V. Molchanov

Low Loss Microwave Piezo-Tunable Devices

Tunable by the mechanical reconfiguration low loss dielectric filter and wide-band phase shifter are elaborated. Dielectric or metallic parts of device should have a piezo-dirigible air gap between them. Key idea is to provide strong perturbation in electromagnetic field in the region influenced by the mechanical control. Energy distribution within the device is controlled by fast piezo-actuator, and can be described as a change in the effective dielectric permittivity. Highly tunable devices are realized experimentally

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

Dielectric resonator with inhomogeneity - simulation method

A method of computations for temperature stable resonant systems based on the use of constituent dielectric resonator (CDR) dielectric inclusions is proposed. System design and the method of computation are discussed.

Microwave dielectric resonant structures with electrically controlled frequency

Functional possibilities of UHF and microwave devices based on dielectric resonators could be essentially extended if their resonant frequency f0 could be controlled. Some dielectric resonant structures capable of electrically controlling f0 in a wide frequency range with the preservation of high Q-factor were studied. Resonant frequency control was realised by means of one structural components small mechanical shift using the electrostrictive actuator. The examined dielectric resonant devices allow change in their resonant frequency as far as 10 - 30%.

Microwave characterization of dielectric substrates for thin films deposition

A new electrode-free method is proposed for microwave characterization of low-loss single crystal and ceramic dielectric substrates used for thin films deposition. The substrate is considered and characterized as a thin dielectric resonator. Both TE_01δ and HE_11δ resonance modes were activated in the substrates with a dielectric permittivity above 10. The in-plane averaged dielectric permittivity and losses of a number of substrates were measured in a broad temperature range using the TE_01δ mode. The HE_11δ modes are proposed for the in-plane dielectric anisotropy characterization. In-plane components of anisotropic dielectric parameters of the (110) DyScO₃ substrate were measured.

Microwave methods of ferroelectrics and related materials investigation

Ferroelectric materialspsila distinct feature is large dielectric permittivity epsiv which sometimes is accompanied by the large loss tangent tandelta. Often this becomes an obstacle to conduct their accurate characterization despite of variety of techniques available. This report is devoted to the selection of proper method for specific cases of bulk or film materials investigation to obtain reliable data of their epsiv and tandelta.

Dielectric Phase Shifter Based on Piezotunable Double-Link Impedance-Step Filter

Possible alternative of low loss and highly tunable MEMS phase shifter is discussed. Dielectric or metallic parts of device should have the piezo-dirigible air gap between them. Important is to provide a strong perturbation in electromagnetic field in the region influenced by the mechanical control. Energy distribution within the device is controlled by piezoelectric actuator, and can be described as a change in effective dielectric permittivity (epsiveff). Some of highly tunable piezoelectric RF MEMS devices are realized experimentally.

Dielectric phase shifter based on the piezo-tunable impedance-step filter

New devices based on the impedance-step filter are developed and studied. One of them is low loss band-puss tunable filter controlled by means of substrate effective dielectric constant change. Second setup is also tunable filter but utilized as a phase shifter. It represents the combination in one device: (1) impedance-step filter controlled from the direction of end- walls, and (2) low voltage multi-layer actuator. Controlled phase shift of ~100deg is obtained under the voltage of ~30 V in the frequency range of 0.7 - 0.9 GHz.

Tunable Microwave Devices Based on the Design Reconfiguration by Piezoelectric Actuator

Highly tunable low loss microwave devices are elaborated by electromechanical alteration in the configuration of device parts. Generally, such a device consists of dielectric and metallic parts with an air gap between them. Gap is located by the way that provides the largest perturbation in electromagnetic field. Energy distribution within the devices is controlled by the fast actuator and can be described as a change in effective permittivity (epsiv eff ). Mini-actuator is used for device control through the change of epsiv eff High tunable dielectric resonators and filters as well as wide-band low-loss phase shifters are realized experimentally.

Electro-mechanically tunable phase shifter

Novel microwave phase shifters utilizing microstrip line and microstrip filters are proposed. The fabricated phase shifters, which consist of either microstrip line or microstrip filter with either dielectric or metallic control element can be electro-mechanically adjusted in order to obtain up to 90deg phase-shift angle with sufficiently small insertion loss