Design and Implementation of Broad Band and Narrow Band Antennas and Their Applications

The thesis deals with the design and implementation of broadband and narrowband antennas and their applications in practical environment. In this thesis, a new concept for designing the UWB antenna is proposed based on the CRLH metamaterials and this UWB antenna covers a frequency range from 2.45 GHz to 11.6 GHz. Based on the design of the UWB antenna, another antenna is developed that can cover a very wide bandwidth i.e from 0.66 GHz to 120 GHz. This antenna can not only be used for UWB applications but also for other communication systems working below the UWB spectrum such as GSM, GPS, PCS and Bluetooth. The proposed antenna covering the bandwidth from 0.66 GHz to 120 GHz is by far the largest bandwidth antenna developed based on metamaterials. Wide band antennas are not preferred for sensing purpose as it is difficult to differentiate the received signals. A multiband antenna which can be used as a strain sensor for structural health monitoring is proposed. The idea is to correlate the strain applied along the length or width with the multiple resonant frequencies. This gives the advantage of detecting the strain applied along any direction (either length or width), thus increasing the sensing accuracy. Design and application of a narrow-band antenna as a temperature sensor is also presented. This sensor can be used to detect very high temperature changes (>10000C). This sensor does not require a battery, can be probed wirelessly, simple and can be easily fabricated, can withstand harsh environmental conditions

Microwave Metamaterial Applications using Complementary Split Ring Resonators and High Gain Rectifying Reflectarray for Wireless Power Transmission

In the past decade, artificial materials have attracted considerable attention as potential solutions to meet the demands of modern microwave technology for simultaneously achieving component minimization and higher performance in mobile communications, medical, and optoelectronics applications. To realize this potential, more research on metamaterials is needed. In this dissertation, new bandpass filter and diplexer as microwave metamaterial applications have been developed. Unlike the conventional complementary split ring (CSRR) filters, coupled lines are used to provide larger coupling capacitance, resulting in better bandpass characteristics with two CSRRs only. The modified bandpass filters are used to deisgn a compact diplexer. A new CSRR antenna fed by coplanar waveguide has also been developed as another metamaterial application. The rectangular shape CSRRs antenna achieves dual band frequency properties without any special matching network. The higher resonant frequency is dominantly determined by the outer slot ring, while the lower resonant frequency is generated by the coupling between two CSRRs. The proposed antenna achieves about 35 percent size reduction, compared with the conventional slot antennas at the low resonant frequencies. As a future alternative energy solution, space solar power transmission and wireless power transmission have received much attention. The design of efficient rectifying antennas called rectennas is very critical in the wireless power transmission system. The conventional method to obtain long distance range and high output power is to use a large antenna array in rectenna design. However, the use of array antennas has several problems: the relatively high loss of the array feed networks, difficultiy in feeding network design, and antenna radiator coupling that degrades rectenna array performance. In this dissertation, to overcome the above problems, a reflectarray is used to build a rectenna system. The spatial feeding method of the reflectarray eliminates the energy loss and design complexity of a feeding network. A high gain rectifying antenna has been developed and located at the focal point of the reflectarray to receive the reflected RF singals and genterate DC power. The technologies are very useful for high power wireless power transmission applications

Wideband and UWB antennas for wireless applications. A comprehensive review

A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems

Static and reconfigurable devices for near-field and far-field terahertz applications

The terahertz frequency electromagnetic radiation has gathered a growing interest from the scientific and technological communities in the last 30 years, due to its capability to penetrate common materials, such as paper, fabrics, or some plastics and offer information on a length scale between 100 µm and 1 mm. Moreover, terahertz radiation can be employed for wireless communications, because it is able to sustain terabit-per-second wireless links, opening to the possibility of a new generation of data networks. However, the terahertz band is a challenging range of the electromagnetic spectrum in terms of technological development and it falls amidst the microwave and optical techniques. Even though this so-called “terahertz gap” is progressively narrowing, the demand of efficient terahertz sources and detectors, as well as passive components for the management of terahertz radiation, is still high. In fact, novel strategies are currently under investigation, aiming at improving the performance of terahertz devices and, at the same time, at reducing their structure complexity and fabrication costs. In this PhD work, two classes of devices are studied, one for near-field focusing and one for far-field radiation with high directivity. Some solutions for their practical implementation are presented. The first class encompasses several configurations of diffractive lenses for focusing terahertz radiation. A configuration for a terahertz diffractive lens is proposed, numerically optimized, and experimentally evaluated. It shows a better resolution than a standard configuration. Moreover, this lens is investigated with regard to the possibility to develop terahertz diffractive lenses with a tunable focal length by means of an electro-optical control. Preliminary numerical data present a dual-focus capability at terahertz frequencies. The second class encompasses advanced radiating systems for controlling the far-field radiating features at terahertz frequencies. These are designed by means of the formalism of leaky-wave theory. Specifically, the use of an electro-optical material is considered for the design of a leaky-wave antenna operating in the terahertz range, achieving very promising results in terms of reconfigurability, efficiency, and radiating capabilities. Furthermore, different metasurface topologies are studied. Their analytical and numerical investigation reveals a high directivity in radiating performance. Directions for the fabrication and experimental test at terahertz frequencies of the proposed radiating structures are addressed

