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Lemaitre-Auger P.,Ecole Polytechnique de Montreal | Abielmona S.,Poly Grames Research Center | Caloz C.,Poly Grames Research Center
IEEE Transactions on Antennas and Propagation

Bessel beams are proposed as a practical way to generate well collimated and confined beams at mm-waves or THz for quasi-optical applications. To achieve that, we propose the use of two-dimensional antenna arrays as realizable launchers. Truncated Bessel beams with a main lobe width of few wavelengths (λ) can propagate over several hundreds of λ if the antenna aperture is electrically large. Because such a large aperture would require a large number of antenna elements, sub-sampling distributions are proposed in this work. It is found that arrays with spacings of approximately 4λ generate high quality beams with very low amplitude oscillations over distances of about 300λ in vacuum. The optimal excitation function for such arrays greatly departs from the Bessel one. It is synthesized with an analytical method based on a least mean square error minimization. The synthesis method is scalar, but the pseudo-Bessel beams obtained are vectorial and linearly polarized. Theoretical predictions are confirmed by full-wave simulations using Ansoft Designer. © 1963-2012 IEEE. Source

Nikfal B.,Poly Grames Research Center | Zhang Q.,South University of Science and Technology of China | Caloz C.,University of Montreal
IEEE Microwave and Wireless Components Letters

The concept of signal-to-noise ratio (SNR) enhancement in impulse radio transceivers based on phasers of opposite chirping slopes is introduced. It is shown that SNR enhancements by factors M-2 and M are achieved for burst noise and Gaussian noise, respectively, where M is the stretching factor of the phasers. An experimental demonstration is presented, using stripline cascaded C-section phasers, where SNR enhancements in agreement with theory are obtained. The proposed radio analog signal processing transceiver system is simple, low-cost and frequency scalable, and may therefore be suitable for broadband impulse radio ranging and communication applications. © 2014 IEEE. Source

Djoumessi E.E.,Poly Grames Research Center | Wu K.,Poly Grames Research Center
IEEE MTT-S International Microwave Symposium Digest

A varactor-based tunable diplexer is proposed and experimentally validated for IEEE802.16 standard-based system applications. The proposed transmit/receive (TxlRx) diplexer consists of two tunable dual-mode bandpass filters. Size reduction and band tunability are achieved by using the capacitance of varactors diodes. With two-tone nonlinear characterization test, the diplexer (with higher biased voltage) is found to introduce, in Tx frequency band, a high level of intermodulation product (IIP3). A better insertion loss inf passbands is observed for a lower room temperature. Measuredf insertion loss of our fabricated diplexer is obtained between 5.3 to 2.89 dB and 5.2 to 3.7 dB over the tuning frequency range for the Tx and Rx channels filters bands, respectively. Both filters exhibit better than 40 dB rejection in the passband of its counterpart. The varactors diodes attached to both filters allow 24.5% and 23.3% center-frequency tunability in Tx and Rx filters bands, respectively. © 2010 IEEE. Source

Li D.,Poly Grames Research Center | Mallat N.K.,Al Ain University of Science and Technology | Wu K.,Poly Grames Research Center
International Journal of Numerical Modelling: Electronic Networks, Devices and Fields

Electrical properties and geometrical characteristics of frequency-selective-surface-loaded quasi-transverse electromagnetic (TEM) rectangular waveguides are investigated in detail. The properties of electrical field distributions over the cross section of waveguides at various periodical phase shift points are studied. The phenomena, in connection with artificial magnetic conductor (AMC), cavity resonance, and surface resonance, are discussed. A definition of bandwidth for AMC is proposed on the basis of the variation of average z-polarized electric fields along z-axis between two side dielectric surfaces. Standard deviation technique is used to describe the uniformity of electrical fields and cavity efficiency is defined to represent the percentage of useful cavity with uniform electrical fields. The dispersion relationship, bandwidths of AMC and single mode, and cavity efficiency for various types of AMC surfaces are examined and compared. The geometrical characteristics of quasi-TEM waveguides are studied in both theory and experiment. Design rules for high-quality quasi-TEM waveguides are proposed. Copyright © 2013 John Wiley & Sons, Ltd. Source

Ladan S.,Poly Grames Research Center | Wu K.,Poly Grames Research Center
IEEE Transactions on Microwave Theory and Techniques

This paper presents and demonstrates a harmonic harvesting technique, which aims at rerectifying and recycling the rectifier output harmonics in order to increase the RF-to-dc conversion efficiency. Firstly, an analytical framework is developed based on the Ritz-Galerkin technique to investigate the output power distribution of a simple millimeter-wave rectifier circuit over its dc and generated harmonics components. The numerical results show that about 32% and 66% of the output power is distributed over the dc component and the first harmonic, respectively. In order to recycle and harvest the first harmonic power component, a 35-GHz voltage doubler rectifier implemented in microstrip technology and capable of harmonic harvesting is then studied and designed. To evaluate the performance of the proposed rectifier, the conventional voltage doubler and the harmonic signal rectifiers are fabricated and measured. The measured RF-to-dc conversion efficiencies of 34% at 20-mW input RF power for the harmonic harvester configuration, and 23% at the same input RF power level for the conventional voltage doubler are observed. Moreover, it is shown that the proposed harmonic rectifier suggests about 12% efficiency improvement compared to previously reported millimeter-wave rectifiers at the same level of input power (20 mW). The proposed rectifier configuration can find potential applications in the development of millimeter-wave wireless power transmission devices operating at medium power range (1-100 mW). © 2015 IEEE. Source

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