Rainee N. Simons, Edwin G. Wintucky, Jeffrey D. Wilson, and Dale A. Force

Glenn Research Center, Cleveland, Ohio

Ultra High Power and Effi ciency Space TravelingWave Tube Amplifi er Power Combiner With

Reduced Size and Mass for NASA Missions

NASA/TM—2009-215584

March 2009
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Rainee N. Simons, Edwin G. Wintucky, Jeffrey D. Wilson, and Dale A. Force

Glenn Research Center, Cleveland, Ohio

Ultra High Power and Effi ciency Space TravelingWave Tube Amplifi er Power Combiner With

Reduced Size and Mass for NASA Missions

NASA/TM—2009-215584

March 2009

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Acknowledgments

The authors would like to thank Todd T. Peterson, NASA GRC Program Manager for supporting the Lunar Reconnaissance 

Orbiter (LRO) Traveling-Wave Tube Amplifi er (TWTA) development. In addition, the authors greatly appreciate the support 

that they have received from Neal R. Robbins, Daniel R. Dibb, Dr. William L. Menninger, Dr. Xiaoling Zhai, Robert Benson, 

James Burdette, David E. Lewis, and Paul C. Spitsen at L-3 Communications, Electron Technologies Inc.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5285 Port Royal Road

Springfi eld, VA 22161

Available electronically at http://gltrs.grc.nasa.gov

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—2009-215584 1

Ultra High Power and Efficiency Space Traveling-Wave Tube Amplifier 

Power Combiner With Reduced Size and Mass for NASA Missions 

Rainee N. Simons, Edwin G. Wintucky, Jeffrey D. Wilson, and Dale A. Force 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

In the 2008 International Microwave Symposium (IMS) 

Digest version of our paper, recent advances in high power 

and efficiency space traveling-wave tube amplifiers (TWTAs) 

for NASA’s space-to-Earth communications are presented. 

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. In this extended paper, a high 

power, high efficiency Ka-band combiner for multiple TWTs, 

based on a novel hybrid magic-T waveguide circuit design, is 

presented. The measured combiner efficiency is as high as 90 

percent. In addition, at the design frequency of 32.05 GHz, 

error-free uncoded BPSK/QPSK data transmission at 8 

megabits per second (Mbps), which is typical for deep space 

communications is demonstrated. Furthermore, QPSK data 

transmission at 622 Mbps is demonstrated with a low bit error 

rate of 2.4×10–8, which exceeds the deep space state-of-the-art 

data rate transmission capability by more than two orders of 

magnitude. A potential application of the TWT combiner is in 

deep space communication systems for planetary exploration 

requiring transmitter power on the order of a kilowatt or 

higher. 

I. Introduction 

Communications signals transmitted from spacecrafts 

orbiting the outer planets 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 ultra 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 electronics technology. Solid-state devices 

based on GaAs or GaN high electron mobility transistor 

(HEMT) technology, when characterized on-wafer using loadpull 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 overall efficiency 

of Ka-Band high power solid-state power amplifiers (SSPAs) 

are on the order of 15 to 20 percent, as described in the 2008 

International Microwave Symposium (IMS) Digest version of 

our paper (Ref. 3). The low efficiency results in thermal 

management issues, which impacts reliability. On the other 

hand, microwave vacuum electronics based devices for space 

applications such as helix traveling wave tubes (TWTs) have 

demonstrated reliability at higher microwave frequencies with 

power output in the range of ten to several hundred watts and 

corresponding efficiency in the range of 40 to 60 percent 

(Refs. 4 and 5). 

Deep space missions in the past have typically relied either 

on solar cells or radioactive thermal generators as a source of 

electrical power, which greatly limits the power available for 

communications. As an alternative, NASA has been 

developing nuclear fission electric power and propulsion 

technologies, which would provide orders of magnitude more 

power for science instruments onboard the spacecraft. An 

example was the Prometheus project (Ref. 6). This would 

potentially make possible the support of high power 

communications systems with data transmission rates 1000X 

higher (8 to 10 Mbps) than that previously achieved 

(10 kilobits per second (kbps)) from deep space. To enable 

such high data rates, several approaches to develop an onboard 

RF transmitter with an output power on the order of about 

1 kW at Ka-Band, including power combining, are being 

considered. 

