A varactor tuned branch-line hybrid coupler

This paper introduces a novel branch-line 90° hybrid coupler incorporating varactor diodes which allow tuning of the frequency response. A design covering the DCS, PCS and IMT2000 cellular frequency bands (1710-2170 MHz) is presented. Given a varactor tunability of 2.5:1, simulations suggest 20 dB return loss and 3±1 dB coupling is achievable across each transmit and receive sub-band by tuning the varactors. These results offer an improvement over a conventional single-section branch-line hybrid centred at 1950 MHz, and some miniaturisation is also achieved due to the capacitive loading. A prototype is constructed using commercially available varactor diodes, and reasonable agreement between the measured and simulated results is achieved

Electronically tunable lumped element 90° hybrid coupler

A method for tuning the centre frequency of a 3 dB hybrid coupler using varactor diodes is presented. The circuit is suitable for recon-figurable or multifunction transceivers that switch between several narrow frequency bands. A prototype covering the PCS, DCS and IMT2000 cellular bands (1710-2170 MHz) is demonstrated

Barium strontium titanate thin films on r-plane sapphire

This paper presents the microwave properties of barium strontium titanate (BST) thin films on r-plane sapphire substrates. A series of films with thickness 25-400 nm was prepared by pulsed laser deposition (PLD). Microwave properties of the films, including capacitance tunability and loss tangent, were extracted by patterning interdigitated capacitors (IDCs) on the film surface. The highest tunability of 64% was observed in the 200 nm film. These results demonstrate the possibility of integrating BST into the silicon on sapphire process

Barium strontium titanate thin films for tunable microwave applications

There has been unprecedented growth in wireless technologies in recent years; wireless devices such as cellular telephones and wireless local area network (WLAN) transceivers are becoming ubiquitous. It is now common for a single hardware device, such as a cellular telephone, to be capable of multi-band operation. Implementing a dedicated radio frequency (RF) front-end for each frequency band increases the component count and therefore the cost of the device. Consequently, there is now a requirement to design RF and microwave circuits that can be reconfigured to operate at different frequency bands, as opposed to switching between several fixed-frequency circuits. Barium strontium titanate (BST) thin films show great promise for application in reconfigurable microwave circuits. The material has a high dielectric constant which can be controlled by the application of a quasi-static electric field, combined with relatively low losses at microwave frequencies. Tunable microwave components based on BST-thin films have the potential to replace several fixed components, thereby achieving useful size and cost reductions. This thesis is concerned with the growth and microwave circuit applications of BST thin films on c- and r-plane sapphire substrates. Sapphire is an ideal substrate for microwave integrated circuit fabrication due to its low cost and low loss. Electronically tunable capacitors (varactors) were fabricated by patterning interdigital electrode structures on top of the BST films. High capacitance tunabilities of 56% and 64% were achieved for the films grown on c-plane and r-plane sapphire, respectively, at 40 V bias. A novel electronically tunable 3 dB quadrature hybrid circuit was also developed. Prototypes of this circuit were initially implemented using commercial varactor diodes, in order to validate the design. An integrated version of the coupler was then fabricated using BST varactors on c-plane sapphire. The results achieved demonstrate the potential of sapphire-based BST thin films in practical microwave circuits

Enhanced tunability of magnetron sputtered Ba[sub 0.5]Sr[sub 0.5]TiO[sub 3] thin films on c-plane sapphire substrates

Thin films of Ba0.5Sr0.5TiO3 (BST) were deposited on c-plane (0001) sapphire by rf magnetron sputtering and investigated by complementary materials analysis methods. Microwave properties of the films, including tunability and Q factor were measured from 1 to 20 GHz by patterning interdigital capacitors (IDCs) on the film surface. The tunability is correlated with texture, strain, and grain size in the deposited films. An enhanced capacitance tunability of 56% at a bias field of 200 kV/cm and total device Q of more than 15 (up to 20 GHz) were achieved following postdeposition annealing at 900°C

