Phase Calibration Method Research Articles

Foreign Object Intrusion Detection on Metro Track Using Commodity WiFi Devices with the Fast Phase Calibration Algorithm.

With continuous development in the scales of cities, the role of the metro in urban transportation is becoming more and more important. When running at a high speed, the safety of the train in the tunnel is significantly affected by any foreign objects. To address this problem, we propose a foreign object intrusion detection method based on WiFi technology, which uses radio frequency (RF) signals to sense environmental changes and is suitable for lightless tunnel environments. Firstly, based on extensive experiments, the abnormal phase offset between the RF chains of the WiFi network card and its offset law was observed. Based on this observation, a fast phase calibration method is proposed. This method only needs the azimuth information between the transmitter and the receiver to calibrate the the phase offset rapidly through the compensation of the channel state information (CSI) data. The time complexity of the algorithm is lower than the existing algorithm. Secondly, a method combining the MUSIC algorithm and static clutter suppression is proposed. This method utilizes the incoherence of the dynamic reflection signal to improve the efficiency of foreign object detection and localization in the tunnel with a strong multipath effect. Finally, experiments were conducted using Intel 5300 NIC in the indoor environment that was close to the tunnel environment. The performance of the detection probability and localization accuracy of the proposed method is tested.

Cylindrical MIMO Array-Based Near-Field Microwave Imaging

Microwave/millimeter-wave imaging has a wide prospect in applications of concealed weapons detection. The main problem of the existing techniques lies in the contradiction between the imaging speed and the system cost. In this respect, a cylindrical sparse multiple-input–multiple-output (MIMO) array topology is proposed, which has no mechanical scanning so as to achieve fast sampling process. Furthermore, it can provide more angular observations than the mainly used systems with a planar aperture. To speed up the image reconstruction process, a phase center approximation-based transformation is made to convert the multistatic sampling scheme to its monostatic counterpart for which there are more fast and tractable imaging algorithms. Then, a phase calibration method is presented after we analyze the error of such an equivalence. In so doing, the cylindrical MIMO topology is transformed into an approximate monostatic one. Finally, a wavenumber domain algorithm is employed to attain the fast image reconstruction. Numerical simulations are provided to demonstrate the performance improvement of the proposed technique.

Generalized phase calibration method of liquid crystal spatial light modulator with absolute reference system of obnoxious background light

Spatial light modulators (SLMs) are widely used in many optical fields such as wavefront modulation, beam shaping and diffractive optical elements. It is necessary to calibrate SLM to determine the initial state of device before using it. Here a simple and generalized interferometry is proposed to calibrate the phase modulation curve with good robustness, stability and high precision, in which the obnoxious background light is no longer an undesired signal, but is utilized as an absolute reference system that provides the self-reference functionality. Combined with centroid localization algorithm, the phase modulation curve can be easily calculated by the fringes shift. Besides, multi-channel detector simultaneously provides three groups of data that further improve the calibration accuracy of gamma curve by weighted average algorithm. An experiment on phase-shifting holography was carried out and verified the validity of our proposed method. The larger the CCD target surface, the better the calibration accuracy is.

Rapid phase calibration of a spatial light modulator using novel phase masks and optimization of its efficiency using an iterative algorithm

ABSTRACT We develop an improved phase calibration method of a reflective SLM using interferometry by employing novel phase masks. In the process, we definitively determine the actual maximum phase throw of our SLM which provides a recipe for users to verify supplier specifications. We generate optimised phase masks by using Iterative Fourier Transform Algorithm (IFTA) and compare their performance with global linear corrections in the look-up table (LUT) and find that the former perform with around 20 better efficiency. Besides obtaining an array of 1D/2D spots having high uniformity (90) using IFTA, our result exemplifies the use of iterative algorithms for improving efficiency of phase limited SLMs. Finally, our improved phase calibration method enables threefold faster phase measurements, and to the best of our knowledge, is the first endeavour directed towards enabling rapid phase characterisation of an SLM using interferometric measurements. We believe that it can have very useful applications in settings which may require fast phase calibrations as well as for real-time, multi-wavelength spectroscopic applications.

Single-shot phase calibration of a spatial light modulator using geometric phase interferometry.

