High Efficiency Power Combining of Ka-Band TWTs for High Data Rate - - PDF document

High Efficiency Power Combining of Ka-Band TWTs for High Data Rate Communications

E.G. Wintucky, R.N. Simons, K.R. Vaden – NASA Glenn Research Center G.G. Lesny - Alphaport Inc., J.L. Glass – Zin Technologies, Inc. ABSTRACT Future NASA deep space exploration missions are expected in some cases to require telecommunication systems capable of operating at very high data rates (potentially 1 Gbps or more) for the transmission back to Earth of large volumes of scientific data, which means high frequency transmitters with large bandwidth. Among the Ka band frequencies of interest are the present 500 MHz Deep Space Network (DSN) band of 31.8 to 32.3 GHz and a broader band at 37-38 GHz allocated for space science [1]. The large distances and use of practical antenna sizes dictate the need for high transmitter power of up to 1 kW or more. High electrical efficiency is also a requirement. The approach investigated by NASA GRC is a novel wave guide power combiner architecture based

• n a hybrid magic-T junction for combining the power output from multiple TWTs [1,2]. This

architecture was successfully demonstrated and is capable of both high efficiency (90-95%, depending

• n frequency) and high data rate transmission (up to 622 Mbps) in a two-way power combiner circuit

for two different pairs of Ka band TWTs at two different frequency bands. One pair of TWTs, tested

• ver a frequency range of 29.1 to 29.6 GHz, consisted of two 110-115W TWTs previously used in

uplink data transmission evaluation terminals in the NASA Advanced Communications Technology Satellite (ACTS) program [1,2]. The second pair was two 100W TWTs (Boeing 999H) designed for high efficiency operation (>55%) over the DSN frequency band of 31.8 to 32.3 GHz [3]. The presentation will provide a qualitative description of the wave guide circuit, results for power combining and data transmission measurements, and results of computer modeling of the magic-T and alternative hybrid junctions for improvements in efficiency and power handling capability. The power combiner results presented here are relevant not only to NASA deep space exploration missions, but also to other U.S. Government agency programs. [1] E.G. Wintucky et al., “Ka-Band Technology Developments for Space Communications at the NASA Glenn Reseach Center,” Proc. 10th Ka and Broadband Communications Conf., Vicenza, Italy, pp. 501-508, Sep. 30-Oct. 2, 2004. [2] E.G. Wintucky et al., “Waveguide Power Combiner Demonstration for Multiple High Power Millimeter Wave TWTAs,” Fifth IEEE Inter. Vacuum Electronics Conf., Monterey, CA, pp. 98-99, April 27-29, 2004. [3] N.R. Robbins et al., “High Power, High Efficiency 32 GHz Space Traveling wave Tube,” Fifth IEEE

• Inter. Vacuum Electronics Conf., Monterey, CA, pp. 261-262, April 27-29, 2004.

https://ntrs.nasa.gov/search.jsp?R=20060005222 2018-08-07T06:30:27+00:00Z

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs

for High Data Rate Communications

E.G. Wintucky, R.N. Simons, K.R Vaden – NASA Glenn Research Center G.G. Lesny – Alphaport, Inc. J.L. Glass – Zin Technologies Inc. 2005 Tri-Service Vacuum Electron Device Workshop (TVED 2005) 13-15 September 2005 Albuquerque, NM

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

Objectives and Approach

• Demonstration of high efficiency power combining of multiple high power

Ka-band TWTs for potential generation of 1000 W of RF power

• Two-way wave guide power combiner circuit based on hybrid junction magic-

T for combining power output from multiple TWTs

• Two 110-115 W ACTS TWTAs – 500 MHz BW (29.1-29.6 GHz)
• Two 100W Boeing space TWTs (999H) – 500 MHz DSN BW (31.8-32.3

GHz)

• Demonstration of high data transmission rates of >10 Mbps (error-free or

low BER) for future NASA deep space exploration missions

• 8 Mbps (BPSK and QPSK) – ACTS TWTAs and Boeing 100W TWTs
• 622 Mbps (QPSK) - Boeing 100W TWTs
• Computer modeling of hybrid junctions for improvements in efficiency and

power handling

• CST Microwave Studio modeling and design for optimization of transmission

characteristics of magic-Ts and alternative hybrid junctions

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

32.05 GHz Down-converter 32.05 GHz Up-converter Out B P.M. Out A P.M.

Load

∆ (180o) Σ (0o)

High Power Load

Variable Attenuator Phase Shifter

3 dB Coupler

Hybrid Magic-T

Sum P.M. Diff P.M. 8 or 622 Mbps Modem/BERT TWT A TWT B Microwave Signal Generator P.M. – Power Meter

Two-way TWT power combiner circuit

32.05 GHz Down-converter 32.05 GHz Up-converter Out B P.M. Out A P.M.

Load

∆ (180o) Σ (0o)

High Power Load

Variable Attenuator Phase Shifter

3 dB Coupler

Hybrid Magic-T

Sum P.M. Diff P.M. Diff P.M. 8 or 622 Mbps Modem/BERT TWT A TWT B Microwave Signal Generator P.M. – Power Meter

