FMCW Signal Research Articles

Influences of Thermal Effect on the Performance of FMCW Signal Generated by Current-Modulated DFB-LDs

Influences of Thermal Effect on the Performance of FMCW Signal Generated by Current-Modulated DFB-LDs

Clutter Cancellation Methods for Small Target Detection Using High-Resolution W-band Radar.

Drones are currently being used for various applications. However, the detection of drones for defense or security purposes has become problematic because of the use of plastic materials and the small size of these drones. Any drone can be placed under surveillance to accurately determine its position by collecting high-resolution data using various detectors such as the radar system proposed in this paper. The W-band radar has a high carrier frequency, which makes it easy to design a wide bandwidth system, and the wideband FMCW signal is suitable for creating high resolution images from a distance. Unfortunately, the huge amounts of data gathered in this way also contain clutter (such as background data and noise) that is usually generated from unstable radar systems and complex environmental factors, and which frequently gives rise to distorted data. Accurate extraction of the position of the target from this big data requires the clutter to be suppressed and canceled, but conventional clutter cancellation methods are not suitable. Four clutter cancellation algorithms are assessed and compared: standard deviation, adaptive least mean squares (LMS), recursive least squares (RLS), and the proposed LMS. The proposed LMS has combined LMS with the standard deviation method. First, the big data pertaining to the target position is collected using the W-band radar system. Subsequently, the target position is calculated by applying these algorithms. The performance of the proposed algorithms is measured and compared to that of the other three algorithms by conducting outdoor experiments.

Intra-Pulse Frequency Coding Design for a High-Resolution Radar against Smart Noise Jamming

Smart noise jamming forms active jamming by intercepting, modulating, and forwarding radar signals into the radar receiver, which seriously affects the radar range recovery performance. In this paper, we propose a novel waveform design approach and an efficient range recovery method for high-resolution radar in the jamming scenario. Firstly, we propose an intra-pulse frequency-coded frequency-modulated continuous waveform (IPFC-FMCW), which contains multiple FMCW chips with different widths and frequencies, to combat the smart noise jamming. After the jamming suppression, the proposed waveform has a low sidelobe level, which is different from traditional FMCW signals for which the observations are periodically missing, resulting in high sidelobe levels. Then, to improve the range recovery performance of the waveform after jamming suppression, we optimize the range profile by designing the transmit waveform and then solve it by a simulated annealing algorithm. Next, based on the designed waveform, we derive the echo model after jamming suppression and propose a gridless compressed sensing (CS) method to recover the range of the targets. Compared with the existing waveforms and methods, the proposed waveform and the processing method achieve better range recovery performance in the jamming scenario. Numerical simulations are utilized to demonstrate the range recovery effectiveness of the proposed waveform and method in smart noise jamming.

Self-propelled Subsurface Radar Detector of Low-Depth Objects

Portable, mobile and mobile subsurface radar detectors are in high needed for localizing inhomogeneities and hidden defects in monitoring the condition of road surfaces, studying the upper layer of the earth's surface during humanitarian demining and identifying caches. Despite the presence of a number of specialized devices, the problem of ensuring reliable operational detection of near-surface and shallow objects has not been fully resolved. One of the promising directions in the development of a subsurface radar detector with an increased efficiency of object detection when deepening up to 1,5 ... 2 λ is associated with the use of a continuous ultra-wideband FMCW signal and optimization of the structural design of the system, which ensures the maintenance of a given height of rise of the antenna unit above the studied environment with its high mobility. The article presents the results of the development of a self-propelled subsurface radar detector with a continuous probing signal, including the substantiation of the technical appearance of the device, the development of a concept layout and the results of experimental studies. The device is made on a four-wheeled automated platform with an adjustable console on which the antenna unit moves. With the forward movement of the platform, a sequential radar survey of the upper soil layer is performed, the results of which in the form of a surface projection of the normalized power of depth portraits are displayed on the monitor screen. The conducted field tests of the device showed reliable detection of near- and subsurface objects made of dielectric and metallic materials.

Fully Integrated FMCW LiDAR Optical Engine on a Single Silicon Chip

We present the demonstration of two novel chip-scale FMCW LiDAR optical engines in which all photonic components, including the laser sources, were integrated on single silicon chips. Using the first LiDAR chip design, with an integrated distributed Bragg reflector laser and grating couplers as input/output ports for the receive/transmit light, we demonstrated a maximum range of 28 m limited by transmit light output power of 2 mW. We further demonstrated a maximum range of 75 m using a second LiDAR chip architecture having an on-chip sampled grating distributed Bragg reflector master laser with integrated power amplifier in which the local oscillator light was obtained from the laser back facet. This maximum range can be further increased by improving the laser linewidth. The measured range dependence of the FMCW signal level for both LiDAR chips agreed well with theory. The chip-scale FMCW LiDAR optical engines can be used in conjunction with a variety of off-chip two dimensional beam scanners to realize a chip-scale scanning LiDAR solution. To the best of our knowledge, this is the first published demonstration of fully integrated FMCW LiDAR optical engines on a single silicon chip.