Communication from the vicinity of the Moon is considered 

to be near-Earth while that from the planets of our solar 

system is considered to be from deep space. The 

corresponding downlink frequency band designated for nearEarth is 25.5 to 26.5 GHz (K-Band) and for deep space 

communications is 31.8 to 32.3 GHz (Ka-Band). In the 2008 

IMS Digest version of our paper (Ref. 3), we presented 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 

were manufactured by L-3 Communications, Electron 

Technologies Inc. (ETI) under contracts from NASA Glenn 

Research Center (GRC). 

In this extended paper, we present the development of a 

novel Ka-Band power combiner architecture based on the use 

of hybrid magic-T’s for combining the power output from 

multiple TWTs in a binary configuration with the potential to 

achieve 1 kW (Ref. 7). This architecture avoids the need to 

develop a single ultra-high power TWT, which would be 

technically challenging. To the best of our knowledge this 
NASA/TM—2009-215584 2

work demonstrates the highest power combining achieved 

with a Ka-Band magic-T. The TWTs utilized in the combiner 

experiment were also manufactured by L-3 Communications 

ETI under a contract from NASA GRC. Our approach has the 

following unique features: first, the size and mass are small, 

which are desired features for space applications. Second, it 

has low insertion loss and excellent output amplitude/phase 

balance, which ensures high combining efficiency. Third, it 

has very high isolation between the two input ports, which 

allows a TWT to continue operating if the other fails. Fourth, 

the circuit is capable of operating over nearly 60 percent of the 

waveguide band and hence has wide bandwidth if needed for 

high data rates. Fifth, the ports are impedance matched and 

hence minimize reflection introduced inter-symbol 

interference, which degrades bit error rate (BER). Sixth, the 

experiments reported in this paper have been carried out over 

the NASA’s Deep Space Network (DSN) downlink Ka-Band 

frequency range of 31.8 to 32.3 GHz. 

II. TWT Design and Modeling 

Until recently, the design of TWTs was mainly done 

through trial and error, which was time consuming and 

expensive. The advances made in desktop computing and 

electromagnetic 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 

MICHELLE 3-D Code for multi-stage depressed collector 

design (Refs. 8 to 10). 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 B-H (magnetic flux-magnetic field) 

product samarium cobalt permanent magnets, which are used 

in focusing the electron beam. Moreover, advances in 

tungsten/osmium cathode technology have resulted in cathode 

lifetimes exceeding 20 years in space (Ref. 11). 

III. K-Band and Ka-Band Space TWT 

Requirements and Measured 

Performance 

A. L-3 ETI Model 9835H K-Band TWT 

The K-Band TWT was developed for communications from 

the Lunar Reconnaissance Orbiter (LRO) spacecraft to Earth. 

This spacecraft is scheduled for launch in April 2009. The 

specifications for this TWT are presented in (Ref. 3). Three 

TWTs were manufactured and characterized and all three meet 

full specification, resulting in first pass design success and 

100 percent yield. The measured output power, overall 

efficiency, and saturated gain of the three TWTs are presented 

in (Ref. 3). 

B. L-3 ETI Model 999H Ka-Band TWT 

This Ka-Band TWT was developed for communications 

from a spacecraft orbiting Mars to NASA’s DSN ground 

stations. The power output and overall efficiency of the TWT 

are 100 W and 60 percent, respectively. This TWT also served 

as an engineering model to validate the advanced design codes 

described earlier in Section II and paved the way for the 

successful development of the space qualified 200-W TWT 

described next. 

