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. Keywords: FMICW, range resolution, aliasing, radar receiver Classification: Electron devices, circuits, and systems References

Abstract:Several field experiments were conducted to detect and track ships using a multi-frequency high-frequency surface-wave radar (HFSWR) system on the coast of East China Sea during 2009. Shipborne Automatic Identification System (AIS) was used to verify the results. And the algorithm of detection and tracking was proved to be efficient and practical.

We present an eddy current angle sensor for high-pressure electrohydraulic rotary valves. An oblique ring-shaped sensing coil and a symmetric semi-cylindrical rotor are utilized, making the coil impedance and the output voltage proportional to the angular displacements. Analysis based on an electrical equivalent circuit and the finite-element method is provided, and good agreement is obtained between the simulated and measured results. Extensive experiments have shown that the sensor has a linear working range of about 30° with nonlinearity 0.8% and temperature drift less than 1% over 30 °C–90 °C.

Currently, shore-based HF radars are widely used for coastal observations, and airborne radars are utilized for monitoring the ocean with a relatively large coverage offshore. In order to take the advantage of airborne radars, the theoretical mechanism of airborne HF/VHF radar for ocean surface observation has been studied in this paper. First, we describe the ocean surface wave height with the linear and nonlinear parts in a reasonable mathematical form and adopt the small perturbation method (SPM) to compute the HF/VHF radio scattered field induced by the sea surface. Second, the normalized radar cross section (NRCS) of the ocean surface is derived by tackling the field scattered from the random sea as a stochastic process. Third, the NRCS is simulated using the SPM under different sea states, at various radar operating frequencies and incident angles, and then the influences of these factors on radar sea echoes are investigated. At last, a comparison of NRCS using the SPM and the generalized function method (GFM) is done and analyzed. The mathematical model links the sea echoes and the ocean wave height spectrum, and it also offers a theoretical basis for designing a potential airborne HF/VHF radar for ocean surface remote sensing.

The large leakage current of the roof arrester caused by the high-frequency resonant overvoltage on the high-speed train occurs intermittently, which will cause the arrester to overheat locally. In this work, the overheating issue of the arrester under Ultra Harmonics Overvoltage is studied. Then, the relationship between the active power and the voltage (including amplitude and frequency) of the arrester is investigated, and the impact mechanism of the harmonic voltage on the overheating fault of the arrester is analysed based on experiments in this work. It is found that the total leakage current of the arrester is proportional to the amplitude and frequency of the applied voltage. The internal resistance of the arrester is independent of the amplitude of the voltage, but it will decrease with the increase of the frequency. The main reason that leads to thermal breakdown of the arrester valve under high-frequency harmonic voltage is the heating power elevation of the arrester valve. The research study can provide theoretical basis and data support for the design, type selection and monitoring of the high-speed train roof arrester.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.