*3.5. Simulation 5: Simulated Space–Time Distribution for Di*ff*erent Elliptical Eccentricity*

The space–time distribution of the Doppler frequency shift of the first-order sea clutter and the simulation results of the first-order sea clutter spectrum for a CTSR bistatic HFSWR at different elliptical eccentricity are shown in Figures 12–15, respectively. Here, we set the frequency as 4.7 MHz, heading ϕ*<sup>R</sup>* = 48.9◦, wind direction as 90◦, and velocity *vT* = 18.5 km/h (approximately 10 knots) when ship was navigating.

**Figure 12.** Space–time distribution of the Doppler frequency shift of the first-order sea clutter for a CTSR bistatic HFSWR when the ship was anchored: (**a**) e = 0.33 and (**b**) e = 0.7.

**Figure 13.** Simulation results of the first-order sea clutter spectrum for a CTSR bistatic HFSWR when the ship was anchored: (**a**) e = 0.33 and (**b**) e = 0.7.

**Figure 14.** Space–time distribution of the Doppler frequency shift of the first-order sea clutter for a CTSR bistatic HFSWR when the ship was navigating: (**a**) e = 0.33 and (**b**) e = 0.7.

**Figure 15.** Simulation results of the first-order sea clutter spectrum for a CTSR bistatic HFSWR when the ship was navigating: (**a**) e = 0.33 and (**b**) e = 0.7.

As can be seen from Figures 12–15, the first-order sea clutter spectrum of e = 0.7 was wider than that of e = 0.33 when the heading ϕ*<sup>R</sup>* = 48.9◦ in the anchored case, whereas the width of the sea clutter was largely unchanged under different elliptical eccentricity when the ship was navigating with the velocity of 18.5 km/h.

Based on analysis of simulations of the first-order sea clutter spectrum of a coast–ship bistatic HFSWR in navigational state, the range of the detection blind area caused by broadening of the first-order sea clutter spectrum and its influence on target detection can be understood and overcome. The findings could be used to develop appropriate strategies for actual target detection, such as adopting the most suitable navigational speed and heading. For a CTSR bistatic HFSWR system, the principal axis angle of the receiving array and the Doppler frequency shift of the detected target can be changed by adjusting the heading of the platform without changing the platform position. In this way, a moving target signal submerged within each area of sea clutter could be separated from the range of the blind area or adjusted to the side of the sea clutter blind area with less influence. It should be noted that such strategies do not apply to STCR bistatic HFSWR systems.
