The 6th Symp. on Accelerator Science and Technology, 1987, Tokyo, japan (©lonics, Tokyo, 1987)

ALL SOLID STATE RF POWER AMPLIFIER FOR PROTON LINAC

Z.Igarashi, S.Machida, Y.Mori, E.Takasaki, and S.Fukumoto

National Laboratory for High Energy Physics Oho-machi, Tsukuba-gun, Ibaraki-ken, 305, Japan

ABSTRACT

Preliminary study of solid state rf power amplifier for KEK proton linac is described, putting emphasis on tests of high power rf transistors.

INTRODUCTION

Recently progressed semiconductor tech­nologies make it possible to produce high power rf transistors which deliver more than a £ew hundred watts.Particularly,transmitters of broadcasting or radars introduce solid state systems in place of vacuum tube sys­tems. TV transmitters of 50kWCVHF), 30kW(UHF) and radar systems of a few hundred kW are working well now.

The merits of solid state systems are 1)unnecessity of high voltage power

supply---free from dangerous apparatus.

2)high reliability---easy maintenance.

3)redundancy.---using transistors excessively, the system maintain the essential rf power !evel in case of failures of a few number of transistors.

The key points of solid state system are !)selection of rf transistor 2)design of power divider/combiner 3)arrangement of isolators and interlock

systems for protection of reflection and rf discharge.

Figure 1 and Table 1 show the present rf system of KEK proton linac. We intend to re­place pre-driver stage, at first.

Debuncher -4- -~ L_-f>--n--f'-__J b& ""

r : Coupling Loop

~ : ~~~~-~:~r~~r V : Phase Shifter

..1\11/'-: High Power Dummy Load

:Power Splitter

:Solid Stale

Fig.l Block diagram of the present rf system for KEK proton linac.

Table 1

Parameters of the rf system for KEK proton linac. ----------------------- ---------------------

output power frequency pulse width pulse width(driver repetition rate

stage)

1.5 MW 201.07 300 400 20

X 2 MHZ )is flS Hz

--------------------------------------------

HIGH POWER RF TRANSISTORS

Figure 2 shows the largest rf transistors which can be obtained in Japan now. Righthand side of them is MOSFET ( 2SK317 ), the others are bipolar transistors ( 2SC3812,2SC3266 ) with twin structure for push-pull operation. Figures 3-5 and Table 2 show the test cir­cuits and conditions. Experimental results are shown in Figs. 6-8, and these transistors endured the total reflection at maximum out­put power.

-86-

Fig.2 Rf power transistors (2SC3812,2SC3286,2SK317)

Table 2

Test conditions of rf transistor.

2SC3812, 2SC3286 (grounded emitter circuits)

Vee (collector-emitter voltage) 35 V

Icq (quiescent collec-tor current) 0.1 A X 2

2SK317 (grounded source circuit) Vds (drain-source

voltage) 120 V Idq (quiescent drain

current) 0.1 A

I I 100

400 f.- 0 0 ,..... 0 - 80 Is= 0 l?=j .......- '%j

p:j 0 '%j .....

~ - 60 0 0

...... 0

l?=j

p.. z 200 f.- X X X X 0

E-< 0 X - 40 ....::

p X X ,.....

p.. 1S ~

5 .......-o OUTPUT POWER - 20

0 x EFfiCIENCY

0 I I I 0 0 20 40 60 80

INPUT POWER (W)

Fig.3 Output power versus input power. Fig.6 Tes~ circuit of 2SC3812. 2SC3812

I I 100

400 1-,..... - 80 c l?=j

'%j

p:j !S 0 '%j

X X X ......

~ X 0 - 60 0 X X

1?::1 0 0 X z p..

200 f.- 0 0 E-<

0 - 40 ....:: p

X 0 ,.....

p.. ~ E-< 0 p o OUTPUT POWER - 20 0 x EFF1CIENCY

0

0 I I 0 0 20 40

INPUT POWER (W)

Fig.4 Output power versus input power. Fig.7 Test circuit of 2SC3286. 2SC3286

I I I 100

400 1-,..... - 80 c 0 0 l?=j

0 '%j

p:j 0 X X X '%j

X ......

~ - 60 0 !! ......

l?=j 0 X z p..

200 1- X 0 0 E-<

X - 40 ....:: p

0 ,.....

p.. ~ E-< .......-p 0 o OUTPUT POWER - 20 0 x EFFICIENCY

0 I I I 0

0 10 20 30 40 INPUT POWER (W)

Fig~8 Test circuit of 2SK317. Fig.S Output power versus input power.

2SK317

-87-

The criteria for selection of transistor are !)output power 2)power gain J)input/output matching network 4)toughness for thermal shock and ref-

lection power S)power effi"ciency 6)cost per output power.

For the present, we adopt 2SC3286 (bipolar) and 2SK317 (FET).

POWER DIVIDER/COMBINER

The solid state rf system contains many transistor amplifiers operated in parallel so input signal must be divided into th~ amplifiers equally and the output signals of the amplifiers must be combined effectively. The power divider and combiner are identical in their structure but their input and out­put sides are reversed. The output(input) ports of the divider(combiner) must be matched and isolated from one another. The matching and isolation are essential for the graceful degradation of the system when one or more component amplifiers fail, because in that case the failures should not affect the r~m?ining a~plifiers. Radial and fork type d1V1der/comb1ners are suitable for the pur­pose and S-port power divider/combiners of both types are being designed now.

References

l)NEC Corporation "Microwave device data book 1986/1987".

2)Hitachi,Ltd "Transistor data book". 3)Motorola "Rf device data•. 4)Y.Tomonaga et al.,Hosoh~gijutsu,l985,No,l0,

p.971. S)N.Habuka et al.,Hosoh-gijutsu,l985, No,S ,

p.778. 6)M.Kawamura et al.,Hosoh-gijutsu, 1983,

No,6, p.S64. 7)K.Lee, C.Corson, and G. Mols, "A 250-kW

Solid state AN/SPS 40 Radar Transmitter," Microwave journal 26 (7) (July 4983),93.

8)E.J.Wilkinson, "An N-way hybrid power divider," IRE Trans.Microwave Theory Tech., vol.MTT-8,pp.116-118,Jan. 1960.

9)A.A.M.Saleh,"Planar Electrically-Symmetric, N-way, Hybrid Power Divider/Combiners," IEEE Trans. Microwave Theory Tech.,vol. MTT-28,pp.SSS-563,June 1980.

lO)ZVI Galani et al.,"Single-Frequency Analysis of Radial and Planar Amplifier Combiner Circuits,• IEEE Trans. Microwave Theory Tech.,vol.MTT-29,pp.642-654,July 1981.

-88-