Frequency Diverse MIMO Techniques for Radar

Abstract

It has been shown over several decades of radar research that the exploitation of diversity in a number of domains (space, frequency, time, polarization, and, recently, waveform) can provide increased agility, flexibility, robustness, and capabilities to the radar system. However this is often achieved either through efforts in system design, increased hardware complexity, or by employing additional resources. A conventional antenna array is considered with the intention of introducing, not major, but minor mismatches, in particular in the carrier frequencies and, eventually in the codes at the element level. The starting point of this analysis is the frequency diverse array (FDA), which has been demonstrated to generate a range-angle pattern. Through a reconsideration of the organization of the array, which we have termed the wavelength array (WA), a new pattern, "orthogonal" to that of the standard phased array, can be achieved. The bistatic combination of a WA and a receiver leads to the frequency diverse bistatic system (FDBS), which can be a significant application of this concept. In a second stage the analysis focuses on the effects of introducing waveform diversity in such a system. In particular, if the elements of an electronically steered array (ESA) simultaneously transmit a number of pseudonoise (PN) codes at slightly different carrier frequencies, the coherent summation of the codes gives rise to a waveform whose shape is a function of both angle and range. In fact this is the consequence of applying the multiple-input multiple-output (MIMO) technique to the FDA, which has the result of associating a waveform to each point range/angle of the space, with the possibility of recovering this information in receive after appropriate processing.