# Development of the Romanian Radar Sensor for Space Surveillance and Tracking Activities +
## 3 Cheia Space Surveillance and Tracking Radar Design Overview
The design of the new radar sensor had to take into account the existing antenna characteristics [19]:  
* The two 32 m diameter parabolic Cassegrain beam-waveguide-type antennas were initially designed for large bandwidth operation in the range 3.6 to 6.4 GHz. The antenna main reflector, subreflector, and feed waveguide were improved to achieve the largest possible gain and the best parameters in this bandwidth. The antenna analysis determined that any modification of the antenna system would incur high costs and likely lower the antenna merit factor (G/T ratio); the conclusion was to employ them without any customization. Within the C band, the International Telecommunication Union (ITU) allocates for Radiolocation services in Region 1 the sub-band of 5250-5850 GHz (ITU Radio Regulations, Edition 2012). Investigations were performed on the composite feed-antenna assembly in this sub-band, and the results showed a very good voltage standing wave ratio (VSWR) of 1.02 at 5840 GHz. Based on the antenna and antenna feeder system measurements, the optimal 20 MHz bandwidth was determined as 5830-5850 GHz; therefore, this bandwidth was selected for the operation of the new Cheia tracking radar. * The originally designed transmitted-power-handling capability of the antennas in the 6 GHz band using the original structure of the feed was limited to 10 kW CW. Radar modelling showed that 2.5 kW of CW-transmitted power provided satisfactory dimensions of the discovered space objects. In the CW mode of operation, the radar would be able to detect and track objects with dimensions of over 40 cm in LEO at a maximum of 2000 km altitude. In the pulsed mode, using a duty cycle of 30% would increase the dimensions of discovered objects by a factor of three. * The original antenna positioning system provided a positioning and slewing velocities limited to 0.3\({}^{\circ}\)/s on both axes, which was considered to be insufficient for tracking fast space objects. It was determined that the technically obsolete existing system should be reformed and upgraded by replacing main parts of the driving mechanism in order to increase the tracking and slewing speeds to 1.0\({}^{\circ}\)/s on each axis. * An analysis of the results to be achieved in terms of separation between objects close to each other in orbit showed that, as the antenna beamwidth at the selected operating frequency was 0.11\({}^{\circ}\), the angular resolution was limited to 0.06\({}^{\circ}\). Even if the radar system would not use monopulse technology to improve the angular accuracy, taking into account the limited antenna positioning and slewing speed, the radar would provide good results in tracking LEO objects based on TLE data. * The tracked radar targets must be located within a limited visibility domain to be detected. Each antenna has an azimuth scanning range of \(\pm\)170\({}^{\circ}\) around south and 0\({}^{\circ}\) to 92\({}^{\circ}\) in elevation. Additional limitations that are due to existing buildings, installations, trees, or other natural terrain features in the close vicinity of the antennas were determined during in situ tests.