Analysis, Design and Applications of Reflectarrays

A brief overview of reflectarray antennas mainly focused on some efficient analysis and design techniques and on recent developments has been presented. A technique based on the local periodicity and Method of Moments in Spectral Domain has been presented as very efficient for the analysis of reflectarray antennas. The technique has been validated by comparing simulations and measurements in several breadboards. Based on the previous analysis technique, several design procedures have been implemented for different antenna performances, including requirements of broad-band, dualfrequency and stringent contoured beams. Finally some recent developments for applications in space and LMDS antennas are presented

Location, Orientation and Aggregation of Bardoxolone-ME, CDDO-ME, in a Complex Phospholipid Bilayer Membrane

Bardoxolone methyl (CDDO-Me), a synthetic derivative of the naturally occurring triterpenoid oleanolic acid, displays strong antioxidant, anticancer and anti-infammatory activities, according to diferent bibliographical sources. However, the understanding of its molecular mechanism is missing. Furthermore, CDDO-Me has displayed a signifcant cytotoxicity against various types of cancer cells. CDDO-Me has a noticeable hydrophobic character and several of its efects could be attributed to its ability to be incorporated inside the biological membrane and therefore modify its structure and specifcally interact with its components. In this study, we have used full-atom molecular dynamics to determine the location, orientation and interactions of CDDO-Me in phospholipid model membranes. Our results support the location of CDDO-Me in the middle of the membrane, it specifcally orients so that the cyano group lean towards the phospholipid interface and it specifcally interacts with particular phospholipids. Signifcantly, in the membrane the CDDO-Me molecules specifcally interact with POPE and POPS. Moreover, CDDO-Me does not aggregates in the membrane but it forms a complex conglomerate in solution. The formation of a complex aggregate in solution might hamper its biological activity and therefore it should be taken into account when intended to be used in clinical assays. This work should aid in the development of these molecules opening new avenues for future therapeutic developments

Diseño construcción y medida de un reflectarray para antena terminal en banda KA

This contribution describes the design, manufacturing and test of a printed reflectarray for a Ka-band terminal antenna. The reflectarray has been designed to produce a focused beam at 30 GHz (uplink) in V polarisation and also at 20 GHz (downlink) in H polarisation. Two separate feeds are used to illuminate the reflectarray for H (20 GHz) and V polarisation (30GHz). The reflectarray element is made of two stacked varying-sized patches, being one dimension adjusted to focus the beam at 20 GHz in H polarization, and the other to focus the 30 GHz beam in V-polarization. A breadboard has been manufactured and tested. The measured radiation patterns show very good agreement with those obtained from the simulations. A 10% bandwidth has been obtained in both frequency bands, with an antenna efficiency of 62% at 30 GHz and 70% at 20 GHz

Reflectarray for K/Ka Band Terminal Antenna

Different satellite systems have been defined to provide broadband communications and internet access in remote geographical areas in Ka band (20-30 GHz) [1-2], being the up-link at 30 GHz and the down-link at 20 GHz. Costeffective antennas are required for fixed and portable terminals in Ka-band. Conventional reflectors are a preferred option to maintain reduced costs. However, the different receive (Rx) and transmit (Tx) frequencies obliges to use either a dual-frequency horn or two independent horns. The dual-frequency horn presents some difficulties, mainly because the phase-centre is different at each frequency, which would cause a reduction of the antenna gain. The use of independent feeds for Tx and Rx is simpler, but this solution is not possible using reflector antennas, because the two horns located at different positions cannot generate a beam in the same direction

Multifed Printed Reflectarray With Three Simultaneous Shaped Beams for LMDS Central Station Antenna

A two-layer reflectarray is proposed as a central station antenna for a local multipoint distribution system (LMDS) in the 24.5-26.5 GHz band. The antenna produces three independent beams in an alternate linear polarization that are shaped both in azimuth (sectored) and in elevation (squared cosecant). The design process is divided into several stages. First, the positions of the three feeds are established as well as the antenna geometry to produce the three beams in the required directions. Second, the phase distribution on the reflectarray surface, which produces the required beam shaping, is synthesized. Third, the sizes of the printed stacked patches are adjusted so that the phase-shift introduced by them matches the synthesized phase distribution. Finally, the radiation patterns are computed for the central and lateral beams, showing a shaping close to the requirements. A breadboard has been manufactured and measured in an anechoic chamber, showing a good behavior, which validates the designing methodology

