Ferroelectric Phase Shifter Research Articles

Optimum Reflection-Type Phase Shifter Using (Ba,Sr)TiO3 Thin Film

In this paper, in order to obtain a large differential phase shift with a little change in applied voltage, a ferroelectric reflective load circuit has been designed on top of barium strontium titanate (Ba,Sr)TiO3 [BST] thin film. The design of the ferroelectric reflection-type phase shifter is based on a reflection theory of terminating circuit, which has a reflection-type analogue phase shifter with two ports terminated in symmetric phase-controllable reflective networks. To achieve large amounts of phase shift in low bias-voltage range, the effects of change of capacitance and transmission line connected with two coupled ports of a 3-dB 90° branch-line hybrid coupler have been investigated. A large phase shift with a small capacitance change in the parallel terminating circuit has been demonstrated in the paper.

Widening of Operational Temperature Range of Microwave Ferroelectric Tunable Devices

The ways to solve a problem of providing stable operation of microwave ferroelectric phase shifters for steerable antennas in a wide temperature range are briefly considered. A ferroelectric phase shifter based on cascaded tunable ferroelectric planar capacitors is properly described. The connection of the tunable capacitors in series with transmission line sections allows obtaining a voltage tunable phase shift, which practically does not depend on temperature in the range 250–350 K. Such phase shifters can find a wide application in phased-array antennas.

Theoretical Estimation of Achievable Figure of Merit of Microwave Ferroelectric Phase Shifters

The goal of this paper is estimation of an achievable figure of merit of microwave phase shifters. The microwave dissipation in ferroelectric material, conducting electrodes of ferroelectric components and the loss in an external circuitry are taken into account. Equations for a theoretical estimation of an achievable value of the phase shifter figure of merit have been derived and used for simulations. It has been shown that the achievable figure of merit is at least three times as high as the figure of merit of practically realized microwave phase shifters described in literature.

Influence of Narrow Transverse Slit in Ferroelectric Based Voltage Tunable Phase Shifter

We report on gold/Ba0.5Sr0.5TiO3 (BST) ferroelectric thin film Ku-band phase shifters designed and fabricated on MgO substrates using two different structures; the coplanar waveguide (CPW) meander line phase shifter and the new phase shifter with narrow transverse slits in the ground plane of the CPW structure. The ability of these devices to provide a variable phase shift is based on the change in dielectric constant of BST with an applied dc bias. The phase shifter with narrow transverse slits showed larger phase shift capability than that of the conventional meander line phase shifter. In the former phase shifter, the phase shift of about 10.6 as a maximum value for the frequency range from 16 GHz to 18 GHz was obtained. In the latter, the phase shift of 9.7 deg at 18 GHz and at an applied voltage of 30 V was measured.

A finline 60-GHz phase shifter based on a (Ba,Sr)TiO3 ferroelectric thin film

The design and microwave characteristics of a ferroelectric thin film slotline-waveguide phase shifter operating in the millimeter wavelength range (f∼60 GHz) are presented. In this frequency range, the phase shifter possesses a figure of merit F=32 deg/dB and provides for a continuous phase shift in the interval from zero to 255 deg. The ferroelectric films are characterized by a dielectric loss tangent of tan δ=0.04 at a tunability factor of K≈1.7, which are promising parameters for the given frequency range.

Microwave Tunable Components and Subsystems Based on Ferroelectrics: Physics and Principles of Design

The most promising microwave ferroelecric device is a ferroelectric phase shifter, aimed to be an element of a phased-array antenna. The following characteristics of the phase shifter are important: microwave insertion loss, range of operational temperatures, life time. Designing microwave tunable components is based on carefully developed models of ferroelectrics and appropriate software of the circuit design. The quality of a phase shifter is determined by the figure of merit ( F ) defined as a ratio phase shift/insertion loss and measured in deg/dB. For competitive applications one needs F = 200-300 deg/dB. An extended temperature range of operation is urgently required. There are the following ways of improvement of the ferroelectric phase shifters: i) utilizing an appropriate chemical compound of ferroelectric material, ii) developing the structure of the device, for example, the film with a variable composition factor, iii) application of the digital mode of operation.

