A.A. Volkov, V.I. Karpuchin

Side-looking ground surface radars find wide application in the military sphere, first of all in surveillance systems and are of particular interest as electronic countermeasure objects. High-resolution is the most important requirement to be imposed on the said radars. Research to increase resolution for airborne surveillance radars up to 10 cm have been currently carried on that corresponds to band-width of the signals utilized up to 1500 MHz. With such bandwidth values, conditions of desired signal and frequency band-matched interference acquisition get different. Sector of possible interference arrival is by far wider than sector of desired signal acquisition and includes those directions where dispersive characteristics of antenna array have significant impact on direction pattern generation, that is to say frequency dependence of phase incursions of interference spectrum components at the antenna output. Therefore, to get reliable results in jamming effectiveness evaluation for high radar range resolution it is required to employ direction pattern models bearing interference spectrum width in mind. In the context of broadband interference, suitable for simulation analytic expressions of direction patterns are not available in the known references. Object of this paper is to obtain analytic expressions of energy direction pattern for side-looking radar antenna within broadband and probability estimate of radar countermeasures by broadband interference with consideration of the results obtained. Frequency signal analysis method for antenna array model of radar with frequency-independent and non-directional receiving elements and frequency-independent phase shifters is used as the basis for the research. As a result of the problem solution, analytic expressions of direction patterns for antenna array have been obtained with account of spectrum width of the received signal for three kinds of field distribution: uniform and two with monotone field decrease from the middle to the array edges with different decrease rate. Smoothing of «gaps» in the structure of side lobe direction pattern at increase of the signal bandwidth has been estimated. Using the results obtained, calculations for probability of typical side-looking radar countermeasures by broadband interference to be spectrum-matched with desired signal and being active on side lobes of the direction pattern in the cases of high range resolution at low azimuth resolution and high two coordinate resolution have been made. Based on the calculations performed it has been established that at evaluation of effectiveness of side-looking radar countermeasures with high range resolution smoothing effect of the direction pattern through interference broadbandness and side lobe structure must be taken into account only at low azimuth resolution. With high azimuth resolution, it is sufficient to consider smoothing effect of the direction pattern within interval of changing angular position of jamming source during antenna aperture synthesizing.