Ambiguity Function of the Transmit Beamspace-Based MIMO Radar

TL;DR

This paper derives a generalized ambiguity function for transmit beamspace MIMO radar, incorporating waveform diversity and processing gain, and compares it with existing AFs to optimize radar performance.

Contribution

It introduces a new AF formulation for TB-based MIMO radar, relating it to existing AFs, and proposes a design strategy to reduce sidelobe levels.

Findings

Derived a generalized AF for TB-based MIMO radar.

Established bounds for the 'clear region' in Doppler-delay domain.

Proposed a TB design strategy to reduce AF sidelobes.

Abstract

In this paper, we derive an ambiguity function (AF) for the transmit beamspace (TB)-based multipleinput multiple-output (MIMO) radar for the case of far-field targets and narrow-band waveforms. The effects of transmit coherent processing gain and waveform diversity are incorporated into the AF definition. To cover all the phase information conveyed by different factors, we introduce the equivalent transmit phase centers. The newly defined AF serves as a generalized AF form for which the phased-array (PA) and traditional MIMO radar AFs are important special cases. We establish relationships among the defined TB-based MIMO radar AF and the existing AF results including the Woodward's AF, the AFs defined for the traditional colocated MIMO radar, and also the PA radar AF, respectively. Moreover, we compare the TB-based MIMO radar AF with the square-summation-form AF definition and identify two limiting cases to bound its 'clear region' in Doppler-delay domain that is free of sidelobes. Corresponding bounds for these two cases are derived, and it is shown that the bound for the worst case is inversely proportional to the number of transmitted waveforms K, whereas the bound for the best case is independent of K. The actual 'clear region' of the TB-based MIMO radar AF depends on the array configuration and is in between of the worst- and best-case bounds. We propose a TB design strategy to reduce the levels of the AF sidelobes, and show in simulations that proper design of the TB matrix leads to reduction of the relative sidelobe levels of the TB-based MIMO radar AF.