The Rf Stealth Technology Of Airborne Radio Altimeter Research

As an important airborne electronic equipment, the RF stealth technology of radio altimeter is very important to improve its adaptation to complex environment and the way to against electronic interference under the conditions of modern warfare. The low probability of intercept is the key to achieve the RF stealth technology, therefore, the probility of signal is intercept and interference can be reduced, the surivivability of airplane could be improved by studying the LPI method of airborne radio altimeter.LPI radar technology were made as research center in this dissertation, the Direct Sequence(DS) Spread Spectrum, Frequency-Hopping(FH) Spread Spectrum and transmitting power management technology in which communication system commonly used were studied, and the LPT performance of airborne radio altimeter based on signal research and power management is proved by many simulation experiments. The main research contents of this dissertation are as follows:Firstly, the basics of LPI radar were introduced, including principle, concept and intercept factor. Then various factors that affect the performance of the LPI according to this factor and the evaluation of LPI were studied to make sure the the way to study LPI follow-up.Secondly, the design and principle of LPI radio altimeter system was discussed, and objects and processes of altimetry and interception were studied.Thirdly, the designed requirements of LPI radio altimeter signal, and choose the ideal type of signal. m code sequence in which DS systems commonly used and RS sequence in which FH systems commonly used were studied, and their squence properties were analysed, then they were mixed as the DS-FH signal. The LPI performance of DS signal was 15 dB better than the LPI performance of STLFMCW signal in which tranditional radio altimeter commonly used on intercept distance, and the LPI performance of 7 frequcncies’ DS-FH signal was 3 dB better than the LPI performance of DS signal by simulating.Finally, the transmitting power management system of LPI radio altimeter was studied. The range of transmitting power was determined according to electromagnetic wave attenuation in various conditions; the step of transmitting power management system was determined by studying step of modern 3G communication system; the accurace will not be influenced by hardware error according to closed-loop algorithm.The radio altimeter with DS-FH system and power management system will keep sufficient accuracy of altitude estimation, and its LPI performance was better than tranditional radio altimeter by simulating.