Microwave-frequency filtering structures

Abstract

A microwave-frequency filtering structure includes two dielectric layers separated by a conducting layer that is etched in the pattern of a filter, the upper and lower exterior faces of the stack being covered over the larger part of their surface by a conducting plane constituting ground planes of the structure, which are interlinked by a metallization of the periphery of the structure; two identical devices, an input and an output transition device, each allowing the passage from a microstrip mode to a stripline mode and vice versa, configured so that the geometry of the transition device is optimized to minimize the standing wave ratios at the ports of the filter, and to minimize the excitation and the coupling of the TE10 mode, two conducting pillars perpendicular to the plane of the structure and situated close to its principal axis, without being coupled with the filter, and linking the upper and lower ground planes.

Claims

1. A microwave-frequency filtering structure comprising: two dielectric layers separated by a conducting layer, the conducting layer being etched in a pattern of a filter, wherein upper and lower exterior faces of a stack of the two dielectric layers are covered over a larger part of their surface by a conducting plane constituting upper and lower ground planes of the structure, wherein said upper and lower ground planes are interlinked by a metallization of a periphery of the structure, except in the vicinity of microwave-frequency ports, two identical devices, one of the two identical devices being an input transition device and the other one of the two identical devices being an output transition device, each allowing a passage from a microstrip mode to a stripline mode and vice-versa, configured such that a geometry of the transition device is optimized so as to minimize standing wave ratios at the ports of the filter, and to minimize an excitation and a coupling of a TE10 mode, and at least two conducting pillars perpendicular to the plane of the structure, which are situated as close as possible to a principal axis of the structure, without there being any coupling with the filter, and linking the upper and lower ground planes.

2. The structure according to claim 1, wherein each device of the two identical devices includes: a metallized pad situated on a lower face of the device and on a minor side of the filter, an interconnection hole allowing a connection between the metallized pad and a stripline access line of the filter, and eight metallized pillars connected at each end to the ground planes.

3. The structure according to claim 1, wherein the two identical devices enable the structure to be assembled to a microwave-frequency microstrip-type printed circuit by soldering.

4. The structure according to claim 1, wherein the pillars are made as metallized interconnection holes passing through the two dielectric layers.

5. The structure according to claim 1, wherein the pillars are solid metal rods.

6. A printed circuit including a set of active and/or passive components, comprising one or more structure(s), according to claim 1.

7. The structure according to claim 1, wherein the at least two conducting pillars perpendicular to the plane of the structure include two pillars arranged on a first side of the conducting layer and two pillars arranged on a second side of the conducting layer, the second side being opposite to the first side, and wherein a first pillar of each of the two pillars is arranged closer to the conducting layer than a second of each of the two pillars so that the first of each of the two pillars is provided between the conducting layer and the second of each of the two pillars.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention will be better understood upon reading the description that follows and upon examining the accompanying figures. These are only presented by way of illustrating purposes, but in no way limiting for the invention. The figures show:

(2) FIG. 1: schematic representation of a filter feasible in striplines, according to the state of the art;

(3) FIG. 2: overview of the structure, according to one embodiment of the invention;

(4) FIG. 3: detailed view of the stripline/microstrip transition, according to one embodiment of the invention.

DESCRIPTION OF THE INVENTION

(5) It is now noticed that the figures are not drawn to scale.

(6) The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the characteristics only apply to a single embodiment. Simple characteristics of different embodiments can also be combined to provide other embodiments.

(7) The invention which will be described hereinafter aims at providing a new integratable filter structure the frequency response of which is free of distortion and of spurious response on a wide frequency band, thereby improving the filtering performance.

(8) FIG. 2 illustrates an overview of the structure, according to one embodiment of the invention. In this FIG. 2, a stripline structure 20 is comprised of two dielectric layers 21, 23 separated by a conducting layer 22. The conducting layer 22 is etched in the pattern of a filter according to the principle of FIG. 1. The filter according to FIG. 1 is described in more detail in documents hereinafter referenced as George L. Matthaei, Leo Young & E. M. T. Jones. Microwaves Filters, Impedance-Matching Networks and Coupling Structures. Editions McGraw-Hill Inc.

(9) In the rest of the description, the conducting layer 22 will be called a filter 22. The upper and lower exterior faces of the stack of both dielectric layers 21, 23 are covered over the larger part of their surface with a conducting plane (not represented to facilitate the understanding of FIG. 2) constituting the ground planes of the structure 20. The ground planes are interlinked by a metallization of the periphery of the structure 20 except in the vicinity of the microwave-frequency ports.

(10) The structure 20 also includes two identical devices 24, 25, one of them being an input transition device 24 and another one being an output transition device 25, illustrated in FIG. 3. These devices 24, 25 allow the passage from a microstrip mode to a stripline mode and vice-versa. These devices 24, 25 each include: a metallized pad 30 situated on its lower face and on the minor side 26 of the filter 22 as well as an interconnection hole 31 allowing the connection between the metallized pad and the stripline access line of the filter 22, and eight metallized pillars 32 connected at each end to the ground planes.

(11) The geometry of the transition device 24, 25 is optimized in order to minimize the Voltage Standing Wave Ratio (SWR) at the ports of the filter 22 and also to minimize the excitation and coupling of the TE10 mode in a rectangular guide structure included in the structure 20. These devices 24, 25 further enable the structure 20 to be transferred or assembled to a microwave-frequency microstrip-type printed circuit by soldering.

(12) Further, the structure 20 includes at least two conducting pillars 27 perpendicular to the plane of the structure 20, situated as close as possible to its principal axis without there being a coupling with the filter 22 and linking the upper and lower ground planes. In one embodiment of the invention, these pillars 27 are made as metallized interconnection holes passing through both dielectric layers 21, 23. In a second embodiment of the invention, the pillars 27 are solid metal rods.

(13) The entire structure 20 according to the invention constitutes a band-pass filter free of distortion and of spurious response on a wide frequency band, and able to be assembled to a microwave-frequency microstrip-type printed circuit.

(14) A non-negligible advantage of the structure according to the invention is its capability to be made by means of standard techniques for manufacturing microwave-frequency circuits and hence results in a relatively low production cost.