Vol. 5 No. 6 December 1997
MM WAVE COMMUNICATION SYSTEM
The bulk of communication systems, including line-of-sight and terrestrial systems are currently operating in microwave band. However, the overcrowding of microwave spectrum has led to the development and use of communication systems in millimeter (MM) wave region also. The MM wave communication systems provide secured, short haul, reliable communication with large channel capacity. These systems are particularly suitable where a clear line-of-sight is available and are considered iDEAL for providing secured point-to-point communication due to their high directivity, low probability of intercept, large bandwidth, and compact size.
DRDO has developed MM Wave Communication System in 35 GHz frequency band. The system consists of MM wave transceiver and base band. The transmitter consists of a 35 GHz Gunn oscillator, PIN diode modulator and the receiver consists of BPF, mixer, IF and AGC amplifiers and detector. The antenna is common to both transmitter and receiver and is connected through an orthomode transducer. Being a homodyne system, a part of the transmitter power is coupled to mixer through a directional coupler. The PIN diode modulator provides on-off keying to MM wave signal in accordance with digital data stream. The base band circuit consists of voice codec, data amplifier, PCM-MUX and provides 120 voice channel transmission.
Various components of MM wave transmitter/receiver are realised in planar waveguide configuration and hybrid MIC technology. A built-in test facility is incorporated in the MM wave system to monitor the health of the terminals. A separate voice channel is used as supervisory channel and also as hot line in case PCM-MUX fails to operate/function. The system has undergone extensive field trials and is now under trial for its commercial application. Presently, the system has been set up at some of the DRDO labs/estts providing hotline communication link between these establishments.