This thesis presents the design, fabrication, and measurement of tunable frequency microstrip antennas using RF MEMS (Microelectromechanical Systems) technology. The integration of RF MEMS components with radiators enable to implement tunable systems due to the adjustable characteristics of RF MEMS components. In the frame of this thesis, different types of structures have been investigated and designed. The first structure consists of a microstrip patch antenna which is loaded with a microstrip stub whose length is controlled by RF MEMS switches. In the other structure, the length of a microstrip patch antenna is changed by connecting a metal plate using RF MEMS switches. The third structure is composed of a microstrip patch antenna and a microstrip stub on which RF MEMS variable capacitors are placed periodically to control the resonant frequency. In order to maintain an easier integration with RF MEMS capacitors, another structure consisting of a microstrip patch antenna and a coplanar waveguide (CPW) stub which is loaded with variable RF MEMS capacitors is designed. The final structure is a dual frequency CPW-fed rectangular slot antenna whose resonant frequencies are shifted by RF MEMS variable capacitors placed on a short circuited stub inserted inwards the antenna. The fabrication of CPW-fed rectangular slot antenna is completed in the MEMS fabrication facilities of METU using RF MEMS process based on electroforming on glass substrate. The measurement results show that RF MEMS components might be a proper solution to obtain tunable frequency antenna structures.

Thesis (M. App. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 110-113). Also available in electronic format on the Internet.

This thesis provides novel contribution to the field of body-centric wireless communications (BCWC) with the development of a measurement methodology for wearable antenna characterisation on the human body, the implementation of fully-textile wearable antennas and the on-body channel modelling considering different antenna types and user's dynamic effects. More specifically, a measurement methodology is developed for characterising wearable antennas on different locations of the human body. A cylindrical near-field (CNF) technique is employed, which facilitates wearable antenna measurements on a full-body solid anthropomorphic mannequin (SAM) phantom. This technique allows the fast extraction of the full spherical radiation pattern and the corresponding radiation efficiency, which is an important parameter for optimising wearable system design. It appears as a cost- effective and easy to implement solution that does not require expensive positioning systems to rotate the phantom, in contrast to conventional roll-over-azimuth far-field systems. Furthermore, a flexible fully-textile wearable antenna is designed, fabricated and measured at 2.4 GHz that can be easily integrated in smart clothing. It supports surface wave propagation and exhibits an omni-directional radiation pattern that makes it suitable for on-body communications. It is based on a multilayer low-profile higher-mode patch antenna (HMMPA) design with embroidered shorting vias. Emphasis is given to the fabrication process of the textile vias with conductive sewing thread that play an important role in generating the optimal mode for on-body radiation. The radiation pattern shape of the proposed fully-textile antenna was found to be similar to a copper rigid antenna, exhibiting a high on-body radiation efficiency of 50 %. The potential of the embroidery technique for creating wearable antennas is also demonstrated with the fabrication of a circularly polarised spiral antenna that achieves a broadband performance from 0.9-3 GHz, which is suitable for off-body communications. By testing the textile spiral antenna on the SAM phantom, the antenna-body interaction is examined in a wide frequency range. Finally, a statistical characterisation of on-body communication channels is undertaken both with EM simulations and channel measurements including user's dynamic movement (walking and running). By using antenna types of different polarisation, the on-body channels are examined for different propagation conditions. Four on-body channels are examined with the one part fixed on the waist of the human body while the other part located on the chest, back, wrist and foot. Channel path gain is derived, while large-scale and small-scale fading are modelled by best-fit statistical distributions.

abstract: There is a pervasive need in the defense industry for conformal, low-profile, efficient and broadband (HF-UHF) antennas. Broadband capabilities enable shared aperture multi-function radiators, while conformal antenna profiles minimize physical damage in army applications, reduce drag and weight penalties in airborne applications and reduce the visual and RF signatures of the communication node. This dissertation is concerned with a new class of antennas called Magneto-Dielectric wire antennas (MDWA) that provide an ideal solution to this ever-present and growing need. Magneto-dielectric structures (μr>1;εr>1) can partially guide electromagnetic waves and radiate them by leaking off the structure or by scattering from any discontinuities, much like a metal antenna of the same shape. They are attractive alternatives to conventional whip and blade antennas because they can be placed conformal to a metallic ground plane without any performance penalty. A two pronged approach is taken to analyze MDWAs. In the first, antenna circuit models are derived for the prototypical dipole and loop elements that include the effects of realistic dispersive magneto-dielectric materials of construction. A material selection law results, showing that: (a) The maximum attainable efficiency is determined by a single magnetic material parameter that we term the hesitivity: Closely related to Snoek's product, it measures the maximum magnetic conductivity of the material. (b) The maximum bandwidth is obtained by placing the highest amount of μ" loss in the frequency range of operation. As a result, high radiation efficiency antennas can be obtained not only from the conventional low loss (low μ") materials but also with highly lossy materials (tan(δm)>>1). The second approach used to analyze MDWAs is through solving the Green function problem of the infinite magneto-dielectric cylinder fed by a current loop. This solution sheds light on the leaky and guided waves supported by the magneto-dielectric structure and leads to useful design rules connecting the permeability of the material to the cross sectional area of the antenna in relation to the desired frequency of operation. The Green function problem of the permeable prolate spheroidal antenna is also solved as a good approximation to a finite cylinder. / Dissertation/Thesis / Ph.D. Electrical Engineering 2013

