Recent advances in high power and efficiency space traveling-wave tube amplifiers (TWTAs) for NASA s space-to-Earth communications are presented in this paper. The RF power and efficiency of a new K-Band amplifier are 40 W and 50 percent and that of a new Ka-Band amplifier are 200 W and 60 percent. An important figure-of-merit, which is defined as the ratio of the RF power output to the mass (W/kg) of a TWT has improved by a factor of ten over the previous generation Ka-Band devices

Force, Dale A.

Simons, Rainee N.

Wilson, Jeffrey D.

NASA Technical Reports Server

Rainee N. Simons, Jeffrey D. Wilson, and Dale A. Force
Glenn Research Center, Cleveland, Ohio
High Power and Effi ciency Space Traveling-Wave 
Tube Amplifi ers With Reduced Size and Mass for 
NASA Missions
NASA/TM—2008-215220
June 2008
https://ntrs.nasa.gov/search.jsp?R=20080021209 2019-08-30T04:29:31+00:00Z
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Rainee N. Simons, Jeffrey D. Wilson, and Dale A. Force
Glenn Research Center, Cleveland, Ohio
High Power and Effi ciency Space Traveling-Wave 
Tube Amplifi ers With Reduced Size and Mass for 
NASA Missions
NASA/TM—2008-215220
June 2008
National Aeronautics and
Space Administration
Glenn Research Center
Cleveland, Ohio 44135
Prepared for the
2008 International Microwave Symposium
sponsored by the IEEE Microwave Theory and Techniques Society (MTT–S) and the Institute
of Electrical and Electronics Engineers (IEEE)
Atlanta, Georgia, June 15–20, 2008
Acknowledgments
The authors greatly appreciate the excellent support we received from Neal R. Robbins, Daniel R. Dibb, Dr. W.L. Menninger, 
Dr. Xiaoling Zhai, Robert Benson, James Burdette, David E. Lewis, and Paul C. Spitsen at L–3 Communications, 
Electron Technologies, Inc.
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Level of Review: This material has been technically reviewed by technical management. 
This report contains preliminary fi ndings, 
subject to revision as analysis proceeds.
NASA/TM—2008-215220 1
High Power and Efficiency Space Traveling-Wave Tube Amplifiers 
With Reduced Size and Mass for NASA Missions  
 
Rainee N. Simons, Jeffrey D. Wilson, and Dale A. Force 
National Aeronautics and Space Administration 
Glenn Research Center 
Cleveland, Ohio 44135 
 
