Range-Doppler-angle ambiguity function analysis in modern radar

In this research, the impact of signal bandwidth on the ambiguity function is explored. While this effort focuses on monostatic radar, the concepts developed are fundamentally applicable to distributed sensor geometries. Consider an array of N antenna elements with non-uniform spacing, energized by a doublet, i.e., a single cycle of RF energy approximating the derivative of an impulse. Alternatively, an impulse may be considered, but no radiating element supports propagation of a DC current. In the simplest case, identical broadband signals, W(t), are radiated from each of the uniformly spaced elements. Broadside, these signals sum coherently, while they are dispersed off-broadside (angle θ), with the dispersion proportional to Nd sinθ / c, where d is the element spacing. For broadband signals W(t) of duration T, the far field signal is of duration T + Nd sinθ / c. In the computation of the ambiguity function, the effect of the cross correlation of the radiated waveform with a Doppler shifted replica of itself is dispersed by a factor of two. However, in the case of broad band radiation, the “pulse” duration is itself a function of angle. As such, the ambiguity function is severely distorted as a function of steering angle. In this paper, the impact of signal bandwidth on range-Doppler discrimination as a function of viewing angle will be discussed, as well as implications in MIMO radar.