Rajendra Kumar Sharma

Design and Development of Helix Slow-Wave Structure for Ku-Band TWT

A helix slow-wave structure (SWS) for a high-efficiency (electronic efficiency >; 25%) Ku-band 140-W space traveling-wave tube (TWT) has been designed. The cold circuit parameters of helix SWS, like propagation constant and on-axis interaction impedance, were determined using 3-D electromagnetic field simulators ANSOFT-HFSS and CST-MWS, and those were validated with the experimental results. The in-house developed large-signal code SUNRAY-1D was used to design a complete helix SWS in two sections with sever and taper to achieve desired output power, gain, efficiency, and other linearity parameters like phase shift, AM/PM factor, and I/M components. The simulated RF performance of the Ku-band 140-W helix TWT was validated with the experimental results. A close agreement between the simulated and experimental results has been found.

20.6: Design and development of 100 GHz folded waveguide TWT

In the recent decade there has been a growing interest of the researchers all over the world in the design and development of the high frequency (in terahertz range), moderate power and efficient devices based on MEMS (semiconductor) and vacuum electronics technologies. Development of so-called vacuum microelectronic devices (VMDs) for the mm and sub-mm wave devices surmount the limitations of conventional microwave tubes (MWTs) as well as of solid-state devices. CEERI has started work towards the design and development of Folded wave guide TWT (FWTWT) initially for 100 GHz. This paper would report design and development work done for electron gun and RF structure of 100 GHz FWTWT.

Design and Evaluation of Electron Gun and Beam Focusing for Ku-band 140W Space TWT

A low perveance (0.22 muP) electron gun for Ku-band 140W space traveling wave tube (TWT) has been designed, using E-GUN and TRAK codes. Pierce type electron gun with an electrically isolated beam forming electrode (BFE) and an ion barrier anode (A0) has been opted. An M-type dispenser cathode with low cathode

Dual anode electron gun & PPM focusing for Ka-Band TWT

A low perveance (0.14µp) convergent electron gun with dual anodes has been designed using codes EGUN (2D), TRAK (2D), OPERA (3D) and OMNITRAK (3D) for Ka-Band helix (TWT) for space applications. Pierce type electron gun with an electrically isolated beam forming electrode (BFE), control anode (A1) and an ion barrier anode (A2) has been opted. An M-type dispenser cathode with low cathode emission loading (∼1.0 Amp/cm2), has been selected to ensure the desired long life of more than 10 years and high reliability. The application of +100 to + 250 volts at the ion barrier anode with respect to ground anode (A1) protects the cathode surface from the ion bombardment and hence enhances the life and reliability of the tube. Potential at A1 can be used to regulate the current over the life of the tube without changing the accelerating potential; this also contributes towards the life and reliability of the tube. In order to further enhance the life and reliability, non-evaporating type SAES ST-175 getter, has been incorporated in the gun assembly. Application of BFE negative bias of the order of 10 to 20 volts with respect to the cathode is used to achieve the desired beam transmission in the CW tube.

A comparative study of PPM and solenoid focusing in multibeam electron gun

This paper represents the comparison of periodic permanent magnet (PPM) and solenoid focusing for dual anode multi-beam electron gun using OPERA3D code. The electron gun has been operated at 6 kV having 75 mA beam current with 0.45 mm beam waist radius. The design has an additional feature of cathode protection from ion bombardment with the application of extra ion barrier anode.

Heat dissipation from helical periodic structure in vacuum

Two dissimilar metals, not brazed together, give high thermal contact resistance which further enhanced in vacuum if surface finishing is not good enough. Here, the effect of thermal contact resistance of a periodic structure supported with another dielectric material in vacuum has been studied and presented.

Electron gun design for multi-beam pulsed amplifier

This paper presents the design of an eight beam electron gun using OPERA 3D code for pulsed amplifier. The electron gun has to deliver total current 560 (70×8) mA at voltage 6 kV. Each beam has a perveance of 0.15 μP making a total gun perveance of 1.2 μP corresponding to a total beam power of more than 3 kW. The cathode radius is 13.5 mm and individual emitter radius is 1.55 mm having current density 0.92 A/cm2. Focusing has been accomplished through solenoid. The beam pulsing can be accomplished through beam forming electrode relatively at lower negative potential at BFE with respect to cathode. This design has an added feature of cathode protection from ion bombardment with the application of additional ion barrier anode.

Multi stage depressed collector with reduced size and weight for space applications

Multi-stage depressed collector plays a major role in determining the overall efficiency of high efficiency space TWTs particularly for space applications. This paper presents the dependency of collector efficiency on the radial dimensions of the multi-stage depressed collector. In addition, an approach to reduce the radial dimensions of the collector without significantly compromising the collector efficiency using external magnetic field in the collector region would also be presented.

Design of coaxial transformer for ku-band short length TWT

To extract rf power from a traveling wave tube (TWT), proper impedance transformation of the helix slow-wave structure (SWS) has to be done through coaxial couplers to a standard 50 ohm connector. Mismatch of impedance gives poor return loss (RL) behavior and leads to reflection of rf power causing oscillation and destruction of the TWT. In this paper authors have presented design of a co-axial coupler for high power space TWT using CST Microwave Studio and ANSOFT HFSS.

Selection of helix tape parameters for Ku-band 140 W SL-TWT

This paper presents the optimum selection of helix tape parameters for the design of Ku-band 140W short length TWT for space communication application. CST MWS code and in-house developed SUNRAY-3D codes have been used to design helical slow wave structure. In this model, helix is considered as perfectly conducting tape. The dependency of gain flatness and gain per unit length on tape thickness, tape width and helix pitch have been studied by maintaining the propagation constant(β) fixed at central frequency(i.e. 11.3GHz). Dependency of interaction impedance on helix tape width and tape thickness has also been studied.