Frequency-modulated Continuous-wave Signal Research Articles

Utilizing Passive Intermodulation Response of Frequency-Modulated Continuous-Wave Signal for Target Identification and Mapping

In this paper, a passive-intermodulation-based tracking system working with a frequency-modulated continuous-wave (FMCW) is proposed for target identification and localization. Signals in the microwave range are chosen to realize ranging purposes for the benefits of small device size, lightweight, and wide available bandwidth. Depending on whether the nonlinear properties of electrical components, such as diodes, transistors, and mixers, are exploited, the tracking systems can be categorized as linear and nonlinear systems. By nature, the linear tracking methods are vulnerable to surrounding clutter, such as furniture, walls, and other objects, since the reflection signals from clutter are of the same nature as the target. In comparison, the nonlinear detection methods are attractive owning to the fact that the majority of the clutter does not possess nonlinear properties. Hence, the nonlinear detection system does not “see” the linear clutter and only senses the target exhibiting nonlinear responses. Among all the nonlinear technologies, the intermodulation-based tracking and mapping approach has less path loss than the harmonic-based, smaller circuit size than the subharmonic-based, and simpler tag design and fewer signal licenses required than both of its counterparts. Therefore, in this work, the intermodulation-based technology is adopted, and a new nonlinear tracking system is designed to track the distance of the target in a complex indoor scenario crowded with unwanted objects.

Optical FMCW Signal Generation Using a Silicon Dual-Parallel Mach-Zehnder Modulator

We experimentally demonstrate optical frequency-modulated continuous-wave (FMCW) signal generation utilizing a silicon dual-parallel Mach-Zehnder modulator (DP-MZM). The sideband suppression ratio (SSR) and the sideband-to-carrier suppression ratio (SCSR) of the single-sideband suppressed carrier (SSB-SC) modulation are higher than 15 dB when RF frequency is lower than 20 GHz. With the generated triangular modulated FMCW signal, we demonstrate simultaneous ranging and velocimetry. The chirp bandwidth is 10 GHz and the chirp period is 1 μs, corresponding to a ranging resolution of 13 mm and a velocimetry resolution of 0.5 m/s, consistent with the theoretical calculation. These results show that wideband FMCW signal generation by a silicon DP-MZM is promising for high-resolution light detection and ranging.

Analyze the FMCW Waveform Skin Return of Moving Objects in the Presence of Stationary Hidden Objects Using Numerical Models

In this paper, a high-performance antenna array system model is presented to analyze moving-object-skin-returns and track them in the presence of stationary objects using frequency modulated continuous wave (FMCW). The main features of the paper are bonding the aspects of antenna array and electromagnetic (EM) wave multi-skin-return modeling and simulation (M&S) with the aspects of algorithm and measurement/tracking system architecture. The M&S aspect models both phase and amplitude of the signal waveform from a transmitter to the signal processing in a receiver. In the algorithm aspect, a novel scheme for FMCW signal processing is introduced by combining time- and frequency-domain methods, including a vector moving target indication filter and a vector direct current canceller in time-domain, and a constant false alarm rate detector and a mono-pulse digital beamforming angle tracker in frequency-domain. In addition, unlike previous designs of using M × N fast Fourier transform (FFT) for an M × N array, only four FFTs are used, which tremendously save time and space in hardware. With the presented model, the detection of the moving-target-skin-return in stationary objects under a noisy environment is feasible. Therefore, to track long range and high-speed objects, the proposed technique is promising. Using a scenario having (1) a target with 17 dBm2 radar cross section (RCS) at about 40 km range with 5.936 Mach speed and 11.6 dB post processing signal to noise ratio, and (2) a strong stationary clutter with 37 dBm2 RCS located at the proximity of the target, it demonstrates that the root-mean-square errors of range, angle, and Doppler measurements are about 26 m, 0.68 degree, and 1100 Hz, respectively.

Moving Target Refocusing With the FMCW SAR System MIRANDA-35

Inverse synthetic aperture radar is a commonly adopted technique for producing high-resolution images of moving targets. This article investigates the imaging capabilities of high-frequency and high-bandwidth systems by means of two distinct experiments. The deployed sensor is the Fraunhofer FHR MIRANDA-35, a millimeter-wave synthetic aperture radar airborne system, which transmits frequency-modulated continuous-wave signals at the Ka-band and is capable of achieving centimeter resolution. The performances are assessed by comparing the derived estimates (e.g., radial velocity and acceleration, and dimensions) with independent ground measurements. The resulting accuracy can be summarized as follows: the mean value of the percent error is 2.05% and 2.11% for radial velocity and acceleration, respectively, and 4.27% for the target dimensions.

