UHF SATCOM broadband CP antenna: moxon type bent-dipoles over a ground plane

In this paper, we investigate and compare two different antenna types for UHF SATCOM applications; proposed Moxon type (bent dipole) and conventional egg beater (loop) antennas in terms of antenna performance and physical size. Bent dipole and egg beater antennas are simulated using HFSS software. Prototype antenna for Moxon type is also fabricated and measured for its return loss using Agilent network analyzer and compared to that of an egg beater antenna. Antenna gains are also simulated. Simulation results show that Moxon type antenna has more impedance bandwidth than egg beater antenna with smaller dimensions and hence can be used for broadband SATCOM applications

Broadband circularly polarized antennas for UHF SATCOM

Novel circularly polarized (CP) antenna configurations derived from Moxon type antenna (bent dipole element over a ground plane) for broadband VHF SATCOM applications. A sequence of topologies starting from a single vertical element to two vertical elements of the Moxon arms, then widened strip arm elements were studied. Further, arms were widened to bow tie structures with bents at 900.for achieving broadband operation. Bow tie elements were further split and optimized at a certain angle to achieve wider bandwidth. The logic in this evolution was to obtain highest possible gain based on Fano-Chu limits, which suggests that higher gain can be achieved in an electrically small antenna with maximized metallization in the structure that fill the volume. Circular polarization is obtained by two Moxon based cross elements that are fed through a hybrid 900 quadrature coupler. For the antennas that are prototyped, return loss S11 measurements were performed, and gains are simulated using HFSS. For the band of 225-400 MHz, antenna gain varies between 8-12 dB, and S11 is measured to be below 10 dB. Fabricated antennas coupled to a hybrid coupler yielded excellent bandwidths, low cross-polarization and low back lobes on the finite ground planes

Broadband circularly polarized moxon based antennae for RFID and GPS

Abstract-Novel circularly polarized (CP) VHF SATCOM antenna which was based on Moxon antenna (bent dipole element over a ground plane) has been extended for RFID and GPS applications. A sequence of topologies starting from a single vertical element to two vertical elements of the Moxon arms, then widened strip arm elements were investigated to understand the effects on impedance match over the widened bandwidth. The logic in this evolution was to obtain maximized gain based on Fano-Chu limits, which suggests that more metallization in the radiating configuration that fill the volume would yield higher gain for electrically small antenna. Extending the width of the strip of the equivalent dipole elements lead to a wider bandwidth and improved cross-polarization ratio. Furthermore, splitting the tapered bow tie elements increased the volume filled with radiating elements leading to improved overall performance. Ultimately extended bends at the tip of the tapered sections parallel to the ground plane helped to improve overall performance. In overall, the antenna presented here produced lower physical height, higher gain, wider bandwidth, better crosspolarization and lower back lobe radiation compared to commercial counterparts such as an eggbeater currently used in SATCOM practice as well as similar antennas in RFID and GPS applications. Here, the concept is extended to cover RFID (850-1050 MHz) and GPS (centered at 1227 and 1575 MHz) bands leading to new applications at a significant cost and size reductions and much improved performance. Prototype antennas were built based on HFSS simulations yielded better than -25 dB return loss. During simulations attention was paid to identify the effects of individual antenna elements as an optimization parameter on the overall input impedance matching over the extended bandwidth. Simulated and measured results yielded higher than industrial counterpart antenna gain, bandwidth and cross-polarization for much reduced physical dimensions

Fluoride content of the cementum of rat molars after ingestion of fluoridated water

Thesis (M.Sc.D.)--Boston University. School of Graduate Dentistry, 1969.Bibliography, tables included

Successful Career and Technical Education Students’ Perceptions of the Organizational Features that Contribute to their Academic Achievement and Graduation

Low graduation rates in the United States indicate a need to better connect the high school curriculum with realities of life beyond high school. The purpose of this study was to develop a theory about successful career and technical education students’ perceptions of the organizational features that contribute to their academic achievement and graduation. This study employed a qualitative methodology and participants were high school senior CTE students. Data was transcribed, coded and analyzed using grounded theory methods. Core categories and themes were revealed through the data analysis to help create an emergent theory which is represented in the Linkages for Lifelong Success model which focuses on respect, equity and opportunities as critical classroom components which lead to students’ increased academic success and increased graduation rates. Implications for hiring teachers, for professional practice and for executive leaders were revealed through the student voices in this study. The research participants gave solid examples of how to change their home schools to take a more comprehensive approach to education. Although it seems simple to provide a classroom environment that fosters equity, respect and opportunities as vehicles for increasing student achievement and graduation rates, it still lies in the realm of the ideal and not what actually takes place in American classrooms. Recommendations for teachers and administrators with regard to CTE includes a comprehensive high school curriculum that involves CTE, an environment in which students are treated in a way that allows them to pursue various career options, and the implementation of the Linkages for Lifelong Success model