High-Efficiency L-band TR Module Development Results.pdf
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1、High-Efficiency L-band T/R Module: Development Results Wendy N. Edelstein1, Constantine Andricos1, Feiyu Wang2, David B. Rutledge2 1 Jet Propulsion Laboratory California Institute of Technology 4800 Oak Grove Drive Pasadena, CA 91109-8099 2 Department of Electrical Engineering California Institute o
2、f Technology Pasadena, CA 91125 Abstract Future interferometric synthetic aperture radar (InSAR) systems require electronically scanned phased-array antennas, where the transmit/receive (T/R) module is a key component. The T/R module efficiency is a critical figure of merit and has direct implicatio
3、ns on the power dissipation and power generation requirements of the system. Significant improvements in the efficiency of the T/R module will make SAR missions more feasible and affordable. The results of two high-efficiency T/R modules are presented, each based on different power amplifier technol
4、ogies. One module uses a 30W GaAs Class-A/B power amplifier and the second module uses a 70W LD-MOS Class-E/F power amplifier, where both modules use a common low power section. Each module operates over an 80MHz bandwidth at L-band (1.2GHz) with an overall module efficiency greater than 58%. We wil
5、l present the results of these two T/R modules that have been designed, built and tested. I. INTRODUCTION Recent advances in the scientific understanding of the solid- Earths crustal deformation have been made possible using InSAR techniques to provide centimeter-level surface displacement measureme
6、nts at fine resolution. L-band repeat-pass InSAR techniques have been shown to provide very accurate and systematic measurements of surface deformation and surface strain accumulation due to seismic and volcanic activity. The L-band wavelength (1.25GHz) provides the ability to make these measurement
7、s under a variety of topographic and land cover conditions, day or night, with wide coverage at fine resolution and with minimal temporal decorrelation. The work described in this paper are the results of a three-year task sponsored by the NASA Earth-Sun System Technology Office (ESTO) under the Adv
8、anced Component Technology (ACT) program, Award No. ACT-02-0017, “Ultra-High Efficiency L-band T/R Modules for Large Aperture Scanning Antennas”. The T/R module described in this paper is a critical component in L-band SAR instruments which can be traced to missions found on the NASA strategic roadm
9、aps. Repeat- pass InSAR measurements of Earth surface-displacement are at the foundation of the NASA roadmap for “Solid Earth” science. Because of the great benefits an orbital InSAR capability offers for the study of Earth crustal dynamics, ice sheet motion, volcanism, and other surface-change phen
10、omena, an InSAR mission has been deemed the highest priority for Solid Earth science at NASA 1-2. A. Project Description In this project, a product line of high-efficiency L-band T/R modules has been developed for use in L-band InSAR missions. To achieve high efficiencies at high output powers, we h
11、ave investigated the use of Class-E/F power amplifiers. The Class-E/F power amplifier delivers 70W RF power at L- band. We have also developed a 30W T/R module using a Class-A/B power amplifier. The overall efficiency for both the 30W and 70W T/R module exceeds 58%. Current state- of-the-art T/R mod
12、ules can only achieve moderate efficiencies of 30-40% at L-band. II. T/R MODULE TOPOLOGY The T/R module architecture is shown in Fig. 1 where the only difference between the 30W and 70W module is the power amplifier (PA) stage. The module includes a common phase shifter and variable attenuator, a 3W
13、 driver amplifier to drive the PA and the low noise amplifier (LNA) on receive. A low-loss high-power circulator at the antenna port provides sufficient isolation between transmit and receive channels. Solid state switches are used at the low power input section. The T/R module is controlled by a Xi
14、linx 4005XL field programmable gate array (FPGA) which controls the module amplitude and phase, generates the receiver and transmitter timing window, and measures the ambient temperature. Fig. 1. Block diagram of the L-band T/R module. The 30W Class-A/B or 70W Class-E/F PA is the final power amplifi
15、er in the transmit chain. Out DATA CLOCK +5V -5V ENABLE +27V Control Circuit Pre-Driver Amp Circulator +22d +15dB +22dB +15dB 36W or 70W 33W or 65W Driver Amp Buffer Amp. T/R Switch LNA Buffer Amp T/R Switch +10dB to PA to tx/rx amp switches Phase Shifter 6-Bit Attenuator 3W High Eff. Power Amp Comm
16、on 3W T/R driver At the heart of the T/R module is the high-efficiency power amplifier (PA) where it serves as the last stage in the transmit chain. The efficiency of this PA for the most part determines the overall efficiency of the T/R module. We have developed two different power amplifiers, each
17、 with the same drive level such that either PA can be substituted into the same T/R module architecture. The first T/R module uses a 30W Class- A/B PA using GaAs FET devices. The second module uses a 70W Class-E/F switching amplifier using LD-MOS devices. Switching amplifiers (e.g., Class-D, E, E/F,
18、 F) have only recently been exploited as RF amplifiers due to the availability of transistors with substantial gain and power at microwave frequencies 3-5. A. LD-MOS Push-Pull Class-E/F Power Amplifier We have selected the Class-E/F circuit topology for the 70W T/R module. Fig. 2 shows a simplified
19、schematic of the push-pull amplifier optimized for a Class-E/Fodd,2 operation 6-7. The amplifier uses a pair of transistors driven as switches 180-degrees out of phase. It incorporates two baluns to make single-ended to differential-ended conversion and impedance transformation. To achieve a high co
20、upling coefficient and good balance, a broadside multilayer coupling structure is used as the balun. This novel balun circuit results in higher efficiency, higher operating frequency and wider bandwidth in a very compact layout 8. The input and output matching circuit models incorporate the signific
21、ant package inductance and output capacitance of the power transistors, which was critical to achieving operation at 1.2GHz. A multistage input matching circuit was implemented to increase bandwidth. At the output of the amplifier, the inductance of the balun and the output capacitance of the transi
22、stor are tuned to form a parallel resonance LC tank at the operating frequency of the amplifier. The second harmonic trap, implemented as part of the drain bias circuit, helps shape the current waveform and also reduced the second-harmonic of the output power spectrum, resulting in increased efficie
23、ncy. The circuit uses a low-loss, low-dielectric constant substrate material. Low frequency stabilization circuits were implemented for unconditional stability 9. Fig. 2. Simplified schematic of the Class-E/F power amplifier. B. GaAs Push-Pull Class-A/B Power Amplifier The 30W PA consists of a GaAs
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