In this study, we design and fabricate novel tag antennas, which can be used on the metallic surface for radio frequency identification systems. We first focus on the effects when the antenna is placed on the metallic surface. Based on the simulation results, we investigate how the parameters of the antennas are affected. The helps us find solutions to reduce the effects when the antennas are placed on the metallic surface. In order to conform to the IC chips of RFID and reduce the influence of metal objects, we use the structure of the dipole antenna is used as the basis of the novel tag antenna design. And we employ the high impedance surface periodic structure which behaves similarly to a perfect magnetic conductor in the design of the novel tag antenna. The novel tag antenna is able to work normally when it was attached on the surface of the carton or metallic object. Finally, the tag antenna is fabricated and measured in a chamber. The measured results agree with simulated ones well.

ABSTRACT In this study, the properties of the high impedance surface structure are studied. We proceed to design the low profile and miniature high impedance surface structure. In order to conform to the IC chips of RFID and reduce the influence of metal objects, we add a layer of electromagnetic band-gap (EBG) structure on the back of the antenna. The EBG behaves as a high impedance surface, similar to a perfect magnetic conductor. This property of the EBG structure is able to isolate the antenna and backside environment and reduce the metallic effect. In order to achieve the requirements of small size and low cost on RFID tag antenna, we design the miniature, low profile and low cost high impedance surface structure. In this study, we use the slots and chip capacitance to miniaturize the dimension. Both approaches can reduce the influence of metallic objects. Although using slots can reduce the metallic effect, it does not have the advantage of low profile. Using chip capacitor can miniaturize the dimension and reduce metallic effect effectively. It also has advantages of low profile, low cost and low sensitivity to the frequency of the tag antenna. Finally, the high impedance surface structures are fabricated and measured when they combine with the tag antenna attached to the metallic object. The measured results agree with simulated ones well.

In this thesis, the design rule of the tag antenna and the properties of the high impedance surface structure are studied. We proceed to design the low profile and miniature high impedance surface structure. In order to be more competitive, we use PCB plates for fabrication to reduce the cost. The tags are intended to be placed inside two shorted metallic plates. In order to reduce the effect of the two parallel metallic plates, we use the slots to design the tag antenna. The EBG structure behaves as a high impedance surface and suppresses the surface wave. We add the EBG structure on the back of the antenna to reduce the back metallic effect. We use slot structure to design the non-planar RFID reader antenna that can be placed inside the three metallic plates to read the data. For the slot structure design, the electric field between the slots is perpendicular to the upper and lower metallic plates. According to the image theory, the induced image current will result in constructive effect to reduce the metallic effect. Finally, the hand-held RFID reader may not identify the RFID tag as the RFID tag placed at position deeper inside. The proposed non-planar reader can solve this problem to be used for more applications.

abstract: In this dissertation a new wideband circular HIS is proposed. The circular periodicity made it possible to illuminate the surface with a cylindrical TEMz wave and; a novel technique is utilized to make it wideband. Two models are developed to analyze the reflection characteristics of the proposed HIS. The circularly symmetric high impedance surface is used as a ground plane for the design of a low-profile loop and spiral radiating elements. It is shown that a HIS with circular periodicity provides a wider operational bandwidth for curvilinear radiating elements such, such as loops and spirals, compared to canonical rectangular HISs. It is also observed that, with the aid of a circular HIS ground plane the gain of a loop and a spiral increases compared to when a perfect magnetic conductor (PMC) or rectangular HIS is used as a ground plane. The circular HIS was fabricated and the loop and spiral elements were placed individually in close proximity to it. Also, due to the growing demand for low-radar signature (RCS) antennas for advanced airborne vehicles, curved and flexible HIS ground planes, which meet both the aerodynamic and low RCS requirements, have recently become popular candidates within the antenna and microwave technology. This encouraged us, to propose a spherical HIS where a 2-D curvature is introduced to the previously designed flat HIS. The major problem associated with spherical HIS is the impact of the curvature on its reflection properties. After characterization of the flat circular HIS, which is addressed in the first part of this dissertation, a spherical curvature is introduced to the flat circular HIS and its impact on the reflection properties was examined when it was illuminated with the same cylindrical TEMz wave. The same technique, as for the flat HIS ground plane, is utilized to make the spherical HIS wideband. A loop and spiral element were placed in the vicinity of the curved HIS and their performanceswere investigated. The HISs were also fabricated and measurements were conducted to verify the simulations. An excellent agreement was observed. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2018

