Abstract-Developments in radio astronomy instrumentation drive the need for lower cost front-ends due to the large number of antennas and low noise amplifiers needed. This paper describes cost reduction techniques for the realization of antennas and low noise amplifiers in combination with a noise budget calculation for array systems in the absence of cryogenic cooling.

Aperture array technology is one of the candidate technologies for the 500 MHz to 1500 MHz frequency range of the SKA. The feasibility and low noise potential of aperture arrays have been demonstrated with small test systems before, e.g. with a 50 K system noise temperature, measured on a 1 m² prototype tile in 2010. However, further reduction of the array noise temperature is essential to optimize the ratio of effective collecting area and system noise temperature. This is made possible by applying new, lower noise, technology to the LNA design. Thus the sensitivity requirement for the Mid Frequency Aperture Array of the SKA could be satisfied at lower cost. Results of a step by step approach to reduce the system noise temperature to below 40 K, giving at least 20% improvement, are presented.

-A 0.18 μm CMOS Low Noise Amplifier (LNA) achieves sub-1dB Noise Figure over more than an octave of bandwidth without external noise matching components. It is designed for a future radio telescope, requiring millions of cheap LNAs mounted directly on phased array antenna elements. The short distance between antenna and LNA and low frequency below 2GHz allows for using an LNA with reflective input impedance, increasing the gain with 6dB. Without any matching network, very low noise figure is achieved over a wide bandwidth. At 90mW power, sub-1dB Noise is achieved for 50Ω source impedance over a 0.8-1.8GHz band without external coils, and S21>20dB, OIP2>25dBm and OIP3>15dBm. Preliminary results with 150 Ω source impedance show noise temperatures as low as 25 K around 900 MHz.

The sensitivity of antenna systems increases with increasing active area, but decreases at higher noise figure of the low-noise amplifier (LNA). Cooling the LNA locally results in significant improvement in the gain and in lowering the noise figure of the LNA. Micromachined Joule-Thomson (JT) coolers can provide a cryogenic environment to the LNA. They are attractive because they have no cold moving parts and can be scaled down to match the size and the power consumption of LNAs. The performance of a LNA mounted on a JT microcooler with dimensions of 60.0 × 9.5 × 0.72 mm(3) is reported in this paper. The microcooler is operated with nitrogen gas and the cold-end temperature is controlled at 115 K. The measured net cooling power of the microcooler is about 43 mW when the LNA is not operating. The power dissipation of the LNA is 26 mW, with a supply voltage of 2 V. At room temperature the noise figure of the LNA is 0.83 dB and the gain lies between 17.9 and 13.1 dB, in the frequency range of 0.65 and 1.05 GHz. Upon cooling to 115 K, the noise figure drops to 0.50 dB and the increase in gain varies in the range of 0.6-1.5 dB.

A compact, microstrip, two-stage, room temperature, single-ended low noise amplifier (LNA) is designed using commercial components for Aperture Tile in Focus (APERTIF), a square kilometre array (SKA) pathfinder project. Various techniques are investigated to insert inductance between the source pad of the package and the ground plane of the printed circuit board (PCB), with the chosen design able to do this using standard manufacturing techniques. The desired noise temperature of 25 K (noise figure (NF) of 0.36 dB) is met over the 1.0–1.8 GHz band, with an input return loss better than 10 dB.