Introduction
In this thesis, a set of software tools to improve and speed up the pre-design phase in antenna design workflow has been designed based on theoretical formulation. During an internship at IDS (Ingegneria dei Sistemi) S.p.A, a number of Python-based tools have been developed and integrated in the software Galileo EMT (ElectroMagnetic Toolkit), the electromagnetic toolkit of the CAE (Computer-aided engineering) suite produced by IDS S.p.A.. After the implementation of the tools, a design validation has been done through full-wave simulations, comparison with commercial products or scientific papers, prototypes and measurements. Furthermore, a cavity-backed spiral antenna for GNSS (Global Navigation Satellite System) applications has been designed by using the proper developed tool. The proposed antenna was designed for direction finding application in L-band for GNSS monitors, context in which IDS S.p.A. realized a product to meet the new requirements set by the ICAO(International Civil Aviation Organization) recommendations for civil air navigation systems.
To develop the software tools, in the wide world of the antennas, a set of antennas with different characteristics in terms of capabilities and working principles were selected . The first antenna analyzed in this work was a planar rectangular microstrip antenna, with a narrow bandwidth and linear polarization.
The second type which has been analyzed includes rectangular horn antennas and rectangular ridged horn antennas, that consists of a flared waveguide shaped like a horn, they are characterized for an high gain, a wide bandwidth and linear polarizzation.
The last type of antennas object of this work are Archimedean spiral and equiangular spiral antennas. These antennas are characterized by a wide band with a frequency independent behaviour, circularly polarization, and a planar structure but usually to obtain a unidirectional radiation pattern are placed over a cavity. To feed these antennas
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is needed a balun and in this work a microstrip to double sided parallel stripline transition to feed the spirals is implemented.
For each structure a literature research of design criteria, the software tool implementation and a validation were performed. The validation was performed through prototyping and measuring, otherwise if it was not possible through simulation and comparison with commercial products or scientific papers.
This dissertation is divided in six chapters, through which the development environment, the main characteristics of considerated antennas, and the design criteria on which the developed software tools are based, are described. As well the results of simulations, measurements and comparisons that validates the tools are shown. At the end a complete antenna design workflow is reported.
In the first chapter Galileo EMT, its characteristics and how the developed tools are interfaced with it, are described. The Python programming language and the non standard libraries used in this work are briefly introduced.
In the second chapter the rectangular microstrip antennas and related feeding techniques are introduced, the transmission line model proposed by A. R. Van de Capelle and H. F. Pues implemented in the developed tool is described. Furthermore several comparisons with reference papers, and a comparison with a prototype of rectangular microstrip antenna are reported.
In the third chapter the rectangular horn is introduced, the procedure to obtain an optimum gain horn antenna and the criteria to obtain the wider unimodal bandwidth in a waveguide are explained, and a comparison with a commercial WR90 horn antenna is reported. In the chapter just mentioned the double ridged waveguide, the equation which govern the cutoff conditions of the modes and the theoretical formula to take into account the effect of ridge in the gain calculation are described, at the end as for horn a comparison with a commercial HWRD750 Double ridged horn antenna is reported.
In the fourth chapter the mathematical equations which describes the archimedean spiral and the equangular spiral, the electromagnetic properties of these structure and the design critera for an correctly radiation are reported. In this chapter the properties and behaviors of these structure on dielectric substrate and in self complementary and non-self complementary configuration are analyzed. The results of several simulations of spirals generated by the tool are shown. At last the implemented procedure to design a microstrip to double sided parallel stripline balun is described.
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The fifth chapter deals with the design of a cavity backed spiral antenna for direction finding application. In this section, after briefly introduced the GNSS application and direction finding principles, the design constraints and the antenna design steps are reported. The design steps include a pre-design phase in which the developed tool is used, simulation of generated CAD (Computer-Aided Design) model, optimization to achieve better performance, prototyping and measurement.
In the sixth chapter the results obtained in the previous chapters are analized. For each tool a future improvement is proposed, and for the proposed antenna a future study is suggested.
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