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Microwave masters


Jul 6, 2009
Microwave masters

The MTRDC's work on microwave tubes puts India in an elite club of countries engaged in developing this tough technology.

In the assembly room at the MTRDC.
“OURS is a unique laboratory. Only about 15 countries in the world are engaged in research in microwave tubes, which is a tough technology area,” says Lalit Kumar, Director of the Microwave Tube Research and Development Centre (MTRDC), Bangalore. Microwave tubes, or MWTs, find applications in civilian systems, high-end communication systems and many defence systems. In fact, it is the MWTs onboard satellites that send signals to ground stations. Each satellite carries 30 to 40 travelling wave tubes (TWTs), which have high channel width, efficiency and life.

The MTRDC is one of 52 laboratories of the Defence Research and Development Organisation (DRDO) across the country. Its mandate is to work in the development of MWTs for the DRDO's Electronics and Radar Development Establishment (LRDE), the Defence Electronics Research Laboratory, the Defence Avionics Research Establishment, and the Defence Avionics Application Laboratory (which develops radar, electronic warfare equipment and communication and data link systems for the military). The MTRDC also develops microwave power modules (MPMs), electronic power conditioners (EPCs), high-density cathodes, and so on for various defence systems.

“The technological capability necessary for making these devices include computer-aided design and simulation, ultra-high vacuum, special purpose precision machining, protective atmosphere heat treatment and brazing, thin-film coating, high-frequency measurements, high-voltage testing and environmental testing for reliability,” said Lalit Kumar. “The state-of-the-art J.C. Bose Microwave Tube Facility, inaugurated recently at the MTRDC by V.K. Saraswat, Scientific Adviser to the Defence Minister, willboost research and development of MWTs,” he added. Bharat Electronics Limited (BEL), Bangalore, is the production agency for the MWTs and radars, electronic warfare systems and data links. The MTRDC is situated inside the BEL complex. It was the vision of V.S. Arunachalam, former Scientific Adviser to the Defence Minister, that led to the establishment of the laboratory. Former heads of the MTRDC, such as K.N. Tiwari, M.D. Rajnarayan, K.U. Limaye nurtured it. The MTRDC's goal is “to facilitate Em-power to empower the defence”.

The modern name for MWTs is vacuum electron devices (VEDs). But all VEDs are not necessarily MWTs. VED is the family name, while MWT forms the subset. MWTs are VEDs capable of generating or amplifying high-frequency signals for various defence and civilian applications in communications, radars, electronic warfare and integrated support measures (ISM) systems. Microwaves travel in matter in the same way light waves do but can penetrate most materials other than metals and other electrical conductors. Motion of electrons in vacuum is most critical in MWTs, which also find application in deep space communication, energy generation by fusion, sintering of ceramics in industry, processing of materials and in medical applications such as imaging and hyperthermia.

The purpose behind using MWTs is to amplify power. They can amplify microwave power a million times more, that is, one milliwatt into 100 watts and one watt into a megawatt. They are rugged devices. Some of these devices, used in satellites, last in space for about 15 years. The MTRDC did not develop the MWTs used in satellites but contributed to the design of the high-efficiency multistage collector for the first Indian space-qualified TWT developed for ISRO by the Central Electronics Engineering Research Institute (CEERI) and BEL.

Lalit Kumar said: “The devices we make work for about 10,000 hours. Military systems are much more demanding. Military devices typically work from 1,000 to 10,000 hours. Each of these devices is handcrafted using exotic materials, high melting-point metals and precious metals. They are expensive because they cannot be mass produced. For instance, a magnetron used in a microwave oven may cost about Rs.500. But a military magnetron will cost not less than Rs.500,000 because so much sophistication goes into its microwave tube. We have made devices that will sell at Rs.50 lakh to Rs.60 lakh a piece.”

TWTs are MWTs of special design, made using a broadband circuit in which a beam of electrons interacts continuously with a guided electromagnetic field to amplify waves. Two major classes of TWTs – the helix TWT and the coupled cavity TWT (CCTWT) – have been developed.


K.S. Bhat, Associate Director, MTRDC, said developing VEDS required a coming together of a number of disciplines: vacuum technology, electronics, high-power technology, material science, high-voltage engineering, and so on. The MTRDC has developed a number of devices, mostly TWTs, which are broadband amplifiers. They have a large market share among the MWTs. TWTs contribute to almost half the share of the MWT market in the world, with all the other devices such as magnetrons and klystrons, contributing the rest. Lalit Kumar said: “So we have chosen to work in this field, and this is important. We have already made a high-power X-band CCTWT for the airborne radar, an S-band CCTWT for the ground-based radar surveillance radar and broadband helix TWTs for electronic warfare applications.”

Apart from these tubes, the MTRDC is now making complete MPMs, which are highly compact, efficient amplifier modules combining the best attributes of solid state and vacuum device technologies. Lalit Kumar likened the clubbing of solid state and vacuum device technologies to a relay race, with the first half of the race (for low power) won by the former and the second half (for high power) won by the VEDs. MPMs are used in flight-level radars (FLR) manufactured by BEL, Bangalore. The weight and volume of these radars, which earlier employed big high-power amplifier racks, have come down by ten times after the employment of MPMs.

The MTRDC is also working on vacuum micro-electron devices, which will combine the best of solid state and vacuum devices. The MTRDC has also mastered the development of high-density dispenser cathodes. A cathode, the emitter of electrons, is the most important part of any MWT and is the component that determines the tube's life. “Several batches of cathodes for helix TWTs, CCTWTs and magnetrons have been developed and tested in the actual tube environment. Their performance has been at par with imported equivalents,” Bhat said. There are not more than five manufacturers of cathodes in the world.

The MTRDC has been successful in developing highly compact EPCs, which deliver conditioned power to various electrodes of the TWT and solid state amplifiers. “In layman's terms, the EPCs are called power supplies. But power supply is simple technology. What we are doing is highly sophisticated, state-of-the-art, most compact, 95 per cent efficient power converters for specific devices such as TWTs and solid-state amplifiers. They also monitor the health, control the operation and communicate with the host system of these devices to carry out commands,” explained Lalit Kumar.

He is happy that the Indian capabilities and achievements in vacuum electronics were highlighted to the entire international VED community from 15 countries when the MTRDC hosted the 12th Institute of Electrical and Electronics Engineers' (IEEE) International Vacuum Electronics Conference (IVEC-2011) in Bangalore in February 2011. It was lauded as the largest IVEC gathering outside the United States and had several first-time events.

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