The Shape Synthesis of Non-Planar and Closely-Spaced Electrically-Small Conducting Surface Antennas

Abstract

Antennas are needed in wireless communications of any kind and are key to the quality of any wireless link, irrespective of its use. There remains a need for electrically-small antennas that can fit on/in a restricted physical surface/volume for use in sensors (eg. Internet-of-Things) that need to “talk” to some data centre via the wireless network. The design issues associated with electrically-small antennas are well-known, and thus it will be appreciated that it would be advantageous to be able to design the above antennas in a way that exploits as much of the space allotted to them, as well the proximity of other objects present, to arrive at functioning antennas. Antennas of conventional shape do not necessarily do this. It might thus be best to perform a shape synthesis of an antenna that lets the electromagnetics decide on the shape of the final antenna in order to obtain the performance desired under the geometrical restrictions mentioned. Such shape synthesis has only been done for planar (2D) conducting surface antennas. In this thesis we develop the machinery for a computational electromagnetics-based tool capable of performing the shape synthesis of 3D conducting surface antennas for the first time. It has purposefully been developed in a way that allows it to capitalize on commercially available software for both the computational electromagnetics (CEM) and the genetic optimization algorithm (GA). A comprehensive ‘shaping manager’ software tool has been developed that controls the whole shaping process and communicates with the commercial software, in so doing implementing a desired shaping prescription. It is a complex tool whose development is based on a considerable amount of software engineering. The advantage of being able to utilize the commercial codes is that the work becomes accessible to others, such codes are more powerful and flexible than in-house codes, and they are also able to export files describing the complicated shaped geometries for fabrication. The shaping manager utilizes the characteristic mode concept so that one only needs to select the feed point once the shape synthesis has been completed. Fully 3D electrically-small conducting surface antenna examples are then successfully shape synthesized subject to various geometry restrictions. The validity of the modelling process is experimentally validated. The shape synthesis procedure is then extended to apply to the design of two closely-spaced electrically-small antennas operating at different frequencies, again with some experimental validation. Such shape synthesis has also not been done before. These procedures can be extended to the case where the two antennas in question are mounted on some electrically-large platform. However, if such platforms are electrically very large the full-wave computational burden may become prohibitive. We show that the characteristic modes for the antennas under shaping in such situations can in fact be found using hybrid method of moment / geometrical theory of diffraction (MM/GTD) methods, with only the antenna proper needing to be MM-meshed. An example is provided to demonstrate the computation of characteristic modes in this way. This possibility for characteristic mode computation has not yet been explicitly stated elsewhere (and so perhaps not realised), nor example computations provided. We believe this realisation might widen the scope of application of characteristic mode analysis.