Radiation characteristics of a conical monopole antenna with a partially corrugated ground plane.

In order to preserve broadband performance, the conical monopole antenna is ideally mounted on a semi-infinite ground plane. Practical finite ground planes can introduce unwanted effects in the radiation patterns such as significant back lobes. Periodic surfaces such as rotationally symmetric corrugated structures have been proven capable of improving the radiation characteristics of a variety of antennas. In this paper, the radiation patterns of a conical antenna with a PEC reflector are initially presented. The PEC reflector is then replaced with a partially corrugated reflector surface. The effects of the partially corrugated reflector on the radiation patterns and electric field distribution along the reflector surface are investigated. The simulation results reveal that the radiation patterns of a conical antenna with a partially corrugated reflector are more stable over a wide frequency band than that for the PEC reflector

Planar electromagnetic bandgap structures based on polar curves and mapping functions

A type of electromagnetic bandgap structure is described that is easily parameterized and can produce a range of square and spiral geometries. Individual electromagnetic bandgap (EBG) geometries are defined on a cell-by-cell basis in terms of their convolution factor , which defines the extent to which the elements are interleaved and controls the coupling slot length between adjacent elements. Polar equations are used to define the slot locus which also incorporate a transformation which ensures the slot extends into the corners of the square unit cell and hence extends the maximum slot length achievable. The electromagnetic properties of the so-called polar EBG are evaluated by means of numerical simulation and measurements and dispersion diagrams are presented. Finally, the performance is compared with other similar miniaturized EBG cell geometries. It is shown that the polar EBG has better angular stability than the equivalent square patch design and is comparable in terms of performance to other low frequency EBG elements. At the same time it retains the ability to fine tune the response by adjusting

Measurement techniques for polar electromagnetic bandgap structures using an air spaced microstrip line

The ability to accurately pinpoint with a high degree of accuracy the occurrence of the stop-band property in the newly engineered EBG materials is fundamental to their establishment. Measurement methods capable of achieving this have been proposed in literature but require intricate adjustments to suit particular requirements. In this paper we report on a repeatable measurement technique for characterising the bandgap properties of EBG structures using an air spaced microstrip line. The device constructed is simple, economical, robust and capable of quantifying the properties of a wide range of EBG materials. A tapered microstrip line transition is used to match a 50 coaxial port. Simulation and measurement results using a Polar-EBG are presented to show the versatility of the proposed technique. In addition to this we demonstrate that by changing the orientation of the surface under test (SUT), transverse electric surface wave measurements can be carried out. This apparatus and measurement technique is particularly applicable to fabric based EBG materials where measurements are especially challenging

Effect of training traditional birth attendants on neonatal mortality (Lufwanyama Neonatal Survival Project): randomised controlled study

Objective To determine whether training traditional birth attendants to manage several common perinatal conditions could reduce neonatal mortality in the setting of a resource poor country with limited access to healthcare

Trends in Prevalence of Advanced HIV Disease at Antiretroviral Therapy Enrollment - 10 Countries, 2004-2015.

Monitoring prevalence of advanced human immunodeficiency virus (HIV) disease (i.e., CD4+ T-cell count <200 cells/μL) among persons starting antiretroviral therapy (ART) is important to understand ART program outcomes, inform HIV prevention strategy, and forecast need for adjunctive therapies.*,†,§ To assess trends in prevalence of advanced disease at ART initiation in 10 high-burden countries during 2004-2015, records of 694,138 ART enrollees aged ≥15 years from 797 ART facilities were analyzed. Availability of national electronic medical record systems allowed up-to-date evaluation of trends in Haiti (2004-2015), Mozambique (2004-2014), and Namibia (2004-2012), where prevalence of advanced disease at ART initiation declined from 75% to 34% (p<0.001), 73% to 37% (p<0.001), and 80% to 41% (p<0.001), respectively. Significant declines in prevalence of advanced disease during 2004-2011 were observed in Nigeria, Swaziland, Uganda, Vietnam, and Zimbabwe. The encouraging declines in prevalence of advanced disease at ART enrollment are likely due to scale-up of testing and treatment services and ART-eligibility guidelines encouraging earlier ART initiation. However, in 2015, approximately a third of new ART patients still initiated ART with advanced HIV disease. To reduce prevalence of advanced disease at ART initiation, adoption of World Health Organization (WHO)-recommended "treat-all" guidelines and strategies to facilitate earlier HIV testing and treatment are needed to reduce HIV-related mortality and HIV incidence

Antiretroviral therapy enrollment characteristics and outcomes among HIV-infected adolescents and young adults compared with older adults--seven African countries, 2004-2013.

Although scale-up of antiretroviral therapy (ART) since 2005 has contributed to declines of about 30% in the global annual number of human immunodeficiency (HIV)-related deaths and declines in global HIV incidence, estimated annual HIV-related deaths among adolescents have increased by about 50% and estimated adolescent HIV incidence has been relatively stable. In 2012, an estimated 2,500 (40%) of all 6,300 daily new HIV infections occurred among persons aged 15-24 years. Difficulty enrolling adolescents and young adults in ART and high rates of loss to follow-up (LTFU) after ART initiation might be contributing to mortality and HIV incidence in this age group, but data are limited. To evaluate age-related ART retention challenges, data from retrospective cohort studies conducted in seven African countries among 16,421 patients, aged ≥15 years at enrollment, who initiated ART during 2004-2012 were analyzed. ART enrollment and outcome data were compared among three groups defined by age at enrollment: adolescents and young adults (aged 15-24 years), middle-aged adults (aged 25-49 years), and older adults (aged ≥50 years). Enrollees aged 15-24 years were predominantly female (81%-92%), commonly pregnant (3%-32% of females), unmarried (54%-73%), and, in four countries with employment data, unemployed (53%-86%). In comparison, older adults were more likely to be male (p<0.001), employed (p<0.001), and married, (p<0.05 in five countries). Compared with older adults, adolescents and young adults had higher LTFU rates in all seven countries, reaching statistical significance in three countries in crude and multivariable analyses. Evidence-based interventions to reduce LTFU for adolescent and young adult ART enrollees could help reduce mortality and HIV incidence in this age group

The Application of Periodic Structures to Conical Antenna Design

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Radiation characteristics of a conical monopole antenna with a partially corrugated ground plane

In order to preserve broadband performance, the conical monopole antenna is ideally mounted on a semi-infinite ground plane. Practical finite ground planes can introduce unwanted effects in the radiation patterns such as significant back lobes. Periodic surfaces such as rotationally symmetric corrugated structures have been proven capable of improving the radiation characteristics of a variety of antennas. In this paper, the radiation patterns of a conical antenna with a PEC reflector are initially presented. The PEC reflector is then replaced with a partially corrugated reflector surface. The effects of the partially corrugated reflector on the radiation patterns and electric field distribution along the reflector surface are investigated. The simulation results reveal that the radiation patterns of a conical antenna with a partially corrugated reflector are more stable over a wide frequency band than that for the PEC reflector