Frequency Modulated Interrupted Continuous Wave Research Articles

A Split-Type FMICW-Based Guided Wave Radar With Multisegmental Probe for Liquid Level Measurement

In this paper, a specially designed guided wave radar device for measuring the liquid level in the nuclear industry is proposed. A split-type design is introduced to adapt to a strong radiation environment. An L-band frequency modulated interrupted continuous wave (FMICW) radar is designed to ensure the signal-to-noise ratio of echo signal after long-distance signal transmission, which provides the isolation between transmitter and receiver of more than 60 dB using the gating technology. To overcome the shortcomings of limited installation and maintenance space, a novel coaxial waveguide probe with a multi-segmental structure is proposed and simulated. An adaptive signal processing algorithm is developed to remove false echoes and eliminate measurement fluctuations. A prototype of the proposed measurement system is fabricated and evaluated. Static and dynamic liquid level experiments are performed in an outdoor environment to assess performance and verify the effectiveness of the proposed radar. The results show that the standard deviation measurement error of the proposed radar is within 0.4 cm. The proposed system is expected to have a high potential for applications in liquid level measurement under complex conditions.

Range Aliasing Elimination for FMICW Radar With Uniform Sampling Bursts and Poisson Disk Inter-Burst Delays

As an improvement of regular frequency-modulated continuous-wave (FMCW) radar in transmitter-receiver isolation, frequency-modulated interrupted continuous-wave (FMICW) radar has many advantages such as high range resolution, low peak power and high duty cycle. However, the false targets introduced by range aliasing may interfere with radar performance when it comes to long-range detection. In this paper, a range aliasing elimination method for FMICW radar is proposed based on batch Poisson disk sampling (BPDS) and sparse reconstruction. The received echoes are sampled by the newly developed BPDS pattern, which consists of uniform sampling bursts and Poisson disk inter-burst delays, so that the echoes from the maximum unambiguous range can be collected. Taking advantages of the excellent spectrum anti-aliasing performance of BPDS, the range aliasing phenomenon can be effectively eliminated and the range-Doppler spectrum containing multiple targets can be accurately reconstructed by the Iterative Soft Thresholding like (IST-like) algorithm. Compared with the existing signal processing methods for FMICW radar, the proposed method can obtain a larger maximum detection range without range aliasing. The effectiveness of the proposed method is verified by simulations and experiments on real FMICW radar data.

FMICW와 버니어식 과정을 통한 정밀 빙붕 깊이 측정 레이다에 관한 연구

A radar system has been developed to predict global warming by measuring ice-shelf thicknesses. This system uses a frequency-modulated continuous-wave(FMCW) waveform and phase-sensitive method through the so-called Vernier-like process, which measures the target range by adding the fine range from the phase information to the rough range from the frequency. However, the continuous waves require a large dynamic range of the receiver because short-range and long-range reflection signals are received simultaneously. To improve this, we propose a frequency-modulated interrupted continuous wave(FMICW) method and demonstrate its performance through simulation. Although the proposed method reduces the signal-to-noise ratio(SNR) based on the same peak power, the gain can be adjusted according to the range, and the minimum detection range can be controlled.

Fully digital multi‐frequency compact high‐frequency radar system for sea surface remote sensing

Compared with single-frequency high frequency surface wave radar (HFSWR), a multi-frequency (MF) system provides more feasibility in sea surface dynamic parameters measurement and target detection. In this study, a novel multi-frequency compact HFSWR based on a fully digital architecture is developed. This system employs a flexible signal processing procedure with low hardware complexity. Without changing the circuit, it can realise two typical multi-frequency schemes, including time-division MF (TDMF) and frequency-division MF (FDMF). Furthermore, a waveform selection criterion is proposed by analysing the difference between the TDMF and FDMF schemes in frequency-modulated interrupted continuous wave (FMICW). The system performance is preliminarily validated in two frequencies by both close-loop test and field experiment. It is shown that the range processing of two frequencies are coherent with an amplitude variation 0.93 and a root-mean-square error between 11.0 and 13.0 cm/s.

