EU-SST HSTR Space Surveillance Radar — High-Power SSPA System

Project Overview

The European Union Space Surveillance and Tracking (EU-SST) programme was established to provide Europe with an autonomous capability to detect, catalogue and predict the trajectories of space debris and operational satellites in Earth orbit. As part of this initiative, the HSTR (High-power Surveillance and Tracking Radar) project deployed a new S-band radar installation in Greece. Celestia TTI was contracted to design and manufacture the high-power solid state transmitter system — the core RF subsystem responsible for generating the radar’s surveillance beam.

The Challenge

Space debris tracking radars demand exceptional performance from their transmitter subsystems. The HSTR project presented several engineering challenges that required a purpose-built solution:

High peak power in S-band: The radar specification called for 3 kW peak transmit power at S-band (2.7–3.1 GHz) with precise pulse shaping capability. This power level exceeds the output of individual semiconductor devices, requiring sophisticated power combining architectures while maintaining phase coherence across all amplifier channels.

Continuous operation duty cycle: Unlike communications SSPAs that operate with steady-state signals, surveillance radars transmit high-power pulses with duty cycles up to 25%. The transmitter system must handle rapid transitions between peak power and standby states, with thermal management designed for worst-case continuous pulsed operation over years of uninterrupted service.

Phase stability: Coherent radar processing requires exceptionally tight phase stability across the transmitter. Phase variation between pulses must remain below 2° RMS across the full operating temperature range (−10°C to +45°C ambient), demanding carefully matched amplifier modules and thermal compensation circuitry.

Environmental conditions: The installation site in Greece experiences ambient temperatures exceeding 40°C in summer, high humidity and occasional seismic activity. The transmitter enclosure required ruggedised construction with forced-air cooling dimensioned for worst-case Mediterranean conditions.

Celestia TTI’s Solution

Celestia TTI designed a modular S-band SSPA transmitter system using GaN-on-SiC device technology, optimised specifically for pulsed radar operation:

Modular GaN power amplifier rack: The transmitter comprised multiple hot-swappable SSPA modules, each delivering 500 W peak power. Celestia TTI’s proprietary waveguide combiner architecture aggregated the module outputs to achieve the required 3 kW system-level peak power with N+2 redundancy.

Pulsed-mode optimisation: Each amplifier module incorporated purpose-designed bias sequencing circuitry that optimised GaN device operating points for pulsed radar waveforms. Gate pulsing reduced average DC consumption by 40% compared to continuous-mode operation, while maintaining instantaneous RF performance specifications.

Phase-matched combining: Module-to-module phase matching was achieved through a combination of precision waveguide manufacturing (±0.5° at centre frequency) and digital pre-distortion applied at the exciter interface. The system maintained less than 1.5° RMS inter-pulse phase stability, exceeding the specification by 25%.

Thermal management: Celestia TTI’s thermal design employed direct copper heat spreaders with liquid-to-air heat exchangers, maintaining junction temperatures below 150°C under continuous 25% duty cycle operation at 45°C ambient. The cooling system was dimensioned with 30% thermal margin.

Remote monitoring: The transmitter system integrated with the radar’s central control via Celestia TTI’s M&C interface, providing real-time status monitoring, automated fault detection, and remote firmware update capability. The interface supported SNMP v3 for integration with the EU-SST network operations centre.

Results and Impact

The HSTR transmitter system was delivered on schedule and achieved first light in the planned operational window. Performance results confirmed:

Peak power: 3.15 kW measured at the antenna feed point, exceeding the 3 kW specification by 5%. Power variation across the operating bandwidth remained within ±0.3 dB.

Phase stability: 1.4° RMS inter-pulse phase stability measured over 24-hour operational periods — 30% better than the 2° RMS requirement. This directly improved the radar’s detection sensitivity for small debris objects (diameter <10 cm in LEO).

Reliability: Over the initial 12-month operational period, the transmitter achieved 99.95% availability with zero unplanned outages. Two scheduled maintenance windows (4 hours each) were used for firmware updates — both performed remotely without on-site personnel.

Power efficiency: System-level DC-to-RF efficiency of 42% under operational pulsed conditions, reducing the radar site’s electrical infrastructure requirements and associated operating costs compared to the original klystron-based transmitter concept.

Technology Deployed

• GaN Solid State Power Amplifiers (SSPAs) — S-band pulsed radar modules
• Antenna Systems — RF feed integration
• Ground Station Systems — M&C and system integration
• Government & Defence Solutions