Vol.6 No. 4 August 1998

ISSN: 0971-4413

Bulletin of Defence Research & Development Organisation



DRDO has developed a large number of electronic materials, devices and components that have helped the country in achieving self-reliance to a considerable extent in Defence electronics. These developments have resulted in a force multiplier effect to significantly enhance the strength of our Armed Forces, besides defeating technology control regimes.

An MMIC Amplifier

Electronic Materials

Electronic Devices & Components

Systems & Sub-Systems



Electronic Materials

Conducting Polymers

A large number of new conducting polymers have been developed with tunable electrical and magnetic properties together with very good environmental and thermal stability. Some of these materials have been successfully converted into useful products for defence applications, viz., low density paints for antiradar and antistatic applications and thin film sensor elements for toxic gases.



Electronic Devices & Components

12 GHz MMIC Technology

Microwave monolithic integrated circuits (MMICs) are increasingly being used in microwave systems to reduce weight and size of the systems and increase the speed of signal processing. A variety of MMIC circuits are used in radar communication and missile guidance for several applications.

3" dia wafer processed for 9-10 GHz amplifier

DRDO has successfully developed 12 GHz MMIC technology, an ion implanted technology which uses MESFETs as active devices and spiral inductors, nitride and polyamide capacitors, transmission lines and implanted resistors as passive components. The gate length, which primarily governs the operating frequency, is 0.7  m. The ohmic and gate metallisation are Au/Ge/Ni and Ti/Pt/Au, respectively.  A third layer of metallisation is used for interconnection of both active and passive devices. Silicon nitride is used for final passivation. Two types of MESFETs have been developed for amplifier and switching applications.

The important steps in the MMIC technology developed are: (i) process simulation and optimisation, (ii) modelling of active and passive components and integrated circuits, (iii) design and layout of active and passive components, (iv) process integration, and (v) DC and RF charcterisation.

The technology has been successfully implemented by fabricating MESFETs with a cutoff frequency of 18 GHz. Apart from the DRDO, the other potential users of these MMICs are institutions like, CSIR and ISRO. Besides, the commercial sector also has a bulk requirement of MMICs for DBS, mobile phones, etc.

It is for the first time in the country that an MMIC technology based on GaAs has been indigenously developed and is undergoing production in the country. It is a definite step forward in attaining DRDO’s aim of increasing self-reliance in this strategic area.

Microwave Supercomponents















Production models of some supercomponents developed by DRDO

A supercomponent is an assembly, in one module, of various active and passive functional  sub-assemblies  which normally would have been packaged separately. Supercomponents efficiently combine many microwave functions in a single compact package. There are several advantages of supercomponent approach to microwave subsystems, namely, (i) elimination of excess connectors and line lengths, (ii) reduction in size, weight and volume, (iii) more controllable amplitude and phase response, (iv) easy performance repeatability, and (v) higher reliability.

Supercomponents are custom or semicustom made for meeting specific RF requirements. This technological approach is inescapable  in a microwave sub-system where  amplitude  and  phase match over a number of units is a requirement. Supercomponents are a natural choice for airborne and space applications.

DRDO has designed and developed several supercomponents for specific applications, including wideband amplitude matched detector log video amplifier supercomponents and phase-matched super- components  for direction  finding  application, and digitally tuned oscillator for fast tunable local oscillator and exciter applications.  These supercomponents are productionised by Public Sector Units, like HAL, ECIL, and CEL through concurrent engineering methodology.

Position Servo Amplifier for Brushless DC Motor

This servo amplifier has the following fundamental components:

Pulse Width Modulator, for controlling the average voltage applied to the load for minimisation of power dissipation.

Commutation Circuitry, which switches power to different motor windings based on the rotor position information from Halleffect Sensors in a way analogous to a conventional Motor’s brushes and commutator.

Summing Junction and Error Amplifier, which compares the input and the feedback and the error voltage is applied to the input of the error amplifier.

The servo amplifier can operate in three modes: (a) Current loop for position control, (b) Velocity control loop, and (c) PWM duty cycle control mode.

Under the self-reliance scheme, the power requirements and characteristics of the motor were studied, the six-step trapezoidal commutation logic was understood, the compensators were designed, components were identified, and a compact, light weight BLDC servo amplifier was fabricated.

The main features of the servo amplifier are: (i) current control loop, (ii) velocity control loop, (iii) PWM loop operation, (iv) electronic commutation, (v) PWM wave generation, (vi) high power MOSFET stage, (vii) under voltage protection, (viii) compact size (100 mm x 40 mm x 50 mm), and (ix) low weight (500 g).

