G.P. Srivastava

Non-resonant microwave absorption studies in Bi1.6Pb0.4Sr2Ca2Cu3O10+x

Abstract Non-resonant microwave absorption (NRMA) studies have been carried out on Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+ x pellets sintered for different durations varying from 24 to 168 h by using EPR technique. A detailed study of the temperature dependence of the NRMA signal amplitude, peak-to-peak width, hysteresis area has been carried out. Apart from showing a flux line lattice (FLL) melting temperature T m ( B ) (60–70 K), it is interesting to note that hysteresis loops showed the anomalous magnetic behaviour in the entire temperature regions even far below the fluctuation regime. The results are discussed in terms of several current models for the NRMA effects as well as for its anomalous magnetic hysteresis behaviour.

Modeling of microwave power absorption in high temperature superconductor

This paper compares different phenomenological models (i.e. two fluid model, three fluid model and modified two fluid model) for microwave properties of high temperature superconductors with the experimental results of silver doped BSCCO samples. The modified two fluid model is seen to have a good agreement with the measurements in a wide temperature range and different silver doping levels (0-20 wt%) in samples.

Microwave power dependence of surface resistance in BSCCO superconductors

The effect of silver and microwave power dependence of surface resistance in BiSrCaCuO (BSCCO) superconductors are the subject of interest of this paper. Many interesting features such as low temperature and high temperature peaks and nonlinear power dependence of surface resistance are seen in the experimental results and discussed here briefly.

Anomalous Peak in Microwave Surface Resistance Studies on Silver Doped Bi1.84Pb0.4Sr2Ca2.2Cu3O10 Superconductor

We report surface resistance studies on silver (0 to 25 wt%) doped Bi1.84Pb0.4Sr2Ca2.2Cu3O10 samples prepared by spray drying technique. The XRD studies show the predominance of 2223 phase in the samples. The 10 wt% silver doped sample shows optimum superconducting characteristics viz, improved microstructure characteristics and the reduced resistive grain boundaries. Temperature dependent microwave surface resistance behaviour shows the apparence of two anomalous peaks (high temperature at Tc and low temperature near TCI2) in samples when the Ag dopant level was increased beyond 10 Wt%.

Superconducting Cross Loaded Microstrip Antenna

Metallic cross loaded patch has been studied for its radiation pattern in the present work. Theoretical design and characteristics are being reported for a Superconducting patch antenna.

Anomalous magnetic behaviour in non-resonant microwave absorption study of Bi-2212 superconductors

The non-resonant microwave absorption (NRMA) studies in silver doped polycrystalline Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub 8/ samples have been carried out. The NRMA signal has been observed not only below Tc but also above Tc which is much above the fluctuation regime when the DC magnetic field was swept from -50 G to +50 G through 0G. Anomalous magnetic hysteresis behaviour has been observed where the forward curve lies above the return curve even at lower temperatures. The observed curve has been simulated by taking into consideration the sum of reversible losses as well as irreversible losses using Dulcic and Portis models. This leads to anomalous magnetic hysteresis behaviour as has been observed experimentally.

A Comparative Investigation of Thick and Thin Film Mircrowave Integrated Circuits

The cost advantage over thin-film technology makes the thick-film technology attractive for use at microwave frequencies though the critical requirements on dimensions at these frequencies place restrictions on its use. In the present work, an effort has been made to quantify the comparative performance from loss considerations as well as reliability of thin (high-impedance) lines and fine gaps. This is achieved by studying resonators, parallel-coupled directional couplers, narrow band-pass Biters and power dividers—circuits which are commonly required on large scale. It is concluded that up to A-band, thick-film circuits should possess only a marginally higher loss which is confirmed by fabricating directional couplers. It is also concluded that narrow band-pass filter design upto A-band is feasible though it requires design correction. Further lines upto about 80–85Ω impedance are about the fabrication limit and, therefore, highly unequal power division is not feasible using thick-film technology.

Effect of Flange Angle on Radiation Patterns of Sectoral Horns

E-plane radiation patterns of a flanged H-plane sectoral horn are shown modified considerably by varying the included angle of the flange. Focusing and broadening of the beam are effected by this method. And, a simultaneous adjustment of flange angle and flange position would further improve the radiation pattern, yielding optimum efficiency from flange device.

An Experimental Investigation of the Effect of Conducting Flanges on the H-Plane Radiation Patterns of E-Plane Sectoral Horns

ABSTRACTContrary to the observations of Butson and Thompson, the flange technique is found quite effective in shaping the H-plane radiation patterns of E-plane sectoral horns. The experimental investigations carried out with four different horns and at four frequencies convincingly corroborate the aforesaid observation. Considerable improvement in beam width and gain has been achieved. Besides, a novel device, simple in execution but efficient in performance, to tilt the H-plane beam is being reported.