GB2071922A

GB2071922A - Wide-band directional coupler having a coplanar configuration

Info

Publication number: GB2071922A
Application number: GB8106550A
Authority: GB
Original assignee: CISE Centro Informazioni Studi e Esperienze SpA
Current assignee: CISE Centro Informazioni Studi e Esperienze SpA
Priority date: 1980-03-10
Filing date: 1981-03-02
Publication date: 1981-09-23
Also published as: IT8020486A0; GB2071922B; JPS56160101A; IT1130952B; DE3108653A1

Abstract

A planar directional coupler comprises a dielectric substrate (1) to which a single metallic coating (2) is superposed, the metallic coating (2) being removed centrally (3) to provide a row of parallel grooves (4) defining central conductive strips (5). The conductive strips (5) are alternately connected by wires (6). Four U-shaped lateral grooves (7) are also formed by removal of the metal layer (2) so as to provide lateral conductive strips (8) which are connected by wires (9) to the central strips (5). The arrangement so provided is a wide-band element which is easy and cheap to construct, is reproducible and permits a fine miniaturization. <IMAGE>

Description

SPECIFICATION Wide-band directional coupler having a coplanar configuration This invention relates to a wide-band directional coupler having a coplanar configuration.

Conventional directional couplers having coupled lines are in use long since in the microwave field.

More particularly, due to their constructional properties, have found a wide use their embodiments in the form of microstrips as obtained by metallizing both the faces of a dielectric backing layer.

With the advent of the solid state devices such as diodes of various types and field-effect transistors, it has become of utmost importance to have planar couplers available which avoid circuital complications and assembling difficulties connected to the necessity of boring the dielectric backing to connect the various devices to ground. For this reason, studies have been effected long since in an attempt to obtain planar couplers.

The embodiments proposed heretofore, which provide on a single plane two central conductive strips which effect the directional coupling, four side conductive strips which are the lines of connection to the external circuitry and four discrete conductive areas which are the so-called "ground planes", were not successful, however, both because they do not lend themselves to obtain, in a simple, reproducible and cheap manner, high couplings (which are vital for many applications, such as balanced amplifiers, mixers and others) and because they present a number of problems connected with the provision of a satisfactory connection between the grounding planes. For this reason a few among the prominent search centres have even envisaged to drop the idea and to address themselves to more intricate approaches with concentrated constants.

An object of the present invention is to provide a planar-type directional coupler which, by overcoming the limitations outlined above, has the aspect of a wide-band element having a low first cost, and being easy to build and highly reproducible.

According to the invention, this object is achieved by a planar-type directional coupler comprising a metallic conductive layer superposedly arranged on a dielectric backing, characterized in that said metallic conductive layer completely surrounds a central zone comprised of a plurality of mutually communicating central parallel grooves, between which at least four separate central conductive strips are defined to provide the directional coupling, said strips being alternately electrically connected to each other.

Preferably, the conductive metallic layer aforesaid is removed also in correspondence with four separate, substantially U-shaped, lateral grooves, in the interior of which four discrete lateral conductive strips are formed, which are the lines for connection to the external circuitry, metallic conductive wires being provided, which are so arranged as to connect every couple of said central conductive strips to two of said lateral conductive strips.

Stated another way, the planar directional coupler according to the invention provides, in this way, a single grounding plane, which, apparently, does away with the connection problems which are experienced with the devices of the prior art. In addition, the adoption of at least four central conductive strips alternately connected pairwise in lieu of the usual two paired strips of the prior art enables a high coupling factor two be obtained even with narrow spacing gaps: this fact renders the coupler more easy to be built and reproduced and miniaturization can be pushed farther.

The features of the invention will be better understood having reference, by way of example only, to the accompanying drawings, wherein: Figure 1 is a top plan view, on a much enlarged scale, of a planar directional coupler according to this invention, and Figure 2 is a detail view, on still more enlarged scale, in cross-section taken along the line ll-ll of Figure 1.

The planar directional coupler shown in the drawings comprises a dielectric backing layer, 1, on which a single metallic conductive layer 2 is superposedly arranged.

The metal is removed in a central zone 3 including a plurality of mutually communicating straight-linear parallel grooves 4, between which four discrete central conductive strips 5 are defined which effect the directional coupling. These conductive strips are electrically connected pairwise and alternately at their ends by means of bridging conductive wires 6.

The conductive metallic layer 2, moreover, is removed in correspondence with four discrete later ai substantially U-shaped grooves 7, in the interior of which four discrete lateral conductive strips 8 are defined, which are the lines for connecting the coupler to the external circuitry. The lateral conductive strips 8 are electrically connected to the central conductive strips 5 by conductive metallic bridging wires 9.

As outlined above, the adoption of a single grounding plane which consists of a residual metallized layer outside the central zone 3 and the lateral grooves 7, permits to offset one of the most stringent problems encountered in the conventional embodiments, in which there were as many as four discrete grounding planes, mutually connected by metallic wires.

In addition, the adoption of four (or more) central conductive strips connected alternately to each other permits that narrow spacings may be adopted: these, even for high couplings (typically, aboud 3 dB) on dielectrics such as Al2O3, can be easily made and easily reproduced with the usual thin-film circuit procedures. The fabrication of a 3 dB coupler with the conventional configurations would have imposed, conversely, a prohibitively narrow spacing between the two central strips, typically 5 microns (with a width of 250 microns for the single line and a spacing as wide as 1 mm between the grounding planes), that which cannot be produced with the conventional procedure and is producive of a high increase of the losses.

It should also be noted that it has been field tested that the relative band in which a coupler according to the invention exhibits a variation of 0.7do of the coupling is nearly equal to 65% - 75%, whereas for the same band, in a conventional coupler, it is 25%.

The directional coupler according to the invention has thus a much wider frequency band.

Claims

1. A planar-type directional coupler comprising a conductive metallic layer superposedly arranged on a dielectric backing, characterized in that said metallic conductive layer completely surrounds a central zone formed by a plurality of mutually communicating parallel central grooves, between which are defined at least four separate conductive central strips which effect the directional coupling, said strips being electrically alternately connected to each other.

2. Directional coupler according to Claim 1, characterized in that said conductive metallic layer is removed also in correspondence with four discrete lateral grooves substantially in the shape of a U, in the interior to which four lateral discrete conductive strips are defined which provide the lines for connection to the external circuitry, metallic conductive wires being provided so arranged as to connect each couple or said central conductive strips to two of said lateral conductive strips.