The design of antenna arrays involves, amongst others, the selection of the array elements and geometry, as well as the element excitations. The feeding network to obtain the desired excitations can become quite complex, and hence expensive. One possible alternative would be to make use of micros trip wire-grid antenna arrays. These arrays are composed of staggered interconnected rectangular loops of dimensions a half¬wavelength by a wavelength (in the presence of the dielectric). It is because the short sides are considered to be discrete elements fed via micros trip transmission lines, that these antennas are viewed as arrays. While considerable success has been achieved in the design of these antennas, published work has been either of an entirely experimental nature or based on approximate (albeit clever) network models which do not allow for fine control of the array element excitations or off-centre-frequency computations generally. It is the purpose of this thesis to perform an almost rigorous numerical analysis of these arrays in order to accurately predict their element excitations. Models used to study microstrip antennas range from simplified ones, such as transmission-line models up to more sophisticated and accurate integral-equation models. The mixed-potential integral equation formulation is one of these accurate models which allows for the analysis of arbitrarily shaped microstrip antennas with any combination of frequency and dielectric thickness. The model treats the antenna as a single entity so that physical effects such as radiation, surface waves, mutual coupling and losses are automatically included. According to this formulation, the microstrip antenna is modelled by an integral equation which is solved using the method of moments. By far the most demanding part of the integral equation analysis is its actual numerical implementation. For this reason a complete description of the numerical implementation of the formulation is given in this thesis. To verify the accuracy of the implementation, rectangular microstrip patch antennas were analysed and surface current distributions were shown to compare favourably with published results. The formulation is then applied to the analysis of micros trip wire-grid antenna arrays which makes it possible to accurately predict surface current distributions on these arrays. Radiation patterns are determined directly from computed current distributions in the presence of the dielectric substrate and groundplane, and are essentially exact except for finite groundplane effects. To verify theoretically predicted results for wire-grid antenna arrays, several arrays were fabricated and actual radiation patterns were measured. Good correspondence between measured and predicted co-polar radiation patterns was found, while the overall cross¬polarization behaviour in cases with large groundplanes could also be predicted. The fact that numerical experimentation can be performed on wire-grid antenna arrays to examine element excitations, means that it is now possible to carefully design for some desired aperture distribution. / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

This dissertation investigates a simple LC-matching network for the impedance bandwidth enhancement of microstrip patch antennas. Wideband impedance matching is a standard practice for active circuits. Simple impedance matching of antennas is also quite common, but data on wideband impedance matching of antennas is not found very much in the open literature. The matching circuit presented consists out of a resonant LC-circuit with a quarterwave matching line as part of the design. Results for a number or experimental antennas, on which the new technique was applied, are included in the report. A well-defined design procedure is also presented, and results in a relatively small circuit to implement. It is shown that the antenna VSWR bandwidth could be improved to more than double the original size in most of the antennas investigated. / Dissertation (M Eng (Electronic Engineering))--University of Pretoria, 2006. / Electrical, Electronic and Computer Engineering / unrestricted

No / Radiation efficiency of antennas is shown to be measurable by a modified radiometric technique where the antenna's physical temperature is varied, rather than the noise temperature of its surroundings. The method is accurate, flexible and much more convenient for routine use. A means of avoiding errors caused by temperature-dependent antenna impedance is described. The accuracy of the method is verified by measuring the radiation efficiency of a horn antenna with a 3 dB attenuator to simulate a 50% efficient antenna, and by using microstrip patch antennas, whose measured efficiencies compared well with values computed from a transmission-line model.

no / Reconfigurable beam steering using circular disc microstrip patch antenna with a ring slotis proposed. The overall dimension of the antenna is 5.4×5.4 mm2 printed on a 0.504 mm thick, Rogers RT5870 substrate with relative permittivity 2.3 and loss tangent 0.0012. The designed antenna operates at the expected 5G frequency band 60 GHz with a central coaxial probe feed. TwoNMOS switches are configured to generate three different beam patterns. Activating each switch individually results in a near 70 degree shift in the main beam direction, whereas the frequency characteristics are unchanged. The power gains are between 3.9 dB and 4.8dB for the three states of switches configurations. Simulated results in terms of return loss, peak gains and radiation pattern are presented and show a reasonable agreement at the expected 60 GHz bandfor 5G applications. / The published journal webpage is no longer available.

