Σκοπός της συγκεκριμένης εργασίας είναι η μελέτη και η σχεδίαση τυπωμένων κεραιών ανεστραμμένου – F για φορητές τερματικές συσκευές. Οι κεραίες αυτές χρησιμοποιούνται σε κινητά τερματικά, όπως κινητά τηλέφωνα, φορητοί υπολογιστές, PDA κ.τ.λ. και παρουσιάζουν πολλά πλεονεκτήματα, με κυριότερα το χαμηλό κόστος, την ευκολία κατασκευής, το μικρό τους μέγεθος και τη δυνατότητα μαζικής παραγωγής. Αρχικά στο πρώτο κεφάλαιο παρουσιάζονται ορισμένες γενικές βασικές αρχές των κεραιών και εισάγεται η έννοια της ηλεκτρικά μικρής κεραίας. Επίσης παρουσιάζεται η κεραία ανεστραμμένου – F και διατυπώνεται η θεωρία των ειδώλων στην οποία βασίζεται η αρχή λειτουργίας της συγκεκριμένης κεραίας. Στο κεφάλαιο 2 αναφέρονται οι προτάσεις και οι υλοποιήσεις που έχουν γίνει μέχρι στιγμής για την κεραία ανεστραμμένου – F στην βιβλιογραφία ενώ στη συνέχεια (κεφάλαια 3 μέχρι 7) παρουσιάζονται αναλυτικά ορισμένες κεραίες που έχουν κάποια επιπλέον πλεονεκτήματα ως προς τις υπόλοιπες ομοειδείς. Ιδιαίτερη βάση δόθηκε στις κεραίες που καλύπτουν τις ISM ζώνες στα 2.4 GHz και 5.2/5.8 GHz εξαιτίας της ευρύτατης χρήσης των ζωνών αυτών.Τέλος στο κεφάλαιο 9 επιχειρείται μια μικρή εισαγωγή στα συστήματα απόκλισης χώρου με την παρουσίαση και αξιολόγηση ενός συστήματος με τέσσερις κεραίες. / This diploma thesis includes the analysis, design and simulation of printed inverted - F antennas for dual band operating portable terminal devices. These antennas are widely used in mobile phones,laptops, PDAs,etc and have many advantages over other printed antennas such as extremely low cost, fabrication flexibility and compact size.

The beginning of the 21 st century is characterised, among others, by the evolution in telecommunications. The rapid growth of mobile communications and the variety of applications proposed for the third generation (3G) systems require long operation time, low weight and cost for terminals, as well as improved link quality. For this reason a good efficiency and low profile antennas with low absorption losses by the user are desirable. The Planar Inverted-F Antenna (PIFA) is shown to result into low SAR values and high efficiency when operating in the proximity of the user. Despite these advantages, PIFA is also characterised by narrow bandwidth that limits its practical use. The first part of this work is dedicated to the measurements and evaluation of the radiation characteristics of the PIFA and other wire antennas both in the near and far fields. In addition, novel methods of PIFA tuning are presented. These include the repositioning of the shorting pin and modification of its capacitance. By using these techniques, the effective bandwidth of the PIFA can be increased to satisfy the GSM900 and DCS 1800 system bandwidth requirements. Dual-band and electronically tuned PIFA prototypes are also included. The effects of the handset size on the mass averaged Specific Absorption Rate (SAR), and antenna efficiency are investigated. The appropriate choice of handset can result in up to 30%-reduced peak SAR. The computed SAR values from PIFA are compared with those resulting from the use of a handset equipped with quarter wavelength monopole antenna. A new measure referred to as the 3dB SAR volume is proposed. This measure provides better understanding of the absorbed power distribution in the operator's head. Results obtained in the course of study show that low profile handset antennas, such as the PIFA, present in addition to dual resonance and low reflection losses, reduced SAR values, high efficiency and low 3dB SAR volume. Finally, SAR and 3dB SAR volume values from simulations on 5- and 10- years old child head models are compared with their equivalents for adult models from which appropriate conclusions are drawn.

In this thesis, the studies mainly focus on recent trends in novel MIMO antennas for indoor wireless communication system. Firstly, we propose a novel MIMO antenna for access-point application. This proposed antenna can reduce the lateral length of the conventional access-point antenna for MIMO application. Then, we present MIMO antenna designs for mobile devices such as PDA phones and laptop computers. Although these two devices are of different configurations, the PIFAs are applicable in these two devices, and their design rules are basically the same. Thus, for this study, the design consideration of the MIMO antenna will focus on S-parameter analysis. Detailed antenna designs and experimental results are presented and discussed in this thesis.