Abstract 
Recent advances in high power and efficiency space travel-
ing-wave tube amplifiers (TWTAs) for NASA’s space-to-
Earth communications are presented in this paper. The RF 
power and efficiency of a new K-Band amplifier are 40 W and 
50 percent and that of a new Ka-Band amplifier are 200 W 
and 60 percent. An important figure-of-merit, which is defined 
as the ratio of the RF power output to the mass (W/kg) of a 
TWT has improved by a factor of ten over the previous gen-
eration Ka-Band devices. 
Introduction 
Signals transmitted from spacecrafts orbiting the outer plan-
ets or from the vicinity of the lunar surface need to travel 
enormous distances to ground antennas. In addition, as the 
distance from the sun increases, the amount of solar energy 
that is available for conversion to electrical power on board 
the spacecraft decreases. Hence, there is a need for developing 
reliable space amplifiers, which are capable of delivering high 
RF power as well as operating with very high efficiency 
(ref. 1). In addition, these amplifiers need to be lightweight 
and small in size. The two possible solutions to this problem 
are based on either solid-state or microwave vacuum electron-
ics technology. Solid-state devices based on GaAs or GaN 
high electron mobility transistor (HEMT) technology, when 
characterized on-wafer using load-pull techniques, deliver 
only about 2 to 3 W of RF power at Ka-Band frequencies 
(ref. 2). Although these devices have efficiencies as high as 35 
to 40 percent, the efficiency of the multi-stage monolithic mi-
crowave integrated circuit (MMIC) power amplifier (PA), 
built around these devices, is on the order of 25 to 30 percent 
due to additional circuit losses. In addition, when the output of 
several MMIC PAs are combined to realize a high power Ka-
Band solid-state power amplifier (SSPA), the overall effi-
ciency further drops to 15 to 20 percent due to combiner 
losses. Furthermore, the low efficiency results in thermal 
management issues, which impacts reliability. On the other 
hand, for space applications, microwave vacuum electronics 
based devices such as helix traveling wave tubes (TWTs) have 
demonstrated reliability at higher microwave frequencies with 
power output in the range of 10 to several hundred watts and 
corresponding efficiency in the range of 40 to 60 percent 
(refs. 3 and 4).  
Communication from the vicinity of the Moon is considered 
to be near-Earth while that from the planets of our solar sys-
tem is considered to be from deep space. The corresponding 
frequency band designated for near-Earth is 25.5 to 26.5 GHz 
(K-Band) and for deep space communications is 31.8 to 
32.3 GHz (Ka-Band). In this paper, we present the microwave 
performance of a new K-Band helix TWT for near-Earth 
communications and also a new Ka-Band helix TWT for deep 
space communications. Both of these units are manufactured 
by L-3 Communications, Electron Technologies Inc. (ETI) 
under contracts from NASA Glenn Research Center (GRC). 
TWT Design and Modeling 
In the early eighties, the design of TWTs was mainly done 
through trial and error, which was time consuming and expen-
sive. The advances made in desktop computing and electro-
magnetic simulation/optimization tools have enabled the first 
pass design success of modern TWTs. These include the U.S. 
Naval Research Laboratory’s CHRISTINE 3-D Code for high 
efficiency slow-wave interaction circuit and MITCHELLE 3-
D Code for multi-stage depressed collector design (refs. 5 to 
(7). In addition, efficient thermal modeling/simulation tools 
are also available, which have enhanced the power handling 
capability of TWTs by integrating efficient conduction cooled 
packages. Furthermore, advances in materials technology have 
resulted in lightweight, temperature stable, high BH product 
samarium cobalt permanent magnets, which are used in focus-
ing the electron beam. Moreover, advances in tung-
sten/osmium cathode technology have resulted in cathode 
lifetimes exceeding 20 years in space (ref. 8). 
K-Band and Ka-Band Space 
TWT Requirements 
The K-Band TWT was developed for communications from 
the Lunar Reconnaissance Orbiter (LRO) spacecraft to Earth. 
The specifications for the model 9835H K-Band TWT are 
shown in table I. 
The Ka-Band TWT was developed for communications 
from a spacecraft orbiting any of the outer planets, such as 
Jupiter or its icy moons. The specifications for the model 
999HA Ka-Band TWT are shown in table II.  
 
NASA/TM—2008-215220 2
TABLE I.—TWT MODEL 9835H K-BAND 
TWT SPECIFICATIONS 
Parameter NASA specifications 
Frequency band 25.5 to 25.8 GHz 
Output power, CW 40 W min 
Saturated gain 46 dB min 
Saturated gain 
flatness 
0.5 dB min 
AM-to-PM 4.5 deg/dB max 
VSWR 2.0:1 max 
Overall efficiency 44 percent min 
Overdrive +6 dB 
Mass <1750 gm 
Size 37 by 9 by 9 cm 
Input/output ports WR-34 waveguide 
Operating 
life/mission life 
14/26 months 
Environment Lunar orbit 
 
 
TABLE II.—TWT MODEL 999HA KA-BAND 
TWT SPECIFICATIONS 
Parameter NASA specifications 
Frequency band 31.8 to 32.3 GHz 
Output power, CW 180 W min 
Saturated gain 50 dB min 
Saturated gain 
flatness 
0.25 dB min 
AM-to-PM 4 deg/dB max 
VSWR 1.5:1 max 
Overall efficiency 55 percent min 
Overdrive +5 dB 
Mass <1750 gm 
Size 37 by 9 by 9 cm 
Input/output ports WR-28 waveguide 
Operating 
life/mission life 
7/20 yrs 
Environment Deep space 
 
