COBRA meteor radar antenna designs

A meteor radar system is one of the effective remote sensing techniques in measuring atmospheric parameters such as wind velocities, temperature, pressure and density which are essential in understanding the atmospheric dynamics in the Mesosphere Lower Thermosphere (MLT) region. Previous studies of very high frequency (VHF) meteors radar systems suggest that the minimum error for the estimation of the horizontal wind velocity from a radar interferometry algorithm should occur when the main beams of the transmit and receive antennas are pointing to between 30° to 50° elevation angles. Therefore, an ideal antenna design for VHF meteor radar systems would produce a pencil beam radiation pattern at a 45° elevation angle.However, both the transmit and receive antenna of the COBRA meteor radar system have major beams are pointing to between 60° to 65° degree elevation angles above a perfect ground plane. Besides transmitting maximum power at low elevation angles, the current antennas of the COBRA meteor radar are highly dependent on the ground plane to radiate maximum gains to between 60° to 65° degree elevation angles. Typically, the earth ground is considered as a common ground plane for many VHF antenna with acceptable performance. However, the earth ground could not effectively reflect most of the power at all time. Because the antennas are dependent on ground to radiate power at certain direction, an artificial ground plane or ground screen has to be built for the COBRA antenna system at the South Pole station, which is located on top of more than 2000 meter thick of ice sheet.This dissertation focuses on the analysis of the performance of the individual current antenna design with four different conditions namely in free space, above an infinite ground, lossy ground and finite ground. In the analysis of finite ground, the effects of varying wire spacing and the size of finite ground to the radiation pattern of a cross folded dipole antenna are investigated. This dissertation also discusses the performance of the individual current antenna in the current and proposed COBRA meteor antenna system configuration above an infinite and finite ground. Finally, the performance of linear phased array antenna designs as the proposed transmit antenna for the COBRA meteor radar is analyzed. The results of the performance of all antenna designs in this research are obtained from the 4NEC2 simulations. The accuracy of the 4NEC2 antenna modeler in the modeling of input impedance and radiation pattern is also addressed in this dissertation.