HF Radar

Wide Scanning HF Active Array Radar for Ionospheric Probing at NARL


A 30-MHz radar has been developed at National Atmospheric Research Laboratory (NARL) to study of the low latitude Ionospheric plasma irregularities. The radar has the beam steering capability to scan a larger part of the sky upto ±45o in East-West direction, which will overcome the limitation of slit camera picture obtained by the fixed beam of the Gadanki MST radar on the ionospheric plasma irregularity/structures. The radar system employs an active phased antenna array and high power solid-state Transmit-Receive (TR) modules. The antenna beam is fixed towards 140 North from Zenith direction so that the antenna beam satisfies the perpendicularity condition for the detection of the irregularities from the ionospheric E and F regions. The Radar system comprises of 160 numbers of 140-oriented (from horizontal) two-element Yagi antennas arranged in a 20x8 matrix over an area of 112m x 56m. This array is organised into 20 columns (along the East-West direction) each consisting of 8 antenna elements in the North-South direction. A total peak power of 150 kW is generated by 20 numbers of 7.5- kW solid-state TR Modules, each feeding a column of 8 antenna elements in North-South direction. A low power feed network distributes the radar exciter output to the TR modules and combines the receive signals and delivers to the radar receiver. The received signal, after combining, is suitably amplified, band limited before feeding the digital receiver. Digital receiver performs the analog-to digital conversion, digital down conversion, pulse compression and coherent integration. The time domain data is uploaded into host PC for data processing to compute Doppler spectrum and spectral moments. Master timing and control signal generator (MTCSG) provides the timing and control signals/pulses including the master sync (IPP marker) pulse for other radar subsystems like RF distribution and switching network, Exciter, Receiver unit, multi-channel digital receiver system and phase monitoring unit. The TR modules are controlled by distributed TCSG units (DTCSGs) kept within them. DTCGS, MTCSG and Master Control PC are connected through Ethernet. Figure-1 shows the pictures of the antenna array along with the building (top panel), transmit-receive system (bottom left) and radar controller (bottom right). All the subsystems have been developed, installed and integrated. The system is being operated regularly for scientific validation. Figure-2 shows the sample echoes obtained from E-region (left) and spread-F (right). Figure-3 shows the Range-Time intensity (Signal-to-noise ratio) map showing the E-layer variation. Details will be presented at the Symposium.