Interferometric Angle Research Articles

A method for resolving the phase difference ambiguity in interferometric monopulse angle of arrival estimation

This paper presents a method to eliminate the phase difference ambiguity in angle of arrival (AOA) estimation using the radio-frequency-based interferometric monopulse technique. In order to uniquely determine the AOA, we utilize four directivities which are formed by using selected elements with the same weight function as the AOA estimation. We investigate the AOA estimation accuracy for the direction of the incoming wave from a high elevation angle and in multi-path propagation environments using a three-dimensional fading emulator. The results show that the proposed method is valid for complex propagation environments.

A Linear Technique for Artifacts Correction and Compensation in Phase Interferometric Angle of Arrival Estimation.

Radio localization and radio positioning are relevant research fields for many telecommunications technologies. Usually, the solutions proposed by the literature rely on adaptive techniques related to some parameters that can be extracted from the received signal in cooperative device tracking. In this paper, we explore the artifacts that may be introduced into Angle-of-Arrival estimation based on phase interferometry, and we introduce a simple technique to mitigate their impact. Details of the mathematical discussion are presented and the approach is experimentally validated. The experimental results are compared with raw data to demonstrate the effectiveness of the proposed technique.

Analysis of Group Delay and Phase Delay Algorithms for Short Baseline Interferometry

As a fast direction finding technology, interferometry has the advantages of simple algorithm and high sensitivity, so it is widely used in various direction finding systems. Short baseline interferometer Angle measurement is the basic principle of phase Angle measuring method, it is using the delay difference between different receiving station in the system to obtain the target azimuth information, has the advantage of high accuracy of Angle measuring, but interferometer is inevitable during the high frequency signal direction finding Angle measuring fuzzy problems exist, in order to solve this problem in general with phase delay method improve the interferometer Angle measurement accuracy, The group delay method is used to deblur. In this paper, group delay and phase delay algorithms are simulated and analyzed, and the simulation results prove the effectiveness of the proposed method.

Phased array radar system design based on single-send and multiple-receive for LSS-UAV target

In order to improve the precision of radar target positioning, the phased array frequency modulated continuous wave (FMCW) radar system based on single-send and multiple-receive is proposed for low altitude, slow speed, small Unmanned Aerial Vehicle (LSS-UAV) target. The much lower-cost passive electronically scanned array (PESA) radar technology has been employed for the azimuth electronically scanning. In addition, wide beam scanning beam of elevation direction is used to further expand the range of space coverage. Phase-comparison method is adopted to high-precision angle measurement of elevation direction in interferometer angle measurement system with dual distributed receivers. As a result, the novel radar system possesses the abilities of Doppler velocity measurement and linear FMCW distance measurement, as well as the high precision angle measurement at the same time. It can provide long distance, wide range, all-weather/time detection accurate target location information for optical system and electronic interception system to detect LSS-UAV targets for some more cost-sensitive applications in the homeland security market.

Onboard scanning system for photodetector with time delay and charge accumulation

The study describes scanning space-based assets which, by means of a flat scanning mirror and an optical system, provides the transformation of the object space into a temporal sequence of electronic signals of a photodetector with a time delay and charge accumulation. High accuracy of photodetector elements polling and scanning of the object space is due to the movement of the scanning mirror according to the indications of a non-contact interferometric angle sensor. The reciprocating rotary scanning by a flat mirror is kinetically compensated by the opposite motion of the flywheel, which minimizes residual perturbations on the space platform. To reduce the impulse energy consumption and the time of reversal between the scanning mirror and the compensating flywheel, magnetic reversal energy recuperators are used.

Note: Optimal choice of the reflector by phase analysis for heterodyne interferometric roll angle measurement.

The choice of an actual reflector instead of an ideal or perfect reflector has to be dealt with for heterodyne-interferometric roll angle measurement methods. The candidates of regular reflectors such as corner cube prism and right angle prism are analyzed by the homogeneous coordinate transformation method, which provides a theoretical basis for the determination of the actual reflector. Furthermore, the influences of the phase loss of the determined reflector are strictly argued due to non-perfect or natural characteristics itself. Several tactics are considered to solve this problem by phase analysis. By contrast, it is an optimal choice that mirrors-based right angle prism can improve evidently the phase loss by experiment.

Backprojection SAR interferometry

Synthetic aperture radar (SAR) interferometry uses the phase difference between two SAR antennas to obtain an elevation estimate of the imaged terrain. Using an initial digital elevation model (DEM), the time-domain backprojection algorithm implicitly removes the terrain height phase from images during image formation. The use of a DEM during image formation adds additional information to the process of interferometry, resulting in different sensitivities to conventional interferometry. This article presents a novel method of SAR interferometry using backprojected imagery. It is shown that the sensitivity and performance of backprojection interferometry is significantly different to that of conventional methods. Specifically, it is shown that backprojection interferometry is much less sensitive to errors in measurement of the interferometric baseline length and angle. This comes at the expense of higher sensitivity to phase errors. We conclude that backprojection interferometry is best suited for airborne operation.

