WP11: Implementation blueprint
February 12, 2010
The goal of the EISCAT_3D Design Study was to produce a complete specification and set of appropriately tested and costed design blueprints suitable to support a detailed procurement exercise as the initial task of a successor project which should construct and commission the new radar. This Work Package was tasked with producing the final technical summary of the design study, combining the outputs from all of the other Work Packages into a high-level system description.
The output from this Work Package, and indeed the conclusions of the whole four-year EISCAT_3D Design Study, can be summarised as follows:
The aims of the Design Study was essentially twofold, viz.
- to study the feasibility of constructing a third-generation incoherent-scatter research radar, using cutting-edge technology throughout and providing an order-of-magnitude improvement in temporal and spatial resolution, to replace the existing, aging EISCAT VHF and UHF systems
- to produce a detailed, costed design for such a system.
The design study did not include a task to develop the science case; this was carried out as a parallel activity by EISCAT’s Science Advisory Committee (SAC), later renamed as the Science Oversight Committee (SOC) from 1 January 2007. Members of the design study maintained close links with the science case development, and many of the ideas from SAC fed into the preparation of the EISCAT_3D Performance Specification Document (PSD).
Following extensive consultation with the scientific user community in 2004 and 2005, it was determined that only a multi-static phased array system could reach or approach the performance demanded by present and future users.
Accordingly, the target system specified in the EISCAT_3D Performance Specification Document (PSD) comprises a central active (transmit-receive) site (the “core”) and four receive-only sites, located on two approximately 250 km long baselines oriented N-S and E-W respectively.
To achieve the desired performance, the proposed system design incorporates a number of innovative, ground-breaking concepts, e.g.
- Direct-sampling receivers
- Digital time-delay beam-forming
- Multiple simultaneous beams from each receiving array
- Adaptive polarisation matching and Faraday rotation compensation
- Digital arbitrary-waveform transmitter exciter system
- Full interferometry and imaging capabilities
- Amplitude-domain data recording at full sampling rate
During the four-year study, all mission-critical technical concepts have been modelled, investigated by simulations, in critical cases also by full-scale tests, and found to be realisable. Array sizes, transmitter power levels and receiver noise performance required to reach the desired time and space resolutions have also been established. Based on this work, we propose that the target system should have the following technical characteristics:
The core will comprise
- a 120-m diameter filled circular aperture array with about 16,000 elements, laid out on an equilateral triangular grid
- a number (6 to 9) of smaller outlier receive-only arrays
The core will provide
- a half-power beamwidth of around 0.75°, i.e. comparable to that of the present EISCAT UHF
- a power-aperture product exceeding 100 GW m², i.e. an order of magnitude greater than that of the present EISCAT VHF
- grating-lobe free pattern out to 40° zenith angle
- graceful degradation in case of single-point equipment failure
Each core array element will be made up from a radiator, a dual 300+300 watt linear RF power amplifier, a high performance direct-digitising receiver and support electronics. The recommended radiator is a crossed Yagi antenna with a minimum directivity of about 7 dBi.
Two filled 8000-element receive-only arrays will be installed on each baseline at distances of respectively about 110 and about 250 km from the core. Their radiating elements will be 3- or 4-element X Yagis, essentially identical to those used in the core. The Yagis will be directed towards the core field-of-view and elevated to 45°. Outlier arrays for interferometry will also be installed.
Advanced digital beam-forming systems will allow the generation of a large number of simultaneous beams from each array, thus eliminating the time/space ambiguity plaguing all present incoherent scatter systems and making true volumetric imaging of vector quantities possible for the first time.
We have verified that a system meeting the performance requirements put forth in the EISCAT_3D Performance Specification Document could be built today, using existing technology, if cost were not an issue. Advances in semiconductor technology, signal processing and data storage between now and the time of placing a contract are expected to reduce component and subsystem costs to the point where a full-size core would cost about 60 M€ and each receive-only site 20 M€. We recommend that the member institutions of the EISCAT Scientific Association commit to funding and constructing such a radar system according to the results and guidelines given in our technical reports (EISCAT_3D Deliverables) within the next 5-7 years.
As designed, the system is highly modular and lends itself excellently to gradual expansion if funding should only be forthcoming in instalments. In this case, we recommend that in a first phase, a 5000-element, 70-m diameter core array and at least two, 1500-element receiver sites should be constructed to replace the multi-static capabilities of the present UHF radar, which are going to be lost within the next twelve months. This configuration would already exceed the performance of the current VHF system, providing a 1.3° halfpower beamwidth, a power-aperture product of about 10 GW m², and full beam steerability at the transmitter site. There are also stages beyond the outlined system involving multiple core elements arrays that could then be expanded as additional funding became available or as part of a more comprehensive initial build.
The design study team notes with pleasure that, as a result of our efforts and the hard work of the EISCAT executives, EISCAT_3D was added to the European Strategy for Research Infrastructure (ESFRI) roadmap, at its revision announced in December 2008.
This Work Package was coordinated, and the material compiled, by EISCAT Scientific Association and the Rutherford Appleton Laboratory.
EISCAT_3D Full report [12.4 MB]