In recent years, multi-functional reconfigurable antennas (MRA) has attracted much attention in wireless communication. The reconfigurable antenna can adapt itself with changing system conditions, and it can provide different multi-functionalities which can give better system performances. Instead of using multiple antennas, a single reconfigurable antenna can provide the same performance and occupy less space. By using the parasitic layer technique, an antenna can be turned into a reconfigurable antenna. The main objective of this thesis is to study radiation pattern reconfiguration of the horn antenna by using the parasitic layer concept. The MRA consists of a single horn, dielectric loaded truncated pyramid (DLTP), and the parasitic layer. The antenna that is chosen in this thesis is the horn antenna because it provides high directivity. DLTP is used for magnification purpose. The results show that three modes of operations that provide better performances compared to the single horn antenna are achieved.

An active, broadband antenna module amenable for use in low cost phased arrays is proposed. The module consists of a Vivaldi antenna integrated with a frequency conversion integrated circuit. A method of orthogonally mounting endfire antennas onto an array motherboard is developed using castellated vias. A castellated active isolated Vivaldi antenna package is designed, fabricated, and measured. An 8x1 phased array of castellated, active Vivaldi antenna packages is designed and assembled. Each element has approximately one octave of bandwidth centered in X-band, and each is mounted onto a coplanar waveguide motherboard. Radiation patterns of the array are measured at several frequencies and scan angles.

Submitted in fulfilment of the academic requirements for the Degree Master of Engineering: Electrical Engineering, Durban University of Technology. Durban. South Africa, 2015. / This dissertation describes the development and construction of the Multi-frequency Interferometer Telescope for Radio Astronomy (MITRA) at the Durban University of Technology. The MITRA station consists of 2 antenna arrays separated by a baseline distance of 8 m. Each array consists of 8 Log-Periodic Dipole Antennas (LPDAs) operating from 200 MHz to 800 MHz. The design and construction of the LPDA antenna and receiver system is described. The receiver topology provides an equivalent noise temperature of 113.1 K and 55.1 dB of gain. The Intermediate Frequency (IF) stage was designed to produce a fixed IF frequency of 800 MHz. The digital Back-End and correlator were implemented using a low cost Software Defined Radio (SDR) platform and Gnu-Radio software. Gnu-Octave was used for data analysis to generate the relevant received signal parameters including total power, real, and imaginary, magnitude and phase components. Measured results show that interference fringes were successfully detected within the bandwidth of the receiver using a Radio Frequency (RF) generator as a simulated source. This research was presented at the IEEE Africon 2013 / URSI Session Mauritius, and published in the proceedings.

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / A remotely-operated ground telemetry tracking and receiving station is described. The station, operating in a space-diversity mode, is capable of reception and tracking both at VHF and at UHF. The station can be configured and operated from a distance of 240 km using a wide-band land data link. Uplink command at VHF is included as part of the station.

Wearable technology has attracted global attention in the last decade and the market is experiencing an unprecedented growth. Wearable devices are designed to be low-profile, light-weight and integrated seamlessly into daily life. Comfort is one of the most important requirements for wearable devices. Fabric based antennas are soft, flexible and can be integrated into clothing. State of the art textile manufacturing techniques such as embroidery, combined with advanced conductive textile materials can be used to fabricate flexible fabric based on-body antennas. In this thesis, the feasibility of using computerised embroidery in the fabrication of wearable, flexible yet functional fabric based antennas have been examined. The fabric based antennas are embroidered using conductive threads. The most suitable materials for fabricating embroidered antennas have been identified. The embroidered fabric based antenna systems including transmission lines and low-profile detachable connectors have been fabricated and their RF performances have been tested. The optimal manufacturing parameters related to embroidery such as stitch direction, spacing and length have been examined. The repeatability of embroidered antennas, cost estimation, and complexity of manufacturing process have been clearly presented. The results can be used to inform and provide guidelines for the development of representative products that can be mass manufactured. A new simulation approach has been introduced to analyse the anisotropic properties of embroidered conductive threads. Simulations and measurements indicate that the performances of embroidered antennas are affected by the anisotropic surface current due to the embroidered stitches. Exploiting the current direction, a novel non-uniform meshed patch antenna has been designed. Representative results show that the non-uniform meshed structure can significantly reduce more than 75% of the usage of conductive materials for the microstrip antennas with negligible effect on the antenna performance.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Multiple discrete antennas distributed around the circumference of a large missile and driven by one transmitter are sometimes used to radiate telemetry omnidirectionally. But driving discrete antennas separated by several wavelengths around the missile body with a single transmitter can result in an antenna pattern with deep nulls in the roll plane. Varying the relative signal phase or amplitude among the signals driving the antennas as well as the polarization of the antennas can be used to change the nulls in an attempt to decrease the null depth. In this paper the effects of phase, amplitude, and polarization on the roll-plane pattern are examined and measurement data presented.