COMPACT GAN HIGH POWER AMPLIFIERS

FOR SPACE COMMUNICATION, SENSING

AND GREEN POWER TRANSMISSION

Shigeo Kawasaki and Yuta Kobayashi

ISAS/JAXA, Sagamihara, Japan

kawasaki.shigeo@jaxa.jp, kobayashi.yuta@jaxa.jp

+81-50-3362-5732, +81-50-3362-6450

Keywords: Gallium nitride, High power amplifier, Microwave power transmission, Aerospace electronics, Space

Communication

Abstract: On the base of a green-eco technology, S-bandhigh power GaN amplifiers have been developed with a

microwave power transmission function in the space electronics equipment. High DC-to-RF conversion

efficiency of 63 % was achieved in the 20W GaN amplifier operating at 2.25 GHz and its design technique

was extended to realize 1 kW SSPA for the space communication. Furthermore, wireless sensor operation

and battery charging was also demonstrated by means of microwave power transmission.

1 INTRODUCTION

The RF technology has been used for

communication and sensing, so far. As the third

usage of the microwaves, wireless power

transmission and energy harvesting have been paid

much attention as one of solutions of environmental

problems. With the enormous interest brewing,

researchers around the world started to develop the

wireless energy transfer/power transmission and

energy harvesting/scavenging. This is the green-eco

wireless power technology for the green life

(environmental issues), ecology (nature-human

interaction) and economy (cost effectiveness).

Specifically, it will have a great impact on many

applications such as compact and battery-less

wireless communications and wireless sensor

systems. Wireless power delivery generated from

clean energy may be called wireless green power

transmission.

The wireless power transmission (WPT) is usually

categorized into three, the EM Coupling, the

Magnetic Resonance (MR), and the Microwave

WPT (MPT). It has been known that the carrier

wave without modulation can be delivered the

energy wirelessly. This is the basic feature of MPT.

Comparing with wired systems and other WPT

technologies, the MPT has become one of the most

important technologies on demand to future space

missions as well as green eco technologies (N.

Shinohara, 2009). For instance, the MPT module

with some sensors can reinforce health monitoring

functions in a space craft without wire-harness and

solve a payload problem by removing some of

onboard electrical power subsystems (EPS) in the

space craft.

Reading the space electronics, a compact

communication system is needed both in the

onboard communication system and in the ground

station. On behalf of operation of a space ground

station, such as the Usuda Deep Space Center

(UDSC) shown in Fig. 1, a high power and high

efficiency solid state power amplifier is strongly

requested. For this purpose, a wide band-gap

semiconductor such as GaN and SiC is promising.

Further, reduction of payload is important issue in

the onboard system. In order to solve this problem,

realization of a high power and high efficiency RF

amplifier using the wide band gap semiconductor is

requested. This is also the effective solution for the

single event, total dose radio-isotope problem, and

high temperature operation (N. Adachi, 2005).

Regarding power receiving in the MPT, power

detection by a rectenna directory connected with an

antenna and a detector is typical (M. Furukawa,

2006) (M. Hori, 2011) (T. ITO, 1979). As described

before, wireless power is intentionally delivered to

the rectenna. In the case of MPT, the high

Kawasaki S. and Kobayashi Y.

COMPACT GAN HIGH POWER AMPLIFIERS FOR SPACE COMMUNICATION, SENSING AND GREEN POWER TRANSMISSION.

DOI: 10.5220/0005413700440051

In Proceedings of the First International Conference on Telecommunications and Remote Sensing (ICTRS 2012), pages 44-51

ISBN: 978-989-8565-28-0

breakdown-voltage RF detector is required to obtain

high converted DC power, for instance, battery

charging due to MPT. On the other hand,

electromagnetic energy harvesting can be done in

the RF environment. This harvester also consists of

the rectenna but the harvested RF energy includes

leaked RF energy from a transmitter in other place.

The harvesting energy which tune into RF energy

may include that from a energy converter/transfer.

When the collected energy is weak, this may be

called as “scavenging”.

