Thesis submitted in fulfilment of the requirements for the degree Master of Technology: ELECTRICAL ENGINEERING in the Faculty of Engineering at the Cape Peninsula University of Technology 2014 / The thesis reports on the evaluation and comparison of various signal processing algorithms for estimating the direction of arrival (DOA) of a high frequency (HF) beacon signal from a CubeSat in Low Earth Orbit (LEO). The DOA of the HF beacon signal is expressed in terms of the two angles, azimuth ( α ) and elevation ( ). The azimuth and elevation angles of the received HF signal are calculated from the phase differences between signals observed at three elements of an L-shaped crossed-loop antenna array. The algorithms which were evaluated are the Zero Crossing (ZC), Cross Correlation (CC), Fast Fourier Transform (FFT) and Cross Power Spectral Density (CPSD) algorithms. A theoretical analysis was done to demonstrate that the phase differences at the radio frequency (RF) of the beacon are propagated to the baseband signals. The algorithms were thus tested using simulated baseband signals as would be derived from the RF signals intercepted by the three elements of an L-shaped crossed-loop antenna array. Gaussian noise with a given signal-to-noise ratio (SNR) was added to the simulated baseband signals. The algorithms were implemented in MATLAB. The criteria for the selection of the best algorithm were accuracy and speed. The standard deviation (SD) of the azimuth and elevation errors was used to measure the performance accuracy of each algorithm, while the computational time for a given number of samples and runs was used to express the speed of each algorithm. First the ZC, CC, FFT and CPSD algorithms were evaluated for various SNR values, and compared with respect to SD of the azimuth and elevation errors. The analysis of the simulations demonstrate that the FFT and CPSD algorithms outperform the ZC and CC algorithms by estimating the DOA with a small SD of errors even at the low SNR of 0 dB, where the noise amplitude is the same as the signal amplitude. The ZC algorithm estimates the DOA with a large SD of error at low SNR due to multiple ZC points occurring during the same cycle. The ZC algorithm breaks down when the SNR decreases below 35 dB. The accuracy of the ZC algorithm depends on the method by which the ZC points are detected. The CC algorithm breaks down when the SNR decreases below 10 dB. The CPSD and FFT algorithms break down when the SNR decreases below – 20 dB. However, at a high SNR of 40 dB and above, all the algorithms estimate the DOA with a SD of error smaller than 1˚ for the azimuth and elevation. Next, the ZC, CC, FFT and CPSD algorithms were compared with respect to computation time. The FFT was found to be the fastest algorithm. Although the CPSD and the FFT algorithms reach the same accuracy in the estimation of the DOA, the FFT was selected as the optimum algorithm due to its better computation time. Recommendations are made regarding the implementation of the proposed algorithms for real signals from the HF direction finding (DF) array. At the time of submission of this thesis, such signals were not yet available.

Analysing Frequency Selective Surfaces (FSS) often requires solving integral equations that may have asymmetric and singularity behaved kernels. These singularities together with the array geometry can introduce significant complexities to the solution of the problem. The thesis deals with the solution of such equations using a spectral iterative method. The analysis is based on minimising an error criterion, which is defined as the difference between the scattered and impressed waves. Computer models have been developed as a means of predicting the radiation performance of single and multiple layer FSS. The research involves two separate but related studies. The first study is concerned with finite arrays of conducting elements. The effect of the dielectric substrate and size of the arrays to the scattered field is examined. In the second study the iterative scheme is modified accordingly in order to solve a set of integral equations for a multilayer array where each layer is assumed to be of infinite extent. The analysis takes into account the interlayer coupling and the dielectric substrates/superstrates adjacent to the array elements. The results obtained from both studies are compared with the method of moments solution as well as with experimental results.

This work is an effort to investigate and derive a simple equivalent circuit model to represent an electromagnetically coupled microstrip patch antenna. This provides a simple approach to the complicated electromagnetic coupling behaviour in the patch. A simplified theory based on the broadside coupled line and improved transmission line theories is developed to derive the equivalent circuit of EM coupled patch antenna. The design parameters are determined from the above mentioned theory. Computer programs are developed to provide a practical design of such antennas without involving complicated, time consuming, rigorous methods. A number of sample patches are designed, made and tested to verify the theory. These elements are also incorporated into an array to evaluate their performance in an array environment. The impedance and pattern measurements are made for comparison with theoretical results.

No description available.

The radiation quality factor of small vertically polarized antennas above a ground plane is investigated. Although the quality factor of small antennas in free space has been investigated extensively in the past, the exact effect of a conducting ground plane on the antenna bandwidth is not clearly understood. In this thesis, quality factors of vertically polarized antennas above a ground plane are computed and compared with their free-space counterparts. The theoretical results on quality factors are validated with simulations of electrically small spherical helix antennas.

Yes / This paper presents a novel 2D meta-surface wall to increase the isolation between microstrip patch radiators in an antenna array that is operating in the teraherz (THz) band of 139–141 GHz for applications including communications, medical and security screening systems. The metasurface unit-cell comprises conjoined twin ‘Y-shape’ microstrip structures, which are inter-digitally interleaved together to create the meta-surface wall. The proposed meta-surface wall is free of via holes and defected ground-plane hence easing its fabrication. The meta-surface wall is inserted tightly between the radiating elements to reduce surface wave mutual coupling. For best isolation performance the wall is oriented orthogonal to the patch antennas. The antenna array exhibits a gain of 9.0 dBi with high isolation level of less than −63 dB between transmit and receive antennas in the specified THz-band. The proposed technique achieves mutual coupling suppression of more than 10 dB over a much wider frequency bandwidth (2 GHz) than achieved to date. With the proposed technique the edge-to-edge gap between the transmit and receive patch antennas can be reduced to 2.5 mm. Dimensions of the transmit and receive patch antennas are 5 × 5 mm2 with ground-plane size of 9 × 4.25 mm2 when being constructed on a conventional lossy substrate with thickness of 1.6 mm. / H2020-MSCA-ITN-2016 SECRET-722424 and UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E022936/1

No description available.

No description available.

No description available.

No description available.