*4.1. Introduction of the Coast–Ship Bistatic HFSWR*

A coast–ship HFSWR experiment was conducted in July 2019 using two Compact Over-horizon Radar for Marine Surveillance HFSWR systems (CORMS). One radar was located on the coast near the city of Weihai (Shandong Province, China; Figure 16), and the other was deployed on the M/V *Shun Chang 28*. The experimental area comprised the open-water area off the coast near Weihai. The experiment was divided into two periods. The first period, from 09:18:00 to 10:07:00 local time, is indicated by the green line in Figure 16. During this period, measured experimental data using the CTSR bistatic HFSWR system were obtained. The second period, from 10:50:00 to 14:40:00 local time, is indicated by the red dashed line in Figure 16. During this period, measured experimental data using the STCR bistatic HFSWR system were acquired. The velocity and heading of the shipborne platform during the experiment are shown in Figure 17. Here, the heading is given clockwise relative to north.

**Figure 16.** Location of coast-based radar station and navigation route of shipborne platform.

**Figure 17.** Velocity and heading of shipborne platform.

The CORMS HFSWR system used in the experiment had a solid-state transmitter with maximum peak power of 500 W. The output power of the transmitter could be adjusted continuously. A linear frequency-modulated interrupting continuous wave signal was used, and a double-whip transmitter antenna at the height of 11 m transmitted an omnidirectional pattern. The HF radar receiver was fully digitalized with eight channels, although only five channels were used in the experiment. Each element of the receiving array was a small magnetic cylindrical antenna (length: 0.5 m, diameter: 0.4 m), suitable for shipborne platforms. The radar frequency was 4.7 MHz and the bandwidth was 60 KHz.

In the coast–ship bistatic HFSWR experiment, synchronous transmitter–receiver monostatic HFSWR data were also obtained using a system collocated with the transmitter station. The transmitters and receivers of both radar systems, as well as the two radars, were synchronized using GPS. Both the shore-based receiving array and the shipborne receiving array were composed of five elements but with different element spacing. Owing to the limitation that the length of the shipborne platform was only 88 m, the available array aperture of the shipborne receiving array was only 62 m and its antenna spacing was 15.5 m. Conversely, the antenna spacing of the shore-based receiving array was 29 m, and the array aperture was 116 m, i.e., >100 m. Besides, motion attitude information of the shipborne platform was recorded synchronously using the shipborne inertial navigation system. The measured radar echo spectrum data of the coast–ship bistatic HFSWR system obtained in the experiment are discussed in the following section.