C. L-3 ETI Model 999HA Ka-Band TWT 

This 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 presented in (Ref. 3). Three such 

TWTs were manufactured and characterized and all were able 

to demonstrate at least 180 W. The TWT S/N 202 was tested 

up to 250 W and for long service life space qualified at 

200 W. The measured overall efficiency and saturated gain of 

this TWT exceeded 60 percent and 55 dB, respectively. The 

measured characteristics are presented in (Ref. 3). 

To transmit data from Jupiter at very high rates on the order 

of several megabits per second, the spacecraft transmitter 

power needs to be on the order 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 

depressed collector circuits for high efficiency. The collector 

circuits require high voltages, which are provided by a 

separate electronic power conditioner (EPC) attached by an 

umbilical power cord to the TWT. 

IV. Electronic Power Conditioners 

(EPCs) for TWTs 

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 

manufactured by L-3 Communications ETI. These EPCs are 

highly reliable and efficient (90 percent) and can operate from 

either regulated or unregulated spacecraft bus voltages. A 

single EPC can be used to independently operate two TWTs. 

The masses and dimensions of the TWT and the EPC are 

presented in (Ref. 3). 
NASA/TM—2009-215584 3

V. High Power Combiner Operating 

Principle 

A two-way high power combiner based on a waveguide 

magic-T hybrid coupler is shown in Figure 1(a). In this 

approach, the two TWTAs are coupled to Ports #1 and #4 (HPlane and the E-Plane ports along the plane of symmetry) of the 

magic-T, respectively. The incident power at Port #1 (from 

TWTA #1) is evenly split into two in-phase components 

between Ports #2 and #3. The power incident at Port #4 (from 

TWTA #2) is also evenly split but with 180° phase difference 

between Ports #2 and #3. The magic-T is designed such that the 

electrical lengths between any port and the junction are 

identical. Thus by the superposition principle, the power at Port 

#2 must add in phase while an equal power at Port #3 must 

result in perfect cancellation. Consequently, Ports #2 and #3 are 

referred to as the sum and difference ports, respectively. This 

two-way combiner architecture can be extended in a binary 

configuration to obtain 1 kW by combining 2n

 TWTAs, where n 

is an integer, as illustrated in Figure 1(b). 

VI. High Power Hybrid Magic-T 

The high power hybrid magic-T used in our demonstration 

was manufactured by Millitech, Inc. and is shown in Figure 2. 

The two input ports and the sum and difference ports are 

indicated. The magic-T is fabricated from aluminum and has a 

split block construction for ease of fabrication. In addition 

steel guide pins are provided at all ports for precision 

alignment. The measured worst-case insertion loss and VSWR 

are about 0.45 dB and 1.47, respectively, and they occur at the 

high frequency end of the band. In addition, the measured 

amplitude and phase balance are within 0.27 dB and ±6°, 

respectively. Using equations from (Ref. 12), the calculated 

additional losses in combining efficiency due to the above 

amplitude and phase deviations are about 3.0 and 1.1 percent, 

respectively.

Lastly, measurements show that Ports #1 and #4 of the 

magic-T have very high isolation on the order of 30 dB or 

higher across the band of interest. Therefore, the magic-T was 

chosen over a hybrid 90° coupler, which has an isolation of 

about 20 dB. The mass and size of the magic-T are about 

100 gm and 50×50×50 mm, respectively. 

VII. Power Combiner Measured 

Performance 

The power combiner was successfully demonstrated with a 

pair of 100-W (L-3 ETI Model 999H, Serial Number 101 and 

102) high efficiency Ka-Band space TWTs. Figures 3(a), (b), 

and (c) show the measured power output from the two TWTs 

and the magic-T combiner as a function of the input power to 

the TWT at the lower edge (31.8 GHz), center (32.05 GHz) 

and upper edge (32.3 GHz) of the NASA DSN 500 MHz wide

Figure 1.—(a) Basic configuration of waveguide magic-T based 

power combiner for two coherent TWTs. (b) Binary circuit 

architecture for combining 2n

 TWTs, where n is an integer 

(shown here for n = 2). 

