Instantaneous Bandwidth Research Articles

Comparative analysis of solar radio bursts before and during CME propagation

Context. As is well known, coronal mass ejection (CME) propagation often results in the fragmentation of the solar atmosphere on smaller regions of density (magnetic field) enhancement (depletion). It is expected that this type of fragmentation may have radio signatures. Aims. The general aim of the present paper is to perform a comparative analysis of type III solar and narrow-band type-III-like radio burst properties before and during CME events, respectively. The main goal is to analyze radio observational signatures of the dynamical processes in solar corona. In particular, we aim to perform a comparison of local plasma parameters without and with CME propagation, based on the analysis of decameter radio emission data. Methods. In order to examine this intuitive expectation, we performed a comparison of usual type III bursts before the CME with narrow-band type-III-like bursts, which are observationally detectable on top of the background type IV radio bursts associated with CME propagation. We focused on the analysis of in total 429 type III and 129 narrow-band type-III-like bursts. We studied their main characteristic parameters such as frequency drift rate, duration, and instantaneous frequency bandwidth using standard statistical methods. Furthermore, we inferred local plasma parameters (e.g., density scale height, emission source radial sizes) using known definitions of frequency drift, duration, and instantaneous frequency bandwidth. Results. The analysis reveals that the physical parameters of coronal plasma before CMEs considerably differ from those during the propagation of CMEs (the observational periods 2 and 4 with type IV radio bursts associated with CMEs). Local density radial profiles and the characteristic spatial scales of radio emission sources vary with radial distance more drastically during the CME propagation compared to the cases of quasistatic solar atmosphere without CME(s) (observational periods 1 and 3). Conclusions. The results of the work enable us to distinguish different regimes of plasma state in the solar corona. Our results create a solid perspective from which to develop novel tools for coronal plasma studies using radio dynamic spectra.

Wideband Frequency Reconfigurable Patch Antenna With Switchable Slots Based on Liquid Metal and 3-D Printed Microfluidics

In this paper, a novel wideband frequency reconfigurable patch antenna with switchable slots (PASSs) based on liquid metal manipulation in 3-D printed microfluidic channel has been proposed. The frequency reconfiguration relies on the tuning and switching the slots achieved by continuous movement of the liquid metal volume over the channel that covers the narrow slots. The prototype patch antenna was designed with three pairs of composite slots, with the microfluidic channel bonded on top of the metal layer. The simulation and measurement results show that by tuning and switching the liquid metal-loaded slot in the designed microfluidic channel, a frequency tuning bandwidth of around 70% is achieved with a 2% instantaneous bandwidth, without significant change in the radiation pattern. Prototype has been fabricated, assembled, and measured with very good agreement between simulations and measurements.

