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Multistatic imaging systems are commonly used in radar systems and microwave imaging. In these systems, many antennas are arranged three-dimensionally and connected to RF switches. The length of each transmitter (Tx) and receiver (Rx) channel differs slightly, causing artifacts in high-resolution image reconstruction. This study presents a novel method for the phase calibration of multistatic systems. This method does not require system reconstruction and can automatically perform phase calibration in a short time. This method is expected to facilitate an accurate phase measurement in multistatic systems. The approach involves phase calibration by analyzing the reflection coefficients of antenna elements in the time domain. Imaging experiments were performed on a multistatic imaging system using this calibration method, and the position and shape of a metal rod with a diameter one-fourth of a wavelength were reconstructed by simple back-projection with an accuracy beyond the diffraction limit. [ABSTRACT FROM AUTHOR]

Featured Application: This paper presents the design, validation, and testing of a software-defined radio beamforming platform designed for educational purposes. This paper presents the development and validation of a hybrid beamforming system based on software-defined radio (SDR), designed for telecommunications engineering education. The system provides an agile and user-friendly platform that allows students to observe, test, and evaluate beamforming techniques in real time. The platform integrates a multichannel SDR device (USRP N310) with traditional radiofrequency equipment and open-source software, facilitating hands-on learning experiences. The paper details the proposed hardware and software architecture and documents the calibration and validation phases. The testing and validation processes were conducted using a 3.5 GHz antenna array in both indoor and outdoor environments. The results demonstrated the system's effectiveness in achieving the desired beam orientations, with experimental results aligning closely with simulation and theoretical predictions. Significant differences in the radiation patterns observed between the indoor and outdoor measurements were documented, highlighting the impact of environmental factors on beamforming performance. The insights gained from this research provide valuable contributions to the education of future telecommunications engineers, enhancing their understanding of practical beamforming applications and the integration of modern SDR technology. [ABSTRACT FROM AUTHOR]

Holographic synthetic aperture radar (HoloSAR) introduces a cutting-edge three-dimensional (3-D) imaging mode to the field of synthetic aperture radar (SAR), enriching the scattering information of targets by observing them across multiple spatial dimensions. However, independent phase errors among baselines, such as those caused by platform jitter and measurement inaccuracies, pose significant challenges to imaging quality. The phase gradient autofocus (PGA) method effectively estimates phase errors, but struggles to accurately estimate the linear component, causing vertical shift in HoloSAR subaperture imaging result. Therefore, this paper proposes a PGA-based phase error compensation method for HoloSAR to address the vertical shift issue caused by linear phase errors. This method can achieve phase error correction in both the echo domain and image domain with enhanced efficiency. Experimental results of simulated targets and real data from the GOTCHA system demonstrate the effectiveness and practicality of the proposed method. [ABSTRACT FROM AUTHOR]

Liquid crystal microwave phased arrays (LC-MPAs) are regarded as an ideal approach to realize compact antennas owing to their advantages in cost, size, weight, and power consumption. However, the shortcoming in low radiation deflection efficiency has been one of LC-MPAs' main application limitations. To optimize the steering performance of LC-MPAs, it is essential to model the channel imperfections and compensate for the phase errors. In this paper, a phase error estimation model is built by training a neural network to establish a nonlinear relationship between the near-field phase error and the far-field pattern, hence realizing fast calibration for LC-MPAs within several measured patterns. Simulations and experiments on a 64-channel, two-dimensional planar antenna were conducted to validate this method. The results show that this method offers precise phase error estimations of 3.58° on average, realizes a fast calibration process with several field-measured radiation patterns, and improves the performances of the LC-MPA by approximately 4%–10% in deflection efficiency at different steering angles. [ABSTRACT FROM AUTHOR]

Wideband split-beam fishfinder is widely used in fisheries resource surveys, and the accuracy of its azimuth estimation determines whether the direction and position of target fish schools can be accurately determined. In order to improve the accuracy and efficiency of azimuth estimation, a phase calibration algorithm based on improved orthogonal digital down- conversion technology was proposed, simulated, and implemented using the Field Programmable Gate Array (FPGA). An azimuth estimation intellectual property (IP) core was built on the Vitis HLS platform to improve the accuracy of azimuth estimation while reducing the floating-point computation delay; finally, testing was conducted using a signal generator. The results showed that the azimuth estimation error of the module was no more than 0.05, the total computation delay did not exceed 420 ns, and the logical resource consumption was less than 45%, consistent with the system specifications. This research achievement has been successfully applied in the broadband split-beam fishfinder, significantly enhancing system accuracy and performance and generating certain economic benefits. [ABSTRACT FROM AUTHOR]