Ferroelectric Ba 0.6 Sr 0.4 TiO 3 Phase Shifters Under High Power Microwave

High power microwave properties of the ferroelectric phase shifters have been studied to reduce the effect of the nonlinear response of ferroelectrics under high power microwave with an applied dc bias field of 0 - 40 kV/cm. The Ba 0.6 Sr 0.4 TiO 3 ferroelectric films were prepared on (001) MgO single crystals by pulsed laser deposition. Coplanar waveguide (CPW) phase shifters were fabricated from 2 w m thick Au layer to reduce metal loss. The fabricated CPW phase shifters exhibited more than 100° of differential phase at 10 GHz with a 40 kV/cm dc bias field between ground and center conductors. Furthermore, the CPW phase shifter showed a constant differential phase shift with microwave power range from m 10 to +30 dBm. Microwave power and/or dc bias field dependant responses of phase shifters are presented in the paper.

Commutation Quality Factor as a Working Tool for Optimization of Microwave Ferroelectric Devices

The commutation quality factor (CQF) is suggested as a generalized criterion of the material tunability and its loss factor. The figure of merit of a switchable device is uniquely determined by the CQF. From this point of view the CQF is used as a working tool for optimization of the microwave devices. A comparison between analog and digital ferroelectric phase shifter was performed using the CQF as a criterion. Theoretically was predicted that a digital phase shifter based on lumped tunable ferroelectric capacitors can be designed with minimal achievable insertion loss. As an example, the 180 reflection type phase shifter is discussed.

Microwave Properties of Compositionally Graded (Ba, Sr)TiO 3 Thin Films for Electrically Tunabel Microwave Devices

Compositionally graded ferroelectric thin films have execellent dielectric properties and abnormal ferroelectric properties which can be used in various microelectronic devices. Compositionally graded (BaSr)TiO 3 [BST] thin films were prepared on MgO substrates by pulsed laser deposition. The crystalline orientation and microstructure of graded BST thin films were studied using x-ray diffraction, scanning electron microscopy. The microwave properties of the graded BST films were investigated as a function of the direction of composition gradient with respect to substrate. Also, we report on the fabrication and performance of coplanar ferroelectric phase shifters. Coplanar waveguide(CPW) type phase shifters have been fabricated on the graded BST/MgO using Au/Cr metal electrodes. The phase shifters were tested at frequencies up to 20 GHz

Microwave Properties of Compositionally Graded (Ba, Sr)TiO 3 Thin Films for Electrically Tunabel Microwave Devices

Compositionally graded ferroelectric thin films have execellent dielectric properties and abnormal ferroelectric properties which can be used in various microelectronic devices. Compositionally graded (BaSr)TiO 3 [BST] thin films were prepared on MgO substrates by pulsed laser deposition. The crystalline orientation and microstructure of graded BST thin films were studied using x-ray diffraction, scanning electron microscopy. The microwave properties of the graded BST films were investigated as a function of the direction of composition gradient with respect to substrate. Also, we report on the fabrication and performance of coplanar ferroelectric phase shifters. Coplanar waveguide(CPW) type phase shifters have been fabricated on the graded BST/MgO using Au/Cr metal electrodes. The phase shifters were tested at frequencies up to 20 GHz

Ferroelectric Ba 0.6 Sr 0.4 TiO 3 Phase Shifters Under High Power Microwave

High power microwave properties of the ferroelectric phase shifters have been studied to reduce the effect of the nonlinear response of ferroelectrics under high power microwave with an applied dc bias field of 0 - 40 kV/cm. The Ba 0.6 Sr 0.4 TiO 3 ferroelectric films were prepared on (001) MgO single crystals by pulsed laser deposition. Coplanar waveguide (CPW) phase shifters were fabricated from 2 w m thick Au layer to reduce metal loss. The fabricated CPW phase shifters exhibited more than 100° of differential phase at 10 GHz with a 40 kV/cm dc bias field between ground and center conductors. Furthermore, the CPW phase shifter showed a constant differential phase shift with microwave power range from m 10 to +30 dBm. Microwave power and/or dc bias field dependant responses of phase shifters are presented in the paper.

