The gate-controllable complex conductivity of graphene offers unprecedented opportunities for reconfigurable plasmonics at THz and mid-IR frequencies. However, the requirement of a gating electrode ...close to graphene and the single `control knob' that this approach offers for graphene conductivity limits the practical implementation and performance of graphene-controllable plasmonic devices. Herein, we report on graphene stacks composed of two or more graphene monolayers separated by electrically thin dielectrics and present a simple and rigorous theoretical framework for their characterization. In a first implementation, two graphene layers gate each other, thereby behaving as a controllable single equivalent layer but without any additional gating structure. Second, we show that adding an additional gate --a third graphene layer or an external gate-- allows independent control of the complex conductivity of each layer within the stack and hence provides enhanced control on the stack equivalent complex conductivity. The proposed concepts are first theoretically studied and then demonstrated experimentally via a detailed procedure allowing extraction of the parameters of each layer independently and for arbitrary pre-doping. These results are believed to be instrumental to the development of THz and mid-IR plasmonic devices with enhanced performance and reconfiguration capabilities.
We present a method to design composite right/left handed transmission lines (CRLH-TLs) that exhibit a continuous phase shift around a given frequency of 0deg degree phase shift and optimal matching ...within a large bandwidth. The developments are based on a Bloch wave formulation on general CRLH-TL unit cell circuits. The design method is exact based on these circuits and is therefore valid both for effective or non-effective medium CRLH-TLs, which are shown to be also relevant realizations of CRLH-TLs. In particular, the benefits of the method are demonstrated in the case of different applications such as integrated phase shifters, leaky-wave antennas and low-impedance transmission lines.
This paper addresses the design of Vivaldi antennas with embedded reconfigurable stopband filters, to allow simultaneous multi-standard communication while rejecting interferers. Three designs ...targeting different band stop bandwidths are presented, all of them featuring wideband matching and large rejection-frequency tuning range. The bandstop filters are formed by microstrip resonators coupled to the Vivaldi slot and terminated by varactor diodes. The major benefits of this solution are a continuous reconfiguration of the stopband, the absence of DC bias network, a quasi zero DC consumption, and the fact that resonators and diode ohmic losses positively contribute to the filtering capability. For the potential use in vehicular communications a halved Vivaldi placed over a ground plane is proposed, but the same concept directly applies to standard complete Vivaldi antennas.
In this paper a reconfigurable bandpass filter able to switch between WiFi and UMTS transmit band standards is presented. The filter is designed in such a way that center frequency and bandwidth ...specifications are precisely met by defining a switchable filter topology that includes two folded resonator extensions switched by two PIN diodes. Design specifications require two center frequency states, one at 2.440 GHz with an 80 MHz bandwidth and a second center frequency state at 1.955 GHz with a 140 MHz bandwidth for the WiFi and UMTS transmit bands, respectively. Filter simulations were performed to match the required filter specifications. Measured results on the filter show a very good agreement with the simulations where a 2.428 GHz center frequency with a 71 MHz bandwidth was obtained for the WiFi state, and a 1.939 GHz center frequency with a 144 MHz bandwidth was obtained for the UMTS filter state. The simulated filter insertion losses were −3.339 and −3.796 dB for the WiFi and UMTS states, respectively. Measured insertion losses were −3.345 and −3.837 dB for the WiFi and UMTS states, respectively. The filter specifications were successfully matched with the proposed filter topology, where simulated and measured responses are in good agreement.
This paper discusses the analysis of reflectarray cells comprising MEMS control elements. The method employed allows a very fast and accurate analysis of the reflectarray cell performance, quasi ...independently of the number of embedded MEMS and reconfigurable states. It also allows computing useful design parameters such as the power dissipated in each MEMS within the cell. Based on this method, we present the analysis of a monolayer cell embedding a multitude of MEMS control elements, demonstrating for e.g. the intimate link between phase dispersion and loss in such reconfigurable reflecting cells.
This paper shows how periodic structure theory can be used to precisely model and design conventional distributed MEMS variable true-time delay lines, so as to deduce an improved topology for ...multi-bit operation. Results for the new configuration are then presented along with its conventional counterpart performances, highlighting the advantage of the new configuration in terms of mismatch and delay distortion.
We present MEMS-variable phase shifters based on the 1-dimensional composite right/left handed transmission line (CRLH-TL) metamaterial. The structures, based on coplanar waveguide (CPW) technology, ...are fully integrated on silicon and operate in the ku band. The analysis and design of the devices are based on full-wave simulations and accurate physical equivalent circuits including parasitics inherent to these MEMS implementations. In particular, the computation of the Bloch wave propagation constant and impedance based on the equivalent circuit was employed to achieve optimal performances in the different MEMS states. Two types of phase shifters are presented; in the first class of devices, the phase response can be analogically controlled over a range of several hundreds of MHz by applying a DC voltage between 0 V and 45 V. The MEMS-controlled CRLH-TL has been fabricated and characterized, showing good agreement with predicted performances. The structures are matched over bandwidths larger than 15% and the insertion loss is about −3.5 dB. In a second step, we present an improved design that allows dramatically increasing the tunability of the phase shifters, which are now operated in two discrete position. The linear phase response of the designed digital CRLH-TL can be shifted from 15 GHz to 18 GHz, which represent a tunability of about 20%. This tunability can also be seen as a control of the phase shift from −50° to +50° at a fixed frequency of 17 GHz. Bandwidth larger than 15% and insertion loss of about −3 dB are achieved in both states.
This paper presents the electrical design and characterization of a wafer-level, or 0-level, package for micro-electromechanical resonators. We start by identifying the requirements on the electrical ...parasitics of a packaged resonator, derived from an analysis of the oscillator circuit comprising the resonator. Then, using the deduced requirements as a starting point, an optimized design of the package is developed in a two-step procedure. First, initial choices for the package topology are made on the basis of intuitive and physical circuit models. Second, a more detailed analysis is carried out by means of full-wave simulations and circuit models extractions. Measured results on empty packages are presented, validating both circuit models and full-wave simulation results. Finally, the parasitics values obtained are discussed in the light of the implementation of an oscillator circuit, demonstrating the possibility to implement functioning oscillators based on the proposed package.
A practical approach for accurately modeling reconfigurable lumped components, such as semiconductor diodes or micro-electromechanical systems (MEMS), in commercial full-wave solvers is presented. ...First, an equivalent-circuit model is extracted from a calibrated measurement of the isolated component. This model is then carefully corrected for its insertion into commercial software packages in order to achieve excellent agreement between simulated and measured results. Among other things, it is shown that failing to do such a correction can lead to much higher errors than typical lumped-element manufacturer tolerances. The procedure is illustrated by the precise modeling of a p-i-n diode embedded in a reconfigurable antenna. The approach is obviously also applicable to fixed lumped components used in biasing circuits, for instance.
A practical approach for accurately modeling reconfigurable lumped components, such as semiconductor diodes or micro-electromechanical systems (MEMS), in commercial full-wave solvers is presented. ...First, an equivalent-circuit model is extracted from a calibrated measurement of the isolated component. This model is then carefully corrected for its insertion into commercial software packages in order to achieve excellent agreement between simulated and measured results. Among other things, it is shown that failing to do such a correction can lead to much higher errors than typical lumped-element manufacturer tolerances. The procedure is illustrated by the precise modeling of a p-i-n diode embedded in a reconfigurable antenna. The approach is obviously also applicable to fixed lumped components used in biasing circuits, for instance.
