Research On Direction Finding Algorithms Of Complex Modulated Signals

In this paper, several key technologies for radio direction finding in electronic reconnaissance arestudied, which include wide-band direction finding algorithms based on the phase interferometer anddirection of arrival (DOA) estimation for both broadband and narrow-band signals based on longbaselines.Conventional phase interferometer can achieve phase only for single-frequency narrow-bandsignal, but the signals researched in this paper are mostly wideband. For different radar signals, threedirection finding algorithms are proposed, including the demodulation method for LFM signals、thecorrection method for BPSK、QPSK signals and sub-bands decomposition method for generalwideband signals. Simulation results show that the sub-bands decomposition algorithm has a widerscope and some of the more complex modulation signals still apply it.The direction finding algorithms based on long baselines interferometer are discussed in thispaper. Compared with the single-baseline interferometer, the multiple-baseline interferometer breaksout the limitation that the baseline length is less than half-wavelength. But considering the affection ofsyetem tolerance and system complexity, we find that the baseline set is also limited. Combing withtime of arrival (TOA) estimation, this paper presents a kind of super-long-baseline DOA algorithm.The algorithm is based on the accurate arrival time estimation and only suit for single-frequencysignals. Simulation results show that BPSK、QPSK signals can also apply the algorithm undermoderate SNR after a simple provement.In addition, this paper also studies a long baseline direction finding algorithm which is suit for awider range of broadband signals. It turns the time-delay estimation between signals into thefrequency estimation which is very mature. Simulation results show that the algorithm has certainrequirements for the signals’ bandwidth. For some complex modulated signals, the algorithm also canperform well on the condition of suitable bandwidth. When the bandwidth is not wide enough, a kindof multiple baselines direction finding algorithm by unwapping phase ambiguity based on time-delaycorrection is introduced to improve the measurement accuracy. At last, the azimuth angle estimationand the pitch angle estimation for space objects are discussed by computer simulations.