Formation of lead lanthanum zirconate titanate films by heat treatments

Lead lanthanum zirconate titanate (PLZT) also called lanthanum doped PZT films were deposited by RF magnetron sputtering. PLZT in the perovskite phase is required to obtain a film with a large electro-optic effect. It can also be used as a ferroelectric and piezoelectric material. However films that have not been heat treated either during or after deposition are typically in the pyrochlore phase. Perovskite PLZT films obtained by heating the substrate during sputtering showed little evidence of cracks in the films sputtered without heating the substrate were not in the Perovskite phase and post deposition annealing was required to do so. Both furnace and rapid thermal annealing were investigated but in both cases cracks formed in the films to various degrees. Such films are unsuitable for optical device fabrication. To determine the orientation of PLZT films X-ray diffraction (XRD) spectras were obtained and compared. Samples were prepared on silicon substrates which had a thin film of 20 nm Ti/100 nm Pt deposited by electron beam evaporation. Sputtering was done in an argon atmosphere using a PLZT (9/65/35) target. Thicknesses of 1 mum were obtained. Some samples were heated during sputtering up to a temperature of 650 degC. Annealing temperatures were varied from 500 to 750 degC. The best results (determined by XRD) were obtained for RTA at 750 degC for 10 minutes in air. XRD spectra of before and after annealing show a significant increase in the Perovskite peaks. The patterning of these films to form optical waveguides by ion beam etching is also presented. The samples were patterned with photoresist masks and ion beam etched using argon at a gun voltage of 500

Anomalous left brachiocephalic vein: important vascular anomaly concomitant with congenital anomalies and heart diseases

Background: Anomalous left brachiocephalic vein (ALBCV) is a rare and less known systemic venous anomaly. Infrequently, this vein takes an abnormal course and passes to the right behind or beneath the aortic arch to create the superior vena cava (SVC). Its incidence was reported much higher in patients with congenital heart disease especially in conotruncal and aortic arch anomalies. It could be misdiagnosed with normal or abnormal mediastinal structures. It also could make complication during surgeries or invasive strategies. Previously, this anatomical finding has been reported in case reports and there are just few studies evaluating these patients as a group to find other abnormalities Materials and methods: We conducted a retrospective, multicentre study between 2008 and 2014 at three institutions. We reviewed thoracic computed tomography angiography of 1372 patients referred to these centres. The diagnosis of ALBCV was confirmed by an expert radiologist and the imagings were reassessed to identify new cases and concomitant anomalies. We analysed the imagings’ details and measured the prevalence of each anomaly. Results: Among the 22 cases of ALBCV, 12 (54.5%) and 10 (45.4%) patients were males and females, respectively, with median age of 12.5 years. Tetralogy of Fallot (TOF) was considered as a most concomitant anomaly with ALBCV (54.5%). Two patients had associated atrial septal defect (ASD) and defined as pentalogy of Fallot. Right-sided aortic arc (RSAA) was detected in 12 (54.5%) patients; mirror image was found in 5 of them. Pure ventricular septal defect or pulmonary stenosis without TOF was recognised in 4 patients. Three cases had isolated overriding aorta (13.6%). In 3 patients, we could find patent ductus arteriosus (13.6%). In 2 (9%) patients, abdominal haemangioma was incidentally diagnosed. Aberrant left retrotracheal subclavian artery was detected in 1 (4.5%) patient. One patient only had isolated ALBCV (4.5%). Conclusions: In our study, ALBCV was frequently seen in association with other congenital anomalies. mostly TOF and RSAA. In patients with pulmonary hypoplasia or aplasia, some parts of lung’s blood supply were provided by abnormal aorto-pulmonary connections. For a radiologist, it is important to differentiate this anomaly in cross-sectional imaging from persistent left SVC, partial anomalous pulmonary veins return and an enlarged lymph node. Detection of ALBCV could draw the attention to the more serious heart disease and in isolated forms prevented further evaluations.

Finite temperature Cherenkov radiation in the presence of a magnetodielectric medium

A canonical approach to Cherenkov radiation in the presence of a magnetodielectric medium is presented in classical, nonrelativistic and relativistic quantum regimes. The equations of motion for the canonical variables are solved explicitly for both positive and negative times. Maxwell and related constitute equations are obtained. In the large-time limit, the vector potential operator is found and expressed in terms of the medium operators. The energy loss of a charged particle, emitted in the form of radiation, in finite temperature is calculated. A Dirac equation concerning the relativistic motion of the particle in presence of the magnetodielectric medium is derived and the relativistic Cherenkov radiation at zero and finite temperature is investigated. Finally, it is shown that the Cherenkov radiation in nonrelativistic and relativistic quantum regimes, unlike its classical counterpart, introduces automatically a cutoff for higher frequencies beyond which the power of radiation emission is zero.Comment: To be appear in PR

Two introduced psyllid species (Hemiptera, Psylloidea) in Brazilian eucalypt plantations.

1 CD-ROM. Autoria bilíngue: CONGRESSO E EXPOSICAO INTERNACIONAL SOBRE FLORESTAS, 5., 1999, Curitiba