Ioan E. Lager

Ioan E. Lager (Senior Member, IEEE) received the Ph.D. degrees in electrical engineering from the Delft University of Technology, The Netherlands, in 1996, and the Transilvania University of Brașov, Romania, in 1998. In 1997, he was a Visiting Scientist with Schlumberger-Doll Research, Ridgefield, CT, USA. He successively occupied research and academic positions with the Transilvania University of Brașov and the Delft University of Technology, where he is currently an Associate Professor. He endeavours toward bridging the gap between electromagnetic field theory and the design, implementation, and measurement of antenna front-end architectures. His research interests include applied electromagnetics, especially time-domain propagation and applications, and antenna engineering, with an emphasis on nonperiodic (interleaved) array antenna architectures.

Title of the presentation:
Weekly-dispersive Leaky-Wave Radiation: The Causal Perspective

Abstract:
Leaky-lens antennas (LLAs) count among the most effective (sub-)millimetre wave radiators for ultra-high-rate digital communications and deep-space astronomical instrumentation. In line with, practically, the entire literature on leaky-wave (LW) propagation, the operational principles of LLAs are described in the frequency-domain (FD). Remarkably, the time-domain (TD) perspective on the LLA functioning was missing until recently. While the FD approach yielded a thorough understanding of the radiator’s steady-state, time-harmonic (TH) operation and, primarily, allowed developing extremely effective design tools, concerns surfaced about the adequacy of the FD models in ultra-high-rate systems, especially when extremely narrow beams and agile beam scanning are requisite for the application at hand. Specifically, it was far from obvious if a steady-state TH regime can be still assumed when the propagation consists of extremely short packages of sine-waves.

To address this limitation, efforts were invested in the past years in developing a strictly causal description of the LW radiation. This contribution will then summarise the main findings of this research line, by insisting on specific characteristic aspects of the LW radiation. The conclusions will be drawn based on a careful numerical analysis of the typical, weakly-dispersive, LW configuration underpinning LLAs. That study proves beyond any doubt that the investigated weakly-dispersive, LW radiation is the result of constructive or destructive interference of causal waves launched at regular intervals from a feeding point. This crucial observation falls completely outside the scope of any FD analysis that, inherently, cannot account for the origin of the field values at given locations. While our investigation did in no way question the validity of results inferred via steady-state FD instruments, we gave a first demonstration of the transient mechanism leading to the observed steady-state field behaviour. At the same time, our experiments cogently illustrate that the beam emerging from the feeding point can differ a lot during the transition to the steady-state from the expected, settled, steady-state profile, a matter that must considered in the design of ultra-high-rate communication channels making use of basic, on-off keying modulation.

The reported research was carried out by a group comprising, apart from the author, Dr. Martin Štumpf of the Brno University of Technology, the Czech Republic, and Professor Andrea Neto of the Delft University of Technology. Their support and agreement to reporting our common results is hereby acknowledged.