Novel FMCW-Interferometry Method Testing on an Ultrasonic Clamp-On Flowmeter

Paper represents the extended version of the authors previous works on the transit-time ultrasonic flowmeters accuracy increasing problem. We deal with a new method of ultrasonic clamp-on transit-time flow measurements using the linear frequency modulated continuous wave (FMCW) signals and interferometry based time-of-flight (delay) estimation technique. The analog FMCW signals preprocessing is performed by the heterodyne based scheme of the receiver (the results are so-called the beat signals). A statistically effective time delay estimator for the digitized beat signal model is discussed. The algorithm for the flow velocity (thus the flow rate) measurement based on the proposed estimator is considered, which can be implemented on the modern microcontroller with the relatively high computation performance. The algorithm effectiveness was experimentally proved for the clamp-on ultrasonic liquid flowmeter in the cases of a well and relatively poor matching between the piezo-transducers and pipe material. Experiments show that the standard deviation ( i.e. , the square root of the variance) and the bias can be reduced at 7–10 times in comparison with the traditional FMCW signal processing techniques. Further, we consider application of our approach to a designed type of flowmeters based on the electromagnetic waves.

Dynamic Fluid Ingress Detection in Geomaterials Using K-Band Frequency Modulated Continuous Wave Radar

Frequency modulated continuous wave (FMCW) radar in the K-band has been shown to be an effective detector of geomaterial physical properties being highly sensitive to rock characteristics, particularly mineral composition and, for porous rock, variations in liquid water content. This research demonstrates that contrasts in FMCW return signals with time correlate with changes in geomaterial water content. FMCW signal returns were acquired for porous sandstone samples subjected to controlled water injection while also in a neutron beam, taking advantage of the well-known, and well-calibrated, attenuation of neutrons by hydrogen atoms for the water-containing porous sandstone samples. The sequential neutron tomographic images clearly show water moving up the sample with time while the FMCW observations show increases in radar reflection coefficient as a function of water position in the field of view. The observed FMCW detection of flood-front position is corroborated by the synchronous neutron tomographic images. We also observe repeatable variations in the radar reflection coefficient as a function of sample orientation during fluid injection, verifying that FMCW sensing offers real-time insight into the interactions between fluid movement and sample heterogeneity, via non-contact and non-invasive flood-front tracking. This research demonstrates that FMCW has potential to be a more accessible and easily deployable sensing modality than neutron tomography, enabling dynamic geomaterial testing to be conducted outwith the confines of the highly controlled laboratory environment required for neutron investigation.

Joint Features Extraction for Multiple Moving Targets Using (Ultra-)Wideband FMCW Signals in the Presence of Doppler Ambiguity

This article addresses the joint estimation of range, velocity and azimuth for multiple fast-moving targets using (ultra-)wideband (UWB) frequency-modulated continuous-wave (FMCW) radar with a phased array in the presence of Doppler ambiguities. The range migration of moving targets is described with the coupling of the fast-time and slow-time (chirp index), leading to the smearing of the target Doppler spectrum. This phenomenon degrades the performance of conventional detection and estimation techniques. As with range-Doppler processing, the estimation accuracy for direction-of-arrival (DOA) with conventional narrowband-based algorithms significantly degrades if a UWB signal is deployed. For the FMCW waveform, the wideband DOA differs from the narrowband DOA due to an extra coupling term, similar to the range migration problem. A novel spectral norm-based algorithm for joint estimation of range, velocity and DOA of fast-moving targets is proposed, taking the appropriate wideband signal model with the coupling terms into account. The proposed spectral norm-based algorithm avoids off-grid peak search and can be easily accelerated with power iteration; it outperforms conventional coherent integration methods in both accuracy and efficiency when using moderate data size. The advantages of the proposed algorithm and its super-resolution capability are validated with numerical simulations.

