K. B. Sharma

Radiation performance ofCircularly Polarized Broadband Gap CoupledElliptical Patch Antenna

Abstract In this communication design and performance of a novel single-layer assembly of gap coupled elements in elliptical shape is proposed to achieve broadband performance with circular polarization. Out of five patches considered in this assembly, two pairs of patches having different patch areas are arranged close to an edge truncated elliptical patch. The central edge truncated elliptical patch is fed through inset feed arrangement and the other patches are parasitically gap coupled to the central patch. With such an arrangement, an improved impedance bandwidth of 1.58 GHz or 18.5% with respect to central frequency 8.5 GHz is achieved. Three resonant modes are excited with this arrangement giving improved bandwidth and gain in comparison to a conventional elliptical patch antenna with same semi-major and semi-minor axes. In the entire bandwidth, the simulated radiation patterns of proposed arrangement of patches are more or less identical in shape.

Compact dual band microstrip patch antenna for Wi- Max communication systems

In this communication, a rectangular patch antenna is modified to achieve a compact multi-layered dual band antenna for application in lower and median bands of Wi-Max communication systems. The considered multilayered structure initially had two rectangular patches (with dimensions 28.5 mm × 31.5 mm) designed on two identical Glass epoxy FR-4 substrates and were separated through a thin foam layer. The lower patch was modified later by converting into slotted pentagonal patch. The lower patch was excited using insight feed network and upper patch was parasitically coupled to the lower patch. The proposed antenna operates in the lower band (2.3 GHz to 2.7 GHz) and median band (3.4 GHz to 3.69 GHz) of Wi-Max systems. The measured impedance bandwidth of proposed antenna in lower band with central resonant frequency 2.4 GHz is approx 11.0% while in median band with central resonant frequency 3.51 GHz, impedance bandwidth is close to 4.0% without much loss in its radiation performance. The variation in gain is well within 1dBi in the entire desired bands. The radiation patterns of antenna within two achieved bands are almost identical in shape.

Structural, dielectric and magnetic behavior of nanocrystalline zinc substituted magnesium ferrite

Zinc substituted magnesium ferrites Zn0.2Mg0.8Fe2O4 and Zn0.4Mg0.6Fe2O4 were prepared by sol-gel auto combustion method. Rietveld profile refinement of the XRD patterns confirms the formation of a cubic spinel structure in single phase. The dielectric properties viz. dielectric constant and dielectric loss tangent tanδ increase with increasing temperature. The dielectric behavior is explained by using the mechanism of polarization process, which is correlated to that of electron exchange interaction. The saturation magnetization, coercivity and remanent magnetization decreases appreciably with increase in Zn which could be attributed to change in cation distribution.

Electronic and magnetic correlations in Mn doped ZnO nano-rods

We have investigated correlation between magnetization and electronic structure in Zn0.98Mn0.02O nano-rods. Rietveld analysis of XRD patterns confirms that Mn ions incorporate at the Zn2+ sites. SQUID measurements confirm that Mn doping induces room temperature ferromagnetism (RTFM) in nano-rods and the induced magnetization is an order of magnitude higher than that in the bulk Zn0.98Mn0.02O. The XPS results show that Mn ions are in mixed valent state. Our findings show that bivalence of Mn ions and the oxygen vacancies are responsible for the observed RTFM.

Dielectric behaviour of nanocrystalline Cu0.2Ni0.8Fe2O4 ferrite

Nanocystalline Cu0.2Ni0.8Fe2O4 of average particle size 3 nm was synthesized through chemical coprecipitation method followed by annealing at various temperatures. The formation of cubic spinel structure in single phase and the crystallite growth was confirmed using XRD. The dielectric behavior as a function of frequency in the range 75 kHz to 10 MHz was studied at room temperature. Both dielectric constant (e′) and the loss factor (tanδ) decreases with frequency for all samples. This decrease in the values could be explained on the basis of available ferrous, i.e. Fe2+, ions at octahedral sites such that beyond a certain frequency of applied electric field the electronic exchange between the ferrous and ferric ions i.e. Fe2+↔Fe3+ cannot follow the applied alternating electric field.

TEMPERATURE DEPENDENT DIELECTRIC BEHAVIOR OF NANOCRYSTALLINE Ca FERRITE

Dielectric behaviour of Nanocrystalline CaFe2O4 ferrite synthesized by advanced sol- gel method has been investigated as a function of frequency at different temperatures. Rietveld profile refinement of the XRD pattern confirms formation of cubic spinel structure of the specimen.The dispersion in dielectric behavior of CaFe2O4ferrite sample has been observed in the temperature range of 100-250˚C as a function of frequency in the range 75 kHz to 10 MHz Both the real value of dielectric constant (ɛ′) and the dielectric loss factor (tanδ) decrease with frequency. This decrease in the values of ɛ′ and tanδ could be explained on the basis of available ferrous, i.e. Fe2+, ions on octahedral sites such that beyond a certain frequency of applied electric field the electronic exchange between the ferrous and ferric ions i.e. Fe2+↔Fe3+ cannot follow the applied alternating electric field.

Design and performance of a broadband circularly polarized modified semi-elliptical microstrip patch antenna

In this communication design and performance of a modified semi elliptical microstrip patch antenna is proposed to achieve circularly polarized broadband performance. The proposed structure consists of a semi-elliptical patch having a D-shaped slot designed on three layered substrate material. The structure has two FR-4 substrates separated by a foam material having 1 mm thickness. The simulation analysis is carried out by using IE3D simulation software. The proposed antenna covers entire median band (3.4 to 3.69 GHz) allocated for Wi-Max communication systems. Two modes having resonance frequencies very close to each other (3.36 GHz and 3.66 GHz) are excited to achieve broadband performance. The impedance bandwidth of proposed antenna is close to 21%. The minimum axial ratio is close to 1.8dB while axial ratio bandwidth is close to 4.63%. The radiation patterns within bandwidth are almost identical in shape.

Dielectric Behavior of Nano sized Particles of Zn‐Cr Ferrite

Dielectric behavior of nanosized ZnCrxFe2−xO4 particles with x = 0.2, 0.4, 0.6 and 0.8, synthesized using sol‐gel method have been studied. The XRD patterns confirm formation of single phase cubic spinel structure of the specimens. The dielectric behavior of all the samples has been studied at 300 K as a function of frequency in the range 75 kHz to 10 MHz. Both the real value of dielectric constant (e) and the dielectric loss factor (tanδ) decreases with frequency respectively for all the samples. This decrease in the values could be explained on the basis of available ferrous, i.e. Fe2+, ions on octahedral sites such that beyond a certain frequency of applied electric field the electronic exchange between the ferrous and ferric ions i.e. Fe2+↔Fe3+ cannot follow the applied alternating electric field. Also, a gradual reduction in both e and tanδ observed as Cr concentration increases.