Phase measurements by the quadrature scheme in radio transceivers can be applied to phase-sensitive applications like precision multi-static 3D localization. However, measurements at different channels with individual local oscillators suffer from random phase offsets due to non-repeatable initial phases of phase-locked loops in frequency synthesizers. In this paper, a novel phase calibration method is proposed to cancel out both the random and systematic time-invariant phase offsets at the superheterodyne receiver frontends. Direct phase offset measurements and on-site calibration are made possible by additional hardware connections, achieving simple implementation and accurate differential phase measurements without relying on bandwidth resources. The proposed calibration method generates repeatable phases for each device reboot with standard deviation less than 2 degrees, which translates to 0.9 mm ranging accuracy for 1.8 GHz carrier frequency. This method can also be flexibly extended to accommodate a broad range of practical network scenarios with more channels, various network topologies, and a wider bandwidth.

An optical phased array (OPA) with 2-D circular sparse array aperture has been proposed and demonstrated in the silicon integrated photonic platform. The sparse distribution of the antenna array can realize no grating lobes in 2-D full field of view (FOV). To achieve fast and accurate phase calibration for OPA, an improved rotating element electric field vector algorithm based on golden section search method (GSS-REV) has also been proposed and verified. The 32-element antenna sparse distribution of the proposed OPA is designed and fabricated. A far-field beam steering measurement across 20° × 20° range features the side lobe suppression ratio (SLSR) of larger than 4.81 dB and a full width at half-maximum (FWHM) of approximately 0.63° × 0.59°. The resolvable points are derived to be ∼1076. The OPA chip has also been demonstrated on range measurement with frequency-modulated continuous-wave (FMCW) system.

This paper presents the development and validation of a hybrid beamforming system based on software-defined radio (SDR), designed for telecommunications engineering education. The system provides an agile and user-friendly platform that allows students to observe, test, and evaluate beamforming techniques in real time. The platform integrates a multichannel SDR device (USRP N310) with traditional radiofrequency equipment and open-source software, facilitating hands-on learning experiences. The paper details the proposed hardware and software architecture and documents the calibration and validation phases. The testing and validation processes were conducted using a 3.5 GHz antenna array in both indoor and outdoor environments. The results demonstrated the system’s effectiveness in achieving the desired beam orientations, with experimental results aligning closely with simulation and theoretical predictions. Significant differences in the radiation patterns observed between the indoor and outdoor measurements were documented, highlighting the impact of environmental factors on beamforming performance. The insights gained from this research provide valuable contributions to the education of future telecommunications engineers, enhancing their understanding of practical beamforming applications and the integration of modern SDR technology.

Multistatic imaging systems are commonly used in radar systems and microwave imaging. In these systems, many antennas are arranged three-dimensionally and connected to RF switches. The length of each transmitter (Tx) and receiver (Rx) channel differs slightly, causing artifacts in high-resolution image reconstruction. This study presents a novel method for the phase calibration of multistatic systems. This method does not require system reconstruction and can automatically perform phase calibration in a short time. This method is expected to facilitate an accurate phase measurement in multistatic systems. The approach involves phase calibration by analyzing the reflection coefficients of antenna elements in the time domain. Imaging experiments were performed on a multistatic imaging system using this calibration method, and the position and shape of a metal rod with a diameter one-fourth of a wavelength were reconstructed by simple back-projection with an accuracy beyond the diffraction limit.

Owing to the structural errors in the optical phased array, an initial random phase reduces the quality of the deflection beam. The most commonly applied approach to phase calibration is based on adaptive optics. However, adaptive optimisation approaches have slow convergence and low diffraction efficiency. We proposed a pointwise optimisation approach to achieve fast and accurate beam deflection. This approach conducts phase calibration, combining global traversal and local searches individually for each array element. We built a phase-calibration optical system containing a one-dimensional optical waveguide phase array for further verification and designed the relevant mechanics. The simulation and experimental results demonstrate that the pointwise optimisation approach accelerates the calibration process and improves the diffraction efficiency.

