Design and experimental verification of ridge gap waveguide in bed of nails for parallel-plate mode suppression

This study describes the design and experimental verification of the ridge gap waveguide, appearing in the gap between parallel metal plates. One of the plates has a texture in the form of a wave-guiding metal ridge surrounded by metal posts. The latter posts, referred to as a pin surface or bed of nails, are designed to give a stopband for the normal parallel-plate modes between 10 and 23 GHz. The hardware demonstrator includes two 90° bends and two capacitive coupled coaxial transitions enabling measurements with a vector network analyser (VNA). The measured results verify the large bandwidth and low losses of the quasi-transverse electromagnetic (TEM) mode propagating along the guiding ridge, and that 90° bends can be designed in the same way as for microstrip lines. The demonstrator is designed for use around 15 GHz. Still, the ridge gap waveguide is more advantageous for frequencies above 30 GHz, because it can be realised entirely from metal using milling or moulding, and there are no requirements for conducting joints between the two plates that otherwise is a problem when realising conventional hollow waveguides. © 2011 The Institution of Engineering and Technology.Kildal, P.; Zaman, AU.; Rajo Iglesias, E.; Alfonso Alós, E.; Valero-Nogueira, A. (2011). Design and experimental verification of ridge gap waveguide in bed of nails for parallel-plate mode suppression. IET Microwaves Antennas and Propagation. 5(3):262-270. doi:10.1049/iet-map.2010.0089S26227053Kildal, P.-S., Alfonso, E., Valero-Nogueira, A., & Rajo-Iglesias, E. (2009). Local Metamaterial-Based Waveguides in Gaps Between Parallel Metal Plates. IEEE Antennas and Wireless Propagation Letters, 8, 84-87. doi:10.1109/lawp.2008.2011147Kildal, P.-S.: ‘Waveguides and transmission lines in gaps between parallel conducting surfaces’, (European Patent Application EP08159791.6)7 July 2008Rajo-Iglesias, E., Zaman, A. U., & Kildal, P.-S. (2010). Parallel Plate Cavity Mode Suppression in Microstrip Circuit Packages Using a Lid of Nails. IEEE Microwave and Wireless Components Letters, 20(1), 31-33. doi:10.1109/lmwc.2009.2035960Kildal, P.-S. (1990). Artificially soft and hard surfaces in electromagnetics. IEEE Transactions on Antennas and Propagation, 38(10), 1537-1544. doi:10.1109/8.59765Valero-Nogueira, A., Alfonso, E., Herranz, J. I., & Kildal, P.-S. (2009). Experimental Demonstration of Local Quasi-TEM Gap Modes in Single-Hard-Wall Waveguides. IEEE Microwave and Wireless Components Letters, 19(9), 536-538. doi:10.1109/lmwc.2009.2027051Lier, E. (1990). Analysis of soft and hard strip-loaded horns using a circular cylindrical model. IEEE Transactions on Antennas and Propagation, 38(6), 783-793. doi:10.1109/8.55573Sievenpiper, D., Lijun Zhang, Broas, R. F. J., Alexopolous, N. G., & Yablonovitch, E. (1999). High-impedance electromagnetic surfaces with a forbidden frequency band. IEEE Transactions on Microwave Theory and Techniques, 47(11), 2059-2074. doi:10.1109/22.798001Silveirinha, M. G., Fernandes, C. A., & Costa, J. R. (2008). Electromagnetic Characterization of Textured Surfaces Formed by Metallic Pins. IEEE Transactions on Antennas and Propagation, 56(2), 405-415. doi:10.1109/tap.2007.915442Lindell, I. V. (2000). Ideal boundary and generalised soft and hard conditions. IEE Proceedings - Microwaves, Antennas and Propagation, 147(6), 495. doi:10.1049/ip-map:20000827Valero-Nogueira, A., Alfonso, E., Herranz, J. I., & Baquero, M. (2007). Planar slot-array antenna fed by an oversized quasi-TEM waveguide. Microwave and Optical Technology Letters, 49(8), 1875-1877. doi:10.1002/mop.22586Šipuš, Z., Merkel, H., & Kildal, P.-S. (1997). Green’s functions for planar soft and hard surfaces derived by asymptotic boundary conditions. IEE Proceedings - Microwaves, Antennas and Propagation, 144(5), 321. doi:10.1049/ip-map:19971335CST Microwave Studio 2008. Available at: www.cst.comKehn, M. N. M., & Kildal, P.-S. (2005). Miniaturized rectangular hard waveguides for use in multifrequency phased arrays. IEEE Transactions on Antennas and Propagation, 53(1), 100-109. doi:10.1109/tap.2004.840519Malcolm Ng Mou Kehn, M. N. M., Nannetti, Cucini, Maci, & Kildal. (2006). Analysis of dispersion in dipole-FSS loaded hard rectangular waveguide. IEEE Transactions on Antennas and Propagation, 54(12), 2275-2282. doi:10.1109/tap.2006.879198Grbic, A., & Eleftheriades, G. V. (2003). Periodic analysis of a 2-D negative refractive index transmission line structure. IEEE Transactions on Antennas and Propagation, 51(10), 2604-2611. doi:10.1109/tap.2003.817543Eleftheriades, G.V., and Balmain, K.G.: ‘Metamaterials for controlling and guiding electromagnetic radiation’, (US Patent 6859114 – Filed 2 June 2003)McKinzie, W.F.: ‘Circuit and method for suppression of electromagnetic coupling and switching noise in multilayer printed circuit boards’, (US Patent No. 7,215,007 B2)Schellenberg, J. M. (1995). CAD models for suspended and inverted microstrip. IEEE Transactions on Microwave Theory and Techniques, 43(6), 1247-1252. doi:10.1109/22.390179Anderson, T. N. (1956). Rectangular and Ridge Waveguide. IEEE Transactions on Microwave Theory and Techniques, 4(4), 201-209. doi:10.1109/tmtt.1956.1125063Pozar, D.: ‘Microwave engineering’, 3rd(Wiley 2005), p. 139Bosiljevac, M., Sipus, Z., & Kildal, P.-S. (2010). Construction of Green’s functions of parallel plates with periodic texture with application to gap waveguides – a plane-wave spectral-domain approach. IET Microwaves, Antennas & Propagation, 4(11), 1799. doi:10.1049/iet-map.2009.0399Zaman, A. U., Rajo-Iglesias, E., Alfonso, E., & Kildal, P.-S. (2009). Design of transition from coaxial line to ridge gap waveguide. 2009 IEEE Antennas and Propagation Society International Symposium. doi:10.1109/aps.2009.5172186Sharp, E. D. (1963). A High-Power Wide-Band Waffle-Iron Filter. IEEE Transactions on Microwave Theory and Techniques, 11(2), 111-116. doi:10.1109/tmtt.1963.1125611KIRINO, H., OGAWA, K., & OHNO, T. (2008). A Variable Phase Shifter Using a Movable Waffle Iron Metal Plate and Its Applications to Phased Array Antennas. IEICE Transactions on Communications, E91-B(6), 1773-1782. doi:10.1093/ietcom/e91-b.6.177