High resolution observations with Artemis–JLS

Aims. We examined the characteristics of isolated intermediate drift bursts and their morphologies on dynamic spectra, in particular the positioning of emission and absorption ridges. Furthermore we studied the repetition rate of fiber groups. These were compared with a model in order to determine the conditions under which the intermediate drift bursts appear and exhibit the above characteristics. Methods. We analyzed sixteen metric type IV events with embedded intermediate drift bursts, observed with the Artemis–JLS radio spectrograph from July 1999 to July 2005 plus an event on 1st August 2010. The events were recorded with the SAO high resolution (10 ms cadence) receiver in the 270–450 MHz range with a frequency resolution of 1.4 MHz. We developed cross- and autocorrelation techniques to measure the duration, spectral width, and frequency drift of fiber bursts in 47 intermediate drift bursts (IMD) groups embedded within the continuum of the sixteen events mentioned above. We also developed a semi-automatic algorithm to track fibers on dynamic spectra. Results. The mean duration of individual fiber bursts at fixed frequency was δt ≈ 300 ms, while the instantaneous relative bandwidth was fw/f ≈ 0.90% and the total frequency extent was Δftot ≈ 35 MHz. The recorded intermediate drift bursts had frequency drift, positive or negative, with average values of df/fdt equal to −0.027 and 0.024 s−1 respectively. Quite often the fibers appeared in groups; the burst repetition rate within groups was, on average, ∼0.98 s. We distinguish six morphological groups of fibers, based on the relative position of the emission and absorption ridges. These included fibers with emission or absorption ridges only, fibers with the absorption ridge at lower or higher frequency than the emission, or with two absorption ridges above and below the emission. There were also some fibers for which two emission ridges were separated by an absorption ridge. Some additional complex groups within our data set were not easy to classify. A number of borderline cases of fibers with very high drift rate (∼0.30 s−1) or very narrow total bandwidth (∼8 MHz) were recorded; among them there was a group of rope-like fibers characterized by fast repetition rate and relatively narrow total frequency extent. We found that the whistler hypothesis leads to reasonable magnetic field values (∼4.6 G), while the Alfven-wave hypothesis requires much higher field. From the variation of the drift rate with time we estimated the ratio of the whistler to the cyclotron frequency, x, to be in the range of 0.3−0.6, varying by ∼0.05−0.1 in individual fibers; the same analysis gives an average value of the frequency scale along the loop of ∼220 Mm. Finally, we present empirical relations between fiber burst parameters and discuss their possible origin.

Photonic-Enabled RF Canceller for Wideband In-Band Full-Duplex Wireless Systems

In-band full-duplex (IBFD) wireless systems offer the ability to revolutionize frequency spectrum utilization for future networks. This is only possible if the self-interference generated by each wireless node is sufficiently mitigated, and becomes more challenging as the bandwidth increases. RF cancellation is one of the critical components that enables this interference reduction, but has previously been limited to narrowband operation or restricted to distinctive environments. This paper presents a novel RF canceller that utilizes photonic components to create a wideband vector modulator architecture with tunable time-delay taps. A prototype system with 20 canceller taps has been demonstrated to provide 25 and 20 dB of cancellation over 500-MHz and 1-GHz instantaneous bandwidths, respectively, and is tunable between 0.5 and 5.5 GHz. This unique photonic-enabled RF canceller design provides a path forward to achieve the wideband operation and high tap counts that will be required to successfully deploy future wireless systems with IBFD technology.

Synchrosqueezing transform based feature extraction from EEG signals for emotional state prediction

This paper presents a novel method for emotion recognition based on time-frequency analysis using multivariate synchrosqueezing transform (MSST) of multichannel electroencephalography (EEG) signals. With the advancements of the multichannel sensor applications, the need for multivariate algorithms has become obvious for extracting features that stem from multichannel dependency in addition to mono-channel features. In order to model the joint oscillatory structure of these multichannel signals, MSST has recently been proposed. It uses the concepts of joint instantaneous frequency and bandwidth. Electrophysiological data processing mostly requires joint time-frequency analysis in addition to both time and frequency analysis separately. The short-time Fourier transform (STFT) and wavelet transform (WT) are the main approaches utilized in time-frequency analysis. In this paper, the feasibility and performance of multivariate wavelet-based synchrosqueezing algorithm was demonstrated on EEG signals obtained from publically available DEAP database by comparing with its univariate version. Eight emotional states were considered by combining arousal-valence and dominance dimensions. Using linear support vector machines (SVM) as a classifier, MSST and its univariate version resulted in the highest prediction accuracy rates of ˜93% among all emotional states.

Design of an On-Chip Superconducting Microwave Circulator with Octave Bandwidth

We present a design for a superconducting, on-chip circulator composed of dynamically modulated transfer switches and delays. Design goals are set for the multiplexed readout of superconducting qubits. Simulations of the device show that it allows for low-loss circulation (insertion loss < 0.35 dB and isolation >20 dB) over an instantaneous bandwidth of 2.3 GHz. As the device is estimated to be linear for input powers up to -65 dBm, this design improves on the bandwidth and power-handling of previous superconducting circulators by over a factor of 50, making it ideal for integration with broadband quantum limited amplifiers.

