Yuriy Prokopenko

Loss in tunable microstrip lines

Electromagnetic energy loss in the micro-mechanically tunable microstrip line is studied including dielectric loss in substrates medium and ohmic loss in metal electrodes. When total loss in the device is relatively small, loss mechanisms contribute additively, so complex effective permittivity can be used to account both phenomena. This simplifies analysis and design of tunable microstrip lines. It is shown that with micro-mechanical tuning both dielectric and metal loss decrease comparing to those of conventional line.

Novel concept for microstrip stub resonant frequency control

A novel concept for controlling a low-cost tunable microstrip filter is proposed. The microstrip stub controlling is realized by detaching a part of the stub from the substrate. The air gap between the substrate and the signal electrode is the heterogeneity which controls the stub effective permittivity, in this way providing a resonance frequency shift. By moving the stub 50 microns the resonance frequency is shifted about 1 GHz. An equivalent circuit model of the resonator is developed. Calculation results are in good agreement with finite-difference time-domain method (FDTD) and finite elements method (FEM) simulations.

Quality factor of tunable shielded cylindrical metal-dielectric resonator

The paper discusses quality factor of tunable shielded cylindrical metal-dielectric resonator taking into account dielectric and metal losses. It was shown that both metal and dielectric losses decrease in case of the air gap inclusion. It was investigated that the dielectric loss has local minimum.

Electromechanical Control over Effective Permittivity Used for Microwave Devices

Ferroelectrics are well known tunable dielectric materials. Permittivity of these materials can be controlled by an applied electrical bias field. Controllable permittivity leads to alteration of characteristics of tunable microwave components such as propagation constants, resonant frequency etc. However, dielectric losses in the ferroelectric-type tunable components are comparatively high and show substantial increase approaching to the millimetre waves due to fundamental physical reason.

Ferroelectrics Study at Microwaves

Dielectric materials are of interest for various fields of microwave engineering. They are widely investigated for numerous applications in electronic components such as dielectric resonators, dielectric substrates, decoupling capacitors, absorbent materials, phase shifters, etc. Electric polarization and loss of dielectric materials are important topics of solid state physics as well. Understanding their nature requires accurate measurement of main dielectric characteristics. Ferroelectrics constitute important class of dielectric materials. Microwave study of ferroelectrics is required not only because of their applications, but also because important physical properties of theses materials, such as phase transitions, are observed at microwave frequencies. Furthermore, most of ferroelectrics have polydomain structure and domain walls resonant (or relaxation) frequency is located in the microwave range. Lattice dynamics theory also predicts strong anomalies in ferroelectric properties just at microwaves. That is why microwave study can support the investigation of many fundamental characteristics of ferroelectrics. Dielectric properties of materials are observed in their interaction with electromagnetic field. Fundamental ability of dielectric materials to increase stored charge of the capacitor was used for years and still used to measure permittivity and loss at relatively low frequencies, up to about 1 MHz (Gevorgian & Kollberg, 2001). At microwaves studied material is usually placed inside transmission line, such as coaxial or rectangular waveguide, or resonant cavity and its influence onto wave propagation conditions is used to estimate specimen’s properties. Distinct feature of ferroelectric and related materials is their high dielectric constant (ε = 102 – 104) and sometimes large dielectric loss (tanδ = 0.01 – 1). High loss could make resonant curve too fuzzy or dissipate most part incident electromagnetic energy, so reflected or transmitted part becomes hard to register. Also because of high permittivity most part of incident energy may just reflect from sample’s surface. So generally conventional methods of dielectrics study may not work well, and special approaches required. Another problem is ferroelectric films investigation. Non-linear ferroelectric films are perspective for monolithic microwave integrated circuits (MMIC) where they are applied as linear and nonlinear capacitors (Vendik, 1979), microwave tunable resonant filters (Vendik et al., 1999), integrated microwave phase shifter (Erker et al., 2000), etc. Proper design of these devices requires reliable evidence of film microwave dielectric constant and loss tangent. Ferroelectric solid solution (Ba,Sr)TiO3 (BST) is the most studied material for

Coplanar line based low loss microwave phase shifters with electromechanical control

Paper presents the study of phase shifters with mechanical control based on coplanar line. Reconfiguration in a form where signal line of coplanar waveguide can be lifted above substrate provides strong perturbation of electromagnetic filed and thus ensures strong sensitivity. Utilization of high-Q dielectric materials makes it possible to extend substantially the operation frequency range while maintain low loss. Need displacement may be reduced to the range of tens micrometers, thus allowing utilization of fast piezo-actuators or MEMS.

Waveguide variable attenuator suitable for electromechanical control

The paper continues research of microwave devices consisting of rectangular waveguide section with dielectric slab in it. The air clearance exists between dielectric slab and wide wall of the waveguide. Variation of the clearance by means of external actuator influences on propagation constant of the wave travelling through the device. This way the device can produce variable phase shift. Under certain conditions waveguide section goes beyond cutoff, and variable clearance produces controllable attenuation. Combined with high speed actuator device can operate as fast tunable attenuator or switch. The paper presents electromagnetic field problem and simulation results.