New Integrated Waveguides Concept and Development of Substrate Integrated Antennas with Controlled Boundary Conditions

The unprecedented development of substrate integrated circuits (SICs) has made a widespread necessity for further studies and development of waveguides and antennas based on this technology. As the operating frequency is on the rise, the conventional designs of the substrate integrated components are becoming more problematic and costly. Therefore, some techniques are proposed to improve the performance of the waveguides and antennas based on the concept of substrate integrated technology. First, the problems of the recently developed ridge gap waveguide (RGW) are resolved by introducing a new configuration of this technology which has considerable advantages over the original version of the RGW regarding its construction technology, propagation mode, characteristic impedance, and insertion loss. Second, the configuration of substrate integrated waveguide (SIW), which has been widely accepted for planar and integrated microwave circuits, is modified to operate with low insertion loss at high frequencies without bearing the anisotropic nature of the dielectric material. The substrate integrated antennas have a strong potential to be used in the compact wireless devices as they can be easily integrated with the baseband circuits. In the horn family, the H-plane horn antenna that can be implemented in the integrated form has received considerable attention in recent years. However, numerous problems are associated with this antenna such as limited bandwidth, tapered aperture distribution, high back radiation, and E-plane asymmetry. Several new techniques are introduced to improve the performance of this antenna, especially at millimeter wave frequencies

Dual-polarized, broadband metasurface cloaks for antenna applications

A communication system that reduces the mutual influence of antennas operating in similar or different frequency bands. The communication system includes a first and a second antenna operating in a first and a second frequency band, respectively, and placed in close proximity to each other. The first antenna is covered by a conformal mantle metasurface with anti-phase scattering properties thereby cancelling the scattering in the second frequency band. The conformal mantle metasurface consists of a patterned metallic sheet comprising slits both in an azimuthal and a vertical direction to reduce both vertical and horizontal polarization scattering. When the first antenna is a low-band dipole antenna and when the second antenna is a high-band dipole antenna, the conformal mantle metasurface reduces the low-band blockage without disrupting the performance of both antennas in terms of radiation pattern and impedance matching.Board of Regents, University of Texas Syste

Composite right/left handed antennas for wireless lan applications

The term ‘metamaterial’ has become a buzzword in electromagnetics over the past decade. In recent years, advancement in this new scientific area has given birth to numerous discoveries and inventions based on the exotic properties exhibited by these materials. Some of the exotic properties like negative permittivity, negative permeability, and infinite propagation at a particular non-zero resonant frequency are shown by these artificial materials especially called as Composite Right Left Handed structures. Metamaterials gain these properties from their structural configuration rather than from their material constitution. The electromagnetic characteristics of metamaterials can be exploited to meet the ever increasing demand for lighter, compact, size reduced, multiband antennas. One of the most exciting applications of these CRLH transmission lines (TL) is the Zeroth Order Resonant Antennas. CRLH TL metamaterials when open or short ended produce standing waves and thus behave as resonant antennas. Miniaturization of antennas is possible through these structures as the resonant frequency is independent of the parameters of the antenna aperture. Due to their infinite wavelength propagation property; reduced size, quarter wavelength antennas can be designed

Multi-layer metasurfaces for manipulating the propagation of microwaves along surfaces and edges

