Proposed low-band LNA for the Square Kilometer Array

C. L. Lim, "LNA based on a low cost (~USD1.30) commercial GaAs pHEMT MMIC offers wideband (0.4~1.4 GHz) and room-temperature low noise (~0.3 dB) performances that satisfy the SKA low cost and no-cooling requirements", presented at the 2010 Asia-Pacific Radio Science Conf. (AP-RASC '10),Toyama, Japan, Sep 23, 2010, Paper J1a-6. (slides)

Track: Large telescope in East Asia and possible array connection

Thursday, September 23, 2010, 13:10-15:10 (Room6)

Conveners: H. Kobayashi (Japan) and Z.-Q. Shen (China (CIE))

Introduction: New generations of radio telescopes such as the Square Kilometre Array consist of millions of receivers scattered over a continent. The array’s quantity and geographic considerations ruled out the traditional radio astronomy LNA implementation; i.e. costly InP devices cooled by high-maintenance closed-cycle helium (He) refrigerators. Several LNA designs have been proposed to address the cost and room-temperature operation constraints but none appear a clear winner. Peltier and package-scale cooling have also been proposed as a lower cost/maintenance alternative to He cooling but when multiplied by the quantity required can still carve a significant chunk of the budget. Additionally, cooling complicates the construction because hermetic packaging is required to prevent icicle formation from degrading reliability. We demonstrate a 0.4~1.4 GHz LNA design based on a new, low-cost, plastic QFN 2x2-packaged GaAs ePHEMT MMIC. Using off-the-shelf 0402-size RLC components for low cost, the connectorized LNA achieved a mid-band noise figure of 0.3 dB at IRL ≤ - 15 dB.

Material: The LNA consists of a MMIC and 9 passive (RLC) components mounted on a 21.5x18 mm2 Rogers RO4350 micro-strip PCB with SMA connectors. The MMIC, which comprises a common-source amplifier and temperature-tracking active bias, is fabricated on a new process optimized for noise. As loss in the input matching network is proportional to the source-to-input impedance transformation ratio, the transistor area and its operating current were sized to reduce S11 to almost zero.

Method: Scattering and noise parameters of the MMIC, extracted on a commercial source-pull measurement system, were used to simulate the LNA. Based on the simulated circuit values, prototypes were built and measured. The measured results were used for model validation and for comparing with prior art.

Results: At nominal bias (5V, 50mA), the measured performances at 900 MHz are: Gain G = 18dB, Noise figure F = 0.3, IRL/ORL < - 15 dB, P1dB = 22.3 dBm, OIP3 = 37.2 dBm and Linearity Figure of Merit (LFOM) = 15 dB. RL < -11dB over 400~1400 MHz. From HF to 20 GHz, k > 1; i.e. unconditional stability.

Conclusion: This LNA enables low noise performance comparable to that of more expensive devices and packages. The good IRL does not require an isolator (which can increase cost and input loss). Its linearity performance is also best-in-class. Its low cost is attractive for the large quantity required.

Keywords - GaAs pHEMT MMIC, low noise amplifier, radio astronomy, Square Kilometer Array"