by azimuth beam scanning and azimuthal serious non-uniform sampling in squint sliding spotlight synthetic aperture radar (SAR) with varying repetition frequency technology, the azimuth sampling method of sub-aperture block-varying pulse repetition frequency (SBV-PRF) is proposed, where the sub-aperture division judgement makes the azimuth acquisition time of each sub-block small enough so that the Doppler bandwidth caused by the Doppler center change can be ignored. Based on the echo signal characteristics of a SBV-PRF transmission scheme, an azimuth pre-processing method combining SBV-PRF transmission scheme with sub-aperture division is proposed. Using this method, de-skewing is first performed on each set of sub-aperture data to eliminate the additional Doppler bandwidth introduced by the squint angle, and then the azimuth signal resampling is performed to ensure different sub-aperture data have the same sampling rate. The SBV-PRF technology reduces the difficulty of azimuth signal pre-processing while ensuring the complete acquisition of the complete echo data of the squint sliding spotlight mode. The effectiveness of the SBV-PRF system design and the signal processing method is verified by the point target echo simulation and imaging simulation results.

Self-Complementary Hyperbolic Metasurface Antennas

Anisotropic Self-Complementary Metasurfaces (SCM) are structures constituted by a “self-dual” (according to Babinet’s duality principle) alternance of inductive and capacitive complementary strips. They support orthogonally polarized surface-wave modes with the same phase velocity in the principal direction of propagation. The isofrequency dispersion curves of these modes are hyperbolas, and therefore these metasurfaces (MTSs) fall in the category of hyperbolic MTSs. It is shown here that the hyperbolas may degenerate in same cases into almost straight lines, which implies that the velocity of energy transport is constantly directed along the complementary strips at any frequency and for any possible phasing orthogonal to the strips. In this circumstance, the SCM can be conveniently used to design dual-polarized leaky-wave antennas by modulating the impedances of the complementary strips. Each strip behaves as a channel, which can be independently fed with the desired phase and amplitude. We demonstrate here that these antennas exhibit a strong decoupling between both co-polar and cross-polar channels, even when the distance between strips is electrically small. This increases the performance of the antenna, especially in azimuthal beam scanning. A prototype at 2.6 GHz has been constructed and successfully measured confirming the theoretical conjectures.

High-quality micro/nano structures of 4H-SiC patterning by vector femtosecond laser

High-intensity femtosecond laser processing of hard and brittle materials such as silicon carbide (SiC) has poor surface quality and is prone to micro-cracks, making it difficult to meet the application requirements of silicon carbide microdevices. In this study, a method for fabricating high-quality micro-nanostructures of 4H-SiC using vector polarized light was proposed. The influences of linear polarization and vector polarization on the quality and surface morphology of processed SiC microgrooves were studied, and the micromachined size rule of microgrooves machined under different pulse numbers was summarized. The damage distribution of microstructures machined by linearly polarized light and vector polarized light were characterized by confocal Raman mapping. The study had shown that using vector beam, especially azimuthal polarization beam, can ensure the uniformity of the processing area, effectively reduce micro-cracks and chipping in the processing of hard and brittle materials, and obtain better processing quality. In addition, the vector polarized light can avoid the large microgroove taper during the processing, and ensure good structure size. Finally, a high-quality multi-ring structure was fabricated by an azimuthal polarization beam, which provides an accurate method for preparing microstructures with excellent performance.

Generation of multiple focal pattern via phase modulated radial and azimuthal variant vector beam

Generation of multiple focal pattern via phase modulated radial and azimuthal variant vector beam

A method of attitude error compensation for airship-borne meteorological radar

The attitude of the stratospheric airship is easily changed by various factors, resulting in the deviation of airship-borne meteorological radar beam direction, which is called attitude error. In this paper, an attitude error compensation method for airship-borne meteorological radar is presented. Based on the conversion between different coordinate systems, the method uses the attitude data of the airship to calculate the compensation angle of the beam in azimuth and pitch direction. Then a compensation strategy is proposed, which enables the radar beam to point to the ideal position even though the attitude of the airship changes. Finally,the experiment is carried out, and the experimental result shows that the method is effective.

An End‐Fed Programmable Metasurface Based on Substrate Integrated Waveguide for Novel Phased Array

A programmable metasurface antenna based on electrically tunable elements operating in 5G millimeter‐wave band, which has the features of low cost, easy manufacturing, low profile, easy integration with planar circuits, is proposed herein. The prototype consists of a 128‐element metasurface array, an 8‐channel beamforming chip as equal amplitude power divider networks, and a control network. Elements mounted with varactors to realize different states are controlled by DC bias signal from the back of a printed circuit board (PCB). By assigning different voltage values, array coding can be dynamically changed, thereby realizing beam steering. Both element dimensions and its location along substrate integrated waveguide (SIW) are optimized to better antenna performance. Experiment results show that the proposed metasurface can achieve not only the scanning range of ±70° for unidirectional beam in azimuth and ±40° in elevation but also ±50° for dual beam in azimuth. The whole prototype is fabricated based on PCB technologies, and good agreements among simulated and measured results are obtained. The proposed electrically tunable metasurface array is a good alternative to the traditional expensive phased array and has a great potential application prospect in radar and communication systems.

Azimuthal vector beam illuminating plasmonic tips circular cluster for surface-enhanced Raman spectroscopy

Azimuthal vector beam illuminating plasmonic tips circular cluster for surface-enhanced Raman spectroscopy

Multi-Function Reflective Vector Light Fields Generated by All-Dielectric Encoding Metasurface.

Traditional optics usually studies the uniform polarization state of light. Compared with uniform vector beams, non-uniform vector beams have more polarization information. Most of the research on generating cylindrical vector beams using metasurfaces focuses on generating transmitted beams using the geometric phase. However, the geometric phase requires the incident light to be circularly polarized, which limits the design freedom. Here, an all-dielectric reflective metasurface is designed to generate different output light according to the different polarization states of the incident light. By combining the two encoding arrangements of the dynamic phase and the geometric phase, the output light is a radial vector beam when the linearly polarized light is incident along the x-direction. Under the incidence of linearly polarized light along the y-direction, the generated output light is an azimuthal vector beam. Under the incidence of left-handed circularly polarized light, the generated output light is a vortex beam with a topological charge of -1. Under the incidence of right-handed circularly polarized light, the generated output light is a vortex beam with a topological charge of +1. The proposed reflective metasurface has potential applications in generating vector beams with high integration.