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A GaAs Ka-band (26-36 GHz) LNA
for radio astronomy
Microwave and Communication Systems Group
School of Electrical and Electronic Engineering
The University of Manchester
Applications
I. Low-cost LNA for large arrays
The two major concerns in the near future of radio astronomy are related to increasing the collecting area and extending the field of view. The methods for increasing the collecting area consists of increasing the diameter of the large single-dish telescopes, which may be unaffordable, or of distributing multiple antennas in the appropriate region, which is more feasible. Aperture arrays and Phased Array Feeds (PAFs) are the two methods for extending the field of view.
Fig. 4. ALMA telescope (left) and ASKAP PAFs (right) (pictures courtesy of ALMA and ASKAP)
The future progress in the development of these kind of arrays and multi-pixel systems, which will be composed of tens, hundreds or thousands of elements, will be limited by the cost. For this reason:
II. Yebes Observatory
The RAEGE network is a Spanish-Portuguese project that will consist of four 13.2 meter radio telescopes equipped with S/X/Ka tri-band receivers. The first of these telescopes has been recently constructed in the Yebes Observatory.
The non-cryogenic stage of the Ka-band chain has an amplifier with a maximum noise figure of 2.9 dB. If we replace this amplifier with the one proposed in this work, we will experience a:
Work Description
An LNA has been designed to operate across the Ka-band from 26 to 36 GHz. It has been designed using a commercial GaAs process, and according to the simulations, it is believed that its performance would be superior to any other GaAs based LNA so far reported in the same band at room temperature.
10 % time saving when observing a source with
a fixed sensitivity
It is crucial to use affordable models such as the proposed LNA in order to contribute significantly to reduce the cost.
Table. 1. Specifications of the LNA
LNA Performance
Fig. 5. RAEGE telescope (picture courtesy of Yebes)
Fig. 3. S-parameters (left) and Noise Figure (right) of the LNA
Frequency range 26 – 36 GHz
Noise figure 1.5 dB min. / 1.8 dB max.
Gain 33 dB
Gain ripple 0.7 dB
Input return loss 12 dB min.
Output return loss 12 dB min.
Fig. 1. A MMIC LNA suitable for radio astronomy applications
Due to the increasing importance of arrays and multi-pixel systems in radio astronomy, the utilisation of this low-cost LNA in this new concept of telescopes is discussed. Also an application in the new 13.2 meter radio telescope of Yebes (Spain) is highlighted, and a 10% reduction in the observing time is shown.
Fig. 2. Schematic of the LNA
Design
The proposed LNA design is based on the WIN Semiconductors 100 nm GaAs process. It contains 4 stages, and the transistors have 2 fingers of 50 µm width each. The size of the MMIC is 1.3 x 2.8 mm.
Scattering and noise parameters have been simulated at room temperature, and the associated results are presented here. Special attention has been paid to ensure the stability of the design. When it is fabricated, its performance is expected to be similar to the one shown here - this is a benefit of using a well-established process.
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For details contact: David Cuadrado-Calle
E-Mail: [email protected]
Supervisor: Prof. Danielle George
E-Mail: [email protected]
Acknowledgements: The work of David is sponsored by the
Jodrell Bank Centre for Astrophysics.
