Dissertations / Theses on the topic 'Reconfigurable microstrip antennas'

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.

Millimetre wave beam and polarization reconfigurable antennas for future wireless communications are investigated in this thesis. The millimetre wave frequency spectrum has recently attracted large attention from researchers and the industry of wireless communications. Millimetre wave frequencies is considered to be the frequency spectrum between 30 GHz and 300 GHz. However, the industry considers the spectrum above 10 GHz as millimetre wave, due to the fact that it shows similar propagation characteristics with the spectrum above 30 GHz. The aforementioned spectrum of frequencies offers a lot of advantages compared to lower frequency spectrum, due to the fact that it offers large and mostly unexploited bandwidths. The need for very high data rates, in future wireless communications, increases the need for bandwidth. Millimetre wave frequencies can be used to fulfill future bandwidth demands. Although millimeter wave frequencies offer several advantages and good potential for future wireless communications, they also impose several challenges. This thesis discusses the need for highly directive and beam reconfigurable antennas for such high frequencies. It also discusses how an antenna design can benefit from being circularly polarised for several wireless communication applications and how antennas for future wireless communications must be able to reconfigure several parameters, without compromising the performance, cost and size, giving the exibility to a wireless terminal to operate in several different modes. This thesis proposes novel reconfigurable antennas for portable devices, which can be used at millimetre wave frequencies, and which offer high gain, wide steering range, low scan loss and multi-parameter reconfigurability; essential characteristics that antennas designed for future wireless communications should offer.

The aim of this study is to investigate the effects of changes in the physical parameters of tapered slot antennas (TSA) on their radiation characteristics and also to explore the possibility of reconfiguration in the radiation pattern of TSA by switching between two different types of tapering. There are mainly three physical parameters that affect the radiation pattern of TSAs. These are antenna length, aperture width and the ground extension. After designing a wideband microstrip line to slot line transition, the effect of antenna parameter variations on the beamwidth and sidelobe level of the antenna are investigated through the use of a commercially available electromagnetic simulation software HFSS by ANSOFT. The radiation characteristics of constant width slot antennas (CWSA) and linearly tapered slot antennas (LTSA) are compared. It is observed that CWSAs exhibit narrower beamwidth and higher sidelobe level whereas linearly tapered slot antennas (LTSA) have wider beamwidth with lower sidelobe level compared to each other. A novel switching architecture between CWSA and LTSA is proposed to obtain a reconfigurable antenna.

Made available in DSpace on 2014-12-17T14:55:36Z (GMT). No. of bitstreams: 1 IradilsonFC.pdf: 1175734 bytes, checksum: 1b789bd9fa5e1240b46ecdcefd19f939 (MD5) Previous issue date: 2009-08-11
Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
This work aims to present how the reconfigurable microstrip antennas and frequency selective surfaces can be used to operate at communication systems that require changing their operation frequency according to system requirements or environmental conditions. The main purpose is to present a reconfigurable circular microstrip antenna using a parasitic ring and a reconfigurable dipole frequency selective surface. Thereupon there are shown fundamental topics like microstrip antennas, PIN diodes and the fundamental theory of reconfigurable antennas and frequency selective surfaces. There are shown the simulations and measurements of the fabricated prototypes and it is done an analysis of some parameters like the bandwidth and radiation pattern, for the antennas, and the transmission characteristics, for the frequency selective surface. Copper strips were used in place of the diodes for proof of the reconfigurability concept
Este trabalho tem como objetivo apresentar como as antenas de microfita e as superf?cies seletivas de frequ?ncia reconfigur?veis podem ser alternativas para operar em sistemas de comunica??o sem fio que necessitem alterar sua frequ?ncia de opera??o de acordo com os requisitos impostos a este sistema ou condi??es do meio. O prop?sito central ? apresentar uma antena de microfita com patch circular reconfigur?vel utilizando um anel parasita e uma superf?cie seletiva de frequ?ncia tipo dipolo reconfigur?vel. Para isto s?o apresentados temas fundamentais como as antenas de microfita, diodos PIN e a teoria fundamental de opera??o das antenas e superf?cies seletivas de frequ?ncia reconfigur?veis. S?o apresentadas todas as simula??es e medi??es realizadas dos prot?tipos constru?dos e ? feita uma an?lise de alguns par?metros como largura de banda e diagrama de radia??o, para as antenas, e caracter?sticas de transmiss?o, para as superf?cies seletivas de frequ?ncia. Foram utilizadas fitas de cobre no lugar dos diodos para a prova do conceito de reconfigurabilidade

