SOLID-STATE WIDEBAND  high power radio frequency (RF) amplifiers play a vital role in the electronic attack (EA) or electronic countermeasure (ECM) activity in electronic warfare (EW). Due to technological advances made in the battlefield communications, use of solid-state wideband power amplifiers (SWPAs) has become an inescapable requirement for effectively jamming sophisticated communi-cation signals of the adversary from a distant location. High power amplifiers covering very high frequencies (VHF) and ultra high frequencies (UHF) are widely employed as jamming transmitters for disrupting/jamming the tactical communication links.
When the power output required is more than what a single transistor can deliver, it is mandatory to combine the power output of a number of identical power modules with the help of power dividers and combiners to generate the envisaged power output. The technology of solid-state power amplifiers thus comprises passive components like power combiners, power dividers, dual directional couplers, sub-octave filters, etc. in addition to the active RF power modules. Transmission line transformers are widely employed in designing impedance matching circuits, power combiners and dividers.
Protection and control circuits play an important role in ensuring the safety of the amplifier. Thermal design for efficient removal of heat generated by amplifier is crucial for the reliability and longevity of the amplifier.
DRDO has successfully designed and developed a variety of high power multi-octave amplifiers in HF, VHF and UHF bands covering 1.5 MHz to 2000 MHz. These amplifiers, designed for EA applications, offer instantaneous wideband frequency coverage with high RF power output. DRDO has also established the technology and production base for high power RF generation up to 1.0 kW in HF and VHF bands using state-of-the-art technique of RF power combining.
A facility, called ‘graceful degradation’, has been built into the transmitter system to deliver continuous reduced power output in case of failure of one or more modules to protect the total system from catastrophic failure as observed in the earlier valve version transmitter systems. Also, unlike in valve transmitters, which operate at high voltage, SWPAs have no high voltage hazards as they operate at 28 V DC.
Apart from EW area, SWPAs find application in meteor burst communications, EMI/RFI testing, power handling, testing of high power RF subassemblies like switches, power combiners, antennas, etc. The amplifiers are being widely used for countering remotely controlled improvised explosive devices.
This issue of Technology Focus comprises some of the solid-state RF transmitter technologies developed by DRDO.