Dielectric rod waveguide components at sub-THz frequencies

Abstract

This thesis is focused on the development of dielectric rod waveguide (DRW) components at sub-THz frequencies. DRWs proved themselves as low loss transmission lines at sub-millimeter wave and THz frequencies; they can be well matched with rectangular metal waveguides, and also used as antennas. In addition, the DRW allows integration of various components using standard microfabrication techniques, e.g. the bolometric power sensor can be integrated in the center of the DRW and measure the power travelling in the DRW, and a phase shifter based on a high impedance surface (HIS) can be manufactured on the surface of the DRW and can change the phase of the propagating wave inside the DRW. In the first part of this thesis the narrow band and wide band DRW antennas were designed, manufactured and tested. The DRW antennas are lightweight, compact and easy to manufacture. The narrow band DRW antenna proved to operate in the range of 220 – 325 GHz. The wideband DRW antenna showed a constant performance over the band of 75 – 1100 GHz according to numerical simulations and over the band of 75 – 325 GHz experimentally. The radiation patterns of the antenna were measured in co- and cross-polarization. The co-polarization radiation patterns are nearly independent of frequency. The 3 dB beamwidth is 50º - 60º, and the 10 dB beamwidth is about 95º. The return loss of the antenna is better than 15 dB. In the second part of this thesis the bolometric power sensor integrated into DRW was designed, manufactured and tested at frequencies 75 – 1010 GHz. The power sensor consists of a metallic antenna -like structure in the center of the DRW in E-plane suspended on a membrane over an airgap to improve the thermal insulation. The power sensor showed good matching with the rectangular metal waveguides and constant responsivity over the wide band of frequencies, as well as a linear responsivity up to 500 mW applied power. In the third part of this thesis the microelectromechanical system (MEMS) tunable HIS was developed for integration on to the surface of a DRW using suspended carbon nanotube (SWCNT) film as a movable element of the HIS. The implementation of a SWCNT network as a material for movable suspended film allows to significantly simplify the fabrication process of the HIS due to a simple technique of the SWCNT film deposition by dry transfer, and additionally it allows to reduce the actuation voltage of the HIS due to the low Young's modulus of the SWCNT network. The unique deposition technique of the SWCNT film allows to design a HIS phase shifter directly on the surface of the DRW. The suspended SWCNT film structure showed the tunability of the capacitance of 100% at 0 – 10 V applied bias voltage. Such properties allow to create a SWCNT MEMS HIS with a phase shift of 260° at 0 – 7 V bias voltage.