Linear Frequency Modulated Continuous Wave Radar Research Articles

Correction of Dechirp Distortion in Long-Distance Target Imaging with LFMCW-ISAR

The combined linear frequency modulation continuous wave (LFMCW) and inverse synthetic aperture radar (ISAR) can be used for imaging long-distance targets because of its long-distance and high resolution imaging abilities. In this paper, we find and study the dechirp distortion phenomenon (DDP) for imaging long-distance targets by a dechirp-on-receive LFMCW radar. If the targets are very far from the radar, the maximum delay-time is not much smaller than a single sweep duration, and the dechirp distortion is triggered since the distance of the target is unknown in a LFMCW-ISAR system. DDP cannot be ignored in long-distance imaging because double images of a target appear in the frequency domain, which reduces resolution and degrades image quality. A novel LFMCW-ISAR signal model is established to analyze DDP and its negative effects on long-distance target imaging. Using the proportionately distributed energy of double images, the authors propose a method to correct dechirp distortion. In addition, the applicable scope of the proposed method is also discussed. Simulation results validate the theoretical analysis and the effectiveness of the proposed method.

Application of Compressive Sensing in LFMCW Radar

Compressive Sensing (CS) theory is a newly developed theory which combines the signal sampling and compression based on the sparsity characteristics of the signal. Applying CS theory in radar signal processing may lead to a reduction in sampling rate, complexity, power consumption, and cost. On the other hand, performance is a critical point to be considered. In the present paper, an important question of the worthy of applying CS in the signal processing of Linear Frequency Modulated Continuous Wave (LFMCW) radar is considered. Two approaches of CS are considered; Nyquist rate based approach, and pseudo random based approach. The detection performance of LFMCW radar signal processor using CS based approaches is compared to the traditional one which is based on Fast Fourier Transform (FFT) through Receiver Operating Characteristics (ROC) curves. Comparative analysis between CS approaches and the traditional one regarding the performance and complexity is presented.

Detection and Parameter Estimation of Multi-targets Based on Secondary Mixing Combined DPT Method in LFMCW Radar

To solve the detection problem of high-speed accelerating targets in LFMCW (Linear Frequency- Modulated Continuous Wave) radar, a secondary mixing combined DPT (Discrete Polynomial-phase Transform) method is proposed. Utilizing the modulation symmetry of tri-LFMCW signals, up-sweep beat signal is secondary mixed with down-sweep one to eliminate MTRC (Migration Through Range Cell) induced by the high-speed. And DPT processing in terms of range cell leads to the estimation of acceleration and initial velocity. Furthermore, parameter estimation of multi-targets is emphasized. By analyzing the characteristics of the cross terms, the conditions for first order cross terms forming effective interfere and for second order cross terms emerging are derived, respectively. Resorting to Clean algorithm, multi-targets can be dealt with successfully, which detects and removes the strongest target for the current time. Processing steps of multi-targets cases are given. Simulation results testify the effectiveness of the method and the conclusions.

A 34 to 36 GHz Vector Modulator for Reflected Power Canceller Techniques in LFMCW Radar

In this paper, a 34 to 36 GHz vector modulator for using in low cost and high performance RPC (Reflected Power Canceller) is presented. The key circuit consists of two push-pull (bi-phase) attenuators arranged in phase quadrature and a 3dB quadrature coupler (branch line couplers but not Lange couplers which is different from traditional circuits in Ka band) and a Wilkinson combiner, and then transition from micro-strip to waveguide using antipodal finline. To fully exploit this circuit’s capacity to generate accurate constellations at millimeter-wave frequencies, a generalized theoretical analysis of the (push-pull) vector modulator is presented. Based on the theoretical model and the measured results, the I-Q (push-pull) vector modulator promises to be a vital component for the realization of reflected power canceller in LFMCW (Linear Frequency Modulated Continuous Wave) radar.

Helicopter Classification with a High Resolution LFMCW Radar

Helicopter classification using a high resolution linear frequency modulated continuous wave (LFMCW) radar is addressed. A blade echo modelling for this radar system is derived, taking into account that the stop-and-go assumption is not longer applicable. The standard classification schemes based on the L/N-quotient and the evenness of the number of blades are easily reproduced in this high resolution context, although two main advantages are added: a high pulse repetition frequency (PRF) to acquire the Doppler bandwidth is no longer necessary, and the time for which we receive returned signal from the target may be maximized. On the other hand, a characteristic critical classification problem, for which the standard approaches do not properly work, is presented. Two classification schemes are proposed for this situation, the first one based on coherent matched masks and the second one based on incoherent masks where a robustness parameter has also been defined. Identification probabilities as a function of the signal-to-noise ratio (SNR) are obtained in order to characterize the performance of both techniques. Real data validate both the derived model and the proposed classification algorithms.

Uniform rotational motion compensation for inverse synthetic aperture radar with non-cooperative targets

In the current scenario of high-range resolution radars, the rotational motion of the target usually generates migration through resolution cells (MTRC) in the inverse synthetic aperture radar (ISAR) images. A technique to correct the MTRC in the case of uniform rotation rate is proposed. An estimation of the rotation vector of the non-cooperative targets is not required. The approach compensates the rotational motion in two steps: the slant-range rotation compensation (SRRC) and the cross-range rotation compensation (CRRC). CRRC is based on an extension of phase difference (PD) and on a robust method to delete outliers. The technique is verified both with simulated and live data from a millimetre-wave linear frequency-modulated continuous wave radar. A comparison with a minimum entropy-based technique is also made.

Noise analysis of digitised FMCW radar waveforms

A staircase phase approximation for generating a linear frequency-modulated continuous wave radar signal is considered and the use of filtering on the samples of the signal has been assumed in both transmission and reception. It is shown that an excellent spectrum of the radar signal can be obtained, provided that the appropriate value of the sample duration is used. The effect of noise due to the discrete representation of the signal is analysed for both transmitted and received signal. It is shown that the level of the noise may be kept below the noise level of a high-quality oscillator even in the absence of any filter smoothing.