Gallium nitride MMIC power amplifier for use in Ka-band HTS applications

Abstract

There is a need for solid-state power amplifiers (SSPAs) to be used in commercial satellite applications. Specifically with respect to high throughput satellites (HTS) where the amount of information passed through the transponders, that is, capacity, is determined mainly by the quantity of beams the satellite can generate. This application is well suited for SSPAs over the conventional TWTA solution as they are smaller and lighter weight enabling a simplification of HTS payload architectures, higher density physical integration, and the ability to support active array transmit solutions all of which increases the quantity of beams and thus capacity. However, this is also dependent on the SSPA's DC power and thermal dissipation as these are limited by a satellite's ability to generate the DC power and remove the thermal energy created by these types of units. Gallium nitride (GaN) power amplifiers (PAs) have shown the ability to generate high RF output power levels with small size and high efficiency thereby enabling step-function improvement in capacity for our emerging generation of HTS [1]. For this effort, K-band power amplifier breadboards were designed, fabricated, and tested. The purpose of the breadboards was to validate the baseline approach to meet the challenging performance required for HTS. These requirements were based on the need to increase satellite capacity. Maxar Space Infrastructure leads the industry in launched HTS capacity, with SSL having built some of the world's highest capacity spacecraft, with initial HTS systems of 50 GBps, innovating 100 GBps class, then to 200 GBps class, and now over 500 GBps class solutions [2]. This trend of nearly doubling the throughput capacity with each innovated new generation continues to project forward with the need for higher capacity solutions. This chapter will describe the design and performance of the GaN PA breadboards. Measurements of three key parameters-RF power out (Pout), power added efficiency (PAE), and carrier to third order intermodulation level (C/3IM) and/or noise power ratio (NPR)-will be presented to describe the performance of the PA. Additionally, a description of the GaN PA MMICs and the module integration approaches utilized will be given. To the author's best knowledge, the results presented are the best reported for a GaN PA module in this frequency band.