Antenna And Wave Propagation By Kd Prasad Pdf Free Download
Tilo Chopin
Srinivas is currently a Systems Engineer in the Radar concepts and formulation group. He is working on the development of multiple radar and remote sensing instruments. His previous work as a graduate student focused on developing Ultra Low Frequency mechanical antennas for underwater and underground communications. His current research interests include millimeter wave antenna and passive RF component design for multifrequency SmallSat radars, Quantum Rydberg radars, Quasi-static sensing and navigation.
The e.m. wave propagation in a parallel-plate wave guide withone boundary corrugated and filled with uniaxial warmdrifting plasma has been studied. The dispersion relation and the field expressions for the TM-modes have been derived. The effects of the temperature and the drift velocity on the propagation modes have been studied in detail. The fast and the slow waves are greatly affected by the temperature and the drift velocity, whereas the wave guide wave is insignificantly affected. The effect of the corrugation has also been discussed. The dispersion relation of the TE-modes, in this case, has been derived and found to be same as that of the wave guide filled with free space.
Figure 13(b) shows the improved circuit model and Fig. 14 shows input impedance of the pendulum array prototype, coil and the circuit model plotted across frequency. The peaking of the input impedance indicates a greater portion of the input power is coupled to the pendulum system while the power consumption caused by the Ohmic resonance of coil is relatively reduced. Note that not all the modes were predicted by the circuit model due to the fact the mutual coupling among the pendulum elements are not included in the model demonstrating the superiority and completeness of the full wave model. The estimated Q factor at the in-phase mode is around 62.2 as previously demonstrated using the circuit model. To our knowledge, this is the first time such a high Q factor has been achieved in a mechanical antenna system using magnetic dipoles at ULF, demonstrating the potential of magnetic pendulum arrays for efficient ULF transmission.
Over the last couple of decades analog-to-digital and digital-to-analog technologies have advanced exponentially, resulting in tremendous design degrees of freedom and arbitrary waveform generation (AWG) capabilities that enable sophisticated design of emissions to better suit operational requirements. However, radar systems typically require high powered amplifiers (HPA) to contend with the two-way propagation. Thus, transmitter-amenable waveforms are effectively constrained to be both spectrally contained and constant amplitude, resulting in a non-convex NP-hard design problem.
Estimating the spatial angle of arrival for a received radar signal traditionally entails measurements across multiple antenna elements. Spatially diverse Multiple Input Multiple Output (MIMO) emission structures, such as the Frequency Diverse Array (FDA), provide waveform separability to achieve spatial estimation without the need for multiple receive antenna elements. A low complexity Multiple Input Single Output (MISO) radar system leveraging the FDA emission structure coupled with the Linear Frequency Modulated Continuous Wave (LFMCW) waveform is experimentally demonstrated that estimates range, Doppler and spatial angle information of the illuminated scene using a single receiver antenna element. In comparison to well-known spatially diverse emission structures (i.e., Doppler Division Multiple Access (DDMA) and Time Division Multiple Access (TDMA)), LFMCW-FDA is shown to retain the full range and Doppler unambiguous spaces at the cost of a reduced range resolution. To combat the degraded range performance, an adaptive algorithm is introduced with initial results showing the ability to improve separability of closely spaced scatterers in range and angle. With the persistent illumination achieved by the emission structure, demonstrated performance, and low complexity architecture, the LFMCW-FDA system is shown to have attractive features for use in a low-resolution search radar context.