Christos Christodoulou

Christos Christodoulou
University of New Mexico | UNM · Department of Electrical and Computer Engineering

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488
Publications
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Citations

Publications

Publications (488)
Article
Full-text available
This paper describes the design of a planar antenna array system with pattern reconfiguration in the azimuthal plane. The antenna array system is designed based on four antenna units where each unit is composed of two printed Yagi-Uda elements that radiate in directional beams over a dedicated sector, thus ensuring maximum isolation with neighborin...
Article
This paper describes a right-hand circularly polarized planar filtenna that can reconfigure its operation between two center frequencies in the Ka-band. The filtenna structure is composed of four-element array radiator and a reconfigurable bandpass filter, occupying an area of 31 mm x 14 mm. The circularly polarized array elements are fed by a sequ...
Article
This paper discusses the design of a cross-slotted waveguide array structure to be adopted for W-band communication between 84 86 GHz. Each array waveguide element contains 16 cross-slots along the broad wall to enable circularly polarized radiation behavior with a gain reaching up to 14 dBi and a cross-polarization isolation of more than 20 dB in...
Article
Full-text available
This paper discusses the design of a high gain right-hand circularly polarized millimeter-wave frequency reconfigurable antenna array. The 16-element antenna array is designed to reconfigure its operating frequency over both K-and Ka-bands. More specifically, the reconfigurability is ensured through the integration of a modified ring resonator alon...
Article
This article discusses the design and dual functionality of two antenna arrays that operate from 1.8 to 2.4 GHz. Each antenna array is composed of two elements and proposed for either communication or radio-frequency (RF) energy harvesting. The antenna arrays are integrated vertically on top of a solar panel. Copper-based and transparent inverted-F...
Article
In this paper the design and implementation of a quadrifilar helix antenna is presented where the four arms are 3D printed. The antenna structure is miniaturized by resorting to a combination of two approaches. The first approach is based on loading the tips of the four helical arms with circular conductive disks. The size and location of these ele...
Article
Full-text available
The importance of having an optimal material for fabricating Optically Transparent Antennas (OTAs) is crucial for designing highly efficient antennas that can be integrated with photovoltaics. Transparent Conductor Oxides are promising for OTA fabrication due to their capability of being simultaneously transparent at optical frequencies and conduct...
Article
In this paper, a frequency and pattern reconfigurable V-shaped printed antenna is presented. The proposed structure operates at two different frequency bands. The variation in the frequency of operation is achieved by individually extending the length of each of the two antenna arms. The directional behavior of the proposed antenna structure is imp...
Article
In this paper, a frequency reconfigurable antenna system with a directional selectivity is presented. The reconfiguration of the antenna’s radiation characteristics is wirelessly controlled through a mobile phone and a microcontroller. The antenna system is a multi-element radiator composed of four monopoles on top of a hexagonal ground plane, in a...
Chapter
In this chapter, a summary of the various components, categorization, and design process of reconfigurable antennas is presented. The various applications where reconfigurable antennas have been implemented and the association of various antenna properties with new communication applications are discussed. The chapter takes into consideration new a...
Article
The design process and the deployment mechanism of a quadrifilar helix antenna (QHA) and a conical log spiral antenna (CLSA) are presented. The two antennas are proposed to operate in the UHF frequency band. They are composed of conductors that are embedded and supported by innovative structural techniques. This allows efficient folding, packaging,...
Conference Paper
This paper presents the design of a 3D printed quadrifilar helix antenna. The antenna is miniaturized by loading the tip of each helix by metallic circles of equal dimensions. The effect of decreasing the resonant frequency is also achieved by introducing a dielectric material within the antenna's physical structure. A prototype is fabricated and t...
Conference Paper
In this paper, a new reliable radio frequency (RF) rectifier topology with an enhanced operating power range is proposed. The presented RF harvester possesses an efficient RF to DC conversion ratio over an enhanced power range. A typical RF rectifier is initially optimized, and then the RF input is equally split into two branches. Splitting the inp...
Conference Paper
The design process for transparent conductive aluminum zinc oxide film AZO is presented in this document. The optimized RF conductivity and light transmittance properties of such film make it an attractive candidate for transparent antennas that are proposed for integration with solar cells.
Conference Paper
A Liquid Crystal (LC) based reconfigurable antenna array design at W/V-band is presented in this paper. The array exhibits both frequency tuning and beam steering due to the dielectric anisotropy of the LC at microwave frequencies. The design of the array is optimized to ensure reconfiguration while having the least number of connections to DC sour...
Conference Paper
This paper discusses various deployable antenna designs that are proposed for CubeSat platforms. The antennas discussed vary in their topology and structure from arrays of crossed dipoles to helical structures. Several concepts are presented and their performance is described and evaluated.
Conference Paper
The implementation of a four sectorial reconfigurable MIMO antenna system is discussed in this paper. The proposed antenna system consists of two MIMO structures that operate at two different frequencies. The reconfigurability of the antenna system is software controlled through an arduino board and a mobile phone application. A prototype is fabric...
Conference Paper
This paper proposes a new RF rectifier with a dynamically extendable RF-DC power conversion (> 50%) range. Compared to typical rectifiers, the adopted power combining topology extends the dynamic efficient range by ∼ 3 dB, while maintaining acceptable performance at low powers. A 1.84 GHz rectifier with the proposed topology is designed. A prototyp...
Conference Paper
In this paper, two compact multiband and reconfigurable planar inverted-F antenna (PIFA) designs operating at GPS, 3G, WiFi, GSM and 4G (UMTS and LTE) frequencies are presented. The multiband operation is accomplished by the multi-resonant slots while the reconfigurable PIFA operation is based on the appropriate integration of PIN diodes switches....
Conference Paper
The advent of CubeSats has revolutionized the space research industry. The small physical size and constraints owing to outer space applications present significant challenges for antenna engineers to come up with innovative solutions. This paper presents a novel wide band antenna high gain antenna which is capable of deploying from a CubeSat platf...
Conference Paper
This paper presents a new antenna system that reconfigures its radiation pattern through feed rotation. The radiation pattern reconfiguration allows a better Wireless LAN coverage through a personalized command by resorting to an Android phone application and an Arduino microcontroller.
Article
Full-text available
Prophylactic erythropoiesis-stimulating agent (ESA) administration for chemotherapy-induced anemia (CIA) is not supported by current guidelines. Long-term follow-up of patients WHO had been treated with ESA for CIA in the past may provide useful information. In 2002, we undertook a prospective, randomized phase III trial of prophylactic vs. hemoglo...
Article
Background: Intensive chemotherapy confers benefit to patients with high-risk early breast cancer (BC). We characterized the feasibility and toxicity profile of anthracycline-containing adjuvant chemotherapy (ACAC) in older women with early BC. Patients and methods: Available data from women who received ACAC for BC in 3 randomized trials were r...
Article
Full-text available
Background: The PI3K-AKT pathway is frequently activated in breast cancer. PIK3CA mutations are most frequently found in the helical (exon 9) and kinase (exon 20) domains of this protein. The aim of the present study was to examine the role of different types of PIK3CA mutations in combination with molecular biomarkers related to PI3K-AKT signalin...
Article
Full-text available
Background: Verbal expression of suicidal feelings has rarely been investigated in the literature, particularly regarding individuals who died by suicide. Subjects and methods: We retrospectively collected data on the suicide cases of the period November 2007-October 2009 from the Athens Greater Area and completed psychological autopsy questionn...
Article
Vascular endothelial growth factor C (VEGFC) and vascular endothelial growth factor receptor 1 (VEGFR1) mRNA overexpression has recently been shown to have strong predictive and prognostic value in patients with high-risk early breast cancer undergoing adjuvant chemotherapy. The present study evaluated associations of VEGFC and VEGFR1 with human ep...
Conference Paper
This paper discusses the design of a new conical log spiral antenna that can operate at UHF frequencies. The antenna constitutes a suitable candidate for deployment on top of a 6U CubeSat system. The conical log spiral is designed to operate between 300 MHz and 600 MHz and exhibit circular polarization as well as an acceptable gain. The antenna is...
Conference Paper
Full-text available
A simple method for the design of rectangular slotted waveguide antennas (SWAs) with specified sidelobe levels is briefly described, and is used to design an example SWA with 7 broadwall elliptical slots and sidelobes lower than −20 dB. A special corrugation geometry is then added to the SWA, where the uniform height of the corrugations controls th...
Conference Paper
The design of a reconfigurable cyclical printed antenna is discussed in this paper. The antenna's topology allows a wide bandwidth of operation and an ability for radiation pattern reconfiguration.. The antenna is designed at Ka-band, with different modes of radiation pattern characteristics. The different operational states reshape the radiation b...
Conference Paper
In this paper, a wide power range RF energy harvesting circuit is presented. The proposed idea is based on optimizing the performance of the contained Schottky diodes, while considering their built-in potential, breakdown voltage and variable impedance properties. The carried out analysis revealed a greater than 50% RF-to-DC conversion efficiency o...
Conference Paper
This paper describes the implementation of an efficient transparent log spiral antenna for energy harvesting. The proposed antenna is a wide band antenna with circular polarization which is integrated with solar panels. The goal is to implement an efficient technique to collect RF energy without degrading the performance of the solar cell.
Conference Paper
The integration of arrays of inverted F-antennas on the top of a solar cell is discussed in this paper. The antenna elements are placed orthogonal to the left and right edges of the solar cell. On each edge, one array composed of two element inverted-F antennas covering a specific operating bandwidth are placed. Prototype antennas are fabricated an...
Article
Full-text available
The aim of the study was to evaluate the prognostic ability of the transcriptional profiling of the HER family genes in early breast cancer, as a validation analysis of another previously published HeCOG study. RNA was extracted from 663 formalin-fixed paraffin-embedded (FFPE) tumor tissue samples of high-risk early breast cancer patients enrolled...
