Virtual Mesa Verde: An Interactive Media Program for Young Persons with Physical Disabilities

Not Available Modern satellite-communication transmitters use a single antenna array to form multiple beams. Each power-amplifier (PA) module must amplify multiple carriers simultaneously. The resultant high peak-to-average ratio causes conventional PAs to be very inefficient (5-10 percent). Kahn-technique (EER) transmitters combine nonlinear RF amplifiers with a high-level modulator to implement a high-efficiency linear transmitter. Such transmitters have recently been demonstrated from HF (250 W) through L band. Their average efficiency for multiracial signals is typically several times that of a conventional linear amplifier (e.g., 50-60 percent). Unfortunately, existing modulator designs limit the bandwidth to 50 to 100 kHz. This program will investigate techniques for wideband high-efficiency amplification. The preferred technique uses a high-level modulator that combines a class-S modulator with a class-B amplifier. The class-S modulator amplifies the low-frequency components of the envelope (which constitute most of the power). The class-B amplifier adds the high-frequency components. The result is a transmitter which is nearly as efficient as a Kahn-technique transmitter, but can operate with bandwidths suitable for satcom and other multicarrier applications. The Phase-I program will identify the preferred approach and determine its parameters.