Stelios A. Mitilineos

A New, Low-Cost, Switched Beam and Fully Adaptive Antenna Array for 2.4 GHz ISM Applications

A new, low-cost, switched-beam and fully adaptive antenna array suitable for 2.4 GHz ISM applications is proposed in this paper. The array comprises of four elements, equal in number receiving RF and IF components, as well as a microcontroller based unit which is responsible for the control of the array. The array is designed with the aid of a custom genetic algorithm, while measurements results are presented indicating consistency between design and implementation. In addition, multipath fading mitigation capability of the array is demonstrated via channel measurements results.

Positioning Accuracy Enhancement Using Error Modeling via a Polynomial Approximation Approach

Location information is critical for the development of value-added location-based services, such as fraud protection, location- aware network access, person/asset tracking etc. Herein, a method for the enhancement of localization systems in terms of achieved accuracy is proposed, which can be applied to new as well as existing systems regardless the underlying localization technique. The method is based on modeling the position measurement error introduced by the localization algorithm using a polynomial approximation approach. Measurements results demonstrate the applicability of the proposed technique in enhancing accuracy in a low cost and e-cient manner.

Design and Optimization of ESPAR Antennas via Impedance Measurements and a Genetic Algorithm [Antenna Designer's Notebook]

A method for the design of electronically steerable passive array radiator (ESPAR) antennas is proposed herein, based on impedance-matrix measurements and a genetic algorithm. The proposed technique is best suited for cases where commercial elements are used as building blocks for ESPAR development, since in such cases the conventional numerically based techniques used in the literature may not be applicable. An emulated ESPAR design and respective results are presented. They demonstrate the applicability and performance of the proposed technique, as well as its consistency with results derived from a commercially available electromagnetic simulator.

A Broadband, Vertically Polarized, Circular Switched Parasitic Array for Indoor Portable DVB-T Applications at the IV UHF Band

In this paper, a new broadband, vertically polarized, circular switched parasitic antenna array, appropriate for portable DVB-T applications at the IV UHF band, is developed with the aid of a proposed genetic algorithm approach. The array consists of a central fixed parasitic element and four peripheral ones. At any given time, only two adjacent peripheral elements are active, while each of the remaining two is short-circuited. By appropriately selecting active and short-circuited elements, a set of four radiation patterns can be formed, covering the horizontal plane alternately. Design considerations and results are presented, while array measurements are demonstrated for a single snitching mode.

Design of a Corner-Reflector Reactively Controlled Antenna for Maximum Directivity and Multiple Beam Forming at 2.4 GHz

Electronically steerable passive array radiator (ESPAR) antennas constitute a promising research field and are expected to play important role in future wireless communications. In this paper, a new approach in ESPAR antenna design for base station applications is proposed. A corner-plate reflector is combined with active and passive (reactively loaded) elements in order to implement a corner-reflector ESPAR (CR-ESPAR) configuration. It is shown that when combined with corner reflectors in order to sectorize the coverage area, an ESPAR antenna offers multiple radiation patterns with higher directivity and resolution. A case study of a CR-ESPAR suitable for 2.4 GHz ISM applications is demonstrated, where the performance of the structure is optimized with respect to resonance frequency, input impedance, and multiple switched-beam patterns configuration. The optimization of the array is performed using a Genetic Algorithm (GA) tool as a method of choice, achieving a maximum gain equal to 14 dBi for a 30°3 dB-beamwidth and a gain of 11 dBi for a 45°3 dB-beamwidth, while the VSWR is kept below 1.7 in all cases. Due to its limited physical size, the proposed CR-ESPAR can be used as a portable antenna for deployment in WiFi, WLAN and other applications.

Broadband switched parasitic arrays for portable DVB-T receiver applications in the VHF/UHF bands

A new technique for the design of broadband circular switched parasitic arrays (SPAs) for portable DVB-T receiver applications in the VHF/UHF bands is presented in this paper. Two switched parasitic arrays are presented, consisting of an active central element and a uniform ring of five parasitic elements. At any given time slot, only one parasitic element is open- circuited, while the rest remain short-circuited. By properly selecting the open-circuited element, the array is able of selecting among five horizontal radiation patterns. These cover the horizontal plane in a uniform manner, thus achieving effective beam steering in order to maximize and minimize the received power and bit error rate, respectively. Measurement results for both arrays and for a single switching state are presented, and excellent agreement with design considerations and numerical results is demonstrated.

A new active RF phase shifter using variable gain, drain Voltage controlled PHEMTs:A 2.4-GHz ISM implementation

Phase shifters operating at RF bands are an essential component of phased and adaptive arrays circuits. In this letter, an active phase shifter is proposed, using vector summing of an in-phase and a quad-phase replica of the incoming signal. The proposed scheme was designed and implemented using a Wilkinson power combiner/divider, a branch line hybrid coupler and single-stage variable gain amplifiers (VGAs), achieving continuous phase shift within the range of [0/spl deg/, 90/spl deg/]. The manufactured prototype is suitable for WLAN operations in the 2.4-GHz ISM band. Details of the phase shifter design and experimental results are presented.

Blind Position Location via Geometric Loci Construction

A new position location technique is proposed, using received signal strength measurements, which can be implemented using inexpensive off-the-shelf equipment. The proposed technique is based on geometric loci construction, and overcomes the need for onsite calibration measurements or propagation prediction tools and topographical/architectural plans of the covered area. The proposed algorithm exhibits similar simulated performance compared to a recently proposed positioning technique, but without the need of model calibration. In addition, measurements results are also presented, demonstrating the performance of the algorithm.

DALE: A range-free, adaptive indoor localization method enhanced by limited fingerprinting

A new range-free solution based on simple RSSI measurements is presented herein. The proposed method includes a two-stage algorithm and is able to incorporate fingerprints of specific locations, when available, in order to enhance localization accuracy. The proposed algorithm requires a strategic placement of nodes in each room while being easily scalable to a large number of rooms and adaptable to rooms with complex geometry. Simulation results are derived in order to evaluate the proposed algorithm and compared to relative research results in the literature.

WAX-ROOM: an indoor WSN-based localization platform

Indoor localization is considered to be a key aspect of future context-aware, ubiquitous and pervasive systems, while Wireless Sensor Networks (WSNs) are expected to constitute the critical infrastructure in order to sense and interact with the environment surrounding them. In the context of developing ambient-assisted living and aftermath crisis mitigation services, we are implementing WAX-ROOM, a WSN specially developed for indoor localization but at the same time able to sense and interact with the environment. Currently, WAX-ROOM incorporates three different localization techniques and an optimal fusion rule. The proposed WSNs architecture and advantages, as well as measurements results regarding its performance in terms of localization accuracy are presented herein, demonstrating the eligibility of the proposed platform for indoor localization.