A-Posteriori Versus A-Priori Access Strategies in Slotted All-Optical WDM Rings

The paper presents the concept of "a posteriori" access strategy, as opposed to the previously studied concept of "a priori" strategy, to provide a fair and ecient access technique in slotted wavelength division multiplexing (WDM) rings under a large variety of trac patterns. Using a posteriori strategies, the source node selects the packet for transmission based on the state of the WDM channels in the arriving slot, thus adapting the access decision to the instantaneous trac in the various channels. The packet selection process of a posteriori strategies, when contrasted with a priori strategies, yields fair and ecient utilization of the ring bandwidth without requiring the equalization of the ring latency, nor imposing restrictions on the trac patterns allowed in the system. Since the same features cannot be provided by a priori access strategies, a posteriori strategies oers a more versatile access control that justies the higher implementation complexity due to the multi-channel se..

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium