Automated design optimisation and simulation of stitched antennas for textile devices

This thesis describes a novel approach for designing 7-segment and 5-angle pocket and collar planar antennas (for operation at 900 MHz). The motivation for this work originates from the problem of security of children in rural Nigeria where there is risk of abduction. There is a strong potential benefit to be gained from hidden wireless tracking devices (and hence antennas) that can protect their security. An evolutionary method based on a genetic algorithm was used in conjunction with electromagnetic simulation. This method determines the segment length and angle between segments through several generations. The simulation of the antenna was implemented using heuristic crossover with non-uniform mutation. Antennas obtained from the algorithm were fabricated and measured to validate the proposed method.This first part of this research has been limited to linear wire antennas because of the wide range and flexibility of this class of antennas. Linear wire antennas are used for the design of high or low gain, broad or narrow band antennas. Wire antennas are easy and inexpensive to build. All the optimised linear wire antenna samples exhibit similar performances, most of the power is radiated within the GSM900 frequency band. The reflection coefficient (S11) is generally better than -10dB. The method of moment (MoM-NEC2) and FIT (CST Studio Suite 2015) solvers were used for this design. MATLAB is used to as an interface to control computational electromagnetic solvers for antenna designs and analysis. The genetic algorithm procedures were written in MATLAB. The second part of the work focuses on meshed ground planes for applications at 900 MHz global system for mobile communications (GSM), 2.45 GHz industrial, scientific, and medical (ISM) band and 5 GHz wearable wireless local area networks (WLAN) frequencies. Square ground planes were developed and designed using linear equations in MATLAB. The ground plane was stitched using embroidery machines. To examine the effect of meshing on the antenna performance and to normalise the meshed antenna to a reference, solid patch antenna was designed, fabricated on an FR4 substrate. A finite grid of resistors was created for numerical simulation in MATLAB. The resistance from the centre to any node of a finite grid of resistors are evaluated using nodal analysis. The probability that a node connects to each node in the grid was computed. The circuit model has been validated against the experimental model by measurement of the meshed ground plane. A set of measurement were collected from a meshed and compared with the numerical values, they show good agreement.</div

Electromagnetic Band-Gaps Structure In Microwave Device Design

The research in the field of electromagnetic band gap or well known as EBG structure has becoming attractive in antenna community. This structure has a unique property such as the ability to suppress the propagation of surface wave in specific operating frequency defined by the EBG structure itself. The electromagnetic band gap structure always used as a part of antenna structure in order to improve the performance of the antenna especially for improves the gain and radiation pattern. In this project, microstrip antenna is used due to the advantages such as easy and cheap fabrication, light weight, low profile and can easily integrated with microwave circuit. This project involves the investigation of various EBG structure and the integration of the EBG structure with various antenna design through the simulation and fabrication process. The simulation is done by using microwave office software (MWO) and CST. The fabrication process involves the photo etching technique while the substrate used for antenna fabrication is FR4 board which has relative permittivity 4.7 and tangent loss 0.019. From the simulation done, most of the antenna which has been incorporated with EBG structure show the enhancement of the performance in term of radiation pattern, gain and return loss, S11. The 1 dB gain increment is noticed for microstrip array antenna with incorporated with EBG structure. The radiation pattern also improves where the side and back lobes are decreasing by using EBG structure surrounding the patch antenna. Other than that, the EBG structure also can be used as a band reject especially for ultra wide band application which operates at very wide frequency ranges. The simulation and measurement result for ultra wide band with and without band rejection has been shown in this thesis

