EBG Enhanced Feeds for the Improvement of the Aperture Efficiency of Reflector Antennas

We describe the use of electromagnetic bandgap (EBG) super-layers to improve the shape of reflectors illumination function. Following an investigation of the leaky wave pole singularities of the EBG Green's function, the shape of the radiation patterns of small apertures in ground planes are optimized. The maximization of the reflector aperture efficiency can be obtained by properly tuning the super layers geometrical parameters. A prototype of such feed has been designed, manufactured and tested. The results indicate that the inclusion of the EBG, increases the aperture efficiency of the feed+reflector system to values higher than 80%, over a 10% bandwidth. These low profile feeds are compatible with printed circuit board and/or integrated technology.     

Optical Measurements of SuperSpec: A Millimeter-Wave On-Chip Spectrometer

SuperSpec is a novel on-chip spectrometer we are developing for (sub)millimeter wavelength astronomy. Our approach utilizes a filterbank of moderate resolution ( \(R \sim 500{)}\) channels, coupled to lumped element kinetic inductance detectors (KIDs), all integrated onto a single silicon chip. The channels are half-wave resonators formed by lithographically depositing segments of superconducting transmission line, and the KIDs are titanium nitride resonators. Here we present optical measurements of a first generation prototype, operating in the 180–280 GHz frequency range. We have used a coherent source to measure the spectral profiles of 17 channels, which achieve linewidths corresponding to quality factors as high as \(Q_\mathrm {filt} = 700{,}\) consistent with the designed values plus additional dissipation characterized by \(Q_i \approx 1440{.}\) We have also used a Fourier Transform Spectrometer to characterize the spectral purity of all 72 channels on the chip, and measure typical out of band responses \({\sim }30\) dB below the peak response.     

Detection of nacelle anemometer faults in a wind farm minimizing the uncertainty

The performance assessment of wind farms requires the acquisition of accurate power and wind speed data of each turbine. Nowadays, the nacelle anemometry is widely studied as an option for power performance verification. Therefore, systems to detect the nacelle anemometer faults in a wind farm in operation are necessary for maintenance purposes. In this paper, we propose a method to detect wind speed deviations of the nacelle anemometers by comparing them with the nearby anemometers. This comparison is made through an approach to estimate the wind speed in each nacelle. The approach is based on the discretization of wind speed data using the bin method. The key issue of this proposal is the estimation of the anemometer deviations considering the range of data with lower uncertainty. To this end, an average uncertainty model per bin and direction sector has been integrated into the method. The tests show that using wind speeds higher than 4.5 m s ^{? 1} gives the lowest uncertainty. Data from two wind farms have been used to test this method, and the obtained results have allowed the detection of problematic anemometers. Copyright © 2012 John Wiley & Sons, Ltd.     

Spanish cheese screening and selection of lactic acid bacteria with high gamma-aminobutyric acid production

Gamma-aminobutyric acid (GABA) is a non-protein four-carbon amino acid which is considered a bioactive component known for its physiological functions, including a regulator of blood pressure, neurotransmitter, diuretic and anti-stress effects. Its use in foods might confer health benefits. Microorganisms such as yeast, fungi or bacteria can produce GABA naturally. Among them, the lactic acid bacteria are being studied for the potential development of fermented foods because their physiological activities and their designation of generally recognized as safe (GRAS). The objective of this study was to evaluate the GABA-production capacity in a whole wheat flour medium of lactic acid bacteria strains that showed a high conversion of glutamic acid to GABA in a screening conducted in 58 Spanish artisanal cheeses. Synthesis of GABA by these strains in a non-optimized whole wheat flour in water solution (1:5) was quantified by High-Performance Liquid Chromatography. The 4 strains showing the highest GABA production were genotypically and phenotypically characterized. Results indicated an interesting fermentative variability between strains. The addition of these isolated lactic acid strains in fermented food products could allow a potentially functional food for regulating hypertension.     

Statistical Analysis of Wind Power Forecast Error

Wind power forecast error usually has been assumed to have a near Gaussian distribution. With a simple statistical analysis, it can be shown that this is not valid. To obtain a more appropriate probability density function (pdf) of the wind power forecast error, an indirect algorithm based on the Beta pdf is proposed. Measured one-year time series from two different wind farms are used to generate the forecast data. Three different forecast scenarios are simulated based on the persistence approach. This makes the results comparable to other forecast methods. It is found that the forecast error pdf has a variable kurtosis ranging from 3 (like the Gaussian) to over 10, and therefore it can be categorized as fat-tailed. A new approximation function for the parameters of the Beta pdf is proposed because results from former publications could not be confirmed. Besides, a linear approximation is developed to describe the relationship between the persistence forecast and the related mean measured power. An energy storage system (ESS), which reduces the forecast error and smooths the wind power output, is considered. Results for this case show the usefulness of the proposed forecast error pdf for finding the optimum rated ESS power.      

