Three‐dimensional, ultra‐wideband micromachined millimetre‐wave hemispherical shell antenna: theoretical concept and calibration

Abstract

This study presents a theoretical design study of a novel three-dimensional micromachined hemispherical shell antenna for ultra-wideband millimetre-wave imaging applications. The antenna is composed of a hemispherical metallic shell which is suspended on top of a high-resistivity silicon substrate using a thin silicon stem. The antenna exhibits two different operational modes and an exceptionally wide bandwidth of more than 80 GHz at the centre frequency of 120 GHz. Simulation results indicate that the antenna performance is highly sensitive to geometrical variations and hence to fabrication inaccuracies. Performing a complete sensitivity analysis using full-wave simulations requires numerous simulation steps and is therefore time-intensive and impractical. This study provides closed-form solutions for all performance metrics of the antenna, followed by a comprehensive theoretical-based sensitivity analysis for evaluating the effects of fabrication imperfections on its bandwidth. The antenna structure is then calibrated for ultra-wideband operations and low sensitivities to fabrication inaccuracies.

Design of a quasi-hemispherical UWB antenna

“…The spherical antennas are divided into spherical monopoles (composed of a solid sphere and a ground plane) and spherical dipoles (composed of two solid spheres) [8]- [11]. Also, designs with hemispherical and hollow radiators have been presented in [9], [12]. One of the designs in [9] is similar to the design presented in this paper.…”

“…The latter changes the antenna performance by: 1) reflecting or scattering the radiated fields incident on the cable, and 2) radiation from the cable caused by the surface current flowing on the outer surface of the cable, i.e. the cable acts as an unintentional radiator [12]. All this leads to a distortion of the antenna radiation pattern and in order to assess the extent of this distortion for the presented antenna, a coaxial cable is attached to it.…”