Yes / This paper presented a new circular polarization reconfigurable antenna for 5G wireless communications. The antenna, containing a semicircular slot, was compact in size and had a good axial ratio and frequency response. Two PIN diode switches controlled the reconfiguration for both the right-hand and left-hand circular polarization. Reconfigurable orthogonal polarizations were achieved by changing the states of the two PIN diode switches, and the reflection coefficient |S11| was maintained, which is a strong benefit of this design. The proposed polarization-reconfigurable antenna was modeled using the Computer Simulation Technology (CST) software. It had a 3.4 GHz resonance frequency in both states of reconfiguration, with a good axial ratio below 1.8 dB, and good gain of 4.8 dBic for both modes of operation. The proposed microstrip antenna was fabricated on an FR-4 substrate with a loss tangent of 0.02, and relative dielectric constant of 4.3. The radiating layer had a maximum size of 18.3 18.3 mm2, with 50 W coaxial probe feeding. / European Union’s Horizon 2020 research and innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424.

The purpose of this thesis is to investigate a novel method to develop broadband microstrip (patch) antennas using substrates containing photonic crystals. Photonic crystals are a class of periodic dielectric, metallic, or composite structures that when introduced to an electromagnetic signal can exhibit a forbidden band of frequencies (or bandgap) in which the incident signal destructively interferes and thus is unable to propagate. It is proposed that such photonic crystals will reduce surface waves and prohibit the formation of substrate modes, which are commonly known inhibitors of patch antenna designs. By reducing or eliminating the effects of these electromagnetic inhibitors with photonic crystals, a broadband response can be obtained from inherently narrowband antennas. In addition, it is also proposed that the behavior of the photonic crystals will lead to a reduction in pattern sidelobes resulting in improvements in radiation pattern front-to-back ratio and overall antenna efficiency. This research is verified through analytical simulations and experimental investigations in the Virginia Tech anaechoic chamber. / Master of Science

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This thesis focuses on the coaxial-microstrip T-resonator measurement technique to determine the aperture plane capacitance and radiation resistance of electrically short monopoles above a finite ground plane at Radio Frequencies. The determination of these impedance parameters is of interest as they are needed in the Thévenin equivalent circuit of the monopole to establish the relationship between the monopole, the electromagnetic field within which it is immersed, and its surrounding medium properties. Electromagnetically short monopoles are used in various applications such as in permittivity and biomedical measurement techniques and near-field metrology. The coaxial-microstrip device allows the measurement of transmission coefficient nulls when connected to the network analyser. By measuring the frequency shift in transmission null points and analysing the results, the capacitance of short monopoles of various lengths can be obtained. The radiation resistance of the monopole can also be determined by comparing the depth of transmission coefficient nulls points at various resonant frequencies. Monopoles ranging from flush-mounted to various sizes of protruding centre conductors, both bare and insulated, are investigated in the frequencies ranging from 45 MHz to 3 GHz. The experimental results compare well with FEKO numerical predictions at the ranges where this technique is applicable. The technique is however not applicable near and beyond the resonant frequency of the monopole where it is considered to be electrically long. Measurements to obtain monopole impedance parameters were conducted by connecting the device to the HP 8510C Network Analyser. To enhance accuracy, the Network Analyser was calibrated using a high quality calibration kit with precisely defined standards. The technique used was found to accurately yield capacitances in the range of 0.0211 to 1 pF and radiation resistances in the range of 0.9245 to 12.1 Ohms. These results were obtained for monopoles of length 0.0062 < h/l < 0.24. Results from literature, viz. W.R Scott, R.W.P. King and L.J. Cooper, show radiation resistance in the ranges: 2.5 to 35 Ohms (0.079 < h/l < 0.22), 1.26 to 74.08 Ohms (0.026 < h/l < 0.28) and 5.59 to 74.98 Ohms (0.1 < 0.28) for electrically short monopoles. The results of this work are compared with those in the literature and show variations of less than 6%. A technique capable of accurately measuring capacitance and radiation resistance of the monopole at various lengths of protruding centre conductor has been developed. The capacitance for a flush probe compares very well (agreement is less than 6%) when compared with those obtained by the previous researchers. The technique is capable of yielding accurate results radio frequencies in the challenging low radiation resistance range around 1 Ohm.

