Low-SAR Miniaturized Handset Antenna Using EBG

Advances in wireless communications have paved the way for wide usage of mobile phones in modern society, resulting in mounting concerns surrounding its harmful radiation. Energy absorption in human biological tissues can be characterized by specific absorption rate (SAR). This value refers to the actual amount of electromagnetic energy absorbed in the biological tissues, thus a lower value of SAR indicates a lower radiation exposure risk to the human body. So, our challenge is to introduce mobile handset antennas with low SAR and operating at all mobile and wireless applications. In this chapter, novel configurations of single-element antenna are designed, simulated, fabricated, and measured. The antennas operate for most cellular applications: global system for mobile (GSM)-850/900, digital cellular system (DCS)-1800, personal communication service (PCS)-1900, universal mobile telecommunication system (UMTS)-2100, and long-term evolution (LTE) bands. The antennas also support wireless applications. The proposed antennas have a compact size and low SAR at all bands. Also, this chapter presents a comprehensive study on the performance of the antenna in the different environments. Furthermore, the antenna performance is tested in the presence of head and hand in free space and in a car. The simulation and measurement results are in good agreement

Techniques to reduce the Mutual Coupling and to improve the Isolation between antennas in a Diversity System

En los últimos años, la demanda de nuevas aplicaciones y servicios para dispositivos móviles ha experimentado un gran incremento. Estas nuevas aplicaciones necesitan una velocidad de bits mayor para funcionar correctamente. En este escenario, se implementan varios sistemas MIMO (Multiple In-Multiple Out). En los sistemas MIMO, se ubican múltiples antenas dentro de los dispositivos para aprovechar la diversidad que proporcionan estos sistemas. Una condición para lograr este propósito se basa en la relación entre antenas, esto significa baja correlación y alto aislamiento. El problema con los dispositivos móviles debido a su pequeño tamaño es la corta distancia entre antenas que aumenta la correlación y reduce el aislamiento. Esta tesis se centra en la investigación de una solución óptima que mejore el aislamiento de antenas en teléfonos móviles. Para este propósito se han utilizado tres tipos de antenas: ILA (Inverted-L Antenna), IFA, (Inverted-F Antenna), y PIFA (Planar Inverted-F Antenna). Y se han probado dos métodos para aumentar el aislamiento: paredes dieléctricas y plano de tierra dieléctrico DGP.Erasmus (solamente la tesis final de carrera se hizo en la Universidad de Aalborg en Dinamarca bajo el marco de la beca Erasmus. El resto de la carrera se hizo en la Universidad de Oviedo sin beca.)Tesi