Optimization of Reflection Type Ferroelectric Phase Shifter with Respect to Sensitivity to Statistical Dispersion of Circuit Characteristics at Microwaves

Commercial applications of ferroelectrics at microwaves can be realized in a case of mass production of field effect phase shifters (FEPS), aimed to be element of electronically steerable antennas (ESA). Such phase shifters are designed as microwave integrated circuits based on ferroelectric films. In order to provide a high reproducibility of FEPS integrated circuit, one needs to know how the operational parameters of FEPS are influenced by variation of the phase shifter circuit characteristics. This information is generalized in sensitivity of the phase shifter to statistical dispersion of its circuit characteristics and characterized numerically by tolerance sensitivity factor. The reflection type digital FEPS was investigated. The sensitivity of FEPS was taken as efficiency function of the optimization procedure. It was found that the minimum of the tolerance sensitivity factor is highly dependent on a particular design of the FEPS.

Beam scanning of array using ferroelectric phaseshifters

The beam scanning characteristics of a two-element array utilising a ferroelectric phase shifter are presented for the first time. Applying a DC voltage across the ferroelectric material changes the velocity of the input signal, a beam scan of 26° being achieved. The S11 performance and the radiation patterns of the array at two frequencies are presented.

Evaluating voltage-tunable materials for RF phase shifter technology

Today's phased-array antennas use hundreds of radiating elements that use relatively high-loss phase shifters that operate over a limited bandwidth. The number of elements and the phase shifter losses affect the overall cost of the antenna system. Ferroelectric RF phase shifters have the potential to meet the low-loss, low-cost requirements driving many phased-array applications. Some of the issues affecting the development of ferroelectric phase shifters include ferroelectric tunability, dielectric losses, conductor losses, and impedance mismatch. We used the measured tunability (250 kHz, room temperature), dielectric constant, and loss tangent (10 GHz, room temperature) of Ba1-xSrx/TiO3 (0.4x 0.6) with various amounts of MgO additive, 0 to 60 wt.%, to estimate the device performance of microstrip phase shifters. The electromagnetic model of the microstrip (which uses a standard 3-mil-wide 1-oz. copper line, 3-mil-thick BST/MgO composite and the bias criteria of 2 V/μm) has produced performance benchmarks for a number of composites providing 360° of phase shift. While the accuracy of the electromagnetic model used to evaluate these materials has limitations, the results do provide some insight as to which materials may be better suited for 10-GHz phase shift devices.

A model for ferroelectric phase shifters

Novel microwave phase shifters consisting of coupled microstriplines on thin ferroelectric films have been demonstrated recently. A theoretical model useful for predicting the propagation characteristics (insertion phase shift, dielectric loss, impedance, and bandwidth) is presented here. The model is based on a variational solution for line capacitance and coupled strip transmission line theory.

Microwave phase shifter employing srtio3 ferroelectric varactors

Nonlinear microwave properties of thin SrTiO3 ferroelectric films at ambient temperatures were investigated. A tunability factor of 1.7 and loss tangent of about 0.01–0.015 were measured at frequencies of 2–10 GHz for SrTiO3 thin film planar varactors at room temperature. The performance of an X-band microstrip phase shifter employing the SrTiO3 planar varactors at room temperature is reported. Continuous phase shift in the range of (0–55) deg under bias voltage of 0–400 V at operating frequency band (8.6–9.0) GHz was observed. A figure of merit for the phase shifter is 110 deg/dB and the phase error is smaller than 5 deg. To our knowledge, it is the first demonstration of the microwave application of SrTiO3 varactors operating as nonlinear elements at room temperature and a record result for figure of merit for ferroelectric phase shifters.