The phase calibration of distributed multi-node receiving system is required considering the phase synthesis working mode of distributed radar system for echo signals. Whereas, in respect to the traditional calibration tower and unmanned aerial vehicle scheme, there are many disadvantages. The wide range distributed multi-node receive chain calibration method based on GNSS software receiver was proposed in this paper, taking advantage of the software receiver to calculate and obtain the actual phase difference among the receiving nodes as well as the coordinate information of satellites in transmitting signal. Therefore, the phase difference resulted from different transmit path can be deleted, and the phase inconsistencies among the receiving nodes can be obtained. Besides, the fingerprint maps database regarding inconsistencies among nodes and two-dimensional angle of relative receiving node for satellites was constructed in this paper, the correspondence between the omnidirectional two-dimensional angle and the inconsistencies among different nodes was established by the actual results and two-dimensional fitting, and the phase inconsistency results among nodes can be obtained only by solving the satellite coordinate information. There are many advantages for the method proposed in this paper, such as slight influence of multipath effect, capability of all-weather all-day calibration, low costs.

With the development of launch vehicles, the number of satellite-based synthetic aperture radar (SAR) has been increasing. Satellite-based SAR can acquire high-resolution images at day and night regardless of the weather. Since SAR resolution is determined by a chirp bandwidth, corresponding a generation technology of wideband chirp is essentially required for high-resolution SAR images under consideration of relatively small and light weight SAR system. Therefore, an ideal chirp waveform generation, which is challenging task in actual hardware, is proposed by modifying a chirp equation for phase calibration, and is verified based on Sentinel-1 satellite SAR parameters. The proposed method is applied to our SAR hardware and we confirm the calibrated waveform. Evaluation results using SAR observation simulation show that the impulse response with the proposed method has better performances.

Objectives The very long baseline interferometry(VLBI) global observing system (VGOS) is a new generation of geodetic VLBI system which is equipped with broadband receiver and fast slewing antenna in order to achieve very high accuracy for measuring station coordinates, source positions as well as Earth rotation. Within the framework of the international VLBI service (IVS) for geodesy and astrometry, the first UT1 observing session was conducted using the VGOS stations at Kokee in USA and Wettzell in Germany, with a goal to validate VGOS data processing pipeline and estimate UT1 parameters. Methods The raw data were correlated at Shanghai VLBI correlator, followed by post-correlation processing and data analysis. The UT1 measurement results were derived and compared using VGOS database files produced from Shanghai correlator and the other correlator. Moreover, VGOS results were compared with those from the parallel UT1 session, which was conducted in the same time span using co-located legacy S/X-band stations. Results The UT1 estimation results obtained from Shanghai correlator output agree very well with those from the other correlator. The UT1 formal error obtained from VGOS observations is about 7 μs, approximately 2 times lower than the UT1 formal error obtained from the parallel legacy S/X-band observations. Conclusions VGOS system has the capability to obtain better UT1 measurement results than the legacy S/X-band system. The data processing pipeline established at Shanghai VLBI correlator has been validated and laid a foundation for regular VGOS data correlation in the near future. [ABSTRACT FROM AUTHOR]

The ultrasonic actuator can be used in medical applications because it is label-free, biocompatible, and has a demonstrated history of safe operation. Therefore, there is an increasing interest in using an ultrasonic actuator in the non-contact manipulation of micromachines in various materials and sizes for therapeutic applications. This research aims to design, fabricate, and characterize a single-sided transducer array with 56 channels operating at 500 kHz, which provide benefits in the penetration of tissue. The fabricated transducer is calibrated using a phase reference calibration method to reduce position misalignment and phase discrepancies caused by acoustic interaction. The acoustic fields generated by the transducer array are measured in a 300 mm × 300 mm × 300 mm container filled with de-ionized water. A hydrophone is used to measure the far field in each transducer array element, and the 3D holographic pattern is analyzed based on the scanned acoustic pressure fields. Next, the phase reference calibration is applied to each transducer in the ultrasonic actuator. As a result, the homogeneity of the acoustic pressure fields surrounding the foci area is improved, and the maximum pressure is also increased in the twin trap. Finally, we demonstrate the capability to trap and manipulate micromachines with acoustic power by generating a twin trap using both optical camera and ultrasound imaging systems in a water medium. This work not only provides a comprehensive study on acoustic actuators but also inspires the next generation to use acoustics in medical applications. [ABSTRACT FROM AUTHOR]

