Grating lobe suppression in phased arrays composed of identical or similar subarrays
The grating lobe suppression methods for non-equidistant array antennas composed of identical or similar subarrays are proposed. Subarrays have equidistant rectangular or triangular grid. The grating lobes of an antenna array are reduced due to the irregular arrangement of subarrays. The following methods are considered: relative shift of neighbor subarrays, arranging gaps between subarrays, using different element spacing in different subarrays, rotation of subarrays, and combination of these methods. The methods provide suppression of the grating lobes from −2.6 dB to −11 dB as compared to equidistant arrays while side lobes envelop grows slightly.
Grating Lobe Suppression in Aperiodic Phased Array Antennas Composed of Periodic Subarrays with Large Element Spacing
The techniques of grating lobe (GL) suppression in planar phased array antennas composed of periodic subarrays with rectangular or triangular grids with large element spacing are considered. GL suppression is achieved using an aperiodic arrangement of subarrays. This approach provides a means to decrease GLs without a significant increase in structural complexity relative to periodic arrays; moreover, other antenna parameters do not essentially change compared with periodic arrays. Estimations of maximum GL suppression are presented. Antenna characteristics such as sidelobe level, beam efficiency, and aperture efficiency are also considered. The influences of element radiation pattern and amplitude tapering are analyzed. Examples of radiation patterns of such phased arrays are given.
Negatively charged phospholipids trigger the interaction of a bacterial Tat substrate precursor protein with lipid monolayers.
Folded proteins can be translocated across biological membranes via the Tat machinery. It has been shown in vitro that these Tat substrates can interact with membranes prior to translocation. Here we report a monolayer and infrared reflection-absorption spectroscopic (IRRAS) study of the initial states of this membrane interaction, the binding to a lipid monolayer at the air/water interface serving as a model for half of a biological membrane. Using the model Tat substrate HiPIP (high potential iron-sulfur protein) from Allochromatium vinosum, we found that the precursor preferentially interacts with monolayers of negatively charged phospholipids. The signal peptide is essential for the interaction of the precursor protein with the monolayer because the mature HiPIP protein showed no interaction with the lipid monolayer. However, the individual signal peptide interacted differently with the monolayer compared to the complete precursor protein. IRRA spectroscopy indicated that the individual signal peptide forms mainly aggregated β-sheet structures. This β-sheet formation did not occur for the signal peptide when being part of the full length precursor. In this case it adopted an α-helical structure upon membrane insertion. The importance of the signal peptide and the mature domain for the membrane interaction is discussed in terms of current ideas of Tat substrate-membrane interactions.