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Frequency diverse arrays (FDAs) provide range-angle time-invariant transmit–receive beamforming, although a fine focus of their radiation patterns is costly since high-resolution mixers and phase shifters are required. An innovative approach to FDAs is proposed in which mixers and phase shifters are replaced by the application of periodic linear-phase time-modulating waveforms to the antenna excitations implemented with 2-bit variable phase shifters controlled with periodic on–off instants of binary sequences, which leads to a simple and precise method for FDA beam focusing. [ABSTRACT FROM AUTHOR]

Bio-inspired cyclopeptidic heterodimers built on [beta]-sheet-like hydrogen-bonding networks and bearing photoactive and electroactive chromophores on the outer surface have been prepared. Different cross-strand pairwise relationships between the side chains of the cyclic [alpha],[gamma]-peptides afford the heterodimers as three nonequivalent dimeric species. Steady-state and time-resolved spectroscopies clearly show an electron transfer process from [PI]-extended tetrathiafulvalene, covalently attached to one of the cyclopeptides, to photoexcited [60]fullerene, located on the complementary cyclopeptide. The charge-separated state was stabilized for up to 1 [mu]s before recombining and repopulating the ground state. Our current example shows that cyclopeptidic templates can be successfully used to form light-harvesting/lightconverting hybrid ensembles with a distinctive organization of donor and acceptor units able to act as efficient artificial photosystems. cyclic peptide nanotubes | fullerenes | self-assembly

Efficient total syntheses of the marine hydrocarbon polyacetylenes callyberynes (A-C) are achieved using highly convergent routes, which involved metal-catalyzed cross-coupling reactions to sp centers as the key steps. The convergent approaches to the three polyacetylenes rely on bond disconnections at the end of central sp centers and employ transition-metal-catalyzed alkynylation reactions (sp-sp, sp(super 2)-sp, or sp(super 3)- sp).

The synthesis of several benzo[b]-, benzo[c]-, and dibenzo[b,g]fluorenones is achieved by the thermal cyclization of 1-[2-(arylethynyl)phenyl]-3-trimethylsilypropynones. The introduction of substituents with the right electronic and steric properties on the aryl rings can cause the ratio of the two isomers to vary between 100.0 and 0:100.

Frequency diverse arrays (FDAs) allow the synthesis of dot-shaped radiated patterns in the range-angle space by applying frequency offsets to the antenna elements. Conventional FDAs are usually implemented with costly variable phase shifters and mixers and require an independent feeding network per beam for multibeam operation. In this letter, we propose an innovative approach to FDA that makes use of time-modulated array (TMA) building blocks modeled with inexpensive single-pole dual-throw switches. Our approach is able to simultaneously and independently steer two dot-shaped beam patterns, over the two most significant TMA harmonics, with an almost 90% time modulation efficiency. [ABSTRACT FROM AUTHOR]

The application of frequency offsets to the elements of a conventional phased array with variable phase shifters (VPSs) leads to frequency diverse arrays (FDAs) with the ability to provide range-angle spatial focusing. In this letter, we propose an innovative approach to FDA using switched time-modulated arrays (TMAs) instead of VPSs. The time modulation efficiency of the combined FDA-TMA approach is over 94% when using Kaiser windows to determine the frequency offsets. Such windows have the advantage of flexibly handling the tradeoff between the beam collection efficiency and the half power beamwidth without the need of difficult optimizations. [ABSTRACT FROM AUTHOR]

In this letter, sinusoidal pulsewidth modulation (PWM) is applied to the design of time-modulated arrays (TMAs). The array excitations are modulated using PWM-synthesized sine waveforms. This provides increased signal bandwidth, excellent rejection of the undesired harmonics, and modulation efficiencies aligned with the best ones in the literature. The simplicity of the technique allows for an easily implementable antenna array feeding network. [ABSTRACT FROM AUTHOR]

Time-modulated arrays (TMAs) can effectively perform beamsteering over the first positive harmonic pattern by applying progressively delayed versions of stair-step approximations of a sine waveform to the antenna excitations. In this letter, we consider synthesizing such stair-step sine approximations by means of Haar wavelets. Haar functions constitute a complete orthonormal set of rectangular waveforms, which have the ability to represent a given function with a high degree of accuracy using few constituent terms. Hence, when they are applied to the TMA synthesis, employing single-pole double-throw switches, such a feature leads to an excellent rejection level of the undesired harmonics as well as a bandwidth greater than that supported by conventional TMAs with on-off switches. [ABSTRACT FROM AUTHOR]

Doubly-selective channels, such as those that occur when the transmitter and the receiver move relative to each other at high speeds, are a key scenario for fifth generation (5G) cellular systems, which are mostly based in the use of the orthogonal frequency-division multiplexing (OFDM) modulation. In this paper, we consider an OFDM system using quadrature amplitude modulation (QAM) symbols and we show that, when transmitting over deterministic doubly-selective channels, the inter-carrier-interference (ICI) affecting a symbol can be well approximated by a complex-valued normal distribution. Based on this, we derive a lower bound for the link capacity using the Shannon-Hartley theorem. Finally, we provide an approximation of the bit error probability (BEP) using the well-known BEP expressions for Gray-coded QAM constellations over additive white Gaussian noise (AWGN) channels, and show numerical results that confirm that the proposed BEP expression approximates accurately the bit error ratio (BER) of the OFDM system for standardized channel models. The proposed closed-form analytical expressions for the capacity and the BEP do not only allow for discarding the need of computationally-costly Monte-Carlo system simulations, but also provide a theoretical framework to optimize the system parameters directly impacting on the achievable performance. [ABSTRACT FROM AUTHOR]

Presents informationon on the 27th European Signal Processing Conference in A Coruna, Spain: Looking Into the Future of Signal Processing [Conference Highlights] [ABSTRACT FROM AUTHOR]