Radio Frequency Interference Cancelation in High-Frequency Surface Wave Radar Using Orthogonal Projection Filtering

The characteristics of radio frequency interference (RFI) are analyzed for high-frequency surface wave radar (HFSWR), which adopts a linear frequency-modulated interrupted continuous wave. If RFI enters the receiver, it contaminates the positive and negative frequency range bins simultaneously, whereas the negative frequency range bins contain the RFI and noise only. Moreover, RFI is always spatially structured over a short duration. Based on the above characteristics, a new orthogonal projection filtering algorithm is proposed for RFI cancelation. The proposed method uses the information of antenna channel and sweep dimensions in negative frequency range bins to estimate the interference covariance matrix. To suppress RFI, the signals of interest in the positive range bins are projected onto the interference subspace, which is obtained by eigendecomposition of the covariance matrix. Experimental results suggest that the proposed method can achieve effective RFI cancelation by using data collected by a multifrequency HFSWR.

HF hybrid sky‐SWR system based on MIMO technology

High-frequency (HF) hybrid sky-surface-wave radar (SWR) is very useful for sea-state extraction, and the rich content echo information is very meaningful. On the basis of the multiple-input–multiple-output technology, a new HF hybrid sky-SWR system is designed. The radar transmits multi-frequency signals and synchronously receives the echoes through multiple channels. By adding linear phase shift between frames of the frequency-modulated interrupted continuous wave, the multi-frequency echo signals can be separated in the Doppler spectrum after two fast Fourier transforms. It expanded the HF hybrid sky-SWR from the single-frequency mode to a simultaneous multi-frequency one. Through this system, the ocean dynamics parameters at different frequencies can be simultaneously obtained. Moreover, multi-angle information can be obtained to use for the inversion of the sea surface current and its temporal and spatial variations. Since the transmitter site and the receiver site of the radar are placed in different areas but synchronously work with multiple channels, it is very universal and convenient for network configuration and extension. As validated by the ocean exploration experiment, this system is feasible and reliable.

Validation of Sensing Ocean Surface Currents Using Multi-Frequency HF Radar Based on a Circular Receiving Array

To reduce the floor space of receiving antenna arrays, the Radio Ocean Remote SEnsing (RORSE) laboratory of Wuhan University developed a circular receiving array for a multi-frequency high frequency (MHF) radar system in 2014, consisting of seven uniformly spaced antenna elements positioned on a circle with a diameter of 5 m. The new system, which is abbreviated MHF-C radar, adopts frequency modulated interrupted continuous wave (FMICW) chirps and is capable of simultaneously operating at a maximum of four frequencies in the band of 7.5–25 MHz, and providing current, wave and wind maps every ten minutes. The phase direction-finding method is utilized to estimate the directions of the current signals, and array phase uncertainties are also taken into consideration in the signal model. This paper introduces the system in detail and investigates the performance of current measurements using MHF-C radars installed at Shengshan and Zhujiajian along the coast of the East China Sea. Radial current measurements derived from 8.27 MHz and 19.20 MHz at the same range are compared. Observations and comparisons between MHF-C radars and acoustic Doppler current profilers (ADCPs) are also presented in this paper. The results preliminarily demonstrate that the MHF-C radar system is capable of maintaining the same performance for current measurements whenever it steers to any other azimuth in the coverage and has a good ability to measure currents.

Integration of SPDT Antenna Switch With CMOS Power Amplifier and LNA for FMICW Radar Front End

A single-pole double-throw antenna switch integrated with a CMOS power amplifier (PA) and a low-noise amplifier (LNA) by using a three-piece transmission line transformer (TLT) for a frequency-modulated interrupted continuous-wave (FMICW) radar front end is presented. The three-piece TLT consists of a PA output TL, an LNA input TL, and a TL connected to an antenna. Parallel switches and $\lambda$ /4 effective impedance transformers are used to provide high isolation. Due to the effective integration, the chip size and overall insertion loss are reduced significantly. The measured results demonstrate that the proposed switch achieves an insertion loss of 2.2 (2.6) dB with an isolation of 33 (33.4) dB in the antenna-to-LNA input (PA output to antenna) direction. The chip, including the PA, LNA, and switch, for a 79-GHz FMICW radar front end is fabricated in 65-nm CMOS technology, and its size is 0.394 mm2. The PA output power is 10.2 dBm at 79 GHz, and the LNA gain is 15 dB at 79 GHz. FMICW radar waveforms are successfully generated with the switch in this chip. The measured results verify that the proposed device generates an FMICW radar waveform at the switching frequency at 6 kHz.