abstract: High Impedance Surfaces (HISs), which have been investigated extensively, have proven to be very efficient ground planes for low profile antenna applications due to their unique reflection phase characteristics. Another emerging research field among the microwave and antenna technologies is the design of flexible antennas and microwave circuits to be utilized in conformal applications. The combination of those two research topics gives birth to a third one, namely the design of Conformal or Flexible HISs (FHISs), which is the main subject of this dissertation. The problems associated with the FHISs are twofold: characterization and physical realization. The characterization involves the analysis of scattering properties of FHISs in the presence of plane wave and localized sources. For this purpose, an approximate analytical method is developed to characterize the reflection properties of a cylindrically curved FHIS. The effects of curvature on the reflection phase of the curved FHISs are examined. Furthermore, the effects of different types of currents, specifically the ones inherent to finite sized periodic structures, on the reflection phase characteristics are observed. After the reflection phase characterization of curved HISs, the performance of dipole antennas located in close proximity to a curved HIS are investigated, and the results are compared with the flat case. Different types of resonances that may occur for such a low-profile antenna application are discussed. The effects of curvature on the radiation performance of antennas are examined. Commercially available flexible materials are relatively thin which degrades the bandwidth of HISs. Another practical aspect, which is related to the substrate thickness, is the compactness of the surface. Because of the design limitations of conventional HISs, it is not possible to miniaturize the HIS and increase the bandwidth, simultaneously. To overcome this drawback, a novel HIS is proposed with a periodically perforated ground plane. Copper plated through holes are extremely vulnerable to bending and should be avoided at the bending parts of flexible circuits. Fortunately, if designed properly, the perforations on the ground plane may result in suppression of surface waves. Hence, metallic posts can be eliminated without hindering the surface wave suppression properties of HISs. / Dissertation/Thesis / Ph.D. Electrical Engineering 2013

This dissertation is focused on design of compact electromagnetic magnetic band-gap structures (EBG). Several popular compact techniques are introduced and analyzed with equivalent surface impedance model. A novel compact EBG structure is investigated. Compared to the conventional uniplanar compact photonic band gap (UC-PBG) structure, a size reduction of 64.7% is achieved. A distinctive band gap is observed at 2.45 GHz with around 100 MHz bandwidth and zero reflection phase. Antenna applications of this novel EBG structure, including EBG patch antenna and EBG antenna array, have been presented. Simulation results further verify its characteristic of suppressing surface waves. For the EBG patch antenna, a more focused radiation pattern is obtained compared to a normal patch antenna. For an antenna array, the presence of EBG structure reduces the mutual coupling between the two radiating elements by 6 dB.

This thesis reports the development and analysis of high performance CMOS readout electronics for increasing the performance of MEMS gyroscopes developed at Middle East Technical University (METU). These readout electronics are based on unity gain buffers implemented with source followers. High impedance node biasing problem present in capacitive interfaces is solved with the implementation of a transistor operating in the subthreshold region. A generalized fully differential gyroscope model with force feedback electrodes has been developed in order to simulate the capacitive interfaces with the model of the gyroscope. This model is simplified for the single ended gyroscopes fabricated at METU, and simulations of resonance characteristics are done. Three gyroscope interfaces are designed by considering the problems faced in previous interface architectures. The first design is implemented using a single ended source follower biased with a subthreshold transistor. From the simulations, it is observed that biasing impedances up to several gigaohms can be achieved. The second design is the fully differential version of the first design with the addition of a self biasing scheme. In another interface, the second design is modified with an instrumentation amplifier which is used for fully differential to single ended conversion. All of these interfaces are fabricated in a standard 0.6 &micro / m CMOS process. Fabricated interfaces are characterized by measuring their ac responses, noise response and transient characteristics for a sinusoidal input. It is observed that, biasing impedances up to 60 gigaohms can be obtained with subthreshold transistors. Self biasing architecture eliminates the need for biasing the source of the subthreshold transistor to set the output dc point to 0 V. Single ended SOG gyroscopes are characterized with the single ended capacitive interfaces, and a 45 dB gain improvement is observed with the addition of capacitive interface to the drive mode. Minimum resolvable capacitance change and displacement that can be measured are found to be 58.31 zF and 38.87 Fermi, respectively. The scale factor of the gyroscope is found to be 1.97 mV/(&deg / /sec) with a nonlinearity of only 0.001% in &plusmn / 100 &deg / /sec measurement range. The bias instability and angle random walk of the gyroscope are determined using Allan variance method as 2.158 &deg / /&amp / #8730 / hr and 124.7 &deg / /hr, respectively.