Ambiguity function and imaging performance of coded FMCW waveforms with fast 4D receiver processing in MIMO radar

In this paper, a novel design and processing of nearly orthogonal waveforms based on frequency modulated continuous wave (FMCW) signals for multiple-input, multiple-output (MIMO) radars is presented. The design, implementation and results of the complete system, capable of detection and imaging of radar targets, are here described. The orthogonality of sounding signals is critical for multi-channel radar applications since the interference between signals can significantly limit the radar's ability for observation of weak targets in presence of stronger targets and background clutter. The orthogonal waveforms are designed by coding consecutive complex FMCW signals in a frame so that they can be sent to the different transmit antennas of the radar allowing the simultaneous operation of all transmit channels. Unlike time division switching approaches, the orthogonality in the proposed architecture, is achieved by applying several coding techniques, at a symbol level: Golay complementary, Zadoff Chu, Direct Spread Spectrum (DSS), Space-Time Block Coded, Discrete Fourier Transform (DFT) and Costas based sequences. Moreover, a radar receiver processing, based on a complex frame based convolution between transmit and received waveforms together with 4-dimensional Fast Fourier Transform (4D-FFT) beamforming, is presented. This allows for a fast and complete sensing of range, azimuth, elevation and Doppler in a single frame. The performance of the proposed waveforms is evaluated through the analysis of their cross ambiguity functions and imaging capabilities, while the general performance of the radar's receiver processing is shown through the use of multiple radar images. The flexibility in generating such orthogonal coded waveforms and the proposed general receiver architecture are an important first step for developing a future software programmable MIMO radar.

Joint Doppler and DOA estimation using (Ultra-)Wideband FMCW signals

The joint Doppler and Direction-of-Arrival (DOA) estimation of moving targets using an (Ultra-)Wideband (UWB) frequency modulated continuous-wave (FMCW) antenna array radar is investigated. Besides the well-known range migration problem, another concern for wideband signals is the DOA estimation problem. For the first time, both problems are considered in this paper simultaneously, where the wideband DOA is transformed into a second-order coupling system similar to the range migration problem by using the property of the FMCW signal. A novel embedded compensation approach to eliminate the coupling terms caused by range migration and wideband DOA is proposed and 2D multiple signal classification (2D MUSIC) algorithm is subsequently applied with dynamic noise subspace to joint estimation of Doppler and DOA. Further, to reduce the computational load caused by multiple eigendecompositions of large matrices, efficient implementation methods are proposed and their performance in speed, accuracy and robustness is compared. The performance of the proposed methods is validated by the numerical simulations and is compared with Keystone MUSIC. Finally, it is shown that for a small number of targets, the Rayleigh-Ritz is the most efficient approach among them.

Identification of Linear Time Invariant Systems Using FMCW Signals and Stretch Processing Receivers

The paper deals with the identification of linear time invariant (LTI) systems by a special observer. An observer emitting an frequency modulated continuous wave (FMCW) signal and having a stretch processor as receiver will be considered for system identification. A thorough derivation of the gathered baseband signal for arbitrary LTI systems will be given. It is shown, that the received signal is approximately given by the transfer function of the LTI system over the frequency sweep of the FMCW signal. The proof relies on an infinite large time-bandwidth product of the transmit signal, such that errors remain in practical applications with a finite time-bandwidth product. Monte–Carlo simulations are conducted to verify the approximation and to quantify its accuracy and remaining errors. The findings are important for e.g. calibration or derivation of a device model in FMCW radar applications.

Simple‐structure and cost‐effective FMCW radar test system using a PLL‐Gunn oscillator and fundamental mixer in the E‐band

The authors explain the development of a cost-effective frequency-modulated continuous wave (FMCW) radar test system in the E-band with a simple-structure, and demonstrate it for an automotive application using an FMCW radar chipset evaluation board and an FMCW radar. The system consists of a down-converter, based on a fundamental mixer with a phase-locked loop-Gunn oscillator, and a mixed domain oscilloscope or a conventional digital oscilloscope. It is able to evaluate an FMCW signal in the time domain, such as the chirp rate, chirp length, chirp width, linearity, and the relative power level.

Frequency-modulated continuous-wave generation based on an optically injected semiconductor laser with optical feedback stabilization.

