Optimisation of DTV coverage and broadcasting antennas

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel UniversityThe increased use of the available radio frequency spectrum by many existing as well as new technologies brings up the need of more advanced and specialised antennas, designed for very specific purposes. A very good example is the withdrawal of analogue TV from the radio spectrum, which has given space to be used by newer technologies such as 4G and 5G. Optimising the design of an antenna for a specific purpose is a goal that becomes more and more necessary. This suggests that an investigation of methods to optimise an electromagnetic design with the best possible results at the best possible time is also necessary. Evolutionary Algorithms (EA) are a very well know method which exhibits solid results within a smallest possible time for electromagnetic problems (e.g. antenna design optimisation). EA are nature inspired algorithms, and some very popular examples, which are widely used in antenna optimisation are the Differential Evolution (DE), Particle Swarm Optimisation (PSO) and Invasive Weed Optimisation (IWO). This thesis researches a comparison between the aforementioned methods, while also proposing a novel method, which is a modified version of IWO and has proven to be very solid. To determine the efficacy of the proposed method, all the algorithms were compared on some of the most major test functions for such purposes. Some examples are Ackley’s, De Jong’s, Holder table, Rastrigin and Rosenbrock. By employing these test functions, it was possible to determine the optimum settings of the modified IWO version. These methods are compared for different antenna design optimisation simulations using software such as MATLAB and CST Microwave Studio, to determine which method yields the best results and to output novel optimised antenna designs for different purposes. Some of the novel antenna designs that were applied to EAs for optimisation are a collinear dipole array with a specifically shaped radiation pattern and a log-periodic dipole antenna (LPDA) with flat gain response across its operating spectrum for Digital TV (DTV) broadcasting purposes. Other novel designs include a planar elliptical dipole antenna for Ultra-Wideband (UWB) Electromagnetic Compatibility (EMC) applications such as EMC measurements and a pin-fed notched circular patch antenna with circular polarisation for satellite communications, in which cases the small size of the generated geometries was also a goal so that portability is achieved. The geometrical parameters of the best possible antenna design were in some cases fabricated and compared to the simulated results so that the latter is compared to real world applications

1.62 GHz Circularly Polarized Pin-Fed Notched Circular Patch Antenna

This paper studies a circular patch antenna which is fed by using a coaxial pin, which is a suitable antenna design for applications where small size is of importance. Such applications are wearable antenna designs. The main purpose of this paper is to design an antenna with wearable capabilities and adequate radiation characteristics for satellite communications and more specifically for the Iridium satellite constellation. The goals for the radiation characteristics of the antenna are the tuning of the antenna to 1.62GHz which is the Iridium's frequency, maximum boresight gain for this frequency, as well as circular polarization

1.62GHz Circularly Polarized Pin-Fed Notched Circular Patch Antenna

This paper studies a circular patch antenna which is fed by using a coaxial pin, which is a suitable antenna design for applications where small size is of importance. Such applications are wearable antenna designs. The main purpose of this paper is to design an antenna with wearable capabilities and adequate radiation characteristics for satellite communications and more specifically for the Iridium satellite constellation. The goals for the radiation characteristics of the antenna are the tuning of the antenna to 1.62GHz which is the Iridium's frequency, maximum boresight gain for this frequency, as well as circular polarization

Comparison of evolutionary algorithms for LPDA antenna optimization

A novel approach to broadband log-periodic antenna design is presented, where some of the most powerful evolutionary algorithms are applied and compared for the optimal design of wire log-periodic dipole arrays (LPDA) using Numerical Electromagnetics Code. The target is to achieve an optimal antenna design with respect to maximum gain, gain flatness, front-to-rear ratio (F/R) and standing wave ratio. The parameters of the LPDA optimized are the dipole lengths, the spacing between the dipoles, and the dipole wire diameters. The evolutionary algorithms compared are the Differential Evolution (DE), Particle Swarm (PSO), Taguchi, Invasive Weed (IWO), and Adaptive Invasive Weed Optimization (ADIWO). Superior performance is achieved by the IWO (best results) and PSO (fast convergence) algorithms.NATO's Public Diplomacy Division in the framework of “Science for Peace”. Grant Number: SfP-984409 ORC