# Development of the Romanian Radar Sensor for Space Surveillance and Tracking Activities +
## 3 Cheia Space Surveillance and Tracking Radar Design Overview
It was considered to be a great advantage because the cost of the antenna system represents an important portion of the total budget of a radar system. Based on the site constraints, the radar possible architectures are presented below[19]:  
* C-band quasi-monostatic fadar: In this architecture, both Cheia antennas are retrofitted. One of the Cheia antennas performs transmission on one circular polarization, while the second antenna performs reception on the opposite polarization. This is a complex solution that eliminates the need for the RF switch in front of the LNA and offers a significant reduction of the power amplifier noise based on the very low coupling between the two antennas. This increases the radar's sensitivity and, furthermore, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Specification** & **Antenna Cheia 1** & **Antenna Cheia 2** \\ \hline Model & Intelsat Standard A Earth Station \\ Manufacturer & Nippon Electric Co., Ltd. (NEC), Tokyo, Japan \\ Diameter & & 32 m \\ Year of installation & 1976 & 1979 \\ Satellite originally used & Intelsat IS—905 at 335.5\({}^{\circ}\) E & Intelsat IS—904 at 60.0\({}^{\circ}\) E \\ Total weight & 309 ton & 260 ton \\ Effective gain at feed & \textgreater{}63 dB & \textgreater{}63 dB \\ Noise temperature \(\varepsilon=20^{\circ}\) & 37.0 & 36.5 \\ Bandwidth & & 3.6–6.4 GHz \\ Isolation between antenna & & \textgreater{}93 dB \\ sidelobes & & \\ Polarization & Dual circular \\ Polarization isolation & & 30 dB \\ Azimuth scanning domain & \(-170^{\circ}\) to +170\({}^{\circ}\) relative S \\ Elevation scanning domain & & \(0^{\circ}\)–92\({}^{\circ}\) \\ Tracking speed & & \(0.3^{\circ}\)/s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main technical specifications of antennas in Cheia Communications Center. Figure 3: The two antennas at Cheia Satellite Communications Center. allows operation in the CW mode, as well as the pulsed mode. Operation in the CW mode could increase the radar's sensitivity or allow a reduction in the transmitted power. * C-band monostatic: In this architecture, only one of the Cheia antennas is retrofitted. It performs both transmission and reception. The radar transmits to the LHCP port and receives at the RHCP port of the same antenna. The receiving chain must use an RF switch in front of the LNA, and the transmitting chain PA must have a blanking facility so that its final stages are blocked during reception in order to reduce the power-amplifier-induced noise. The presence of the RF switch, as well as the noise leaked from the transmitter's PA, strongly reduces the radar's sensitivity. The radar is only be able to use the pulsed mode. * C-band bistatic: In this architecture, only one of the Cheia antennas is retrofitted. It performs transmission, while the reception sites must be placed at another site, probably outside Romania. Several reception sites can be used simultaneously. This architecture is, in principle, the easiest to implement, but it does not represent a truly viable alternative due to its nonindependence. Furthermore, either of the previous two solutions can be used in this configuration if required, for example, in international observation campaigns. All of the three proposed architectures require an upgrading or a redesigning of the antenna positioning system. To increase the radar's tracking capabilities, the redesigning of the antenna positioning system was considered of utmost importance. From the point of view of choosing the modulation of probing signals, the availability of two separate operational antennas allows the implementation of a continuous wave (CW) radar, either frequency-modulated or unmodulated, using both antennas or a pulsed radar that employs just a single antenna. A mixed design of CW and pulsed radars working with the two antennas was also considered as a possibility.