In this paper, the wireless power transmission is

explained as the green-eco technology. From this

view point, demonstration of space communication

and wireless sensor by means of microwave power

transmission is described by using high power GaN

amplifiers. The 1kW SSPA combined with the high

power GaN amplifiers is shown.In addition, thermal

sensor operation and battery charging by microwave

power transmission are introduced.

2 MICROWAVE GAN CIRCUITS

FOR SPACE

COMMUNICATION AND MPT

2.1 Semiconductor devices

In space communication, high efficient power device

is necessitated. In this view point, a wide band-gap

semiconductor is very promising. Among them, the

gallium nitride (GaN) has recently been focused on

as a high power and high efficiency device in the

microwave region. Therefore, the GaN is one of the

most significant elements to achieve effective use of

energy in space not only for communications but

also for power transmissions. The GaN has several

superior material properties, such as wide band gap,

high saturation velocity, and good thermal

conductivity. Due to these properties, the GaN is

considered to have advantages in high efficiency,

and high temperature conditions in addition to the

high power characteristics. Thus, GaN is expected to

be used in space applications such as, high power

amplifiers (DC-to-RF conversion modules) and

rectifiers (RF-to-DC conversion modules).

Fig. 1.The kW-class SSPA for the space communication

2.2 High power amplifiers

The S-band GaN based high power amplifiers

(HPAs) have been designed, developed, and

evaluated for space applications of the

communication, a wireless sensor and microwave

energy transfer intended for the green-eco

technology. As examples for the onboard

application, the 20W and 100W GaN amplifiers with

the high power added efficiency were developed.

2.2.1 The 20W-class GaN HPA

The 20-W-class single-stage high power amplifier

was designed in the S-band by using the commercial

available CAD(Agilent: Advanced Design System)

with small signal S-parameters. The package type of

20-W-class GaN HEMT on a Si substrate and the

circuit substrate (Rogers RO4350 : the copper

thickness of 70 um, the substrate thickness of 0.762

mm, the permittivity of 3.46) were used. The size of

the 20-W-class amplifier was 50*55*17 mm. The

circuit overview is shown in Fig. 2.

The measured small signal S-parameters from the

20W-class GaN HPA are shown in Fig. 3. Between

2.1 and 2.4 GHz, it was observed from Fig 3 that

peaks of measured return loss of S11 and S22were

achieved below -10 dB and the peak of measured

forward gain of S21 was larger than 15 dB. In

addition, characteristics of input-output, gain, drain

efficiency and power added efficiency (PAE) from

the fabricated 20W HPA at 2.25 GHz are shown in

Fig. 4. It is confirmed that P1dB and P3dB were

42.2 dBm and 43.7 dBm and the PAE at these points

were 55.1 % and 63.3 %, respectively. (Y.

Kobayashi, 2012)

2.2.2 The 100W-class GaN HPA Unit

The 100-W-class single-stage high power amplifier

was also designed and fabricated in the S-band with

the package type 100W-class GaN HEMT on the Si

substrate and the circuit substrate (RogersRO4350).

The size of the 100-W-class is 100*76*30 mm

shown in Fig. 5.

Compact Gan High Power Amplifiers for Space Communication, Sensing and Green Power Transmission

Fig. 5. 100 W-classGaN HPA

S11

S21

S22

Fig. 6. Measured S-Parameters

20 22 24 26 28 30 32 34 36 38 40

Pin[ dBm]

Pout[dBm],Gain[dB],η [%],PAE[%]

NPT25100: Vds:28 V, Freq:2.25 GHz

Pout

Gain

PAE

Fig. 7. Input-output characteristics

Fig. 2. 20 W-classGaN HPA

S11

S21

S22

Fig. 3. Measured S-Parameters

16 18 20 22 24 26 28 30 32 34

Pin[ dBm]

Pout[dBm],Gain[dB],η [%],PAE[%]

NPT25015: Vds:28 V, Freq:2.25 GHz

Pout

Gain

PAE

Fig. 4. Input-output characteristics

The measured small signal S-parameters of the

100W-class GaN HPA are shown in Fig. 6. In this

figure, it was found that the S11 was measured with

smaller than -11 dB, the S22 was smaller than -6.5

dB, and S21 was larger than 15 dB at the frequency

rangebetween 2.1-2.4 GHz. In addition, the input-

output characteristics of the 100W-class HPA at

2.25 GHz are shown in Fig. 7. It is confirmed that

P1dB and P3dB were 45.3 dBm and 48.0 dBm and

the power added efficiency (PAE) at these points

were 43.0 % and 52.6 %, respectively.