This thesis comprises original experimental studies on surface waves propagating on metasurfaces at microwave frequencies. These studies are supported by matching simulation data, obtained by means of Finite Element Method modelling. The structures studied throughout this thesis are comprised of more than one layer of sub-wavelength elements arranged in different periodic lattices. However, these layers are very thin compared to the size of the elements comprising the arrays, resulting in structures that are extremely sub-wavelength in the (out-of-plane) dimension. The work carried out as part of this thesis is divided in three main blocks, each of them looking at different features of metasurfaces, aiming to maximise different properties. The first type of structure presented in this thesis are designed and engineered to maximise three main properties. These are the mode index of the modes bound to the structures, its in-plane isotropy and the bandwidth of operation of prospective devices based on such metasurfaces. Whereas previous work in this field has considered single layers, the novelty here is the introduction of additional layers in order to increase the effective mode index of the modes supported by the structures. These extra layers create a capacitive effect between the overlapping areas of metal, therefore increasing the confinement of the waves. This is increased even further by minimising the separation between such layers. The second main goal in the design of the metasurfaces was to create a frequency independent mode index, aiming for the prospective development of broadband devices. For this, higher symmetries between the layers comprising the structures were introduced. Following the studies of the infinitely periodic metasurfaces and its properties, the suitability for their implementation as graded index devices is proven. Such devices are based on a graded mode index or surface impedance profile across the structure, which modifies the propagation of the wave. In the case of metasurfaces, the grading of the mode index is achieved by gradually varying the size or shape of the elements comprising the structure. This technique is used to design and manufacture two working planar Luneburg lenses, which are characterised experimentally and their performance compared with simulation data. The Luneburg lenses designed and manufactured as part of the work contained in this thesis have the novelty of a higher fractional bandwidth of operation compared to similar metasurface devices, reaching $73\%$. Another piece of work contained in this thesis involves a structure that guides microwaves with very high phase and group indices compared to similar metasurfaces. Its design is a simple two-layer discontinuous crossed metal-strip array. However, the novelty of this structure resides in the length of the metal strips, which extend to several unit cells. This work focuses on the isotropic wave dispersion shown at the lower frequencies. However, in addition to this, two of the higher frequency bands give rise to very strong negative dispersion, and also strong beaming occurs, which can be tailored easily by modifying the relative orientation of the layers. The third piece of work included in this thesis focuses on the propagation of edge modes along the termination of a particular metasurface structure with hexagonal symmetry. Our metasurface is comprised of two layers of hexagonal arrays of circular metal patches. This structure, in addition to supporting a bound wave that propagates isotropically across the two-dimensional structure, also supports an edge mode that propagates only along its termination. Here, the propagation of the mentioned edge mode has been extensively studied. Firstly, its propagation along finite strips is considered, followed by its use to guide the electromagnetic field around different shapes. Finally, the coupling of two of these edge modes across small gaps between two terminated structures is explored, with different symmetries between them. In all cases, samples are designed, fabricated and experiments have been carried out and the original results obtained have been compared with simulation data calculated with a finite element method modelling software.Engineering and Physical Sciences Research Council (EPSRC

Metamaterial-Inspired Frequency-Selective Surfaces.

This dissertation presents a new approach to designing frequency-selective surfaces having extensive applications in communications and radar systems. Unlike conventional surfaces composed of resonance-length elements, the new structures use sub-wavelength elements, and therefore, operate in TEM mode. Consequently, their frequency response is harmonic-free up to a frequency where their elements' dimensions become comparable with the wavelength. Hence, their behavior is described through quasi-static circuit models. These surfaces, which will be referred to as miniaturized-element surfaces, are easily synthesized since filter theory and circuit simulators are utilized in their design process. The small dimensions of the elements of the surface and its TEM mode of operation decrease the surface sensitivity to the incidence angle of the excitation (plane-wave). This allows the application of such surfaces in conjunction with phased-arrays and their placement in close proximity to an antenna. These surfaces can also operate properly with smaller panel dimensions. The theory of the new surfaces is introduced in Chapter 3 where a surface consisting of an array of wavelength/12-long elements is presented. The transmission response of this surface includes a passband and a transmission zero. For this design, the first harmonic is located at a frequency six times higher than the operation frequency. Using varactors, frequency tuning of nearly an octave is shown. Chapter 4 presents multipole spatial filters. Through an accurate circuit model, dual-bandpass and maximally flat filters that are wavelength/240 thick are demonstrated. Chapter 5 introduces a reconfigurable surface that produces a frequency response with two operation modes: bandstop and bandpass. Moreover, using varactors, the center frequency and the bandwidth are tuned independently. The discussion on tunability is continued in Chapter 6 which introduces another varactor-tuned structure that operates, similar to the previous designs, without additional biasing circuitry for the varactors. However, this structure is immune to single point failure as it uses a parallel biasing method. Finally, Chapter 7 demonstrates a wavelength/10-thick, coupled filter-antenna array to achieve a high-order filtering for beamforming arrays. This design eliminates the need for integrating bulky filters required in the receive chain of array elements.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64588/1/farhadbp_1.pd