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 78-80).
Reconfigurable antennas with adaptable frequency, pattern, and polarization offer flexibility and size reduction for wireless systems that must increasingly execute multiple missions with less volume. These antennas will also complement anticipated cognitive radio systems, which promise more efficient use of the electromagnetic spectrum. Microscale liquid metal switches are proposed to overcome the series loss, mechanical fatigue, and limited power handling reliability of common methods of antenna reconfiguration such as semiconductor diodes and microelectromechanical switches. The proposed microswitches consist of mercury droplets that selectively connect solid metal traces. Both fluidic and electrostatic switch actuation mechanisms are investigated, and an electrostatic switch is demonstrated. Electrostatically actuated switches are designed into a compact single-feed patch antenna configurable between two communication frequency bands and a GPS band with different circular polarizations. The antenna topology is based on a corner truncated square patch with switched sets of extensions to achieve resonant frequency and axial ratio control. Measurements of reconfigurable prototypes demonstrate frequency and polarization configurability in good agreement with full-wave simulations. The proposed reconfiguration mechanism is compared to other methods, and future directions for the integration of microfluidics in reconfigurable radio frequency systems are proposed.
by Steven Christopher Yee.
S.M.

The master's thesis deals with the design and implementation of a reconfigurable patch antenna. The antenna is fed by a microstrip transmission line. To the microstrip feeder, tuning stubs are connected. Each stub matches the input impedance of the antenna to 50 ? for different operation frequencies. Stubs can be individually connected to the feeder by PIN diodes; operation frequency of the antenna can be switched that way. In the project, the antenna is initially designed for antenna substrate RO3006. Then, the design will be converted to the substrate ARLON AD600 selected for the realization. In the project, modifications of stubs will be proposed to properly connect the PIN diodes. Functionality of the designed antenna will be verified by modeling in Ansoft Designer. The last part will be dealt with implementation of the antenna and the experimental measurement of their properties.