Phase Noise Spectral Density Measurement of Broadband Frequency-Modulated Radar Signals

In continuous-wave (CW) radar systems, such as frequency-modulated (FMCW), frequency-stepped (FSCW), or orthogonal frequency-division multiplexing (OFDM) radar systems, the range and velocity uncertainty are significantly impaired by phase noise decorrelation. Therefore, radar designers require accurate knowledge of their synthesizers’ phase noise profiles to assess and predict radar performance. However, commercial phase noise analyzers cannot determine phase noise during modulation, and this may differ notably from phase noise in the pure CW mode. Recent methods for FMCW phase noise analysis usually require comprehensive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${a}$ </tex-math></inline-formula> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">priori</i> knowledge of modulation parameter and are prone to systematic deviations. To overcome these issues, we propose a new approach based on differential analysis of subsequent time-domain measurements. This method retains, statistical phase noise information while reducing systematic influences. For the first time, less <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${a}$ </tex-math></inline-formula> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">priori</i> signal knowledge is required, and the method works for nearly any kind of broadband signal modulation. The concept requires only a digitizer (e.g., an oscilloscope) and some digital signal processing. The proposed method is first experimentally tested with different phase-locked-loop (PLL)-based synthesizer phase noise profiles. The obtained phase noise profiles agree perfectly with the results of an established measurement system. After this proof of basic functionality, the unique phase noise analysis capability for BB modulated signals is demonstrated with PLL-generated FMCW signals. The results reveal a significant phase noise difference between the different setups and clearly show the capability and benefit of the novel phase noise spectral density measurement concept.

A Self-Adapted Two-Point Modulation Type-II Digital PLL for Fast Chirp Rate and Wide Chirp-Bandwidth FMCW Signal Generation

Different from the conventional two-point modulation (TPM) type-II phase-locked loops (PLLs) requiring non-trivial gain calibrations and TPM type-III PLLs with loop stability concern and limited chirp rate, a self-adapting gain mismatch TPM type-II digital PLL is proposed in this article. It directly detects frequency error as its input signal, allowing frequency ramp tracking with zero steady-state frequency error using a type-II PLL. In addition, the maximum trackable slope in the case of the proposed TPM type-II PLL is intrinsically larger than that of the conventional TPM type-III PLL. A polarity navigator is embedded in the digital loop filter to improve the linearity at the chirp turning-around points (TAPs). Fabricated in a 28-nm complementary metal–oxide–semiconductor (CMOS) technology, the proposed PLL consumes 23 mW from a 1-V power supply and occupies 0.31 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measurement results indicate that the proposed PLL can generate a precise triangular chirp with 2.27-GHz bandwidth (BW) and 18.2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> period at 12.5 GHz. To the best knowledge of the authors, this work demonstrates the widest normalized Chirp-bandwidth and the fastest chirp rate simultaneously.

Testing RFoF link for transmitting HF-OTHR signal between transmitter and receiver shelters

HF-OTHR site contains two equipment shelters, up to 1 km away from each other, that need to be connected for transmitting a FMCW signal. This connection, if realized using a coaxial cable, has shown itself to be vulnerable to external electromagnetic discharges, which can damage the sensitive radar equipment. This paper explores and tests the possibility of using Radio-Frequency-over-Fiber (RFoF) link as an alternative to a coaxial cable for transmission of signal, in order to ensure the immunity from external sources of electromagnetic interference (EMI).

Silicon-based FMCW signal generators: A review

FMCW radars with high resolution necessities the generation of highly linear, low phase noise, and low spur chirp signals with large bandwidth and a short modulation period. This paper reviews recent research progress on silicon-based FMCW signal generators, identifies advances in architecture, fundamental design, performance analysis, and applications of the FMCW synthesizer.

