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GaN powered Ka-band high-efficiency multi-beam transceivers for satellites

Pires, S.P. ; Cruz, P.M. ; Jang, W. ; Carvalho, N.B.C.

GaN powered Ka-band high-efficiency multi-beam transceivers for satellites, Proc ESA Microwave Technology and Techniques Workshop: Enabling Future Space Systems, Noordwijk, Netherlands, Vol. 1, pp. 1 - 7, November, 2014.

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Abstract
Wireless communication service providers are continuously offering larger volumes of data and speed. In order to accommodate those needs, complex modulation schemes, with higher number of bits per symbol have been adopted in the recent communication standards. However, the non-constant amplitude modulation schemes require high-linear systems. In the transmitter, this is a severe issue since linear radio frequency power amplifiers (RF PA), operating in Class-A or Class-B, have low average power efficiency, and a large part of the total transmitter power consumption is absorbed by this block.
In the space domain, Travelling Wave Tube Amplifiers (TWTA) continues to cover the majority of the amplifying stage on-board of satellites. This is mainly due to the lower efficiency and limited power capabilities provided by solid state transistors, commonly based on Gallium Arsenide (GaAs) technology. However, in payload architectures requiring a large amount of amplifiers w.r.t the platform capability, for instance more than 200 for a medium to large platform, it becomes difficult to use TWTAs because of their size. Typical such architectures are the multi-beam ones where flexibility in coverage is required and where beams are electronically steered using active array antennas.
The emerging Gallium Nitride (GaN) HEMT solid state technology is changing this paradigm. It is becoming a promising solution when high/medium (depending on frequency) power/high efficiency are required. GaN technology presents several advantages, namely: wide band-gap, high breakdown voltage, immunity against radiation, excellent thermal dissipation, good dynamic characteristics, linear HF noise characteristics and good nonlinear noise characteristics
In this communication the results obtained so far in the EU project “GaN powered Ka-band high-efficiency multi-beam transceivers for SATellites” (GaNSAT) will be presented. GaNSAT is aiming at a new approach to satellite communication by utilizing active antenna transceivers in Ka-band and powering them with a multitude of individual GaN-based power and low noise amplifiers. The microwave radiated power level (EIRP) required for downlink communication will be obtained by constructively combining in the far field the fields transmitted from all radiating elements of the antenna array. This approach allows to obtain high power levels given by many, comparably small microwave transceivers. Such a concept is particularly interesting for active antennas as it directly falls in the capability of the continuously improving solid state microwave power and low noise amplifiers. GaN powered Ka-band monolithic microwave integrated circuits (MMICs) are foreseen for the pixel amplifiers. They combine high power density, high efficiency and comparably high output power levels with the flexibility that is needed for active multi pixel antenna arrays.
Figure 1 depicts the proposed concept, that will allow to meet the coverage and power flexibility requirements here applied to a GaNSAT MEO mission. More generally such a technology will enable to design and manufacture payload architectures with a high level of flexibility, allowing the dynamic allocation of the satellite resources in power and spectrum to the user areas where the capacity demand is.
This implementation is a technology step towards more and more advanced payloads that will find applications in the fields of Telecommunication and Observation for the commercial, governmental and institutional markets.