Figure 2.—Waveguide (WR-28) hybrid magic-T used in 

high power combiner circuit showing sum and difference 

output ports. 
NASA/TM—2009-215584 4

frequency band. It can be seen that the two TWTs are well 

balanced with the combined output power at about 3 dB (2X) 

greater. The AM-to-PM values for the two TWTs are less than 

Figure 3.—Measured power output from individual TWTs 

(Model 999H) and magic-T combiner as function of input 

power to TWT. (a) 31.8 GHz. (b) 32.05 GHz. 

(c) 32.30 GHz. 

3.5 deg/dB at saturation. The phase changes at the output of 

the two TWTs when the input RF drive is increased from 

small signal (–20 dBm) to saturation (0 dBm) are 44° and 32°, 

respectively. 

For these measurements, a microwave signal generator and 

a 3 dB power divider were used as the RF source to the two 

TWTs. In addition, one of the input arms to the TWTs 

included a variable attenuator and a variable phase shifter. The 

magic-T input powers were balanced with the variable 

attenuator. The magic-T input phases were balanced by 

adjusting the phase shifter for a minimum power reading at the 

difference port, which corresponds to a maximum combined 

power at the sum port. Consequently, the phase changes, AMto-AM, and AM-to-PM characteristic differences of the TWTs 

did not impact the output power. 

Figure 4 shows the power combining efficiencies at the 

center (32.05 GHz) and ±250 MHz band edge frequencies. 

The combining efficiencies were about 88.5 percent or greater. 

As shown in Figure 4, the power combining efficiency is 

maintained over a broad range of input powers. The 

importance of this is that the power combiner is equally 

efficient at both the lower output power linear region, where 

multi-channel commercial satellite transmitter TWTs usually 

operate, and the non-linear saturation region, where deep 

space communications systems typically operate for maximum 

TWT power and efficiency. In Figure 4 at a fixed frequency, 

the difference in efficiency as a function of the total input 

power to the combiner is within ±0.5 percent. 

Improvements in performance are possible by optimizing 

the magic-T for efficiency and higher power handling 

capability over a narrow frequency range of specific interest. 

This was demonstrated with computer modeling of the magicT and alternative hybrid junctions using Microwave Studio 

(Ref. 13). The folded E-plane magic-T appears to be the most 

promising of all the types that were investigated. A custom 

optimized magic-T with about 500 MHz bandwidth and 

improved waveguide surface properties is estimated to have an 

insertion loss on the order of 0.25 dB (Ref. 13). 

Figure 4.—Measured efficiency of magic-T based power 

combiner as function of total input power. 
NASA/TM—2009-215584 5

VIII. Combiner Reliability 

In the event of a single TWT failure, the combined power 

output would decrease by 6 dB. However, with appropriate 

placement of two waveguide switches as shown in Figure 5(a), 

the power loss would be only 3 dB. In this arrangement under 

normal operation, the waveguide switches allow the TWT 

outputs to be combined in the magic-T. If either one of the 

TWTs fail then the other TWT is directly connected to the RF 

output. The sensor connected to Port #3 detects the power 

imbalance and commands the switches to reroute the TWT 

output. In addition, a ferrite circulator present between the RF 

output port and the antenna prevents the reflections from the 

antenna from influencing the imbalance sensor control. 

With the addition of a back-up TWT and appropriate 

placement of two waveguide switches as shown in 

Figure 5.—Combiner with redundancy. (a) Includes two 

waveguide switches. (b) Includes two waveguide 

switches and standby TWT. Ports #1 through #4 

correspond to ports of magic-T in Figure 1(a). 

Figure 5(b), the power loss would be zero. In this scheme 

under normal operation, TWT #1 and #2 are combined. In the 

event of a TWT failure, the standby TWT #3 can be switched 

in place of the failed TWT without loss in system 

performance. The circuits in Figures 5(a) and (b) are work in 

progress requiring additional efforts for performance 

optimization and the design details are not available yet. 

