Phase Calibration Method Research Articles

A fast phase calibration method for a liquid crystal microwave phased array antenna assisted by neural network

A fast phase calibration method for a liquid crystal microwave phased array antenna assisted by neural network

Coupling Michelson-like lateral shear interferometric microscopy with self-referencing numerical phase calibration for quantitative measurement of 3D surface morphology of biological cells

A Michelson interferometer is commonly used for evaluating the morphology of a cell. However, the interference imaging with reference and object beams is easily affected by external vibrations and environmental disturbances, leading to unstable interference patterns. In this paper, the three-dimensional surface morphology of the biological cell is evaluated by a new quantitative phase imaging method, which couples Michelson-like lateral shear interferometric microscopy with self-referencing numerical phase calibration. The Michelson-like lateral shear interferometric microscopy is constructed by replacing the two plane mirrors of the traditional Michelson interferometer with two common right-angle prisms and generates interference fringe patterns. The lateral shear is created and freely adjustable by simply translating/or rotating one right-angle prism. To calculate the phase information of the biological cells quantitatively, the classical Fourier transform method is used to process the recorded interferogram, and then the self-referencing numerical phase calibration method is utilized for acquiring accurate phase information. Successfully achieving quantitative phase imaging of a cell verifies the feasibility and practicability of the proposed method.

Carrier frequency phase calibration method for global navigation satellite system signal simulators

Carrier frequency phase calibration method for global navigation satellite system signal simulators

Carrier frequency phase calibration method for global navigation satellite systems signal simulators

Measurements of carrier frequency phase differences of global navigation satellite system signals between multiple antennas are used in many coordinate and navigation applications. Global navigation satellite systems signal simulators are used for controlling global navigation satellite systems receiver’s instrumental errors. Therefore, it is necessary to determine the systematic error of the carrier frequency phase of generated signals for signal simulators. For this purpose a new calibration method of global navigation satellite systems simulators was developed. Method is based on refined errors model of generated phase differences of two radio frequency channels of the simulator. The proposed method was implemented using a wideband oscilloscope as an analog-to-digital converter. Approbation of the calibration method was carried out by comparison with the measurement results obtained using the State secondary standard of units of complex transmission coefficients in the range of 0...–60 dB and complex reflection coefficients in the range of 0.002–1 in the frequency range of 0.05–65 GHz (registration No. 2.1.ZZT.0210.2015). The calibration method allows one to determine carrier frequencies phase offsets of navigation signals for global navigation satellite systems simulators with expanded uncertainty (with a coverage factor of 3) of 1°. The proposed method provides the required accuracy of generating phase differences of the carrier frequencies of global navigation satellite systems signals is ensured for modern types of global navigation satellite systems simulators.

An On-Chip Calibration Method for Optical Phased Array With No Blind Spot in the Steering Range

We demonstrate an on-chip phase calibration method in the silicon-based optical phased array (OPA) using multimode interferences (MMIs) and germanium silicon photodetectors (GeSi PDs), which are integrated at the end of the grating array. Two groups of MMIs with staggered symmetrical distribution are utilized to obtain the phase difference between adjacent gratings and linked to the PDs. With this method, a 1 × 32 OPA with thirty-two PDs realizes a 36.4° × 11.5° beam steering range without any blind spot, and the optimal side-lobe suppression ratio is 9.3 dB.

Calibration Method of Liquid-Crystal Spatial Light Modulator Based on a 1-D Phase Retrieval Algorithm

Liquid-crystal spatial light modulator (LC-SLM) has been widely applied as a programmable digital device. However, the LC-SLM can only manipulate on light fields accurately under designated wavelengths since, when being uploaded a specific grayscale image onto it, the phase retardance offered by the LC-SLM is relevant to the wavelength of the incident light. This means that the calibration of LC-SLM is indispensable once the working wavelength changes. In this paper, based on a phase retrieval algorithm, a novel phase calibration method with high efficiency and accuracy is proposed for scaling LC-SLM. In the method, a 1-D phase retrieval algorithm for recovering the phase of a 1-D light field distribution is used to measure the voltage-phase characteristic curve of LC-SLM, where the gradient descent algorithm with a Root Mean Square propagation is introduced to obtain the phase. Simulations and experiments show that this method is stable and has the ability of anti-noise on some conditions and can eliminate the influence caused by crosstalk between pixels on the calibration. Compared with the traditional diffraction-based method, our method improves the calibration error up to 30% under the same experimental conditions.