Heterogeneous mixtures for synthetic antenna substrates

Heterogeneous mixtures have the potential to be used as synthetic substrates for antenna applications giving the antenna designer new degrees of freedom to control the permittivity and/or permeability in three dimensions such as by a smooth variation of the density of the inclusions, the height of the substrate and the manufacture the whole antenna system in one process. Electromagnetic, fabrication, environmental, time and cost advantages are potential especially when combined with nano-fabrication techniques. Readily available and cheap materials such as Polyethylene and Copper can be used in creating these heterogeneous materials. These advantages have been further explained in this thesis. In this thesis, the research presented is on canonical, numerical and measurement analysis on heterogeneous mixtures that can be used as substrates for microwave applications. It is hypothesised that heterogeneous mixtures can be used to design bespoke artificial dielectric substrates for say, patch antennas. The canonical equations from published literature describing the effective permittivity, ε_eff and effective permeability, μ_eff of heterogeneous mixtures have been extensively examined and compared with each other. Several simulations of homogenous and heterogeneous media have been carried out and an extraction/inversion algorithm applied to find their ε_eff and μ_eff. Parametric studies have been presented to show how the different variables of the equations and the simulations affect the accuracy of the results. The extracted results from the inversion process showed very good agreement with the known values of the homogenous media. Numerically and canonically computed values of ε_eff and μ_eff of various heterogeneous media were shown to have good agreement. The fabrication techniques used in creating the samples used in this research were examined, along with the different measurement methods used in characterising their electromagnetic properties via simulations and measurements. The challenges faced with these measurement methods were explained including the possible sources of error. Patch antennas were used to investigate how the performance of an antenna may be affected by heterogeneous media with metallic inclusions. The performance of the patch antenna was not inhibited by the presence of the metallic inclusions in close proximity. The patch measurement was also used as a measurement technique in determining the ε_eff of the samples

Integration of Antennas and Solar Cells for Autonomous Communication Systems

Solar energy is becoming an attractive alternative for powering autonomous communication systems. These devices often involve the use of separate photovoltaics and antennas, which demand a compromise in the utilization of the limited space available. This thesis deals with the design, analysis, fabrication and validation of different techniques for the integration of antennas and solar cells in a single multifunctional device. Four different photovoltaic technologies are considered within this work, namely, polycrystalline silicon (poly-Si), monocrystalline (mono-Si) emitter-wrap-through (EWT) rear contact solar cells, amorphous silicon (a-Si) thin film on glass substrate, and bifacial solar cells. The use of a poly-Si solar cell was investigated as ground plane for a microstrip patch antenna as well as reflector for a half-wave dipole antenna. Looking forward to further minimize the shade of the solar element on the solar cell and to increase the smart appearance, a film that is both transparent and conductive, the AgHT-4, was evaluated as an antenna radiating element for the integration with an a-Si thin film photovoltaic module on glass substrate. A different approach involves the use of EWT solar cells as a folded dipole for integration with solar concentration. The solar cells in this structure are used both for power generation and as radiating element, and a parabolic trough is employed as well with a double function as solar concentrator for the PV cells as well as reflector for the folded dipole antenna. Numerical simulation results obtained with CST Microwave Studio were validated experimentally with the construction of the corresponding prototypes. The performance of these prototypes is thoroughly evaluated in an anechoic chamber. The approaches proposed in this work for integration of antennas and PV technology will help to reduce the marginal cost of renewable energy, improving its economic viability due to the possibility of an integrated production and easier maintenance. It also reduces the need for cable deployment and leads to compact reliable systems with decreased exposure to natural disasters and vandalism

Wideband Metasurface Antenna

This effort explored design of metasurface antennas and evaluated their suitability for ultra-wideband applications (2 to 18 GHz). Six unit cell types were characterized. Eigenmode simulations produced frequency vs. phase data for the unit cells, from which impedance vs. gap size data was computed. A holographic design equation was used to generate the metasurface antenna designs. The unit cell simulations revealed that the assumption of single mode operation is a constraint for wideband designs. An 8 by 8 metasurface antenna with a Rogers 3010 dielectric and a design frequency of 10 GHz was fabricated and tested. It had a 1.5:1 SWR bandwidth of 8.06 GHz (6.47 to 14.53 GHz) and a 2:1 SWR bandwidth of 12.09 GHz (5.91 to 18 GHz). The main beam was 30° wide and had a peak gain of 1.8 dBi. The center of the main beam was ΘL = 0° (+Z direction), which resulted in weaker gain as this is the endfire direction from the driven element. Despite that challenge, this antenna demonstrated that metasurface antennas show promise for ultra-wideband applications when high gain is not a requirement

