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Design and Development of 20kW, 499.75 MHz Solid State RF Power Amplifiers

This research paper discusses the design, development, and test results of 20kW, 499.75 MHz solid state RF power amplifiers for the CLIC injector pre-buncher. The paper covers the technical requirements, device selection, amplifier architecture, and test results of the amplifier.

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Design and Development of 20kW, 499.75 MHz Solid State RF Power Amplifiers

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  1. Design, Development and test results of 20kW, 499.75 MHz Solid State Wide Band RF Power Amplifiers for the CLIC injector pre-buncher * Purushottam Shrivastava, P. Mohania, A. Mahawar, P.D. Gupta Raja Ramanna Centre for Advanced Technology Indore, India CLIC Workshop Jan 18-22, 2016 * DAE (India) CERN Collaboration under NAT Protocol

  2. Motivation • Under DAE (India) CERN collaboration in Novel Accelerator Technologies, of which CLIC collaboration is a part, a 20kW Solid State RF Power Amplifier R, D & D effort by RRCAT, Indore was agreed an as R & D and protyping in this state of the art area. • RRCAT had earlier built a 476 MHz, 10kW Solid State RF Power Amplifier for use in its FEL projects. RRCAT has also built solid state RF systems for the characterization of Superconducting cavities at 325 MHz, 650MHz, 1.3 GHz. • In order to achieve the desired specifications and feasibility RRCAT first developed 1kW, 5 kW intermediate SSPA stages as a part of development and improvements/ modifications were incorporated for realising the final 20kW power level. • In earlier workshop we reported a prototype 5kW SSPA development which served as a base for development of present wide band 20kW SSPA. We have developed the complete amplifier in-house using the design, fabrication, testing and qualification facilities available at RRCAT. Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  3. Outline • Technical requirements & Specifications of the 20kW SSPA • Device selection and amplifier design • 20kW SSPA architecture • 5kW prototype development for feasibility and performance characteristics studies • Final amplifier development • Test results • Conclusion Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  4. CLIC DB front end Modulator-klystrons, 1 GHz, 15 MW IOTs ?, SSPA 500 MHz Diagnostics SHB 1-2-3 Gun PB Buncher Acc. Structures ~ 3 MeV ~ 12 MeV ~ 140 keV For time being only major component development: GUN, SHB, high bandwidth 500 MHz source, 1 GHZ MBK, modulator and accelerating structure in an high power test stand Courtesy: Steffen Doebert

  5. Sub-harmonic bunching system Status: RF design existing, mechanical design done, Discussion with CERN work shop on realization Power source: 500 MHz, 20-115 kW, wide band (60 MHz) sources needed for fast phase switching. Solid state favoredComment: On 20kW prototype Done under collaboration with RRCAT Hamed Shaker Courtesy: Steffen Doebert

  6. Compact, 10kW solid state RF power amplifiers, @476 MHz using LDMOS transistors and novel planar combiners and dividers for pre-buncher cavity of injector LINAC for CUTE FEL and IR-FEL project at RRCAT 10kW SSPA during tests A compact 10 kW, 476 MHz solid state radio frequency amplifier for pre-buncher cavity of free electron laser injector linear accelerator. Published in: Review of Scientific Instruments (Volume:84 , Issue: 9 ) Sept 2013. Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  7. Specifications of the 20kW Solid State Amplifier Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  8. RF Power LDMOS Transistors Rugged N—Channel Enhancement--Mode Lateral MOSFETs Withstands high VSWR industrial (including laser and plasma exciters), broadcast (analog and digital), aerospace and radio/land mobile applications. • Unmatched Input and Output Allowing Wide Frequency Range Utilization 1.8 and 600 MHz,1250 W CW, 50 V • Single--Ended or in a Push--Pull Configuration • Qualified Up to a Maximum of 50 VDD Operation • Characterized from 30 V to 50 V for Extended Power Range • Suitable for Linear Application with Appropriate Biasing • Integrated ESD Protection with Greater Negative Gate--Source Voltage Range for Improved Class C Operation • Characterized with Series Equivalent Large--Signal Impedance Parameters Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  9. Salient Features of 20kW SSPA • Developed using high power push-pull LDMOS transistors • The push-pull devices are operated under single ended configuration to reduce space and improve repeatability. • The same design has been used to develop two 10 kW SSPA at 476 MHz for injector LINACs of CUTE FEL and Indus synchrotrons. • The 20 kW is achieved by combination of 32 transistors. • The high power combination is achieved using microstrip line planar combiner (Wilkinson Type). • Design is highly modular, and size of each amplifier pallet (one transistor based amplifier), is 5cmx10cm only. A single pallet can provide upto 1400W peak power.