This article presents a novel built-in test equipment (BITE) for phase measurements in millimeter-wave integrated circuits (ICs). The BITE targets 5G New Radio (NR) applications. It is able to measure the phase in good agreement with $\mathbf {S_{21}}$ measurements and has a relative rms phase error lower than 6° over the frequency band of interest. Aside from the relative phase, this BITE also addresses the absolute phase difference of all ICs on the same phased array. To the authors’ best knowledge, this is the first BITE and built-in self-test (BIST) to do so. The BITE is able to reduce the absolute phase discrepancy by a factor of 3. To reduce the measurement complexity, the BITE is implemented as a homodyne architecture to output a dc voltage relative to the phase of the channel. A built-in algorithm is used, mitigating the impairments normally associated with a homodyne receiver. This reduces the design complexity and hence the area overhead. The BITE occupies an area of 480 $\mathbf {\mu m} \times 135\,\,\mathbf {\mu m}$ , facilitating easy integration. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Optical phase errors are inherent to practical waveguides and will degrade the beam quality of optical phased arrays. This paper demonstrates a scalable approach to on-chip phase calibration of optical phased arrays using a compact phase interrogator structure. This phase interrogator is designed for optical phased arrays with a $2.5 \,{\mu }\mathrm{m}$ pitch and demonstrated in a 64-channel optical phased array realized in a Si/SiN photonic stack. The optical phased array exhibits $38 \,\mathrm{^{\circ }}$ of unambiguous beam steering range and a side lobe level of at most $-9.8 \,\mathrm{d}\mathrm{B}$ after calibration. The calibration algorithm is model-based and does not rely on any iterative optimization algorithm. This enables calibration with linear scaling of both the computational complexity and the area of the calibration structures. By including wavelength dependent effects, the model allows for 2D beam steering without any need for re-calibration. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, wepropose a novel two-stage transmission framework for an intelligent reflecting surface (IRS) assisted millimeter wave (mmWave) system in the presence of phase error caused by hardware impairments. Specifically, in Stage I, we introduce a pilot-based phase calibration task and reformulate it as an alternating optimization program. Building on this formulation, an efficient iterative algorithm is developed to jointly estimate the phase error, which needs to be calibrated, and the channels corresponding to the first user. Stage II consists of two blocks, channel estimation and data transmission. During the channel estimation block, by leveraging on the sparsity of mmWave channels, we propose a fast Fourier transform based scheme to estimate the IRS-BS channel and user-IRS channels. During the data transmission block, based on the estimated channel state information, base station precoders and IRS phase shifts are jointly optimized to maximize the sum signal-to-leakage-plus-noise ratio of all users. To handle this non-convex problem, we further develop a low-complexity joint beamforming algorithm by exploiting fractional programming techniques. Moreover, to examine the performance of the proposed phase calibration scheme, we derive the Cramer-Rao lower bound for the intended phase error estimation. Simulation results validate the effectiveness of our proposed transmission framework and the necessity of IRS phase calibration. [ABSTRACT FROM AUTHOR]

Abstract The fingerprint indoor localization method based on channel state information (CSI) has gained widespread attention. However, this method fails to provide a better localization effect and higher localization accuracy due to poor fingerprint accuracy, unsatisfactory classification and matching effect, and vulnerability to environmental impacts. In order to solve the problem, this paper proposes a CSI fingerprint indoor localization method based on the Discrete Hopfield Neural Network (DHNN). The method mainly consists of off-line and on-line phases. At the off-line phase, a low-pass filter is applied to conduct a preliminary processing on the fingerprint information of each reference point, and then, phase difference is adopted to correct the fingerprint data of all reference points. In this way, the quality of fingerprint data is improved, hence avoiding problems such as indoor environmental changes and multipath effect of signals, etc. in which impact the fingerprint data. Finally, the characteristic fingerprint database is established after acquiring relatively accurate fingerprint data. At the on-line phase, to maintain the consistency of data, the data of each reference point in the fingerprint database is set as an attractor. Meanwhile, the localization information of the test point is processed to make convergence judgment through DHNN. Eventually, the localization result is obtained. The experimental results show that the localization accuracy with a median error of 1.6 m can be achieved through the proposed method in the experimental environment. Compared with similar methods, it has a higher stability which can significantly reduce the cost of manpower and time.

