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In the last few years, the architectural design of satellite communications payloads has benefited from the view point of flexibility, from the adoption of Multiport Power Amplifiers (MPA). Multiport power amplifiers offer a means to combine discrete amplifiers in a way that is reconfigurable and will degrade gracefully in the event of any failures. The first reference to the basic element of a multiport power amplifier dates back to 1960,¹ although the application of MPAs to satellite transponders was first envisioned at Comsat Laboratories in 1974.²

The first practical application of the MPA concept to satellite communications came many years later, when it was adopted by Nippon Telephone and Telegraph Co. (NTT) for the S-band mobile communications payload on board the experimental Japanese satellite ETS VI.³ After intense R&D activity on MPAs applied to antenna architectures performed at the European Space Agency (ESA),⁴ multiport power amplifier configurations were then adopted for the Inmarsat III satellites⁵ and for the Artemis L-band payload.⁶ Nowadays, MPAs are being used on board several mobile communications satellites including the Inmarsat IV fleet.⁷ At present, an MPA configuration is implemented in the payload at Ka-band of the recently launched Japanese Kizuna satellite (WINDS, Wideband InterNetworking engineering test and Demonstration Satellite).⁸

The suitability of MPAs to satellite payloads is closely related to multiple beam antenna configurations. Multiple beam coverages are adopted to provide higher edge of coverage (EOC) antenna gains and/or to implement frequency reuse schemes among the beams (that is, a more efficient use of the available bandwidth). While obtaining higher gain and reducing interference from and to other systems, they also limit the freedom to assign bandwidth and RF power resources. The application of MPAs in multibeam adaptive antenna (MAA) configurations allows efficient and flexible sharing of the total power from the power amplifiers among the beams, thus meeting varying traffic conditions⁹ or variable link conditions.¹⁰

The conventional transmit front-end of a multiple beam satellite transponder is depicted in Figure 1. The main drawbacks of such configurations are related to failure mechanisms and traffic allocation. First, the failure of one high-power amplifier (HPA) might lead to the total loss of one beam, unless appropriate redundancy schemes are adopted. The share of the total traffic capability that can be handled at an individual beam level is limited by the size of the HPA assigned to that same beam. Moreover, there is no way to take advantage from the statistical distribution of the traffic among the beams in order to divert RF power (that is, traffic capability) where the traffic demand is higher.