Bandwidth Improvement in Large Reflectarrays by Using True-Time Delay

A significant improvement in the bandwidth of large reflectarrays is demonstrated using elements which allow true-time delay. Two identical, large reflectarrays have been designed using different phase distributions to generate a collimated beam. In the former, the phase distribution is truncated to 360deg as is usual in reflectarray antennas, while in the second, the true phase delay is maintained (three cycles of 360deg). The chosen phase-shifter elements are based on previously measured and validated patches aperture-coupled to delay lines. The radiation patterns for both reflectarrays have been computed at several frequencies and the gain is represented as a function of frequency for both cases. Bandwidth curves are presented as a function of the reflectarray size

The current status and future prospects for therapeutic targeting of KEAP1-NRF2 and β-TrCP-NRF2 interactions in cancer chemoresistance

Drug resistance is one of the biggest challenges in cancer treatment and limits the potential to cure patients. In many tumors, sustained activation of the protein NRF2 makes tumor cells resistant to chemo- and radiotherapy. Thus, blocking inappropriate NRF2 activity in cancers has been shown to reduce resistance in models of the disease. There is a growing scientific interest in NRF2 inhibitors. However, the compounds developed so far are not target-specific and are associated with a high degree of toxicity, hampering clinical applications. Compounds that can enhance the binding of NRF2 to its ubiquitination-facilitating regulator proteins, either KEAP1 or β-TrCP, have the potential to increase NRF2 degradation and may be of value as potential chemosensitising agents in cancer treatment. Approaches based on molecular glue-type mechanisms, in which ligands stabilise a ternary complex between a protein and its binding partner have shown to enhance β-catenin degradation by stabilising its interaction with β-TrCP. This strategy could be applied to rationally discover degradative β-TrCP-NRF2 and KEAP1-NRF2 protein-protein interaction enhancers. We are proposing a novel approach to selectively suppress NRF2 activity in tumors. It is based on recent methodology and has the potential to be a promising new addition to the arsenal of anticancer agents

Analysis of dual-reflector antennas with a reflectarray as subreflector

In this paper, a modular technique is described for the analysis of dual-reflector antennas using a reflectarray as a subreflector. An antenna configuration based on a sub-reflectarray and a parabolic main reflector provides better bandwidth than a single reflectarray, and has a number of advantages compared with a conventional dual-reflector antenna. Examples include the possibility of beam shaping by adjusting the phase on the sub-reflectarray, and potential capabilities to scan or reconfigure the beam. The modular technique implemented for the antenna analysis combines different methods for the analysis of each part of the antenna. First, the real field generated by the horn is considered as the incident field on each reflectarray element. Second, the reflectarray is analyzed with the same technique as for a single reflectarray, i.e., considering local periodicity and the real angle of incidence of the wave coming from the feed for each periodic cell. Third, the main reflector is analyzed using the Physical Optics (PO) technique, where the current on the reflector surface is calculated by summing the radiation from all the reflectarray elements. Finally, the field is calculated on a rectangular periodic mesh at a projected aperture, and then a time-efficient fast Fourier transform (FFT) algorithm is used to compute the radiation pattern of the antenna. The last step significantly improves the computational efficiency. However, it introduces a phase error, which reduces the accuracy of the radiation patterns for radiation angles far away from the antenna's axis. The phase errors have been evaluated for two integration apertures. It has been demonstrated that accurate patterns are obtained in an angular range of plusmn6deg, which is sufficient for large reflectors. The method of analysis has been validated by comparing the results with simulations obtained from GRASP8. Finally, the theoretical beam-scanning performance of the antenna is analyzed

Demonstration of a Shaped Beam Reflectarray Using Aperture-Coupled Delay Lines for LMDS Central Station Antenna

A shaped-beam reflectarray based on patches, aperture-coupled to delay lines is demonstrated for local multipoint distribution system (LMDS) central station antennas, in the 10.10-10.70 GHz band. The antenna must cover a 60deg-sector in azimuth with a squared cosecant pattern in elevation. The design process consists of two steps. First, a phase-only pattern synthesis technique is applied to obtain the required phase-shift distribution on the reflectarray surface which generates the shaped pattern. The second stage consists of determining the length of the delay lines, aperture-coupled to the square patches, in order to achieve the phase distribution synthesized in the previous step. Two reflectarray antennas have been designed, one for vertical (V) and the other for horizontal (H) polarization. A breadboard for V-polarization has been manufactured and tested in an anechoic chamber, showing a good agreement between theoretical and measured radiation patterns