[EN] Nowadays, due to the fast development of wireless communication systems, the need to have radiating elements has arisen. These elements allow an efficient radiation of electromagnetic waves that transmit the information among the different points of the system. Owing to this growing demand and based on certain requirements, several prototype antennas fabricated with planar technologies such as PCB "Printed Circuit Board" and LTCC "Low Temperature Co-fired Ceramic" are presented in this thesis. Every proposed prototype is presented as a solution for a project which requires an antenna with specific characteristics. Based on the requested specifications such as working frequency, bandwidth, polarization type, size and shape, the most appropriate design alternatives were selected. For satellite communications at 5.8 GHz, two types of antennas with circular polarization are proposed. The former is a square patch with a diagonal slot, the latter is a polarization reconfigurable antenna fabricated with LTCC technology. For the operation in Ku band at 17 GHz, slot arrays with substrate integrated waveguide technology were proposed, whereas for vehicular applications, monopole antennas were the better solution due to the restrictions in the form and space available for assembly. In addition, due to the growing interest in the applications operating at no licensed frequency bands, patch antenna arrays conformed in a cylindrical shape to operate at 2.4 GHz and 5.8 GHz, were designed. These arrays will be placed in UAVs. Each proposed design meets with the required specifications for the different projects such as: appropriate matching levels, radiation patterns according to the application, specific dimensions and material type
[ES] En la actualidad, con el rápido desarrollo de los sistemas de comunicaciones inalámbricos, se presenta la necesidad de contar con elementos radiantes que permitan la radiación eficiente de las ondas electromagnéticas que transportan la información. Ante la creciente demanda y en base a ciertos requerimientos, en esta tesis se presentan varios prototipos de antenas fabricados con tecnologías planares como PCB "Printed Circuit Board" y LTCC "Low Temperature Co-fired Ceramic". Cada prototipo que se propone, se plantea como solución para proyectos que requieren que la antena presente determinadas características. En base a las especificaciones solicitadas como: frecuencia de trabajo, ancho de banda, tipo de polarización, tamaño y forma, se buscaron las alternativas de diseño más apropiadas. Para aplicaciones satelitales a 5.8 GHz se proponen dos tipos de antenas con polarización circular: la primera que es un parche cuadrado con ranura inclinada y la segunda que es una antena reconfigurable en polarización fabricada con tecnología LTCC. Para operar en la banda Ku a 17 GHz, se propuso utilizar agrupaciones de ranuras en guía de onda integrada en sustrato, mientras que para aplicaciones vehiculares, los monopolos fueron las antenas que mejor se adaptaron a las formas y espacios disponibles para su montaje. Además, por el gran interés que han despertado las aplicaciones que operan en bandas de frecuencia que no requieren de permiso o licencia para su utilización, se diseñaron agrupaciones de antenas tipo parche conformados a una forma cilíndrica para operar a 2.4 GHz y 5.8 GHz. Estas agrupaciones serán ubicadas en vehículos aéreos no tripulados. Cada diseño propuesto cumple con especificaciones planteadas por las necesidades de los diferentes proyectos como: niveles adecuados de adaptación, diagramas de radiación acorde con la aplicación, dimensiones y material específico.
[CAT] En l'actualitat, amb el ràpid desenvolupament dels sistemes de comunicacions sense fils, es presenta la necessitat de comptar amb elements radiants que permitisquen la radiació eficient de les ones electromagnètiques que transporten la informació. Davant la creixent demanda y en base a certs requeriments, en aquesta tesi es presenten diversos prototips d'antenes fabricades amb tecnologies planars com PCB "Printed Circuit Board" i LTCC "Low Temperature Co-fired Ceramic". Cada prototip que es proposa es planteja com a solució per projectes que requereixen que l'antena presente determinades característiques. D'acord amb les especificacions sol·licitades, com poden ser la freqüència de treball, l'ample de banda, el tipus de polarització, o la mida y la forma, es buscaren les alternatives de disseny més apropiades. Per aplicacions satel·litals, a 5.8 GHz es proposen dos tipus d'antenes amb polarització circular: la primera és una antena plana "patch antena" quadrada amb ranura inclinada y la segona és una antena reconfigurable en polarització fabricada amb tecnologia LTCC. Per tal d'operar a la banda Ku a 17 GHz, es va proposar utilitzar agrupacions de ranures en guia d'ona integrada en substrat, mentre que per aplicacions vehiculars, el monopols foren les antenes que millor s'adaptaren a les formes y espais disponibles per al seu muntatge. A més a més, pel gran interès que han despertat les aplicacions que operen en bandes de freqüència que no requereixen de permís o llicència per a la seua utilització, es dissenyaren agrupacions d'antenes planes conformades a una forma cilíndrica per operar a 2.4 GHz i 5.8 GHz. Estes agrupacions seran ubicades en vehicles aeris no tripulats. Cada disseny proposat compleix amb les especificacions plantejades per les necessitats dels diferents projectes com: nivells adequats d'adaptació, diagrames de radiació d'acord amb l'aplicació, dimensions i material específic.
Navarro Méndez, DV. (2015). NUEVOS SISTEMAS RADIANTES REALIZADOS CON TECNOLOGÍAS IMPRESAS [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/54118
TESIS

