Novel broadband designs of microstrip antennas have been proposed in this dissertation, including bandwidth enhancement using integrated reactive loading, broadband circularly polarized designs, broadband dual-frequency design, bandwidth enhancement using a slotted ground plane and practical applications. First, bandwidth enhancement of microstrip antennas using integrated reactive loading is proposed and experimentally studied. Results show that the proposed antennas can have an operating bandwidth more than 2.0 times that of a conventional one at a given operating frequency. Second, by selecting a thick air substrate, a wideband circularly polarized microstrip antenna with improved CP quality has been implemented. In addition to the improved CP quality obtained, a 2-dB axial-ratio bandwidth as large as about 38% is also achieved. Third, by bending a planar rectangular patch into an inverted L-shaped patch, a dual-frequency planar antenna has been obtained. Experimental results show that the proposed antenna has a tunable frequency ratio of about 1.66-2.29. Fourth, by embedding meandering slots or slits in the antenna¡¦s ground plane, it is observed that the impedance bandwidth of the microstrip antenna is twice larger than the conventional one. The experimental results show that the resonant frequency is significantly lower, which can lead to a large antenna size reduction for a fixed frequency operation. In addition, enhanced antenna gain is also obtained. Finally, a shorted patch antenna suitable for applications in DCS (1710-1880 MHz) base station is presented.

Design of the circularly polarized ceramic antenna, suitable for GPS system, on an asymmetric ground plane is presented in this thesis. Firstly, to obtain two isolated ground planes, we insert an L slit on an asymmetric ground plane, making the antenna with a symmetric ground plane. Then, we isolate the excited surface current between the two ground planes by using a quarter-wavelength mini-coaxial cable. The surface current can distribute uniformly on the ground plane when the proposed antenna is in operation, which makes possible a good circularly polarized radiation pattern in the operation band.

Design considerations and experimental results of a dual-band circularly polarized stacked microstrip antenna for GPS operations at 1227 and 1575 MHz are presented. The antenna is achieved by stacking two corner-truncated square microstrip patches. The obtained circular polarization (CP) bandwidths, determined from 3-dB axial ratio, are about 15 MHz (about 1.2%) and 17 MHz (about 1.1%) at 1227 and 1575 MHz, respectively. Good CP radiation patterns and antenna gain have also been observed.

Novel printed slot antennas are demonstrated in this thesis. For the linear polarization design, CPW-fed strip-loaded square slot antenna is presented for achieving broadband operations. For the circular polarization, two novel antenna designs are also presented¡Fone is a CPW-fed square slot antenna with an inverted L tunning stub, and the other is a microstrip line-fed square slot antenna with a conducting strip from ground plane for broadband circularly polarized radiation. Finally, an antenna design having compact size and broadband characteristic is shown.

In nature, both fundamental and sophisticated ecological functionality alike are driven by the display or, conversely, the concealment of colour and visual contrast. Through scientific investigation, the evolutionary genius manifested in numerous light manipulating biological systems has provided many blueprints for innovative photonic devices and other smart materials. The development of innovative bioinspired materials that harness the optical properties exhibited by chiral structures, such as those found in certain Scarabaeidae, offer widespread potential. In this thesis, the species-specific circularly polarised optical behaviour corresponding to a variety of Scarabaeidae beetles is investigated. The helicoidal morphology giving rise to circularly polarised photonic properties is first described for several beetles displaying a narrowband colour appearance. A structural analysis of the native surface structures encountered in these species is presented alongside a discussion of their role in defining the species' optical characteristics. Experimental measurements of the circularly polarised scattering behaviour are presented and discussed with respect to the electron microscopy and surface morphology measurements comprising the structural analysis. Following this, the origins of the subtle differences in the metallic colour appearance of several broadband coleopteran structures are deciphered. The broadband response of these species is attributed to chirped configurations of the helicoidal lamellar structure, elucidated using electron microscopy. Results of this structural analysis are applied to theoretical simulations of the structures' electromagnetic response and consolidate experimental measurements of the circularly polarised reflectance. Rigorous experimental measurement demonstrated that the circularly polarised spectral response is relatively robust to small structural defects or `biological noise'. Building from this, the intraspecific colour variation displayed in the species Chrysina aurigans is a useful lens through which the nuances of the chirped multilayer structure are further examined. As a result, this work provides detailed insights into the fine-tuning of chirped biological photonic systems. Likewise, the topic of biological wave retarders is afforded significant attention, primarily with reference to the biological half-wave plate encountered in the cuticle structure of Chrysina resplendens. A rigorous analysis of the photonic system in C. resplendens is presented, leading to novel conclusions describing this system's opto-structural relationship. Additionally, this thesis reports, for the first time, the presence of a biological wave retarder in the cuticle structure of Chrysina cupreomarginata.

