Gain and Bandwidth Enhancement of 3D-Printed Short Backfire Antennas Using Rim Flaring and Iris Matching.

In this article, we present new design techniques to improve the gain and impedance bandwidth of short backfire antennas. For the gain enhancement procedure, our approach was to flare the rim of the antenna, which simultaneously led to an increase in the impedance bandwidth of the antenna. Parametric studies were carried out to obtain the optimal flaring angle. The peak realized gain was obtained as 17.2 dBi with an impedance bandwidth of 55% (2.4 dB and 28.6% increase in gain and bandwidth, respectively, compared to the unflared antenna). To further enhance the impedance bandwidth, an inductive iris was added to improve impedance matching at the waveguide aperture. We varied the width of the iris to obtain the optimal width that provided the best gain and impedance bandwidth result of 17.1 dBi and 66% (~40% increase compared to the unflared antenna without iris). To experimentally verify the work, prototypes were fabricated and tested. We found good agreement between simulation and measurement. The results of this study indicate that gain and bandwidth can be enhanced through optimized geometrical modification of the SBF structure. Furthermore, our 3D-printed technique demonstrates a mass reduction compared with conventional metallic structures.

Mass Reduction Techniques for Short Backfire Antennas: Additive Manufacturing and Structural Perforations.

This paper presents novel approaches for reducing the mass of the classical short backfire (SBF) antenna by using additive manufacturing and structural perforations. We first investigated techniques to create a 3D-printed structure with a conductive coating material. This approach resulted in a significant mass reduction (70%) compared with the conventional metallic structure. We performed parametric simulation studies to investigate the effects of the manufacturing process and showed that there was practically no difference in the performance. The largest source of error was the surface roughness and the conductivity of the metal paint. In a second design, we created perforations in the structure to further reduce the mass. We performed parametric studies to optimize mass reduction and to characterize the effects of the perforations and the surface roughness introduced during the 3D-printing process on the antenna. Antenna prototypes were fabricated and tested. The masses of the perforated 3D printed antenna were approximately 30% and 20% of the original aluminum design, respectively (70% and 80% reductions in mass, respectively). The good agreement among the original design, simulation, and measurements demonstrated the effectiveness of the approach.

Gain Enhancement and Cross-Polarization Suppression of Cavity-Backed Antennas Using a Flared Ground Cavity and Iris.

Herein, we present new design principles for gain enhancement and cross-polarization suppression in dual-polarized cavity-backed antennas and demonstrate the capability in an octagonal cavity-backed open prism antenna (OCROP). In our approach, the gain is enhanced through an optimal flaring procedure and a novel metallic iris is used to control the electromagnetic fields and thereby reduce the cross-polarization. Previously, we investigated a dual-polarized OCROP antenna configuration and were able to simultaneously achieve 50% impedance bandwidth, 40% cross-polarization bandwidth (≤25 dB), and 10.2 dBi peak gain. In this study, we investigated gain enhancement by flaring an upper section of the ground cavity sidewalls, while maintaining a constant cavity height. Two cases were investigated: (1) the flare angle was modified, while the ratio of the non-flared to flared sidewall heights was kept constant, and (2) the ratio of the non-flared to flared sidewall heights was varied. In case 1, we established that, while increasing the flare angle results in a gain increase, there is a limit, as cross-polarization at the upper operating frequencies increases. In case 2, we were able to reduce the aperture phase error and achieve a higher peak gain of 12.8 dBi. To address the increased cross-polarization at the high frequency end when a large flare was used, we added a metallic iris at the junction of non-flared and flared sidewalls. We showed that increasing the iris width generally decreases the cross-polarization at high frequencies, without compromising the gain and impedance bandwidth. At an optimal width, it provides a nearly constant, low cross-polarization (below -25.8 dB) and a peak gain of 13.3 dBi, across the entire 50.7% impedance bandwidth of the antenna. We fabricated and successfully tested a prototype to verify the design and simulation approach. These results prove that incorporating an aperture flare with a metallic iris can significantly improve the gain and cross-polarization performance of cavity-backed antennas.

Wideband Dual-Polarized Octagonal Cavity-Backed Antenna with Low Cross-Polarization and High Aperture Efficiency.

Simultaneously enhancing multiple antenna performance parameters is a demanding task, especially with a challenging set of design goals. In this paper, by carefully deriving a compatible set of enhancement techniques, we propose a compact/lightweight/low-cost high-performance L-band octagonal cavity-backed hybrid antenna with multiple attractive features: dual-polarization, wide impedance bandwidth, low cross-polarization, high gain, and high aperture efficiency. The ground cavity is octagonal, which allows the antenna to have a small footprint, and, more importantly, low cross-polarization and high aperture efficiencies when compared to a commonly-used square design. The hybrid design relies on the resonance merging of two radiating elements, i.e., radiating feedlines and a conductive open prism, to form a wide impedance bandwidth. To permit polarization diversity and low cross-polarization, it is differentially and orthogonally fed. Herein, a series of parametric simulation studies on antenna configurations provide information on how to improve the impedance bandwidth and cross-polarization performance. To verify the simulation studies, an antenna prototype was fabricated and tested. Excellent agreement between the simulated and measured results was reached.

