European Space Agency

PAASAR - Phased Array Antenna for Search and Rescue

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Objectives

The PAASAR (Phased Array Antenna for Search and Rescue) Consortium has developed a novel technology for the monitoring of Search and Rescue (SAR) signals: a Phased Array Antenna (PAA) capable of receiving the signals of at least 4 and up to as many as 20+ GNSS/SAR (Galileo, GPS and/or GLONASS) satellites in view with a single antenna array, allowing for the simultaneous reception of the SAR signals relayed by all the satellites in view. The goal is to create a Phased Array Antenna Monitoring Facility to replace the need for traditional MEOLUT facilities requiring multiple tracking dish antennas for reception of SAR signals from multiple spacecraft.
The prime objectives of the PAASAR project is to:
  1. Implement a prototype PAA consisting of 50 antenna elements
  2. Achieve beam forming to at least 4 satellites, and more if available
  3. Acquire SAR/Galileo signal from those satellites
  4. Verification and Validation of the prototype system
  5. MEOLUT design and Business Case development
The development of a SAR receiver and localisation determination is not included in this project.
 
All the prime objectives of the project were achieved.
 
The accuracy of the system is dependent on the number of satellites that can be tracked simultaneously. Conventional systems are restricted in the number of satellites that can be tracked by the number of dishes. The PAASAR Proof of Concept (POC) system is a single, compact phased array composed of 50 small antennas that are combined in the digital domain to multiple independent beams. This will allow for simultaneous tracking of all satellites in view with a single, stationary antenna array, and thus has no limitation in the number of satellites that can be tracked simultaneously. Therefore the PAASAR system provides a better performance than conventional systems by maximizing the # of tracked satellites and processing them on one location. Further advantages of using a solid-state antenna instead of multiple steerable dish antennas includes a smaller footprint, no re-pointing time (satellite hand-over) and less maintenance costs therefore providing in a more reliable system. Additionally the PAASAR system is able to calibrate itself continuously.

The developed PAASAR POC (Figures 1 and 2) shows all advantages of a phased array for SAR able to track multiple satellites and calibrate itself in order to provide increased performance over existing systems.

The copyright in this information and webpage is vested in Science & Technology B.V. on behalf of the PAASAR consortium. This information may only be reproduced in whole or in part, or stored in a retrieval system, or transmitted in any form, or by any means electronic, mechanical, photocopying or otherwise, either with the prior permission Science & Technology B.V. and the PAASAR consortium in accordance with the terms of ESTEC Contract no 4000108533/13/NL/US.

Challenges

During the design and development phase of the project the baseline PAASAR requirements and design have been developed, extended with a requirement baseline for a full Phased Array MEOLUT station. The following key issues for developing and system integration of the PAASAR prototype have been identified, addressed and implemented in in final PAASAR POC:
  • Global beam forming algorithms
  • Clock distribution system
  • Calibration method: Phase and Amplitude calibration on satellite signal itself.
  • Digital stream distribution system
  • Control system
  • System health management system
  • EMC environmental analysis

Benefits

The PAASAR concept provides major benefits with respect to a more traditional (multi dish) MEOLUT. The principal benefits of a full PAASAR phased array are:
  1. Technical: maximizing the number of tracked satellites from a single MEOLUT (no limitation; all spacecraft in view): high standalone performance;
  2. Technical: Integrated SAR Receiver covering: SAR/Galileo + DASS + SAR/GLONASS: total turn key solution;
  3. Technical: processing many satellites on one location, i.e. working with TDOA (Time Difference of Arrival) rather than TOA and avoiding the uncertainties linked with TOA determination and sharing: high standalone performance; 
  4. Technical: Since all satellites can be tracked, no re-pointing (satellite hand-over) time, which is a major issue with dishes: high availability;
  5. Reliability: No moving parts: reliable antenna infrastructure;
  6. Reliability: Graceful decay: full PAASAR has 550 antennas and is therefore not sensitive to malfunction of a few antennas: increased reliability;
  7. Maintainability: no moving parts, self-calibration, graceful decay imply low maintenance Local user terminal in (remote) locations: reduced maintenance costs;
  8. Logistics: one relatively small phased array antenna replaces multiple tracking dishes (a normal MEOLUT site has 4): small physical footprint;
  9. Industrial policy: gives European industry a competitive edge in this niche market;
  10. Support & Service: technical knowhow of all systems available for customer support.
  11. Cost: savings of factor 3 in cost-coverage w.r.t. current solutions, due to its better performance.
  12. Spin off: apart from further developing the current POC into a full PAA MEOLUT there are, owing to high degree of centralsymmetry of the array, possibilities for additional spin-off technology, such as optimizing the system for Galileo/GPS navigation signal reception and processing (anti spoofing), and many other.

Features

A graphical representation of a full MEOLUT is given in Figure 5.

