Scielo RSS <![CDATA[Journal of Microwaves, Optoelectronics and Electromagnetic Applications]]> http://www.scielo.br/rss.php?pid=2179-107420160003&lang=en vol. 15 num. 3 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[Miniaturized Triple Wideband CPW-Fed Patch Antenna With a Defected Ground Structure for WLAN/WiMAX Applications]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742016000300157&lng=en&nrm=iso&tlng=en Abstract— A coplanar waveguide (CPW)-fed patch antenna with triple wideband is presented for simultaneously satisfying Wireless Local Area Network (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX) applications. The proposed antenna mainly consists by three radiating elements: inverted L-shaped Stub1, inverted L-shaped Stub2, and a rectangle Stub3 with a defected ground structure for band broadening. By adjusting the lengths of the three Stubs, three resonant frequencies can be achieved and adjusted separately. The proposed antenna with overall size of only 20×37mm2 explores good triple wideband operation with −10 dB impedance bandwidths of 25.70%, 45.63% and 50.10% at 2.47, 3.20, and 4.92 GHz, respectively, covering the 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX operation bandwidths. This design gives suitable results with a reduction in size and weight and allows integration in handheld devices. Furthermore, nearly omnidirectional radiation patterns over the operating bands have been obtained. <![CDATA[Spectral Method for Localization of Multiple Partial Discharges in Dielectric Insulation of Hydro-Generator Coils: Simulation and Experimental Results]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742016000300170&lng=en&nrm=iso&tlng=en Abstract A methodology based on spectral analysis for localization of multiple partial discharges in dielectric region of hydro-generator coils is proposed. This pinpointing of multiple discharges aims to provide means for performing diagnosis of insulating regions of the coil. A numerical model of the structure was developed by using the finite-difference time-domain method (FDTD-3D) to solve Maxwell’s equations. Transient voltage associated with partial discharges that occurs at different positions of the coil is calculated at specific point and its spectrum is used to perform the diagnosis. In 90% of simulations, accurate estimates of simultaneous discharges location were obtained. Physical phenomena allowing the development of the methodology are assessed numerically and experimentally. Finally, a localized artificial PD injection schema is proposed and used for validating our numerical results and physical analysis. <![CDATA[A flat-gain LNA based on LTCC technology at UHF (300-500 MHz)]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742016000300191&lng=en&nrm=iso&tlng=en Abstract This paper presents a design and simulation of a low noise amplifiers (LNA) with all passives elements embedded on low temperature co-fired ceramic (LTCC) substrate. Simulation results in ANSYS Designer and CST Studio Suite reveal that the proposed LNA has a flat-gain of 23.34 dB from 300 to 500 MHz, a noise figure below 0.73 dB and a compact size of 16.7 mm x 8.5 mm. <![CDATA[A correction method for the analytical model in Raman amplifiers systems based on energy conservation assumption]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742016000300198&lng=en&nrm=iso&tlng=en Abstract This paper presents a modification for the already consolidated analytical model that calculates the gain and ripple in multi-pump Raman amplifiers by considering energy conservation. The original analytical model precisely computes the pump-pump interaction to the C- and L-band for a WDM input signal. However, when this method is used to amplify a large bandwidth, as the entire C and a part of the L band, the increase in the number of pump lasers impacts the obtained results. The error, if compared with results obtained by a numerical method, becomes significant. An analysis in terms of energy is proposed to minimize the discrepancy between analytical and numerical results. An improvement is observed to the gain results. <![CDATA[A New Triple Band Microstrip Fractal Antenna for C-band and S-band Applications]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742016000300210&lng=en&nrm=iso&tlng=en Abstract Recently research show that some parameters such as the shapes of antenna patch and the ground plane when geometrically altered produces changes in the current density distribution of the planar structure and consequently in the resonant modes. This paper presents a new microstrip fractal antenna using the technique of inserting slots of shape fractal in ground plane in order to increase the bandwidth and insertion discontinuities in the feed line to reach specific behaviors in three resonant modes. The FR-4 substrate with dimensions 85.0 x 85.0 x 1.57 mm3 is used. Also, it used different techniques of impedance matching in feed line of antenna with changes of the width of the transmission line in order to obtain a variation in the current distribution and consequently of the impedance bandwidth for S11 ≤ -10dB for C-band (3.625 GHz – 4.2 GHz) and S-band (2.0 GHz – 4.0 GHz). Good agreement between measured and simulated results is achieved. Proposed fractal microstrip antenna can be easily designed, built and applied in wireless communication. <![CDATA[Dual-band X/Ku Reflectarray Antenna Using a Novel FSS-Backed Unit-Cell with Quasi-Spiral Phase Delay Line]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742016000300225&lng=en&nrm=iso&tlng=en Abstract A novel FSS-Backed reflectarray unit cell is introduced to design a dual-band X/Ku Reflectarray Antenna (RA). A Ku-band RA based on this FSS-Backed cell element is designed and located on the top of a conventional X-band RA. Actually, the band-stop Frequency Selective Surface (FSS) property is applied to a wideband element to create isolation between X and Ku band RAs which utilizing the same radiating element. A wideband cell element with attached quasi-spiral phase delay line is employed for phase compensation in both bands. As a FSS-backed cell element, the remarkable feature of the proposed dual band unit cell compared to previous works is its possibility of operation in closer frequency bands in comparison with other dual band FSS-backed RAs. Two reflectarrays with aperture size of 7.65λ×7.65λ and 7.35λ×7.35λ are designed, fabricated and measured for X band and Ku band, respectively. Measured results show 1-dB gain bandwidth of 12% for X band and 11% for Ku band which demonstrate wideband operation of this dual-band reflectarray antenna. <![CDATA[Effect of Complementary Split Ring Resonator Structure on PIFA Antenna]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742016000300237&lng=en&nrm=iso&tlng=en Abstract This paper proposes a new design of Planar Inverted-F Antenna with complementary split ring resonators (CSRRs). The operating frequency of this antenna is 2.425 GHz for Wireless Local Area Network (WLAN) application. The method is to incorporate a single CSRR cell and a periodic array CSRRs on the radiating patch. We studied the effect of this method on the characteristics of antenna in free space and in the presence of the user. We used a homogeneous model of a human head near our antenna. The parameters that considered in these works are gain, electric field, magnetic field, return loss, radiation pattern, power loss density and Specific Absorption Rate. The addition of CSRRs on to PIFA antenna will improve the gain from 4.76 dB to 4.81 dB and will reduce the Specific Absorption Rate from 3.57 W/kg to 2.95 W/kg. <![CDATA[New Design Procedure to Determine the Taper Transition for Impedance Matching Between Microstrip Line and SIW Component]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742016000300247&lng=en&nrm=iso&tlng=en Abstract Normally the physical dimensions of the taper transition that realizes the impedance matching between the impedance of the feeding line built in microstrip line technology and the impedance of the component built in Substrate Integrated Waveguide (SIW) technology are obtained by computational optimization processes due the difficulty of analytical treatment. This research work presents a new empirical approach to determine all the physical dimensions of this particular planar transition without using any computational optimization process. The well-defined design procedure is based on an approximation according with electromagnetic simulations and electromagnetic theory. The main goal is to facilitate the integration between SIW technology and planar circuits. The whole design procedure considers central frequency for the recommended bandwidth in the TE10 propagation mode and power-voltage impedance definition for the SIW. Two structures are designed on RT/duroid 5880 to operate in the X band and Ku band, and the frequency response for both structures are compared by electromagnetic simulation and experimental results. The structure operating in X Band demonstrated return loss better than 10.0 dB at 61.67% of the considered bandwidth and the structure operating in Ku Band demonstrated return loss better than 10.0 dB at 72.88% of the considered bandwidth. <![CDATA[Adaptive Wideband Beamforming Based on Digital Delay Filter]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742016000300261&lng=en&nrm=iso&tlng=en Abstract A novel adaptive wideband beamforming method is proposed, where beamforming is achieved by LMS based space-time adaptive filtering algorithm. Conventional broadband beamforming requires desired signal to be incident from the broadside i.e. direction normal to the array. The new method overcome this constraint by make use of digital delay filters which compensate the delay of receiving data, so that the signal of interest can be treated as if it had arrived from the broadside. Then LMS based space-time adaptive filtering algorithm is applied to achieve beamforming. Another advantage of the proposed methodology is its low computational complexity while sustaining high resolution. The effectiveness and advantage of the proposed methodology is theoretically investigated, and computational complexity is also addressed. To verify the theoretical analysis, computer simulations are implemented and comparisons with other algorithms are made.