IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 52, NO. 5, MAY 2005 653 Development of High-Power Ka-Band and Q-Band Helix-TWTs Chae K. Chong, Jon A. Davis, Ronald H. Le Borgne, Michael L. Ramay, Richard J. Stolz, Rod N. Tamashiro, Member, IEEE, John P. Vaszari, and Xiaoling Zhai Abstract—Recent advancements made in millimeter-wave helix-traveling wave tubes (TWTs) at L-3 Communications Elec- tron Technologies (L-3 ETI), Inc. (formerly Electron Dynamic Devices, Inc. and originally Hughes Electron Dynamics Division), in continuous-wave (CW) output power capability and the overall efficiency of Ka-band and Q-band devices are presented. The 8921HP, L-3 ETI’s latest high-power communications Ka-band TWT model, demonstrates 250–300-W CW output power and 47% minimum overall efficiency with a two-stage collector over 27.5–31 GHz. Another Ka-band device, the 8922HP, developed for pulsed radar applications over 33.4–36 GHz, produces 230-W minimum output power over the bandwidth with 49% minimum overall efficiency. This device was developed for pulsed operations but has demonstrated CW power-handling capability up to 270 W. In Q-band, the 8925HP, derived from the current production 120-W Q-band helix-TWT (8905HP), significantly extends the CW output power capability, demonstrating 230-W minimum over 43.5–45.5 GHz. The beam focusing is improved in both the Ka-band and the Q-band TWT models, with saturated radio-fre- quency beam interception well below 1% of the nominal beam current of 95 mA. The devices can be operated in pulsed mode by using the focus electrode to cut off the beam. The electron gun typically requires a focus electrode voltage of 800 to 900 V with respect to cathode for beam cutoff. Index Terms—Helix-traveling wave tubes (TWTs), millimeter- wave. I. INTRODUCTION T HERE is significant interest in compact and light weight millimeter-wave amplifiers with moderately high-power (100–1000 W) and wide-bandwidth capabilities for applications in high data rate communications and high-resolution radar. One of the most promising millimeter-wave amplifiers that can sat- isfy the above requirements, specifically at the Ka-band and the Q-band frequencies, is the helix-TWT due to its unique ability to provide wide-bandwidth interaction with an extremely compact and lightweight structure. Over the last decade, helix-TWTs have demonstrated unsurpassed combined performance in band- width, gain variation, linearity, size, weight, and overall effi- ciency [1]–[4] over many other types of vacuum microwave devices across the microwave and millimeter-wave spectrum. Therefore, helix-TWTs continue to draw strong interest and de- mand for further improvements in performance for the various Manuscript received August 4, 2004; revised November 12, 2004. The review of this paper was arranged by Editor P. Waller. The authors are with L-3 Communications Electron Technologies, Inc. (formerly Electron Dynamic Devices, Inc. and originally Hughes Electron Dynamics Division), Torrance, CA 90505 USA. Digital Object Identifier 10.1109/TED.2005.845842 communications, electronic warfare, and radar systems that re- quire such attributes. Among the various attractive performance characteristics of the helix-TWTs, however, power-handling ca- pability is not one of them, especially at the millimeter-wave frequencies where a significant portion of recent helix-TWT de- velopment efforts are directed. Compared to the other possible higher power millimeter-wave amplifiers [5]–[7] that can pro- vide in some cases orders of magnitude higher power helped by their rugged interaction structures, the helix-TWT power-han- dling capability is significantly lower due to the fragile helix interaction circuit. The delicate nature of millimeter-wave helix circuits has limited the CW operation to around 100 W in both Ka-band and Q-band [8]–[10]. Although high-power capability is not the single most important performance parameter in de- termining overall performance of microwave devices in gen- eral, it is one of the important determinants. The development of the millimeter-wave devices that will be discussed in this paper was recently initiated at L-3 ETI to extend the power- handling capability of millimeter-wave helix-TWTs to above 200 W, and to make additional improvements in beam trans- mission and overall efficiency. The main challenges in the high-power millimeter-wave helix-TWT designs are in realizing a thermal design that can dissipate the generated heat efficiently, and a focusing system that provides a well-controlled high area compressed beam. Other issues include maintaining stability from possible os- cillations such as the backward-wave oscillation (BWO) or drive-induced oscillation (DIO), and achieving accurate control of the very small circuit dimensions. Benefiting from the many years of development history in millimeter-wave helix-TWTs, and advancements made in computer-aided design tools, L-3 ETI has made considerable progress in the above areas, and the results are discussed in this paper. The organization of this paper is as follows. Section II describes the computational pro- cedures and tools used in designing the presented devices, and Section III discusses the performance of the devices, followed by the conclusion in Section IV. II. COMPUTATIONAL PROCEDURES In designing the presented development millimeter-wave helix-TWTs, various L-3 ETI proprietary computer codes as well as the codes that are available from outside of the company were utilized. Benefiting from the advancements made in computer-aided design capabilities both in L-3 ETI proprietary codes and in imported codes, the development time for millimeter-wave helix-TWTs has considerably shortened and no longer requires the usual experimental iterations [11]. 0018-9383/$20.00 © 2005 IEEE