Desired Amplitude Distribution Research Articles

Terahertz meta-polarizers for simultaneous control of the amplitude, phase, and polarization

Terahertz (THz) waves hold immense potential for advancements in areas such as in 6G wireless communications, non-destructive testing, and biomedicine. However, the underdeveloped control level of THz devices has been a severe obstacle. Here, a THz meta-polarizer, comprising rectangular metallic holes, is proposed to achieve the simultaneous control of the amplitude, phase, and polarization. Each unit of this meta-polarizer can function as a miniature linear polarizer. The component polarized along the short side can pass through the unit, while the component polarized orthogonally is unable to do so. Leveraging the principles of the Malus' law, we can adjust the desired amplitude distribution of the transmitted x-polarized wave by modifying its polarization distribution. This adjustment is made possible by tuning the azimuth angle of each hole. The phase delay of the transmitted wave can be further manipulated by adjusting the hole dimensions perpendicular to the polarization direction. For given near-field amplitude distributions, the required phase distributions for generating far-field target holograms can be calculated using the Gerchberg–Saxton algorithm based on Fresnel diffraction theory. The meta-polarizer then realizes calculated phase distributions, enabling the creation of the required holograms. As a proof of concept, we designed THz meta-polarizers that can achieve two- and four-level amplitude holograms in the near field, respectively. Moreover, we also manipulated the phase distributions, allowing us to decouple the near- and far-field holograms. The experimental results agree well with the simulations. Owing to its ability to simultaneously control the phase, amplitude and polarization, the proposed THz meta-polarizer holds great application potential in 6G wireless communications, radar detection systems, and holography.

Amplitude Matching for Multizone Sound Field Control

A multizone sound field control method, called amplitude matching, is proposed. The objective of amplitude matching is to synthesize a desired amplitude (or magnitude) distribution over a target region with multiple loudspeakers, whereas the phase distribution is arbitrary. Most of the current multizone sound field control methods are intended to synthesize a specific sound field including phase or to control acoustic potential energy inside the target region. In amplitude matching, a specific desired amplitude distribution can be set, ignoring sound propagation directions. Although the optimization problem of amplitude matching does not have a closed-form solution, our proposed algorithm based on the alternating direction method of multipliers (ADMM) allows us to accurately and efficiently synthesize the desired amplitude distribution. We also introduce the differential-norm penalty for a time-domain filter design with a small filter length. The experimental results indicated that the proposed method outperforms current multizone sound field control methods in terms of accuracy of the synthesized amplitude distribution.

Low-Sidelobe-Level Circularly Polarized Short Leaky-Wave Antenna With A-Shaped Element Based on Substrate Integrated Image Guide

In this letter, a low-sidelobe-level (SLL) circularly polarized (CP) leaky-wave antenna with A-shaped elements is proposed based on substrate integrated image guide (SIIG). The A-shaped CP radiating element consists of a horizontal linearly polarized (LP) structure and a vertical LP structure. The horizontal LP wave and the vertical LP wave can be excited by a pair of inclined transversal metal strip patches and a longitudinal metal strip patch, respectively. Their phases are orthogonal and amplitudes can be controlled to be equal by adjusting the tilted angle of the horizontal LP structure and the length of the vertical LP structure. Moreover, the longitudinal metal strip patch is modified to the V-shaped strip patch, which can realize the field cancellation, thereby achieving the boresight radiation for such a leaky-wave antenna. Furthermore, a low SLL is realized by controlling the aperture-field distribution to obtain the desired amplitude distribution and the relatively small axial ratio. In addition, because of the short waveguide wavelength of the SIIG, this feedline can be used to achieve the small interelement spacing and element size, thereby realizing the short length of the array. The measured peak gain of this antenna is 12.3 dBic, the SLL is –19.1 dB and the efficiency is 92.3% at the center frequency of 14 GHz.

Substrate Integrated Waveguide Slot Array Antenna to Generate Bessel Beam With High Transverse Linear Polarization Purity

The transverse linearly polarized beam can maintain its polarization when reflected, which is important for a detection system. Most of the existing planar Bessel beam generators are implemented in a central feeding radial topology and hard to generate the Bessel beam with the transverse linear polarization. In this communication, a substrate integrated waveguide (SIW) slot array antenna is proposed to generate the transverse linearly polarized Bessel beam. The desired phase and amplitude distribution of the Bessel beam can be easily realized by such an array. With the inherent 0°/180° output phase of the comb-like divider considered, the desired 0°/180° phase distribution is implemented by placing adjacent slots on the opposite (0°) or the same side (180°) within a linear array and by employing adjacent linear arrays with the inverse (180°) or the same (0°) slot offset direction accordingly. The offset of the slot, as well as the tuning metalized vias within the comb-like divider, is modulated to generate the desired amplitude distribution. After reducing the influence of the rectangularly truncated aperture by adding a Gauss-tapered amplitude distribution, a transverse linearly polarized Bessel beam SIW slot array antenna is designed with more than 100 mm depth-of-field (DoF) and less than −25 dB cross polarization. To the best of our knowledge, it is the first design to generate the transverse linearly polarized Bessel beam by a planar array antenna.

W‐band low‐sidelobe series‐fed microstrip antenna array based on impedance matching section weighting method

A W-band low-sidelobe series-fed microstrip antenna array is proposed here. Impedance matching section weighting method is used in element series-fed weighting. This feeding method can effectively realise the desired amplitude distribution and sidelobe level of −30.1 dB is obtained in this design. The designed low-sidelobe antenna has great practical value in antenna of W-band portable radar.

