Riana Helena Geschke

Compact Tri-Band Bandpass and Bandstop Filters Based on Hilbert-Fork Resonators

In this work, a multi-mode Hilbert-fork resonator consisting of two dual-mode resonators is presented. The behavior of the proposed configuration is analyzed in detail. To demonstrate the potential of the proposed resonator, tri-band bandpass and bandstop filters operating at 2.4/3.5/5.2 GHz have been designed, fabricated and measured. Both filters are characterized by good performances and very compact size of only 0.21λ<i>g</i> × 0.11λ<i>g</i> and 0.22λ<i>g</i> × 0.1λ<i>g</i> , respectively.

Filter Parameter Extraction for Triple-Band Composite Split-Ring Resonators and Filters

A configuration of composite resonators consisting of three split-ring resonators is proposed to obtain a triple-band response with two transmission zeros between the passbands. Two new topologies are presented to design triple-band filters with controllable responses. A systematic filter design approach is presented based on a filter coupling model. The model is established to enable triple-band filter design with controlled passbands. Two methods are proposed and compared for the extraction of filter parameters. Coupling between nonadjacent elements is considered in the model and shown to have a significant effect. By changing the orientation of the coupled composite resonators, it is possible to introduce additional transmission zeros. Two sixth-order filter examples illustrate the use of the coupling model with the filter design approach to design filters with specified responses. The limitations of this filter topology are discussed.

Radio Frequency Interference and Lightning Studies of a Square Kilometre Array Demonstrator Structure

We study the radio frequency interference and lightning protection of the South African Square Kilometre Array demonstrator: the Karoo Array Telescope. Increasingly-realistic scale models of the demonstrator have been built and computationally modeled using FEKO. Minimally-invasive S-parameter measurements are made on physical scale models in an anechoic chamber with good agreement to simulation. The modeling has enabled insightful investigations into current paths and field distributions for interference mitigation and structure lightning protection, with direct bearing on the demonstrator implementation.

A Tune-All Wideband Filter Based on Perturbed Ring-Resonators

A dual-mode resonator is presented for tunable wideband filters, which allows tunability in both the centre frequency and bandwidth. It is based on a new perturbation arrangement in a ring-resonator that is electronically tuned with varactor diodes. A filter is designed for a radio astronomy receiver application. It consists of 6 cascaded dual-mode resonators with a 49% bandwidth in the L-band. High selectivity and low insertion losses are achieved. The centre frequency is tunable by 9% and the bandwidth by 25.3%. This design is unique in that it achieves wide bandwidth, is realisable in microstrip and tunable in both the centre frequency and bandwidth.

Karoo Array Telescope: Lightning protection issues and RFI

A computational electromagnetic (CEM) code and a reduced scale model were used to characterize the design of the Karoo Array Telescope (MeerKAT), South Africas demonstrator for the Square Kilometer Array (SKA). Different excitation techniques were used in the CEM code and are compared to actual scale model measurements in an anechoic chamber. With verified computational modeling, the optimized lightning down conductor layout and earth termination system interconnections were investigated, keeping cost and RFI in mind.

Cable Trays in EMC: Measurement and Modeling to 30 MHz

Common mode (CM) currents are a major source of interference in electrical and electronic systems. Cable trays are often used to shield cables from unwanted CM electromagnetic interference, and their shielding characteristics are defined in terms of transfer impedance. We present the measurement and modeling of nonmagnetic U-shaped cable trays from 300 kHz to 30 MHz. A calibrated vector network analyzer in a screened environment is required for the high dynamic range measurements. We use method of moments simulations to determine the transfer impedance and mutual inductance within the interior region of a cable tray. We refined the modeling after detailed attention to the code. The computational and measured data are in good agreement. We propose the simulation as a means to predict the magnetic fields, mutual inductance, and transfer impedance associated with victim cable loops in the cross section of nonmagnetic cable trays to frequencies well beyond our studied range of 30 MHz.

The Solution of Waveguide Scattering Problems by Application of an Extended Huygens Formulation

The implementation of a recent new hybrid integral-equation/vector finite-element method formulation applicable to inhomogeneous obstacle scattering in hollow waveguide, requiring discretization just of the obstacle, is presented. The integral equation links the given incident modes with the discontinuity-surface electric and magnetic fields. The finite-element equation is expressed in terms of the entire magnetic and surface electric field of the obstacle. Compatible vector finite-element basis function expansions are inserted, resulting in a pair of matrix equations soluble for the unknown electric and magnetic basis coefficients. Corresponding two-port scattering parameters are further derived. Test cases of posts in the TE10 waveguide, with details of the matrix constructions, are described. Numerical results verified against an established commercial code are given. The ability to model inhomogeneous, lossy, and multiple scatterers is demonstrated

Vector based higher-order 3D finite element simulation of microwave cavities

Finite elements (FE) for microwave device simulation are reviewed, with specific emphasis on vector elements. The FE analysis of microwave cavities, and the resulting generalised eigenvalue equation, is discussed. Results for two benchmark cavity analysis problems are shown. Applications are briefly outlined. The paper concludes with an overview of current work, including sparse linear algebra and incorporating the FE code within the advanced FEKO code suite.

Correction to “Radio Frequency Interference and Lightning Studies of a Square Kilometer Array Demonstrator Structure” [May 2011]

We studied computational electromagnetic and scale models of a Square Kilometer Array demonstrator structure in our paper listed above (ibid., vol. 53, no. 2, pp. 543-547, May 2011). During the final publication process, one of our figures was inadvertently duplicated and the pivotal point of the paper was lost. The omitted numerical simulation would have illustrated the value of the optimized lightning down conductor (LDC). Fig. 1 here (intended [Fig. 10 in the above paper]) should be compared to Fig. 2 ([above paper, Fig. 11]). The considerably lower surface current density acheived due to the LDC reconfiguration was the purpose of the above listed work.

Erratum: Radio frequency interference and lightning studies of a square kilometer array demonstrator structure (IEEE Transactions on Electromagnetic Compatibility (2011) 53:2 (543-547))

We studied computational electromagnetic and scale models of a Square Kilometer Array demonstrator structure in our paper listed above (ibid., vol. 53, no. 2, pp. 543-547, May 2011). During the final publication process, one of our figures was inadvertently duplicated and the pivotal point of the paper was lost. The omitted numerical simulation would have illustrated the value of the optimized lightning down conductor (LDC). Fig. 1 here (intended [Fig. 10 in the above paper]) should be compared to Fig. 2 ([above paper, Fig. 11]). The considerably lower surface current density acheived due to the LDC reconfiguration was the purpose of the above listed work.