A 12-GHz Calibration-Free All-Digital PLL for FMCW Signal Generation With 78 MHz/μs Chirp Slope and High Chirp Linearity

A novel all-digital phase-locked loop (ADPLL) for fast and high-linear FMCW signal generation is presented in this paper. Fast chirp slope is enabled by two-point modulation (TPM) technique and ramp linearity distortion induced by digitally- controlled oscillator (DCO) is suppressed by wide loop bandwidth. A calibration-free retiming fractional frequency dividing (FFD) scheme based on digital phase interpolator (DPI) is proposed to suppress the $\Delta \Sigma $ quantization noise and break the loop bandwidth limitation. A parasitic insensitive DPI is utilized in the retiming FFD scheme to achieve high-linear phase interpolation. A high frequency resolution DCO with 9.8-kHz/bit least significant bit (LSB) and a vernier time-to-digital convertor (TDC) with 2.3-ps time resolution are employed to further minimize the quantization noise. Implemented in 40-nm CMOS, the ADPLL prototype consumes 33.8 mW power and 0.32 mm2 chip area. Measurement results show that 78 MHz/ $\mu \text{s}$ maximum chirp slope is achieved with 167 kHz root-mean-square (RMS) frequency error. The minimum RMS frequency error is only 5.6 kHz when 300 MHz frequency is swept in 1 ms. The phase noise from 12.15 GHz carrier is −113.6 dBc/Hz at 1-MHz offset.

Analysis of processing features of ultrasonic flowmeters with FMCW signals

Проведен анализ и показана возможность использования ЛЧМ сигналов и гетеродинной схемы приема в УЗ ЛЧМ накладных вре мя - пролетных расходомерах . Показано , что при измерениях расхода по разностям задержек в рамках рассмотренной модели в качестве инфор мационного параметра может быть использована полная фаза сигналов биений ( зависимость фазы сигнала от времени ). Для данного случая по строена модель сигнала биений . Проведен анализ предложенных в лите ратуре , в том числе нами , алгоритмов в классе гладких центральных ко нечно - разностных оценок и их экспериментальное исследование в рамках поставленной задачи . Полученные результаты подтверждают эффектив ность рассмотренных методов измерения разностей задержек на практике . Рассмотренные методы позволяют быть реализованными на базе совре менных микроконтроллеров и при этом являются статистически эффек тивными в рамках рассмотренной задачи . Результаты проведенной ра - боты доказывают эффективность использования рассмотренной модели сигналов и методов оценки их параметров в задачах измерений расхода при помощи ультразвуковых накладных ЛЧМ расходомеров .

A 24 GHz High Frequency-Sweep Linearity FMCW Signal Generator with Floating-Shield Distributed Metal Capacitor Bank

A 24 GHz FMCW generator based on ADPLL was implemented in this work. Two-point modulation technology was used to achieve high sweep linearity. Meanwhile, a floating shield distributed metal capacitor bank was proposed to provide high frequency-sweep linearity DCO. By using these technologies, the FMCW generator’s frequency error can be controlled as small as 60 kHzrms when 180 MHz frequency was swept in 1.3 ms. High speed part of the FMCW generator was fabricated in 65 nm CMOS technology and the low speed digital part was implemented on FPGA. Power consumption of the chip excluding IO buffers is 29 mW.

Use of a time-staggered FMCW signal for portable high-frequency surface wave radar

ABSTRACTHerein is proposed a low-power-density signal based on time-staggered frequency modulated continuous waveform (TS-FMCW) for portable high-frequency (HF) radar. According to the principle of pulse compression that the signal-to-noise ratio (SNR) is related to the total energy, the proposed signals can carry more energy to get higher SNR within same level power density in time–frequency plane. The range grating lobes and Doppler grating lobes shown in the ambiguity function of our proposed waveform can be avoided in the practical HF radar application. A signal processing architecture containing low-pass filtering and fast Fourier transform is proposed. Experimental results demonstrate that higher SNRs are achievable with the same range and Doppler resolution when the same power density is used as the conventional FMCW.

A General Range-Velocity Processing Scheme for Discontinuous Spectrum FMCW Signal in HFSWR Applications

Discontinuous spectrum signal which has separate subbands distributed over a wide spectrum band is a solution to synthesize a wideband waveform in a highly congested spectrum environment. In this paper, we present a general range-velocity processing scheme for the discontinuous spectrum-frequency modulated continuous wave (DS-FMCW) signal specifically. In range domain, we propose a simple time rearrangement operation which converts the range transform problem of the DS-FMCW signal to a general spectral estimation problem of nonuniformly sampled data. Conventional periodogram results in a dirty range spectrum with high sidelobes which cannot be suppressed by traditional spectral weighting. In this paper, we introduce the iterative adaptive approach (IAA) in the estimation of the range spectrum. IAA is shown to have the ability to provide a clean range spectrum. On the other hand, the discontinuity of the signal spectrum has little impact on the velocity processing. However, with the range resolution improved, the influence of the target motion becomes nonnegligible. We present a velocity compensation strategy which includes the intersweep compensation and in-sweep compensation. Our processing scheme with the velocity compensation is shown to provide an accurate and clean range-velocity image which benefits the following detection process.

