Open AccessWhen emitting the orthogonal signals the MIMO radar generally uses widely directional antennas of transmitting and receiving elements (sites). Principles of MIMO radar are generally applicable at highly directional antennas. For a small sites spacing and application of narrowly focused and synchronous scanning antenna provides new benefits for MIMO radar. These include an increase in the power potential, detection range and easy of synchronous radar zone scanning with equivalent narrow spatial beam.
For MIMO radar with narrow radiation patterns it is typical to have a diffraction pattern within the equivalent scanning beam, consisting of a large number of intense grating lobes. The structure of the diffraction pattern and the width of the lobes depend on the inter-element distance (base) and the coordinates of MIMO radar position. The angular width of the diffraction pattern is equal to the width of the identical patterns at positions. Removing the angular ambiguity will require special measures to reduce the level of the lateral lobes This paper is devoted to assessing the degree of side lobes reduction by the use of multi-band multi-frequency signals with non-overlapping groups of multi - frequency bands with two versions of the co-processing between the groups of frequency components - additive and multiplicative.
It is shown for the embodiment of MIMO radar with 5- receiver and 5-transmitter positions and narrow beam patterns and 5-frequency signal in the band of 1.6 MHz that increasing initial frequency of spectrum up to 10% leads to the fact that diffraction maxima of the lobe for increasing frequencies coincide with minima in the diffraction pattern at the original frequency. This was the basis for using multi-band signals when suppressing the diffraction lobes in MIMO radar. The embodied MIMO radar with two-way 5-frequency signal and detuning initial frequencies 10% shows that the additive treatment gives diffraction of lobe suppression -3.0...-3.5 dB in comparison with the case of a single-sideband signal. Increased band spacing up to 20% leads to further decreasing diffraction lobes down to -6 dB compared to single-sideband signal. With multiplicative processing it is determined that the signal level for suppression of diffraction is -16 dB, i. e. 12 dB better than suppression with additive treatment. In the case of three-band signal the suppression increases by 4 ... 5 dB, while the expansion of the relative bandwidth up to 20% allows us, for a three-band signal, to increase suppression of diffraction lobes to -26 dB.
The study suggests the prospect of multiband multi-frequency space-time signals in MIMO radar with narrow positions beam patterns in order to effectively suppress the diffraction side lobes within the equivalent spatial scanning beam.