Beam-Steerable and Reconfigurable Reflectarray Antennas for High Gain Space Applications

Reflectarray antennas uniquely combine the advantages of parabolic reflectors and phased array antennas. Comprised of planar structures similar to phased arrays and utilizing quasi-optical excitation similar to parabolic reflectors, reflectarray antennas provide beam steering without the need of complex and lossy feed networks. Chapter 1 discusses the basic theory of reflectarray and its design. A brief summary of previous work and current research status is also presented. The inherent advantages and drawbacks of the reflectarray are discussed. In chapter 2, a novel theoretical approach to extract the reflection coefficient of reflectarray unit cells is developed. The approach is applied to single-resonance unit cell elements under normal and waveguide incidences. The developed theory is also utilized to understand the difference between the TEM and TE10 mode of excitation. Using this theory, effects of different physical parameters on reflection properties of unit cells are studied without the need of full-wave simulations. Detailed analysis is performed for Ka-band reflectarray unit cells and verified by full-wave simulations. In addition, an approach to extract the Q factors using full-wave simulations is also presented. Lastly, a detailed study on the effects of inter-element spacing is discussed. Q factor theory discussed in chapter 2 is extended to account for the varying incidence angles and polarizations in chapter 3 utilizing Floquet modes. Emphasis is laid on elements located on planes where extremities in performance tend to occur. The antenna element properties are assessed in terms of maximum reflection loss and slope of the reflection phase. A thorough analysis is performed at Ka band and the results obtained are verified using full-wave simulations. Reflection coefficients over a 749-element reflectarray aperture for a broadside radiation pattern are presented for a couple of cases and the effects of coupling conditions in conjunction with incidence angles are demonstrated. The presented theory provides explicit physical intuition and guidelines for efficient and accurate reflectarray design. In chapter 4, tunable reflectarray elements capacitively loaded with Barium Strontium Titanate (BST) thin film are shown. The effects of substrate thickness, operating frequency and deposition pressure are shown utilizing coupling conditions and the performance is optimized. To ensure minimum affects from biasing, optimized biasing schemes are discussed. The proposed unit cells are fabricated and measured, demonstrating the reconfigurability by varying the applied E-field. To demonstrate the concept, a 45 element array is also designed and fabricated. Using anechoic chamber measurements, far-field patterns are obtained and a beam scan up to 25o is shown on the E-plane. Overall, novel theoretical approaches to analyze the reflection properties of the reflectarray elements using Q factors are developed. The proposed theoretical models provide valuable physical insight utilizing coupling conditions and aid in efficient reflectarray design. In addition, for the first time a continuously tunable reflectarray operating at Ka-band is presented using BST technology. Due to monolithic integration, the technique can be extended to higher frequencies such as V-band and above

Computational fluid dynamic (CFD) analysis of parachute canopies design for aludra SR-10 UAV as a parachute recovery systems (PRS)

Unmanned Systems Technology (UST) Aludra SR-10 Unmanned Aerial Vehicle (UAV) was purposely designed for survey and mapping mission. In the early design stage of Aludra SR-10 UAV, skid and belly landing method was used as a recovery method. This type of landing method may encounter a harsh landing on hard soil and gravel, producing high impact momentum on the aircraft body and may cause structural or system damage. To increase the safety of Aludra SR-10 UAV operation, Parachute Recovery System (PRS) are purposely design to replace the belly landing technique for landing method. This study was performed by simulation approach (using Computational Fluid Dynamic, CFD) to analyse an aerodynamic performance for selecting the best canopy design that can produce higher drag during recovery process. This computational study focuses on an aerodynamic flow simulation over threedimensional surface on two different canopy designs (i.e. annular canopy and cruciform canopy), and also focuses on drag coefficient in a steady and turbulent condition. Two‐equation k-ε turbulence flow was modelled by adopting Navier-Stokes numerical equations to simulate aerodynamic characteristics and drag. The computational results with an efficient grid study shows an annular parachute canopy produced highest drag coefficient (1.03) than cruciform parachute canopy (0.91). The findings also highlighted the significance of separation and recirculating flows behind studied geometries, which in turn was responsible in producing the drag. This computational simulation analysis successfully provided a baseline annular parachute design was about 2.41 meter of the nominal diameter was selected as the main parachute which can be applied for this research

Reconfigurable Reflectarray Antennas with Bandwidth Enhancement for High Gain, Beam-Steering Applications

