Analysis, design and optimisation of various antenna types based on equivalent magnetic-current concept

Abstract

The field equivalence principle is a classical technique, simple to use but remarkably effective to analyse aperture antennas. For most of thin planar structures, the aperture can be approximated as perfect magnetic conductor. Thus, the field equivalence principle typically yields a well-approximated equivalent problem that is much easier to solve than the original geometry. Inspired by this principle, a wide range of novel antenna structures are proposed in this thesis. These structures are further developed, optimised and tailored for various practical applications. Three main types of antennas are investigated, including travelling-wave antennas, low-profile monopolar antennas and reconfigurable antennas, corresponding to three major parts of this dissertation.

The first part examines various realisations of travelling-wave half-mode substrate- integrated waveguide (HMSIW) antennas and their optimisations. This type of antenna is equivalent to a magnetic dipole. In this part, the core contribution is a generalised semi-analytical model to effectively analyse continuous-source travelling-wave antennas, based on which different optimisation techniques for bandwidth and radiation patterns are proposed. An optimisation procedure that includes parameter uncertainties is also demonstrated. The second part focuses on a type of low-profile monopolar antennas that can be interpreted as magnetic-current loops using the field equivalence principle. The main contributions are different configurations of symmetrical radiating slots that act as additional magnetic-current loop sources.

The last major part covers a wide range of reconfigurable antennas targeting various applications. These includes a family of stub-loaded substrate-integrated antennas, a circular resonant cavity, and low-profile monopolar antennas that have been introduced in the second major part. These antennas not only cover three main application types of reconfigurable antennas, i.e. frequency- , polarisation-, and pattern-tunability, but also combine those in a single device. Moreover, significant improvements in performances compared to antennas available in the literature are demonstrated.

Overall, the thesis provides different frameworks to design many types of antennas. The

analytical models, using the field equivalence principle as a common fundamental technique, provide not only thorough understandings on antennas’ radiation mechanisms but also an effective means for rapid antenna optimisations.