N. G. Parhomenko, G. G. Vertogradov, I. А. Yarovoy, V. N. Shevchenko

A rapid development of airborne targets passive radar with external illumination is taking place in last decade. The devices using HF diapason are of special interest, for this diapason has a huge number of regular special and broadband transmitters of known characteristics. Paper objectives are the experimental research of the wave scattering effects for HF diapason on civil airplanes when for long-distance illuminating diagnostic transmitters running on several frequencies simultaneously. Experimental research of the wave scattering effects for HF diapason has been carried out during 2010 on a 24-hour basis. Correct time station RWM transmitters was used as the diagnostic emission source. The distance between the object and these transmitters is about 1000 kilometers, the transmitters work synchronously in equal cycles at three frequencies of 4996, 996 and 14996 kHz simultaneously. Time intervals of 0 to 8 minutes and 30 to 38 of every hour was used for the measurements because these are the intervals for the monochromatic transmission. Multifrequency Doppler radar was used for receiving the signal. The radar was based on one digital tuned RF radio with simultaneous swath of 2-30 MHz. The receiver output is digitized by 16-bit ADC with 100 MHz frequency. Then the receiving band is divided into 30 secondary narrow-band subchannels by the methods of digital frequency translation, filtration and decimation. Hence, Doppler radar is able to detect signal quadrature-phase components coherently at 30 secondary receiving channels placed within the band of 2 to 30 MHz. The band of each secondary channel is 50 Hz, sampling rates are 200 Hz. The terrestrial receiver coordinates are 47.239° of latitude and 39.642° of longitude. The distance between the receiver and the transmitter is 949 km and the direction to the transmitter is 354.6°. The processing is divided into two stages. Airplane tracks (the dependence of Doppler frequency shift on time) were isolated. Specter power density normed by direct signal maximum is calculated basing on sliding sample captures of 10 seconds length. Then the dependence of scattered signal power on the time was calculated for each track. It is obtained that the signal depression varies at the range of 35 dB to 75 dB comparing to spatial wave signal of target illumination. It is shown that the peculiarities of multibeam propagation of spatial waves illuminating the scattering object affect the quality of the signal scattered by the target.