Anne Vilcot

Tunable Bandstop Defected Ground Structure Resonator Using Reconfigurable Dumbbell-Shaped Coplanar Waveguide

A modification of the conventional dumbbell-shaped coplanar waveguide defected ground structure (DGS) is proposed. This modification permits the continuous tuning of the rejected frequencies by using reconfiguration technique and it allows the control of the DGS equivalent-circuit model. The modified DGS possesses two-dimensional symmetry, hence, it has been studied under different symmetry conditions and the corresponding equivalent-circuit model in each case has been developed. Based upon this study, a tunable bandstop DGS resonator is proposed. 19% tuning range centered at 3.7 and 7.4 GHz, respectively, is achieved. The equivalent-circuit model of the resonator is also developed. All proposed structures have been fabricated. Measurements as well as three-dimensional simulations are found to be in a very good agreement with theoretical predictions

Tunable microwave load based on biased photoinduced plasma in silicon

The frequency tuning of a quarter-wave resonator using an optoelectronic control is reported. Sharp notch characteristics with a small decibel-insertion loss and tunable frequency with matching better than 45 dB are obtained by varying both the optical power and the DC bias. The measured frequency shift is more than 60% below the dark resonant frequency and is carried out without altering the shape of the response. The biased photoinduced plasma (BPP) loading the open terminated microstrip line is then analyzed by comparing microwave simulations and measurements. The deduced complex load equivalent to this biased photoinduced plasma is then confirmed by semiconductor simulations. Results show the great possibilities offered by this BPP load (BPPL), which can be easily and widely tuned by means of a simple optoelectronic control. The frequency bandwidth of tuning is limited by the geometrical parameters and may be extended to millimeter-wave operation.

Toward a simulation of an optically controlled microwave microstrip line at 10 GHz

This paper deals with a microwave microstrip line that is terminated by a laser illumination, which alters the behavior of this microwave device. The first result is the numerical simulation of the microstrip line ended by a photoinduced load with the finite element method (FEM) and with hexahedral edge elements. The main difficulties of this kind of simulation remains in the fact that we deal with an open structure and that the photoinduced load is complex and inhomogeneous.

Narrow bandpass filter based on the modified DGS

In this paper, a bandpass filter based on the modified defected ground structure (MDGS) is proposed and its corresponding transmission line (TL) model is developed as well. The resulting bandpass filter provides 1.89 dB insertion loss and 19.2% relative bandwidth. A second order narrow bandpass filter is then investigated by closely coupling two unit cells. This leads to an improvement of 44% in the quality factor. The resulting passband insertion loss is 2.27 dB and the relative bandwidth is 10.7% around 4.2 GHz. Both structures were realized on FR4 substrate, EM simulation, TL model, as well as measurement results are in a very good agreement.

A compact tune-all bandpass filter based on coupled slow-wave resonators

A compact hybrid tune-all bandpass filter based on coupled slow-wave resonators is demonstrated. The performance of such a filter electronically tuned with commercially available low-cost semiconductor varactors is promising in terms of center-frequency (f/sub c/) and bandwidth wide continuous tunings. Indeed, the -3 dB bandwidth of this filter can be tuned between /spl sim/50 MHz and /spl sim/78 MHz for a /spl plusmn/ 18%-center-frequency tuning around 0.7 GHz, an insertion loss smaller than 5 dB and a return loss higher than 13 dB at the center frequency. Moreover, for a /spl sim/50 MHz fixed bandwidth, the center frequency can be tuned between 0.51 GHz and 0.81 GHz leading to a relative /spl plusmn/ 24%-center-frequency tuning. Finally, the total physical length of the prototype filter is about 0.27/spl lambda//sub c/ for a 0.7 GHz center frequency.

Optically controlled phase-shifter based on gaps on microstrip line

An optically controlled phase-shifter has been designed taking benefit of high resistive silicon photo-absorption at 843 nm. Phase-shift of 85/spl deg/ has been achieved in the frequency range 18 GHz-28 GHz under very low optical power while the magnitude remains practically constant. Physical and electromagnetic modelling has been performed to explain optically controlled microwave effects in these microstrip structures.

A new optoelectronic technique for microwave passive structures tuning

An optoelectronic technique useful for microwave passive structures tuning is reported. It is based on the biasing of a photoinduced plasma loading an open terminated microstrip line. Experimental results for a tapped half-wave resonator are presented. Sharp notch characteristics with a few dB insertion loss and a tunable resonant frequency with a matching better than 45 dB are obtained by varying both the optical power and the DC bias. The observed frequency shift is more than 30% below the dark resonant frequency and is carried out without altering the Q-factor. Moreover an experimental investigation on the realisation of an optoelectronically tunable bandstop filter seems to give promising results.

Coplanar Waveguide Filters Based on Multibehavior Etched-Ground Stubs

In this paper, coplanar waveguide filters with etched-ground stubs that have multiple behaviors are proposed. The response of a unit cell is a band reject with one or more transmission zeros according to the number and the lengths of the stubs. A library of transmission line models is being built for the basic cells and then used for the design of more elaborated structures. The potential of these new topologies is highlighted by providing different filtering structures with interesting features: a second-order narrow bandpass filter, and two configurations for a lowpass filter with a wide stopband. All theoretical predictions have been verified by electromagnetic simulation and measurements.

3-dimensions analytical modeling of the optical carriers injection in a semiconductor substrate

In order to be faster and more precise than numerical way in the computation of the photo-induced plasma in semiconductor, we have to use an analytical approach to solve the problem. In this study, we use the Hankel transform to simplify the resolution of the differential equation of second order with non-constant coefficient, known as the diffusion equations. As a result, we obtain the 3-dimensions carrier density based on all the physical parameters of the substrate and of the laser beam and so we are able to study the sensibility to several parameters.

Optically Controlled Microstrip Phased Arrays

We propose here to apply the technique of the optical control of microwave devices to perform phase-shifting for microstrip phased arrays. The physical principle used is the photoconductive effect which enables the creation of a variable microwave load, when a gap in a line is illuminated with an optical signal of adequate wavelength. This principle is applied on a hybrid microwave ring. We have designed a phase-shifter with continuously varying phase and quasi-constant |S21|, with few return losses. The measurements have given interesting results. A low cost, and small size microstrip phased array antenna has been designed. By illuminating the phase-shifter under different optical powers, the main beam can be scanned in the H-plane continuously from -25° to 25°.