Jean-Jacques Laurin

Study of a CPW inductively coupled slot antenna

Coplanar waveguide (CPW) fed slot antennas are attractive due to fabrication simplicity and ease of integration with active devices. A new concept for exciting slots with a CPW line based on inductive coupling is presented. It is described how this coupling structure can be designed to tune the impedance of the antenna over a wide range. Single elements and arrays designed for 5- and 25-GHz operation are described. Simulated and measured characteristics are presented. This new coupling topology is particularly suitable for series-fed array configurations and broad-band design.

Design of an Electronically Beam Scanning Reflectarray Using Aperture-Coupled Elements

The design of a C-band electronically beam scanning reflectarray is presented. The reconfigurable reflectarray element consists of a microstrip patch, printed on a flexible membrane substrate, aperture-coupled to a transmission line loaded with two varactor diodes. The designed element allows continuous tuning of the reflected signals phase over a 360deg range with a maximum loss of 2.4 dB at 5.4 GHz. The measured results on a 30-element reflectarray breadboard show that by varying the bias voltages on each element the main beam can be steered to large angles, up to 40deg from broadside in the H-plane. A loss analysis of the proposed reflectarray is also presented

Analysis and Design of Thin Circular Polarizers Based on Meander Lines

A circular polarizer is a single layer or multi-layer structure that converts linearly polarized waves into circularly polarized ones and vice versa. In this communication, a simple method based on transmission line circuit theory is proposed to model and design circular polarizers. This technique is more flexible than those previously presented in the way that it permits to design polarizers with the desired spacing between layers, while obtaining surfaces that may be easier to fabricate and less sensitive to fabrication errors. As an illustrating example, a modified version of the meander-line polarizer being twice as thin as its conventional counterpart is designed. Then, both polarizers are fabricated and measured. Results are shown and compared for normal and oblique incidence angles in the planes φ = 0° and φ = 90°.

Fan-Beam Millimeter-Wave Antenna Design Based on the Cylindrical Luneberg Lens

A new design of two-dimensional cylindrical Luneberg lens is introduced based on TE10 mode propagation between parallel plates, with special focus on ease of manufacturing. The parallel plates are partially filled with low cost polymer material (Rexolite epsivr = 2.54) to match Lunebergs law. A planar linear tapered slot antenna (LTSA) is inserted into the air region between the parallel plates at the edge of the Luneberg lens as a feed antenna, with fine positioning to the focal point of the Luneberg lens to optimize the antenna system performance. A combined ray-optics/diffraction method is used to obtain the radiation pattern of the system and results are compared with predictions of a time domain numerical solver. Measurements done on a 10-cm Luneberg lens designed for operation at 30 GHz agree very well with predictions. For this prototype, 3-dB E- and if-plane beamwidths of 6.6deg and 54deg respectively were obtained, and the sidelobe level in the E-plane was -17.7-dB. Although the parallel plate configuration should lead to a narrow band design due to the dispersion characteristics of the TE10 mode, the measurement results demonstrate broadband characteristics with radiation efficiencies varying between 43% and 72% over the tested frequency band of 26.5-37 GHz. The designed cylindrical Luneberg lens can be used to launch multiple beams by implementing an arc array of planar LTSA elements at the periphery of the lens, and can be easily extended to higher mm-wave frequencies.

Near-field diagnostics of small printed antennas using the equivalent magnetic current approach

A near-field to far-field transformation based on the antenna representation by equivalent magnetic current (EMC) sources has been proposed and validated experimentally on large high-directivity antenna arrays. In this paper, the use of EMC is extended to the diagnostics of low-directivity printed antennas. The limitation of the near-field to far-field transformation applied to EMC models of low-directivity antennas, caused by the finite dimensions of the antenna ground plane, is demonstrated. A method to partially overcome this limitation by including the contribution of diffracted rays is implemented, and its effectiveness is demonstrated with antenna prototypes. It is shown that the agreement between the far-field patterns measured in an anechoic chamber and the patterns computed from the EMC model obtained from the near-field measurements is significantly improved upon, within a sector of /spl plusmn/90/spl deg/ with respect to the antenna boresight in the E plane. The influence of the near-field sampling density and topology of the EMC model on the accuracy of the predicted far-field pattern is examined.

EMI-induced failures in crystal oscillators

An electromagnetic interference (EMI) induced failure mode pertaining to crystal-based voltage-controlled oscillators (VCO) has been studied. The failure consists of a transition to a frequency of oscillation that differs from the crystals fundamental resonant frequency, when the circuit is temporarily exposed to continuous or pulsed radio-frequency electromagnetic fields. The new state persists even after the EMI source is removed and leads to hang-up in digital systems. This mode transition has been observed experimentally. Its essential properties have been predicted theoretically and simulated numerically, using simplified oscillator models. The likelihood of observing such a failure in a noisy electromagnetic environment is assessed with respect to the radiated susceptibility levels given in MIL-STD-461B. >

Near-field imaging of radiated emission sources on printed-circuit boards

This paper presents a technique to assess the level of radiated emissions generated by printed-circuit board (PCB) structures based on equivalent magnetic currents. These currents are extracted from near-field measurements taken with a very high resolution (step size << ?) in comparison with near-field antenna applications. Near-field data allow the visualization and extraction of common-mode currents near transmission line discontinuities such as bends. This effect is investigated for microstrip and CPW lines.

On the prediction of digital circuit susceptibility to radiated EMI

The effects of radiated radio-frequency interference (RFI) on the operation of digital systems are studied by simulating the response of simple logic circuits to incident plane waves. The simulation is accomplished by combining a linear electromagnetic moment-method model of the wire structure with a nonlinear circuit model of the solid-state components. The complete model is analyzed in the linear and nonlinear regimes as an example. It is shown how a circuit simulator, such as SPICE, can be used in the analysis of an arbitrary wire network loaded with logic circuits, by the process of representing the linear wire network as a lumped-element N-port /spl pi/ network and interfacing it to the nonlinear circuit simulator. Examples are given that demonstrate the occurrence of both static and dynamic failures under various RFI-field excitations and wire structure geometries. The prediction methods presented in this paper, can be used by EMC engineers to assess the likelihood of failures in RFI-exposed digital systems,.

Optically Modulated Probe for Precision Near-Field Measurements

In this paper, the design and implementation of an accurate, sensitive, and cost-effective near-field (NF) probe are discussed. The probe is based on the modulated scatterer technique (MST), providing very low perturbation on the field to be measured. It consists of a commercial off-the-shelf (COTS) photodiode chip and an antenna acting as a scatterer. The optically modulated scatterer (OMS) essentially makes the NF measurements perturbation free. A matching network is added to the probe structure to increase its sensitivity. The radiation characteristics of the probe, including cross-polarization response and omnidirectional sensitivity, are both theoretically and experimentally investigated. Finally, the performance and reliability of the probe are studied by comparing the measured NF distributions to the simulated distributions.

Design and Analysis of a Cascade Circular Polarization Selective Surface at K Band

This paper proposes a circular polarization selective surface (CPSS) design consisting of two meander-line circular polarizers and a linear polarizer. No vias are required. These polarizers are individually designed with ANSYS-HFSS (High Frequency Structure Simulator) software whereas the response of the overall cascade CPSS is computed with the GSM approach. A cascade CPSS which includes three-layer meander-line polarizers is designed and fabricated. Good agreement is shown between experimental and simulated results, with only the TE00 and TM00 modes in the GSM analysis. Finally, analysis of the circular polarizers based on simple filter theory is done to better understand how the performance of the whole structure can be improved.