Bistatic Applications Research Articles

General space‐time clutter model for multi‐channel airborne radar

Ground clutter of looking-down airborne radar is spread in Doppler because of the platform motion, and thus the interested moving targets may be masked by the ground clutter. In order to enhance the performance of clutter suppression, the clutter characteristics should be analysed in detail. So here, a general clutter model which suits for the conventional-phased array radar, multiple-input-multiple-output (MIMO) radar, and hybrid MIMO-phased array radar, all with arbitrary array shape, whether in monostatic or bistatic applications, is developed. Clutter characteristics under two typical scenarios are presented by simulation examples, simultaneously; the effectiveness of the general clutter model is demonstrated.

Effects of bistatic clutter dispersion on STAP systems

The performance of several space-time adaptive processing (STAP) approaches in bistatic applications is analysed. Specific consideration is given to the effects of bistatic clutter spectral dispersion on covariance estimation and the algorithm's resulting clutter-rejection capability. The role of adaptive processing methods capable of high performance with efficient utilisation of the required training data is emphasised. A deterministic two-dimensional (angle-Doppler) compensation technique is used as a pre-processor and is compared to the Doppler warping approach. The algorithm performance is assessed using the output signal to interference plus noise ratio (SINR) compared to that of the matched filter with a known covariance.

Measurements of signal spread and coherence on the New Jersey Shelf and in the Straits of Sicily using time-forward and time-reversed signals

Mid-frequency shallow-water propagation measurements were made at a variety sites on the New Jersey Shelf and in the Straits of Sicily during three joint trials with the SACLANTCEN (Boundary Characterization: 2000–2002) in order to extract measures of signal spread and coherence, and to evaluate the spatial robustness of time-reversal techniques. The experiments had the NRV Alliance periodically transmitting a 1-s, 200-Hz-bandwidth LFM while it traversed an arc about a stationary platform, which captured these signals and transmitted back time-forward and a set of time-reversed versions of them, as well as transmitting its own version of the original signal. Analysis of normalized matched-filter data indicate that while the two-way time spreads were generally modest, marked decorrelation was observed and that time reversal did well in reconstructing the original impulse response of the LFMs. As the various stored time-reversed versions of the original signals corresponded to different source–receiver paths, a comparison of their signal correlations provided a measure of the spatial robustness of phase conjugation in the different shelf environments. That statistically the stored time-reversed signals often did as well as in situ time-reversed signals suggests the potential for bistatic applications of phase-conjugation concepts. [Work supported by ONR.]

On the polarimetric contrast optimization

The problem considered is one of finding the polarization state of an antenna such that a power ratio due to two different objects is optimized. It is reduced to an optimization problem of two Hermitian forms which can be simultaneously diagonalized using a well-known linear-algebraic construction. The corresponding polarization vectors are found. The calculations are performed directly on the expression for the energy density of the reflected wave as a function of the transmitter polarization and are, therefore, decoupled from the receiving antenna parameters. Such decoupling is particularly convenient in bistatic applications.

Bistatic scattering matrix for a finite right-circular cylinder

The bistatic scattering matrix for a finite conducting right-circular cylinder has been derived using the geometrical theory of diffraction. Initial evaluation of the analysis showed a very good agreement between theoretical predictions and monostatic measurements of radar cross-section as a function of polarisation and aspect angle. This letter now establishes the validity of that analysis in bistatic applications and for calculating scattering phase as well as radar cross-section.