Perfect phase-shifting is challenging to realize due to the inherent hardware impairments at the intelligent reflecting surface (IRS). In this letter, we propose an efficient calibration framework for IRS-aided millimeter-wave (mmWave) systems in the presence of both the direction-independent phase error and the direction-dependent phase error. For the proposed scheme, we first introduce an uplink pilot transmission protocol, based on which the angle information of each uplink path can be obtained through the 2-D discrete Fourier transform and angle rotation. Then, by utilizing the technique of majorization-minimization and gradient projection, an efficient calibration algorithm is developed to separately estimate the direction-independent phase error and the direction-dependent phase error. Simulation results validate effectiveness of the proposed calibration algorithm and show substantial performance improvement over benchmarks. [ABSTRACT FROM AUTHOR]

Coherent processing in cooperative multi-agent networks can achieve significant performance gain via accurate alignment of observed signals. However, the inaccessibility of phase information in mobile scenes prevents the acquisition of a high degree of coherence for target detection. This paper presents a quasi-coherent mobile detection framework for cooperative multi-agent networks, which exploits the phase information inherent in the carrier wave of direct-path signals. Specifically, we derive the quasi-coherent detector with the aid of phase calibration by incorporating the maximum likelihood estimation of phase-related parameters obtained from direct-path signals. Next, we characterize the detection performance degradation induced by the mismatch of initial phase, transmitter position, orientation and clock. We further demonstrate the near-optimal detection capability of the proposed detector compared with generic coherent detectors and validate the effectiveness of phase information exploitation via numerical simulations. [ABSTRACT FROM AUTHOR]

In this article, we present a novel nonlinear vector network analyzer (NVNA) setup for charactering the in-band full-duplex (IBFD) performance of millimeter-wave antenna systems. To achieve millimeter-wave modulated measurements on dense spectral grids, this NVNA setup utilizes user-defined: 1) digitally-modulated test stimuli; 2) multisine phase reference; and 3) pulsed-radio frequency (RF) phase calibration standards for test bench establishment and calibration. To create the IBFD test scenario, a special design of test stimuli is developed for antenna characterization, where the spectral components of two periodical transmitting signals (digitally modulated within the same frequency band) do not overlap with each other. In this way, the desired magnitude and phase information of transmitted and received signals can be easily separated and extracted from the NVNA measurements, to support various frequency-, time-, and digital-domain analysis. The validity of the proposed NVNA setup is experimentally verified at 28 GHz, where the error vector magnitude (EVM) results of 100 MSymbol/s 64-QAM test signals are from 2.0% to 2.3%. From the application perspective, this measurement setup and test method can be widely used for fifth-generation (5G)-oriented over-the-air test of IBFD antenna systems. [ABSTRACT FROM AUTHOR]

Optical phased arrays (OPAs) are promising in various applications owing to their excellent beam steering performance but suffer from the random initial phases ruining the beam patterns. In this work, an interference-based calibration method to align the random phases for OPA operations is proposed. Briefly, the phase differences are directly extracted from the interference fringes and used to build up the phase map. The feasibility and effectiveness of the proposed method were verified from an 8 × 8 OPA chip, in which the side-lobe suppression ratio of 10.1 dB was achieved. The proposed method can be utilized as a supplement of conventional calibration algorithms to reduce requirements for the sensitivity of the feedback system and avoid local optima, thus providing practical assistance for many OPA applications.

The ultrasonic actuator can be used in medical applications because it is label-free, biocompatible, and has a demonstrated history of safe operation. Therefore, there is an increasing interest in using an ultrasonic actuator in the non-contact manipulation of micromachines in various materials and sizes for therapeutic applications. This research aims to design, fabricate, and characterize a single-sided transducer array with 56 channels operating at 500 kHz, which provide benefits in the penetration of tissue. The fabricated transducer is calibrated using a phase reference calibration method to reduce position misalignment and phase discrepancies caused by acoustic interaction. The acoustic fields generated by the transducer array are measured in a 300 mm × 300 mm × 300 mm container filled with de-ionized water. A hydrophone is used to measure the far field in each transducer array element, and the 3D holographic pattern is analyzed based on the scanned acoustic pressure fields. Next, the phase reference calibration is applied to each transducer in the ultrasonic actuator. As a result, the homogeneity of the acoustic pressure fields surrounding the foci area is improved, and the maximum pressure is also increased in the twin trap. Finally, we demonstrate the capability to trap and manipulate micromachines with acoustic power by generating a twin trap using both optical camera and ultrasound imaging systems in a water medium. This work not only provides a comprehensive study on acoustic actuators but also inspires the next generation to use acoustics in medical applications.