Figure 5 MEOLUT block diagram


click for larger image

The PAASAR project has prototyped and validated the Front-end Set
(FES) of a MEOLUT utilizing phase array technology. The FES consists
of the following elements:
  • The Radio Frequency components (Antenna, Filtering, ADC) consisting of 5 antenna tiles each containing 10 antenna elements; constituting 50 antennas in total.
  • The Digital Beam Forming (DBF) processor, responsible for the electronic steering of the antenna beams.
  • The Time and Frequency Reference (TFR) component, responsible for providing input to the local oscillators.
  • The Antenna Controller (AC), responsible for the control of the Front-End Set.
The FES interfaces with the following subsystems:
  • Core Processor Set (CPS): for the exchange of tracking data and Monitoring and Control (M&C) data.
  • Receiver Set (RS): delivering the SAR streams to the Receiver Processors (RP). Each RP digitally tracks individual satellite signals. The Master RP combines these individual processed signals and determines the position of distress.

The implemented features of the PAASAR POC is indicated in Figure 6 and Figure 7.

PAASAR POC outline

PAASAR POC System overview

 

Target Users

The following different types of customers are evident:
  • MEOLUT and LEOLUT operators
  • Cospas-Sarsat member states that do not yet operate a GEOLUT or MEOLUT
  • Phased Array Technology (antenna) procurement entities
  • Defense & Security entities
  • Monitoring & Telecomunications operators

 

Needs

Galileo will add a substantial capability to the SAR infrastructure currently provided by Cospas-Sarsat MEOSAR (Medium Earth Orbit Search and Rescue) system. Therefore, a large number of MEOLUTs are required in the near future. An expensive element of a MEOLUT is its antenna system. Nowadays, the antenna system of a MEOLUT comprises at least 4-6 large dish antennas that need to mechanically track the individual satellites. The operation and maintenance of such an antenna system is challenging.
 
For the implementation of the European Ground Segment of SAR/Galileo ESA has procured 3 times 4-dish antenna MEOLUTs. These 12 antennas are needed to create sufficient coverage of Europe. However, even with these 12 antennas the currently defined MEOSAR Implementation Plan (MIP) target requirements cannot be met. It is expected that with a PAASAR system, the performance of the system is significantly improved. PAASAR provides phased array antenna technology to easily match the
current system performance.
 
On the operational aspect, it is a challenge to find a site where 4 or more tracking dish antennas can be installed without interfering each other. Also the scheduling of these antennas to make sure that the optimal satellites (with respect to e.g. geometry) are tracked is not an easy task. It can take up to 1 minute to reassign an antenna to another satellite. Even then, there is a risk that critical signals are lost because not all satellites can be tracked simultaneously with the available number of antennas.
 
Installation of a grid of dish antennas can be costly. Since the LEOSAR system will be phased out when the MEOSAR systems become operational, it would be economically beneficial if LEOLUT sites could be re-used. Since LEOLUTs use only one dish antenna, it is typically not possible to host 4 dish antennas on the same site. Additionally, since the maintenance of tracking dish antennas can be expensive, there is a need to reduce the running cost of the MEOSAR system.
 
To summarize, there is a need for a PAASAR MEOLUT to:
  • track as many satellites simultaneously as possible,
  • have a small physical footprint,
  • have reliable antenna infrastructure, and
  • have a low maintenance cost
The Phased Array Antenna technology has a multitude of application areas to replace conventional antenna systems and architectures given its superior performance and lower cost. The need for high performance phased arrays for large sky coverage monitoring of RF emitting entities (eg. spacecraft) is evident.
 

Service Concept

With the Phased Array Antenna (PAA) approach demonstrated in this project we are able to improve the currently available MEOLUT performance and at the same time to lower the cost. 
 
The improvement in performance is based on the ability to track as more satellites simultaneously with a phased array compared to a traditional MEOLUT, providing a reliable and technical optimal solution. The lower cost is based on the fact that the cost of a PAASAR type MEOLUT is lower than the currently available MEOLUT solution.
 

Space Added Value

Phased Array Antenna approach is a technological breakthrough by allowing the system to track at least 12 satellites from a single base station, significantly increasing the performance of the system. Since the system consists of a single sphere of about 2.5 m diameter, it has a relative small footprint compared to a dish array. This would facilitate the replacements of LEOLUTs, because PAASAR enables a solution where the site infrastructure can be reused and thus decreasing cost significantly. Furthermore the maintenance cost of this solution will be lower than for a dish network since it is a solid-state solution whereas the traditional antennas are electro-mechanical.
 
The PAA technology by itself, and its performance, provide an additional added value in the ground station and user terminal market. The PAA technology can be applied to a multitude of space ground segment applications where complete sky coverage with a single station is required or localization of RF emitting entities.

Plan

The baseline PAASAR requirements and design have been developed in the first (design) phase of the PAASAR Project, extended with a requirements baseline for a full MEOLUT. During the following development phase existing available (sub)system components are combined and the algorithms for Beam Forming and Calibration are developed, and in parallel the development and design of all PAASAR components/features to meet the program objectives has taken place. The PAASAR production plan has encompasses a structured build-up to the final functional PAASAR POC, in sequential order:

  1. PAASAR Early Development and Test Setup: controlled signal, not over–the-air
  2. PAASAR Development and Test Setup: 1 antenna tile, over-the-air signals
  3. PAASAR Final Proof of Concept (POC): 5 antenna tiles, over-theair signals

The final functional PAASAR POC was tested and validated for final acceptance. In addition an antenna characterization was performed. A field test of the PAASAR POC also supported the successful verification and acceptance of the PAASAR POC.

Current status

The project has started in July 2013 and finished in July 2016.

Contacts

Status date

Friday, February 24, 2017 - 10:32