Through-The-Wall Detection With Gated FMCW Signals Using Optimized Patch-Like and Vivaldi Antennas

This paper presents the design and optimization of patch-like antennas for through-the-wall imaging (TTWI) radar applications in the frequency range 0.5–2 GHz. A basic antenna configuration is analyzed and modified through an optimization aiming at reducing the size of the antenna and focusing the radiated power in a single lobe to be directed toward the wall and the targets to be detected. Both the basic and the optimized antennas have been manufactured and tested. The optimized patch antennas and a conventional Vivaldi antenna have been successfully used in the frequency-modulated interrupted continuous wave (FMICW) radar system developed at Durham University. Results of a novel wall-removal technique for TTWI using numerical simulations and measurements aimed at the detection of stationary targets and people are presented.

Research on the Single Target Recognition of Car Collision Avoidance Radar Based on the FMCW Technology

The signal processing algorithm mainly for the FMCW automotive collision avoidance radar is studied in this paper. Through discussing the FMCW signal processing works with two-dimensional FFT algorithm, we use CZT transform to refine the velocity spectrum so as to accurately extract the velocity of the target.

Design of FMCW Radar Data Acquisition and Signal Processing System Based on Labview

For virtual instrument technologys character of high performance, easy to implement hardware and software integration, etc., virtual instrument technology and Labview are applied to test fields. Using computer and NI PCI-6221 data acquisition card as the hardware and LabVIEW8.5 software as a development platform, a data acquisition and signal processing virtual test system is built. The system is consisted of signal source and the signal processing module, in which the signal source is he FMCW radar level differential frequency signal connected by data acquisition card; signal processing section includes a time-domain measurement signal source, waveform display, filtering, spectral analysis, etc. Connecting, analysis and processing of FMCW radar level meter difference frequency signal are completed.

High-resolution automobile FMCW SAR and signal processing

The paper presents a high-resolution automobile Frequency Modulation Continuous Wave Synthetic Aperture Radar (FMCW SAR) named MiniSAR and the procedure of its signal processing. The imaging geometry of automobile SAR is very different from that of airborne SAR, leading to a different data processing method for automobile SAR. Therefore, in the paper, we propose an image formation approach that can well handle the focusing issues of automobile SAR. The effects of the strong reflected signal and the spatial-variant synthetic aperture length are analyzed. The processed results with automobile FMCW SAR read data validate the presented method.

Improved time-frequency analysis of ASDEX Upgrade reflectometry data using the reassigned spectrogram technique

The spectrogram is one of the best-known time-frequency distributions suitable to analyze signals whose energy varies both in time and frequency. In reflectometry, it has been used to obtain the frequency content of FM-CW signals for density profile inversion and also to study plasma density fluctuations from swept and fixed frequency data. Being implemented via the short-time Fourier transform, the spectrogram is limited in resolution, and for that reason several methods have been developed to overcome this problem. Among those, we focus on the reassigned spectrogram technique that is both easily automated and computationally efficient requiring only the calculation of two additional spectrograms. In each time-frequency window, the technique reallocates the spectrogram coordinates to the region that most contributes to the signal energy. The application to ASDEX Upgrade reflectometry data results in better energy concentration and improved localization of the spectral content of the reflected signals. When combined with the automatic (data driven) window length spectrogram, this technique provides improved profile accuracy, in particular, in regions where frequency content varies most rapidly such as the edge pedestal shoulder.

Signal processing agorithms for unmanned undersea vehicles navigation and collision avoidance.

In this paper, signal processing algorithms for dynamic UUV homing and docking, navigation, and collision avoidance are presented. Many conventional techniques are image-based, which involved computation-intensive image reconstruction procedures, which is ineffective in dynamic real-time environment. Therefore, it is of great importance to develop computationally effective signal processing algorithms for high-precision UUV geolocation. To optimize the applicability, the algorithms presented in this paper cover all key modalities, including both active and passive, with temporal pulse and FMCW signal formats. In terms of operating configurations, the first case is classified as the passive-receiver systems. The transmitting signal format for this case is in the form of a twin-pulse set, with opposite polarity. The bearing angle is estimated from the temporal offset of the pulses. The dual version of this configuration is in the form of an active system and the double-integration algorithm can be effectively applied to both versions. The active configuration can then be extended to incorporate the FMCW signaling format. For the FMCW case, estimation of the bearing angle and range distance can be accomplished with the Fourier transform methods. In this paper, the presentation includes theoretical analysis, signal processing algorithms, and experiments.