Orientador: Naasson Pereira de Alcântara Junior / Banca: José Carlos Sartoti / Banca: José Alfredo Covolan Ulson / Resumo: Neste trabalho, apresenta-se o desenvolvimento de uma metodologia utilizando redes neurais artificiais, para auxiliar na determinação da freqüência de ressonância no projeto de antenas tipo microfita de equipamentos móveis, tanto para antenas retangulares como para antenas triangulares. Compararam-se modelos deterministas e modelos empíricos baseados em Redes Neurais Artificiais (RNA) da literatura pesquisada com os modelos apresentados neste trabalho. Apresentam-se modelos empíricos baseados em RNAs tipo Perceptron Multicamadas (PMC). Os modelos propostos também são capazes de serem integrados em um ambiente CAD (Computed Aided Design) para projetar antenas tipo microfita de equipamentos móveis. / Abstract: This work presents the development of models that can be used in the design of microstrip antennas for mobile communications. The antennas can be triangular or rectangular. The presented models are compared with deterministic and empirical models based on artificial neural networks (ANN) presented in the literature. The models are based on Perceptron Multilayer (PML). The models can be embedded in CAD systems, in order to design microstrip antennas for mobile communications. / Mestre

Modeling of patch antennas and resonators on arbitrary dielectric substrates using surface RWG and volume edge based basis functions and the Method of Moments is implemented. The performance of the solver is studied for different mesh configurations. The results obtained are tested by comparison with experiments and Ansoft HFSS v9 simulator. The latter uses a large number of finite elements (up to 200K) and adaptive mesh refinement, thus providing the reliable data for comparison. The error in the resonant frequency is estimated for canonical resonator structures at different values of the relative dielectric constant ƒÕr, which ranges from 1 to 200. The reported results show a near perfect agreement in the estimation of resonant frequency for all the metal-dielectric resonators. Behavior of the antenna input impedance is tested, close to the first resonant frequency for the patch antenna. The error in the resonant frequency is estimated for different structures at different values of the relative dielectric constant ƒÕr, which ranges from 1 to 10. A larger error is observed in the calculation of the resonant frequency of the patch antenna. Moreover, this error increases with increase in the dielectric constant of the substrate. Further scope for improvement lies in the investigation of this effect.

Design and performance of fully-printed Ku-band aperture coupled patch antennas fabricated by a direct digital manufacturing (DDM) approach that integrates fused deposition modeling (FDM) of acrylonitrile butadiene styrene (ABS) thermoplastic with in-situ micro-dispensing of conductive silver paste (CB028) are reported. Microstrip line characterizations are performed and demonstrate that misalignment of ABS substrate deposition direction with microstrip line micro-dispensing direction can degrade the effective conductivity up to 60% within the Ku-band, and must be taken into consideration in antenna array feed network designs. Specically, over 125 µm thick ABS substrate, RF loss of 0.052 dB/mm is obtained at 18 GHz, demonstrating the feasibility of additively manufactured RF devices within the Ku-band. By varying ABS inll ratios and resorting to multi-layer printing with custom substrate thicknesses, single and stacked patch antennas are designed, fabricated, and characterized with bandwidth performances up to 35%, and radiation efficiencies up to 90%. This extensive utilization of the design flexibilities provided by the direct digital manufacturing (i.e. customized substrate thicknesses, multiple substrates with varying infill ratios, and in-situ micro-dispensing of conductors) distinguishes the present work from the recently reported 3-D printed antennas. Compared to the existing work in literature, the antennas presented within this thesis stand out as being fully printed structures, operating in higher frequency range (i.e. Ku-band), and exhibiting high radiation efficiencies with wide bandwidth performances.