System for Automatic Detection and Analysis of Targets in FMICW Radar Signal

Abstract This paper presents the automatic system for the processing of the signals from the frequency modulated interrupted continuous wave (FMICW) radar and describes methods for the primary signal processing. Further, we present methods for the detection of the targets in strong noise. These methods are tested both on the real and simulated signals. The real signals were measured using the developed at the IAP CAS experimental prototype of FMICW radar with operational frequency 35.4 GHz. The measurement campaign took place at the TU Delft, the Netherlands. The obtained results were used for development of the system for the automatic detection and analysis of the targets measured by the FMICW radar.

Multi‐frequency high frequency surface wave radar based on phase offset

Multi-frequency high frequency surface wave radar (MHFSWR) shows good capability of anti-interference, sea-state information extraction and target detection. The authors develop a new technique to produce a specified Doppler frequency offset on the echoes spectra for each operating frequency in simultaneous MHFSWR system. The radar transmits frequency modulated interrupted continuous wave signals with different linear phase offsets which are counted up from sweep cycle to sweep cycle. After the echoes being demodulated, the signals of different operating frequencies from same range can be distinguished by the preset frequency offsets in a single Doppler spectrum, though they are indiscernible in the A-Scope display. In the receiver, both the data transmission channel and the signal processing channel of different operating frequency, including digital down-conversion, data rate conversion and range–Doppler transform, are shared significantly reducing the hardware cost and system complexity. The simulation results and the initial observations obtained by the radar verify the feasibility of the proposed technique. This technique is applicable in monostatic radars, bistatic radars and networking radars to apply multi-frequency observations simultaneously.

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.

Frequency-Modulated Interrupted Continuous Wave as Wall Removal Technique in Through-the-Wall Imaging

Undesired wall reflections in through-the-wall imaging can mask the return from actual targets and saturate and block the receiver. We propose frequency-modulated interrupted continuous wave (FMICW) signals as a novel wall removal technique and validate its effectiveness through numerical simulations and experiments performed using a radar system built for the purpose. FMICW waveforms appear to mitigate wall reflections and benefit the through-wall detection of stationary targets and of people moving or breathing behind different kinds of wall.

위상잡음이 레이더 시스템에 미치는 영향 분석

In this paper, the effects of phase noise on the radar system were analyzed in terms of 3 point of view. The impact(s) on the compressed pulse waveform, the FMICW(Frequency Modulated Interrupted Continuous Wave) radar performance and the receiver sensitivity were investigated. From the investigation, it was indicated that the phase noise over 10 kHz offset frequency makes the side lobe level of compressed pulse worse. Also it was founded that the FMICW radar performance, especially at the noise level of range profile, is related to the phase noise. Finally, the investigation showed that the phase noise at local oscillator affects the receiver sensitivity.

최소 자승법을 이용한 고해상도 밀리미터파 탐색기의 비선형 위상 오차의 추정

본 논문 연구에서는 고해상도 레이더 탐색기에 쓰이는 FMICW(Frequency Modulated Interrupted Continuous Wave) 또는 FMCW(Frequency Modulated Continuous Wave) 시스템의 비선형 특성에 의해서 발생되는 거리 해상도(range resolution) 성능 저하 현상을 보상하기 위하여, 하드웨어의 비선형 위상 오차 성분을 다양한 진폭, 위상을 가지는 사인함수와 랜덤 성분으로 모델링하고, 이를 추정할 수 있는 신호 처리 알고리즘을 새롭게 제안하였다. 이 방법은 알고 있는 거리에 위치한 두 개의 기준점 목표물(point target)로부터 각각 측정된 두 개의 IF 신호를 연립방정식화하여 희소 선형식(sparse linear equation)을 세우고, 최소 자승법(least squares) 관점에서 최적 해로서의 비선형 오차 성분을 추정하는 방법으로써 추정된 비선형 오차 성분은 비선형 오차 특성 보상을 위한 사전 왜곡(predistortion) 기법을 위해 사용될 수 있다. In this thesis, to compensate the sweep nonlinearity occurring in the high resolution radar system using FMICW or FMCW, the method of the estimation of the nonlinearity is proposed. The nonlinear phase component caused by the nonlinear characteristic of the radar system is modelled as a linear combination of the sinusoidal functions consisting of various magnitudes and phases(systematic nonlinear phase error) and a random component(stochastic nonlinear phase error). From two IF signals that are measured respectively independently for two reference point targets lying in different distances which are known, a sparse linear equation is made and solved by least squares method to estimate the nonlinear phase component. The estimated component can be used for predistortion method to compensate the sweep nonlinearity.