30 GHz Electronically Steerable Antennas Using BaxSr1−xTiO3-Based Room-Temperature Phase Shifters

AbstractWe report the performance of 16-element phased array antennas operating at 30 GHz and ambient temperature. These antennas use BaxSr1−xTiO3(BST)-based phase shifters to produce the beam steering. Ferroelectric phase shifters offer advantages over current semiconductor and ferrite devices including faster switching speeds and lower costs. Also, ferroelectric phase shifters offer higher power handling capability than semiconductor devices and also have high radiation resistance. We made phase shifters from laser-ablated epitaxial BST films as well as from polycrystalline BST-oxide composite films. Although neither the devices nor the materials themselves are fully optimized, phase shifters have shown > 360° of phase shift with < 350 V DC bias (E < 9 V/µm) and ∼8 dB insertion loss. With ferroelectric phase shifters incorporated, antennas show radiation patterns with central-lobe half-power widths of ∼13° and side lobe intensities down by more than 10 dB. Using the phase shifters, the central lobe can be shifted, or “steered,” by ±18° in either direction. These results demonstrate a first step toward a prototype steerable antenna for 20–30 GHz satellite communications as well as other applications.

Analysis and Optimization of Thin-Film Ferroelectric Phase Shifters

AbstractMicrowave phase shifters have been fabricated from (YBa2Cu3 O7-δ or Au)/SrTiO3 and Au/BaxSr1−xTiO3 films on LaAlO3 and MgO substrates. These coupled microstrip devices rival the performance of their semiconductor counterparts at Ku- and K-band frequencies. Typical insertion loss for room temperature ferroelectric phase shifters at K-band is ≈5 dB. An experimental and theoretical investigation of these novel devices explains the role of the ferroelectric film in overall device performance. A roadmap to the development of a 3 dB insertion loss phase shifter that would enable a new type of phased array antenna is discussed.

Fabrication and performance of coplanar ferroelectric phase shifter

Coplanar ferroelectric phase shifters have been fabricated from thin films of barium strontium titanate (BST) and gold coplanar waveguide. The ability for these devices to provide a variable phase shift is based upon the change in dielectric constant of the BST with an applied de bias. We have fabricated coplanar phase shifters by three different series of fabrication steps. For each of the three devices, MgO was used as the substrate, and the BST films were deposited by laser ablation. We describe the coplanar design, material deposition, and the high frequency testing. The phase shifters were tested at frequencies up to 35 GHz.

Several microstrip-based conductor/thin film ferroelectric phase shifter designs using (YBa2Cu3O7-δ,Au)/SrTiO3/LaAlO3 structures

We have designed, fabricated, and tested several novel microstrip-based YBa2Cu3O7-δ/SrTiO3/LaAlO3 (YBCO/STO/LAO) and Au/SrTiO3/LaAlO3 (Au/STO/LAO) phase shifters. The first design consists of eight coupled microstrip phase shifters (CMPS) in series. This design using YBCO achieved a relative insertion phase shift (Δφ) of 484° with a figure of merit of 80°/dB at Vdc=375 V, 16 GHz, and 40 K. A Δφ of 290° was observed while maintaining the insertion loss below 4.5 dB. At 77 K, a Δφ of 420° was obtained for this phase shifter at the same bias and frequency. Both results correspond to an effective coupling length of 0.33 cm. A second compact design, consisting of an Au meander line and a CMPS section was also tested. Of the two samples tested, the best showed a figure of merit of 43°/dB with Δφ = 290° and 6.8 dB loss, at 40 K, 10 GHz and 400 V. Experimental and modeling results on these circuits will be discussed in the context of potential applications.