碩士
國立彰化師範大學
電機工程學系
96
This thesis presents the designs for reconfigurable microstrip antenna. Three types of the reconfigurable antenna are studied. The first one is a circularly-polarized (CP) microstrip antenna capable of switching polarisation sense. The microstrip antenna is excited by an open-loop microstrip line through the coupling of a ring slot in the ground plane. The polarisation diversity is achieved by using a pair of pin diodes to reconfigure the flowing path of the current on the open-loop microstrip feed line. The measured results show the 3dB-axial-ratio bandwidth of more than 10 % can be obtained at the two polarisation senses. The second one is a CP reconfigurable microstrip antenna with dual-frequency operation. The antenna has a square radiating patch, and each side of the square patch is connected a shorting wall via a diode. By switching the four diodes, the CP operating frequency of the antenna can be varied. Several prototypes of the reconfigurable dual-frequency antennas with different frequency ratios were fabricated. The last one is a CP reconfigurable microstrip antenna with polarization and frequency diversities. The antenna is excited through the coupling of a cross slot with unequal lengths. Two diodes are used to reconfigure the radiating patch, and by controlling the states of the diodes, the polarization sense of the antenna can be switched between left-hand and right-hand CP. Moreover, the two CP modes are operated at different frequencies. An antenna prototype was also implemented and the obtained results are shown.

碩士
逢甲大學
電機工程學系
101
This thesis focuses on reconfigurable slot antenna research, and two types of reconfigurable slot antennas are proposed. To achieve frequency or polarization diversity for the proposed slot antenna, pin-diodes were used for switching purposes. A reconfigurable slot antenna with switchable polarization is initially proposed in this thesis. The proposed antenna is comprised of a square-shaped radiating element loaded with an eccentric circular slot. It is fed by a microstrip feed line, and can excite TM11 mode. In order to generate circularly polarization (CP) radiation, two identical perturbed circular shaped slot are loaded below the eccentric ring-shaped slot at -20° and 20° position with respect to the –Y axis. By switching the pin-diodes embedded into the slot, the proposed antenna can switch between left hand circular polarization (LHCP), right hand circular polarization (RHCP), and linear polarization (LP). Besides possessing the ability to switch between the three polarizations, the advantages of this proposed antenna also include compact size (50 × 50 mm2), simple DC bias circuit, and the ability to cover the required operating band (2400-2480 MHz) for WLAN 2.4 GHz applications. The second proposed antenna is a reconfigurable slot antenna design with switchable frequency. In this design, a circular slot is first embedded into a square-shaped ground plane; follow by embedding a semi-circular patch into the slot, forming a semi-circular slot structure with the bottom section analogous to a halve-annular ring slot. Here, a meandered stub is also loaded above the semi-circular patch, and the proposed antenna is fed by a microstrip line. To achieve frequency reconfiguration, three pin-diodes are embedded along the meandered stub. By switching these three pin-diodes in a certain sequences, the electric field distribution along the halve-annular ring slot will be affected, and four resonant modes (2.66, 2.94, 3.52, and 4.4 GHz) can be separately excited. Therefore, operating bands between 2.6 and 4.7 GHz can be controlled by the proposed antenna. Compared with the first proposed antenna, the latter has also exhibited small size characteristics (50 × 50 mm2) and simple DC bias circuit.

碩士
國立中央大學
電機工程學系
105
The operating frequency of an antenna can be made reconfigurable by incorporating tuning elements. In this thesis, microstrip patch antennas are loaded with variable capacitors (varactors) to acquire frequency tunability. We design and fabricate two kinds of frequency-reconfigurable microstrip patch antennas, both of which use ferroelectric varactors with barium strontium titinate (BSTO) as the dielectric material for the capacitive loading. One of the microstrip patch antennas uses benzocyclobutene (BCB) as its dielectric whereas the other patch antenna uses high-resistivity silicon substrate. The operating frequency of the frequency-reconfigurable patch antenna with BCB as its dielectric is set at around 15 GHz. The ferroelectric capacitors and the patch are connected using the BCB stacked via process developed by our lab. Measurement results show that, when the bias voltage of the varactor is tuned from 0 V to 25 V, the operating frequency of the antenna varies from 13.8 GHz to 14.3 GHz, which translates into a 3.5% frequency tuning range (FTR). The operating frequency of the microstrip patch antenna with high-resistivity silicon as its dielectric is also designed to be around 15 GHz. The ferroelectric varactors are connected to the ground plane on the backside of the silicon substrate by through substrate vias (TSVs). Measurement results of this antenna show that the operating frequency is fixed at 9.7 GHz. No frequency tunability is observed. We find that the reason why the antenna is not tunable is because the annealing temperature for the BSTO thin film is too low for this sample. As for the large frequency shift, it is due to a mistake in layout. The layout mistake results in an unexpected silicon-nitride capacitor with a large capacitance, which becomes part of the capacitive loading. In this thesis, we successfully realize a frequency-reconfigurable microstrip patch antenna with BCB as its dielectric and with ferroelectric varactors as its capacitive loading. On the other hand, we successfully fabricate a capacitively loaded microstrip patch antenna using the TSV process we develop. Though the measured operating frequency has deviated from the designed value and cannot be tuned, we have discovered the reasons that result in these problems. We believe that the expected performance can be obtained after these issues are resolved.

