Motivated by classical coincidence imaging which has been realized in optical systems, an instantaneous microwave-radar imaging technique is proposed to obtain focused high-resolution images of targets without motion limitation. Such a radar coincidence imaging method resolves target scatterers based on measuring the independent waveforms of their echoes, which is quite different from conventional radar imaging techniques where target images are derived depending on time-delay and Doppler analysis. Due to the peculiar features of coincidence imaging, there are two potential advantages of the proposed imaging method over the conventional ones: 1) shortening the imaging time to even a pulse width without resolution deterioration so as to improve the performance of processing noncooperative targets and 2) simplifying the receiver complexity, resulting in a lower cost and platform flexibility in application. The basic principle of radar coincidence imaging is to employ the time-space independent detecting signals, which are produced by a multitransmitter configuration, to make scatterers located at different positions reflect independent waveforms from each other, and then to derive the target image based on the prior knowledge of this detecting signal spatial distribution. By constructing the mathematic model, the necessary conditions of the transmitting waveforms are analyzed for achieving radar coincidence imaging. A parameterized image-reconstruction algorithm is introduced to obtain high resolution for microwave radar systems. The effectiveness of this proposed imaging method is demonstrated via a set of simulations. Furthermore, the impacts of modeling error, noise, and waveform independence on the imaging performance are discussed in the experiments.

Radar Coincidence Imaging: an Instantaneous Imaging Technique With Stochastic Signals

Inverse synthetic aperture radar (ISAR) imaging is a powerful tool for the characterization of scattering properties of radar targets. In particular, near-field techniques allow for short distance imaging with results comparable to those of standard far-field ISAR techniques. The resulting near-field images can be used to extract the far-field radar cross section (RCS) of the target overcoming the need for long-range measurement setups. This paper compares different near-field imaging techniques and reveals an in-depth insight into the imaging process, especially with regard to the subsequent RCS extraction. The performance of the different techniques together with processing improvements are demonstrated by means of numerical target models as well as by measured data of test objects and a scaled aircraft model.

Comparison and Application of Near-Field ISAR Imaging Techniques for Far-Field Radar Cross Section&#160;Determination

With the inverse synthetic aperture radar (ISAR) imaging model, targets should move smoothly during the coherent processing interval (CPI). Since the CPI is quite long, fluctuations of a target's velocity and gesture will deteriorate image quality. This paper presents a multiple-input-multiple-output (MIMO)-ISAR imaging method by combining MIMO techniques and ISAR imaging theory. By using a special M-transmitter N-receiver linear array, a group of M orthogonal phase-code modulation signals with identical bandwidth and center frequency is transmitted. With a matched filter set, every target response corresponding to the orthogonal signals can be isolated at each receiving channel, and range compression is completed simultaneously. Based on phase center approximation theory, the minimum entropy criterion is used to rearrange the echo data after the target's velocity has been estimated, and then, the azimuth imaging will finally finish. The analysis of imaging and simulation results show that the minimum CPI of the MIMO-ISAR imaging method is 1/MN of the conventional ISAR imaging method under the same azimuth-resolution condition. It means that most flying targets can satisfy the condition that targets should move smoothly during CPI; therefore, the applicability and the quality of ISAR imaging will be improved.

An ISAR Imaging Method Based on MIMO Technique

The airborne synthetic aperture radar (SAR) image of ship target will be blurred for the complex motion of the target, which will influence the performance of feature extraction and target classification. In this article, a refocusing method of ship target in airborne SAR image though the inverse synthetic aperture radar (ISAR) technique is presented. The novel contributions of this article can be summarized as follows: 1) the residual phase of processed signal is analyzed in detail to illustrate the necessity of adopting ISAR technique; 2) a valid, labor-saving, and automatic image segmentation approach via clustering algorithm is put forward for automatic data extraction and inverse mapping. The clustering algorithm we choose is the agglomerative hierarchical cluster algorithm, which does not require the number of categories in advance; 3) the refocused individual ISAR image of individual ship target is yielded though the range-instantaneous Doppler algorithm. Finally, the simulated and real measured data are processed, and imaging results verify the effectiveness of the novel algorithm presented in this article.

