Design of Tip Loss Profile on Support Rod for a Helix TWT
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Design of Tip Loss Profile on Support Rod for a Helix TWT Mukesh Kumar Alaria & A. K. Sinha & V. Srivastava
Received: 16 January 2009 / Accepted: 6 April 2009 / Published online: 5 May 2009 # Springer Science + Business Media, LLC 2009
Abstract This paper describes the design of tip loss profile on support rod for a high gain, high efficiency helix TWT. The tip loss profile at sever ends for the input and the output section of the helix slow wave structure has been designed for return loss at severs ends better than -20 dB. The experimental results have been carried out in the input and the output section of the helix assemblies for the high gain helix TWT to find the return loss in the region of carbon coated tip loss on the support rods. The experimental result has been compared with the simulated performance for the return loss at the sever ends. The design of tip loss profile on the support rod for helix TWT has been carried out in real situation using Ansoft HFSS. A good agreement has been found in the simulated and experimental results. Keywords Helix slow-wave structure (SWS) . Tip loss . Sever . Attenuation . Traveling wave tube (TWT)
1 Introduction Helix traveling wave tube is a vacuum microwave device that is used as high power microwave amplifier in communication satellites [1]. It works on the principle of continuous interaction between the electric field and the electron beam. The main components of a helix TWT are electron gun, helix slow wave structure, input and output coupler and collector. The helix slow wave structure has been designed in 2-section with input and output couplers and tip loss at sever ends in real situation of helix TWT [2]. The helix made from the metallic tape is commonly used as SWS for moderate output power and wide-band applications. The helix is supported by three dielectric rods normally of APBN (Anisotropic pyrolytically deposited Boron Nitride), Beryllia (Beo) or Alumina (Al2O3). These materials have high thermal conductivity as compared to other ceramics M. K. Alaria (*) : A. K. Sinha : V. Srivastava Microwave Tubes Area, Central Electronics Engineering Research Institute/ Council of Scientific and Industrial Research (CSIR), Pilani 333031 Rajasthan, India e-mail: [email protected]
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J Infrared Milli Terahz Waves (2009) 30:651–656
Fig. 1 Helix with support rods and attenuator coating.
Attenuator Coating suitable for operation at high temperature in vacuum. A Ku-band high gain high efficiency helix TWT has been designed in two sections separated by sever for gain more than 50 dB and electronic efficiency more than 25%. Helix TWT may oscillate in the presence of reflections from the terminations of the input and output section. In order to avoid this problem of oscillation caused by reflections [3], coating of a lossy material known as attenuator has been done on the helix support rods. Helix with support rods and tip loss coating is shown in Fig. 1. Stable performance of a TWT against the reflected signals, high tip loss profiles at severs ends for the inp
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