Two-way TWT power combiner circuit

(Agilent 83640B)

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

Input H-plane Input E -plane Output difference port Output sum port

Hybrid Magic Tee

• Input ports – 3 dB coupling to output ports, 90

deg phase shift

• Sum port – input powers add in phase
• Difference port – phase cancellation of input

powers

Sum and difference power variations with change in phase

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

High power load Logimetrics TWT Varian TWT Magic-T Variable attenuator Variable phase shifter High power load Logimetrics TWT Varian TWT Magic-T Variable attenuator Variable phase shifter

Power combiner test bed for ACTS 100W TWTAs Power combiner test bed for Boeing 999H 100W TWTs

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

Power/efficiency measurements

• AM-AM measurements
• Manual variation of input power (20 dBm range) and phase for

power/phase balance into magic-T

• Power measurements made with Agilent dual power meters (E4419B)
• Offsets based on network analyzer (Agilent E8363B) measurements
• f insertion losses
• Accuracy of power/efficiency measurements critically dependent
• n calibration accuracy (0.1 dBm ∼ 2.3%)
• Power measurement results shown only for center frequencies of ACTS

(29.35 GHz) and DSN (32.05 GHz) frequency bands

• Output powers shown for Boeing TWTs are actual powers going

into magic-T and reflect power loss in directional couplers used for power meter measurements. Actual saturated powers are about 50.2 dBm.

• Efficiencies are for center and band edge frequencies for each

frequency band

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

Pin - dBm

• 30
• 25
• 20
• 15
• 10
• 5

5

Pout - dBm

30 35 40 45 50 55 Logimetrics Varian Combined

Pin - dBm

• 18
• 16
• 14
• 12
• 10
• 8
• 6
• 4
• 2

Pout - dBm

38 40 42 44 46 48 50 52 54 SN101 - Pout = 49.63 dBm SN102 - Pout = 49.63 dBm Pcomb - 52.19 dBm

ACTS TWTA and combined

• utput powers at 29.35 GHz

Boeing TWT and combined

• utput powers at 32.05 GHz

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

P1 + P2 - W

50 100 150 200 250

Efficiency - %

88 90 92 94 96 98 100 29.10 GHz 29.35 GHz 29.60 GHz

P1 +P2 - watts

20 40 60 80 100 120 140 160 180 200

Combiner efficiency - %

88 89 90 91 92 93 31.80 GHz 32.05 GHz 32.30 GHz

(a) ACTS TWTAS (b) Boeing TWTS

Power combining efficiencies for (a) ACTS TWTAS and (b) Boeing TWTS at center frequencies and 500 MHz band edges

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

Demonstration of data transmission

• Error-free transmission of 8 Mbps, BPSK and QPSK, (Comstream Digital Modem,

CM701) successfully achieved with both ACTS and Boeing TWT combiner circuits

• No correction required for differences in phase-vs-frequency (dϕ/df) between RF output
• f the two TWTs (narrow BW of signal & small dependence of peak of combined power
• n phase)
• Low BER (2.4x10-8) 622 Mbps QPSK successfully demonstrated (Synthesis

Research 622 BitAlyzer) with mod-1 for Boeing TWT combiner circuit

• Correction required for 622 Mbps because of large phase imbalance at magic-T over signal

BW (311 MHz BW – QPSK)

• Initially dϕ/df = 0.991 deg/MHz
• Added wave guide: mod 1 – 0.147 deg/MHz, mod 2 – 0.018 deg/MHz
• Useful bandwidth of magic-T for data transmission shown to be at least 3 GHz
• Gain ripple of combined power output < 1dBm and equal to or less than outputs of

individual TWTs

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

S21 comparison - Initial results before circuit modification

FRQpowcompF1S (chart 2)

• 40
• 35
• 30
• 25
• 20
• 15
• 10
• 5

5 10 31.80 31.85 31.90 31.95 32.00 32.05 32.10 32.15 32.20 32.25 32.30 frequency - GHz S21 - dBm S21-101-sat S21-102-sat S21-sum 320 MHz BW

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

Phase difference comparison - before and after circuit mods

FrqSwp_compare1 (chart 9)

• 300
• 200
• 100

100 200 300 31.80 31.85 31.90 31.95 32.00 32.05 32.10 32.15 32.20 32.25 32.30

frequency - GHz phase difference - deg

phase diff-cpled ports-after mod1 phase diff-cpled ports-before mods phase diff-cpled ports-after mod2 dϕ/df=0.991 deg/MHz dϕ/df=0.147 deg/MHz dϕ/df=0.018 deg/MHz 311 MHz

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

Comparison of sum port S21 before & after circuit modification

FrqSwp_compare1 (chart 2)

• 40
• 35
• 30
• 25
• 20
• 15
• 10
• 5

5 31.80 31.85 31.90 31.95 32.00 32.05 32.10 32.15 32.20 32.25 32.30 frequency - GHz S u m p o rt S 2 1 - d B Sum port S21 before circuit mod Sum port S21 after circuit mod S21 = 0 dB at 32.05 GHz 311 MHz BW