Reconfigurable reflectarrays are a class of antennas that combine the advantages of traditional parabolic antennas and phased array antennas. Chapter 1 discusses the basic operational theory of reflectarrays and their design. A review of previous research and the current status is also presented. Furthermore the inherent advantages and disadvantages of the reflectarray topography are presented. In chapter 2, a BST-integrated reflectarray operating at Ka band is presented. Due to the monolithic integration of the tuning element, this design is then extended to V band where a novel interdigital gap configuration is utilized. Finally to overcome loss and phase limitations of the single resonant design, a BST-integrated, dual-resonance unit cell operating at Ka band is designed. While the losses are still high, a 360° phase range is demonstrated. In chapter 3, the operational theory of dual-resonant array elements is introduced utilizing Q theory. An equivalent circuit is developed and used to demonstrate design tradeoffs. Using this theory the design procedure of a varactor tuned dual-resonant unit cell operating at X-band is presented. Detailed analysis of the design is performed by full-wave simulations and verified via measurements. In chapter 4, the array performance of the dual-resonance unit cell is analyzed. The effects of varying angles of incidence on the array element are studied using Floquet simulations. The beam scanning, cross-polarization and bandwidth performance of a 7 x 7 element reflectarray is analyzed using full-wave simulations and verified via measurements. In chapter 5 a loss analysis of the dual-resonant reflectarray element is performed. Major sources of loss are identified utilizing full-wave simulations before an equivalent circuit is utilized to optimize the loss performance while maintaining a full phase range and improved bandwidth performance. Finally the dual-resonance unit cell is modified to support two linear polarizations. Overall, the operational and design theory of dual resonant reflectarray unit cells using Q theory is developed. A valuable equivalent circuit is developed and used to aid in array element design as well as optimize the loss and bandwidth performance. The proposed theoretical models provide valuable physical insight through the use of Q theory to greatly aid in reflectarray design

A review of wideband reflectarray antennas for 5G communication systems

The advancement in the current communication technology makes it incumbent to analyze the conventional features of reflectarray antenna for future adaptability. This work thoroughly reviews the design and experimental features of reflectarray antenna for its bandwidth improvement in microwave and millimeter wave frequency ranges. The paper surveys the fundamental and advanced topologies of reflectarray design implementations which are needed particularly for its broadband features. The realization of its design approaches has been studied at unit cell and full reflectarray levels for its bandwidth enhancement. Various design configurations have also been critically analyzed for the compatibility with the high frequency 5G systems

Simulation of fractal like branching microchannel network on rectangular heat sink for single phase flow

Performance of microelectronic devices has been greatly enhanced owing to the development of the very large-skill technology. However, with the increase of circuit density and operating speed, more heat was generated by the microelectronics devices. So, the objective of this project is to do a comparative study between two different types of fractal microchannel at the same size and boundary condition by using Computational Fluid Dynamics (CFD) Besides that, this study also will investigate the hydrodynamic and thermal characteristics of T-shaped and Treeshaped fractal microchannel network heat sinks by solving three-dimensional Navier– Stokes equations and energy equation, taking into consideration the conjugate heat transfers in microchannel walls. For the simulation, ANSYS software was used with the inlet temperature set to be 300 K, inlet velocity will be in the range of 0.1 m/s to 0.5 m/s and uniform heat flux be set at 325 W/cm2. From this study, it was found that due to the structural limitation of right-angled fractal-shaped microchannel network, hotspots may appear on the bottom wall of the heat sink where the microchannel are sparsely distributed. With slight modifications in both fractal-shaped structure of microchannel network, great improvements on the hydrodynamic and thermal performance of heat sink can be achieved. A comparison of the performance of modified fractal-shaped microchannel network heat sink with parallel microchannel heat sink is also conducted numerically based on the same heat sink dimensions. It is found that the modified fractal-shaped microchannel network is much better in terms of thermal resistance and temperature uniformity under the conditions of the same pressure drop or pumping power. Therefore, the modified fractal-shaped microchannel network heat sink appears promising to be used for microelectronic cooling in the future

Phase Shaping In The Infrared By Planar Quasi-periodic Surfaces Comprised Of Sub-wavelength Elements

Reflectarrays are passive quasi-periodic sub-wavelength antenna arrays designed for discrete reflected phase manipulation at each individual antenna element making up the array. By spatially varying the phase response of the antenna array, reflectarrays allow a planar surface to impress a non-planar phasefront upon re-radiation. Such devices have become commonplace at radio frequencies. In this dissertation, they are demonstrated in the infrared for the first time--at frequencies as high as 194 THz. Relevant aspects of computational electromagnetic modeling are explored, to yield design procedures optimized for these high frequencies. Modeling is also utilized to demonstrate the phase response of a generalized metallic patch resonator in terms of its dependence on element dimensions, surrounding materials, angle of incidence, and frequency. The impact of realistic dispersion of the real and imaginary parts of the metallic permittivity on the magnitude and bandwidth of the resonance behavior is thoroughly investigated. Several single-phase reflectarrays are fabricated and measurement techniques are developed for evaluating these surfaces. In all of these cases, there is excellent agreement between the computational model results and the measured device characteristics. With accurate modeling and measurement, it is possible to proceed to explore some specific device architectures appropriate for focusing reflectarrays, including binary-phase and phase-incremental approaches. Image quality aspects of these focusing reflectarrays are considered from geometrical and chromatic-aberration perspectives. The dissertation concludes by briefly considering two additional analogous devices--the transmitarray for tailoring transmissive phase response, and the emitarray for angular control of thermally emitted radiation