MMW Components for Radar & Communication

Several leading edge technologies have been developed and exploited to realise operational systems. For example, high power solid-state transmitters have been realised using resonance cavity power and hybrid power  combining techniques at 35 GHz and 94 GHz. Technology has also been developed to produce ruggedised planner integrated front-ends, pulsed millimeter wave sources using IMPATT diodes and W-band gun diode oscillators. Further, various components, such as Fin line and wave guide circulators, isolators, twists, bends, terminations, short slot hybrids and directional couplers at Ka- and W-band have been realised. Microwave integrated circuit (MIC) technology has been utilised to develop Fin line components like MM wave filters and high performance mixers at 20, 35 and 94 GHz bands. The same technology has been refined to realise supercomponents like compact hybrid MIC receivers in 35 GHz band. CAD/CAM techniques and precision CNC machining have been utilised in the realisation of batch production of these components.

MMW Sensor for Top Attack

The sensor developed at W-band has been integrated with the complete smart munition system. The sensor has been fabricated using planar waveguide circuits and MMW components into a single compact, rugged plate capable to withstand the firing shock of 10000 g.

MMW Seeker

An MMW seeker at 94 GHz for antitank missile has been developed. As a technology base, various MMW components like IMPATT oscillators with 40 W peak power, gun oscillators, circulators, mixers, etc have been realised and a compact ruggedised seeker has been fabricated using milling technology and hybridised signal processing.

Versatile Acoustic Target

Versatile Acoustic Target

This is a microprocessor-based target simulator operating over a wide range of underwater weapons and sonar applications. In the active mode it generates a simulated echo and in the passive mode it generates random noise (typical submarine signature), like a rattler. Different parameters like target strength pulse delay, pulse stretch and Doppler pattern generation can be preset before deployment.

Linear Actuator Motor

This is used for deflecting the control surfaces of Light Weight Torpedo. This achieves the high bandwidths and high torque-to-weight ratios by using rare earth         permanent magnet DC motors. The motor drives a recirculating ball screw with zero backlash. The hall effect sensors provide the rotor position information to the servo controller. The motor is connected through flying leads and achieves a bandwidth of 35 Hz and may find applications in missiles, RPVs and space programmes.

Detection & Measurement of Gamma RaDIATion

Flash Sensor

This sensor gives the first signature of a nuclear detonation and activates the automatic NBC system of the tanks. The equipment can be mounted in tracked vehicles and can be connected to the other control units through multicore cable of convenient length.

Roentgenometer RMI 102

This vehicle-mounted instrument measures the gamma raDIATion level at a place due to a nuclear fallout or leakage in a nuclear reactor installation.

The above two indigenous products have been approved for use in MBT Arjun and T-72 tanks and have replaced imported systems fitted till now in these tanks thus saving valuable foreign exchange. These are under production through trade.

Portable Dose Rate Meter

This is a portable instrument developed to measure the gamma raDIATion level at a place due to a nuclear fallout or leakage in a nuclear reactor installation.



Systems & Sub-Systems

Jam Resistant Data Link

A jam resistant data link has been developed employing spread spectrum, channel coding and digital data compression techniques. Field experience has been acquired in real-time transmission of battlefield surveillance and reconnaissance information for effective control of airborne platforms using target tracking and acquisition techniques.

VLF Receiver & MSK Modulator

Technological expertise has been established in the field of very low frequency (VLF) communication using state-of-the-art DSP techniques for demodulation, synchronization and error corrections in a multimode multichannel VLF receiver. A low level MSK modulator is also developed to drive VLF transmitter installed by Indian Navy.

A ruggedised VLF receiver has been developed for the reception of VLF messages by naval ships and submarines operating under water at thousands of kilometers away from a transmitting station. The receiver is capable of receiving a fraction of microvolt signal and is able to record the data in OOK, FSK, and multichannel MSK modes using low bit rate teleprinters. The process of demodulation, demultiplexing and FEC are implemented through software and using state-of-the-art DSP techniques.

DRDO has also developed a MSK modulator compatible with high power VLF transmitter. Self-reliance in VLF technology has helped the country in saving valuable foreign exchange to the tune of Rs. 6.5 crore.

MM Wave Communication

DRDO has developed a few MMW communication systems at Ka-band, V-band, and W-band, covering a maximum range up to 20 km with clear LOS under severe radio interference environment. The system can be used for point-to-point communication up to 120 voice channels.

MM wave communication system

Processor-Based Mines

Ground Mine

The processor-based ground mine (PBGM) is a microprocessor- controlled advanced mine to be laid either by a surface ship or launched from a submarine. It is classified as an intelligent mine as it can assess and quantify the environment and accurately identify and destroy actual targets. The mine is designed to detonate using any one or a combination of the three influences created by a target. Advanced digital signal processing techniques are incorporated in the mine to discriminate between acoustic noise generated by real target and acoustic countermeasure. The mine design also includes advanced digital filtering techniques to extract pressure signature generated by ships and submarines in the presence of high sea ambient. Classical safety features are also provided. The mine is designed for long storage and operating life.