Split Ring Antennas and Their Application for Antenna Miniaturization.

This paper investigates the miniaturization capability of split ring array antennas embedded in a low-permittivity dielectric substrate, in comparison with the same-sized high-permittivity dielectric resonator antennas (DRAs). In order to understand the miniaturization performance, a size-fixed dielectric substrate with different split ring arrays is studied. The simulation results show that the miniaturization capability increases with decreased unit cell resonant frequency and/or increased unit cell induced permeability. Miniaturizations as high as 25.54 times that of a high-permittivity DRA are obtained with split rings, etched on a dielectric substrate having a low permittivity of 2.2. Furthermore, this excessive miniaturization does not come at the expense of excessive deterioration of the antenna impedance bandwidth, gain, and radiation efficiency. Consequently, the miniaturized split ring arrays still provide high gains over wider bandwidths. This inference is further verified by comparing the miniaturization and other antenna performance parameters with three other modified split ring configurations. To experimentally verify this work, a split ring antenna was fabricated and tested, and good agreement between the simulated and measured results was observed. The results of this study indicate that adding resonant metallic inclusions into low- permittivity DRAs significantly increases their miniaturization capability, without overly deteriorating the performance.

Methods for Interpreting the Partitioning and Fate of Petroleum Hydrocarbons in a Sea Ice Environment.

Decreases in Arctic Sea ice extent and thickness have led to more open ice conditions, encouraging both shipping traffic and oil exploration within the northern Arctic. As a result, the increased potential for accidental releases of crude oil or fuel into the Arctic environment threatens the pristine marine environment, its ecosystem, and local inhabitants. Thus, there is a need to develop a better understanding of oil behavior in a sea ice environment on a microscopic level. Computational quantum chemistry was used to simulate the effects of evaporation, dissolution, and partitioning within sea ice. Vapor pressures, solubilities, octanol-water partition coefficients, and molecular volumes were calculated using quantum chemistry and thermodynamics for pure liquid solutes (oil constituents) of interest. These calculations incorporated experimentally measured temperatures and salinities taken throughout an oil-in-ice mesocosm experiment conducted at the University of Manitoba in 2017. Their potential for interpreting the relative movements of oil constituents was assessed. Our results suggest that the relative movement of oil constituents is influenced by differences in physical properties. Lighter molecules showed a greater tendency to be controlled by brine advection processes due to their greater solubility. Molecules which are more hydrophobic were found to concentrate in areas of lower salt concentration.

Dual-band millimetre wave MIMO antenna with reduced mutual coupling based on optimized parasitic structure and ground modification.

In this study, a high-isolation dual-band (28/38 GHz) multiple-input-multiple-output (MIMO) antenna for 5G millimeter-wave indoor applications is presented. The antenna consists of two interconnected patches. The primary patch is connected to the inset feed, while the secondary patch is arc-shaped and positioned over the main patch, opposite to the feed. Both patches function in the lower 28 GHz band, while the primary patch is accountable for inducing the upper 38 GHz band. An expedited trust-region (TR) algorithm is employed to optimize the dimensions of the antenna components, ensuring the antenna operates efficiently with high reflection at both bands. The antenna demonstrates a gain exceeding 7 dBi at both frequencies. An array of four antennas is configured orthogonally to create a MIMO system with isolation surpassing 19 dB. The isolation is further enhanced through the addition of a circular parasitic patch at the front and modifications made to the ground. The TR method is employed again to optimize their parameters and achieve the desired isolation, exceeding 32 dB at both bands. The MIMO system demonstrates outstanding diversity performance at both frequencies, characterized by low values of the envelope correlation coefficient (ECC) (< 10 - 4), channel capacity loss (CCL) (< 0.03 bit/s/Hz), and total active reflection coefficient (TARC) (< - 10 dB). Additionally, it secures a diversity gain (DG) exceeding 9.99 dB. The MIMO system is manufactured and tested, showing good alignment between simulation and measurement data for all performance metrics.

wideband high-gain low-profile series-fed antenna integrated with optimized metamaterials for 5G millimeter wave applications.

This paper presents a series-fed four-dipole antenna with a broad bandwidth, high gain, and compact size for 5G millimeter wave (mm-wave) applications. The single dipole antenna provides a maximum gain of 6.2 dBi within its operational bandwidth, which ranges from 25.2 to 32.8 GHz. The proposed approach to enhance both gain and bandwidth involves a series-fed antenna design. It comprises four dipoles with varying lengths, and a truncated ground plane. These dipoles are connected in series on both sides, running in parallel through a microstrip line. The proposed design significantly enhances the bandwidth, which extends from 26.5 to 40 GHz. This frequency range effectively covers the 5G bands of 28 and 38 GHz. The expedited trust-region (TR) gradient-based search algorithm is utilized to optimize the dimensions of the antenna components, resulting in a maximum gain of 11.2 dBi at 38 GHz. To further enhance the gain, modified H-shaped metamaterial (MTM)-based unit cells are integrated into the antenna substrate. The TR algorithm is employed once more to optimize the MTM dimensions, yielding a maximum gain of 15.1 dBi at 38 GHz. The developed system is experimentally validated, showing excellent agreement between the simulated and measured data.

