Study on Passive Radar Imaging Using Distributed Apertures with Illuminators of Opportunity
|School||Nanjing University of Aeronautics and Astronautics|
|Course||Signal and Information Processing|
|Keywords||Passive radar Imaging Distributed aperture Illuminator of opportunity Wave equation Hypothesis Test|
In recent years, passive radar detection or imaging using illuminators of opportunity gains much attention in the development of modern new radar system. Radio broadcasting station, television station, mobile communication base station, navigation satellite, wireless network (WiFi) etc. can all be used as illuminators of opportunity. With the rapid development of the human society, the number of these illuminators of opportunity increases greatly, particularly in urban areas, which promotes the development of this radar modality, i.e., passive detection or imaging using illuminators of opportunity. For a distributed aperture, the transmission elements (transmitter) and receiver element (receiver) can be distributed spatially in an arbitrary fashion with several hundred wavelength apart. Passive radar using distributed apertures relying on illuminators of opportunity has the following advantages: 1) there is no need of a dedicated transmitter. Furthermore, the structure of the receiver can be so simple and with relatively low cost; 2) the system can be deployed rapidly; 3) the diversity of the observation angle leads to good angle resolution. Combined with the diversity of trasnsmitted waveform, the radar can obtain good detection capability by using information in three freedoms, i.e., space, time and waveform; 4) it has good performance of electromagnetic countermeasure.For passive radar detection and imaging, the location and waveforms of the illuminators are generally not known. Existing passive detection methods usually need an additional receive channel or a dedicated receiver to obtain the transmitted waveform required by the optimum matched receiving, or estimates the waveform from the received signals. Thus, considering reducing the complexity of the system and making the methods more applicable in practice, it is necessary to develop passive detection and imaging methods without the need of the transmitted waveforms. On the other hand, for urban areas, the free space propagation model is not applicable any more, it is necessary to reconsider the modeling of the received signal, which should be able to account for the practical wave propagation. Furthermore, the effect of the multipath scattering on the detection and imaging is needed to be studied deeply, including the possibility of improving the detection capability by exploiting the multipath scattering.Based on the considerations above, passive radar imaging using distributed apertures is studied in this thesis. In Chapter 1, the development of the passive radar is reviewed and then the research background of the thesis is presented. In Chapter 2, the development of a measurement model applicable to arbitrary scattering environments is firstly discussed from the perspective of the scalar wave equation originated from physics. Then, the study focuses on developing a passive measurement model for passive detection and imaging using distributed apertures, which doesn’t require any knowledge of the transmitter. Both non-cooperative and cooperative illuminators of opportunity are considered. For non-cooperative illuminators, the information regarding the location, waveform of is not available, while for cooperative illuminators, the location is assumed to be only available. In Chapter 3, the imaging method for passive radar using distributed apertures is studied. The imaging problem is addressed as a spatially resolved binary hypothesis test, where the test statistic is determine by maximizing the signal to noise ratio (SNR). The image is formed by the resulting spatially resolved test-statistic. The optimum template and test-statistic for a point taget imaging using cooperative and non-cooperative illuminators of opportunity are presented in both free space and multipathing environment. In Chapter 4, the performance of the imaging method is analyzed in detail in terms of the point spread function (PSF) of the imaging operator. The analysis involves the effects of the number of the transmitters and receivers, the geometry of the transmitters and receivers, the transmitted waveforms and the multipath scattering on the imaging. In Chapter 5, the numerthe simulations are conducted under a variety of scenarios to demonstrate the passive radar imaging method presented in chaper 3. Chapter 6 concludes the work in the thesis.