Pregnancy outcomes and cytomegalovirus DNAaemia in HIV infected pregnant women with CMV

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Rate , correlates and outcomes of repeat pregnancy in HIV-infected women

Objectives: The aim of the study was to assess the rate, determinants, and outcomes of repeat pregnancies in women with HIV infection. Methods: Data from a national study of pregnant women with HIV infection were used. Main outcomes were preterm delivery, low birth weight, CD4 cell count and HIV plasma viral load. Results: The rate of repeat pregnancy among 3007 women was 16.2%. Women with a repeat pregnancy were on average younger than those with a single pregnancy (median age 30 vs. 33 years, respectively), more recently diagnosed with HIV infection (median time since diagnosis 25 vs. 51 months, respectively), and more frequently of foreign origin [odds ratio (OR) 1.36; 95% confidence interval (CI) 1.10–1.68], diagnosed with HIV infection in the current pregnancy (OR: 1.69; 95% CI: 1.35–2.11), and at their first pregnancy (OR: 1.33; 95% CI: 1.06–1.66). In women with sequential pregnancies, compared with the first pregnancy, several outcomes showed a significant improvement in the second pregnancy, with a higher rate of antiretroviral treatment at conception (39.0 vs. 65.4%, respectively), better median maternal weight at the start of pregnancy (60 vs. 61 kg, respectively), a higher rate of end-of-pregnancy undetectable HIV RNA (60.7 vs. 71.6%, respectively), a higher median birth weight (2815 vs. 2885 g, respectively), lower rates of preterm delivery (23.0 vs. 17.7%, respectively) and of low birth weight (23.4 vs. 15.4%, respectively), and a higher median CD4 cell count (+47 cells/μL), with almost no clinical progression to Centers for Disease Control and Prevention stage C (CDC-C) HIV disease (0.3%). The second pregnancy was significantly more likely to end in voluntary termination than the first pregnancy (11.4 vs. 6.1%, respectively). Conclusions: Younger and foreign women were more likely to have a repeat pregnancy; in women with sequential pregnancies, the second pregnancy was characterized by a significant improvement in several outcomes, suggesting that women with HIV infection who desire multiple children may proceed safely and confidently with subsequent pregnancies