Low-Profile Transmitarray Antenna With Cassegrain Reflectarray Feed

This paper proposes a novel hybrid antenna configuration, which combines two kinds of high-performance antennas, i.e., reflectarray and transmitarray, creating a low-profile low-cost low-mass design with both amplitude and phase distribution controls. In this hybrid arrangement, a flat Cassegrain reflectarray, with compact ring focus, is implemented as the feed to illuminate the upper transmitarray. In the process of reflectarray design, the particle swarm optimization technique is utilized to synthesize the phase distribution on the reflectarray aperture to generate a desired amplitude distribution on the upper transmitarray aperture. During the transmitarray design process, the dimensions of the double-loop elements of the upper transmitarray are adjusted to compensate for the phase delay of the wave from the lower reflectarray and form a desired phase distribution on the transmitarray aperture. A detailed design procedure for a Cassegrain-reflectarray-fed transmitarray antenna with a small focus-to-diameter ratio of 0.3 is presented. The simulated and measured results demonstrate that the hybrid-configuration antenna can achieve an aperture efficiency of around 40%.

Effective iterative method for accurate amplitude modulation in complex optical field generation

We experimentally demonstrate an iterative method for a vectorial optical field generator (VOF-Gen) to achieve accurate amplitude modulation in creating arbitrary complex beams. The method could converge rapidly in several steps and is effective to optimize the patterns applied to the liquid crystal spatial light modulators on a pixel-by-pixel basis to obtain arbitrary desired amplitude distribution. Meanwhile, this method could also mitigate the speckles caused by the defects of the optical components used in the VOF-Gen system and calibrate the wavefront related to the amplitude distribution. Several kinds of optical fields with different intensity distributions are successfully generated to verify the capability and versatility of the presented technique. This effective method may find many important applications in optical tweezers, microscopy, and unidirectional coupling.

A New Strategy to Design Microstrip Antenna Array With Low Side-Lobe Level and High Gain

A new strategy for designing low side-lobe level (SLL) antenna array is presented. This strategy utilizes special arrangement of antenna elements rather than direct tapered excitation amplitude to obtain an equivalent desired amplitude distribution in the main planes and thus achieve low SLL and high gain concurrently. To illustrate the strategy, 9-element microstrip antennas are arranged in four manners. An equivalent analysis method is also proposed to predict the SLL of the arrays. Using this method, a fast analysis of the trend of a microstrip array for a low SLL can be performed and thus a proper array-element arrangement is acquired. Both numerical and experimental results demonstrate that the SLLs in E and H planes of the novel array are fairly low. Meanwhile, the main beam of the novel array is almost the same with that of a conventional high-gain array. The antenna arrangement manner and the proposed strategy are particularly suitable for applications when low SLL and high gain are both demanded.

Speckle-suppressed phase-only holographic three-dimensional display based on double-constraint Gerchberg-Saxton algorithm.

The Gerchberg-Saxton (GS) algorithm is widely used to calculate the phase-only computer-generated hologram (CGH) for holographic three-dimensional (3D) display. However, speckle noise exists in the reconstruction of the CGH due to the uncontrolled phase distribution. In this paper, we propose a method to suppress the speckle noise by simultaneously reconstructing the desired amplitude and phase distribution. The phase-only CGH is calculated by using a double-constraint GS algorithm, in which both the desired amplitude and phase information are constrained in the image plane in each iteration. The calculated phase-only CGH can reconstruct the 3D object on multiple planes with a desired amplitude distribution and uniform phase distribution. Thus the speckle noise caused by the phase fluctuation between adjacent pixels is suppressed. Both simulations and experiments are presented to demonstrate the effective speckle noise suppression by our algorithm.

PARAMETRIC STUDY OF WAVEGUIDE SLOTS AND ANALYSIS OF RADIATION PATTERN FOR THE DESIGN OF WAVEGUIDE ARRAY ANTENNA

The characteristics of radiating longitudinal slots in a rectangular waveguide have been studied. A moment method solution is used with entire basis expansion and testing functions (Galerkin) including the effect of wall thickness. It is shown in this paper. 1) The determination of different parameters like VSWR, reflection coefficients and insertion loss are calculated with the results of normalize reactance and conductance. 2) The Taylor distribution approach with specific SLL for desired linear aperture array antenna. The resonant conductance or resistances are calculated from desired amplitude distribution. The formulation uses transmission matrix approach. The computed result shows excellent agreement with measured results. CST Microwave studio is used for the simulation and is totally based on FIT techniques.

Synthesis of the sequence of phase correctors forming the desired field

We propose a novel procedure for synthesis of a sequence of phase correctors forming a scalar wave beam with desired amplitude distribution. The synthesis procedure is based on successive compensation of the beam phase to the value determined by the desired field at the system output. Each subsequent phase corrector increases the coupling coefficient between the obtained and desired fields. The procedure is used for designing quasi-optical converters of gyrotrons and millimeter-wave transmission lines.

An improved thinning method for density tapering of planar array antennas

A thinning method is presented to realize the desired aperture distribution in a planar array antenna with elements fixed on an array lattice. In this method elements to be excited are determined by quantizing cumulative weights which are calculated from the desired aperture distribution. At first, this method is applied to density tapering on orthogonal axes of a planar array. Radiation patterns of the planar array determined by this method are compared with those by the desired amplitude distribution, and the results show good coincidence. Next, this method is extended to density tapering on four axes, that is, orthogonal and diagonal axes of a planar array. Moreover, this method is applied to density tapering with multi-amplitude level elements in order to enhance directive gain of thinned array. Lastly, a rectangular planar array was fabricated, and its radiation patterns were measured. Measured results were in good coincidence with calculated ones, and the usefulness of this method was verified.