IX. Bit Error Rate (BER) 

Characterization 

To demonstrate the TWT and combiner performance, we 

employed un-coded BPSK and QPSK bit streams. However, 

in an actual space-to-Earth link both block coding as well as 

convolution coding would be used for error correction. In 

addition, QPSK allows the TWTA to operate in saturation and 

consequently at the highest possible efficiency, which is a 

desired attribute in situations where prime power is scarce. Bit 

error rate (BER) tests were performed at the output of the 

magic-T combiner when the data rate was on the order of 8 

and 622 Mbps. 

At 8 Mbps, error-free (BER < 1×10–9) un-coded BPSK and 

QPSK data transmission was observed. This was possible 

because the bandwidth occupied by the BPSK and QPSK 

signals were 8 and 4 MHz, respectively. Over these narrow 

bands, the rate of change in phase with frequency along the 

two TWT paths was small. The energy per bit/noise power 

spectral density ratio (Eb/N0) was 21 dB at a BER of 10–9 for a 

QPSK data rate of 8 Mbps. Since there was no equalizer in the 

receiver, the BER was due primarily to inter-symbol 

interference. The 8 Mbps is in the range of data rates proposed 

for some of the planetary exploration missions. 

Future deep space missions are calling for data rates 

approaching a gigabit per second at Ka-Band. The bandwidth 

allocated at Ka-Band is 500 MHz (31.8 to 32.3 GHz). A high 

data rate QPSK signal would occupy a significant portion of 

this bandwidth. However, in the characterization of our TWT 

combiner we were limited by our test equipment, which could 

deliver only 622 Mbps of QPSK data and required a 

bandwidth of 311 MHz. Initially, over this band, the rate of 

change in phase with frequency along the two TWT paths was 

large. This created a significant phase imbalance at the inputs 

to the magic-T combiner. The phase imbalance resulted in an 

observed reduction in signal amplitude of about 15 dB at the 

band edges. The above phase and amplitude changes made it 

impossible to detect the transmitted signal. By adding an 

appropriate dispersive component on one of the TWT paths, 

the disparity in electrical lengths and effect on RF amplitude 

was eliminated. The phase compensation was made by adding 

a section of a standard WR-28 waveguide at the input of one 

of the TWTs. With the waveguide in place, the measured rate 

of change of phase difference with frequency at the input ports 

to the magic-T was 0.147 deg/MHz compared to 

0.991 deg/MHz before compensation and is presented in 

Figure 6. The 0.147 deg/MHz rate of change of phase with 
NASA/TM—2009-215584 6

Figure 6.—Measured rate of change of phase difference at 

input ports to magic-T as function of frequency before and 

after phase compensation. For both cases, phase difference 

is set equal to 0° at center frequency of 32.05 GHz. 

Figure 7.—Measured combined saturated relative power at 

sum port of magic-T as function of frequency before and 

after phase compensation. For both cases, relative power is 

set equal to 0 dB at 32.05 GHz. 

frequency was observed out to at least 3 GHz (30.55 to 

33.55 GHz). 

Although further improvement is possible, this was 

adequate for a 622 Mbps data transmission rate QPSK signal 

with low BER, which required only 311 MHz of the available 

bandwidth. Figure 7 shows the measured combined saturated 

relative power at the sum port of the magic-T as a function of 

the frequency before and after compensation. As a result of 

this circuit modification, we were able to successfully 

demonstrate QPSK data transmission at 622 Mbps with a low 

BER of 2.4×10–8, which exceeds the data rate required for a 

typical deep space mission by more than two orders of 

magnitude. 