 
To transmit data from Jupiter at very high rates on the order 
of Mb/s, the spacecraft transmitter power has to be on the or-
der of 1 kW. To achieve this kind of power level, the outputs 
from four of the above TWTs would be combined. Combining 
efficiency as high as 90 percent has been demonstrated at Ka-
Band frequencies for a two-way combiner. 
Both the K-Band and Ka-Band TWTs have four-stage de-
pressed collector circuits for high efficiency. The collector 
circuits require high voltages, which are provided by a sepa-
rate electronic power conditioner (EPC), which is attached by 
an umbilical power cord to the TWT. 
K-Band and Ka-Band TWT Measured 
Performance 
Model 9835H K-Band TWT 
Three TWTs were manufactured and characterized and all 
three meet full specifications, resulting in first pass design 
success and 100 percent yield. The measured output power, 
overall efficiency, and saturated gain of the three TWTs are 
summarized in table III. 
 
TABLE III.—LRO PROGRAM GOALS AND PERFORMANCE 
DATA OF MODEL 9835H K-BAND TWT AT f0 = 25.65 GHz 
Performance parameters LRO program goals 
RF power output, (CW) (W) 40 
Overall efficiency, (%) (min) 44 
Saturated gain, (dB) (min) 46 
Model 9835H TWT S/N 201 
RF power output, (CW) (W) 41.90 
Overall efficiency, (%) (min) 50.84 
Saturated gain, (dB) (min) 47.85 
Model 9835H TWT S/N 202 
RF power output, (CW) (W) 41.79 
Overall efficiency, (%) (min) 45.93 
Saturated gain, (dB) (min) 47.10 
Model 9835H TWT S/N 203 
RF power output, (CW) (W) 41.92 
Overall efficiency, (%) (min) 51.15 
Saturated gain, (dB) (min) 47.00 
Model 999HA Ka-Band TWT 
A photograph of the fully packaged Model 999HA TWT is 
shown in figure 1. Three such TWTs were manufactured and 
characterized, and three units were able to demonstrate 180 W. 
The TWT S/N 202 was tested up to 250 W and set up at 
200 W for additional flight qualification testing. The measured 
overall efficiency and saturated gain of this TWT exceeded 
60 percent and 55 dB, respectively. The measured characteris-
tics are presented in figure 2. 
 
 
 
Figure 1.—The Model 999HA Ka-Band space TWT in a  
conduction cooled package. 
 
NASA/TM—2008-215220 3
 
 
Figure 2.—Measured performance of Model 999HA 
space TWT over design bandwidth. 
Electronic Power Conditioners (EPC) 
The model 2300HE 7-kV electronic power conditioner 
(EPC) is mated with the 40-W K-Band TWT and the model 
1693HC 14-kV EPC is mated with the 180-W Ka-Band TWT 
to form two new TWT amplifiers. These EPCs are also manu-
factured by L-3 Communications ETI. These EPCs are highly 
reliable and efficient (90 percent). They can operate from ei-
ther regulated or unregulated spacecraft bus voltages. The 
mass and dimensions of the TWT and the EPC are summa-
rized in table IV. 
 
TABLE IV.—MASS AND DIMENSIONS OF TWT AND EPC 
Device type Mass, 
(gm) 
Dimensions, 
(cm) 
L×W×H 
9835H 
K-Band TWT 
1500 35.1×8.9×8 
 
2300HE 
7-kV EPC 
1300 19.8×6.7×10.2 
999HA 
Ka-Band TWT 
1600 36.6×8.9×7.1 
 
1693 HC 
14-kV EPC 
4300 33.8×12.2×13.7 
Conclusions and Discussions 
The performance parameters of a K-Band TWT for NASA’s 
near-Earth and a Ka-Band TWT for deep space communica-
tions are presented. These results are state-of-the art and pro-
vide unprecedented performance. Prior to this development, 
the highest CW RF power produced by a space TWT at Ka- 
Band and flown in space was the Model 910H TWT manufac-
tured by L-3 ETI for the Cassini-Huygens Mission with 10 W, 
 