no
Reconfigurable beam steering using circular disc microstrip patch antenna with a ring slotis proposed. The overall dimension of the antenna is 5.4×5.4 mm2 printed on a 0.504 mm thick, Rogers RT5870 substrate with relative permittivity 2.3 and loss tangent 0.0012. The designed antenna operates at the expected 5G frequency band 60 GHz with a central coaxial probe feed. TwoNMOS switches are configured to generate three different beam patterns. Activating each switch individually results in a near 70 degree shift in the main beam direction, whereas the frequency characteristics are unchanged. The power gains are between 3.9 dB and 4.8dB for the three states of switches configurations. Simulated results in terms of return loss, peak gains and radiation pattern are presented and show a reasonable agreement at the expected 60 GHz bandfor 5G applications.
The published journal webpage is no longer available.

Yes
This paper presented a new circular polarization reconfigurable antenna for 5G wireless communications. The antenna, containing a semicircular slot, was compact in size and had a good axial ratio and frequency response. Two PIN diode switches controlled the reconfiguration for both the right-hand and left-hand circular polarization. Reconfigurable orthogonal polarizations were achieved by changing the states of the two PIN diode switches, and the reflection coefficient |S11| was maintained, which is a strong benefit of this design. The proposed polarization-reconfigurable antenna was modeled using the Computer Simulation Technology (CST) software. It had a 3.4 GHz resonance frequency in both states of reconfiguration, with a good axial ratio below 1.8 dB, and good gain of 4.8 dBic for both modes of operation. The proposed microstrip antenna was fabricated on an FR-4 substrate with a loss tangent of 0.02, and relative dielectric constant of 4.3. The radiating layer had a maximum size of 18.3 18.3 mm2, with 50 W coaxial probe feeding.
European Union’s Horizon 2020 research and innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424.

Yes
This paper presents a circular polarization reconfigurable antenna for 5G applications, which is compact in size and has good axial ratio and frequency response. The proposed microstrip antenna is designed on a FR-4 substrate with a relative dielectric constant of 4.3 and has a maximum size of 30×30 mm2 with 50 Ω coaxial probe feeding. This design has two PIN diode switches controlling reconfiguration between right hand circular polarization (RHCP) and left hand circular polarization (LHCP). To achieve reconfigurability, a C-slot rectangular patch antenna with truncated corner techniques is employed by cutting off two corners on the radiating patch. The proposed antenna has been simulated using CST microwave studio software: it has 3.35-3.77 GHz and 3.4-3.72 GHz bands for both states of reconfiguration, and each is suitable for 5G applications with a good axial ratio of less than 1.8 dB and good gain of 4.8 dB for both modes of operation.
Innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424, UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E022936/1.

