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A compact wideband printed slot antenna, suitable for wireless local area network (WLAN) and satisfying the worldwide interoperability for microwave access (WiMAX) applications, is proposed here. The antenna is microstrip-fed and its structure is based on Koch fractal geometry where the resonance frequency of a conventional triangular slot antenna is lowered by applying Koch iterations. The antenna size inclusive of the ground plane is compact and has a wide operating bandwidth. The proposed second iteration Koch slot antenna operates from 2.33 to 6.19 GHz covering the 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands. The antenna exhibits omnidirectional radiation coverage with a gain better than 2.0 dBi in the entire operating band. Design equations for the proposed antenna are developed and their validity is confirmed on different substrates and for different slot sizes. [ABSTRACT FROM AUTHOR]

A novel algorithm is presented for harmonic estimation in an active power filter. The current signal whose harmonics are to be estimated is modelled by using Fourier series. The fundamental frequency is estimated by using a non-linear least-squares approach and involves a one-dimensional search over the allowable frequency range in the power system. The estimated frequency is then used in the signal model to compute the harmonic magnitudes. The performance of a shunt APF using this approach for frequency and harmonic extraction has been studied by using both computer simulation and hardware implementation. It is shown that the active filter is able to track the changes in the load current waveform (both with respect to magnitude and waveshape) more accurately and faster than in the conventional methods. [ABSTRACT FROM AUTHOR]

Position sensorless methods for brushless DC motors based on back-EMF zero crossing suffer from a starting problem since there is no back-EMF at standstill. A simple method by which the motor is started from standstill up to a speed wherein sensorless methods will be able to detect the correct commutation instants is proposed. The proposed method relies on a difference of line voltages measured at the terminals of the motor. It is shown that this difference of line voltages provides an amplified version of an appropriate back-EMF at its zero crossings. It is further demonstrated that this information can be used to trigger devices so as to develop an accelerating torque from zero speed. This method is simple to implement and it can reliably start the motor even with load. The effectiveness of the proposed method is demonstrated through simulation and hardware results. [ABSTRACT FROM AUTHOR]

A novel ultra-wideband (UWB) antenna consisting of a linear tapered slot in the ground plane and a microstrip to slotline transition is investigated. The antenna possesses a wide bandwidth from 2.95–14 GHz for |S11|<-10 dB and shows stable radiation patterns with an average gain of 3 dBi throughout the band. Measured group delay and transmission characteristics indicate that the antenna has good pulse handling capabilities. [ABSTRACT FROM AUTHOR]

A nonlinear least-squares approach for measuring the power system frequency is presented, wherein the voltage at the point of common coupling is modelled using the Fourier series. The fundamental frequency is estimated by performing a one-dimensional search over the range of allowed frequency variation. The robustness of this algorithm is studied and validated by hardware implementation using an FPGA. The performance of this method is also compared with that of the phase-locked loop. [ABSTRACT FROM AUTHOR]

A compact dual-band uniplanar antenna for operation in the 2.4/5.2/5.8 GHz WLAN/HIPERLAN2 communication bands is presented. The dual-band antenna is obtained by modifying one of the lateral strips of a slot line, thereby producing two different current paths. The antenna occupies a very small area of 14.5×16.6 mm2 including the ground plane on a substrate having dielectric constant 4.4 and thickness 1.6 mm at 2.2 GHz. The antenna resonates with two bands from 2.2 to 2.52 GHz and from 5 to 10 GHz with good matching, good radiation characteristics and moderate gain. [ABSTRACT FROM AUTHOR]

Effective use of fractal-based metallo-dielectric structures for enhancing the radar cross-section (RCS) of dihedral corner reflectors is reported. RCS enhancement of about 30 dBsm is obtained for corner reflectors with corner angles other than 90°. This may find application in remote sensing and synthetic aperture radar. [ABSTRACT FROM AUTHOR]

An ultra-wideband (UWB) printed slot antenna, suitable for integration with the printed circuit board (PCB) of a wireless universal serial-bus (WUSB) dongle is presented. The design comprises a near-rectangular slot fed by a coplanar waveguide printed on a PCB of width 20 mm. The proposed design has a large bandwidth covering the 3.1–10.6 GHz UWB band, unaffected by the ground length, and omnidirectional radiation patterns. A linear phase response throughout the band further confirms its suitability for high-speed wireless connectivity. [ABSTRACT FROM AUTHOR]

Design of a dual linearly-polarised microstrip patch antenna, excited by two orthogonal microstrip feed lines, is presented. A reduction in patch size of 35% is obtained when compared to a square patch operating at the same frequency. The polarisations are oriented at +45 and -45° with an isolation of more than 36 dB between the ports. Unlike earlier designs, the proposed structure provides better gain. [ABSTRACT FROM AUTHOR]

A compact dual-band printed antenna covering the 2.4 GHz (2400–2485 MHz) and 5.2 GHz (5150–5350 MHz) WLAN bands is presented. The experimental analysis shows a 2:1 VSWR bandwidth of up to 32 and 8% for 2.4 and 5.2 GHz, respectively. The measured radiation patterns are nearly omnidirectional, with moderate gain in both the WLAN bands. [ABSTRACT FROM AUTHOR]

A new electronically reconfigurable dual frequency microstrip patch antenna with highly simplified varactor tuning circuitry is presented. The proposed design allows relatively independent selection of the two operating frequencies. Tuning ranges of 7.1 and 4.1% are realised for the two resonant frequencies without the use of any matching circuits. [ABSTRACT FROM AUTHOR]

The design and implementation of a novel asymmetric coplanar waveguide (ACPW) band rejection filter using defected ground structure (DOS) is presented. The proposed ACPW DOS technology provides bandgap characteristics with only one cell in the lateral ground plane. The equivalent circuit model of the proposed DOS unit section is described. Measurements of ACPW DGS showed good agreement with simulation and the proposed model. [ABSTRACT FROM AUTHOR]

Electromagnetic scattering behaviour of a superstrate loaded metallo-dielectric structure based on Sierpinski carpet fractal geometry is reported. The results indicate that the frequency at which backscattering is minimum can be tuned by varying the thickness of the superstrate. A reduction in backscattered power of ∼44 dB is obtained simultaneously for both TE and TM polarisations of the incident field. [ABSTRACT FROM AUTHOR]