Accelerated bone formation on photo‐induced hydrophilic titanium implants: an experimental study in the dog mandible

The purpose of this study was to investigate the effect of photo-induced hydrophilic titanium dioxide (TiO₂) on serum fibronectin (sFN) attachment, and further to evaluate initial osseointegration responses in the dog mandibles. To apply the anatase TiO₂ film, plasma source ion implantation (PSII) method followed by annealing was employed for the titanium disks and implants, which were then illuminated with UV-A for 24 h for the experimental groups. Non-deposited titanium disks and implants were prepared for the control group. Surface characterization was performed using the interferometer and contact angle analyzer. The attachments of sFN were evaluated using fluorescence emission analysis. Thereafter both groups of implants were placed in the mandible of six beagle dogs. Bone response was investigated with histological and histomorphometrical analyses after periods of 2 and 4 weeks. The experimental groups exhibited strong hydrophilicity under UV-A illumination and showed significant improvement in sFN attachment. And further, the experimental implants enhanced the bone formation with the bone-to-implant contact of 42.7% after 2 weeks of healing (control: 28.4%). The combined applications of plasma fibronectin and PSII to produce hydrophilic titanium surfaces could accelerate early osseointegration.

Research of Angle Measurement Technique in Transponder Landing System

In t his paper , a spatial smoothing technique based on MUSIC algorithm is introduced to substitute the traditional phase interferometer angle measurement algorithm of Transponder Landing System (TLS). It m ainly researched the non-uniform linear receiving arrays design scheme under the new algorithm. This proposed algorithm aims to solve the multi-path or multi-targets interference problems of reply signal and eliminate the phase ambiguity caused by receiving arrays’ baseline. It contrasted the feasibility, validity, resolving power and precision of the designed arrays with the uniform arrays in the same condition through computer simulation. The effectiveness and advantage of the proposed algorithm include the usability and reliability of the designed arrays is theoretically investigated. At last, we can obtain the real-time azimuth and elevation information relative to the touchdown point of landing aircraft through c oordinate transformation.

RF angle of arrival-based node localisation

Several localisation algorithms exist for wireless sensor networks that use angle of arrival measurements to derive node position. However, there are limited options for actually obtaining the angle of arrival using resource-constrained devices. In this paper, we describe a technique for determining node bearings based on radio interferometric angle of arrival measurements from multiple anchor nodes to any number of target nodes at unknown positions. Least squares triangulation is then used to estimate node position. The position estimation is carried out by the node itself, hence the method is distributed, scalable, and fast. Furthermore, this technique does not require modification of the mote hardware because it relies only on the radio. Experimental results demonstrate that our approach can estimate node bearing with an average accuracy of 3°, and node position with sub-metre accuracy in approximately 1 s.

Development for detecting upper atmospheric wind and temperature from satellite

中高层大气风场和温度场是重要的大气基本参数, 其全球高精度测量具有广泛的应用前景, 探测需求日趋强烈. 干涉光谱仪由于其多通道、高通量和高光谱分辨率等优点而成为本项目的首选. 目前被成功应用的干涉式测风/测温仪器主要有Fabry-Perot 干涉仪和广角Michelson 干涉仪两大类. 本文对干涉光谱仪用于中高层大气风场和温度场探测的发展状况进行了分析, 同时比较了几种干涉仪测风和测温的可行性及优缺点, 为中国开展中高层大气风场和温度场星载探测打下基础.

Single beam interferometric angle measurement

We present an application of a quadrature phase interferometer to the measurement of the angular position of a parallel laser beam with interferometric precision. In our experimental realization we reach a resolution of 6.8 × 10 −10 rad (1.4 × 10 −4″) for 1 kHz bandwidth in a 2 × 10 −2 rad (1°) range. This alternative to the optical lever technique features absolute calibration, independence of the sensitivity on the thermal drifts, and wide range of measurement at full accuracy.

Analysis of Glint Phenomenon in a Monopulse Radar in the Presence of Skin Echo and Non-Ideal Interferometer Echo Signals

Angle tracking noise in monopulse tracking radars has been an important study topic during the last decades. This phenomenon otherwise known as "Glint" is studied in present article assuming the presence of a non-perfect interferometer transponder placed on a target with a non-zero radar cross section. The effects of interferometer angle and amplitude balance and the target echo signal strength is analyzed theoretically and numerical results are computed and presented for a wide set of parameter values. The required power ratio of interferometer and echo signals to achieve significant angle noise is derived. Numerical results and analytical approximations of the angle noise are presented in the form of parametric curves.

Spherical grating monochromator with interferometer control and in-vacuum reference

Physical Science Laboratory’s new generation of spherical grating monochromators incorporates a laser interferometer to control scan angle and an in-vacuum absolute angle reference, as well as other improvements. The design accommodates up to six gratings which can be moved axially (under motor control, with encoder position readback) at any scan angle. The gratings are cooled by means of spring-loaded clamps which conduct heat to a water-cooled plate. The instruments feature hollow roller bearings on the scan axis to minimize bearing runout, and a pseudosine-bar drive for precise control of grating angle. The interferometer angle-measuring optics are mounted inside the vacuum chamber and measure the angle between the grating scan axis and the instrument’s granite base. The laser interferometer measures the grating angle with a resolution of approximately 0.02 arcsec over the entire scan range of 40°. To provide a reference for the interferometer angle measurement, we have built an in-vacuum optical reference which uses custom chrome-on-glass reticles mounted inside the vacuum chamber. Collimated light from a source outside the vacuum passes through the reticles to yield quadrature signals which precisely define an absolute reference angle for the interferometer. Repeatability of the grating angle is within a range of ±0.05 arcsec. Two of these instruments are in operation at SRRC (Taiwan) and a third instrument has been delivered to NSLS (Brookhaven).

