Alexander Schuchinsky

Electro-Thermal Theory of Intermodulation Distortion in Lossy Microwave Components

An analytic formulation of dynamic electro-thermally induced nonlinearity is developed for a general resistive element, yielding a self-heating circuit model based on a fractional derivative. The model explains the 10 dB/decade slope of the intermodulation products observed in two-tone testing. Two-tone testing at 400 MHz of attenuators, microwave chip terminations, and coaxial terminations is reported with tone spacing ranging from 1 to 100 Hz.

Spatial demultiplexing in the submillimeter wave band using multilayer free-standing frequency selective surfaces

In this paper, we show that a multilayer freestanding slot array can be designed to give an insertion loss which is significantly lower than the value obtainable from a conventional dielectric backed printed frequency selective surface (FSS). This increase in filter efficiency is highlighted by comparing the performance of two structures designed to provide frequency selective beamsplitting in the quasioptical feed train of a submillimeter wave space borne radiometer. A two layer substrateless FSS providing more than 20 dB of isolation between the bands 316.5-325.5 GHz and 349.5-358.5 GHz, gives an insertion loss of 0.6 dB when the filter is orientated at 45/spl deg/ incidence in the TM plane, whereas the loss exhibited by a conventional printed FSS is in excess of 2 dB. A similar frequency response can be obtained in the TE plane, but here a triple screen structure is required and the conductor loss is shown to be comparable to the absorption loss of a dielectric backed FSS. Experimental devices have been fabricated using a precision micromachining technique. Transmission measurements performed in the range 250-360 GHz are in good agreement with the simulated spectral performance of the individual periodic screens and the two multilayer freestanding FSS structures.

Passive Intermodulation in Finite Lengths of Printed Microstrip Lines

This paper addresses the theoretical aspects of passive intermodulation (PIM) generation in printed transmission lines. In order to elucidate the mechanisms of PIM generation, a new model of the transmission line length with distributed nonlinearity is proposed. The developed model has been validated by the near-field measurements of PIM product distributions along the microstrip lines. The contributions of nonlinear mixing, power dissipation, and load matching to PIM products have been analyzed in detail. The obtained results reveal the fundamental properties of PIM generation in finite lengths of printed lines with distributed nonlinearity and identify possible means for PIM mitigation. It was shown for the first time that the reverse PIM products in a matched transmission line with distributed nonlinearity are generated due to nonlinear scattering.

2-D Isotropic Effective Negative Refractive Index Metamaterial in Planar Technology

We present a fully printable effective negative refractive index (NRI) metamaterial responsive to arbitrarily linearly polarized incident waves. The proposed metamaterial is composed of a periodic array of tightly coupled Jerusalem cross conductor pairs printed on the opposite sides of a dielectric substrate. Each pair supports both symmetric and antisymmetric resonance modes, whose superposition can lead to an effective NRI of the composite medium. A thorough characterization of the transmission properties of such metamaterial is performed, and conclusive evidences of the medium exhibiting effective NRI properties and impedance matching to free space are presented for a range of the structure parameters.

Phase conjugating wire FSS lens

Analysis of a microwave lens formed using a pair of frequency selective surfaces comprised of back-to-back double-periodic wire arrays interconnected through phase-conjugating microwave circuitry is given in this paper. It is shown that such a structure when illuminated with a plane wave generates a phase-conjugated forward-transmitted plane wave which experiences negative refraction. Negative refraction makes it possible to produce focusing of wave packets incident on such structures both in the far- and near-field regions. We provide analytical formulation of the problem and develop a rigorous calculation of the EM field transmitted through the structure: i) when excited by a plane wave; and ii) due to an electric line source suspended above it. Numerical simulations illustrate the focusing properties of the proposed lens. These properties are shown to include half wavelength compression of the focused line source image in the transverse direction in the far-field zone. A physical explanation of why this effect occurs is also provided

