Ray Tracing and Physical Optics for Geodesic and GRIN Lens Antennas
Time: Mon 2025-09-29 13.00
Location: Room nr. 132, F3, Lindstedtsvägen 26 & 28
Video link: https://kth-se.zoom.us/j/67589198814
Language: English
Doctoral student: Mingzheng Chen , Elektromagnetism och fusionsfysik
Opponent: Professor Christophe Craeye, Universite Catholique de Louvain
Supervisor: Professor Oscar Quevedo-Teruel, Elektromagnetism och fusionsfysik; Professor Francisco Mesa, University of Seville; Associate professor Mariana Dalarsson, Elektromagnetism och fusionsfysik
QC 20250828
Abstract
This thesis investigates the ray tracing (RT) and physical optics (PO) method for geodesic and gradient-index (GRIN) lens antennas in both far and near fields at millimeter-wave frequencies (from around 30 GHz up to 110 GHz). In particular, parallel-plate-waveguide (PPW) based GRIN lenses and geodesic H-plane horns are studied to realize high-gain antennas in the far-field region. In addition, radial GRIN lenses are investigated to produce quasi-nondiffracting beams in the near-field region. Ray techniques are used in all cases.
First, a highly time-efficient and reasonably accurate RT-PO model is proposed as a fast design tool. The model can be divided into three steps:(i) calculation of ray trajectories and the corresponding phase distribution applying geometric optics, (ii) evaluation of the amplitude distribution using ray-tube power conservation theory, and (iii) calculation of radiation far fields applying the field equivalence principle in PO. In this thesis, important antenna parameters are obtained from the model, including the radiation pattern, directivity, dielectric loss, and gain. Two PPW-based GRIN lenses, the Mikaelian and Luneburg lenses with H-plane beam steering capabilities, are studied to validate the proposed RT-PO model.
The RT-PO model is also used to design novel geodesic H-plane horn antennas. An appropriate geodesic shape is proposed and optimized using the fast RT-PO tool to correct for phase errors in regular H-plane horns.The resulting fully metallic antennas maintain a stable fan-shaped beam in a large bandwidth with high gain, high aperture efficiency, and high radiation efficiency. Furthermore, a metal-only additive manufacturing (AM) technique is used to monolithically manufacture them in a compact and lightweight manner. Successful prototyping has been shown up to the W-band.
In addition to far-field applications, this thesis also investigates radial GRIN lenses for near-field beamforming. A quasi-closed-form radial GRIN profile is derived based on optical path lengths of the traced rays to generate quasi-nondiffracting beams. The proposed profile can be applied for a wide range of lens parameters and operating frequencies. Quasi-periodic structures arranged in a highly symmetric lattice are used to experimentally realize this lens using a dielectric AM technique to cover the entire Ka-band. The proposed profile is also equally applicable for higher frequencies.