Design of high-efficiency antennas for mobile communications devices

This thesis deals with the design of high-efficiency antennas for small mobile communications devices. Owing to the continuously stricter requirements set for multisystem mobile terminals, the ongoing need for efficient antennas in personal mobile communications is evident. In this work, the entire system consisting of the antenna; the mobile terminal working actually as part of the antenna; and the user of the terminal is considered. The ratio between the power radiated into the free space and the antenna input power, i.e. the total efficiency of this system, forms a general concept for the studies. The total efficiency is partly affected by the losses in the antenna element. As the antenna efficiency, bandwidth, and volume are strongly interrelated exchangeable quantities, it is essential to find other approaches for enhancing the antenna efficiency than simply sacrificing other performance. Further, the metal chassis of a mobile terminal has to be part of the antenna element design because of its considerable effect on antenna performance. In addition, the total efficiency of the entire system is partly affected by the losses owing to the user. Thus, the evaluation of antenna performance is equally important when the mobile terminal is located near a user or when it is in free space. The main goal of this work is to provide novel and useful information for the design of mobile terminal antennas with special emphasis placed on the maximization of the total efficiency. To obtain necessary background understanding for the design of antennas with minimized user interaction, the general energy-absorption mechanism in the human tissue is studied in this thesis. It is shown that the peak SAR (specific absorption rate) is not actually related to the antenna current, as has been commonly believed. Instead, the SAR maximums can be explained by inspecting the antenna's quasi-static electric near field components perpendicular and parallel to the surface of the tissue at the air-tissue interface and utilizing the boundary conditions of quasi-static fields at the interface. As SAR is directly proportional to the total electric field in the tissue, the SAR distributions caused by a certain antenna differ considerably in tissues with different permittivity values, e.g. brain and fat. The bandwidth, efficiency in talk position, and SAR performance of a typical monoblock handset antenna-chassis combination is comprehensively investigated in this work for clarifying the roles of different parts of the radiating system. The system is treated as a combination of the separate wavemodes of the antenna element and the chassis. Based on the results, guidelines are given to control or analyze the combined performance both in the sense of radiation properties (bandwidth, efficiency) and user interaction (SAR). It is also demonstrated that there is a connection between the studied three performance parameters: a local maximum in SAR values and a local minimum in radiation efficiency occur when the bandwidth reaches its maximum and the resonant frequency of the chassis equals that of the antenna. The suitability of dielectric resonator antennas (DRA) for mobile terminals is studied theoretically and experimentally with the main attention paid to the loss characteristics. It is observed that DRAs are appropriate for this purpose especially when very small antenna elements are needed. As an application example, a novel means to realize a high-performance dual-resonant antenna design for mobile terminals is presented. In addition, losses in the frequency-tuning circuits of small resonant antennas are systematically investigated. Design guidelines for tuning circuits with minimized losses with respect to the achievable tuning range are given. Based on the proposed theory, a low-loss tuning circuit with suitable characteristics for mobile terminal antennas is introduced.reviewe

Kannettavan DVB-vastaanottimen ja monijärjestelmäradion antennit

In this licentiate thesis the implementation of small internal DVB-H antennas for handheld multisystem radios is studied, and several prototypes and simulated designs are presented and evaluated. Since the volume that can be reserved for antennas is very restricted, the limits for the size of capacitive coupling element based antenna structures inside handsets of different size were studied. The results indicate that the smallest required volume of the coupling element which ensures sufficient performance in today's typical-size monoblock mobile handsets would be about 3 - 4 cm3. Instead, for tablet-size and open clamshell-size terminals the antenna element are shown to be significantly smaller and thinner. Direct-feed-based structures can provide very low profile antenna solutions for tablet and clamshell-type terminals. The effect of the user on performance of the DVB-H antenna was studied for some cases. Maximum of 5 - 9 dB decrease in the total efficiency was shown and thus the effect of the user seems to be a significant challenge for the operation of DVB-H. Relatively low isolation, about 18 dB, between the DVB-H and GSM900 antennas was demonstrated and thus the interoperability of DVB-H and GSM900 systems seems impossible without additional filtering.Tässä lisensiaattityössä on tutkittu sisäisen DVB-H-antennin toteuttamista monijärjestelmäpäätelaitteessa ja esitetty muutamia antenniprototyyppejä ja simuloituja antennikonstruktioita. Koska antenneille varattu tila päätelaitteen sisällä on rajallinen, työssä on tutkittu pienimmän mahdollisen kytkentäelementtiin perustuvan antennin vaatimaa tilavuutta erikokoisissa päätelaitteissa. Tutkimuksen tuloksena esitetään, että riittävään suorituskykyyn tyypillisen kokoisessa päätelaitteessa päästään kytkentäelementillä, jonka tilavuus on noin 3 - 4 cm3. Tabletti- ja avonaisessa simpukkapäätelaitteessa riittää tilavuudeltaan ja korkeudeltaan huomattavasti kompaktimpi antennielementti tai suorasyöttörakenne. Työssä tutkittiin myös käyttäjän vaikutusta DVB-H-antennin toimintaan. Simuloimalla tehty tutkimus osoitti, että käyttäjä voi aiheuttaa jopa 5 - 9 desibelin häviöt kokonaishyötysuhteeseen. Simuloidussa esimerkkikonstruktiossa osoitettiin, että DVB-H- ja GSM900-antennien välillä on noin 18 desibelin isolaatio, joka ei riitä takaamaan järjestelmien samanaikaista toimintaa, vaan isolaatiota jouduttaisiin kasvattamaan muilla keinoilla