First International Conference on Telecommunications and Remote Sensing

Fig. 8. Block diagram of 1-kW-class GaN HPA equipment

Fig. 9. 1-kW-class GaN HPA equipment

Fig. 10. 1-kW-class HPA equipment characteristics

3 APPLICATION AND TEST

For the space green power transmission as well as

the ground-to-satellite application, the 1 kW GaN

solid state power amplifier (SSPA) using a power

combiner technique was fabricated. The total DC-to-

RF conversion efficiency of more than 50 % was

achieved. Using these components, some

preliminary experiments of space power

transmission have also been conducted.

Wireless power transmission (WPT) is one of the

most important technologies for future space

missions. WPT can be applied to not only inside of

space crafts but also outside of ones. Comparing

wired systems, there are various advantages using

WPT. For instance, WPT with some sensors can

easily reinforce health monitoring functions of space

crafts and WPT between space crafts will be able to

reduce onboard electrical power subsystems (EPS)

of each space craft. However, the resources such as

size, weight, power consumptions are generally

limited in a space craft. In addition, mission

requirements and environments are completely

different in each mission, especially in space science

or space exploration missions. Besides, from a radio

frequency (RF) technical standpoint, the higher the

frequency of WPT is, the smaller the size of WPT

components become. However, in high-frequency

WPT, circuit designs are more complicated and free-

space span losses are larger than those of low-

frequency WPT. Therefore, the specifications of

WPT such as frequency, power, etc. must not be

determined without considering both mission

requirements and RF features.

3.1 High power GaN amplifier

combiner for space communication

ground station

A 1kW-class GaN high power amplifier equipment

was designed and fabricated in the S-band. It

consists of three parts, a GaAs driver amplifier,

200W-classs high power amplifier units and a

circular waveguide combiner. The Block diagram

and overview of 1kW-class GaNSSPA Unit are

shown in Fig. 8 and Fig. 9, respectively.

Input-output characteristics of the 1kW-class

SSPA Unit including nonlinear amplification at 2.1

GHz, allocated for earth-to-space link are shown in

Fig. 10. More than 60 dBm output power was

achieved in this evaluation. In addition, measured

combining efficiency can be seen in table 1. High

combining efficiency of 87.1 % was obtained.

Further, the output power stability during more than

half an hour operation is shown in Fig. 11. About 5

% degradation of the output power was observed. (H.

Noji, 2011)

Compact Gan High Power Amplifiers for Space Communication, Sensing and Green Power Transmission

3.2 The wireless sensor and batter

charging by MPT

The applications of GaN modules for space use are

numerous such as onboard communication system,

ground station communication system, wireless

power transmission system, and wireless sensor

network system. Here, the combination of

microwave power/energy transmission with the

sensor network, namely the wireless sensor and

energy transfer (WiSEnT), was conducted. The

WiSEnT with a thermal sensor was evaluated inside

an anechoic chamber as the first step toward future

spacecraft health monitoring system. The thermal

sensor was connected with the rectifier directly and

it can operate without any batteries. The thermal

sensor was operated as the normal sensor system

with a battery and the fundamental data were

obtained through the preliminary experiment. These

are indicated in Fig. 12.

Further, the application of the GaN based HPA to

MPT for the purpose of battery charging with a

rectifier was checked inside an anechoic chamber.

The block diagram of MPT experiment is shown in

Fig. 13. The inside and outside appearances of the

anechoic chamber are shown in Fig. 14 and 15

respectively. In Figs. 13 and 14, the distance

between transmission and receiving antenna was 1.2

Table 1 Combining efficiency of

1-kW-class HPA equipment

HPA1 output power 158.5 W

HPA2 output power 141.3 W

HPA3 output power 154.9 W

HPA4 output power 147.9 W

HPA5 output power 154.9 W

HPA6 output power 138.0 W

HPA7 output power 147.9 W

HPA8 output power 144.5 W

Total input power to combiner 1188 W

Output power from combiner 1035 W

Combining efficiency 87.1 %

Fig. 11. Ouput power stability of

1-kW-class HPA equipment

In Fig. 13, 2.25 GHz sine wave generated by the

SG was amplified by the GaN HPA. Then, the

amplified signal was supplied to the divider. After

that, the divided signals were radiated by the 16-

element transmission array antenna. The radiated

signal was received by the 16-element receiving

array antenna and combined by the power combiner.

