Integrated Active Antenna Noise Figure Characterization Using a Cryogenic Anechoic Noise Source

For the phased array concept of the next generation radio telescopes, the Square Kilometre Array (SKA), a large number of broadband, low noise amplifiers are necessary. The envisaged array antennas for SKA are printed circuit type antennas (Vivaldy, bunny ear) Smolders (1), which should be integrated with the first amplifier stages. To enable optimum performance over a decade bandwidth it is advantageous to directly match the antenna impedance to the required impedances for low noise matching and maximum power transfer of the active device, without an intermediate matching step to 50 ohm as is common for most microwave and RF systems. This paper describes the design, but more importantly the characterization, of the integrated active antenna. An accurate characterization of e.g. noise figure cannot be executed with standard equipment due to the non-50 ohm intermediate impedance levels. To overcome this problem, a hot/cold noise figure measurements has been developed for the complete active antenna.