# S-Band Doppler Wave Radar System
## 3 MORSE Radar System
### Radar System Architecture  
Based on a LXI(LAN eXtensions for Instrumentation) bus, the overall design of MORSE is guided by modularity. All devices involved in MORSE are solid state. The whole system consists of small-scale wideband antennas, high-power switches, power amplifiers, an RF analog front end, a high speed digital receiver, a synchronizing controller, a frequency synthesizer, Ethernet switches and a host computer. The whole system architecture is shown in Figure 2.  
The working process of MORSE is as follows. First, after the initialization of the system, the software installed on the computer generates a certain set of waveform parameters based on the radar installation environment and user requirements. Then, the parameters are sent to the synchronizing controller and frequency synthesizer via an Ethernet connection to generate synchronizing and RF signals. The RF signals are sent to the transmitter while the synchronizing signals coordinate the whole system. After the amplification, the RF signals are emitted onto the ocean surface with a low grazing angle by a selected antenna. When the echoes arrive at the radar, they are received by the same antenna and then routed to the RF analog front end for down-conversion. After that, the RF signals are converted into IF signals. Then, the IF signals are sent to digital receivers to generated IQ baseband signals. Finally, these base band signals are fed to the host computer to analyze and deduce the wave parameters. \begin{table}
\begin{tabular}{l c c c} \hline \multirow{2}{*}{**Wave Height Spectrum**} & **Range** & **Resolution** & **Update Time** \\ \cline{2-4}  & **0.01–0.5 Hz, 0–360\({}^{\circ}\)** & **0.01 Hz/10\({}^{\circ}\)** & **2.5 min/Sector, 3 min/Avg** \\ \hline
**Wave Parameters** & **Range** & **Resolution** & **MSE** \\ \hline Wave Height & 0–30 m * & 0.1 m & \(\pm\)5\% \\ Wave Period & 3–30 s & 0.1 s & \(\pm\)5\% \\ Wave Direction & 0–360\({}^{\circ}\) & 1\({}^{\circ}\) & \(\pm\)7\% \\ \hline Range Resolution & & 5/7.5/15 m Variable & \\ \hline Detecting Range & & 5 km & \\ \hline
**Polarization** & **Wavelength** & **Antenna Beam Width** & **Doppler Speed Range** \\ \hline VV & 10.5 cm & 30\({}^{\circ}\) & \(\pm\)8.6 m * \\ \hline \end{tabular}
* These parameters vary with different radar waveform parameters.  
\end{table} 
Table 1: Microwave Ocean Remote SEnsor (MORSE) radar system specifics. FMICW (Frequency Modulated Interrupted Continuous Wave) is the waveform that is used by MORSE, and it achieves high range resolution, a long detecting range and the time division multiplexing mode for antennas. The operating frequency of MORSE ranges from 2.75 GHz to 2.95 GHz. A relatively lower operating frequency (compared with X band) deduces the impact caused by the water in the air, which means that MORSE can operate in rainy weather. Because of the pulse compression technique, MORSE uses a small transmitting power of 5 Watts. The frequency sweeping bandwidth is variable among 10 MHz, 20 MHz and 30 MHz, which results in a corresponding range resolution of 15 m, 7.5 m, and 5 m, respectively. The duration of a single frequency sweeping is 4096 \(\upmu\)s and the interval between two frequency sweeping is 16 \(\upmu\)s. In addition, a single frequency sweep consists of 128 transmitting pulses with a duty cycle near 50%. Therefore, a Doppler dataset consists of 128 echoes. To obtain the full directional wave height spectra, MORSE is equipped with six standard horn-shaped antennas. The shape and placement of antennas are illustrated in Figure 3. These antennas have horizontal and vertical beam widths of 30 degrees and 25 degrees respectively and 15 dB gain. Because the FMICW is adopted by MORSE, these antennas function in time division multiplexing mode. The detecting range could reach 1.5 km with a maximum transmitting power of 5 watts. The antennas cooperate in an electronic scanning mode, and every antenna covers an area of 30 degrees.