Based on the period-one (P1) dynamics of an optically injected semiconductor laser (SL), a photonic scheme enabling the generation of a tunable high-quality frequency-modulated continuous-wave (FMCW) signal is investigated experimentally. Under a modulated optical injection, the laser is driven into P1 oscillation with a modulated microwave frequency. In this work, optical feedback is also introduced to further reduce the microwave phase noise. The experimental results show that the central frequency of the generated FMCW signal can be widely tuned from 11.41 to 50.05 GHz by simply adjusting injection parameters while the frequency sweep range of the FMCW signal can be controlled by varying the modulation index. Under proper operating parameters, the sweep range and rate of the FMCW signal are 18.42 GHz (13.73 GHz- 32.15 GHz) and 1.14 GHz/ns, respectively. Further, by introducing an optical feedback loop, the frequency comb contrast of the FMCW signal is drastically increased by 27.15 dB when the reciprocal of the feedback delay time matches with the modulation frequency exactly due to the locking effect of the external cavity optical modes.

Adaptive wideband equalization for frequency dispersion correction in HF band considering variations in interference characteristics and ionosphere parameters

Paper presents the outcomes of the studies into the adaptive wideband equalization for frequency dispersion correction in HF band considering variations in interference characteristics and ionosphere parameters. The subject matter of the research were megahertz-bandwidth channels with single-hop F layer propagation mode. There are presented data on variations in the channel amplitude frequency response that are caused by the interference of magneto-ionic components (intramodal multipath). Test facility for carrying out full-scale experiments was developed with the use of Universal Software Radio Peripheral platform supported by the groundbreaking software-defined radio technology. Verification of the developed methods and algorithms was performed in the experiments on oblique sounding over the Cyprus-to-Yoshkar-Ola propagation path by the linearly frequency modulated continuous wave signal.

Fractional-N PLL Synthesizer for FMCW Signal Generator with Dual-Mode Modulation Pattern

Radar signal generator is a critical component in radar system as it determines the best achievable resolution. Single chip Fractional-N PLL synthesizer with built-in VCO and sweep modulator become more popular as Frequency Modulated Continuous Wave (FMCW) signal generator due to the simplicity and overall cost reduction. This paper presents a realization process and experimental result of dual-mode modulation pattern FMCW signal generator using HMC769LP6CE PLL. The PLL is controlled by ATMega328 microcontroller and Altera EPM240T100C5 CPLD to operate in two difference mode: 1-way sweep mode and 2-way sweep mode. The PLL is programmed with four different sweep bandwidth from 6.75–54 MHz for different range and resolution radar purpose. The performance of FMCW signal generator is measured using the output of passband signal spectrum. The experimental results indicate that the PLL-VCO with 2-way sweep mode has clearer frequency passband compared to 1-way sweep mode.

A 77-GHz Mixed-Mode FMCW Signal Generator Based on Bang-Bang Phase Detector

A 77-GHz frequency-modulated continuous-wave (FMCW) signal generator is presented for automobile millimeter-wave (mm-wave) radar applications. The reconfigurable chirp is generated by a mixed-mode synthesizer operating at 38.5 GHz, in which the frequency doubling scheme is used to improve the chirp bandwidth and simplify the design. The bang-bang phase detector (BBPD) is employed for phase detection in the synthesizer, avoiding complicated linear time-to-digital converter (TDC) as well as reducing design complexity and power consumption. A 1-bit third-order single-loop $\Delta \Sigma$ modulator (SLDSM3), combining with the hybrid finite-impulse-response (FIR) filtering technique, significantly suppresses the BBPD induced quantization noise. A type-III slope estimator with a switchable polarity is embedded in the digital loop filter (DLF) to improve the linearity around the chirp turning-around points (TAPs). Two infinite-impulse-response (IIR) filtering stages smoothen the generated chirp waveform by reducing the instant variation of the DLF’s output. Implemented in 65-nm CMOS, the proposed FMCW signal generator consumes 43.1-mW power and occupies 2-mm2 die area, including testing pads. The measured phase noise from the 38.5-GHz carrier is −87.7 dBc/Hz at 1-MHz offset. The measured root-mean-square (rms) frequency errors of the generated triangle chirps over the 1-ms period are 189 and 336 kHz, with 0.914- and 1.827-GHz chirp bandwidth, respectively.

340-GHz 3-D Imaging Radar With 4Tx-16Rx MIMO Array

A standoff 3-D imaging radar for security body scan at 340 GHz has been described. This terahertz imager incorporates a multiple input multiple output (MIMO) array as an electronic beam former in a horizontal dimension and an elliptic cylinder as a focusing reflector in elevation. Frequency-modulated continuous-wave (FMCW) emission with 16-GHz bandwidth caused a 10-mm-range resolution after calibration for nonlinearities of the distorted radar signals. The horizontal MIMO array contains 4 transmitters and 16 receivers (4Tx-16Rx) to generate a 64-Tx/Rx full virtual array corresponding to an antenna size of approximately 128 mm, which caused a horizontal resolution of about 14 mm at a distance of 3 m. FMCW signals were transmitted from the 4-Tx sequentially and focused as narrow beam lines by the elliptic reflector to get a 12-mm vertical resolution at 3 m. A fast-scanning mirror swings in the light path to make these beam lines screen in the vertical direction. A 4-Hz frame rate is now possible for a personal screen with a field of view of 2 m × 0.6 m.