Detection of spike-like structures near the front of type-II bursts

Aims. We examine high time resolution dynamic spectra for fine structures in type II solar radio bursts Methods. We used data obtained with the acousto-optic spectrograph receiver of the Artemis-JLS (ARTEMIS-IV) solar radio spectrograph in the 450–270 MHz range at 10 ms cadence and identified more than 600 short, narrowband features. Their characteristics, such as instantaneous relative bandwidth and total duration were measured and compared with those of spikes embedded in type IV emissions. Results. Type II associated spikes occur mostly in chains inside or close to the slowly drifting type II emission. These spikes coexist with herringbone and pulsating structures. Their average duration is 96 ms and their average relative bandwidth 1.7%. These properties are not different from those of type IV embedded spikes. It is therefore possible that they are signatures of small-scale reconnection along the type II shock front.

HRR profile estimation using SLIM

In this study, authors address high-range-resolution (HRR) profile reconstruction, when stepped-frequency waveforms are eventually used to maintain a narrow instantaneous bandwidth, resorting to the sparse learning via iterative minimisation (SLIM) paradigm, a regularised minimisation approach with an -norm constraint (for ), providing a variant to the original method. Particularly, the proposed method resorts to the regularised maximum-likelihood estimation paradigm including a term promoting the sparsity of the profile and related to the -norm of the vector containing the scatterers’ reflectivities. A priori information on the interference power level is also accounted for, at the design stage, and, assuming that each range cell under test contains at most one scatterer, the actual active scatterers composing the target are determined by exploiting the Bayesian information criterion (BIC). BIC is also used to automatically select the optimised q , so as to make the procedure adaptive with respect to q . Once the location of the active scatterers has been determined, a least-squares approach is also used to obtain even more precise HRR reconstruction. Furthermore, an efficient algorithm to define optimised frequency hopping patterns, in the presence of a continuous and coordinated feedback between the transmitter and receiver, is presented and assessed. The carried out analysis shows that the SLIM-based procedure presents higher accuracy in the HRR profile recovery than other widely used techniques, i.e. the iterative adaptive approach (IAA). Moreover, results demonstrate that the target range profile estimation capabilities are enhanced, both for SLIM and IAA, when the cognitive paradigm is employed.

High frame rate doppler ultrasound bandwidth imaging for flow instability mapping.

PurposeFlow instability has been shown to contribute to the risk of future cardiovascular and cerebrovascular events. Nonetheless, it is challenging to noninvasively detect and identify flow instability in blood vessels. Here, we present a new framework called Doppler ultrasound bandwidth imaging (DUBI) that uses high‐frame‐rate ultrasound and Doppler bandwidth analysis principles to assess flow instability within an image view.MethodsDoppler ultrasound bandwidth imaging seeks to estimate the instantaneous Doppler bandwidth based on autoregressive modeling at every pixel position of data frames acquired from high‐frame‐rate plane wave pulsing. This new framework is founded upon the principle that flow instability naturally gives rise to a wide range of flow velocities over a sample volume, and such velocity range in turn yields a larger Doppler bandwidth estimate. The ability for DUBI to map unstable flow was first tested over a range of fluid flow conditions (ranging from laminar to turbulent) with a nozzle‐flow phantom. As a further demonstration, DUBI was applied to assess flow instability in healthy and stenosed carotid bifurcation phantoms.ResultsNozzle‐flow phantom results showed that DUBI can effectively detect and visualize the difference in Doppler bandwidth magnitude (increased from 2.1 to 5.2 kHz) at stable and unstable flow regions in an image view. Receiver operating characteristic analysis also showed that DUBI can achieve optimal sensitivity and specificity of 0.72 and 0.83, respectively. In the carotid phantom experiments, differences were observed in the spatiotemporal dynamics of Doppler bandwidth over a cardiac cycle. Specifically, as the degree of stenosis increased (from 50% to 75%), DUBI showed an increase in Doppler bandwidth magnitude from 1.4 kHz in the healthy bifurcation to 7.7 kHz at the jet tail located downstream from a 75% stenosis site, thereby indicating flow perturbation in the stenosed bifurcations.Conclusion DUBI can detect unstable flow. This new technique can provide useful hemodynamic information that may aid clinical diagnosis of atherosclerosis.

