Anja K. Skrivervik

Design, Realization and Measurements of a Miniature Antenna for Implantable Wireless Communication Systems

The design procedure, realization and measurements of an implantable radiator for telemetry applications are presented. First, free space analysis allows the choice of the antenna typology with reduced computation time. Subsequently the antenna, inserted in a body phantom, is designed to take into account all the necessary electronic components, power supply and bio-compatible insulation so as to realize a complete implantable device. The conformal design has suitable dimensions for subcutaneous implantation (10 × 32.1 mm). The effect of different body phantoms is discussed. The radiator works in both the Medical Device Radiocommunication Service (MedRadio, 401-406 MHz) and the Industrial, Scientific and Medical (ISM, 2.4-2.5 GHz) bands. Simulated maximum gains attain -28.8 and - 18.5 dBi in the two desired frequency ranges, respectively, when the radiator is implanted subcutaneously in a homogenous cylindrical body phantom (80 × 110 mm) with muscle equivalent dielectric properties. Three antennas are realized and characterized in order to improve simulation calibration, electromagnetic performance, and to validate the repeatability of the manufacturing process. Measurements are also presented and a good correspondence with theoretical predictions is registered.

Monolithic MEMS-Based Reflectarray Cell Digitally Reconfigurable Over a 360

In this letter, we present a reconfigurable reflectarray cell operating at 12 GHz and fabricated in a monolithic MEMS process. A 5-bit digital control allows reconfiguration of the reflection phase over the full 360deg range, while alleviating the impact of MEMS and bias voltage tolerances on the device performances. The designed reflectarray cell exhibits low frequency phase error (large bandwidth) and excellent measured reflection loss (-0.3 dB) with regard to state-of-the-art. Close agreement between measurements and full-wave simulations is observed.

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The main purpose of the System Fidelity Factor (SFF) is to incorporate frequency and time domain characteristics of an antenna system into a comparison method for ultrawideband (UWB) antennas. The SFF is an interesting tool because both simulations and measurements can be done in a simple and straight-forward manner. Simulations of a single antenna are combined into a two-antennas system analysis by means of a simple post-processing, where the transfer function of the transmitting and receiving antennas are calculated. Measurements of the SFF are done using a two port Vector Network Analyzer (VNA). The polar representation of the SFF allows an equitable comparison between antennas. The procedure to derive the SFF is described in detail in the paper. Two examples are given where the UWB performance of three antenna systems are compared. In the first example antenna systems of two identical monopoles are studied. In the second example the transmitting antenna is a Vivaldi and the receiving antenna a monopole.

Phase Range

A method for the analysis of large phased arrays of microstrip patches is presented. It is based on an infinite array approach where the edge effects are taken into account through the convolution with a proper window function. In the first step, a rigorous Greens function corresponding to a finite array of elementary sources is derived. This Greens function is then used to analyze the finite phased array of microstrip patches. Results are shown for the active impedance and element patterns of several arrays, and compared with measurements or, in the case of small arrays, with results obtained by a rigorous element-by-element approach. It is shown that the method, even if developed for the analysis of large arrays, is able to handle small arrays. Indeed, the results obtained are good even for single patches. Although the method has been developed for the microstrip phased array case, the results are general and are valid for any phased array with a rectangular grid. >

System Fidelity Factor: A New Method for Comparing UWB Antennas

This work presents the analysis of the influence of insulation on implanted antennas for biotelemetry applications in the Medical Device Radiocommunications Service band. Our goal is finding the insulation properties that facilitate power transmission, thus enhancing the communication between the implanted antenna and an external receiver. For this purpose, it has been found that a simplified model of human tissues based on spherical geometries excited by ideal sources (electric dipole, magnetic dipole and Huygens source) provides reasonable accuracy while remaining very tractable due to its analytical formulation. Our results show that a proper choice of the biocompatible internal insulation material can improve the radiation efficiency of the implanted antenna (up to six times for the investigated cases). External insulation facilitates the electromagnetic transition from the biological tissue to the outer free space, reducing the power absorbed by the human body. Summarizing, this work gives insights on the enhancement of power transmission, obtained with the use of both internal, biocompatible and external, flexible insulations. Therefore, it provides useful information for the design of implanted antennas.