Then, the combined signal was converted into DC

signal by the rectifier. After that, the DC signal was

supplied to the DC/DC converter and the converted

signal was supplied to the battery. The transmission

and receiving RF powers divided by directional

couplers were measured by power meters. The

measured power of transmission antenna (EIRP) and

that of rectifier realized 58.8 dBm and 33.3 dBm,

respectively.

The battery voltage during the MPT experiment is

shown in Fig. 16. The Figure 16 indicates that the

charging achieved totally up to 1615.5 Ws (=0.449

Wh) in about 6 hours 43 minutes. The DC/DC

converter was inserted between the rectifier and the

battery so as to keep the conversion efficiency of the

rectifier high. In general, the efficiency strongly

depends on the load resistance of a rectifier and it is

important to keep the resistance at the optimum

value. However, a load resistance of a battery is

usually changing while it is charging. Therefore,

when the output signal of a rectifier is directly

supplied to a battery, the conversion efficiency

changes widely. In Fig. 13, however, it is indicated

that the battery charging rate was not constant.

Therefore, the load resistance of the rectifier must

have been changing although the DC/DC converter

was used.

First International Conference on Telecommunications and Remote Sensing

Fig. 12. The preliminary experiment for the thermal sensor operating with microwave power transmission

Fig. 13. Block diagram of WPT experiment

16‐element‐transmission

arrayAntenna

Rectifier

16‐element‐receiving

arrayAntenna

Powerdivider

Powercombiner

DC/DC

converter

Batteryvoltagemeter

Battery

Rectifier

output

signal

Fig. 14.Componentsused inside of anechoic chamber Fig. 15. Components used forbattery charging

3.3 Space environmental testing

For an actual space use, the space environmental

testing such as temperature, thermal vacuum, and

radiation are significant. GaN is expected to tolerate

these harsh environmental testing due to its

characteristics. The space environmental testing

listed in table 2 was conducted with the 20-W-class

GaN HPA. The test facilities are shown in Fig. 17.

02468

BatteryVoltage[V]

time[hour]

BatteryVoltage

Fig. 16. Battery voltage

Compact Gan High Power Amplifiers for Space Communication, Sensing and Green Power Transmission

Results of thermal vacuum testing and radiation

testing are shown in Figs. 18 and 19 respectively.

Figure 18 indicates that the GaN amplifier continued

to function normallyduring the thermal cycle

although the PAE of each temperature were a little

different. Further, Fig. 19indicates theGaN amplifier,

once degraded by the radiation, came back to its

previous operation by the aging test. This is named

as annealing effect. From these results, it was greatly

enhanced that the GaN will be able to be used in the

space.

Table 2

Conditions of space environmental testing

Test name Conditions

Temperature -5 degC ,25 degC, 55degC

Thermal

vacuum

Thermal cycle(-20 to 60 degC)

1E-4 ~ 1E-3 Pa

Radiation

Co, Total Ionizing Dose (TID) :

320 krad (Rate: 20krad/h)

(After radiation test, aging test was

done.) (100 degC, 168hours

continuous operation)

(a) Temperature

(b) Thermal vacuum

©JAEA

0 5 10 15 20 25 30 35

Pout[dBm],Gain[dB],PAE[%]

Pin[dBm]

Thermalvacuum（25℃，‐20℃，60℃）（NPT25015＠2.25GHz）

Pout（25℃，1.7E‐3Pa）

Gain（25℃，1.7E‐3Pa）

PAE（25℃，1.7E‐3Pa）

Pout（‐20℃，5.2E‐4Pa）

Gain（‐20℃，5.2E‐4Pa）

PAE（‐20℃，5.2E‐4Pa）

Pout（60℃，1.3E‐3Pa）

Gain（60℃，1.3E‐3Pa）

PAE（60℃，1.3E‐3Pa）

Fig. 18. Result of thermal vacuum testing

0.2

0.4

0.6

0.8

1.2

1.4

1.6

1.8

5 101520253035

Ids[A]

