This thesis focuses on three research topics on the design about planar ultrawide-band (UWB) monopole antennas, namely, the design of band notches for UWB monopole antennas, the ground-plane and cable effects on the measurement of compact UWB monopole antennas, and the design of a chipless UWB radio-frequency-identification (UWB-RFID) system. The designs of single, dual, triple and quadruple band-notched UWB monopole antennas using coplanar waveguide (CPW) resonators, quarter-wavelength (λ/4)-resonators and meander lines (MLs) are presented. The center frequencies and bandwidths of the individual notches in all these designs can be adjusted independently by varying the dimensions of the resonators. Studies of the designs are carried out by computer simulations using the EM software tool, CST MWS. For verification of the simulation results, these antennas are fabricated and measured using the antenna measurement system, Satimo Starlab. The frequency-domain performances, in terms of return loss, peak gain, efficiency and radiation pattern, and the time-domain performances, in terms of pulse responses and fidelity, are investigated by simulation and measurement. Results show that these UWB antennas have approximately omnidirectional radiation patterns with good band-notched characteristics and fidelities of more than 85% in the pulse responses. Results of studies show that, using a small ground plane in the design of the compact UWB antennas, there will be larger discrepancies between the measured and simulated radiation patterns, radiation efficiencies and peak gains at low frequencies. The discrepancies are due to diffraction of the electric fields at the edges of the small ground plane, which leads to currents flowing back to the measuring cable and hence secondary radiation. Computer simulation and measurement are used to study the ground-plane effects using a group of nine UWB antennas. These antennas have the same radiator but with rectangular ground planes of different sizes. Results show that the width of the ground plane affects the efficiency more than the length, while the length affects the lower cut-off frequency. The cable effects are further studied by modeling the measuring cables. Results show that, by using the cable model, the simulation and measurement efficiencies agree extremely well. The design of a novel chipless UWB-RFID system is presented. The system employs uniplanar chipless tags and a pair of high-gain reader antennas. The chipless tag is composed of two UWB monopole antennas connected by a CPW. Tag identification (ID) is represented by a spectral signature in the UWB and created by using a multi-resonator embedded on the CPW. Detection of spectral signature is based on only the amplitude of the spectral signature. Vertically and horizontally polarized signals are used to reduce mutual coupling between the uplink and downlink signals. Further reduction of the mutual coupling is achieved by using a copper plate in the reader to separate the uplink and downlink signals. Results of studies in an anechoic chamber show that the proposed RFID system can achieve a read range larger than 30 cm, indicating that the proposed system has great potentials for short-range item tracking at low-cost. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Thesis (MS)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Richard Wolff. Includes bibliographical references (leaves 109-112).

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (p. 51-53 ). Also available in electronic version.

Thesis (Ph.D.)--Syracuse University, 2008. / "Publication number: AAT 3333567."

The thesis report presents the designs of compact planar ultra-wideband (UWB) antennas for wireless devices applications. Three main designs of UWB antennas are studied, namely, single UWB antennas, UWB multiple-input-multiple-out(MIMO)antennas, and transparent UWB antennas on the screens of mobile phones. For single UWB antennas, the designs of two compact planar monopole antennas with compact sizes of 26×28 mm2and 30×39.3mm2are presented. The UWB operations of the antennas are achieved using a ground slot under the feed line, offsetting the feed line and the radiator from the middle of the ground plane and smoothly transforming the feed line. Simulation and measurement show that the two antennas can achieve an ultra-wide bandwidth with approximately omnidirectional patterns. A deep notch-band in5.1-5.85 GHz is created in one of the UWB antennas by employing two pairs of meander lines (MLs), one pair being close to the feed line and the other pair along the upper edge of the ground plane. At the notch frequency, the simulated efficiency is only 4%. Three compact UWB-MIMO antennas with very compact sizes of 26×40 〖mm〗^2, 21×38 〖mm〗^2, and 22×36 〖mm〗^2 are designed. Each of them is designed using two UWB antenna elements perpendicularly or symmetrically placed. Different techniques such as using ground stubs besides the radiators, cutting inclined slots on the ground, and adding a T-shaped protruding from ground are proposed to lower mutual coupling between the two antenna elements. One of the antennas is designed to generate a notched band in 5.15-5.85 GHz using two ground strips. Simulation and measurement results show that these antennas can cover the entire UWB of 3.1-10.6GHz with mutual coupling of less than -15 dB, and envelope correlation coefficient of less than 0.1. An UWB antenna is designed using a transparent conductive film for applications on mobile phone screens. The effects of a finger touching the screen are studied. Results show that, with the radiator on the bottom side of the screen and a thin film with a thickness of 0.05 mm on the top side to separate the finger and the antenna, the effects of the finger can be minimized. In measurement of monopole antennas with small ground planes, due to the feeding cable used, there are always discrepancies between the simulated and measured results in radiation patterns, efficiencies, and gains at lower frequencies. To verify that the discrepancies in the results of these studies are indeed due to the feeding cable used in measurement, the models of the feeding cables are developed and used for simulation. Results show that, by using the cable model, the simulated and measured results in radiation patterns, efficiencies, and gains agree very well. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 215-220).

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (p. 59-63). Also available in electronic version.

No / A small dielectric resonator antenna has been designed for ultra wideband (UWB) communication system applications. The antenna element is a rectangular low permittivity ceramic block, with a dielectric constant of 9.4, and the modified T-shaped feed network includes a 50 ohm microstrip line to achieve strong coupling, and some bandwidth enhancement. The antenna performance is simulated and measured over a frequency band extending from 3100 MHz to 5500 MHz; the impedance bandwidth over this interval is 55.8% with VSWR <; 2, making the antenna suitable for UWB applications.

