Optimum Design of Broadband Passive Sonar

In this paper, a new design principle is proposed for the frontend-hardware (FEHW) chain of broadband passive sonars. This principle embraces the ultimate purpose of broadband passive sonars, which is to maximize the detection of passive targets. FEHW chains were conventionally designed as noise whiteners to guarantee the data bit dynamic range in analog-to-digital converters (ADCs) rather than being optimized for target detection. The conventional design was due to the restriction of electronic hardware in the early days and is still used in modern broadband passive sonars even with the great relaxation of hardware restriction today. The proposed principle optimizes the frequency response function (FRF) of FEHW chains by means of maximizing the output signal-to-noise ratio (SNR). The optimal FRF obtained using the design principle counts for the spectral characteristics of the entire sonar system (hydrophones, FEHW chain, and beamformer) as well as those of broadband passive sources and background noise. It turns out that maximizing the SNR is equivalent to maximizing the so-called deflection ratio (DR) in broadband passive sonars, but the former is directly used as a statistical test in the sonar engineering. The relationship between the optimal FRF and the Eckart filter is also discussed, with both of them counting for spectral shapes at their input, but with the former also counting for the change of spectral shapes after its output. Design examples are included to demonstrate the merit of the optimal FRF over the noise whitener with both theoretical and simulation results.