Development of 500 W Ka-band helix-TWT and 200 W Q-Band helix-TWT for communications applications

Abstract

L-3 ETI is continuing development of high power mmwave helix-TWTs for next generation military satellite systems and broadband commercial satellite systems. In 2004 L-3 ETI developed the 8925H and demonstrated its power handling capability of 200 W at Q-Band [1]. In 2006 L-3 ETI developed the model 8926H, a 400 W KaCommunications-Band helix-TWT [2], and later increasing it's power handling capability to 500 W, as reported in 2007 [3]. During 2007, using L-3 ETI IR&D funding, two more engineering units of the 500 W TWTs were built and tested with the result that the 8926HB model TWT is now ready for production. This paper discusses the latest development efforts and performance testing for the 500 W Ka-Band and 200 W Q-Band TWTs.As reported at IVEC 2007, tests of the first 8926HB engineering model, EM1, demonstrated thermally stable 500 W CW operation from 28 to 31 GHz, satisfying the primary design objective of the 8926HB EM1. For this initial phase, the device was built using components common to L-3 ETI's current, lower power, mm-wave production designs in order to expedite the process. After this successful demonstration of power handling capability, EM2 and EM3 were built using the production configuration. The production configuration included modifications in the magnetic circuit design to provide more robust electron beam focusing. Figure 1 shows the saturated performance of the 8926HB EM2 and EM3. EM2 produces 520 W to 540 W across the commercial-band with overall-efficiency ranging from 55 % to 58 %. EM3 produces 525 W to 535 W across the military-band with 55 % minimum overall-efficiency. EM2 was tested by operating continuously while sweeping the RF drive frequency from 28 to 30 GHz at about 1 dB OPBO from saturation for more than 800 hours. Figure 2(a) presents the saturated output power, cathode current, and gain at 29.5 GHz as a function of time. The initial increase in power and gain is a result of the cathode current increase experienced during first 400 hours. Once the cathode current stabilized at 148 mA, the RF output power remained constant, indicating the thermal stability of the device. EM3 was also subjected to testing as a function of time. This unit was operated for over 100 hours while sweeping over the military-band at full saturation. As shown in Figure 2(b), it exhibited constant cathode current and stable output power throughout the entire test. During the combined processing time of approximately 1000 hours between EM2 and EM3, no supply trip event was recorded.The 200 W Q-Band Helix-TWT development program is divided into three phases. Phase I, completed in 2004, was a feasibility-study to demonstrate 200 W CW capability. Phase II, completed in 2005, was a proof-of-design phase requiring delivery of two TWTs for prototype TWTA integration. Phase III is an engineering-development phase including delivery of 20 TWTs. L-3 ETI has delivered 11 TWTs in Phase III at this time.After successfully demonstrating 200 W of CW output power in Phase I, ETI elected to modify the electron gun desi...

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