Good prenatal detection rate of major birth defects in HIV-infected pregnant women in Italy

What's already known about this topic? Exposure to antiretroviral treatment in pregnancy does not seem to increase the risk of birth defects, but there is no information on the rate of prenatal detection of such defects. What does this study adds? We provide for the first time, in a national case series, information about prenatal detection rate in women with HIV (51.6% for any major defect, 66.7% for chromosomal abnormalities, and 85% for severe structural defect

Consequences of presentation with advanced HIV disease in pregnancy : data from a national study in Italy

Among 469 women with a diagnosis of HIV in pregnancy, 74 (15.8%) presented with less than 200 CD4 cells per cubic millimeter. The only variable significantly associated with this occurrence was African origin (odds ratio: 2.22, 95% confidence intervals: 1.32 to 3.75, P = 0.003). Four women with low CD4 (5.6%), compared with none with higher CD4 counts, had severe AIDS-defining conditions (P < 0.001) during pregnancy or soon after delivery, and one transmitted HIV to the newborn. Early preterm delivery (<32 weeks) was significantly more frequent with low CD4 (6.2% vs. 1.4%, P = 0.015). An earlier access to HIV testing, particularly among immigrants of African origin, can prevent severe HIV-related morbidity

On the Polarization Properties of Metamaterial Lenses

In this letter, the polarization properties of composite planar dielectric structures fed by point sources are investigated. With an appropriate choice of substrate heights and dielectric constants, the structure is a leaky wave antenna (LWA), based on a (Fabry-Perot)-like effect, which enhances the directivity of isotropic sources (e.g., dipoles or slots). These antennas have been deeply investigated in the past, especially from the antenna gain point of view. Nevertheless, the aspect concerning with the polarization has not been well explored yet. In our analysis, we show that this high-gain antenna is very well polarized when the excitation is provided by a perfectly polarized feeding source. This concept is important in the design of overlapped apertures in multifeed aperture systems

Closed form expressions for the modal dispersion equations and for the characteristic impedance of a metamaterial based gap waveguide

In a recent sequence of papers, a parallel-plate ridge gap waveguide has been introduced, that consists of a metal ridge in a metamaterial magnetic conductor surface, covered by a metallic plate at a small height above it. The gap waveguide is relatively simple to manufacture, especially at millimetre and sub-millimetre wave frequencies when compared with other solutions. The metamaterial surface is designed to provide a frequency band where parallel-plate modes are in cut-off, thereby allowing for a confined gap wave to propagate along the ridge. In a previous work, the authors have presented an approximate analytical solution for the confined quasi-TEM dominant mode of the ridge gap waveguide, when the surrounding metamaterial surface is in the form of a bed of nails. In this study, the authors investigation continues by providing an analytical expression of the modal dispersion equation of the first higher order ridge mode and of the characteristic impedance of the dominant mode. As in the previous paper, the field problem is divided in three regions, the central region above the ridge and the two surrounding side regions above the nails. Transverse mode-matching applied to a few modes representation in each region, results in a closed form expression of the dispersion equation of the first higher order mode. After summarising the formulation for the dominant quasi-TEM mode, the dispersion equation of the first higher order mode is derived, in order to give a criterion to maximise the unimodal bandwidth. Furthermore, three different closed form expressions of the dominant mode characteristic impedance are derived and compared with approximate expressions already used in literature

A leaky-wave groove antenna at optical frequencies

In the framework of nanoantennas functioning at optical frequencies, we present here a new kind of leaky-wave antenna realized as a groove in an aluminum superstrate, supported by a silver substrate. The antenna works in the optical frequency range where the silver acts as a dielectric with equivalent refractive index between zero and one. Under these conditions, the dominant mode launched in the structure exhibits a phase velocity larger than the speed of light in free-space, thus producing a leaky-wave radiation in free-space. We propose a simplified analytical form of the dispersioncharacteristic of the fundamental mode supported by the structure, which allows for identification of the radiative leaky-wave condition. We also propose approximate formulas for calculating the antenna gain and loss efficiency. The results obtained through these formulas are successfully compared with full-wave simulations. The final parametric study shows how the radiationcharacteristic is affected by the variation of geometric features