Frequency-modulated Continuous-wave Sensor Research Articles

Low-Complexity Time-Domain Ranging Algorithm with FMCW Sensors.

A time-domain ranging algorithm is proposed for a frequency-modulated continuous wave (FMCW) short-range radar sensor with high accuracy and low complexity. The proposed algorithm estimates the distance by calculating the ratio of the beat frequency signal to its derivative and thereby eliminates the restriction of frequency bandwidth on ranging accuracy. Meanwhile, we provide error analysis of the proposed algorithm under different distances, integral lengths, relative velocities, and signal-to-noise ratios (SNRs). Finally, we fabricate FMCW sensor prototype and construct a measurement system. Testing results demonstrate that the proposed time-domain algorithm could achieve range error within 0.8 m. Compared with the conventional fast Fourier transform (FFT) estimation scheme, the proposed method performs ranging without the requirement of complex multiplications, which makes it reasonable to be implemented in real-time and low-cost systems.

Through Wall Radar Classification of Human Micro-Doppler Using Singular Value Decomposition Analysis.

The ability to detect the presence as well as classify the activities of individuals behind visually obscuring structures is of significant benefit to police, security and emergency services in many situations. This paper presents the analysis from a series of experimental results generated using a through-the-wall (TTW) Frequency Modulated Continuous Wave (FMCW) C-Band radar system named Soprano. The objective of this analysis was to classify whether an individual was carrying an item in both hands or not using micro-Doppler information from a FMCW sensor. The radar was deployed at a standoff distance, of approximately 0.5 m, outside a residential building and used to detect multiple people walking within a room. Through the application of digital filtering, it was shown that significant suppression of the primary wall reflection is possible, significantly enhancing the target signal to clutter ratio. Singular Value Decomposition (SVD) signal processing techniques were then applied to the micro-Doppler signatures from different individuals. Features from the SVD information have been used to classify whether the person was carrying an item or walking free handed. Excellent performance of the classifier was achieved in this challenging scenario with accuracies up to 94%, suggesting that future through wall radar sensors may have the ability to reliably recognize many different types of activities in TTW scenarios using these techniques.

고선형성을 갖는 Ka대역 FMCW 센서

본 논문에서는 전압 제어 발진기의 비선형 영향에 의한 문제점을 개선한 FMCW 신호 생성 구조를 제안한다. 단순히 전압 제어 발진기(voltage controlled oscillator)의 튜닝 전압(tunning voltage)을 스위프(sweep)하여 FMCW(Frequency Modulated Continuous Wave) 신호를 생성하는 방식의 경우에는 전압 제어 발진기 자체의 비선형 영향으로 인해 센서에서 검출하고자 하는 비트 주파수(beat frequency)에 변동(drift)이 발생하게 되어 그로부터 추출된 정보의 정확도가 저하되거나, 잘못 해석될 수 있는 오류를 갖게 된다. 이러한 비선형 영향을 배제하기 위해 본 연구에서는 직접 주파수 합성기(direct digital synthesizer)와 위상 동기 루프(phase locked loop)를 포함한 하이브리드 방식의 신호 생성 방안을 적용하여 고선형성을 갖는 FMCW 신호를 생성하였고, 제작 후 시험을 통해 FMCW 센서에서 검출한 비트 주파수가 매우 정확함을 검증하였다. This paper presents a Ka-band FMCW sensor that has high linearity by improving a nonlinear behavior of the voltage controlled oscillator. Due to the nonlinear characteristics of the voltage controlled oscillator for the conventional method, the drift of beat frequency can cause inaccuracy and errors to the extracted results. A Ka-band FMCW signal with fast transition time could be generated by using both direct digital synthesizer and phase locked loop in this research. The implemented FMCW sensor showed very high accuracy in beat frequency through the test.

Nondestructive testing potential evaluation of a terahertz frequency-modulated continuous-wave imager for composite materials inspection

The sub-terahertz (THz) frequency band has proved to be a noteworthy option for nondestructive testing (NDT) of nonmetal aeronautics materials. Composite structures or laminates can be inspected for foreign objects (water or debris), delaminations, debonds, etc., using sub-THz sensors during the manufacturing process or maintenance. Given the harmless radiation to the human body of this frequency band, no special security measures are needed for operation. Moreover, the frequency-modulated continuous-wave sensor used in this study offers a very light, compact, inexpensive, and high-performing solution. An automated two-dimensional scanner carrying three sensors partially covering the 70- to 320-GHz band is operated, using two complementary measurement approaches: conventional focused imaging, where focusing lenses are used; and synthetic aperture (SA) or unfocused wide-beam imaging, for which lenses are no longer needed. Conventional focused imagery offers finer spatial resolutions but imagery is depth-limited due to the beam waist effect, whereas SA measurements allow imaging of thicker samples with depth-independent but coarser spatial resolutions. The present work is a compendium of a much larger study and describes the key technical aspects of the proposed imaging techniques and reports on results obtained from human-made samples (A-sandwich, C-sandwich, solid laminates) which include diverse defects and damages typically encountered in aeronautics multilayered structures. We conclude with a grading of the achieved results in comparison with measurements performed by other NDT techniques on the same samples.

Combining two radar techniques to implement a collision avoidance system

Many microwave collision avoidance radars have been tested using FMCW (frequency modulated continuous wave) radar and pulsed radar working around 10, 35 and 60 GHz. The aim of this paper is to describe an efficient radar system, termed bimodal, obtained by the combination of these two systems. The FMCW sensor is used for close detection and easier speed calculation, and the pulsed one for large distances and multi-target separation. The bimodal system has been used to improve the performances of the two sensors by retaining the advantages of each. The new radar is able to detect obstacles between 2 and 150 m with low emitted power. The whole system is controlled by a decision program unit. An accuracy of m has been achieved.

Performance of an FMCW radar sensor

An FMCW (frequency modulated continuous wave) sensor that uses triangular modulation is considered. The sampled output from two range gates are processed so that the device will initiate some function when it passes through a desired range. An expression is obtained for the detection probability from which the expected value and standard deviation of the range of function may be obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>