Benefits of space-time diversity for radar

When designing a new radar system, standard resolution trade-offs play a major role, providing the basic parameters of the radar, such as size, update rate, and range. Besides, diversity has long been used for mitigating fading effects due to the fluctuation of targets and clutter. However, with the arrival of more flexible systems, using multiple parallel channels on transmit and receive, and wider instantaneous bandwidths, these standard trade-offs are becoming less simple—and more flexible. In this communication, we will analyse the benefits of diversity and its relations with range, Doppler, and angle, for detection and location of moving targets with wideband/wide-beam radar systems. The idea is to contribute to a better understanding of the real benefits of agile transmissions for detection/localization of moving targets, focusing on range, velocity, and angular measurement improvements, as well as on the benefits for detection of moving targets. Special attention will be given to the quality of the different wideband wide-beam sensor modes for long-range surveillance, and new results on detection of moving targets in clutter will be provided to demonstrate the effectiveness of these new architectures for small target detection at long range, in difficult environments.

Doppler Shift Time Expansion Resolution and Spectral Performance in Wideband Real-Time RF Channel Emulators

The possibility to test a radio frequency transceiver through the use of appropriate channel emulators allows evaluating their performance under various operating conditions. Many systems are able to operate with a relatively limited instantaneous bandwidth by applying known statistical models. Sometimes, it is necessary to evaluate the performance of a RF transceiver installed on high or very high speed platforms over predictable trajectories using optionally DEM (Digital Elevation Model) data of the terrain to estimate the number of stimulated paths and their contributions during the flight. When the instantaneous bandwidth of the signal becomes high (over several hundreds of MHz), one of the most important phenomena to consider is the Doppler spread induced by the channel and traditional narrowband models become useless. This paper presents some results when a time expansion is adopted to emulate the transceiver dynamic and the consequent Doppler spread with the aim of controlling the spectral purity of the emulated propagation channel.

Properties and magnetic origins of solar S-bursts

Context. Solar activity is often accompanied by solar radio emission, consisting of numerous types of solar radio bursts. At low frequencies (&lt;100 MHz) radio bursts with short durations of milliseconds, such as solar S-bursts, have been identified. To date, their origin and many of their characteristics remain unclear. Aims. We report observations from the Ukrainian T-shaped Radio telescope, (UTR-2), and the LOw Frequency ARray (LOFAR) which give us new insight into their nature. Methods. Over 3000 S-bursts were observed on 9 July 2013 at frequencies of 17.4–83.1 MHz during a period of low solar activity. Leading models of S-burst generation were tested by analysing the spectral properties of S-bursts and estimating coronal magnetic field strengths. Results. S-bursts were found to have short durations of 0.5–0.9 s. Multiple instruments were used to measure the dependence of drift rate on frequency which is represented by a power law with an index of 1.57. For the first time, we show a linear relation between instantaneous bandwidth and frequency over a wide frequency band. The flux calibration and high sensitivity of UTR-2 enabled measurements of their fluxes, which yielded 11 ± 3 solar flux units (1 SFU ≡ 104 Jy). The source particle velocities of S-bursts were found to be ∼0.07 c. S-burst source heights were found to range from 1.3 R⊙ to 2 R⊙. Furthermore, a contemporary theoretical model of S-burst generation was used to conduct remote sensing of the coronal magnetic field at these heights which yielded values of 0.9–5.8 G. Within error, these values are comparable to those predicted by various relations between magnetic field strength and height in the corona.