X. Conclusions and Discussions 

The performance parameters of a K-Band and a Ka-Band 

TWT for NASA’s near-Earth and deep space communications 

are presented in the 2008 IMS Digest version of our paper 

(Ref. 3). These results are state-of-the art and provide 

unprecedented performance. The model 999HA Ka-Band 200-

W TWT became available for the very first time in 2006. Prior 

to this development, the highest CW RF power produced by a 

U.S. manufactured space TWT at Ka-Band and flown in space 

is the model 910H TWT. This TWT was manufactured by L-3 

ETI, for the Cassini-Huygens Mission with 10 W, 41 percent 

overall efficiency and a mass of 0.75 kg (Ref. 14). The KaBand model 999HA TWT increases the output power by a 

factor of twenty to 200 W while only doubling the mass to 

1.5 kg. Thus a figure-of-merit (FOM) defined as the ratio of 

the RF power output to the mass (W/kg) shows an increase of 

a factor of ten. 

In this extended paper, a compact Ka-Band high power high 

efficiency combiner based on a hybrid magic-T for combining 

the output from multiple TWTAs has been successfully 

demonstrated over NASA’s DSN frequency band. At the 

design frequency of 32.05 GHz, error-free uncoded 

BPSK/QPSK data transmission at 8 Mbps and QPSK data 

transmission at 622 Mbps with a low BER of 2.4×10–8 was 

demonstrated. The 622 Mbps data rate is significantly higher 

than the state-of-the-art, for example 5.247 Mbps for the Mars 

Reconnaissance Orbiter (MRO) mission (Ref. 15). The 

measurements show that two 100-W TWTs can be combined 

with efficiency as high as 90 percent. Based on these 

measurements, the projected combiner efficiency of an eightway combiner for eight 100-W model 999H TWTs to achieve 

about 800 W would be about 73 percent. On the other hand, if 

four 200-W model 999HA TWTs are used, then the projected 

combiner efficiency would be about 81 percent. The total 

mass of the combiner consisting of four 200-W TWTs 

(Ref. 3), two EPCs (Ref. 3), and a magic-T is about 

15 kg and the total volume is equal to that of a cube with sides 

less than 28 cm. 

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4. TITLE AND SUBTITLE

Ultra High Power and Efficiency Space Traveling-Wave Tube Amplifier Power Combiner 

With Reduced Size and Mass for NASA Missions 

5a. CONTRACT NUMBER

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5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Simons, Rainee, N.; Wintucky, Edwin, G.; Wilson, Jeffrey, D.; Force, Dale, A. 

5d. PROJECT NUMBER

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5f. WORK UNIT NUMBER

WBS 342556.06.01.10.01.02 

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National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

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This publication is available from the NASA Center for AeroSpace Information, 301-621-0390

13. SUPPLEMENTARY NOTES

Submitted to IEEE Transactions on Microwave Theory and Techniques. 

14. ABSTRACT

In the 2008 International Microwave Symposium (IMS) Digest version of our paper, recent advances in high power and efficiency space 

traveling-wave tube amplifiers (TWTAs) for NASA’s space-to-Earth communications are presented. 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. In this extended paper, a high power, high efficiency Ka-band combiner for multiple TWTs, based on a novel 

hybrid magic-T waveguide circuit design, is presented. The measured combiner efficiency is as high as 90 percent. In addition, at the design 

frequency of 32.05 GHz, error-free uncoded BPSK/QPSK data transmission at 8 megabits per second (Mbps), which is typical for deep 

space communications is demonstrated. Furthermore, QPSK data transmission at 622 Mbps is demonstrated with a low bit error rate of 

2.4x10-8, which exceeds the deep space state-of-the-art data rate transmission capability by more than two orders of magnitude. A potential 

application of the TWT combiner is in deep space communication systems for planetary exploration requiring transmitter power on the order 

of a kilowatt or higher. 

15. SUBJECT TERMS

Telecommunications; Transmitters; Deep space network; Space communications; Satellite communication; Microwave transmission; 

Microwave amplifiers; Microwave tubes; Power amplifiers; Power conditioning; Power efficiency; Traveling wave tubes 

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