Exercise Mine

Processor-based exercise mine

This mine is an exercise version of the PBGM. It basically consists of two sections, viz., anchor section and the floating section. Upon launching, the mine moves to the sea bottom and rests vertically. On completion of initial arming delay, the mine acquires sea ambient conditions and sets thresholds automatically. Then, the mine looks for valid targets. When a valid target pass over, the target count gets decremented by one. When the target count becomes zero, the mine gets detached into two sections, namely, anchor section and floating section.

Moored Mine

This is desinged and developed to cover the mine laying in deep water against surface target. On completion of initial bedding delay, the mine gets detached into two parts, namely, anchor section and mooring section. The mooring section floats in underwater at the preset mooring depth.

Modulation Classifier—Hans

Analysis and classification of communication  signals   play  an  important  role  in  the  communication  surveillance operations. Due to large number of signals crowding the spectrum,  manual analysis and classification of signals is time consuming. An automatic modulation classifier has been developed by DRDO to work in conjunction with HF/VHF monitoring receivers. It has been designed primarily to classify most commonly used communication signals like CW, AM, NBFM, WBFM, FSK, SSB, etc. This equipment can also measure the offset frequency of the signals being intercepted. This unit uses mixed signal processing (analog and digital) techniques with statistical estimation algorithm for feature extraction and pattern/template matching to identify the type of main carrier modulation. It carries out the modulation classification and frequency offset measurement within 150 ms of time. For easy integration into any major systems and to facilitate automation, this equipment is provided with standard RS 232C remote interface and can be operated either in the local mode or remotely by the host system controller.  This technology has spin-off potential for areas like spectrum management,  automatic  signal monitoring,  interference identification and signal confirmation for civil monitoring, and spectrum control agencies.

Microwave Rotman Lens Fed Multiple Beam Array Antenna System

This antenna array system provides contiguous high gain antenna beams—all existing simultaneously with each beam possessing the full gain of array aperture. The microwave Rotman lens is a power distribution-cum-phasing network. It is considered a microwave analogue of optical lens. It offers the possibility of variable refractive index which provides many degrees of freedom to design lenses with multiple foci as compared to optical lenses which are made of dielectric with fixed refractive index and hence single on axis focal point.

The Rotman lens consists of TEM mode parallel plate transmission region with input and output ports called beam and array ports, respectively. Coaxial transmission lines of unequal lengths connect the array ports to the raDIATing elements of the array. These variable length transmission lines which constitute a transmission delay dielectrics provide variable refractive index to achieve the path length compensation. The length of these transmission lines and array ports positions are designed to provide perfect focussing along the input circular arc. The focussing is a consequence of providing equal electrical path length from a given focal point out to the corresponding raDIATed wavefront to each element of the array. These lens fed array systems provide optimum utilisation of system resources in time, space and frequency.

Microwave Rotman Lens Fed Multiple Beam Array Antenna System

Microwave Rotman lens fed array system being simple and cost- effective with inertia-less scanning capability is finding extensive application in: (i) ECM against simultaneous multiple threats, (ii) surveillance, (iii) point to multipoint communication, (iv) remotely piloted vehicle system for multiple drone control and broad band data retrieval links, (v) integrated multipurpose system accomplishing the functions of radar, ECM, surveillance and communication, (vi) satellite communication with spot beam coverage capability, and (vii) low side lobe pattern generation.

A microwave Rotman lens fed array antenna system which is a state of the art concept has been designed and developed, covering the frequency band more than 2:1 capable of generating 15 simultaneous beams with ERP more than 50 kW.

Heliborne ESM System  

Heliborne ESM system is developed for maritime reconnaissance. This tactical ESM system provides 100 per cent probability of intercept. The wide open ESM system has the capability to track 20 threats simultaneously together with providing instant warning for hostile threats.

Heliborne ESM System

The system employs four cavity- backed antennas with radomes. The customised RF front end modules realised in a supercomponent version provide high sensitivity and dynamic range. A special fast switching technique is employed to provide elevation          coverage above and below the horizon in the airborne installation. Extensive use of ASICs (application specific integrated circuits), FPGAs (field programmable gate arrays), analog hybrids, and SMTs (surface mounted technology) devices makes the system smaller, lighter and compact. The system employs software calibration to ensure high DOA accuracy. The ESM display uses ruggedised laptop computer and the display formats facilitate easy and faster data dissemination to the operator. The display has different modes (selectable through the keyboard), viz., tactical, situational and TOTE for the convenience of the operator. For on-line system diagnostics, built-in RF bite is included in the system providing the health status on the display continuously.

The system comprising 11 LRUs (line replacement units) weighs less than 25 kg. Though the present system is planned for heliborne platforms, it can be configured for shipborne and land-based, vehicle mounted mobile applications to meet the tactical requirements of the users.

Transportable Satellite Communication Terminals

DRDO has achieved the distinct knowledge and experience in the field of tactical, mobile satellite communication over C-band to provide secure digital communication (both speech and data) under severe climatic conditions. The satellite terminals developed meets the CCIR specification.