Yttrium iron garnet (YIG) film made as a magneto-optical medium suffers from the problem of crack formation, caused by the heating process. YIG thin film is deposited by radio frequency RF magnetron sputtering; the obtained layer is amorphous and it needs annealing to be crystallized. After heat-treatment at 740 o C of the sample realized on quartz substrate, we observe cracks on the entire film surface. This is due to the large difference between the thermal expansion coefficient (5.5 x 10 -7 K -1 for quartz and 10 x 10 -6 K -1 for YIG). In this paper we present a new fabrication method to reduce this problem, we make a multilayer to obtain at the end a uniformly unique layer with excellent crystalline structure. Such films have the possibility to reach a thickness of 500 nm. YIG films have been studied by Rutherford Backscattering Spectrometry (RBS), opticEllipsometry and the Scan Electron Microscope. The RBS spectra were collected in channelling geometry with incident particles energy 2 MeV and 3.5 MeV. The thickness and the stoichiometric value of the thin films have been evaluated. Simulation of all spectra indicates a constant composition. Ellipsometry method is well adapted to model the thin film structure layers, and to measure the thickness of the film and the complex index of refraction. The theoretical ellipsometric value of the index of refraction is (2.22) while the experimental value is ranging from 2.2 to 2.3 for a wavelength of 1550nm.

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resonance effects also play a part. Having the casing would also be a more practical setup as it allows external magnets to be mounted, which are necessary to provide the magnetic bias, H o , out of the disk plane. Figures 1(a)-1(c) show the configurations of the proposed circulator. RESULTS AND DISCUSSIONAnsoft HFSS, which uses the finite element method, is used for the simulation of our CPW circulator design. In the simulation design, the casing and conductors used are assumed to be copper. The uniform applied magnetic bias perpendicular to the YIG disk plane is 450,000 A/m, and the design parameters are given in Table 1. The dimensions of the CPW are chosen such that its characteristic impedance is 50 X, so as to ensure impedance matching to most microwave circuits and probes. The YIG disk of thickness 0.5 mm is taken to have a dielectric constant of 15.3, saturation magnetization of 1750 G, loss tangent of 0.0002, and ferromagnetic linewidth of 50 Oe.From the simulation results in Figure 2, maximum circulation is observed to occur at 9.88 GHz, with the corresponding insertion loss of 20.37 dB, return loss of 218.5 dB, and isolation of 216.8 dB. Bosma's theory for a stripline circulator with the same YIG disk radius predicts circulation at 10 GHz. The fact that our CPW circulator has a maximum circulation frequency close to this value shows that the addition of the metallization above YIG disk is able to circumvent the field mismatch between our CPW structure and the stripline structure. Indeed, the results show the viability of implementing such a CPW circulator due to the good nonreciprocal performance and design simplicity. CONCLUSIONA circulator using pure CPW transmission lines has been designed, with HFSS simulation showing good nonreciprocal performance. Our CPW circulator design is compact, easily patterned using modern lithography techniques at low cost, and compatible with MMICs. This CPW circulator can be useful for many microwave applications, especially acting as passive components in monolithic MMIC.ABSTRACT: The wideband performance of a bowtie antenna with C-shaped strip feed and tuning stubs is presented. Besides two folded elements connecting the patches of the bowtie dipole for a compact dimension, the C-shaped strip feed structure and the four tuning stubs to effectively improve the impendence matching can be used for bandwidth enhancement. A wideband impedance characteristics of about 58.6% for VSWR 1.5 ranging from 1.58-2.89 GHz is obtained and the stable peak gain of around 9 dBi, unidirectional radiation patterns and low crosspolarization over the whole operating band are also achieved. It is very suitable for the recent wireless communication services for the indoor-base station such as 3G, WiFi, WiMax, Bluetooth, and LTE/2.5 applications, and so on.ABSTRACT: Two planar elliptical ultra-wideband (UWB) monopole antennas with total efficiency greater than 97% in the UWB are investigated. One has attractive feature and an excellent impedance matching with return loss lower than 222 dB in ...

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