Design and Prototype of a Phased-Array Antenna for Nanosatellite Radar and Communication Applications

Reconfigurable software defined radios are capable of altering radio frequency parameters of a transceiver to add functionality and improve performance. Initially static by design, reconfigurable radios have become common on nanosatellites, assisting in reduction of launch costs and addition of functionality. Antenna designs have also become reconfigurable, by being able to change frequency range, polarization and many other characteristics. Some antenna designs also perform lobe (beam) steering; however, they are not commercially available for nanosatellites. Some of the added benefits of beam steering are debris detection and satellite-to-satellite communication. Therefore, this research combines antenna frequency reconfigurability and beam steering using an array to design an antenna that can be mounted on a nanosatellite

Design and modelling of photonic band-gap response from doubly periodic arrays

Currently much research is aimed at using light as an information carrier in systems. Photonic crystals are materials with varying dielectric properties designed to interact with photons. If these crystals are arranged in a periodic structure they can control the propagation of electromagnetic waves through the structure. Photonic Bandgap (PBG) crystal is a periodic structure that prohibits propagation of all electromagnetic waves within a particular frequency band. Original PBG research was done in the optical region, but PBG properties are scalable and applicable to a wide range of frequencies. In recent years, there has been increasing interest in microwave and millimetre-wave applications of PBG structures. Currently, research has also extended to Metallo-Dielectric Photonic Crystal (MDPC) which is replacing the photonic crystal with periodic metal elements in low dielectric region. [Continues.

High efficiency planar microwave antennas assembled using millimetre thick micromachine polymer structures

Communication systems at microwave and millimetre wave regimes require compact broadband high gain antenna devices for a variety of applications, ranging from simple telemetry antennas to sophisticated radar systems. High performance can usually be achieved by fabricating the antenna device onto a substrate with low dielectric constant or recently through micromachining techniques. This thesis presents the design, fabrication, assembly and characterisation of microstrip and CPW fed micromachined aperture coupled single and stacked patch antenna devices. It was found that the micromachining approach can be employed to achieve a low dielectric constant region under the patch which results in suppression of surface waves and hence increasing radiation efficiency and bandwidth. A micromachining method that employs photolithography and metal deposition techniques was developed to produce high efficiency antenna devices. The method is compatible with integration of CMOS chips and filters onto a common substrate. Micromachined polymer rims (SU8 photoresist) was used to create millimetre thick air gaps between the patch and the substrate. The effect of the substrate materials and the dimensions of the SU8 polymer rims on the performance of the antenna devices were studied by numerical simulation using Ansoft HFSS electromagnetic field simulation package. The antenna structures were fabricated in layers and assembled by bonding the micromachined polymer spacers together. Low cost materials like SU8, polyimide and liquid crystal polymer films were used for fabrication and assembly of the antenna devices. A perfect patch antenna device is introduced by replacing the substrate of a conventional patch antenna device with air in order to compare with the micromachined antenna devices. The best antenna parameters for a perfect patch antenna device with air as a substrate medium are ~20% for bandwidth and 9.75 dBi for antenna gain with a radiation efficiency of 99.8%. In comparison, the best antenna gain for the simple micromachined patch antenna device was determined to be ~8.6 dBi. The bandwidth was ~20 % for a microstrip fed device with a single patch; it was ~40 % for stacked patch devices. The best bandwidth and gain of 6.58 GHz (50.5%) and 11.2 dBi were obtained for a micromachined sub-array antenna device. The simulation results show that the efficiency of the antenna devices is above 95 %. Finally, a novel high gain planar antenna using a frequency selective surface (FSS) was studied for operation at ~60 GHz frequency. The simulation results show that the novel antenna device has a substantial directivity of around 25 dBi that is required for the emerging WLAN communications at the 60 GHz frequency band