A vibration-insensitive, single-shot phase-calibration method for phase-only spatial light modulators (SLM) is reported. The proposed technique uses a geometric phase lens to form a phase-shifting radial shearing interferometer to enable common-path measurements. This configuration has several advantages: (a) unlike diffraction-based SLM calibration techniques, this technique is robust against intensity errors due to misalignment; (b) unlike two-beam interferometers, this technique offers a high environmental stability; and (c) unlike intensity-based methods, the phase-shifting capability provides a phase uncertainty routinely in the order of ${2}\pi /100$2π/100. The experimental results show a significantly higher accuracy when compared to the diffraction-based approaches.

A Phase Calibration Method Based on Phase Gradient Autofocus for Airborne Holographic SAR Imaging

Holographic synthetic aperture radar tomography can realize full 3-D reconstructions of objects over 360° with very high resolution, and thus becomes an interesting 3-D imaging technique. However, due to the uncompensated platform motion errors, phase errors among different tracks usually exist in this imaging mode, which will hinder the 3-D image focusing. In this letter, a phase calibration method based on phase gradient autofocus is proposed to mitigate the influence of these phase errors. It exploits the space-invariant characteristic of the phase errors in a limited scene and uses an efficient and robust multibaseline autofocus to calibrate the phase errors among the multiple circular tracks. Experimental results with the GOTCHA real data are carried out to demonstrate the validity and feasibility of the proposed method.

Self-referenced multiple-beam interferometric method for robust phase calibration of spatial light modulator.

Phase-only liquid crystal spatial light modulator has wide ranging applications that require accurate phase retardance. The phase calibration of the spatial light modulator is therefore of vital importance. Available self-referenced calibration methods face the challenges of high time consumption, low efficiency, and low stability against the conditions. A self-referenced multiple-beam interferometric method is proposed to derive the global grayscale-phase response. As is presented theoretically and experimentally, the proposed method reduces the measuring time and improves the calibration efficiency by encoding multiple fringes in a single hologram. Results also show that the method is equally accurate when compared with traditional two-beam interferometric method, whereas providing a greater robustness against measuring errors since the standard deviation is only 56% of that of the traditional method.

A Novel Phase Calibration Method for Dual-Channel CSAR-GMTI Processing

Displaced phase center array (DPCA) and along-track interferometry (ATI) have been widely used for ground moving target indication (GMTI) in multi-channel circular synthetic aperture radar (CSAR) system. In ideal conditions, these methods can suppress background clutter effectively. However, the nonideal movement of platform may create a nonzero crab angle, which will induce a cross-track baseline offset and affect GMTI processing seriously. This letter analyzes the influence of crab angle on interferometric phase theoretically. Here, we propose a two-step phase calibration method to greatly improve the performance of CSAR-GMTI by eliminating the range-varying phase error. This method is independent of imaging and GMTI processing. Simulated and measured data results verify the correctness of the theoretical analysis and the validity of the proposed method.

A Phase-Calibration Method for Vector-Sum Phase Shifters Using a Self-Generated LUT

This paper presents a new self-calibration method for vector-sum phase shifters (PS) to compensate for process variations and achieve reconfigurable operating frequency. The calibration system generates a look-up table for the control voltages of the variable-gain amplifiers of the PS to minimize the rms phase error at a frequency of interest. The calibration system consists of a coupled-line coupler, an amplifier, a power detector (PD), an analog-to-digital converter, and a data processing unit. In this calibration method, first, the amplitudes of IQ vectors are swept and their powers are measured. Then, phase errors are calculated from these power measurements using the cosine formula. Finally, the vector pairs providing the least phase error are chosen for each desired phase shift. The practicality of the proposed system is demonstrated by realizing a self-calibrated $X$ -band 7-b PS fabricated in IHP 0.25- $\mu \text{m}$ SiGe BiCMOS technology, including the on-chip coupler, amplifier, and PD. The calibration system improves the rms phase error by at least 1°, does not degrade the rms gain error, and increases the insertion loss by 1.6 dB. The self-calibrated PS achieves a 2° rms phase error across $X$ -band frequencies. The overall chip size is 2.6 mm2. The power consumption of the PS and the overall system are 110 and 233 mW, respectively. This built-in calibration system mitigates process variation effects, and the performance of the PS can be optimized for any center frequency across $X$ -band.