Research on Beam Waveguide Focus Phase Calibration Method of Deep-space TT&C System

The angle auto-tracking capability is needed in the deep space system, but in the sum-differential dual channels tracking model, the deep-space TT&C system must calibrate its phase before tracking a satellite. Because of the big aperture and high frequency of the deep-space TT&C system antenna, it is impossible to build a calibrating tower which satisfy the far-field condition, and the traditional phase calibration method relies on the tower is not suitable. The radio star calibration method selects a appropriate satellite as the calibrating signal source, but the signal of which is very weak and is affected easily. In this paper, the principle of phase calibration is analyzed, and the beam waveguide focus calibration method is studied, the processes of antenna tracking and angle error signal demodulation are given. The beam waveguide focus calibration method simulates the far field signal through controlling the position of horn antenna which is at the focus of the beam waveguide. The method can be realized easily in engineering, and the limit of the traditional calibration tower and the affections of the weather in using radio star calibration method are avoided.

Efficient range migration algorithm for near-field MIMO array imaging

This paper proposes an efficient range migration algorithm (ERMA) for near-field multiple-input multiple-output (MIMO) array-based microwave imaging. For the usual imaging algorithms implemented in the spatial frequency domain for MIMO arrays, the multi-dimensional Fourier transforms (FTs) are first performed with respect to transmitters and receivers, respectively, to transform the echo data in the spatial domain to those in the spatial frequency domain. After performing the matched filtering and the Stolt interpolations usually in a five-dimensional (5-D) domain for common two-dimensional (2-D) planar MIMO arrays, the high dimensional data needs to shrink into a three-dimensional (3-D) domain. The processing in a 5-D domain is time-consuming and requires huge memory storage. The proposed algorithm moves the dimension reduction in advance of the matched filtering and interpolations. To do this, we first perform data completion in respect of the undersampled data. A phase calibration method is employed to preserve precision. In so doing, the higher dimensional matched filtering and interpolations are eliminated, which results in a significant increase in imaging speed. Besides, the ERMA can enhance the resolution of the imaging results, because the dimension reduction discards the convolution between the transmit and receive spectra. Numerical simulations are demonstrated to verify the efficacy and performance of ERMA.

Study on TRX Channel Amplitude and Phase Calibration Method for a Radar Wind Profiler Based on 256 Active Phased Array

Study on TRX Channel Amplitude and Phase Calibration Method for a Radar Wind Profiler Based on 256 Active Phased Array

Efficient Wavenumber Domain Processing for Near-Field Imaging With Polyline Arrays

We propose an efficient wavenumber domain approach for polyline array-based millimeter-wave imaging. The polyline multiple-input–multiple-output (MIMO) array provides more uniform illumination of the target than the planar MIMO array while enjoying the planar array’s easy manufacturing. However, no existing efficient imaging algorithms deal with such an array topology. This article presents an approach that first implements a polyline-to-arc transformation on the polyline array, accompanied by a phase calibration method to maintain the transformation precision. The wavenumber domain technique is then employed to perform image reconstruction. This processing enables the transformation of the polyline array scheme into a monostatic cylindrical aperture, for which efficient imaging algorithms exist. The imaging performance and computational efficiency of the proposed approach are demonstrated with both simulations and experiments.

Elevation Extraction from Spaceborne SAR Tomography Using Multi-Baseline COSMO-SkyMed SAR Data

SAR tomography (TomoSAR) extends SAR interferometry (InSAR) to image a complex 3D scene with multiple scatterers within the same SAR cell. The phase calibration method and the super-resolution reconstruction method play a crucial role in 3D TomoSAR imaging from multi-baseline SAR stacks, and they both influence the accuracy of the 3D SAR tomographic imaging results. This paper presents a systematic processing method for 3D SAR tomography imaging. Moreover, with the newly released TanDEM-X 12 m DEM, this study proposes a new phase calibration method based on SAR InSAR and DEM error estimation with the super-resolution reconstruction compressive sensing (CS) method for 3D TomoSAR imaging using COSMO-SkyMed Spaceborne SAR data. The test, fieldwork, and results validation were executed at Zipingpu Dam, Dujiangyan, Sichuan, China. After processing, the 1 m resolution TomoSAR elevation extraction results were obtained. Against the terrestrial Lidar ‘truth’ data, the elevation results were shown to have an accuracy of 0.25 ± 1.04 m and a RMSE of 1.07 m in the dam area. The results and their subsequent validation demonstrate that the X band data using the CS method are not suitable for forest structure reconstruction, but are fit for purpose for the elevation extraction of manufactured facilities including buildings in the urban area.