This dissertation presents a detailed investigation on the development of a quasi Yagi antenna with end fire radiation at 2.4 GHz (ISM band) over a metal reflector. Realization of an end fire radiator on top of a metal ground is very difficult because the reflected waves and image currents from the ground degrade the frequency bandwidth and steer the radiation pattern in the broadside direction. This destructive interference is reduced in this research through two quasi Yagi-ground configurations. The first arrangement utilizes a substrate of suitable thickness (7.5mm-0.19 ?g) to displace the ground away from the antenna. The second design implements a high impedance surface (HIS) as ground plane for the antenna. The preferred HIS is the Jerusalem Cross Frequency Selective Surface (JC-FSS) because of its compact size, numerous parameters for tuning and frequency stability in the operating band for a large angular spectrum of TE and TM polarized incident waves. In this work a new parameter is added to the model used for the derivation of the JC-FSS which accounts for the substrate of the antenna lying on top of the FSS, this addition allows for a smaller cell grid. The results for the quasi Yagi antenna over the 7.5mm grounded slab presented an operational bandwidth of 190 MHz with 40°; of beam steering in the end fire direction while the quasi Yagi over the JC-FSS offered 260 MHz of functional bandwidth and 54° of beam steering towards the end fire direction. In addition, the quasi Yagi design over the JC-FSS decreases the combined profile (antenna/backing structure) by 33% in relation to the 7.5mm grounded slab. This dissertation combines for the first time a quasi Yagi antenna with a JC-FSS to achieve end fire radiation in the presence of a ground metal.

The conventional mushroom-like Sievenpiper structure is re-visited in this thesis and a relationship is established between the dispersion and reflection phase characteristics of the structure. It is shown that the reflection phase frequency at which the structure behaves as a Perfect Magnetic Conductor (PMC) can be predicted for varying angles of incidence from the modal distribution in the dispersion diagrams and corresponds to the supported leaky modes within the light cone. A methodology to independently tune the location of the PMC frequency point with respect to the surface wave band-gap location is then presented. The influence of having said PMC frequency point located inside or outside the surface wave band-gap on a dipole radiation pattern is then studied numerically. It is demonstrated that the antenna exhibits a higher gain when the PMC frequency and band-gap coincide versus when they are separated. Two design cases are then presented for when the aforementioned properties coincide and are separated and a gain improvement of 1.2 dB is measured for the former case.

The conventional mushroom-like Sievenpiper structure is re-visited in this thesis and a relationship is established between the dispersion and reflection phase characteristics of the structure. It is shown that the reflection phase frequency at which the structure behaves as a Perfect Magnetic Conductor (PMC) can be predicted for varying angles of incidence from the modal distribution in the dispersion diagrams and corresponds to the supported leaky modes within the light cone. A methodology to independently tune the location of the PMC frequency point with respect to the surface wave band-gap location is then presented. The influence of having said PMC frequency point located inside or outside the surface wave band-gap on a dipole radiation pattern is then studied numerically. It is demonstrated that the antenna exhibits a higher gain when the PMC frequency and band-gap coincide versus when they are separated. Two design cases are then presented for when the aforementioned properties coincide and are separated and a gain improvement of 1.2 dB is measured for the former case.