Broadband, Ultra-linear, Extremely High Frequency (EHF) Traveling Wave Tube Amplifier

Power amplifiers that provide both high linearity and high efficiency are essential for the transmission of high data rate bandwidth efficient digital signals used in modern MILSATCOM communications. Achieving this objective at millimeter-wave frequencies is particularly challenging. Linearizer Technology, Inc. (LTI) in conjunction with L-3 Communications Corporation, Electron Devices Division (L-3 EDD) is proposing to develop a TWTA based transmitter including an up-converter covering the frequency from 43.5 to 45.5 GHz with a linear output power > 50 watts and associated efficiency > 30%. This transmitter will have a weight < 15 lbs and a volume < 0.5 cu. ft. when housed in an air-cooled, weather resistant package suitable for antenna mounting. Transmitter linear performance will be based on supporting Quadrature Amplitude Modulation (QAM). A transmitter goal will be an amplitude modulation/phase modulation (AM/PM) of less than 1.5 °/dB from small signal up to saturated input power across the band. This work will be based on L3-EDD’s success in producing Q-band microwave power modules (MPMs) and LTI’s experience in producing linearizers for the Q-band frequency range. BENEFIT: Modern communications systems use complex modulation as QAM, in which the peak to average power ratio is high, and result in a non-constant envelope. Power amplifiers made for these modulations must be highly linear in order to minimize distortion that can negatively affect adjacent channel signals and signal quality. To achieve the required level of linearity, it is common practice to operate amplifiers at reduced power. The consequences of this approach are a very low efficiency, over-sized and heavy transmitters/amplifiers and power supplies, extra unnecessary heat generation, and higher costs. At millimeter-wave these factors can make a communication system impractical to implement, particularly for power-consumption-sensitive applications such as SATCOM and mobile communications. The proposed project will improve the efficiency of compact linear Q-band power amplifiers/transmitters resulting in reduced size, weight, cost and required prime power. The combining of an improved linearizer with a new higher power and efficiency miniature TWT and techniques that enhance amplifier efficiency with QAM modulation could provide an additional 25 to 50% reduction in power consumption. This technology also has value for both space borne as well as ground-based systems. The resulting transmitter will be of great value in virtually all bandwidth efficient Q-band/millimeter-wave communication systems where power consumption is of concern. Portable, mobile and airborne communications systems will be prime candidates for integration of this technology.