Aspects Of Efficiency Enhancement In Reflectarrays With Analytical Investigation And Accurate Measurement

This paper presents a thorough review of the techniques involved in the enhancement of the efficiency performance of the reflectarray antenna. The effect of the selection of a suitable patch element or a proper feeding mechanism on efficiency improvement is studied in detail. Reflectarray loss quantification is examined in relation to the design techniques involved in the efficiency improvement. A low loss patch element with a wide reflection phase range and a properly illuminated reflectarray aperture are supposed to offer high efficiency performance. Additionally, the placement, the orientation and the position of a patch element on the reflectarray surface can also affect its efficiency performance. Mathematical equations were developed to estimate the efficiencies of circular and square aperture reflectarray antennas by considering their feed footprints. Moreover, a step by step practical method of predicting and measuring the total efficiency of a reflectarray antenna is presented. The two selected apertures of the reflectarray consisting of the square patch element configuration are fabricated and measured at a frequency of 26 GHz. Their measured efficiencies have been estimated using the derived equations, and the results were compared and validated using the efficiencies obtained by the conventional gain-directivity relation

Butterflies (Lepidoptera Papilionoidea) diversity at Endau-Rompin Johor national park, Malaysia and prioritising the potential groups for nature tourism product

From a total of 17,461 species of butterfly described worldwide, at least twothird are from the tropics. Peninsular Malaysia is home to 1038 butterfly species. Endau-Rompin Johor National Park (ERJNP) in particular recorded 349 species as analysed from collections of 1987 to 2015. It represents 34% of butterfly fauna in Peninsular Malaysia. This paper aims (i) to document the diversity of butterfly in ERJNP and (ii) identify potential groups of butterfly that satisfy six criteria for good nature tourism product. The criteria are reliability of sighting, safe, with unique morphology and behaviour, rare or endemic and with cultural linkage. The samplings were done manually using aerial net and trapping using fruit baits along two 1 km transects in the eastern part of ERJNP (Nature Education and Research Centre and Kuala Jasin) from February 2014 to July 2015. This study successfully recorded 131 species comprising of 491 individuals from five families. Nymphalidae was the most dominant family, making up 51% of butterfly abundance and richness. Five dominant species were recorded with 31 to 43 individuals per species. The values of Shannon diversity index (H’) and species evenness index (E’) were 4.123 and 0.471 respectively. Significantly, eight species collected were protected under the Wildlife Conservation Act, 2010 and 14 were considered rare and uncommon. Butterflies are frequently encountered, morphologically and behaviourally unique. These attributes fascinate visitors of the park, thus butterfly has a potential to be promoted as new attraction for nature tourism in ERJNP

Additively Manufactured Shape-changing RF Devices Enabled by Origami-inspired Structures

The work to be presented in this dissertation explores the possibility of implementing origami-inspired shape-changing structures into RF designs to enable continuous performance tunability as well as deployability. The research not only experimented novel structures that have unique mechanical behaviour, but also developed automated additive manufacturing (AM) fabrication process that pushes the boundary of realizable frequency from Sub-6 GHz to mm-wave. High-performance origami-inspired reconfigurable frequency selective surfaces (FSSs) and reflectarray antennas are realized for the first time at mm-wave frequencies via AM techniques. The research also investigated the idea of combining mechanical tuning and active tuning methods in a hybrid manner to realize the first truly conformal beam-forming phased array antenna that can be applied onto any arbitrary surface and can be re-calibrated with a 3D depth camera.Ph.D

A Reflectarray Antenna Using Hexagonal Lattice With Enhanced Beam Steering Capability

This paper presents a novel reflectarray antenna with enhanced beam steering capability. The reflectarray antenna is based on the hexagonal distribution of the unit cells on the antenna surface. The hexagonal topology changes the angle between the principal axes of the unit cell distribution, preventing the formation of the grating lobe, and improving the beam steering capability of the reflectarray antenna. To verify the proposed idea, two different sets of reflectarray antennas, which includes square and hexagonal lattice topologies with inter-element spacings of 0.52 lambda and 0.6 lambda, have been designed, fabricated, and measured at 8.23 GHz. The measurements of the all fabricated reflectarray antennas are in very good agreement with the simulations, and the comparison of the square and hexagonal topologies show that the beam steering capability can be improved by 50% for 0.6 lambda inter-element spacing by using a hexagonal topology. This improvement shows that a simple modification in the array configuration can be a viable solution for satellite and 5G communication applications that require increased beam steering capability