Investigation of surface wave radiation by dielectric truncation

Abstract

Surface waves (SWs) widely exist in dielectric-involving applications, and their intriguing properties continue to draw attention from researchers in both academia and industry. Existing studies on SW radiation focus on using periodic structures, such as surface texture, corrugated conductor and multilayered substrate. Conventional planar trapped SW and cylindrical trapped SW radiations require a large additional aperture. In this thesis, a novel approach for utilizing SW radiation for enhancing the antenna performance is proposed. We show that SW diffraction (SWD), which is commonly regarded as a spurious diffraction in dielectric-involving systems, can be manipulated to contribute the objective radiation. By focusing on SWD radiation (SWDR), an equivalent current method is proposed to aid in the design of three novel SWD antennas. Firstly, a novel spiral grounded dielectric slab (GDS) antenna for broadside circularly polarized (CP) radiation is designed by equivalent current method. This physical insightful method can distinguish the radiated part from the entire structure and manifest the key parameter influencing radiation performances. The SWDs on diverse shaped truncations are analyzed to reveal the linkage between physical structure and the SWD property. The Archimedean spiral GDS with sinusoidal-wave-shaped edges is designed resting upon the equivalent current method and SWD structural analysis. This proposed design is fabricated. We experimentally demonstrate that SWDs effectively generate broadside CP radiation. Secondly, we develop a slot-fed circular GDS antenna that is suitable for satellite communications. This antenna works at different SW operating modes. In the low-frequency band, the parasitic SWs are constrained by the outer metal strip annuluses (MSA) because the radiator is the inner MSA functioning as a microstrip ring and SWs are unwanted. At higher frequencies, the desired SW energy is scattered by the two MSAs and diffracted by dielectric truncation. The conflict between suppression and utilization of SWs is addressed by the multifunctional MSAs. The measurements demonstrate that MSAs as concentric radiators at higher frequency can reduce the side-lobe level (SLL) of the SWDR. Finally, an SW-generating dual-mode orbital angular momentum (OAM) antenna is presented. OAM as new attractive degree of freedom in electromagnetic waves provide solutions to the radio-band congestion in an extra dimension. We first use a modified synthesis of equivalent currents with relative coordinate systems to demonstrate that l = ±1 (l is the topological charge) OAM beams can be generated by the simultaneously in-phase-fed radial and circumferential currents. This conclusion enables a simple method to generate OAM without complicated feeding network or bulky wave manipulation plane. A circular GDS is designed to achieve the radial and circumferential currents. The GDS is fed by a centre-fed monopole to excite SWs which are decomposed into radial and circumferential components by polarizers. Simulated and experimental results show that this antenna can generate l = 1 mode OAM at 7.5 GHz and l = −1 mode OAM at 11 GHz. It offers a new mechanism for l = ±1 mode OAM generation.