This paper focuses on the feasibility of tracking micro-motion with coherent Ultra-Wide Band Pulsed Radar. The proposed micro-motion detection principle consists in measuring the phase difference of the Ultra-Wide Band carrier waveform between the transmitted and the received pulse signals. Those signals are acquired directly on the working frequency band, with equivalent time sampling techniques. An experiment based on a double staged equivalent time sampling is set to emulate real-time acquisition with an oscilloscope. This experiment shows clear high precision ranging capabilities by revealing a millimeter order woofer displacement equal to λ⁄10. This reveals a great potential in phase tracking and confirms the choice to go further on the development of a real time radar. This platform provides refreshing rates of 2 ms, required to developed effective phase detection algorithms for micro-motion detection and tracking of human targets, especially for through-the-wall radar applications when humans remain in static position.
This paper discusses the state-of-the-art in through-the-wall surveillance technology (TWS) and examines the detector performances as a function of TWS application. This state-of-the-art is the most exhaustive possible, from the centimetre non-imaging system, to the submillimetre imaging system. This is followed by a review of the various functions and the results which can be expected from a TWS system depending on the situation and the applications (law enforcement and civil security).
Then, different key parameters of a TWS imaging system are studied and discussed according to the applications. Reasons for the choice of wavelength are considered. This appears to be the most important parameter for improving the sensitivity (image contrast), the spatial resolution and the size of the system. Detector performances (noise equivalent power or noise temperature) are also examined as a function of the detection mode (heterodyne or direct) and the imaging system (passive or active).
Among the two categories of superconducting detectors that are actually operational for competitive performance in the submillimeter-wave/terahertz range, SIS devices used as heterodyne mixers offer very low noise level, but are frequency limited by the superconducting energy gap. Bolometric detectors on the other hand, although of lesser performance a priori, have no intrinsic frequency limitation due to their purely thermal sensing principle. Moreover, their inherent slow response can be overcome by developing hot- electron bolometer technologies based on superconducting nanostructures, that allow promising output frequencies of several GHz. In order to implement competitive submillimeter wave detectors, wideband planar antennas are preferred to improve the radiation to device coupling, rather than conventional bolometric structures (of either monolithic or composite type) that do not allow both sensitive and fast detector operation. All these aspects are commented and many realizations covering a large number of technologies, in view of both homodyne and heterodyne detection, are reviewed, commented and discussed.
The main phenomena that may be responsible of radiation detecting mechanisms in superconductors are described in a first part of this paper. Several examples are given, ranging from broadband and sensitive bolometric devices to ultrafast nonbolometric infrared detectors. The second part is devoted to the study of various transition edge bolometers designed to be built at low cost. Polycrystalline zirconia substrates have been used, to grow YBCO films by both in situ and ex situ oxygenation after radiofrequency sputtering. The voltage responsivity at 10.6 micrometers wavelength has been studied with respect to the modulation frequency of the incident radiation, both experimentally and theoretically. A 2D thermal model has been developed, allowing to interpret the complex (amplitude and phase) experimental frequency responses of various devices. In particular, the amplitude response can be described as a succession of f-1 and F-1/2 segments. Noise measurements show NEP and detectivity values reaching a very satisfactory level for granular films.
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