Comparison of sum port S21 before & after circuit modification

FrqSwp_compare1 (chart 1)

• 40
• 35
• 30
• 25
• 20
• 15
• 10
• 5

5 31.55 31.65 31.75 31.85 31.95 32.05 32.15 32.25 32.35 32.45 32.55 frequency - GHz S u m p o rt S 21 - d B Sum port S21 before circuit mod Sum port S21 after circuit mod S21 = 0 dB at 32.05 GHZ

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

S21 comparison - 101,102, sum (1 GHz BW)

PowComp 6-22-05 (chart 1)

6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 31.55 31.65 31.75 31.85 31.95 32.05 32.15 32.25 32.35 32.45 32.55 frequency - GHz S21 - dBm 101 - S21, 1.03 dBm pk-to-pk 102 - S21, 0.78 dBm pk-to-pk Sum - S21, 0.78 dBm pk-to-pk Max: 10.16 dBm, 31.79 GHz, Min: 9.38 dBm, 31.64 GHz, Min: 6.83 dBm, 31.63 GHz, Min: 7.05 dBm, 31.64 GHz, Max: 8.08 dBm, 31.79 GHz, Max: 7.61 dBm, 32.55 GHz,

Power vs frequency - 3 GHz frequency sweep Comp fs 3GHz 6-28-05 (chart 1)

48.5 49.0 49.5 50.0 50.5 51.0 51.5 52.0 52.5 53.0 30.55 31.05 31.55 32.05 32.55 33.05 33.55

frequency - GHz R F p o w e r - d B m

101 - Pout - 1.39 dBm pk-to-pk 102 - Pout - 1.21 dBm pk-to-pk Sum port - Pout - 0.93 dBm pk-to-pk

Power-phase balance at 32.05 GHz

• max. 50.49 dBm, 31.0975 GHz
• max. 50.82 dBm, 31.105 GHz
• max. 50.32 dBm, 33.175 GHz
• min. 49.19 dBm, 33.280 GHz
• min. 49.11 dBm, 30.595 GHz
• min. 51.89 dBm, 31.6375 GHz

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications
• Preliminary computer aided design and modeling of high power Ka-band

4-port hybrid junctions using CST Microwave Studio

• Objectives: Improvement of efficiency and power handling

capability

• Design goals:
• Center frequency of 32.05 GHz (500 MHz BW), WR28 waveguide
• Hybrid junctions: Magic Tee, Folded E-plane Tee, Rat Race
• Use of elements appropriate for powers ranging from hundreds of watts

to kilowatts

• Optimization of S-parameters – matching of ports
• 3 dB insertion loss
• Minimum of 15 dB reflection loss
• Minimum of -40 dB isolation loss

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

Port 4 Port 3 Port 2 Port 1

(E-arm) (H-arm) (E-arm) (H-arm) Magic Tee matched by inductive windows Magic Tee matched by cone- fin structure

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

λ/4 λ/4 3λ/ 4 λ/4

Folded E-plane Tee “Split Co-linear arms” Folded E-plane Tee “Common wall” (H-arm) (H-arm) “Rat Race” hybrid ring

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

Comparison of simulated transmission characteristics of the different hybrid junctions (WR28 wave guide) over a frequency range of 31.8 to 32.3 GHz

Insertion Loss Reflection Loss Isolation |S21| dB |S24| dB |S11| dB |S44| dB |S41| dB Magic Tee (inductive windows)

• 3.072
• 3.17
• 24.17
• 14.48
• 76.4

Magic Tee (cone-fin)

• 3.156

3.426

• 15.44
• 9.823
• 136.3

Folded E-Plane Tee (common wall)

• 3.203
• 3.124
• 13.72
• 15.9
• 151.4

Folded E-plane Tee (split collinear arms)

• 3.068
• 3.073
• 14.84
• 19.17
• 140.6

Rat Race

• 3.569
• 3.467
• 10.2
• 10.42
• 27.38

Hybrid Junction

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Glenn Research Center at Lewis Field

High Efficiency Power Combining

• f Ka-Band TWTs for High Data Rate Communications

Conclusions

• Two-way Ka-band wave guide power combiner circuit based on magic-T

hybrid junction can provide high power (> 200 W) at high efficiency (>90%).

• Readily extendable to combine 4 or 8 TWTs (binary configuration)
• Magic-T can support high data rate transmission rates of at least 622 Mbps

at low BER.

• Wave guide circuit easily modified to compensate for output phase imbalances

(dϕ/df) of TWTs

• Useful bandwidth for high data transmissions rates can be extended to at least 3

GHz.

• Computer modeling of magic-T and other hybrid junctions shows

improvements in efficiency (lower insertion, return and isolation losses) and power handling capability are possible.

• Folded E-plane hybrid junctions very well suited for high power applications.

(Robust, easily fabricated, relatively inexpensive)