A 1060 nm stretched-pulse mode-locked wavelength-swept laser source providing an A-scan rate of 20 MHz

The laser source is the deciding factor in improving the rapid imaging of swept-source optical coherence tomography (OCT) systems. We introduce an intrinsically stable stretched-pulse mode-locking (SPML) laser operating a tuning range of over 92 nm at a center wavelength of 1060 nm. The laser provides variable A-line rates up to ~20 MHz as a function of the duty cycle. The cavity comprises a unidirectional ring cavity with matched positive and negative continuously chirped fiber Bragg gratings generating ± 556 ps/nm dispersion. We demonstrate the ability of the stretched-pulse mode-locking laser to provide rapid optical signals for optical coherence tomography. Finally, we highlight performance by displaying the 3D datasets acquired at > 19,487 × 103 A-lines/s as cross-sectional images, averaging the complex A-scan signals of the voxel, and examining the inter-frame phase variance without the need for trigger signals and a phase calibration method. By integrating three-dimensional coherence-based optical imaging into a video-rate, camera-like deployment using a high-speed digitizer, this laser may potentially leverage the use of optical coherence tomography of complex tissue dynamics in pre-clinical studies

Gain and Phase Calibration of Uniform Rectangular Arrays Based on Convex Optimization and Neural Networks

A calibration method based on convex optimization (CVX) and neural networks is proposed for the large planar arrays of phased array three-dimensional imaging sonar systems. The method only needs an acoustic calibration source at an unknown position in the far field, and the direction of arrival (DOA) and gain and phase error are jointly estimated. The method uses a CVX algorithm to solve an optimization problem and initially estimates the DOA of the calibration source robustly. Subsequently, according to the estimation results, a neural network is used for fitting to obtain off-grid DOA estimation of the calibration source. Thereafter, spatial matched filtering is performed to obtain the gain and phase residual estimations. The root mean square error (RMSE) of the beam pattern calibrated by the method for uniform planar arrays can reach a value of 4.9542 × 10−5. The experimental results demonstrate the efficiency of the proposed method for gain and phase calibration.

High-Precision Calibration of Phase-Only Spatial Light Modulators

In the fields of optics and photonics, phase-only spatial light modulators (SLMs) play an increasingly important role in wave-front engineering. However, the SLMs are subject to wavefront distortion arising from the imperfection in the birefringence effect and physical structure of modulators. This paper presents a simple self-interference phase calibration method applicable to liquid-crystal SLM. We build an interferometric imaging system based on the Pancharatnam phase-shifting to measure the phase distribution of a light beam coming from SLMs. Two types of phase modulation errors of SLMs can be characterized in the measurement process: the erroneous gamma curve and shape aberration. The former belongs to dynamic phase distortion and is measured through a four-step Pancharatnam phase-shifting interference, which allows a one-shot recording of interference pattern via a polarization camera; the latter represents static phase distortion and is extracted from the interference between light waves coming from different regions of the SLM panel by using Zernike polynomial fitting. Our method has the advantages of high-precision pixel-wise phase correction and robustness against environmental disturbance and thus can facilitate the applications of SLM in optical field manipulation.

Research on Direction of Arrival Estimation Based on Self-Contained MEMS Vector Hydrophone.

A self-contained MEMS vector hydrophone with a scalar–vector integrated design is proposed in this paper. Compared with traditional MEMS vector hydrophones, this design solves the problem of ambiguity in the port and starboard during orientation, and also realizes the self-contained storage of acoustic signals. First, the sensor principle and structural design of the self-contained MEMS hydrophone are introduced, and then the principle of the combined beamforming algorithm is given. In addition to this, the amplitude and phase calibration method based on the self-contained MEMS vector hydrophone is proposed. Then, the sensitivity and phase calibrations of the sensor are carried out in the standing wave tube. The sensitivity of the vector channel is −182.7 dB (0 dB@1 V/Pa) and the sensitivity of the scalar channel is −181.8 dB (0 dB@1 V/Pa). Finally, an outdoor water experiment was carried out. The experimental results show that the self-contained MEMS vector hydrophone can accurately pick up and record underwater acoustics information. It realizes the precise orientation of the target by combining beamforming algorithms. The direction of arrival (DOA) error is within 5° under the outdoor experimental conditions with an SNR of 13.67 dB.

Research on the phase-frequency relationship of the field effect amplifier front-end of shipborne USB system

Normally, most researches on phase calibration of shipborne USB system focus on the means of phase calibration. This article starts with the research on the channel of the system. The composition of the channel is introduced, and the characteristics of the channel is analyzed. Taking the channel of the field effect amplifier front-end as the research object, a mathematical fitting algorithm is used to derive the functional relationship between the phase of the field effect amplifier front-end and the working frequency. The actual calibration data is used for simulation analysis to obtain the fitting order of the function. Combining the phase-frequency relationship of the field effect amplifier front-end and the microwave self-checking phase correction of the field effect amplifier back-end, a new phase calibration method is proposed.

