Spatial Frequency Modulation of Probing Signals in Radars with a Planar Active Phased Array

Introduction. Multiband and multi-frequency signals are widely used in radar systems. The use of active phased array antennas, in which each spatial receiving channel has its own transmitter and receiver, offers additional opportunities for covert radar operation, thereby enhancing radar noise immunity and electromagnetic compatibility. The article examines the energy stealth of a radar with a multi-frequency sensing signal with spatial frequency modulation in a planar multielement phased array antenna compared with a similar multi-frequency signal without additional spatial modulation.
Aim. Analysis of the directional and energy stealth characteristics in the radiation mode of a multiband frequency equidistant quasi-continuous radar signal with a planar receiving and transmitting active phased array antenna when additional spatial frequency modulation is used.
Materials and methods. The stealth analysis was performed using a classical energy receiver (ER) with an input filter and an amplitude detector. To obtain stealth characteristics as functions of azimuth and elevation angles, computer modeling of the radar and ER operation was combined with the apparatus of uncertainty functions in time, frequency, and spatial domains. Real signals with quasi-continuous emission and a low duty cycle were considered.
Results. Using a computer model, angular dependences of the signal intensity in the cumulative ER filter were obtained for a radar without spatial modulation and with spatial modulation, along with estimates of the gain in the signal level entering the input of the cumulative ER filter at different positions on the frequency axis of the multiband signal relative to the central frequency of the cumulative filter. The analysis was performed for cases in which the signal spectrum fully overlaps or overlaps by half the ER filter bandwidth. Quantitative relationships between the average signal levels in the cumulative ER filter were obtained for three types of signals. The energy stealth of a radar with spatial modulation was compared with that of a conventional radar with a multifrequency probing signal similar in terms of energy and number of bands, with the main parameters of the signals and phased array antennas being identical. The article provides a block diagram of a multiband radar with an active phased array antenna, as well as a block diagram of the receiving channels corresponding to MIMO technology.
Conclusion. The conducted studies have confirmed the feasibility and effectiveness of introducing additional spatial modulation of a multiband signal in a radar with an active phased array antenna to increase the stealth of its operation. The proposed structure for signal generation and processing with space-frequency modulation is technologically advanced and can be implemented using modern digital electronic components.

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