Design and Analysis of Various Handset Antennas with the Aid of HFSS

In this thesis, an attempt is made to present the design of handset antennas, the proposed handset acts as a thin wire model that represents the backbone of the final antenna. The designed antenna parameters are subjected to optimization to fit into the desired frequency bands. Different antenna types are used, such as wire antennas and planar antennas designed using theHFSS.The design of basic antennas for handset applications, experimented with a simple monopole and dipole in a 3-D form. The monopole and dipole used in handset antennas provides multi-band and broadband properties that cover the desired frequency bands in the handset antennas. The design experiment and analysis of a continuous and unbroken metal rimmed antenna with a monopole which is directly fed with a patch acts as aloo antenna in smart phone applications is proposed. The antenna proposed here provides a straight forward and a good multi-band antenna result for anprotected metal rimmed smart phone. The protected rim and two no-ground portions are set on the both the top and bottom sides of the system circuit board, respectively. The system ground is surrounded between the two no ground portions which are connected to the metal rim with a small grounded patch which divides the unbroken metal rim into two strips. Atlast the dualloop antenna is formed by adjusting the ground plane and the micro strip ina proper way. The design antenna is operated on several number of GSM bands.The second design is study of a balanced antenna with folded architecturefor mobile handset applications with dual-frequency performance (2.40 GHzand 5.00 GHz) for WLAN applications are discussed. The thin-strip planardipole is used as an antenna with folded architecture and two arms on eachmonopole. The folded architectures one on the left and other on the rightacts as a dipole and are capable of providing the multiple bands .The antenna performance is featured by using the antenna radiation pattern,returnloss, power gain and surface current distribution of the antenna. The parametric studies are carried out by varying the antenna height and width of1 mm each, the parameters are optimized for steered impedance matchingwithin the range of frequency bands for both the WLAN and short distance communication systems.The third design is focused on the frequency band (1.8 GHz to 2.45 GHz)in which the balanced antenna for applications of mobile handsets with abandwidth of highly improved performance. The slot planar dipole is usedan antenna here with folded architecture and is having a dual arm on boththe sides of the ground plane. The S-parameter method is used to findthe antenna impedance. In order to obtain the power gain measurementin the antenna.The balanced feed from an unbalanced source is supportedby planar balun which is of wide bandwidth to get the desired gain. The results measured provides a good agreement and also provides good wideband characteristic

Ground plane booster antenna technology for wireless handheld devices

This thesis is framed in the field of mobile communications and more particularly in handset antennas. The wireless industry is constantly growing, which entails challenging handset antenna specifications. Handset antennas not only have to be multi-band for satisfying the great number of communication services, but also sufficiently small as for fitting in the reduced space imposed by the handset platforms. The appearance of the MIMO (Multiple Input Multiple Output) technology, further exacerbates these challenges. In order to satisfy these requirements, this thesis proposes the use of the ground plane, inherently present in any handset platform, as the main radiator. Electrically small nonresonant elements, called along this thesis as ground plane boosters, are used to transfer energy to this ground plane. The solution removes the need of including a dedicated antenna featured by considerable dimensions, thus releasing space to integrate other antennas, as well as, other handset components, services and functionalities.Postprint (published version