Article
Full-text available
To study the characteristics of a sample of suicide victims from the Athens Greater Area using the psychological autopsy method for the first time in Greece. We studied all recorded cases of completed suicide for the 2-year time period November 2007-October 2009 collecting data from the victims' forensic records as well as from the completion of a...
Article
An approach for calculating electromagnetic scattering, valid in the near- and far-field regions, from a homogeneous finite cylindrical vegetation sample at oblique incidence is presented and discussed. The proposed solution will help in taking into account multiple scattering effects due to plant structure. It does not require assumptions on the d...
Article
Introduction Suicide completers have often communicated their intention to die or their deep desperation to their loved ones. Methods We retrospectively collected data on the suicide victims of the period 2007-2009 from the Athens Greater Area and completed psychological autopsy questionnaires after phone interviews with the victims' relatives. Th...
Conference Paper
Full-text available
Introduction Cyclothymic-depressive-anxious-irritable (CDAI) temperament has been linked to increased suicidal risk. Sleep disturbance and short self-reported sleep duration have been associated with suicidal ideation and behavior independently of a current major depressive episode (MDE). Objectives This cross-sectional study in consecutive hospit...
Article
Introduction Since 2008 Greece has entered a long period of economic crisis with adverse effects on various aspects of daily life. In this frame it is quite important to examine the suicide trends in Greece during the period 1992-2012 with particular consideration given in the recent period of economic crisis [2008-2011]. Material and Methods Popu...
Article
In Greece, a European country with a total of population 11,110,000, wine drinking is the most common type of alcohol consumption followed by beer (28%) and spirits (24%). The national policy includes an action plan, a monitoring system, support for community action, excise tax on beer and spirits but not wine. There is no legally binding regulatio...
Article
A conical log spiral antenna is presented with a new feeding scheme. This antenna is proposed for deployment on a CubeSat platform where the new feeding technique allows for easier antenna deployment. The antenna is composed of two arms that are wrapped around each other in a log-periodic manner. It is designed on top of a ground plane allowing its...
Chapter
In this chapter, a summary of the various components, categorization, and design process of reconfigurable antennas is presented. The various applications where reconfigurable antennas have been implemented and the association of various antenna properties with new communication applications are discussed. The chapter takes into consideration new a...
Article
Full-text available
A new cognitive radio antenna system is presented and discussed in this study. The antenna system is composed of a wideband antenna that is used for channel sensing and a communicating antenna that is used for dynamic transmission over various frequencies. The communicating antenna is a software controlled reconfigurable antenna that can tune its f...
Article
Full-text available
This article focused on the relation between the method of last attempted suicide and the method used during the subsequent completed suicide. Using the method of psychological autopsy, the authors studied all suicide cases from the Athens Greater Area during a 2-year period. Twenty-four percent of the victims had history of previous suicide attemp...
Article
Full-text available
Frequency-tunable microstrip antennas, for cognitive radio applications, are proposed herein. The approach is based on tuning the operating frequency of a bandpass filter that is incorporated into a wideband antenna. The integration of an open loop resonator- (OLR-) based adjustable bandpass filter into a wideband antenna to transform it into a tun...
Article
The focus of this Special Section is to showcase a unified vision for future cognitive radios, with an emphasis on antennas and RF front ends, and the algorithms for learning and controlling the RF/antenna front-end of any future cognitive radios as well as the sensing and integration of the propagation environment into the system configuration. Fi...
Article
In this paper cognitive radio is described, discussed and compared with software defined radio (SDR). The two types of cognitive radio are presented and examples on both spectrum interweave and spectrum underlay cognitive radio antenna systems are detailed. Reconfigurable filtennas are proposed as communicating antennas in a MIMO setting for both c...
Article
This paper discusses the fundamental principles of a cognitive-radio RF system. The key points required to achieve a true cognitive-radio device are outlined. The operation of a cognitive-radio system is mainly divided into two tasks. In the first task, a cognitive-radio device searches and identifies any part of the spectrum that is not occupied....
Article
Full-text available
In this paper, frequency-tunable microstrip antennas, for cognitive radio applications, are proposed. The approach is based on electrically tuning the antenna's operating frequency by integrating reconfigurable band pass filters into wideband antenna structures. The design of an open loop resonator (OLR)-based bandstop filter, and its transformatio...
Article
Full-text available
The implementation of a frequency-reconfigurable antenna with the use of a moving feeding technique is described in this letter. A flexible coaxial feed is attached to the main microstripline feed of a perturbed Sierpinski monopole gasket, and it slides with the help of computer-controlled motor mechanism. Single and multiple operational frequencie...
Article
Nominations are solicited for the 2014 AP-S awards. There are six awards that the Society can give this year. A new award, the ??Harrington-Mittra Award in Computational Electromagnetics,?? is being introduced this year. A brief description of each award, its criteria, and a nomination form are provided below.