Photooxidation and biodegradation potential of a light crude oil in first-year sea ice.

Disappearing sea ice in the Arctic region results in a pressing need to develop oil spill mitigation techniques suitable for ice-covered waters. The uncertainty around the nature of an oil spill in the Arctic arises from the ice-covered waters and sub-zero temperatures, and how they may influence natural attenuation efficiency. The Sea-ice Environmental Research Facility was used to create a simulated Arctic marine setting. This paper focuses on the potential for biodegradation of the bulk crude oil content (encapsulated in the upper regions of the ice), to provide insight regarding the possible fate of crude oil in an Arctic marine setting. Cheaper and faster methods of chemical composition analysis were applied to the samples to assess for weathering and transformation effects. Results suggest that brine volume in ice may not be sufficient at low temperatures to encompass biodegradation and that seawater is more suitable for biodegradation.

Investigation into the geometry and distribution of oil inclusions in sea ice using non-destructive X-ray microtomography and its implications for remote sensing and mitigation potential.

As climate change brings reduced sea ice cover and longer ice-free summers to the Arctic, northern Canada is experiencing an increase in shipping and industrial activity in this sensitive region. Disappearing sea ice, therefore, makes the Arctic region susceptible to accidental releases of different types of oil and fuel pollution resulting in a pressing need for the development of appropriate scientific knowledge necessary to inform regulatory policy formulation. In this study, we examine the microstructure of the surficial layers of sea ice exposed to oil using X-ray microtomography. Through analysis, 3D imaging of the spatial distribution of the ice's components (brine, air, and oil) were made. Additional quantitative information regarding the size, proximity, orientation, and geometry of oil inclusions were computed to ascertain discernable relationships between oil and the other components of the ice. Our results indicate implications for airborne remote sensing and bioremediation of the upper sea ice layers.

Effect of dissolution, evaporation, and photooxidation on crude oil chemical composition, dielectric properties and its radar signature in the Arctic environment.

Accidental release of petroleum in the Arctic is of growing concern owing to increases in ship traffic and possible future oil exploration. A crude oil-in-sea ice mesocosm experiment was conducted to identify oil-partitioning trends in sea ice and determine the effect of weathering on crude oil permittivity. The dissolution of the lighter fractions increased with decreasing bulk oil-concentration because of greater oil-brine interface area. Movement of the oil towards the ice surface predominated over dissolution process when oil concentrations exceeded 1 mg/mL. Evaporation decreased oil permittivity due to losses of low molecular weight alkanes and increased asphaltene-resin interactions. Photooxidation increased the permittivity of the crude oil due to the transformation of branched aromatics to esters and ketones. Overall, the weathering processes influenced crude oil permittivity by up to 15%, which may produce sufficient quantifiable differences in the measured normalized radar cross-section of the ice.

Oil behavior in sea ice: Changes in chemical composition and resultant effect on sea ice dielectrics.

There has been increasing urgency to develop methods for detecting oil in sea ice owing to the effects of climate change in the Arctic. A multidisciplinary study of crude oil behavior in a sea ice environment was conducted at the University of Manitoba during the winter of 2016. In the experiment, medium-light crude oil was injected underneath young sea ice in a mesocosm. The physical and thermodynamic properties of the oil-infiltrated sea ice were monitored over a three-week time span, with concomitant analysis of the oil composition using analytical instrumentation. A resonant perturbation technique was used to measure the oil dielectric properties, and the contaminated sea ice dielectric properties were modeled using a mixture model approach. Results showed that the interactions between the oil and sea ice altered their physical and thermodynamic properties. These changes led to an overall decrease in sea ice dielectrics, potentially detectable by remote sensing systems.

Examining the physical processes of corn oil (medium crude oil surrogate) in sea ice and its resultant effect on complex permittivity and normalized radar cross-section.

Due to the effects of heightened warming in the Arctic, there has been an urgency to develop methods for detecting oil in (or under) sea ice, owing to increasing potential for oil exploration and ship traffic in the more accessible Arctic regions. To test the potential for radar utilizing the normalized radar cross section (NRCS) of the sea ice, an oil-in-ice mesocosm experiment was performed. Throughout the experiment, corn oil was used as a surrogate for medium crude oil, to assess oil movement tendencies in sea ice, and the resultant impact on the complex permittivity through measurement and modelling techniques. We performed a modelling study to establish the effects of corn oil on the NRCS of sea ice. The oil presence in the sea ice increased the temperature and reduced the salinity of the sea ice, thereby lowering its complex permittivity and modeled NRCS when compared to control sea ice.