We present the first dual‐frequency overlapping volume radar observations of daytime 150‐km echoes made at 30 and 53 MHz from Gadanki, India. We show remarkably different responses of the 150‐km echoing layers including the spectral characteristics of the echoes at 30 and 53 MHz. Results show that while the echoes in general are remarkably stronger with narrower spectral width at 30 MHz than that of 53 MHz the relationship between radar cross sections at the two frequencies varies depending on the echoing layer. We also show distinctly different spectral broadening in different echoing regions observed by the 53‐MHz radar, which is missing in the 30‐MHz radar observations. These new observations indicate involvement of naturally enhanced incoherent scattering as well as scattering from enhanced electron density fluctuations of plasma instability origin and hence are of utmost importance in understanding the origin of the puzzling 150‐km echoing phenomenon.

An L-band radar wind profiler was established at National Atmospheric Research Laboratory, Gadanki, India (13.5°N, 79.2°E), to provide continuous high-resolution wind measurements in the lower atmosphere. This system utilizes a fully active array and passive beam-forming network. It operates at 1280 MHz with peak output power of 1.2 kW. The active array comprises a 16 × 16 array of microstrip patch antenna elements fed by dedicated solid-state transceiver modules. A 2D modified Butler beam-forming network is employed to feed the active array. The combination of active array and passive beam-forming network results in enhanced signal-to-noise ratio and simple beam steering. This system also comprises a direct intermediate frequency (IF) digital receiver and pulse compression scheme, which result in more flexibility and enhanced height coverage. The scientific objectives of this profiler are to study the atmospheric boundary layer dynamics and precipitation. Observations made by this profiler have been validated using a collocated GPS sonde. This paper presents the detailed system description, including sample observations for clear-air and precipitation cases.

An upgraded version of the Indian MST radar, called Advanced Indian Mesosphere-Stratosphere-Troposphere (MST) radar (AIR), has recently been commissioned. The prime objective of constructing the AIR is to make it a more useful instrument for conducting new experiments, which enable us to broaden our knowledge on the dynamical and electrodynamical processes including coupling from the boundary layer to the ionosphere. The AIR works at 53 MHz, and the system has been rebuilt, keeping the original square antenna array consisting of 1,024 Yagi antennae. The AIR is a high-power, fully active phased array system with dedicated 1-kW solid-state transmit-receive units, providing a total peak power of 1,024 kW, and control systems that allow steering the beam with 360°azimuth and 24°zenith agility. Also, the antenna system has been configured with modularity and scalability, which facilitates selection of antenna subarray and aperture for carrying out multireceiver experiments. The antenna radiation pattern tests reveal that the beam width and first side lobe level are close to the designed values of 2.2°and −13.2 dB, respectively. Currently, the system is equipped with 18 receivers to carry out spaced receiver experiments. The transmitters have been designed to transmit very short and long pulses for studying boundary layer to ionosphere. This paper presents the system description of the AIR and sample observations made using the system in Doppler beam swinging mode demonstrating its capabilities for studying neutral atmosphere and ionosphere.

We present and discuss common-volume dual-frequency radar observations of 150-km echoes made at 30 and 53 MHz from Gadanki by employing identical transmitter power and antenna beam width. These controlled experiments reveal that 150-km echoes are stronger, broader in spectral width, and more frequent in their occurrence at 30 MHz than at 53 MHz. Echo intensities at 30 and 53 MHz are found to be consistent with the rocket-borne observations of wave number spectrum of meter-scale irregularities in the 150-km region. The frequency dependence of spectral widths of the echoes while is found to be somewhat similar to that of electrojet type-1 echoes it is opposite to that of electrojet type-2 echoes and also to that of incoherent scattering in direction perpendicular to magnetic field. Spectral widths of the echoes observed by both radars are found to be independent of SNR. A detailed comparison of these observations with those made earlier suggests that instrument functions play an important role in manifesting SNR-dependent/independent spectral width property of the 150-km echoes. The narrow spectral properties and frequency dependence of echo intensity and spectral width clearly suggest that the irregularities responsible for the radar backscatter are linked with weak plasma turbulence and the meter-scale irregularities responsible for radar echoes ought to be growing with direct injection of energy at the meter scale itself to overcome damping. We surmise the potential role of photoelectrons and atmospheric gravity waves in the underline plasma instability process.

This paper introduces real time application of FPGA based Timing Control Signal Generation card for Active Phased Array Radar Transmit Receive modules wireless radar communication. Active phased array radars usually have Transmit-Receive (TR) modules located near to the antenna elements and all the TR modules are to be synchronized for proper operation of the radar system. The TCSG is the heart of radar system which is designed to provide interface for digital controls, analog parameter monitoring, and timing and control signals generation required for 1 kW TR Module operation. The main objective of TCSG is to control and monitor the field located TR modules remotely from the control and instrumentation room, usually far away from the antenna field. Each TCSG card is provided with unique IP address and port number to distinguish each card though they perform same kind of operations. After remote connection establishment, the TCSG card responds to the commands given for controlling or monitoring the TR module parameters. A PC based user interface allows sending controls and monitoring the health of the TR modules. The functionality of the TCSG card is verified with a test bench setup and the results shows that the TCSG card is working properly for all the user parameters. The proposed framework comprises of detailed design, architecture, visualization, implementation and integration on a 1 kW high power TR module for the radar communication. Simulation of various control pulses for radar real time operations are carried out using Vivado and updated to the real time application using Artix-7 FPGA.