AffiliationJet Propulsion Laboratory, California Institute of Technology
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Collection InformationProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection.
AbstractIn the past, traveling wave tubes have dominated the power amplifier field in space flight transmitter applications. TWTAs however, are expensive, and high-power TWTAs may be relatively unreliable when considering end-of-mission operating requirements of up to 10 years and longer. Recent improvements in reliable solid-state designs including Gallium Arsenide FETs have resulted in efficient X-band devices which operate at multi-watt levels. A number of these devices would be combined in parallel to achieve the power output desired. This paper discusses the development of an efficient 20 watt X-band solid-state power amplifier to be used as a TWTA replacement for space flight applications. The 20-watt assembly shown in Figure 1 consists of two stand-alone, 8-channel, 11-watt assemblies operating in parallel through a 2-way switched power combiner. Particular emphasis is placed on the power amplifiers and a one-step, 8-way power divider/combiner pair. Each power amplifier channel has 3 stages of gain and develops 1.6 watts of RF output with 18 dB of compressed gain. A driver amplifier module provides additional system gain and a 0.5-watt drive level for the high power sections. The GaAs FET devices utilized are from the output of a device improvement program which has a goal of a minimum power added efficiency of 40%. The one-step combiner utilizes a novel technique to achieve a combining efficiency of 90%. The full system, including the DC-DC power converter, yields an overall system efficiency of 25%. A thermal sensor in the power conditioner is used to hold amplitude variations to ±0.3 dB from 0 to 50°C and phase variations to ±10° over the same range. The assembly also operates in a low power mode producing 9 watts of RF when only one 11-watt assembly is powered and the switched combiner open circuits the off channel.
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