Device Development for NASA Space Communications Applications: A Novel Power Combiner for Solid State Power Amplifiers
Research Associate: Andrew Abraham
Principal Investigator: Edwin Wintucky
Purpose and Background:
Many future NASA space missions will require microwave powers on the order of tens of watts to achieve the required data transfer rates currently needed. Specifically, near Earth communications between the Lunar Lander, Crew Exploration Vehicle (CEV), Lunar Relay Satellite, International Space Station (ISS), and the Tracking and Data Relay Satellite System (TDRSS) will require significant power levels at Ka-Band frequencies. Additionally, deep space missions to the outer gas planets, and their moons, will require high power Ka-Band transmitters to successfully communicate with the Deep Space Network (DSN) which operates over a 500 MHz band centered at 32.05 GHz.
Presently, state-of-the-art Solid State Power Amplifiers (SSPAs), which are based on a GaAs Monolithic Microwave Integrated Circuit (MMIC), can only produce a RF power output of 6W or less. However, the missions referenced above shall require 10-20W of RF power at Ka-Band frequencies. To remedy this unfortunate discrepancy, a method must be developed to efficiently combine the RF power of a small number of SSPAs to achieve the desired power output.
Previous studies have been successful when utilizing a “magic-T” combining element to combine the power of two SSPAs. The magic-T operates on the principle of superposition and requires that the two input signals are equally matched in both phase and amplitude for efficient operation. This limits the flexibility of the design of the combiner to binary systems only (SSPAs must come in pairs). Additionally, the amplitude-matching requirement of the magic-T presents another design difficulty because it is highly difficult to produce two SSPAs which produce exactly the same power.
Research Goals and Benefits:
The goal of this project is to design, construct, test, and evaluate a waveguide hybrid coupler for two-way and three-way power combining of signals of unequal power. The design of these circuits will eliminate the need to precisely match the amplitudes of input signals and shall also remove the binary design constraint mentioned above. This will be accomplished via the utilization and testing of two combiners which are being developed by the Electron & Opto-Electron Device Branch at Glenn Research Center. There are four basic designs which may be tested during the course of this research:
- two SSPAs, one 2-way asymmetric or branch-line power combiner
- three SSPAs, one magic-T, one 2-way power combiner
- three SSPAs, and one 3-way branch-line asymmetric power combiner
- three SSPAs, and two 2-way asymmetric or branch-line power combiner
These designs shall be constructed and tested as time permits.
I shall benefit from the skills I acquires during the course of this study. Specifically, I will learn, develop, and apply concepts from numerous disciplines of physics and engineering including:
- Electric and Magnetic Field Theory
- Microwave Circuit and Transmission Line Theory
- Network Analysis
Additionally, I shall become familiar with the theory and operation of various modern microwave testing equipment including, but not limited to:
- Network Analyzer
- Spectrum Analyzer
- Microwave Power Meter