A New Clock Phase Calibration Method in High-Speed and High-Resolution DACs

Current steering digital-to-analog converters (DACs) are well suited for high-resolution, high-speed applications. A serious design challenge is brought by the requirement of solving the setup/hold time violations problem between the output data from the digital clock domain and the analog clock under different process, voltage, and temperature conditions, and simultaneously maintaining high spectral purity of the analog clock. This brief presents a mixed-signal system to detect and correct setup/hold time violations for the critical analog clock in high-speed and high-resolution DACs. A power-efficient, novel 4-bit flash analog-to-digital converter, designed with a new architecture and reference adaptive generation technique while keeping overhead cost low, is proposed in this brief. The detection and correction circuit, together with a 13-bit 2.4-GHz DAC, is implemented in a 0.18- ${\mu }\text{m}$ CMOS technology. The measured spurious free dynamic range and the output spectrum demonstrate the effectiveness of the proposed method. The combined clock phase calibration circuit not only improves the yield of DAC, but also increases the maximum allowable clock frequency for high-resolution DACs, which is especially advantageous for high sampling frequency design.

A USRP-Based Multi-Antenna Testbed for Reception of Multi-Site Cellular Signals

This paper presents a design of a Software Defined Radio (SDR) multi-antenna testbed able to record live cellular signals from multiple sites. This measurement setup based on Universal Software Radio Peripheral (USRP) boards, is used to record live Long Term Evolution (LTE) signals in sub-6 GHz frequency bands. Due to recording of raw I&Q samples, this fully digital testbed is suitable for variety of research activities spanning channel characterization and beamforming performance evaluation. We propose a phase calibration method based on transmission of a single out of band tone to overcome the uncertainty introduced by the USRP's lack of phase alignment. We demonstrate two use cases where the proposed testbed can be used and we validate its performance during two measurement campaigns with self-generated and real cellular signals.

Real-time rapid initial phase calibration method of phased array in near field

Real-time rapid initial phase calibration method of phased array in near field

Multichannel Phase Calibration for Linear Array Based on Extended <inline-formula> <tex-math notation="LaTeX">$\omega K$</tex-math> </inline-formula> Algorithm and Minimum-Entropy Method

Millimeter-wave imaging techniques have been used for security inspection at important checkpoints. With the increase of working frequencies of the imaging systems, the precise multichannel phase calibration becomes more and more important. Most of the traditional algorithms are used for the calibration of passive receiving antenna array, based on the signal model of far-field plane wave. However, the near-field spherical wave model should be utilized for the active wideband near-field imaging applications. Consequently, the traditional calibration algorithms cannot be used in wideband near-field imaging systems. The metal plate is usually employed for the calibration of wideband near-field imaging systems, but the precision is very sensitive to the flatness of the surface of the metal plate, which will result in additional phase error after calibration. In this letter, a multichannel phase error estimation and calibration method is proposed for the wideband linear array system. By using an extended $\omega K$ algorithm and the minimum-entropy method, the additional phase error of each channel after preliminary calibration is estimated and calibrated. Simulations and experimental results show the effectiveness of the proposed method.

A 0.45–0.7 V 1–6 Gb/s 0.29–0.58 pJ/b Source-Synchronous Transceiver Using Near-Threshold Operation

A low-power source-synchronous multi-Gb/s transceiver is presented. Supply voltage is aggressively scaled to reduce power, and the speed penalty resulting from low-voltage operation is overcome by multiplexing transmitter/receiver synchronized by low-rate multi-phase clocks. Phase spacing errors incurred by device mismatches are corrected using a self-calibration scheme. The proposed phase calibration method uses a single digital DLL to calibrate all the phases, which makes it insensitive to offsets in the calibrating DLL. Fabricated in a 65-nm CMOS process, energy efficiency and data rate of the prototype transceiver vary from 0.29 to 0.58 pJ/bit and 1 to 6 Gb/s, respectively, as the supply voltage changes from 0.45 to 0.7 V.

A Frequency Band Phase Calibration Method Based on Differential Group Delay

Due to the disadvantages of single calibration way and low efficiency of the dualchannel monopoles radar phase calibration method and single frequency calibration for one time, we propose a method of phase calibration based on the information plus channel group delay, by which we can deduce the phase of the whole frequency just through one single phase calibration with high efficiency. In this paper, we explain the reason for dual-channel monopoles radar, analyze the disadvantages of current calibration method and prove the feasibility of this phase calibration method based on group delay. By experiments, we testify that the calibration results by this method can satisfy the performance demands of the equipment. This method improves the calibration process and efficiency.