Aliasing radar receiver in FMICW system

This paper analyses the lower bound of range resolution in Frequency Modulated Interrupted Continuous Wave (FMICW) radar, and presents a novel aliasing receiver theory. Through introducing a novel alias-removing algorithm, the receiver allows a certain degree of range aliasing, which leads to a much larger sweep bandwidth and an improved range resolution.

Millimeter-Wave Sensor With FMICW Capabilities for Medium-Range High-Resolution Radars

Frequency-modulated continuous-wave (FMCW) radars offer many advantages such as low peak power, low probability of interception, low interference with other systems, and high-range resolution. However, their major drawback is the isolation required between the transmitter and receiver that typically leads to the use of two separate antennas for transmission and reception. Some schemes have been proposed to enable FMCW radars to operate with a single antenna, such as frequency-modulated interrupted continuous-wave (FMICW) technology. Recently, a stagger procedure has been proposed to overcome the problems associated with the use of the FMICW technique in high-resolution radars. The technique was tested using simulated data. Now, a high-resolution millimeter-wave radar sensor, in <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band, has been developed at the Universidad Politecnica de Madrid, Madrid, Spain, to perform an experimental validation of the theoretical approach of the stagger procedure. The sensor transmits a linear frequency-modulated interrupted continuous wave with a maximum bandwidth of 2 GHz and a transmitted power of +29 dBm.

Stagger procedure to extend the frequency modulated interrupted continuous wave technique to high resolution radars

Frequency modulated continuous wave (FMCW) radars offer many advantages such as low peak power, low probability of interception, low interference to other systems and high range resolution. However, their major drawback is the isolation required between transmitter and receiver that typically leads to the use of two separate antennas for transmission and reception. Some schemes have been proposed to enable FMCW radars to operate with a single antenna. Frequency modulated interrupted continuous wave (FMICW) is a possible solution. However, some considerations must be taken into account before implementing this technique in high resolution radars because of the amount of bandwidth needed. The problems associated with the use of the FMICW technique in broadband radars are analysed and a staggering procedure is proposed to overcome them. This technique is tested using simulated data from a 1 GHz bandwidth millimetre wave sensor, currently under development. The results are compared against other single antenna configurations and the advantages of the staggering technique are shown.

Adaptive radio frequency interference mitigation for HF surface wave radar

The paper analyses the characteristics of radio frequency interference (RFI) in HF surface wave radar (HFSWR) which adopt the linear frequency modulated interrupted continuous wave (FMICW). RFI will influence all the range cells including all the positive and negative frequency, and that the negative frequency range cells contain only the interference information. Based on the above characteristics, we introduce and analyze a new adaptive interference mitigation beamforming algorithm which using the negative frequency range cells samples to estimate the interference covariance matrix. Experimental results confirm this general and robust algorithm can achieve effective RFI suppression using the data recorded by the HFSWR, located near Zhoushan in Zhejiang China.

Adaptive cochannel interference suppression based on subarrays for HFSWR

The paper analyzes the characteristics of cochannel interference (CCI) in the high-frequency (HF) surface wave radar (HFSWR), which adopts the linear frequency modulated interrupted continuous wave (FMICW). CCI will influence all the range bins, including all the positive and negative frequencies, and the negative frequency range bins contain only the external interference information. Based on the above characteristics, we introduce a new adaptive coherent side-lobe cancellation (CSLC) algorithm based on subarrays that use the negative frequency range bin samples to estimate the interference covariance matrix and correlation vector. Experimental results confirm that the general and robust algorithm can achieve effective CCI suppression using the data recorded by the Ocean State Monitor and Analysis Radar (OSMAR2003, manufactured in 2003), located near Zhoushan in Zhejiang, China.

Waveform analysis for HF ground wave radar

According to general radar designing principles, this paper discusses the concepts and processing techniques concerning the radar waveform analysis. For the need in developing HF ground wave system, as requested by a key oceanic project in the national 863 plans, basic theories and parameter design techniques on Frequency Modulated Interrupted Continuous Wave (FMICW) have been studied. This study serves as the waveform design basis for the HF ground wave radar OSMAR2000.