In this dissertation, thin internal antennas for mobile communication devices with a total thickness of less than 10 mm are proposed. There are mainly two differences in the antenna¡¦s construction between the proposed thin internal antennas and conventional planar inverted-F antenna. The first proposed antenna for thin internal antenna is a combo type formed by combining the conventional inverted-F antenna with the monopole antenna. The second proposed antenna is obtained by integrating two radiating arms into a radiating patch. By adjusting the tapering angle and the direction of the end portions, thin internal planar antenna with a thickness of less than 4 mm can be successfully achieved. In these two antennas, their Q-value can be lowered, and then the impedance bandwidth can be effectively improved. This kind of thin internal antennas not only has good impedance matching but also shows good radiation performance. Additionally, by adding a vertical metal wall acting as a RF shielding wall, EM fringing fields between the thin internal EMC antenna and nearby metal components can be effectively supressed. This kind of EMC antennas can effectively eliminate the isolation distance between the antenna and nearby conducting elements to increase the available space on the printed circuit board for additional functions. Besides, multi-band operation is another important function in current mobile devices. In this dissertation, we also studied the effects of the plastic casing and the user¡¦s hand and head on the antenna charateristics. For studying the antenna with the presence of the user¡¦s hand and head, the simulation model provided by SPEAG simulation software SEMCAD is used. From the results obtained, it is seen that the frequency detuning is greatly dependent on the presence of the user¡¦s hand and head. Owing to the presence of the user¡¦s hand and head, large decrease in the radiation efficiency is seen. It also indicates that the radiation efficiency decrease and radiation pattern distortion are mainly owing to the radiation power absorption by the user¡¦s hand and head.

There are large groundplane variations for the folder-type mobile phone in the talk and idle conditions, which makes its embedded antennas not easy to maintain good radiation characteristics in the two states. The radiation efficiencies in the idle condition are often less than 15%. To solve this problem, two novel antennas for the folder-type mobile phone are proposed. The first antenna is the coplanar coupled-fed planar inverted-F antenna. The antenna can cover GSM850/900/DCS/PCS operation in the talk condition, and the radiation efficiencies over the desired operating bands in the idle condition is larger than 32%, which is acceptable for practical applications for the folder-type mobile phone. The second antenna is the ultra-wideband coupled-fed loop antenna. The antenna can cover GSM850/900/DCS/PCS/UMTS penta-band operation in the talk condition. In the idle condition, good performances over the five operating bands can still be obtained, and the radiation efficiencies are better than 53%. The effects of the housing and the user's hand and head on the antenna are also studied. From the obtained results, it is seen that the effects of the housing on the radiation efficiencies are small. However, since the user's hand and head are high-loss materials, large decrease in the radiation efficiencies is usually observed.

The main objective of this research is to design, model and implement several antenna geometries using electromagnetic band gap (EBG) material and a defected ground plane. Several antenna applications are addressed with the aim of improving performance, particularly the mutual coupling between the elements. The EBG structures have the unique capability to prevent or assist the propagation of electromagnetic waves in a specific band of frequencies, and have been incorporated here in antenna structures to improve patterns and reduce mutual coupling in multielement arrays. A neutralization technique and defected ground plane structures have also been investigated as alternative approaches, and may be more practical in real applications. A new Uni-planar Compact EBG (UC-EBG) formed from a compact unit cell was presented, giving a stop band in the 2.4 GHz WLAN range. Dual band forms of the neutralization and defected ground plane techniques have also been developed and measured. The recorded results for all antenna configurations show good improvement in terms of the mutual coupling effect. The MIMO antenna performance with EBG, neutralization and defected ground of several wireless communication applications were analysed and evaluated. The correlation coefficient, total active reflection coefficient (TARC), channel capacity and capacity loss of the array antenna were computed and the results compared to measurements with good agreement. In addition, a computational method combining Genetic Algorithm (GA) with surface meshing code for the analysis of a 2×2 antenna arrays on EBG was developed. Here the impedance matrix resulting from the meshing analysis is manipulated by the GA process in order to find the optimal antenna and EBG operated at 2.4 GHz with the goal of targeting a specific fitness function. Furthermore, an investigation of GA on 2×2 printed slot on DGS was also done.

