Miniaturised Photonics Enabled Next Generation SAR

Project Information

RETINA

Grant agreement ID: 821943

DOI

10.3030/821943

Project closed

EC signature date 22 October 2018

Start date 1 November 2018

End date 31 January 2022

Funded under

• INDUSTRIAL LEADERSHIP - Leadership in enabling and industrial technologies – Space

Total cost

€ 2 991 088,25

EU contribution

€ 2 991 088,25

Coordinated by

DAS PHOTONICS SL
Spain

Periodic Reporting for period 2 - RETINA (Miniaturised Photonics Enabled Next Generation SAR)

Reporting period: 2020-05-01 to 2022-01-31

Summary of the context and overall objectives of the project

There is a natural trade-off between spacecraft size and functionality in all current satellite applications, independently of orbit and mission. Therefore, advances in both miniaturization and integration technologies are required to increase satellites’ lifetime and performance, simultaneously reducing their cost. In case of the next generation of Earth Observation (EO) satellites, one of the key development areas is synthetic aperture radar (SAR) antennas, where expected progress will be to increase the operating bandwidth - requiring, for instance wideband true-time delay (TTD) beamformers - and miniaturization, drastically reducing the mass and volume compared to current implementations.
The use of photonic integrated circuits (PIC) technology in the beamforming network, in combination with an optical fibre harness, are key enabling technologies for future SAR instruments.
RETINA has performed the necessary design and research to demonstrate a compact, suitable for space, broadband frequency operation multi-beam photonic beamformer network (BFN) with centralized processing for Next Generation SAR improving the figures of size, mass, power consumption and bandwidth processing.
The RETINA objectives have been:
• Development of a multi carrier laser with space-grade specifications reducing the power consumption associated to the thermal cooling by a factor of 3 per laser.
• The design of photonic integrated circuits (PIC) designs in silicon-nitride technology implementing a true-time delay (TTD) BFN compatible with large antennas requirements.
• Array antenna element (AAE) design at X-band, amplification section and opto/electronic converters for integration in the AAE.
• Design and manufacturing of a TRL6 small footprint broadband beam optical transmitter (BOT) module up to Ka-band including RF and optical amplification and modulation.
• Design and manufacturing of a TRL6 compact antenna optical receiver (AOR) in X-band with a co-package of amplifiers, optical receiver, and AAE.
• Design, manufacturing, and supply of photoreceivers in the X band with optimized footprint and self-stabilized gain vs temperature. The photodiode within the photoreceiver will cover up to Ka-band to address the objective of broadband frequency operation.
• Flexible beam-shaping and beam-switching in a PIC-based optical BFN, through multi-orthogonal beam synthesis.
• To demonstrate the flexibility of beam-shaping and beam-switching in a PIC-based optical beamformer by the combination of a fixed beamformer network generating massive orthogonal beams with a co-integrated switching network to perform beam-shaping by multi-orthogonal beam synthesis. The level of flexibility should be comparable with a traditional beamforming network based on phase and amplitude control with an order of magnitude less complexity.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first period the main activities were focused on the identification of the application scenarios and its top-level requirements, the system definition and the design of the subsystems integrating the multi-beam photonic beamformer.
Different application scenarios were identified; the baseline scenarios include one related to big platforms, one to small platforms and one to satellites in formation, in order to cover as many applications as possible.
The design of the different subsystems was initiated in the first period, which included important parts of the system as the PIC as part of the BFN, the photoreceivers & the AAE as part of the AOR, a laser array module and the BOT.
During the second period, the main activities were focused on the detailed design and manufacturing of the different modules/devices to achieve a functional demonstrator which was designed to be representative of a full-scale system according with the application scenarios and specifications identified during the first Period.
RETINA main achievements have been:
• Design, fabrication and test of a:
- TRL 7 1x8 sub-array EQM model and TRL6 4x8 BB model at X-band
- TRL4 X-band photoreceiver with optimized footprint and self-stabilized gain vs temperature.
- BFN PIC based on Si3N4 (ultra-low-loss optical waveguides, < 0.1 dB/cm) capable to control 8 beams, providing 64 true-time delays, i.e 8 pointing angles form 20deg to -20deg.
- TRL6 small footprint broadband BOT module up to Ka-band including RF and optical amplification and modulation.
- TRL4 compact AOR in X-band with a co-package of amplifiers, optical receiver and antenna arrays elements.
• Design and validation of an efficient fibre array-to-chip assembly process with a high number of input/output ports.
• Demonstration at bread-board level of a multi carrier laser based on spectral slicing of a mode-locked laser. Estimated reduction in power consumption by a factor of 3.3 comparing with stand-alone BOTs with DFB CW lasers.
• Development and functional validation of a demonstrator representative of a full-scale system confirming the multibeam capability and the suitability of the TTD OBFN for SAR applications.
The project results have been reported in 12 events, including two conferences and a journal publication. Additionally, several communications actions have been carried out by the project's public website and communication channels (Linkedin, Twitter and Research Gate) to reach the widest audience possible and maximize the awareness of the project impacts.
The project exploitation strategy includes a commonly agreed approach within the consortium to use the RETINA results and development plan towards the final product.
BFN is a signal processing technique that can be used for many types of antenna arrays in transmission or reception. Therefore, the potential market is huge and growing, considering both EO and SATCOM.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The photonic technology developed in RETINA will have application to EO but also to much greater market of SATCOM, as well as in other sectors, such as antenna remoting or wideband receivers for spectral monitoring, SAR or Beamforming and LO signal distribution in large installations in the ground segment e.g. for radio telescopes, ground stations or protection of critical infrastructures.
The current competition in the SAR field is showing sensors with everyday more accurate resolution (down to 0.2m) underlining the importance of a unit that enables large range and angular resolutions. This trend imposes strong requirements in the today’s RF and antenna technology since larger antennas means complex, bulky, difficult to route RF harness to transport the signal from/to the beamforming to/from antenna, and strong mechanical and thermal requirements, especially when in-orbit deployable antenna structures are required. Additionally, larger bandwidths associated with larger antennas and scanning angles requires TTD beamforming, resulting in bulky and complex solutions (and very limited for lower frequencies – larger delays) impacting directly in the size, mass and integration cost.
The expected impact of EO in the EU society is major, through jobs creation and by impacting in many ways in the citizens’ life, by exploiting the vast amount, pervasive and diverse data obtained from EO satellites. RETINA will contribute to this scenario by providing a very flexible high-performance SAR antenna for EO that will allow the optimisation of missions and satellite payloads, thanks to the technological features and SWaP reduction, which has a direct impact to EO satellites usability and duration.

Integrated Photoreceiver

1x8 sub-array building blocks antenna array element at X-band

PIC OBFN

4x8 DRA antenna panel