Pout[dBm],Gain[dB],PAE [%]

Pin[dBm]

NPT25015

Pout[dBm](afterTID)

Gain[dB](afterTID)

PAE[%](afterTID)

Pout[dBm](beforeTID)

Gain[dB](beforeTID)

PAE[%](beforeTID)

Pout[dBm](afteraging)

Gain[dB](afteraging)

PAE[%](afteraging)

Ids[A](afterTID)

Ids[A](beforeTID)

Ids[A](afteraging)

Fig. 19. Result of radiation testing

4 SUMMARY

In this paper, the design, fabrication, and evaluation

of high power and high efficiency GaNHPAs were

described. Further, the battery charging experiment

for the space MPT to a rover was demonstrated. In

addition, the environmental testing results for space

use are shown.

The 20W-class GaNHPA realized 43.7 dBm

output signal power with 63.3 % PAE at 2.25 GHz,

the 100W-clas HPA realized 48.0 dBm with 52.6 %,

First International Conference on Telecommunications and Remote Sensing

and 1kW-class SSPA unit realized 60.1 dBm output

signal power with 87.1 % combining efficiency at

2.1 GHz.The experiments of thermal sensor

operation and battery charging by MPT using the

GaN HPAs werecarried out. The thermal sensor

operated as the normal one with a battery supported

by MPT. In addition, the battery was charged up by

the converted DC power under the condition where

the EIRP was 58.8 dBm, the rectifier input power

was 33.3 dBm, and the distance between the power

transmitter and the receiver was 1.2 m. Further, the

GaN amplifier could continue to function normally

during the space environmental testing of

temperature, thermal vacuum, and radiation.

Through these experiments, it is believed that

flexibilities for the future missions in terms of size,

weight, and power consumption using GaN will be

improved.

ACKNOWLEDGEMENTS

The authors would like to express deep gratitude to

Mr. S. Furuta, Mr. Y. Moriguchi, and Mr. M. Ono,

NEC Network and Sensor Systems, Ltd for their

great support in developing GaN amplifiers. In

addition, the authors appreciate to Dr. S. Yoshida

and Prof. Z. Yamamoto, ISAS/JAXA, for their

fruitful discussion, encouragement and information

of the space ground station.

REFERENCES

N. Shinohara and S. Kawasaki., 2009. Recent Wireless

Power Transmission Technologies in Japan for Space

Solar Power Station/Satellite.RWS2009 Digest,

MO2A-4, San Diego, Jan. 2009, pp. 13-15.

M. Furukawa, et al, 2006. 5.8-GHz Planar Hybrid

Rectenna for Wireless Powered Applications,

APMC2006 Digest, FR2E-1, Yokohama, Dec. 2006.

M. Hori, et al., 2011. The 5.8GHz Receiving and Rectenna

Arrayfor Wireless Communication and Power

Transmission, IEICE technical report in Japanese,

MW2010-135(2011-1), Jan. 2011.

T. Ito, et al., 1979. Fundamental Experiment of a Rectenna

Array for Microwave Power Reception, IEICE

Trans.communication, vol.E76-B, no.12, pp.958-968,

Dec.1979.

N. Adachi, et al., 2005. High temperature operation of

AlGaN/GaN HEMT, Microwave Symposium Digest,

2005 IEEE MTT-S International, June 2005.

H. Noji, et al., 2011.A 1kW-Class S-band Compact

Waveguide Combiner Unit with GaN HPAs for WPT

and Space Communication, 41

European Microwave

Conference, Manchester, UK, Oct. 2011.

Y. Kobayashi, et al., 2012. The S-band GaN-Based High

Power Amplifier and Rectenna for Space Energy

Transfer Applications, Proceedings of IMWS-

IWPT2012, Kyoto, Japan, May 2012.

Compact Gan High Power Amplifiers for Space Communication, Sensing and Green Power Transmission