High performance RF filters via bandwidth scaling with Kerr micro-combs

We demonstrate high-resolution photonic RF filters using an RF bandwidth scaling approach based on integrated Kerr optical micro-combs. By employing both an active nonlinear micro-ring resonator (MRR) as a high-quality micro-comb source and a passive high-Q MRR to slice the shaped comb, a large RF instantaneous bandwidth of 4.64 GHz and a high resolution of 117 MHz are achieved, together with a broad RF operation band covering 3.28 to 19.4 GHz (L to Ku bands) using thermal tuning. We achieve programmable RF transfer functions including binary-coded notch filters and RF equalizing filters with reconfigurable slopes. Our approach is an attractive solution for high performance RF spectral shaping with high performance and flexibility.

Ultra wideband and multi-beam signal receiving and processing system of QTT

The proposed 110-m full-steerable radio telescope (Qitai radio telescope, QTT) in Xinjiang is mainly used in the fields of basic scientific research, such as pulsar observation, gravitational wave and black hole detection, star formation, galactic origin. At the same time, it serves national projects such as China Lunar Exploration project and Mars exploration. In order to meet the scientific needs, QTT will be equipped with a variety of ultra-wideband, multi-beam, high-sensitivity receivers and signal processing systems, to treat the weak electromagnetic wave signal received by the radio telescope, such as amplification, filtering, frequency conversion and other processing and sending to the digital terminal and processed. As this system determines the operating bandwidth, instantaneous bandwidth and field of view of radio telescopes, and is closely related to sensitivity, as a key part of the large radio telescope, it plays an important role in the performance of telescopes. In this paper, the configuration scheme and main performance index of QTT UWB and multi-beam signal receiving and processing system are demonstrated in detail. This paper systematically discusses the preliminary technical scheme of QTT receiver and signal acquisition and processing system, and analyzes the key technical problems of signal receiving and processing system.

A Reconfigurable Filter Using Defected Ground Structure for Wideband Common-Mode Suppression

A wideband common-mode (CM) suppression reconfigurable filter is proposed for high-speed all-pass differential circuits. The filter adopts three varactor-loaded compact defected ground structures (DGSs) to achieve continuous reconfigurability in its operation frequency with a large CM suppression dynamic range in the bandwidth. The varactors play an important role in widening the accessible instantaneous bandwidth and miniaturizing the structure. The three DGS cells with a total area of 15 mm × 10 mm are implemented symmetrically under the differential lines, to obtain reconfigurable CM bandstop characteristics which can be continuously adjusted from 1.8 to 8.1 GHz. A coupled LC resonator equivalent model is developed to represent and analyze the proposed filter, which explains its operation principle and assists in accelerating the reconfiguration design method. A good agreement between full-wave simulations and measured results is demonstrated, which validates the proposed design.

Quasi-Octave Bandwidth In-Phase Three-Layer Platelet Orthomode Transducer Using Improved Power Combiners

A 64% instantaneous bandwidth turnstile-junction-based orthomode transducer (OMT) made up of only three layers in a platelet configuration is presented. Such frequency coverage, while maintaining a very much reduced number of layers, is accomplished mainly by incorporating an improved power combiner based on noncontacting matching steps machined in one layer. This solution makes a real impact on the compactness concept of these OMTs while maintaining an excellent electrical performance. An OMT in the 10-20-GHz band was designed and measured by obtaining a return loss of 25 dB, an isolation between rectangular ports of 50 dB, a cross-coupling of 45 dB, and an insertion loss below 0.2 dB.

Wideband signal transceiver module with a Doppler shift function.