Problem-matched basis functions for microstrip coupled slot arrays based on transmission line Green's functions (TLGF)

Problem matched basis functions are proposed for the method of moments analysis of printed slot coupled microstrips. The appropriate equivalent currents of the integral equation kernel are represented in terms of two sets of entire domain basis functions. These functions synthesize on one hand the resonant behavior of slots, microstrips or dipoles and on the other hand the field in proximity of the feeding source and of the discontinuities. In order to define these basis functions, canonical geometries are identified, whose Green's functions have been found in semi-analytical form. The accuracy and the effectiveness of the method in terms of convergence rate and number of unknowns is demonstrated by comparison with a standard fine meshing full-wave analysis. The method is extremely convenient for large arrays, where the subwavelength details should be treated together with large global dimensions. Since the proposed solution is independent of the dimensions of these details, it provides dramatic reduction of the number of unknowns and improvement of condition number.     

1-D Scanning Arrays on Dense Dielectrics Using PCS-EBG Technology

We show how the design of integrated arrays can significantly benefit from planar circularly symmetric (PCS) electromagnetic band gap (EBG) structures. Using this technology, a phased array that scans up to 40deg in one dimension and that is characterized by relatively large bandwidth (BWap15%) is designed, manufactured and tested. The specific advantages coming from the use of PCS-EBGs are two fold. On one hand the losses associated to surface waves are significantly reduced. On the other hand each element of the array has a larger effective area that leads to a higher gain for the complete array when compared with a standard technology. Additional benefits are the low cross-polarization levels, the good front to back ratio considering that the antenna does not include a backing reflector, and the low profile     

An Approach for Sub-Second Imaging of Concealed Objects Using Terahertz (THz) Radar

High-resolution, long-range detection of person-borne concealed weapons has recently been demonstrated using a terahertz imaging radar. However, the radar’s image acquisition time must be greatly shortened, from minutes to less than one second, before the system can be effectively deployed in a real-life threat environment. Here we analyze the major system modifications necessary for increasing the speed of a terahertz imaging radar by up to two orders of magnitude.     

Leaky Wave Enhanced Feed Arrays for the Improvement of the Edge of Coverage Gain in Multibeam Reflector Antennas

The performance of multibeam focal plane arrays feeding a single aperture is usually reduced due to conflicting requirements on the feed elements. Dense packing is usually required to minimize the beam separation, while typically large feed apertures are needed to provide the high feed directivity to reduce spillover losses from the reflector. In this paper the use of dielectric super-layers to shape the radiation pattern of each feed is demonstrated. The shaping is obtained by exciting, according to design, a pair of TE/TM leaky waves. The spillover from the reflector is reduced without physically increasing the dimensions of each single element aperture. A prototype of a feed array composed of 19 waveguides arranged in a hexagonal lattice was designed, manufactured and tested. The measured embedded patterns provided an increase of the edge of coverage gain, with respect to the free space case, of at least 0.6 dB in an operating bandwidth (BW) of ap12%. Moreover when reactive loading of adjacent feeds is adopted the increase in the edge of coverage with respect to the free space case was demonstrated to be larger than 1.6 dB over a 3% BW.     

On the optimal radiation bandwidth of printed slot antennas surrounded by EBGs

This paper describes a design strategy to achieve the maximum bandwidth and efficiency for a printed slot antenna surrounded by EBGs. First the dielectric constant and the thickness of the dielectric slab that guarantees an acceptable front to back radiation ratio is identified. Then electromagnetic bandgap (EBG) structures are designed to achieve the optimal bandwidth (BW) while obtaining high surface wave efficiency in the radiating half space. To achieve this goal the wave interaction between the slot and the EBG structures is investigated in depth and clearly described. For the case of Planar circularly symmetric (PCS) EBGs the maximum of radiation BW is shown to occur when the distance between the central antenna and the EBG is approximately half wavelength of the first surface wave, /spl lambda//sub sw//2.