In modern wireless communication and radar systems, filters play an important role in getting a high-quality signal while rejecting spurious and neighboring unwanted signals. The filters with reconfigurable features, such as tunable bandwidths or switchable dual bands, also play a key part both in realizing the compact size of the system and in supporting multi-communication services. The Chapters II-IV of this dissertation show the studies of the filters for microwave communication. Bandpass filters realized in ring resonators with stepped impedance stubs are introduced. The effective locations of resonant frequencies and transmission zeros are analyzed, and harmonic suppression by interdigital-coupled feed lines is discussed. To vary mid-upper and mid-lower passband bandwidths separately, the characteristic impedances of the open-circuited stubs are changed. Simultaneous change of each width of the open-circuited stub results in variable passband bandwidths. Asymmetric stepped-impedance resonators are also used to develop independently controllable dual-band (2.4 and 5.2 GHz) bandpass filters. By extending feed lines, a transmission zero is created, which results in the suppression of the second resonance of 2.4-GHz resonators. To determine the precise transmission zeros, an external quality factor at feeders is fixed while extracting coupling coefficients between the resonators. Two kinds of feed lines, such as hook-type and spiral-type, are developed, and PIN diodes are controlled to achieve four states of switchable dual-band filters. Beam-scanning features of the antennas are very important in the radar systems. Phase shifters using piezoelectric transducers and dielectric leaky-wave antennas using metal strips are studied in the Chapters V-VII of this dissertation. Meandered microstrip lines are used to reduce the size of the phase shifters working up to 10 GHz, and reflection-type phase shifters using piezoelectric transducers are developed. A dielectric film with metal strips fed by an image line with a high dielectric constant is developed to obtain wide and symmetrical beam-steering angle. In short, many techniques are presented for realizing reconfigurable filters and large beam-scan features in this dissertation. The result of this work should have many applications in various wireless communication and radar systems.

碩士
國立彰化師範大學
電機工程學系
95
The designs of a reconfigurable ring patch antenna are proposed and studied in this dissertation. The thesis is mainly divided into three topics. First, the design of a ring patch antenna with wideband and dual-frequency operations is presented. The antenna consists of a parasitic square ring patch that is shorted to the ground plane through two shorting walls and is excited by a top-loaded coaxial probe. For the proposed design, while the side length of the square ring patch is about 0.3 free-space wavelengths and the antenna height is less than 0.1 free-space wavelengths, a 10 dB-input-impedance bandwidth of more than 50 % can be achieved. Also, the antenna can provide stable monopole-like conical radiation patterns across the impedance bandwidth. In addition, it is also found that two different resonant modes, patch-loaded monopole mode and normal patch mode, can be simultaneously excited in the shorted patch antenna structure by a coupling rectangular strip inside the ring patch. The antenna can radiate monopole-like and broadside patterns at the two operating frequencies, respectively. Second, a reconfigurable patch antenna with the functions of switchable radiation patterns, and polarizations is presented. The antenna is composed of a ring patch and four shorting walls. By controlling the connections states between the ring patch and shorting walls through pin diodes, the antenna can be operated at different modes to achieve the switching of the radiation patterns and polarizations. Moreover, three pairs of the shorting walls with various widths are integrated into the antenna to excite the patch-load monopole mode, and the resonant frequency can be changed by activating various pair of the shorting walls. From the obtained results, the three operating frequencies can occupy a successive impedance bandwidth, which makes the antenna with wide band operation.

碩士
正修科技大學
電子工程研究所
99
In this paper, patch antennas with reconfigurable polarization are presented. The designs use feed mechanism and bias control to alter the polarization. The first design is an L-strip-fed patch antenna. The horizontal and vertical portions of L-strip coupling feed two radiation elements, respectively. It can provide a pair of orthogonal E-fields. Also, the feeding mechanism can adjust impedance matching and suitable phase difference to achieve a RHCP condition. Besides, changing the location of horizontal and vertical portions of L-strip can achieve LHCP easily. Secondly, the design is a T-Strip-fed patch antenna with reconfigurable polarization. It uses T-strip coupling feed two radiation elements to achieve a LP condition. In addition, the antenna can change polarization from LP to LHCP or RHCP conditions by bending the antenna. The antenna does not use another element to change polarization. Lastly, the design is a patch antenna with a varactor. This antenna uses an impedance matching coupling a radiation element to provide a pair of orthogonal E-fields. Besides, we put a varactor on feeding network and use bias to tune the varactor to provide a 90 phase. Then, we can achieve a CP radiation.

