The Radio and Space Plasma Physics Group (RSPPG) of the University of Leicester (UK) have been awarded a research grant by PPARC (Particle Physics and Astronomy Research Council) to construct a major new radar facility, SPEAR, on Svalbard. This revolutionary new radar system is designed to carry out research into the Earth's upper atmosphere and magnetosphere, in the vicinity of the polar cap.
SPEAR will probe the complicated processes associated with the interaction of the Solar atmosphere and the ionised upper atmosphere of the Earth. Direct coupling between these two regions is especially strong and dynamic in the Earth's polar cap, where magnetic field lines stretch out into space. SPEAR will operate as a conventional radar to image the dynamics of the plasma above the polar cap in three-dimensions, and will also create artificial density irregularities in the ionospheric plasma which will act as artificial targets for other coherent backscatter radars, such as the Leicester CUTLASS system, when no natural auroral targets are present.
In addition, SPEAR will be capable of stimulating electromagnetic ULF (Ultra Low Frequency) waves, which will be injected into the Earth's magnetosphere so that its structure can probed actively. Furthermore, these waves will be efficiently trapped on magnetic field lines and will be detected on board spacecraft such as Cluster. This will lead to a great improvement in the quality of co-ordinated satellite/ground based experiments, by identifying common field lines along which the Solar wind and the terrestrial atmosphere communicate.
This research will help us answer some key questions about our aerospace environment, such as, whether solar cycle effects do contribute to climate change on Earth, as has been recently suggested by scientists from the RSPP group. SPEAR, which also has the support of scientists from Scandinavia, Germany and the USA, will be at the forefront of the international effort in space research well into the new century.
The SPEAR system will initially consists of a 6x4 array of full wave, crossed dipoles designed to operate at 5.0 MHz. By designing these antennas as rhombically broadened dipoles, it is possible to achieve an operational bandwidth of approximately +/-20% with a gain of approx. 25 dB. Each antenna is connected to a 4 kW transmitter capable of operating continuously. By adjusting the relative phase of pairs of transmitters driving the crossed dipoles, it is possible to adjust the polarisation and direction of the radiated signal.
Transmitters will be grouped in eights and housed in a modified shipping container. Each container will form a single unit feeding a 2x2 sub array. The complete system consists of 6 separate units and will be capable of extension to the final 6x6 configuration by the addition of three further 2x2 units. Each individual transmitter will contain its own power supply and control unit to provide the ability to operate in the case of failure of a transmitter or antenna making the system suitable for remote operation. Each transmitter container contains a common signal generation unit made up of DDS units allowing individual phase control of the signal at each antenna. This allows the transmit beam to be steered to any position although the antenna design limits the useful pointing direction to +/- 20 degrees from the zenith.
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