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Currently, human sensing draws much attention in the field of ubiquitous computing, and human sensing based on WiFi CSI (channel state information) becomes a hot research topic due to the easy deployment and availability of WiFi devices. Although various human sensing applications based on the CSI signal model are emerging, the model-based approach has not been studied thoroughly. This paper provides a comprehensive survey of the latest model-based human sensing methods and their applications. First, the CSI signal and framework of model-based human sensing methods are introduced. Then, related models and fundamental signal preprocessing techniques are described. Next, typical human sensing applications are investigated, and the crucial characteristics are summarized. Finally, the advantages, limitations, and future research trends of model-based human sensing methods are concluded in this paper. [ABSTRACT FROM AUTHOR]

Channel state information can provide more detailed sub-carrier information,which attracts the attention of researchers in indoor localization technology.In view of the shortcomings of the traditional indoor location method in the accuracy and stability of the complex indoor environment,an indoor localization method named ComLoc was proposed which could be applied to complex indoor environment,solved the influence of the multipath effect and noise interference on the positioning precision.The error of CSI signal was discussed,the sensitivity of CSI phase information to indoor environment was analyzed and the idea of trusted carrier link was proposed.By selecting reliable and stable link signal by phase difference,the misjudgment of position could be reduced.Based on many numerous experiments,the phase error of CSI was calibrated,and the characteristics of signal variation were extracted.The experimental results show that ComLoc is effective and efficient in the complex indoor environment.

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. [ABSTRACT FROM AUTHOR]

A W‐band wide‐beam horn suitable for prime‐focus feed is described in this paper. It was designed to provide better illuminations for outer panels of larger reflector antennas and to improve performance of radio holography systems. Much effort has been spent on precise characterization of the amplitude and phase patterns of the wide beam horn which has a direct impact on the measurement accuracy of the radio holography. A far‐field measurement setup with the correction of phase errors due to cable flexing has been developed. Good beam pattern agreement has been achieved between simulation and measurement. [ABSTRACT FROM AUTHOR]

Predistortion is used to compensate for a waveform or phase of a signal in advance. Although the signal that applies predistortion exhibits a nonideal shape at the baseband, it has an improved phase value after the signal is upconverted in the actual hardware. Most synthetic aperture radar studies have focused on image reconstruction using single-look complex or ground-range detected data. Other studies have only compensated for the peak phase error; thus, discontinuity remains. In this letter, we present a novel method to reduce the phase error by applying a polynomial regression predistortion based on system calibration. The new approach is formulated to minimize the overall pulse error in a signal generator. We use the second-order polynomial regression for the phase error and predistort the phase error using the regression value. The proposed method is applied to the baseband signal, which exhibits an improved phase value at the X-band (9.5–10 GHz). [ABSTRACT FROM AUTHOR]

Device-free passive wireless indoor localization is attracting great interest in recent years due to the widespread deployment of Wi-Fi devices and the numerous location-based services requirements. In this paper, we propose DFPhaseFL, the first device-free fingerprinting indoor localization system that purely uses CSI phase information. It utilizes the CSI phase information extracted from simply a single link to estimate the location of the target, neither requiring the target to wear any electronic equipment nor deploying a large number of access points and monitor devices. In DFPhaseFL, the raw CSI phases are extracted from the CSI measurements through the three antennas of the Intel WiFi Link 5300 wireless Network Interface Card (IWL 5300 NIC) firstly. Then, linear transformation and noise filtering are applied to acquire the calibrated CSI phases. Through experimental observations, we find that the calibrated CSI phase owns an unpredictable characteristic over time. Thus, it cannot be directly applied as a fingerprint. To this end, a transfer deep supervised neural network method combining deep neural network and transfer learning is proposed to obtain feature representations with both transferability and discriminability as fingerprints. Then, the DFPhaseFL system uses the SVM algorithm to obtain the estimation of the target location online. Experiment results demonstrate that the DFPhaseFL owns a better estimation precision compared with the other state of art, and maintain a stable localization accuracy for a long time without reacquiring the fingerprint database. [ABSTRACT FROM AUTHOR]

