Abstracto

Signal Generation and Timing Control of HF Radar

Remya M Nair

The radars are crucial component in assessing the behavior of electro jets and wind current. The working principal of HF radar is based on Doppler shift induced on the incident signal by the electro jets at higher altitudes of atmosphere. The Doppler shift induced on the echoes received from different altitudes indicates the characteristics of the electro jet. The exciter generates low level RF signals of frequency 18MHz. These signals pulse modulated, using timing pulses of selectable width and Pulse Repetition Frequency (PRF) is generated by the radar timing controller and amplified to a peak power of 50Kw by transmitter unit. Phase array antenna consists of 72 wire dipoles arranged in 12X6 rectangular configurations and is designed to operate harmonically at 18MHz. The same antenna array functions as transmitter and receiver and a T/R switch enables use of same phased array antenna for transmission and reception. The timing control unit controls the whole synchronization of the high frequency radar receiver. In order to get synchronization, timing unit has to adjust the timing of transmission and reception. Transmission and reception takes place based on some scientifically proved specification values. User writes these specification values to the system in real time. So there need some system to enter these values. For this RS232, a serial communication protocol is used. Timers take these specification values and thus solve the timing issues related to the High Frequency Radar receiver.