Analysis of finite phase arrays of microstrip patches

This paper presents the modeling and design of one-dimensional metamaterial phase shifters (MPSs) in monolithic-microwave integrated-circuit technology based on the composite right/left-handed transmission-line approach. From a theoretical point-of-view, we show that existing design expressions are restricted to phase shifters behaving as effective media, which is the case only if sufficiently large L and C loading elements can be designed in the given technology and at the frequency of interest. Therefore, we propose new design expressions, which are exact on the basis of the circuit model of a unit cell in the structure. We show that the new expressions must be used to design integrated MPSs and the theory is verified by means of measurements of one- and two-cell phase shifters exhibiting a 0/spl deg/ phase shift at 17.5GHz. The designed one-cell phase shifter provides a -10-dB input return-loss bandwidth larger than 10% with phase shifts of +29/spl deg/ and -30/spl deg/ at 16.5 and 18.5 GHz, respectively. The insertion loss is -1.3 dB at the center frequency and -1.7 dB at the limit of the bandwidth.

The Effect of Insulating Layers on the Performance of Implanted Antennas

This paper proposes a novel, low-profile UWB antenna for wireless body area network (WBAN) applications. The antenna has a polarization perpendicular to the body-free-space interface, which is interesting in order to minimize the coupling into the body. Its structure comprises a modified mono-cone with a top-cross-plate and is coaxially fed through the ground plane. The higher frequency band |S11| performance is due to the mono-cone while the top-cross-plate is responsible for the lower frequency band. This plate also leads to a height reduction when compared to conventional mono-cone antennas. A comprehensive parametric study is done to provide design guidelines. Both frequency- and time-domain results have been measured and presented to validate the design. Results show that the antenna operates from 3.06 to beyond 12 GHz based on |S11| ≤ -10 dB, radiates omni-directionally in the H-plane, and has a radiation efficiency over 95%. The system-fidelity factor for UWB signals is adequate for pulse transmission. Finally, the influence of the human proximity on the antenna matching was tested. Results show that its impedance is nearly unchanged as compared to free-space.

Composite right/left-handed transmission line metamaterial phase shifters (MPS) in MMIC technology

This paper presents the modeling and design methods of true-time distributed microelectromechanical systems transmission lines (DMTLs) making use of periodic structure theory. New contributions to the analysis and reduction of the microelectromechanical systems (MEMS) shunt capacitors parasitics are also introduced. A prototype of a digital DMTL has been fabricated and measured, showing very good agreement with the comprehensive circuit model used for the design. It is believed that the periodic structure approach presented could be useful for other microwave periodic MEMS devices

A Novel, Low-Profile, Vertically-Polarized UWB Antenna for WBAN

Reference LEMA-ARTICLE-1998-001doi:10.1002/(SICI)1098-2760(19980220)17:3 3.0.CO;2-IView record in Web of Science Record created on 2006-11-30, modified on 2016-08-08

Modeling of periodic distributed MEMS-application to the design of variable true-time delay lines

A new compact coplanar-fed antenna suitable for polarization diversity in ultrawideband (UWB) applications is presented. The antenna consists of two identical monopoles that are printed on a low-loss substrate with 3 mm spacing and positioned perpendicular to each other. Both frequency- and time-domain results have been measured and presented to validate the design. Results show that the proposed antenna has not only ultra-wide bandwidth ( ~115% for port 1 and ~107% for port 2), but also good port isolation above 22 dB over the entire band of interest. Moreover, radiation patterns demonstrate good orthogonal polarization operation. Furthermore, the system fidelity factor is adequate for pulse transmission with averages of 85% and 75% for port 1 and 2, respectively. Finally, the envelope correlation coefficient (ρe) has been calculated to evaluate the diversity performance. Results indicate that ρe ≤ -20 dB across the ultra-wide bandwidth. These results show the suitability of the proposed antenna for future UWB diversity applications.