This article presents the evaluation of using pulsed-radio frequency (RF) signals as multitone phase standards for modulated measurements at millimeter-wave (mm-Wave) bands, offering an alternative phase calibration choice for nonlinear vector network analyzers (NVNAs). Based on the NVNA measurements of two pulsed-RF signals generated by square-wave-driven mixers, a high correlation between magnitude and phase errors of unideal pulsed-RF signals is discovered, and an empirical method is developed to accurately estimate the phase errors according to magnitude-only measurements. To confirm its robustness and key preconditions for wide-range applications, theoretical support and explanation to the empirical method is revealed, in which the dominant waveform distortion of an applicable pulsed-RF signal can be decomposed into modulated perturbations with Sinc-like envelopes. The validity of the proposed empirical method, as well as its application for mm-Wave NVNA phase calibration, is verified by both experimental measurements and simulation results, where an estimation error (or phase calibration error) less than ±2° is demonstrated that is reachable in practice. [ABSTRACT FROM AUTHOR]

A laser pistonphone system capable of measuring the sensitivity modulus and phase of microphones is proposed. For the primary vibration calibration, the sine-approximation method has been applied which is used to calculate the complex sensitivity of accelerometers. This method is based on a laser interferometer with quadrature output instead of the fringe-counting method that is used in conventional laser pistonphones. Here, the laser pistonphone system based on the sine-approximation method with the quadrature signal is proposed and the measured results are compared to those obtained by the reciprocity method. The measured sensitivity with the proposed method agrees well with the result of the reciprocity method for the infrasound range. However, in case of the phase sensitivity, the discrepancy is relatively high in comparison to the sensitivity modulus. The results show that the proposed system is capable of calibrating the complex sensitivity of microphones. The improvement of the uncertainty and extension of the frequency range can be achieved by modification of the excitation system for obtaining the required stable excitation with long stroke. [ABSTRACT FROM AUTHOR]

Given the rapidly growing drone market, the development of drone detection radars has become highly important to prevent drones from damaging lives and property. Frequency-modulated continuous-wave (FMCW) radars have been frequently used for drone detection. Among the architectures of FMCW radar, a heterodyne architecture that involves different local oscillators and produces beat signals at the IF stage has often been chosen. The FMCW radar, however, has a chronic problem called leakage. In an earlier study, we proposed the stationary point concentration (SPC) technique to improve the signal-to-noise ratio (SNR) of small drones by reducing the increase in noise floor caused by leakage. We demonstrated that the proposed technique increases the SNR of small hovering drones in the 1-D power spectrum. In this article, we newly analyze the practical problems in the heterodyne FMCW radar system. One is the 2-D noise floor increase in the range-Doppler (r-D) map due to the leakage, and the other is unwanted Doppler shifts. Then, we propose an upgraded theory and realization method of the SPC technique for the detection of the small moving drone by improving the r-D map. We prove that the proposed method not only reduces the 2-D noise floor by mitigating the leakage but also removes the unwanted Doppler shifts by the phase calibration. Consequently, we show that the proposed method increases the SNR of the small moving drone and corrects its velocity information at the same time in the r-D map. [ABSTRACT FROM AUTHOR]

This article presents the first 39-GHz phased-array transceiver (TRX) chipset for fifth-generation new radio (5G NR). The proposed transceiver chipset consists of 4 sub-array TRX elements with local-oscillator (LO) phase-shifting architecture and built-in calibration on phase and amplitude. The calibration scheme is proposed to alleviate phase and amplitude mismatch between each sub-array TRX element, especially for a large-array transceiver system in the base station (BS). Based on LO phase-shifting architecture, the transceiver has a 0.04-dB maximum gain variation over the 360° full tuning range, allowing constant-gain characteristic during phase calibration. A phase-to-digital converter (PDC) and a high-resolution phase-detection mechanism are proposed for highly accurate phase calibration. The built-in calibration has a measured accuracy of 0.08° rms phase error and 0.01-dB rms amplitude error. Moreover, a pseudo-single-balanced mixer is proposed for LO-feedthrough (LOFT) cancellation and sub-array TRX LO-to-LO isolation. The transceiver is fabricated in standard 65-nm CMOS technology with flip-chip packaging. The 8TX–8RX phased-array transceiver module 1-m OTA measurement supports 5G NR 400-MHz 256-QAM OFDMA modulation with −30.0-dB EVM. The 64-element transceiver has a EIRPMAX of 53 dBm. The four-element chip consumes a power of 1.5 W in the TX mode and 0.5 W in the RX mode. [ABSTRACT FROM AUTHOR]