This thesis provides several designs of broadband microstrip antennas for the use in WLAN applications. It also highlights the novel reconfigurable microstrip antenna design. The main objective of this thesis is to design a novel microstrip antenna that is broadband, circularly polarized, multiband, reconfigurable and easy-to-fabricate. The thesis, in the first stage, presents a review of various different options available when designing and manufacturing wideband microstrip antennas. The review includes basic theory of microstrip patch antennas, matching techniques and broadbanding techniques. The second stage concentrates on the development of a couple of working prototype antenna designs and finally presents the design of a reconfigurable antenna that can perform over several frequency bands. The shapes of broadband patch antennas used are rectangular, circular and triangular. The multiple resonance technique is used in the design of the broadband antennas. Numerical and measured results are presented and discussed. The proposed patch antennas give measured bandwidth up to 28.5%. The reconfigurable antenna on the other hand is designed to possess frequency and polarization reconfigurability, and can operate in six different frequency bands. In addition to the bandwidth advantage, the proposed configuration offers easy reconfigurability with the ability to exclude switches in the combination part of the feed network. The important aspect of this design is that it provides a high size reduction for all the operating frequencies compared to conventional rectangular patches. Besides compactness all proposed antennas have gain better than 7dB. The proposed antennas are found to be suitable for WLAN standards.

博士
義守大學
電機工程學系
102
This dissertation presents a series of design of active reconfigurable polarization microstrip antenna in wireless local area network. The proposed antennas are designed as the single feed structure with the microstrip circuit module. The circuit module consists of microstrip line, pass component and active component. The circuit module can be managed to control the surface current on radiator and function as the reconfigurable switching of circular polarization modes for the proposed antennas. First antenna design uses the capacitor to control the phase of microstrip line and being reached the dual circular polarization. Second antenna design and third antenna design can be switched the circular polarization modes by using of the PIN diodes and the perturbing structure. Fourth antenna design is the stack structure with dual circular polarization. In this dissertation, the advantages of the four antennas are the small size, the function as reconfigurable polarization and the dual circular polarization radiation. The proposed antennas can be improved the receiving quality of products and reduced the number of antennas on the system. Details of the antenna design are shown, and the simulated and measured results are also presented and discussed.

Communication and reconnaissance systems are requiring increasing flexibility concerning functionality and efficiency for multiband and broadband frequency applications. Circuit-based reconfiguration mechanisms continue to promote radio frequency (RF) application flexibility; however, increasing limitations have resulted in hindering performance. Therefore, the implementation of a "wireless" reconfiguration mechanism provides the required agility and amicability for microwave circuits and antennas without local overhead. The wireless reconfiguration mechanism in this thesis integrates dynamic, fluidic-based material systems to achieve electromagnetic agility and reduce the need for "wired" reconfiguration technologies. The dynamic material system component has become known as electromagnetically functionalized colloidal dispersions (EFCDs). In a microfluidic reconfiguration system, they provide electromagnetic agility by altering the colloidal volume fraction of EFCDs - their name highlights the special considerations we give to material systems in applied electromagnetics towards lowering loss and reducing system complexity. Utilizing EFCDs at the RF device-level produced the first circuit-type integration of this reconfiguration system; this is identified as the coaxial stub microfluidic impedance transformer (COSMIX). The COSMIX is a small hollowed segment of transmission line with results showing a full reactive loop (capacitive to inductive tuning) around the Smith chart over a 1.2 GHz bandwidth. A second microfluidic application demonstrates a novel antenna reconfiguration mechanism for a 3 GHz microstrip patch antenna. Results showed a 300 MHz downward frequency shift by dielectric colloidal dispersions. Magnetic material produced a 40 MHz frequency shift. The final application demonstrates the dynamically altering microfluidic system for a 3 GHz 1x2 array of linearly polarized microstrip patch antennas. The parallel microfluidic capillaries were imbedded in polydimethylsiloxane (PDMS). Both E- and H-plane designs showed a 250 MHz frequency shift by dielectric colloidal dispersions. Results showed a strong correlation between decreasing electrical length of the elements and an increase of the volume fraction, causing frequency to decrease and mutual coupling to increase. Measured, modeled, and analytical results for impedance, voltage standing wave ratio (VSWR), and radiation behavior (where applicable) are provided.