All Solid-State Transmitter (ASTRAM) for Next-Generation Ground-Based Planetary Radar

This paper presents the development of a new type of transmitter for next-generation ground-based planetary radar. The transmitter is based on mature, reliable solid-state technology, and provides an alternative to traditional amplifier tube-based transmitter systems. The technology described is a scalable transmitter system that utilizes a low-loss method of power combining the RF outputs of multiple Gallium Nitride (GaN)-based Monolithic Microwave Integrated Circuits (MMICs) in parallel to achieve a coherent amplified output signal. The power combining takes place within modular devices that we refer to as spatial power combining amplifiers (SPCAs). The SPCA discussed in this paper combines an arrangement of sixteen 85 W MMIC amplifiers to produce ~1.3 kW continuous-wave power at a center frequency of 8.56 GHz. The modular nature of the SPCA units allows them to be further combined hierarchically via waveguide-combining techniques to form scalable high-power transmitter systems. This paper presents the basic architecture and full laboratory characterization of an X-band solid-state SPCA unit, including key device performance results, reliability analysis, and environmental sensitivities.