The fingerprint indoor localization method based on channel state information (CSI) has gained widespread attention. However, this method fails to provide a better localization effect and higher localization accuracy due to poor fingerprint accuracy, unsatisfactory classification and matching effect, and vulnerability to environmental impacts. In order to solve the problem, this paper proposes a CSI fingerprint indoor localization method based on the Discrete Hopfield Neural Network (DHNN). The method mainly consists of off-line and on-line phases. At the off-line phase, a low-pass filter is applied to conduct a preliminary processing on the fingerprint information of each reference point, and then, phase difference is adopted to correct the fingerprint data of all reference points. In this way, the quality of fingerprint data is improved, hence avoiding problems such as indoor environmental changes and multipath effect of signals, etc. in which impact the fingerprint data. Finally, the characteristic fingerprint database is established after acquiring relatively accurate fingerprint data. At the on-line phase, to maintain the consistency of data, the data of each reference point in the fingerprint database is set as an attractor. Meanwhile, the localization information of the test point is processed to make convergence judgment through DHNN. Eventually, the localization result is obtained. The experimental results show that the localization accuracy with a median error of 1.6 m can be achieved through the proposed method in the experimental environment. Compared with similar methods, it has a higher stability which can significantly reduce the cost of manpower and time. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Optical phased arrays (OPAs) are promising in various applications owing to their excellent beam steering performance but suffer from the random initial phases ruining the beam patterns. In this work, an interference-based calibration method to align the random phases for OPA operations is proposed. Briefly, the phase differences are directly extracted from the interference fringes and used to build up the phase map. The feasibility and effectiveness of the proposed method were verified from an 8 × 8 OPA chip, in which the side-lobe suppression ratio of 10.1 dB was achieved. The proposed method can be utilized as a supplement of conventional calibration algorithms to reduce requirements for the sensitivity of the feedback system and avoid local optima, thus providing practical assistance for many OPA applications. [ABSTRACT FROM AUTHOR]

Channel phase calibration is a crucial issue in high resolution and wide swath (HRWS) imagery with azimuth multi-channel synthetic aperture radar (SAR) systems. Precise phase calibration is definitely required in reconstructing the full Doppler spectrum for precise HRWS imagery without high-level ambiguities. In this paper, we propose a novel calibration for HRWS SAR imagery by optimizing the reconstructed unambiguous Doppler spectrum. The sharpness of the reconstructed Doppler spectrum is applied as the metric to measure the unambiguity quality, which is maximized to retrieve the element phase error caused by channel imbalance. Real data experiments demonstrate the performance of the proposed calibration for ambiguity suppression in HRWS SAR imagery.

The calibration of phase offsets between RF chains on commodity WiFi chips has been an key obstacle for many WiFi-based applications. In this paper, we conduct extensive experiments to explore the characteristics of the phase offsets. The real experimental results reveal that the phase offsets are actually deterministic. We explain such a phenomena via the circuit design of WiFi chips. We also show that the phase offsets are even the same among different chips. With extensive experiments, we obtain and report the measured phase offset values for the commodity Intel 5300 and Atheros AR9380 WiFi chips. With the observation illustrated in this paper, the calibration of the phase offsets can be simplified greatly. [ABSTRACT FROM AUTHOR]

A method is presented to estimate and compensate the ionospheric and clock-drift perturbations that affect bistatic synthetic aperture radar (SAR) images acquired under a quasi-monostatic acquisition geometry. This is accomplished through multisquint-based processing of the interferometric phase, which allows separating the ionospheric component from the rest of the phase perturbations by processing small azimuth subapertures. It is demonstrated how the absolute, i.e., nondifferential, ionospheric phase can be estimated by exploiting the baseline of the acquisition geometry, which further allows an individual correction of each image of the bistatic pair. A mathematical model of the bistatic SAR phase perturbations, as well as an algorithm for performing their estimation and compensation, is presented. The performance of the method is assessed with end-to-end simulations of bistatic acquisitions over synthetic distributed targets. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]