Pixel-addressable phase calibration of spatial light modulators: a common-path phase-shifting interferometric microscopy approach

As spatial light modulators (SLMs) are becoming flexible and the preferred device for light steering, the SLM’s modulation calibration still remains challenging. No pixel-addressable measurement of the SLM has yet been practically implemented. We present a quantitative phase measurement and calibration method for a parallel aligned liquid crystal spatial light modulator (PAL-SLM) based on Pancharatnam phase-shifting interferometric microscopy. The pixel-wise phase of SLM can be detected from microscopic interference pattern formed from two orthogonally polarized light waves reflected off the PAL-SLM. The wave phase is modulated or non-modulated depending on its polarization direction parallel or orthogonal to the liquid crystal director. Owing to self-referencing common-path interferometric microscopic imaging, the proposed method is quite robust against environmental disturbance and enables a high-precision pixel-wise characterization of SLM.

High-precision self-adaptive phase-calibration method for wavelength-tuning interferometry

We introduce a high-precision self-adaptive phase-calibration method for performing wavelength-tuning interferometry. Our method is insensitive to the nonlinearity of the phase shifter, even under random control. Intensity errors derived from laser voltage changes can be restrained by adopting this approach. Furthermore, this method can effectively overcome the influences from the background and modulation intensities in the interferogram, regardless of the phase structure. Numerical simulations and experiments are implemented to verify the validity of this high-precision calibration method.

Interferometric method for phase calibration in liquid crystal spatial light modulators using a self-generated diffraction-grating.

An auto-referenced interferometric method for calibrating phase modulation of parallel-aligned liquid crystal (PAL) spatial light modulators (SLM) is described. The method is experimentally straightforward, robust, and requires solely of a collimated beam, with no need of additional optics. This method uses the SLM itself to create a tilted plane wave and a reference wave which mutually interfere. These waves are codified by means of a binary diffraction grating and a uniformly distributed gray level area (piston) into the SLM surface. Phase shift for each gray level addressed to the piston section can then be evaluated. Phase modulation on the SLM can also be retrieved with the proposed method over spatially resolved portions of the surface. Phase information obtained with this novel method is compared to other well established calibration procedures, requiring extra elements and more elaborated optical set-ups. The results show a good agreement with previous methods. The advantages of the new method include high mechanical stability, faster performance, and a significantly easier practical implementation.

Employment of New Techniques for Characterizing Indian MST Radar Phased Array

ABSTRACTScientific investigations of dynamical processes in the earth's atmosphere are being performed over the past two decades using a 53 MHz mesosphere–stratosphere–troposphere (MST) radar, which is located at Gadanki, India. This radar consists of a phased antenna array of 1024 Yagi-Uda antennas. Antenna phase calibration is an important aspect for accurate measurements of atmospheric parameters by phased array MST/ST radars. In this paper, we describe two newly employed techniques to calibrate the large phased array antenna system of the Indian MST radar and the results obtained by these techniques. A “total power radiometer” technique has been employed for the first time to calibrate the antenna pattern in the receive mode. Radio source Virgo-A has been used as source in the far field for this purpose. The new technique has enabled us to characterize for the first time the first side lobe level of the antenna pattern and also the beam pointing accuracy in the E-plane. In the receive mode, antenna pattern is characterized with a 3 dB full beam width of 2.8o, first side lobe level of −18 dB, beam pointing accuracy is better than 0.12o. While the beam width and beam pointing accuracy are found to be close to the design values, the first side lobe level is 2 dB higher than that expected. To characterize the two-way antenna beam, active radar experiments are conducted and beam pointing accuracy has been estimated to be ∼0.1o using radar echoes from the moon; again for the first time. Improvement of signal-to-noise-ratio is observed with the newly developed antenna phase calibration method that used receiver quadrature detector. The agreement in comparison of wind vector derived from radar observations and Global Positioning System (GPS)-radiosonde measurements shows the performance status of the array antenna with the applied phase calibration.

Polarimetric 3-D Reconstruction From Multicircular SAR at P-Band

Multicircular synthetic aperture radar (SAR) (MCSAR) is an extension of circular SAR (CSAR) characterized by the formation of a synthetic aperture in elevation with several circular flights. This imaging mode allows an improved resolution in the plane perpendicular to the line of sight ( LOS⊥), thus suppressing the 3-D cone-shaped sidelobes that are formed when focusing with CSAR. This letter presents the first polarimetric MCSAR airborne experiment acquired at P-band by the German Aerospace Center (DLR)'s F-SAR system over a forested area in Vordemwald, Switzerland. This letter also includes a phase calibration method based on the singular value decomposition (SVD) using ground signatures to estimate constant phase offsets within a stack of 2-D images. Focusing methods, such as fast-factorized back projection (FFBP), beamforming (BF), and compressive sensing (CS), described in previous publications are used to solve the complex reflectivity in the (x, y, z) space.