Low-frequency array active-antenna system

The Low Frequency Array (LOFAR) will be a radio telescope that opens up a hardly explored part of the spectrum range for astronomy. LOFAR will operate between at least 10 MHz and 150 MHz. Due to its advanced concept using among others active antenna arrays, adaptive interference cancellation and calibration techniques, it will provide unique arc second resolution and milliJansky sensitivity. Key element for this instrument is a compact active, broadband antenna and this will be the main topic of presentation. Information will be provided on the basic design and performance of both antenna structure and integrated low noise amplifier. The antenna element is optimized in terms of beam pattern, while the associated amplifier is optimized for very low noise performance and high dynamic range. Insight is given how the antenna design is systematically tailored to the system requirements. Both simulated and measure performance regarding among others beam pattern and noise performance will be presented. The active antenna technology developed for LOFAR is the first application of this technology in radio astronomy and will be an important step towards future large radio telescopes.