A <inline-formula> <tex-math notation="LaTeX">$K_{{u}}$ </tex-math> </inline-formula>-Band CMOS FMCW Radar Transceiver for Snowpack Remote Sensing

This paper presents a $K_{u}$ -band (14–16 GHz) CMOS frequency-modulated continuous-wave (FMCW) radar transceiver developed to measure dry-snow depth for water management purposes and to aid in retrieval of snow water equivalent. An on-chip direct digital frequency synthesizer and digital-to-analog converter digitally generates a chirping waveform which then drives a ring oscillator-based $K_{u}$ -Band phase-locked loop to provide the final $K_{u}$ -band FMCW signal. Employing a ring oscillator as opposed to a tuned inductor-based oscillator (LC-VCO) allows the radar to achieve wide chirp bandwidth resulting in a higher axial resolution (7.5 cm), which is needed to accurately quantify the snowpack profile. The demonstrated radar chip is fabricated in a 65-nm CMOS process. The chip consumes 252.4 mW of power under 1.1-V supply, making its payload requirements suitable for observations from a small unmanned aerial vehicle.

Visualization of frequency-modulated electric field based on photonic frequency tracking in asynchronous electro-optic measurement system

We propose a new asynchronous measurement system to visualize the amplitude and phase distribution of a frequency-modulated electromagnetic wave. The system consists of three parts: a nonpolarimetric electro-optic frequency down-conversion part, a phase-noise-canceling part, and a frequency-tracking part. The photonic local oscillator signal generated by electro-optic phase modulation is controlled to track the frequency of the radio frequency (RF) signal to significantly enhance the measurable RF bandwidth. We demonstrate amplitude and phase measurement of a quasi-millimeter-wave frequency-modulated continuous-wave signal (24 GHz ± 80 MHz with a 2.5 ms period) as a proof-of-concept experiment.

Microwave-photonics direction finding system for interception of low probability of intercept radio frequency signals

Direction finding (DF) systems are fundamental electronic support measures for electronic warfare. A number of DF techniques have been developed over the years; however, these systems are limited in bandwidth and resolution and suffer from a complex design for frequency downconversion. The design of a photonic DF technique for the detection and DF of low probability of intercept (LPI) signals is investigated. Key advantages of this design include a small baseline, wide bandwidth, high resolution, minimal space, weight, and power requirement. A robust postprocessing algorithm that utilizes the minimum Euclidean distance detector provides consistence and accurate estimation of angle of arrival (AoA) for a wide range of LPI waveforms. Experimental tests using frequency modulation continuous wave (FMCW) and P4 modulation signals were conducted in an anechoic chamber to verify the system design. Test results showed that the photonic DF system is capable of measuring the AoA of the LPI signals with 1-deg resolution over a 180 deg field-of-view. For an FMCW signal, the AoA was determined with a RMS error of 0.29 deg at 1-deg resolution. For a P4 coded signal, the RMS error in estimating the AoA is 0.32 deg at 1-deg resolution.

Simultaneous Real-Time Ranging and Velocimetry via a Dual-Sideband Chirped Lidar

A dual-sideband (DSB) chirped lidar for simultaneous real-time ranging and velocimetry is proposed and demonstrated, in which a Mach–Zehnder modulator (MZM) is applied to generate the required optical DSB frequency-modulated continuous-wave (FMCW) signal. The inherent opposite frequency chirp and contrary wavelength offset to the optical carrier of the two generated sidebands make it possible to measure the distance and velocity by frequency mixing without complex post digital signal processing, meanwhile, make the measurement of velocity immune to the nonlinearity of the FMCW optical signals. An experiment is carried out, in which an 8–18 GHz saw-tooth FMCW signal is used to drive an MZM, generating a wideband optical DSB FMCW signal. The distance and the velocity are simultaneously derived from the real-time frequency spectra. Accurate velocimetry with a nonlinear FMCW signal is also investigated.