Upgrade of the Westerbork synthesis radio telescope: The multi frequency front end

The performance of a novel front end system, the Multi Frequency Front End (MEFE), for use in a synthesis radio telescope is discussed. This front end covers 9 frequency bands in the range from 250 MHz to 8600 MHz. All receivers are based on the double superheterodyne principle. Each receiver has two channels which are connected to dual polarized feed systems. These linearly polarized, orthogonal channels allow the measurement of all four Stokes parameters of the received electromagnetic wave. An improvement in sensitivity and extension in frequency coverage is realized compared to present systems. Other important goals that are satisfied are compact design and frequency agility. These goals were met by using innovative designs for feed systems and local oscillator. The application of cryogenic cooling to feed components and HEMT based low noise amplifiers results in very low system temperatures. Emphasis is given to the constructional details and measured performance of a prototype front end.