This paper presents an active array demonstrator for the mid-frequency range (i.e.: from 300 MHz to 1000 MHz) of the Square Kilometre Array (SKA). We describe the design process of FIDA 3 (FG-IGN Differential Active Antenna Array), which is the FG-IGN contribution for the task DS4-T4 of the SKADS project. The main advantages provided by this design include the use of a dielectric-free structure, and the use of differential amplifiers directly connected to the feeding lines of the antennas. The

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... rray has been optimized in order to exhibit well active impedance matching properties in the band of interest. On the other hand, the differential low noise amplifiers are designed in order to obtain a very low noise temperature for such antenna impedance. A 1 m 2 array tile has been manufactured, and both the antenna impedance and the amplifier noise performance have been measured. Thus, the radiating structure provides scanning capabilities up to ±45 deg with acceptable impedance matching. With respect to the amplifiers, the measured noise temperature is better than 40 K.