No description available.

The novel designs of circular microstrip antennas have been investigated in this dissertation. In the linearly polarized designs, the study of single-feed dual-frequency circular microstrip antenna with an open-ring slot has been firstly presented. As for the broadband circular microstrip antenna designs, antennas with two open-ring slots, embedded reactive loading by probe feed and microstrip-line feed have been presented. The antenna bandwidth of them can be enhanced about 4% to 6%. In the circularly polarized designs, we have proposed a circularly polarized microstrip antenna with a spur line. By choosing a suitable length of the spur line, CP operation can be obtained. And then, such a design can be applied to a compact circular patch antenna with bent slots. These reduced the antenna size to be 40%~50% of that of the simple case. Finally, we use the ideas of CP operation with elliptic patch and dual-frequency operation with stacked patch to propose a dual-band circularly polarized stacked elliptic microstrip antenna design. The frequency ratio of this design is about 1.39.

Due to high demand for planar structures with low loss, a considerable amount of research has been done to the design of substrate integrated waveguide (SIW) components in the mm-wave and microwave range. SIW has many advantages in comparison to conventional waveguides and microstrip lines, such as compact and planar structure, ease of fabrication, low radiation loss, high power handling ability and low cost which makes it a very promising technology for current and future systems operating in K-band and above. Therefore, all the work presented in this dissertation focuses on SIW technology. Five di erent antenna systems are proposed to verify the advantages of using SIW technology. First, a novel K-band end- re SIW circularly polarized (CP) antenna system on a single layer printed-circuit board is proposed. A high gain SIW H-plane horn and a Vivaldi antenna are developed to produce two orthogonal polarizations in the plane of the substrate. CP antennas have become very popular because of their unique characteristics and their applications in satellites, radars and wireless communications. Second, a K-band front-end system for tracking applications is presented. The circuit comprises an antenna array of two Vivaldi antennas, a frequency-selective power combiner, and two frequency-selective SIW crossovers, which eliminate the need for subsequent ltering. The integration of monopulse systems in planar, printed circuit SIW technology combined with the added bene ts of ltering functions is of great importance to the antennas and propagation community. Third, a phased array antenna system consisting of 24 radiating element is designed as feed system for reflector antennas in radio astronomy applications. A Ku-band antipodal dipole antenna with wide bandwidth, low cross-polarization and wide beamwidth is suggested as the radiating element. Forth, four di erent right-angled power dividers including in-phase and out-of-phase dividers as feed systems for antenna arrays are introduced. TE10 - to - TEq0 mode transducers are used for obtaining two, three, and four output dividers with phase control ability at K- and Ka-band. This feature is practical, for instance, when designing tracking systems since they are employed to obtain controllable phase distributions over the output ports. Fifth, a Ku-band beam steering antenna system which is applicable to use for wireless communications, radar systems, and also 5G applications is proposed. This antenna system uses variable reflection-type phase shifters which electrically steer the beam over a 50-degree scan range. Therefore, the SIW technology's reliability and also promising behavior in the microwave frequency range is proven for di erent applications. / Graduate

No description available.

<p> </p><p> </p><p> </p><p><p>The main</p><p>objective of this thesis is to study the polarization effects of the beetle <em>Cetonia aurata </em>using Mueller-matrix ellipsometry. The outer shell of the beetle consists of complex microstructures which control the polarization of the reflected light. It has metallic appearance which originates from helicoidal structures. When these microstructures are exposed to polarized or unpolarized light, only left-handed circularly polarized light is reflected. Moreover, the exo-skeleton of the beetle absorbs right-handed polarized light. Multichannel Mueller-matrix ellipsometer or dual rotating compensator ellipsometer, called RC2, from J.A.Woollam is used to measure the polarization caused by different parts of beetle’s body. The 16 Mueller matrix elements are measured in the spectral range 400-800 nm at multiple angles of incidencein the range 40⁰-70⁰. An Optical model is developed to help us understand the nature and type of microstructure which only reflects the green colour circularly polarized light. With the help of multiparametric modeling, we were able to find optical properties and structural parameters. The parameters are: the number of layers, the numbers of sub-layers, their thicknesses, and the orientation with respect to optical axes. This optical model describes the nanostructures which provide the reflection properties similar to the nanostructure found in the beetle <em>Cetonia aurata. </em>The model is also useful for analysis of the optical response data of different materials with multilayer structures.</p></p><p> </p>