Monday, 21 February 2011

EISCAT-Kiruna Demonstrator Array

KAIRA is not the only project working on the issue of antenna and receiver technology for EISCAT_3D. In addition, there is the so-called 'demonstrator-array', which is located at the EISCAT receiver station at Kiruna, Sweden. I contacted Lars-Göran Vanhainen from the Kiruna site and he explained what this project is all about.

The demonstrator array is a phased array of 48 Yagi antennas, arranged in a 4×12 grid. It operates at VHF frequencies and is capable of detecting signals from the VHF transmitter in Tromsø. The photograph from Lars-Göran shows these Yagi antennas in the foreground. The large dish behind the control building is the 32-metre receiver antenna of the existing EISCAT system.

The demonstrator array was mainly built to be an experimental test bed for the digital receivers and digital beam steering that was proposed in the EISCAT_3D design study. Although the design study has now been concluded, the prototype work is being continued.

The array has now been equipped with fixed delay co-axial beam steering. As it is set up, the array points towards Tromsø at an elevation of 55 degrees, which corresponds to an altitude of 300 km above the Tromsø VHF transmitter. Successful tests have been conducted and bi-static VHF data has been recorded.

Work is now in progress to tilt down the beam to 100 km above Tromsø. The 'beam' is the direction in which a radio receiver array is sensitive. It is a concept like the beam of a search-light, but in reverse; receiving, rather than transmitting.

The objective is to modify the array to be able to do E-region measurements and VHF bi-static studies of meteors and PMSE. These phenomena are both coherent and much stronger than the incoherent scattering from the ambient ionosphere, so even a decrease of the total gain due to the change in the array geometry from optimal should not have an great impact on the measurements in mind.

We'll be talking a lot more about these crucial experiments in future web-log posts!

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