Study of UHF and VHF Compact Antennas

This thesis presents and describes designs of small antennas that operate in UHF and VHF frequency bands. The proposed antennas are designed for integration into small volumes, therefore low profile, compact size and good radiation properties are the key parameters in this work. A further investigation on miniaturization techniques, as well as the ground plane effects on the general performance, is also made. The main objective is the design of novel compact sized geometries, lightweight and cost efficient, operating in the lower UHF and VHF frequency bands. The groundplane size and the antenna position with respect to it, are two parameters which are investigated and contribute to optimum design performance. Compact solutions are realised in this work based on folded, meander-line and inverted-F geometries providing broadband operation and omnidirectional radiation properties. The investigation of broadband properties of a dual band folded monopole led to a controllable frequency-ratio with wide range, operating in the WLAN frequency spectrum. The proposed solution offers high efficiency and gain and stable omnidirectionality across the operating frequency band. The study also deals with planar inverted-F antennas (PIFA) operating in the LTE frequency bands. The two highly efficient broadband antennas provide compactness, gain stability and are fabricated using low-cost materials. By configuring an optimised position of the PIFA on the groundplane, the impedance bandwidth, the gain and the total efficiency can be significantly improved. A more compact solution of a dual band PIFA structure is provided with omnidirectional radiation characteristics and large frequency ratio for machine-to-machine applications. A novel tuneable meander line structure operating over the frequency range of 412 − 475 MHz is designed for integration into smart meter devices. The resonant frequency of this antenna can be tuned using a sliding via connector. A matching stub is introduced into the proposed geometry to improve the impedance matching and to shift the resonant frequency to lower values. This innovative solution overcomes material loading problems when installed on a concrete wall, as well as the S11 characteristic are not impaired with the small sized ground plane. Finally, a dual band meander line folded monopole antenna in the lower UHF and VHF frequency bands is proposed for smart metering and Wireless M-Bus applications. The miniaturization of the proposed solution is based on a double-sided meandering structure which also offers good isolation between the two sections and an easily controlled large frequency-ratio. The introduction of a shunt lumped inductor improves the impedance matching at both frequencies. The antenna despite its compact size offers high total efficiency and gain across the operating frequency bands

Fixed and reconfigurable multiband antennas

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel UniversityWith the current scenario of development of antennas in the wireless communication field, the need of compact multiband, multifunctional and cost effective antenna is on the rise. The objective of this thesis is to present fixed and reconfigurable techniques and methods for small and slim multiband antennas, which are applicable to serve modern small and slime wireless, mobile and cognitive radio applications. In the fixed designs, independent control of the operating frequencies is investigated to enhance the antennas capabilities and to give the designer an additional level of freedom to design the antenna for other bands easily without altering the shape or the size of the antenna. In addition, for mobile phone antenna, the effect of user’s hand and mobile phone housing are studied to be with minimum effect. Although fixed multiband antennas can widely be used in many different systems or devices, they lack flexibility to accommodate new services compared with reconfigurable antennas. A reconfigurable antenna can be considered as one of the key advances for future wireless communication transceivers. The advantage of using a reconfigurable antenna is to operate in multiband where the total antenna volume can be reused and therefore the overall size can be reduced. Moreover, the future of cell phones and other personal mobile devices require compact multiband antennas and smart antennas with reconfigurable features. Two different types of frequency reconfigurability are investigated in this thesis: switchable and tunable. In the switchable reconfigurability, PIN diodes have been used so the antenna’s operating frequencies can hop between different services whereas varactor diode with variable capacitance allow the antenna’s operating frequencies to be fine-tuned over the operating bands. With this in mind, firstly, a switchable compact and slim antenna with two patch elements is presented for cognitive radio applications where the antenna is capable of operating in wideband and narrow bands depending on the states of the switches. In addition to this, a switchable design is proposed to switch between single, dual and tri bands applications (using a single varactor diode to act as a switch at lower capacitance values) with some fine tuning capabilities for the first and third bands when the capacitance of the diode is further increased. Secondly, the earlier designed fixed antennas are modified to be reconfigurable with fine-tuning so that they can be used for more applications in both wireless and mobile applications with the ability to control the bands simultaneously or independently over a wide range. Both analytical and numerical methods are used to implement a realistic and functional design. Parametric analyses using simulation tools are performed to study critical parameters that may affect the designs. Finally, the simulated designs are fabricated, and measured results are presented that validate the design approaches