A Sensing-Based Over-the-Air Phased Array Antennas Phase Calibration Method With Greedy Algorithm

Phase errors of phased array antennas (PAA) can cause gain degradation that necessitates calibration to compensate this effect. Over the air (OTA) calibration methods are promising for avoiding interruption of communication applications for specific calibration conditions. However, typical calibration methods have the assumption that precise knowledge about calibration should be exchanged, such as relative positions and cost function (CF) values, which are difficult to obtain in practical mobile communication systems. To overcome this, a sensing-based OTA calibration method is proposed, in which sensing methods aided by cameras or infrastructure sensors could locate user equipment (UE) and regard it as calibration reference source. Then greedy algorithm (GDA) is integrated into NR (New Radio) beam management process, where UE measures directional Channel State Information-Reference Signals (CSI-RSs) reserved for calibration and feeds back the optimal beam index instead of CF values. Consequently, UE received power is maximized, so as to achieve phase calibration. Simulation results exhibit that even when locating error exists, the proposed method can correct phase errors with a low overhead in terms of reserved NR CSI-RSs.

Phase calibration method for microphone array based on multiple sound sources

In the microphone array, the phase error of each microphone causes a deviation in sound source localization. At present, there is a lack of effective methods for phase error calibration of the entire microphone array. In order to solve this problem, a phase mismatch calculation method based on multiple sound sources is proposed. This method requires collecting data from multiple sound sources in turn, and constructing a nonlinear equation setthrough the signal delay and the geometric relationship between the microphones and the sound source positions. The phase mismatch of each microphone can be solved from the nonlinear equation set. Taking the single frequency signal as an example, the feasibility of the method is verified by experiments in a semi-anechoic chamber. The phase mismatches are compared with the calibration results of exchanging microphone. The difference of the phase error values measured by the two methods is small. The experiment also shows that the accuracy of sound source localization by beamforming is improved. The method is efficient for phase error calibration of arrays with a large number of microphones.

The spatially resolved broad line region of IRAS 09149−6206

We present new near-infrared VLTI/GRAVITY interferometric spectra that spatially resolve the broad Brγ emission line in the nucleus of the active galaxy IRAS 09149−6206. We use these data to measure the size of the broad line region (BLR) and estimate the mass of the central black hole. Using an improved phase calibration method that reduces the differential phase uncertainty to 0.05° per baseline across the spectrum, we detect a differential phase signal that reaches a maximum of ∼0.5° between the line and continuum. This represents an offset of ∼120 μas (0.14 pc) between the BLR and the centroid of the hot dust distribution traced by the 2.3 μm continuum. The offset is well within the dust sublimation region, which matches the measured ∼0.6 mas (0.7 pc) diameter of the continuum. A clear velocity gradient, almost perpendicular to the offset, is traced by the reconstructed photocentres of the spectral channels of the Brγ line. We infer the radius of the BLR to be ∼65 μas (0.075 pc), which is consistent with the radius–luminosity relation of nearby active galactic nuclei derived based on the time lag of the Hβ line from reverberation mapping campaigns. Our dynamical modelling indicates the black hole mass is ∼1 × 108 M⊙, which is a little below, but consistent with, the standard MBH–σ* relation.

Precisely Synchronized NVNA Setup for Digitally Modulated Signal Generation and Measurement at 5G-Oriented Millimeter-Wave Test Bands

In this article, we present a novel nonlinear vector network analyzer (NVNA) setup for generating and measuring digitally modulated signals at millimeter-wave test bands. The first difference between this setup and commercial NVNAs is the use of a user-defined multisine signal as the phase reference, in order to enable more precise synchronization and denser spectral grid. To achieve this, a single 12.5-GHz microwave source is used for generating both the digitally modulated test signal and the phase reference, which not only offers the clock to the arbitrary waveform generator for user-defined intermediate frequency (IF) waveform generation but also provides the local oscillator drive after frequency multiplication. The second novelty of this work is the use of pulsed-radio frequency (RF) signals for NVNA phase calibration. By replacing the digitally modulated IF waveform with pulsed-RF signals, tone-by-tone phase calibration on dense spectral grids can be easily achieved under the same synchronization scheme. The validity of the proposed NVNA setup (as well as its simplified modification) and the phase calibration method is verified at the fifth-generation (5G)-oriented millimeter-wave bands of 28, 39, 43, and 70 GHz in this work, where the EVM measurements of 64-QAM test signals with a wide range of symbol rates from 0.1 to 1.5625 GSymbol/s are demonstrated reachable in practice.