Maria Del Castillo Velazquez-Ahumada

Parallel coupled microstrip filters with ground-plane aperture for spurious band suppression and enhanced coupling

Parallel coupled microstrip sections with a slotted ground plane are proposed as building blocks of coupled-line microstrip filters with enhanced performance. It is shown that, by proper adjustment of the ground-plane slot dimensions, the double frequency spurious band associated with unequal even/odd electrical lengths can be suppressed or meaningfully reduced. As an additional feature, this simple design relaxes tolerances of strip width and spacing in those cases where tightly coupled high-impedance sections are required. A rough preliminary design can be obtained within a few seconds using a fast optimization algorithm based on a quasi-TEM analysis of the coupled sections. Fine tuning is based on the use of a commercial electromagnetic simulator. Finally, experimental check of filter performance is provided.

Open Complementary Split Ring Resonators (OCSRRs) and Their Application to Wideband CPW Band Pass Filters

In this letter, open complementary split ring resonators (OCSRRs) are introduced for the first time. Such resonators are the dual counterparts of the open split ring resonators (OSRRs), introduced in 2004 by some of the authors, and consist on a pair of concentric hooks etched on a metal layer in opposite orientation. It is shown in the letter that OCSRRs can be modeled by means of an LC parallel resonant tank and that this particle roughly exhibits half the resonance frequency of the complementary split ring resonator (CSRR), hence being electrically very small. The interest of these resonators is illustrated through their application to a wideband coplanar waveguide band pass filter.

Parallel coupled microstrip filters with floating ground-plane conductor for spurious-band suppression

Floating strip conductors printed on the backside of the substrate are shown to be useful to suppress the spurious transmission band appearing at twice the central frequency of coupled-line microstrip filters. It is shown that proper adjustment of the dimensions of the floating conductors yields equal even and odd electrical lengths. An attractive feature of this design is its flexibility because the equalization of the modal electrical lengths can be achieved with various geometries. Additionally, the floating conductor provides an extra coupling mechanism that relaxes tolerances of strip width and spacing in those cases where tightly coupled sections are required. A fast quasi-TEM analysis is used to find the structure yielding equal mode phase velocities. Fine tuning to equalize the modal electrical lengths for each coupled stage is based on the use of a commercial electromagnetic simulator. Experimental verification is finally provided.

Design of Compact Low-Pass Elliptic Filters Using Double-Sided MIC Technology

A novel implementation of stepped-impedance low-pass elliptic filters is presented in this paper. The filters are based on the well-known technique of cascading high- and low-impedance sections to simulate the ladder LC lumped-circuit prototype. We propose in this study a new approach to build up the constitutive circuit elements by taking advantage of the use of both sides of the substrate. The use of double-sided technology yields both design flexibility and good circuit performance. High-impedance sections are achieved by using slots in the backside of the substrate, whereas low-impedance sections are obtained with parallel-plate capacitors. In order to achieve the transmission poles corresponding to the elliptic design, these capacitors are series connected to the ground plane by means of high-impedance coplanar-waveguide lines, which mainly act as inductors. As a final step, meandering techniques have been applied to the high-impedance sections of the filter to reduce the overall circuit size. The measurement of several fabricated filters shows fairly good agreement between theory and experiment

Metamaterial applicator for microwave hyperthermia

In this work, it is studied the application in hyperthermia of a microwave focusing device based on meta-materials. The device consists of a planar array of split-ring resonators placed between two parallel metallic plates and it is fed by a small loop antenna which excites the split-rings. The device is modelled as an homogeneous uniaxial slab of negative permeability placed between two metallic plates. Both the fields and the temperature distribution in model of breast tissue and a tumor are numerically obtained. The field produced by the fabricated device inside a phantom resembling the breast tissue was measured with a probe to check the theoretical predictions.

Design of a dual band-pass filter using modified folded stepped-impedance resonators

A folded stepped impedance resonator (SIR) modified by adding an inner quasi-lumped SIR stub is used as the basic block of a new configuration of dual band-pass filter. The main advantage of the proposed filter is to allow independent control of the features of the first and the second pass bands. Additional design flexibility can be achieved by allowing the stub to be located at an arbitrary position along the high impedance line section of the main SIR. The positions of the tapped lines have been optimized in order to match the filter at the central frequencies of both pass bands. Some designs are reported to illustrate the possibilities of the structure.

Demonstration of negative refraction of microwaves

An experimental setup to demonstrate negative refraction is described. A simple method for designing and fabricating a metamaterial with negative refractive index at microwave frequencies is discussed. The metamaterial is made of a multilayer planar arrangement of flat unit cells. A prism was fabricated and used to demonstrate negative refraction at the prism-air interface. The prism is designed for demonstrations and works at the frequency of commercial microwave transmitters and receivers.

Low-pass Elliptic Filters Using Mixed Microstrip-CPW Technologies

Stepped-impedance low-pass elliptic fllters are presented in this paper which make use of patterning of both sides of the microstrip substrate. Microstrip and coplanar waveguide components as well as their interactions are used jointly to synthesize the required fllter elements. Relatively compact implementations with good electrical performance are obtained in this way. Conventional stepped-impedance low pass fllters (SI-LPF) consist of a cascading of electrically short high and low impedance sections to approximate the corresponding ladder LC lumped circuit prototype (1). However, this kind of fllter inherently presents two problems. One of them is the degradation of the stop band rejection level because of the frequency-distributed behavior of the flnite section lines. The second problem comes from the limits imposed by the microstrip technology to achieve very narrow strip widths and, consequently, high impedance section lines.

Efficient area reduction in microstrip cross-coupled resonator filters by using split rings resonators and spiral resonators

In this work, it is demonstrated that microstrip band pass filters with a pair of attenuation poles at finite frequencies can be implemented by introducing cross coupling between non-adjacent split ring resonators (SRRs) or spiral resonators (SRs). As compared to filter implementations that use conventional open loop resonators, a reduction of layout area by a factor of 4 is demonstrated in the SR-based filter implementation. The filter synthesis method is based on the calculation of the coupling coefficients of intercoupled resonators and external quality factors of the input and output resonators, as reported in previous realizations based on open loop resonators. This reduction in device dimensions is related to the sub-wavelength operation of SRRs and SRs. It is believed that the approach proposed in this work can be of interest to optimize the size of microstrip band pass filters.

Microwave-induced water flow in a microchannel built on a coplanar waveguide

We present experimental and numerical investigations of water flow in a microsystem induced by microwave electric fields. Microwave dielectric heating induces gradients of temperature which produce spatial variations in mass density and dielectric permittivity that lead to buoyancy and dielectric forces in the liquid, respectively. The experimental system consists of a microchannel, filled with water, which is built on top of a coplanar waveguide operating in the fundamental transversal electromagnetic (TEM) mode at frequencies in the range 1–4 GHz. The flow originated by standing waves is studied. Maxima and minima of electric field amplitude lead to maxima and minima of fluid flow. This observation allows us to measure the TEM wavelength and good agreement is found with the theoretical results for the TEM mode inside the microchannel. We also present three dimensional finite-element calculations of the electric, temperature and fluid velocity fields in the microchannel. In a first approach, the calculat...