  10. 5kW Amplifier Module 210mmx300mm Test results of the 5kW prototype amplifier Amplifier Module enclosed and mounted on heat sink Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  11. Test Results of the 5kW prototype SSPA module Test conditions: 50Hz repetition rate, 150µs pulse width, Input Power, 12.5dBm Output Power vs Frequency response. Gain characteristics at 499.75 Mhz Gain characteristics at 470.75 Mhz Gain characteristics at 528..75 Mhz Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  12. 5kW Wideband SSPA Delivery to CERN from RRCAT 5kW prototype SSPA received at CERN undergoing tests during August 2015 PurushottamShrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  13. Amplifier design The amplifier is developed using eight amplifier modules capable of providing up to 4 kW of pulse power, which are combined by planar Wilkinson combiner and divider to generate 20 kW of pulsed output.

  14. Description of stages of amplifier The amplifier has been developed as a three stage amplifier which consists of the following stages. 1 W Pre-driver amplifier 100 W GaN HEMT based driver amplifier 4kW High Power stage which is developed by combining 4 LDMOS transistors using Wilkinson combiner and divider networks on low loss flexible PTFE based laminates. 8 units of 4kW modules combined to provide over 20kW output. The switching ON time is defined by a RF switch which is having a controlled mono-shot circuit which sends TTL signal to switch for 150µs at rising edge of the input trigger (delay in RF ON ~200ns) The three stages of the amplifier uses the following power supplies 1. 1W Pre-driver amplifier 24V, 600mA 2. Driver Amplifier 32V, 200mA for drain and -3.15V for Bias 3. High power stage 55V, 2A for drain and 2.15V for Bias Input trigger signal 2.5V-5 V, 2 µs (high Impedance) Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  15. 4kW module with 8:1 micro-strip power combiner 4kW amplifier modules High Power Microwave combiner (microstrip line based) 8:1

  16. 20kW pulsed Wide band solid state

  17. 20 kW SSPA Cabinet Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  18. Details of the Front Panel Controls Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  19. 7/16 DIN ( Deutsches Institut für Normung) output connector of SSPA Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  20. Tests done on the 20kW SSPA at RRCAT, Indore, India • Heat run tests conducted in lab environment with temperature around 25°C. • The amplifier takes half an hour to reach thermal equilibrium, the amplifier power reduced by around 0.2dB from cold condition to thermal equilibrium and afterwards it remains consistent. • The pre-driver, driver, all the eight amplifier modules and the complete amplifier system were characterized. • The characterization was done using a signal generator in pulsed mode with pulse width 140.3μs and duty cycle 50 Hz. Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  21. Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  22. Amplifier amplitude and phase response • The subsequent images shows the amplitude and phase response of the output pulse power at different frequencies across the frequency band. • The amplitude shape is obtained by using a Peak Power analyzer and the phase response is obtained using a phase detector card. • Test conditions: 50 Hz repetition rate, 140.3 μs pulse width, Input Power 14 dBm; Phase card response: 10 mV/degree Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  23. Phase and amplitude response at 470.75 MHz Picture on left is the output of the phase card which shows the variation of the output power phase with respect to input during pulse. The right image is of detected power at peak power analyzer. The phase card response is 10mV/degree. The two markers are set at 40 μs and 130 μs in the lower image. The phase variation in pulse is 1.5 degree and amplitude variation ~0.2dB. PurushottamShrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  24. Phase and amplitude response at 499.75 MHz The picture on left is the output of the phase card which shows the variation of the output power phase with respect to input during pulse. The right image is of detected power at peak power analyzer. The phase card response is 10mV/degree. The two markers are set at 40 µs and 130 µs in the lower image. The phase variation in pulse is 3.3 degree and amplitude variation ~0.2dB. PurushottamShrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  25. Phase and amplitude response at 528.75 MHz the picture left above is the output of the phase card which shows the variation of the output power phase with respect to input during pulse. The image on right is of detected power at peak power analyzer. The phase card response is 10mV/degree. The two markers are set at 40 μs and 130 μs in the lower image. The phase variation in pulse is 1.5 degree and amplitude variation ~0.2dB. Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  26. Conclusion: • The complete 20kW wide band SSPA has been designed, developed and subjected to long duration endurance testing at RRCAT, Indore. • Amplifier power reaches thermal equilibrium after 30 minutes and has excellent phase and amplitude stability meeting specifications. • 4 channel D. C. power supply which has stability of better than +/-0.05% have been used as bias supplies. • The desired specifications have been achieved and scope for further improvements/upgrades depending upon application in the buncher can be taken up as per feedback from the users. • The 20kW SSPA has been delivered to CERN. Some misalignments in the box and RF routing during transportation is being corrected after which the final tests will be repeated at CERN. Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

  27. THANK YOU Purushottam Shrivastava, RRCAT: CLIC WS Jan 18-22, 2016 CERN

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