Two novel, compact, simple 2nd and 3rd harmonic rejection coplanar waveguide (CPW) feeding mechanisms for a 5.8 GHz rectenna are proposed. Both of them make use of the CPW compact microstrip resonant cell (CMRC). In the first topology, the blockage is realized by a CMRC in combination with a U-slot. In the second topology a pair of strongly coupled CMRCs is optimized. Both these new feeding mechanisms are realized in prototypes and experimentally validated, first in two back-to-back configurations, and then in combination with two CPW fed wideband monopole antennas. The measured antenna return loss at the 2nd and 3rd harmonic is in the order of 0.5 dB and 1.5 dB, respectively, which corresponds to a return loss suppression of about 4 -5 dB compared to a reference monopole antenna. Both antennas reach an 18% 10 dB return loss bandwidth, which is the highest working bandwidth reported in literature for harmonic rejection antennas. Bandwidth could become an issue when wireless power transfer systems would be implemented with a reconfigurable working frequency in order to minimize interference with local telecom equipment.

Wideband harmonic rejection filtenna for wireless power transfer

Wideband Harmonic Rejection Filtenna for Wireless Power Transfer

This paper presents a highly sensitive phase-variation sensor for dielectric constant measurements based on a capacitively-loaded periodic slow-wave transmission line. Such line is implemented in microstrip technology, and the loading capacitors are formed by closely spaced rectangular patches. The sensing area of the device is delimited by the region occupied by the capacitive patches, where the material under test (MUT) must be located. The presence of the MUT modifies the coupling capacitance between adjacent patches, thereby producing a variation in the electrical length, or phase of the transmission line, which is the output variable. A detailed analysis of the equivalent circuit model of the unit cell, useful for design purposes, is carried out in the paper. Based on such analysis, a prototype device sensor is designed and fabricated. It is demonstrated in the paper that the sensitivity of the proposed sensor is by far superior to the one achieved in an ordinary meandered line with similar sensing area. Thus, the proposed slow-wave structure constitutes a good alternative to meandered lines for the implementation of phase-variation sensors with simultaneously high sensitivity and compact size.

Highly Sensitive Phase-Variation Dielectric Constant Sensor Based on a Capacitively-Loaded Slow-Wave Transmission Line

In this work, a step-by-step development of a compact microstrip rat-race coupler (RRC) has been presented and discussed. A high degree of miniaturization has been obtained by substituting six quarter-wavelength uniform atomic building blocks of a RRC by their nonuniform counterparts. The miniaturization procedure has been real- ized in three progressive steps: (i) the first layout solution of a miniatur- ized RRC has been acquired using an accurate mathematical model of a nonuniform transmission line (NUTL); (ii) the second layout solution has been obtained by a manual refinement and electro-magnetic (EM) fine-tuning of the NUTL geometry aimed at the utilization of the interior of the RRC in a highly efficient manner; (iii) the final layout, occupying only 8.5% estate area in comparison to a conventional RRC, is the result of the EM optimization. The experimental results confirm the theo- retical predictions, proving the vital usefulness of the approach. V C 2014

A compact microstrip rat-race coupler constituted by nonuniform transmission lines

In this paper, a methodology for fast multiobjective optimization of the miniaturized microwave passives has been presented. Our approach is applicable to circuits that can be decomposed into individual cells [e.g., compact microstrip resonant cells (CMRCs)]. The structures are individually modeled using their corresponding equivalent circuits and aligned with their accurate, EM simulated representations, by means of implicit space mapping (ISM). The ISM-corrected cells are then assembled into the entire structures and their Pareto-optimal solutions (here, representing the best possible tradeoffs between the structure size and electrical performance) are obtained using evolutionary methods. The refinement is then carried out for the selected structure realizations using, again, SM. The latter stage is necessary, because the cell-based equivalent circuit models do not account for EM cross-couplings between the cells. The proposed methodology allows for rapid identification of compromise geometries concerning size-performance tradeoffs and, more importantly, permits quality comparison of particular CMRC realizations from the point of view of their suitability for a given compact circuit implementation. Our approach is demonstrated using several variations of the three-section wideband impedance matching transformers consisting of two types of CMRC structures. Numerical validation of the results is provided.

Rapid Simulation-Driven Multiobjective Design Optimization of Decomposable Compact Microwave Passives

A comprehensive comparison of a wide collection of compact microstrip resonant cells (CMRCs) found in the extensive body of literature has been presented. The evaluation of different CMRC designs has led to the selection of the most promising CMRC geometry for the efficient miniaturisation of modern microwave components. To showcase the vital effectiveness of the approach, the initially selected CMRC has been notably improved and applied to an exemplary microwave component, that is, a branch-line coupler, to obtain its size reduction without degradation in its performance. Exemplary prototype circuits have been designed to mimic the frequency characteristics of a classic coupler, simultaneously presenting a substantial 75, 80 and 85% surface area reduction. The best solution obtained has been experimentally validated. The measured in-band results are in excellent accordance with the theoretical characteristics, whereas the broadband performance depicts an additional effect, that is, the strong suppression of unwanted signals in 2.6-7 GHz frequency band. The multi-step CMRC evaluation and improvement procedure proposed presents an efficient design methodology for novel compact circuit topologies developed in microstrip technology.

Development of a compact microstrip resonant cell aimed at efficient microwave component size reduction

A conventional compact microstrip resonant cell (CMRC)has been thoroughly investigated to enhance its slow-wave properties and subsequently ensure an efficient miniaturization of a microstrip circuit. The geometry of a classic CMRC has been improved in terms of slowwave effect in two progressive steps: (i) a single-element topology has been replaced with a double-element one and (ii) a high-impedance section has been refined by means of an optimized meander line characterized by the minimal number of discontinuities. Vital usefulness of the novel CMRC in the process of microstrip circuit miniaturization has been proven and experimentally validated on the basis of a compact 3-dB branch-line coupler illustrating the possibilities of the approach. A prototype structure has been designed to mimic the performance of a classic coupler, simultaneously presenting a substantial 85% surface area reduction. The measured in-band results are in excellent accordance with theoretical characteristics, whereas the broadband performance depictsan additional phenomenon, that is, the efficient suppression of unwanted signals up to the sixth harmonic.

Jan Filipcewicz

Papers

Development of a compact microstrip resonant cell aimed at efficient microwave component size reduction

Design considerations for compact microstrip resonant cells dedicated to efficient branch-line miniaturization