The new high resolution ultra small-angle neutron scattering instrument at the High Flux Reactor in Grenoble

In 1998, the combined Interferometer and Ultra Small Angle Neutron Scattering (USANS) instrument S18 at the 58 MW High Flux Reactor at the Institute Laue-Langevin in Grenoble (France) started operation. The instrument has been upgraded to allow more advanced neutron optics experiments for fundamental, nuclear and condensed matter physics. The new supermirror guide along with the two channel cut silicon perfect crystals, configured as an advanced high resolution Bonse-Hart camera, provides optimal intensity conditions. A large range of wavelengths is accessible by variations of the Bragg angle and by using different reflecting planes of a properly cut silicon monochromator block in combination with different channel-cut analyzer crystals. The fine adjustment analyzer system is achieved by an advanced piezo drive, which has an accuracy of 0.036 seconds of arc. The basic features of the USANS camera, which takes advantage of a new tail suppression method, and the results of various test measurements concerning intensities, long term stability and the accessible wavelength range will be presented. A high resolution position sensitive detector can either be used to analyze beam profiles or to perform neutron radiography experiments.

Distorted laser interferometric angle measurements of a disk drive pivot

A laser interferometric measurement sensor is used for angle measurements of rotating ultralight structures in order to avoid the mechanical interaction between the system and the sensor. The laser interferometer detects a linear displacement which is a distorted image of the angle displacement. The distortion depends strongly on the amplitude and the laser misalignment angle. In this paper, a measurement procedure is presented based on an analytical expression that describes the nonlinear relationship between the measured displacement and the actual angle displacement. Furthermore, a distortion map is presented to quantify the nonlinear effects and to indicate the necessity for compensation of these effects. Finally, a calibration procedure for identifying the geometrical parameters, i.e., the arm length and laser misalignment angle, is included. The method is applied to the pivot of a Kitty Hawk, a miniature hard disk drive.

Random tropospheric effects in command guidance by multilateration and interferometry

Statistical models are developed for the random spatial variations in refractivity in the troposphere, and are used to derive spatial correlation functions for the errors in range measurement and interferometer angle measurement. These are then used to analyze the relative errors between two tracked targets, for application to command-guided intercept problems. It is shown that multilateration, using range measurements, yields much smaller relative errors than does the interferometer approach.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Interferometric angle encoder

Four unusual features are combined in the construction of an interferometric angle encoder: (1) a robust optical configuration, (2) a three-port lenticular fringe receiver, (3) a hexaflash phase-analysis circuit, and (4) a recursive phase unwrapping and smoothing filter. Raw performance of the instrument is about 600 prad resolution at 2 MHz sample rate. That is about a factor of 25 away from the shot noise limit. Resolution is improved to about 13 prad by on-the-fly smoothing to a 500 Hz bandwidth and data acquisition of 32-bit values is implemented at up to 5376 samples per second. The overall range of the system can be up to 18°.

Spatial interferometer measurements with the Chung‐Li VHF radar

The Chung‐Li VHF radar consists of three phase‐coherent transmitting‐receiving antenna systems, which allow an optimum application of interferometer and incidence angle measurements of radar echoes from the troposphere and the stratosphere. We briefly describe the applications of the spatial domain interferometry and present here the first measurements of cross spectra and the corresponding phases, which vary as function of frequency due to the mean wind. We also present the first incidence angle measurements and show that the scattering‐reflecting structures in the troposphere can be inclined to the horizontal by a tilt or inclination of l°–2°. We also notice a periodic change of this inclination as well as the radial velocity measured with vertical antenna beam as a function of altitude and time which we attribute to long‐period waves or mountain waves. There are clear indications that the radial velocity measured with the vertical beam is diluted by the projection of the horizontal wind in the presence of inclined or tilted reflectivity structures. We also describe observations of long‐period waves seen in the horizontal wind pattern, which could be of the same origin as the quasi‐periodic pattern observed in the inclination and the reflectivity.

Curved crystal spectrometer for precise energy measurements of gamma rays from 30 to 1500 keV

A DuMond-type spectrometer with an interferometric angle measuring system is described. It has a focal length of 464 cm, a crystal window of 22 cm 2, and uses the (110) plane of quartz. The interferometer yields an angular accuracy of about 0.01 seconds of arc. Therefore, the spectrometer permits extremely precise measurements of the relative energies of X- or γ-lines. Strong transitions can be recorded with a relative precision of (1–5) × 10 −6, as is shown through the measurement of γ-lines from the decay of 198Au, 199Au, 182Ta, and 183Ta.