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Ship Target Imaging in Airborne SAR System Based on Automatic Image Segmentation and ISAR Technique

Cross-range scaling is an important procedure for inverse synthetic aperture radar (ISAR) imaging since the cross-range resolution is always unknown due to the noncooperative targets. In fact, the essential problem of scaling is to estimate the rotation velocity of the target from echoes. Considering that most of the scaling methods have limitations on the requirement of some prior knowledge of the target’s motion, difficulties in handling some complicated-structure targets, and low-signal-to-noise ratio (SNR) conditions, we propose a novel scaling approach based on the multidelay discrete polynomial-phase transform (DPT) combined with keystone transform. Different from the second-order-DPT-based method, the proposed method separates the different components on the 2-D spectrum of time and delay time, which avoids the interference of cross terms and enhances the anti-noise ability. The experiments on linear frequency-modulated (LFM) signals, simulated ISAR echoes, and real-measured data verify the effectiveness and robustness of the proposed method.

Novel Approach for ISAR Cross-Range Scaling Based on the Multidelay Discrete Polynomial- Phase Transform Combined With Keystone Transform

In view of the importance of electromagnetic compatibility (EMC), universities worldwide are paying more attention to training electronic engineers with good EMC design knowledge. As part of the EMC training, a practical printed circuit board (PCB) layout project has been offered as an elective to the undergraduates in the authors' universities. The project requires the students to design the PCB layout of a standard digital circuit twice, the first time with no EMC consideration at all, and the second time with careful EMC consideration. The significant difference in the levels of radiated emissions of the two layouts allows the students to appreciate the importance of EMC design at an early stage of product development.

A practical approach to EMC education at the undergraduate level

Inverse synthetic aperture radar (ISAR) imaging is a powerful tool in microwave imaging for moving target. It provides high range resolution by transmitting wide-band signal, and high cross-range resolution by coherently accumulating echoes, where phase compensation is one core technique for range-Doppler image formation. However, conventional phase compensation methods usually have problems to compensate the translational motion between radar and target with sufficient accuracy when the motion has high order or even random terms. To solve this problem, the minimum entropy idea is introduced in this paper for ISAR imaging via a nonparametric estimation method.

Phase compensation for ISAR imaging combined with entropy principle

An internal impedance measurement system of switch power-supply EMI noise source based on Hibert transform and current probe comprises line-impedance stable network, common mode/difference mode impedance test module, signal generator and frequency spectrum analyzer. It is featured as inputting power supply wire directly to impedance stable network then inputting to switch power supply and load for forming a complete power supply loop through common mode/different mode impedance test module. The method for measuring said internal impedance is also disclosed.

System for measuring internal impedance of noise source of switching power supply EMI based on Hilbert transform and current probe, and measuration method

The invention discloses an impedance testing system and method in the noise source of switch power EMI, which comprises the following parts: stable line impedance network, single-current probe method impedance testing mode and spectrum analyzer, wherein the power line is connected in the stable line impedance network directly to input the switch power and load through single-current probe method impedance testing mode, which constitutes an integral power circuit; the spectrum analyzer tests the respond signal in the mode. The invention can test general internal or unknown impedance for kinds of noise source, which provides premise of the design of EMI filter to mate the property of filter.

Switch power source EMI noise origin internal impedance test system and measuring method thereof

The invention discloses a measuring device of switch power supply EMI noise source internal impedance that comprises line impedance stabilization network, common mode/differential mode impedance test module, signal generator and spectrum analyzer; power cord is directly input to the line impedance stabilization network, passes the common mode/differential mode impedance test module, and then input to the switch power supply and load to construct a whole power circuit; the signal generator provides a input signal for the common mode/differential mode impedance test module, response signal in the module is detected by the spectrum analyzer. The measuring method of switch power supply EMI noise source internal impedance IA also disclosed. The measuring device and method can measure the all-purpose internal impedance for all kinds of noise source, but also measure the unknown impedance, the accuracy is high and the operation is simple. The measuring method can judge the nature of internal impedance and provide a precondition for designing of EMI filter that is the designing of filter fulfills the impedance matching property of filter.

Yang Zhao

Papers

A practical approach to EMC education at the undergraduate level

Phase compensation for ISAR imaging combined with entropy principle

System for measuring internal impedance of noise source of switching power supply EMI based on Hilbert transform and current probe, and measuration method

Switch power source EMI noise origin internal impedance test system and measuring method thereof

Device and method for measuring internal impedance of noise source of switch power supply EMI