Geometrical defects of a high gain reflector antenna can cause the radiation pattern of the antenna to fail to meet its specifications. These defects give rise to loss of gain, widening of the main beam and raising of sidelobes. The geometrical defects can be identified, and subsequently corrected, by utilizing information contained in the phase of the copolar aperture field distribution. For technical reasons, this phase can be difficult or inconvenient to measure directly. Therefore, indirect methods of deducing the phase are often preferred. This thesis introduces an iterative algorithm, called the modified Gerchberg-Saxton algori thm, which has been developed for retrieving the copolar aperture field phase distribution from the far field copolar amplitude pattern. In order to aid convergence of this algorithm, it incorporates information concerning the design and any known aspect of the antenna. The modified Gerchberg-Saxton algorithm is based on the conventional Gerchberg-Saxton algorithm, originally developed for electron microscopy, but incorporates features of Fienup's phase retrieval algorithms. This thesis reviews radio engineering theory with an emphasis on high gain reflector antennas. In particular, the Fourier transform relationship between the copolar aperture field distribution and the copolar radiation pattern is critically examined. The problem of retrieving the copolar aperture field distribution from the amplitude of its Fourier transform is called a Fourier phase problem. The Fourier phase problem, the uniqueness of its solutions and iterative algorithms for solving it are discussed. Other established methods for determining geometrical defects of an antenna are descri bed and their relative advantages and disadvantages are assessed. The main advantage of the modified Gerchberg-Saxton algorithm is that it requires measurement of only a single copolar amplitude pattern. The modified Gerchberg-Saxton algorithm is evaluated by applying it to computer simulated data and to measured amplitude patterns of an acoustic antenna. This evaluation illustrates the relationship between the accuracy of the data to which the algorithm is applied and the accuracy of the retrieved copolar aperture field phase distribution. The performance of the algorithm appears to be insensitive to the location and dimensions of the geometrical defects of the antenna. The optimum form of the algorithm seems to be versatile and robust enough to offer real hope of being able to retrieve, to a useful level of accuracy, the phase of the aperture field from a single measured radiation pattern amplitude (i.e. there is no need to measure the phase of the radiation pattern).

Antenna aperture phase retrieval

This article provides a macrolevel overview of the System-by-Design (SbD) paradigm and then applies it to the design of a representative complex system. By introducing a set of archetypes of the SbD paradigm (i.e., Architecture-by-Design, Material-by-Design, Algorithm-by-Design, and Component-by-Design), the synthesis of large complex-shaped radomes is addressed by combining the Material-by-Design and the Architecture-by-Design concepts. The results of a numerical assessment are discussed to give the interested readers some insights on the SbD effectiveness and potentialities also in comparison with traditional design approaches. 

System-by-Design Paradigm-Based Synthesis of Complex Systems: The case of spline-contoured 3D radomes

An efficient knowledge-based artificial neural network (KBANN) is proposed, and it is used for the design of circularly polarized (CP) lens antenna in this paper. In this KBANN, the forward neural network (FNN) and the inverse neural network (INN) are included. In this model, the INN is the major component to predict the antenna structure parameters. As multiple performance indices are required, the INN requires large number of training samples to deduce the complex mapping relationship. To solve this problem, FNN is introduced to provide prior knowledge for the INN. The FNN generates a huge training dataset for INN training, and then the trained INN can directly output the geometric parameters by feeding the target electromagnetic responses as input. This paper solves the problem of multiple performance indices in antenna design, and a CP lens antenna with wideband, good axial ratio and high gain is designed and fabricated to verify the effectiveness of the KBANN model.

An Efficient Knowledge-Based Artificial Neural Network for the Design of Circularly Polarized 3D-Printed Lens Antenna

In this paper, a comparison between electromagnetic scattering from periodic and aperiodic gratings is made. The effects of strip grating truncation are included for both cases. A Galerkin formulation with entire domain basis functions is utilized to solve for the induced currents on the strips for both TE and TM polarizations. Current densities and bistatic scattering results are presented for both periodic and aperiodic profiles. Moreover, the focusing capability of aperiodic gratings is also presented.

Electromagnetic scattering from aperiodic strip gratings

An efficient knowledge-based artificial neural network (KBANN) is proposed, and it is used for the design of circularly polarized (CP) lens antenna in this article. In this KBANN, forward neural network (FNN) and inverse neural network (INN) are included. In this model, INN is the major component to predict the antenna structure parameters. As multiple performance indices are required, INN requires a large number of training samples to deduce complex mapping relationship. To solve this problem, FNN is introduced to provide prior knowledge for INN. FNN generates a huge training dataset for INN training, and then the trained INN can directly output the geometric parameters by feeding the target electromagnetic responses as input. This article solves the problem of multiple performance indices in antenna design, and a CP lens antenna with wideband, good axial ratio, and high gain is designed and fabricated to verify the effectiveness of the KBANN model. 

An Efficient Knowledge-Based Artificial Neural Network for the Design of Circularly Polarized 3-D-Printed Lens Antenna

A parametric study of the constraints related to Gregorian/Cassegrain offset reflectors having negligible cross polarization was undertaken with the aid of design equations linking the defining parameters of the primary reflectors to those of the secondary reflectors. This study resulted in the mapping of a very large number of Gregorian/Cassegrain offset reflectors having negligible cross polarization. The domains of definition of the equations derived are deduced from geometrical considerations. Physical insights into the above constraints are presented. >

N. Fourikis

Papers

A parametric study of the constraints related to Gregorian/Cassegrain offset reflectors having negligible cross polarization