Abstract In this thesis, bandwidth (BW) enhanced antennas for mobile terminals and multilayer ceramic packages are presented. The thesis is divided into two parts. In the first part, electrically frequency-tunable mobile terminal antennas have been studied. The first three antennas presented were of a dual-band planar inverted-F type (PIFA) and were tuned to operate in frequency bands appropriate to the GSM850 (824–894 MHz), GSM900 (880–960 MHz), GSM1800 (1710–1880 MHz), GSM1900 (1850–1990 MHz) and UMTS (1920–2170 MHz) cellular telecommunication standards with RF PIN diode switches. The first antenna utilized a frequency-tuning method developed in this thesis. The method was based on an integration of the tuning circuitry into the antenna. The tuning of the second antenna was based on a switchable parasitic antenna element. By combining the two frequency-tuning approaches, a third PIFA could be switched to operate in eight frequency bands. The planar monopole antennas researched were varactor-tunable for digital television signal reception (470–702 MHz) and RF PIN diode switchable dual-band antenna for operation at four cellular bands. The key advantage of the former antenna was a compact size (0.7 cm3), while for the latter one, a tuning circuit was implemented without using separate DC wiring for controlling the switch component. The second part of the thesis is devoted to multilayer ceramic package integrated microwave antennas. In the beginning, the use of a laser micro-machined embedded air cavity was proposed to enable antenna size to impedance bandwidth (BW) trade-off for a microwave microstrip in a multilayer monolithic ceramic media. It was shown that the BW of a 10 GHz antenna fabricated on a low temperature co-fired ceramic (LTCC) substrate could be doubled with this technique. Next, the implementation of a compact surface mountable LTCC antenna package operating near 10 GHz was described. The package was composed of a BW optimized stacked patch microstrip antenna and a wide-band vertical ball grid array (BGA)-via interconnection. Along with the electrical performance optimization, an accurate circuit model describing the antenna structure was presented. Finally, the use of low-sintering temperature non-linear dielectric Barium Strontium Titanate (BST) thick films was demonstrated in a folded slot antenna operating at 3 GHz and frequency-tuned with an integrated BST varactor.

This work describes an electrically small antennas used for mobile devices in the ISM band. The aim of this work is to select an antenna for a universal transmitter/receiver working in the 868 MHz band. The work contains description of the universal transmitter/receiver, and a list of suitable antennas. Tolerance analysis is performed by numerical model. The proposed antenna is manufactured and measured.

The main objective of this research is to design, model and implement several antenna geometries using electromagnetic band gap (EBG) material and a defected ground plane. Several antenna applications are addressed with the aim of improving performance, particularly the mutual coupling between the elements. The EBG structures have the unique capability to prevent or assist the propagation of electromagnetic waves in a specific band of frequencies, and have been incorporated here in antenna structures to improve patterns and reduce mutual coupling in multielement arrays. A neutralization technique and defected ground plane structures have also been investigated as alternative approaches, and may be more practical in real applications. A new Uni-planar Compact EBG (UC-EBG) formed from a compact unit cell was presented, giving a stop band in the 2.4 GHz WLAN range. Dual band forms of the neutralization and defected ground plane techniques have also been developed and measured. The recorded results for all antenna configurations show good improvement in terms of the mutual coupling effect. The MIMO antenna performance with EBG, neutralization and defected ground of several wireless communication applications were analysed and evaluated. The correlation coefficient, total active reflection coefficient (TARC), channel capacity and capacity loss of the array antenna were computed and the results compared to measurements with good agreement. In addition, a computational method combining Genetic Algorithm (GA) with surface meshing code for the analysis of a 2×2 antenna arrays on EBG was developed. Here the impedance matrix resulting from the meshing analysis is manipulated by the GA process in order to find the optimal antenna and EBG operated at 2.4 GHz with the goal of targeting a specific fitness function. Furthermore, an investigation of GA on 2×2 printed slot on DGS was also done. / Ministry of Higher Education Malaysia and Universiti Tun Hussein Onn Malaysia (UTHM)

The performance of commercial Radio Frequency Identification (RFID) tags is primarily limited by present techniques used for tag antenna design. Currently, industry techniques rely on identifying the RFID tag application (books, clothing, etc.) and then building antenna prototypes of different configurations in order to satisfy minimum read range requirements. However, these techniques inherently lack an electromagnetic basis and are unable to provide a low cost solution to the tag antenna design process. RFID tag performance characteristics (read-range, chip-antenna impedance matching, surrounding environment) can be very complex, and a thorough understanding of the RFID tag antenna design may be gained through an electromagnetic approach in order to reduce the tag antenna size and the overall cost of the RFID system. The research presented in this thesis addresses RFID tag antenna design process for passive RFID tags. With the growing number of applications (inventory, supply-chain, pharmaceuticals, etc), the proposed RFID antenna design process demonstrates procedures to design tag antennas for such applications. Electrical/geometrical properties of the antennas designed were investigated with the help of computer electromagnetic simulations in order to achieve optimal tag performance criteria such as read range, chip-impedance matching, antenna efficiency, etc. Experimental results were performed on the proposed antenna designs to compliment computer simulations and analytical modelling.