The wideband signal transceiver module forms the core component of the radar signal target simulator and the key module in measuring the Doppler shift. In this paper, we present a design for a miniaturized wideband signal transceiver module based on a PXIe bus, with an operating frequency range of 65 MHz-3 GHz, an instantaneous measurement bandwidth of 800 MHz on a standard 3U (where 1U = 4.445 cm) board with three slots. The module adopts a zero intermediate frequency transceiver, and the baseband uses two analog to digital converters, a field programmable gate array, and two digital to analog converters as the core hardware architecture. The module combines key technologies including variable-frequency local oscillator synthesis, radio-frequency broadband signal conditioning, and high-speed high-resolution baseband signal acquisition and generation. This paper describes a novel design for the Doppler shift function. Considering the limited size and volume of the module, Doppler shift technology combining a complex signal and a real signal was adopted to achieve full band coverage with an operating frequency range of 65 MHz-3 GHz. We verified that this module could generate the Doppler shift in the frequency band from -400 Hz to 400 Hz in steps of 2 Hz and with an error of ±2 Hz.

광대역 디지털 수신기 동적 범위 확장을 위한 A/D 변환모듈 연구

In this paper, an A/D conversion module was designed and fabricated to improve the dynamic range of wideband digital receivers. The A/D conversion module for expanding the dynamic range converts signals into a digital signal by branching the input signal into the normal path and the amplification path according to the input signal level. Test results of the fabricated module show that the normal path of the A/D conversion module converts an input level of −57 dBm to −12 dBm into a digital signal, and the amplification path converts an input level of −30 dBm to +12 dBm into a digital signal without distortion. This translates to an input dynamic range characteristic of 69 dB. Moreover, it is confirmed that the constant output characteristic is exhibited at an instantaneous bandwidth of 100 MHz.

Human Activity Classification With Radar: Optimization and Noise Robustness With Iterative Convolutional Neural Networks Followed With Random Forests

The accurate classification of activity patterns based on radar signatures is still an open problem and is a key to detect anomalous behavior for security and health applications. This paper presents a novel iterative convolutional neural network strategy with an autocorrelation pre-processing instead of the traditional micro-Doppler image pre-processing to classify activities or subjects accurately. The proposed strategy uses an iterative deep learning framework for the automatic definition and extraction of features. This is followed by a traditional supervised learning classifier to label different activities. Using three human subjects and their real motion captured data, 12 000 radar signatures were simulated by varying additive white Gaussian noise. In addition, 6720 experimental radar signatures were captured with a frequency-modulated continuous radar at 5.8 GHz with 400 MHz of instantaneous bandwidth from seven activities using one subject and 4800 signatures from five subjects while walking. The simulated and experimental data were both used to validate our proposed method, with signal–noise ratio varying from −20 to 20 dB and with 88.74% average accuracy at −10 dB and 100% peak accuracy at 15 dB. The proposed iterative convolutional neural networks followed with random forests not only outperform the feature-based methods using micro-Doppler images but also outperform the classification methods using other types of supervised classifiers after our proposed iterative convolutional neural network.

A Discrete-Time RF Signal-Processing Technique for Blocker-Tolerant Receivers With Wide Instantaneous Bandwidth

A new signal-processing approach aimed at improving the intermodulation performance of wideband receivers implemented in CMOS technologies is described. The receiver operates by downconverting an input signal to $N$ decimated baseband signals. The local oscillator signals used in this process are each a different phase of a pseudo-random bit sequence of length $N$ . The baseband signals are amplified and digitized before the original RF signal is reconstructed in the digital domain. The operating principles of the system are described and the performance specifications of this system are studied using a combination of analytical and numerical techniques. A prototype integrated circuit has been designed and fabricated using a 130-nm CMOS process. Detailed measurements demonstrating the narrowband and wideband operation of the system are presented and compared to theory. The measured in-band $IIP3$ has been found to be greater than 5.7 dBm from 40 to 300 MHz. The blocker tolerance of the circuit has also been characterized and it was found that a 10-MS/s −50-dBm 16-QAM signal could be received with nearly constant error-vector magnitude as the power of an in-band blocker signal was swept from −20 to −7 dBm.