TECHNOLOGY AREAS: Air Platform, Sensors, Electronics

ACQUISITION PROGRAM: PMA 265 F/A-18 Hornet, ACAT I

OBJECTIVE: Develop a predistortion linearization scheme for the quadrature Linear Amplification Using Non-Linear Component (LINC) architecture that will support both Laterally Diffused Metal Oxide Semiconductor (LDMOS) and gallium nitride (GaN) power amplifiers in the UHF through L-Band frequency range for airborne platforms.

DESCRIPTION: Recent advances in linear power amplifier architectural design, using LINC has shown improvements in both linearity and efficiency (size, weight and power)[1]. A LINC transmitter system often suffers from branch complex gain imbalance that, being a distortion source, has a direct effect on linearity displayed in adjacent channel power ratio and dynamic range[2]. Digital predistortion can improve linearity when considering the imbalanced LINC transmitter as a memoryless, nonlinear system but suffers from a limited dynamic range restitution at the output of the LINC transmitter. Cross talk between the branch amplifiers in a LINC transmitter becomes unavoidable when using isolationless combiners that are necessary to keep the transmitter�s efficiency high. This cross talk causes imbalance in the branch complex gain that in turn has a negative impact on linearity. The use of the digital predistortion linearization restores linearity of the LINC transmitter system while maintaining high efficiency.

A mixed digital signal processing/field programmable gate array (DSP/FPGA) implementation for the linearization architecture is proposed that is suitable for an accurate impairment detection and compensation for the LINC transmitter system linearity. The predistortion architecture must provide the capability to operate with LDMOS or GaN power amplifiers while optimizing the following parameters: adjacent channel leakage ratio (ACLR), error vector magnitude (EVM), power added efficiency (PAE), linearity, efficiency, duty cycle, weight, dimensions, two-tone intermodulation distortion (IMD), fifth order IMD, broadband noise, spurious emissions, noise power ratio, harmonics, instantaneous bandwidth, stability, automatic and power recovery.

PHASE I: Develop a design concept by utilizing computer simulations, analytical or experimental approaches. Provide trade-offs which summarize the design approaches for the predistortion scheme.

PHASE II: Develop and demonstrate the capability of the predistortion linearization circuit in a laboratory environment. Provide design concepts to address packaging the quadurature LINC power amplifier architecture.

PHASE III: Demonstrate the operation of the quadurature LINC power amplifier architecture in an Unmanned Aerial Vehicle (UAV) and/or F-18 aircraft operating on an active network.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: New highly efficient linear amplifiers will support all spectrums of communications, from radios to cell phones to wireless networks. The RF power amplifier has the largest impact on the cost, size, weight and power of wireless communication systems. There is a continuing demand to transmit multimedia information while minimizing signal distortion.

REFERENCES:
1. Gamal M. Hegazi, Thanh T. Chu, and Richard A. Groshong, "Improved LINC Power Transmission Using a Quadrature Outphasing Technique", IMS 2005.

2. Garcia, P.; Ortega, A.; de Mingo, J.; Valdovinos, A.; "Nonlinear Distortion Cancellation in OFDM Systems Using an Adaptive LINC Structure", Personal, Indoor and Mobile Radio Communications, 2004. PIMRC 2004. 15th IEEE International Symposium on, Volume 2, 5-8 Sept. 2004 Page(s):1506 - 1510 Vol.2.

KEYWORDS: Linearization; Efficiency; Predistortion; Power Amplifier; Communication Systems; Aircraft

TPOC: (301)995-8751
2nd TPOC: (301)342-9094

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