1.2: Development of Ka-Band 500 W CW Helix TWTTetsuo Machida*, Wako Suzuki, Minoru Yoshida,

Junichi Matsuoka and Kunio TsutakiNetcomsec Co. Ltd., 1120, Shimokuzawa, Chuo-ku, Sagamihara, Kanagawa 252-5298, Japan

E-mail: *t-machida@netcomsec.com

Keywords: Ka-band, Helix TWT, High power

Introduction This paper describes the performance of a new Ka-band 500W power Helix TWT (LD7338) which is a currently under development for the Broadband Digital Satellite Communication. The first engineering model is now under evaluation and has achieved the output power of more than 500W CW at saturation.

Netcomsec Co., Ltd. started the development of Ka-band microwave tubes for Japanese communication satellite programs in the early 1970’s. Since then, the Ka-band microwave tubes development effort has been carried out in order to achieve high performance, high reliability and cost reduction. During that time, we developed the 100W helix TWT in 1985[1], the 150W helix TWT in 1996[2], 250W CW TWT in 2004, 350W CW TWT in 2005[3] and 500W peak TWT in 2008 [4]. The total shipment number of these TWTs exceeded 1800 pieces this year. The RF loss reduction technology used in the 100W peak power mini-TWT [5] and the 500W peak TWT. The improvements of both electron beam transmission and the collector cooling structure have enabled higher cathode current operation. Also thermal conductivity at the output circuit section has been improved.

Performances Figure 1 is a photograph of the LD7338 TWT. The

mechanical dimensions of this TWT are compatible to our existing Ka-band line-up 150W, 250W and 350W TWTs. Table 1 shows typical operating parameters and performances. The DC helix current is less than 0.1% of beam current. The LD7338 achieved 532W CW output power at the frequency of 30GHz. Figure 2 and 3 show the Small Signal Gain and Saturated Output Power over the frequency range of 27.5 - 31.0GHz. The LD7338 obtained the output power of more than 517W CW over the frequency range. Figure 4 and 5 show the power transfer curve and third order intermodulation products (IM3), respectively.

Figure 1. LD7338 Helix TWT

Table 1. Typical Operation

Parameter ValueFrequency 30.0 GHz Saturated Output Power 532 W CW Gain at Saturated Power 38.1 dB Helix Voltage 17.0 kV Collector-1 Voltage 41% of Ehel Collector-2 Voltage 16% of Ehel Cathode Current 208 mA

Helix Current 0.12 mA (DC) 0.84 mA (Psat)

Dissipated Power 590 W (DC) Dimensions 400x67x69 mm Weight 3.5 kg

41

42

43

44

45

46

47

48

49

27.5 28 28.5 29 29.5 30 30.5 31

Frequency (GHz)

Gai

n (d

B)

Figure 2. Small Signal Gain

978-1-4244-8660-1/11/$26.00 ©2011 IEEE 17

18

0

100

200

300

400

500

600

700

27.5 28 28.5 29 29.5 30 30.5 31Frequency (GHz)

Sat

urat

ed O

utpu

t Pow

er (W

)

Figure 3. Saturated Output Power

30

35

40

45

50

55

60

-10 -5 0 5 10 15 20 25Drive Power (dBm)

Out

put P

ower

(dB

m)

27.5GHz28.0GHz29.0GHz30.0GHz31.0GHz

Figure 4. Power Transfer Curve

-45

-40

-35

-30

-25

-20

-15

-10

40 45 50 55

Total Output Power(dBm)

IM3(

dBc)

27.5GHz28.0GHz29.0GHz30.0GHz31.0GHz

Figure 5. 3rd order Intermodulation Products

Conclusion Netcomsec Co., Ltd. continues to develop Ka-band high

power helix TWTs according to the customer requirements. We are going to evaluate the LD7338 at 500W CW operation in the engineering model.

References 1. T.Kageyama, K.Tsutaki, H.Fukui and T.Machida,

”Design Considerations for High Reliable Ka-band Helix TWTs”, 2nd IEEE International Electronics Conference, Noordwijk, the Netherlands, 2001.

2. S.Tonegawa, T.Machida, J.Matsuoka and H.Fukui, ”30GHz 150W high gain helix travelling wave tube”, ESA TWT/TWTA Workshop, Noordwijk, the Netherlands, 1997.

3. T.Machida, T.Kanamoto, H.Fukui, K.Tsutaki, ”Development of Ka-band 250W peak power Helix TWT”, The third IEEE International Vacuum Electronics Conference, Monterey, California, USA, 2002.

4. T.Machida, T.Kanamoto, K.Tomikawa and K.Tsutaki, ”Development of Ka-band 500W peak power Helix TWT”, 8th IEEE International Vacuum Electronics Conference, Kitakyushu, Japan, 2007.

5. Kunio TSUTAKI, Ryouichi SEURA, Eiji FUJIWARA, Kunihiro TOMIKAWA, “Development of Ka / Q-band 100W peak power MMPM”, 4th IEEE International Vacuum Electronics conference, Monterey, California, USA, 2004.