<p> The allocation of 7.5 GHz of bandwidth by the Federal Communication Commission (FCC) for ultra-wideband (UWB) applications has provided an exciting and a challenging opportunity to design short range wireless communication and microwave imaging systems. To fully realize the potential of the UWB, communication and microwave imaging systems are required to operate over the entire UWB frequency band. The combination of the wide bandwidth requirement and the target application of the UWB systems have led to a surge of interest in designing of novel integrated circuits and antennas for the UWB applications. In any wireless communication and microwave imaging system, the antenna has a fundamental effect on the overall performance of the system, and as a result, it has attracted considerable research interest.</p> <p> This thesis focuses on the design of UWB antennas that are suitable for UWB cancer detection and wireless communication systems. Two planar antennas, one a printed monopole antenna, and the other, a printed slot antenna fed with a coplanar waveguide, are presented in this work. First, the antennas have been designed to operate in air, making them suitable for the UWB wireless short range communication applications. Measurement and simulation results indicate that both antennas achieve input impedance matching in a bandwidth of more than 7.5 GHz. The effect on the input matching of the antennas due to the variation in their geometrical parameters has been studied and both antennas have been fully characterized in air. Next, the two antennas have been redesigned to operate in a coupling medium for medical imaging applications. Both antennas achieve return loss of less than -10 dB over the entire UWB spectrum. Also, the antennas have been fully characterized while operating in the coupling medium and in proximity to a human body model. Finally, a two-element antenna array, based on the printed monopole antenna and the printed slot antenna, in co- and cross-polarized array formation, has been designed. The tumor detection capabilities of all antenna arrays for different scenarios have been studied through electromagnetic simulation and measurements.</p> / Thesis / Master of Applied Science (MASc)

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This dissertation presents modal-based techniques for the effective systematic design of quadruple-ridged flared horns (QRFHs) as reflector feeds for radio astronomy applications. A new excitation technique is proposed, consisting of a quadraxial line that terminates in the quad-ridges through the back lid of the QRFH, which allows for the integration with differential low-noise amplifiers. An equivalent circuit of this quadraxial feed is presented that allows fast synthesis of optimal feeding designs for QRFHs. In addition, the quadraxial feeding network suppresses higher-order modes significantly. The effect of eliminating these unwanted modes are investigated and the quadraxial feed is shown to outperform the coaxial feed in the known detrimental aspects of the QRFH – beamwidth narrowing for increased frequency, beamwidth variation over the upper bandwidth, high cross-polarisation levels, high co-polar sidelobes and variable phase centre – for the specific QRFH designs. Ridge-loaded modes are analysed and a large number of cut-off frequencies presented which are unavailable in literature. The pure-mode excitation of the quadraxial feed allows more effective control over the modal content in the QRFH. This is exploited in a proposed design technique where the cut-off frequencies throughout the horn are used to synthesise the ridge taper profile, in order to achieve the desired modal distribution in the aperture. The proposed feeding solution is compact and therefore is also attractive for use with cryocoolers, typically employed with front-end electronics in telescopes for radio astronomy. A prototype was successfully manufactured and the mechanical implementation of the quadraxial feed proved to be much more simple than that of the conventional feed – consisting of a coaxial line realised within the thin ridges. / AFRIKAANSE OPSOMMING: Hierdie proefskrif stel modus gebasseerde tegnieke voor vir die effektiewe sistematiese ontwerp van viervoud gerifte oopgesperde horings (VGOHs) as weerkaatser voere vir radio astronomie toepassings. ’n Nuwe voertegniek word voorgestel, wat bestaan uit ’n kwadraksiale lyn wat termineer in die vier riwwe deur die agterkant van die VGOH, wat die integrasie met differensiële laeruis versterkers toelaat. ’n Ekwivalente stroombaan van hierdie kwadraksiale voer word aangebied vir die vinnige sintese van optimale voer ontwerpe vir VGOHs. Boonop onderdruk die kwadraksiale voer netwerk ook beduidend hoër orde modusse. Die effek van die uitskakeling van hierdie ongewensde modusse word ondersoek en die kwadraksiale voer oortref die gedrag van die koaksiale voer in die bekende nadelige aspekte van die VGOH – bundelwydte vernouing met toenemende frekwensie, bundelwydte variasie oor die boonste bandwydte, hoë kruispolarisasie vlakke, hoë kopolarisasie sybande en wisselvallige fase senter – vir die spesifieke VGOH ontwerpe. Rifgelaaide modusse word geanaliseer en ‘n groot aantal afsnyfrekwensies word aangebied wat nie beskikbaar is in literatuur nie. Die suiwermodus opwekking van die kwadraksiale voer bied meer effektiewe beheer oor die modusinhoud in die VGOH. Hierdie aspek word benut in ‘n voorgestelde tegniek waar die afsnyfrekwensies deur die horing gebruik word om die rif tapsheid profiel te sintetiseer, sodat die gewensde modale distribusie in die stralingsvlak behaal word. Die voorgestelde voer oplossing is kompak en daarom ook aantreklik vir die gebruik met krioverkoelers, wat tipies gebruik word met die voorkant elektronika in teleskope vir radio astronomie. ‘n Prototipe was suksesvol vervaardig en die meganiese implimentasie van die kwadraksiale voer toon dat dit eenvoudiger is as met die gebruiklike koaksiale voer – wat bestaan uit ‘n koaksiale lyn bewerkstellig binne die dun riwwe.