41 percent overall efficiency, and mass of 750 gm. The figure-
of-merit (FOM) is defined as the ratio of the RF power output 
to the mass (W/kg), which for this TWT is about 13. In con-
trast, the Ka-Band Model 999HA traveling wave tube pre-
sented in this paper has a FOM of 133, which is an 
improvement by a factor of ten.  
References 
1. J.H. Booske, D.R. Whaley, W.L. Menninger, R.S. Hollis-
ter, and C.M. Armstrong, “Traveling-wave tubes,” in 
Modern Microwave and Millimeter-Wave Power Elec-
tronics, R.J. Barker et al., Ed. New York: Wiley-
Interscience, 2005, Ch. 4, pp. 171–245. 
2. J.C. Freeman, E.G. Wintucky and C.T. Chevalier, “High 
power high Efficiency Ka-band power combiners for 
solid-state devices,” NASA Technical Memorandum, 
NASA/TM—2006-214447, Nov. 2006. (Available elec-
tronically at http://gltrs.grc.nasa.gov) 
3. J.M. Weekley and B.J. Mangus, “TWTA versus SSPA: A 
comparison of on-orbit reliability data,” IEEE Trans. 
Electron Devices, vol. 52, no. 5, pp. 650–652, May 2005. 
4. E.F. Nicol, B.J. Mangus, and M.K. de Pano, “TWTA ver-
sus SSPA: A new look at Boeing fleet on-orbit reliability 
data and comparison factors,” 2006 IEEE International 
Vacuum Electronics Conference, pp. 61–62, Monterey, 
CA, April 25–27, 2006.  
5. D. Chernin, T.M. Antonsen, Jr., B. Levush, and D.R. 
Whaley, “A three-dimensional multifrequency large sig-
nal model for helix traveling wave tubes,” IEEE Trans.  
Electron Devices, vol. 48, no. 1, pp. 3–11, Jan. 2001. 
6. D.K. Abe, B. Levush, T.M. Antonsen, Jr., D.R. Whaley 
and B.G. Danly, “Design of a linear C-band helix TWT 
for digital communications experiments using the 
CHRISTINE suite of large-signal codes,” IEEE Trans. 
Plasma Science, vol. 30, no. 3, Part 1, pp. 1053–1062, 
June 2002. 
7. J.J. Petillo, E.M. Nelson, J.F. DeFord, N.J. Dionne, and B. 
Levush, “Recent developments to the MICHELLE 2-D/3-
D electron gun and collector modeling code,” IEEE 
Trans. Electron Devices, vol. 52, no. 5, pp. 742–748, 
May 2005. 
8. J.D. Wilson, K.R. Vaden, E.G. Wintucky, D.A. Force, 
I.L. Krainsky, R.N. Simons, N.R. Robbins, W.L. Men-
ninger, D.R. Dibb, and D.E. Lewis, “Advances in Space 
Traveling-Wave Tubes for NASA Missions,” Proc. IEEE, 
Special Issue on Technical Advances in Deep Space 
Communications & Tracking: Part 1, vol. 95, no. 10, 
pp. 1958–1967, Oct. 2007. 
 
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14. ABSTRACT 
Recent advances in high power and efficiency space traveling-wave tube amplifiers (TWTAs) for NASA’s space-to-Earth communications 
are presented in this paper. The RF power and efficiency of a new K-Band amplifier are 40 W and 50 percent and that of a new Ka-Band 
amplifier are 200 W and 60 percent. An important figure-of-merit, which is defined as the ratio of the RF power output to the mass (W/kg) 
of a TWT has improved by a factor of ten over the previous generation Ka-Band devices. 
15. SUBJECT TERMS 
Telecommunications; Transmitters; Deep space network; Space communication; Satellite communications; Microwave transmission; 
Microwave amplifiers; Microwave tubes; Power amplifiers; Power conditioning; Power efficiency; Traveling wave tubes 
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