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A mutual-synthesis approach is presented for the design of subsystems combining two microwave circuits. In this paper, we are focused on subsystems combining a filter and an antenna, in a first step, the methodology consists of synthesizing the global subsystem, which realizes both filtering and radiation functions, with respect to overall specifications. Considering circuits interactions within the subsystem, the resulting constraints are distributed optimally between the two circuits. The latter mutual synthesis then leads, on one hand, to a set of optimal impedances for their connection and, on the other hand, to the corresponding ideal characteristics of each circuit. A solution can then be selected by carrying out a compromise between the simplicity of achieving the characteristics of each circuit and the performances and compactness of the subsystem. In a second step, the circuits are designed independently with respect to the synthesized characteristics. Compared to a classical synthesis approach, where circuits are synthesized independently with respect to a common reference impedance (generally 50 or 75 [OMEGA]), the proposed mutual synthesis allows to simplify the global subsystem since interactions between the two circuits are considered and used optimally. The technique is illustrated with the design of a filter-antenna at K u-band. Index Terms--Antennas, filters, synthesis.

A new ultrawide-band (UWB) antenna named the 'scissors antenna' has been designed specially for transient ultra-wide-band applications. The scissors antenna, which is composed of conducting wires, radiates ultrashort pulses with very low dispersion. The radiation of this antenna has been characterized by a transient measurement method suitable for characterizing UWB antennas with very low dispersion. After a presentation of the scissors antenna, this measurement method is described. The last part of the paper presents a comparison between the radiation characteristics of the scissors antenna obtained by the transient measurements and those obtained by the classical harmonic measurements. Index Terms--Transient measurements, ultrawide-band (UWB) antenna.

This paper introduces a new explanation of the electromagnetic bandgap (EBG) material properties using the study of the EBG structures in the frequency domain and reciprocal space. Once the behavior of such a material is understood, properties of the EBG are used in order to make an EBG antenna. The antenna is realized with dielectric EBG rods. Its directivity is increased compared to a simple patch antenna. Such a device allows us to obtain a high gain with a very thin structure. Index Terms--Electromagnetic bandgap (EBG), high directivity, resonator antenna.

A new experimental transient approach is proposed for multifilar connector characterization and more particularly for the scattering parameters evaluation and the maximum electrical field radiation estimation. This paper describes the analysis principle used to calculate the scattering parameters ([S.sub.ij]) of the connector, and the method proposed for electrical field magnitude estimation. Thereafter, the experimental setup and the calibration procedure for the multifilar measurement is explained. Finally, measurements using a vector network analyzer show the efficiency of the transient test setup. Index Terms--Calibration, multifilar conector, radiation, scattering parameters, time windowing, transient setup.

It is well known that the temperature rise in a material modifies its physical properties and, particularly, its dielectric permittivity. The dissipated electromagnetic power involved in microwave heating processes depending on [Epsilon]([Omega]), the electrical characteristics of the heated media must vary with the temperature to achieve realistic simulations. In this paper, we present a fast and accurate algorithm allowing, through a combined electromagnetic and thermal procedure, to take into account the influence of the temperature on the electrical properties of materials. First, the temperature dependence of the complex permittivity ruled by a Debye relaxation equation is investigated, and a realistic model is proposed and validated. Then, a frequency-dependent finite-differences time-domain ([(FD).sup.2]TD) method is used to assess the instantaneous electromagnetic power lost by dielectric hysteresis. Within the same iteration, a time-scaled form of the heat transfer equation allows one to calculate the temperature distribution in the heated medium and then to correct the dielectric properties of the material using the proposed model. These new characteristics will be taken into account by the EM solver at the next iteration. This combined algorithm allows a significant reduction of computation time. An application to a microwave oven is proposed.

In this paper, an optoelectronic sampler and an autocorrelator are described. The devices are made with microstrip propagation lines, and ultra-rapid photoconductive switches are integrated in the same substrate. These devices are studied along two interacting directions: sampler description and operation, and electromagnetic study. In particular, the electromagnetic study is discussed here. The purpose of the first is to understand the electromagnetic behavior of the optoelectronic sampler. The second study enables us to simulate the autocorrelator operation in order to characterize the ultra rapid photoconductive switch.

Modeling of experiments using mixed methods. This paper shows the relevance of associating theoretical approach to experiments. However in the case of complex structures, no modelization is possible using entire field methods. Therefore, we propose a mix of entire fields methods applied in several concret examples.

In this paper, a static electromagnetic study of planar structures is effected. The determination of electric and magnetic field distributions is used to deduce the characteristic impedance of these structures. The second application concerns the simulation of the line feed when a transient analysis using the Finite Difference Time Domain Method is used to analyse the line behaviour. In the case of a microstrip line, this new excitation method is compared to two excitations which are generally used.

Modeling of interfaces between two media, using time-domain surface impedances, permits one to reduce the discretization volume in the finite-difference time-domain (FDTD) technique. The method presented here is based on an exact formulation of surface impedances, starting from Fresnel reflection coefficients for oblique incidence of the incident wave. The concept, valid for homogeneous and frequency-independent media, is then introduced in an FDTD algorithm where it is converted into a surface-impedance boundary condition (SIBC) for vertical or horizontal polarizations of locally plane waves. In this paper, two- and three-dimensional results are compared to those computed with classical FDTD or Fresnel reflection coefficients involving a Fourier transform.

The modeling of a 90 degree bend in a microstrip, carried out via a time frequency approach based on the Finite Difference Time Domain technique, is presented. Inthe study, the scattering parameters and radiated energy are derived from the Fourier transformed currents of the microstrip. A discussion of the stratified medium concept which was used to compute the radiation and surface wave losses is also included.

A complete electrical wire link between equipment boxes is analyzed using a theoretical method based on the finite-difference time-domain (FDTD) algorithm. This paper describes how the asymmetry of the transmission line created by different terminations has a direct impact on the radiation level. Thereafter, a transient experimental method is proposed to evaluate the behavior of localized defects on transmission links. The transient results lead to (S) parameters and radiation power. Simulations using the FDTD method validate experimentation. Index Terms--Calibration, finite-difference time-domain, transient experimental set-up, transient method.

This paper introduces two new photonic bandgap (PBG) material applications for antennas, in which a photonic parabolic reflector is studied. It is composed of dielectric parabolic layers associated to obtain a PBG material. The frequency gap is used to reflect and focus the electromagnetic waves. This device has been designed using a finite-difference time-domain (FDTD) code. FDTD computations have provided the theoretical reflector's directivity. These results are in good agreement with measurements, and it appears that the PBG reflector presents the same directivity as a metallic parabola. A second application uses a defect PBG material mode associated with a metallic plate to increase the directivity of a patch antenna. We explain the design of such a device and propose experimental results to validate the theoretical analysis. Index Terms--Antenna, defect, directivity, FDTD, parabolic reflector, photonic bandgap.