Monica Martinez-Mendoza

Design of Bandpass Transversal Filters Employing a Novel Hybrid Structure

A novel structure for the implementation of compact transversal bandpass filters is proposed in this paper. This new proposal consists of a hybrid structure, based on the combination of two different technologies: the waveguide and microstrip. It is shown that the novel hybrid microwave filter is able to implement both a second- and third-order filtering function with up to two or three transmission zeros, respectively. In this way, a practical implementation of a fully canonical transversal filter with a third degree response is for the first time directly achieved. In addition, the way to control the positions of transmission zeros with the new technology is treated in this paper. It is shown that symmetric or asymmetric responses and also filtering functions with a complex pair of transmission zeros can be easily obtained. To demonstrate the validity of this novel structure, several implementation examples are presented. A prototype has been designed, manufactured, and successfully tested, showing the practical validity of the new structure.

Design of Dual-Bandpass Hybrid Waveguide–Microstrip Microwave Filters

A simple dual-bandpass filtering structure is proposed. The filter is implemented by means of a new hybrid waveguide-microstrip technology. The novelty of the structure is that it combines two standard printed microstrip coupled line resonators, with a resonance of the base waveguide cavity, to implement a dual-band operation. Important aspects about the filter design, useful for practical applications are treated. This includes a study on the maximum coupling that can be achieved to the cavity resonance, and guidelines to control the positions of the two passbands and the transmission zeros. Besides, an example has been designed, manufactured and tested. The measurements on the fabricated prototype have confirmed the validity of the new structure to perform dual-band operation.

Practical Implementation of the Spatial Images Technique for the Analysis of Shielded Multilayered Printed Circuits

In this paper, a practical implementation of the spatial images technique for the analysis of shielded multilayered printed circuits inside convex cavities is proposed. A new method is introduced in order to automatically locate the images surrounding the structure in order to impose the appropriate boundary conditions for the potentials. The boundary conditions are imposed at discrete points along the cavity wall and, therefore, the technique proposed is an approximation to the exact cavity modeling. Furthermore, for the analysis of electrically long cavities, the use of several rings of images surrounding the entire cavity at different heights is employed. Using the special features of the formulation, a new method of moments implementation combined with the spatial images technique is proposed in order to efficiently analyze practical multilayered printed filters, considerably reducing the computational cost. Several examples with CPU time comparisons are provided, demonstrating the accuracy and efficiency of the new technique. A novel transversal filter in a trapezium-shaped cavity is designed, manufactured, and tested for the first time using the spatial images technique.

Formal Expression of Sensitivity and Energy Relationship in the Context of the Coupling Matrix

Precise formulas to express the formal relationship between the time average stored energy in the resonators of a low-pass filter network and the sensitivity of the reflection S -parameter with respect to the coupling matrix terms are demonstrated in this paper, considering the normalized frequency axis. These relationships are found in the modern context of the N+2 coupling matrix, and for both diagonal and general nondiagonal coupling elements of the matrix. The results are valid for any type of coupling topology represented by the N+2 coupling matrix. Different examples are included as validation. Furthermore, important implications and applications derived from the new relationships are highlighted.

Design of a Bandpass Transversal Filter Employing a Novel Hybrid Waveguide-Printed Structure

This paper introduces a novel hybrid structure to implement a bandpass transversal filter based on the combination of two well known technologies. The structure combines for the first time the waveguide and the microstrip technologies for the design of transversal filters with maximum selectivity. By combining these technologies, very compact structures are obtained to implement the so called modified doublet. One of the resonators of the doublet is formed with the TM111 mode of a waveguide cavity, while the second resonator is implemented using a standard printed line microstrip resonator. It is shown that all the parameters of the N + 2 coupling matrix can be controlled by means of the dimensions of the proposed structure. Results validate the novel structure, and show how a second order filtering function of a specific coupling matrix can be easily synthesized.

On the Relation Between Stored Energy and Fabrication Tolerances in Microwave Filters

In this paper, a new approach for the sensitivity analysis of microwave filter networks is presented. It is shown that the standard method of sensitivity calculation based on a tuned filter is only valid for infinitesimal geometry changes and not meaningful for practical tolerance values. However, when the sensitivity calculation is expanded to also include sensitivities of detuned filters, it is shown that accurate tolerance predictions can be made even for large geometry variations. It is found that sensitivities can be related to the stored energy distribution in the filter. Transversal and ladder network-type topologies are examined, and it is demonstrated for the first time that, for in-line topologies, sensitivity can be predicted directly from the group delay of the filter in Chebyshev filters. In order to demonstrate the usefulness of the results obtained, the maximum degradation of the in-band performance has been directly obtained from the group delay for different inline filters.

Numerical Evaluation of the Green's functions for Arbitrarily Shaped Enclosures

In this paper, a new spatial method has been implemented for the efficient calculation of the mixed potential Greens functions associated to electrical sources, when they are placed inside arbitrarily-shaped cylindrical cavities. The technique consists of placing electric dipole images and charges outside the cavity, imposing, at discrete points of the metallic wall, the appropriate boundary conditions for the potentials. Results show that the numerical convergence is attained fast. The cut-off frequencies and potential patterns for a trapezium-shaped waveguide are compared to those obtained by a standard finite elements technique, showing excellent agreement. Furthermore, a printed planar filter shielded in a square cavity has been analyzed with the new Greens functions, showing the practical value of the new theory.

Enhanced topology for the design of bandpass elliptic filters employing inductive windows and dielectric objects

This work presents a new topology for the design of bandpass elliptic filters employing inductive windows and dielectric objects. The proposed filtering structure combines, for the first time, the modified TE102 resonating mode with the modified TE201 mode. The TE201 mode is excited by placing a wide dielectric post inside a waveguide cavity. The main advantage of the new topology is that two transmission zeros can be synthesized in the insertion loss response of the filter, for a second order structure. Also there is a high flexibility on the location of the transmission zeros. They can be synthesized along the frequency axis for maximum selectivity, or as a pair of complex poles for phase equalization.

Comments on “On the Relation Between Stored Energy and Fabrication Tolerances in Microwave Filters”

In the above paper, the authors propose a new analytical methodology for the sensitivity analysis of microwave filter networks. However, an errata has been found which may affect the readers understanding, and it will be clarified in this comment.

Novel Broadside Trisection Filters Employing Nonresonating Nodes

This work presents novel filter topologies implemented in microstrip technology. The topologies combine printed line resonators with non resonating nodes (NRN) to implement transmission zeros in a very flexible way. Depending on the number of resonators and NRN, the filtering response exhibits a single transmission zero either below or above the passband, or two transmission zeros, one at each side of the passband. Several examples are designed and validated, using the new proposed structures.