Entwined Planar Spirals for Artificial Surfaces

Entwining planar quadrifilar spirals arranged in doubly periodic arrays enables a strong subwavelength response of the unit cell smaller than 1/40 of wavelength. It is shown that interleaving counterwound spiral arms extended into adjacent unit cells dramatically increases the equivalent capacitance while reducing the inductance. The dielectric substrate enhances this effect of the unit cell miniaturization with concurrent bandwidth expansion. The proposed topology of compact planar spiral array exhibits excellent angular and polarization stability and circular polarization selectivity in a broad frequency band. Negligible variations of the resonance frequency are demonstrated for both TE and TM polarized waves at incidence angles up to 45 with a common fractional bandwidth over 40% at the level of -10 dB.

Passive Intermodulation Generation on Printed Lines: Near-Field Probing and Observations

The phenomenological mechanisms of passive intermodulation (PIM) in printed lines have been explored by mapping intermodulation products generated by the two-tone traveling waves in microstrip lines. Near-field probing based upon a commercial PIM analyzer has been employed for identification of the PIM sources in printed lines. The results of extensive near-field probing provide the direct experimental evidences of cumulative growth of the intermodulation products in the matched uniform microstrip lines and reveal the fundamental role of the nonlinear scattering by the lumped nonlinear inclusions in the intermodulation production. The distributed nature of the PIM generation in microstrip lines has been conclusively demonstrated and comprehensively described in terms of the four-wave mixing process that proved to be fully consistent with the results of experimental observations of third-order PIM products on the matched and mismatched microstrip lines.

Distributed sources of passive intermodulation on printed lines

The sources of passive intermodulation (PIM) on matched uniform microstrip lines have been investigated. The results of PIM measurements and SEM analysis of the conductor traces fabricated on the PCB laminates coated by copper foils of different grades suggest that PIM sources on the printed transmission lines are of non-local nature being distributed along the signal path. Quality of the copper foil and roughness of its surface proved to critically affect PIM performance of the microstrip lines on the low loss PTFE based dielectric substrates.

Computing Zeros of Analytic Functions in the Complex Plane without using Derivatives

Abstract We present a package in Fortran 90 which solves f ( z ) = 0 , where z ∈ W ⊂ C without requiring the evaluation of derivatives, f ′ ( z ) . W is bounded by a simple closed curve and f ( z ) must be holomorphic within W . We have developed and tested the package to support our work in the modeling of high frequency and optical wave guiding and resonant structures. The respective eigenvalue problems are particularly challenging because they require the high precision computation of all multiple complex roots of f ( z ) confined to the specified finite domain. Generally f ( z ) , despite being holomorphic, does not have explicit analytical form thereby inhibiting evaluation of its derivatives. Program summary Title of program: EZERO Catalogue identifier: ADXY_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADXY_v1_0 Program obtainable from: CPC Program Library, Queens University of Belfast, N. Ireland Computer: IBM compatible desktop PC Operating system: Fedora Core 2 Linux (with 2.6.5 kernel) Programming languages used: Fortran 90 No. of bits in a word: 32 No. of processors used: one Has the code been vectorized: no No. of lines in distributed program, including test data, etc.: 21045 Number of bytes in distributed program including test data, etc.: 223 756 Distribution format: tar.gz Peripherals used: none Method of solution: Our package uses the principle of the argument to count the number of zeros encompassed by a contour and then computes estimates for the zeros. Refined results for each zero are obtained by application of the derivative-free Halley method with or without Aitken acceleration, as the user wishes.

Enhanced transmission in microwave arrays of periodic sub-wavelength apertures

Several configurations of aperture arrays have been investigated using a rigorous numerical–analytical technique. The characteristics of optical transmission through a periodic array of sub-wavelength holes in metal films have been simulated and the mechanisms of the transmittance enhancement ar ed iscussed. The effects of topological factors and array arrangement have been explored from the perspective of enhancing microwave transmission through arrays of sub-wavelength apertures. The features and properties of aperture arrays used in quasi-optical filters and wavelength selective structures are presented.