US 3886500 A
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United States Patent 11 1 Baril et al.
[451 May 27, 1975 1 FLAT HYBRID-T STRUCTURE FOR TRANSMITTING WAVE ENERGY  Inventors: Michel Baril; Hoang Vu San, both of Paris, France  Assignee: Thomson-CSF, Paris, France  Filed: Dec. 5, 1973  App]. No.: 422,103
 Foreign Application Priority Data Dec. 12, 1972 France 7244176  US. Cl 333/11; 333/10 [5|] Int. Cl. H0lp 5/12  Field of Search 333/84 R, 84 M, 10, 11; 325/446  References Cited UNITED STATES PATENTS 3,678,395 7/1972 Hunton et al. 333/84 M 3,735,267 5/1973 Napoli 325/446 OTHER PUBLICATIONS Ronde, F. C., A New Class of Microstrip Directional [OPLA/VAR 4m Couplers," Digest of Tech. Papers G-MTT lnternation Microwave Symposium, 1970, Newport Beach, Cal. U.S.A., 5-21-1970, pp. l84-I89.
Primary Examiner-Alfred E. Smith Assistant Examiner-Wm. H. Punter Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [57} ABSTRACT A flat hybrid-T structure comprises an array of transmission lines formed on a ceramic substrate. One line exhibits a symmetrical field structure and another line exhibits an asymmetrical field structure, the propagation axes of both lines being aligned. A third line is divided into two identical branches and is perpendicular to the other two. Depending on which line is excited by a potential difference, the junction produced at the intersection of the lines behave like a shunt or series T-junction depending on the type of the third line.
5 Claims, 8 Drawing Figures Pmimanmv ms 3.886; 500
SHEET PATENTEDMAYZT ms 3.886; 500
SHEET 3 5107' LINE METAll/ZED FACE 6 (MAM/c SUBSTRATE (OPZA/VAR L l/VE FLAT HYBRID-T STRUCTURE FOR TRANSMITTING WAVE ENERGY BACKGROUND OF THE INVENTION.
The present invention relates to hybrid-T structures for the transmission of electromagnetic waves, more particularly to structures known as magic T's.
A magic-T structure belongs to a larger class of structures known hybrid T's which take the form of an octopole assembled from a series T and a parallel T, both made from rectangular waveguides.
FIG. 1 shows such an assembly, which thus has four arms marked 1, 2, 3 and 4. The properties of such an assembly are well known and will be summarized in what follows. If arms 2, 3 and 4, for example, are closed off by non-reflecting terminations and an incident wave is fed into arm I, the symmetry of the system is such that no energy will be received from arm 4, while equal electrical fields will appear at arms 2 and 3. Similarly, if excitation takes place through arm 4, no energy will be received from arm 1 while opposing electrical fields will appear at arms 2 and 3. These properties result from the fact that there is no coupling between arms I and 4. If matching members are inserted into these arms so that their coefficients of reflection are zero, there is obtained what is termed a magic T, in which there is complete electromagnetic symmetry between the two groups of arms 2, 3 and l, 4.
Standard magic Ts are easily assembled problems to which a simple solution has not been found in joining from series and shunt waveguide junctions.
This is no longer true if it is desired to produce hybrid-T structures from transmission lines of coaxial type, or the three-plate type, or the micro-strip or ribbon-line type. In this case shunt junctions can be produced easily and without upsetting the propagation modes. When lines such as to be incorporated in a hybrid-T, it is not possible to produce a series junction directly without upsetting the propagation modes to a considerable extent; generally it is necessary to use, for example, quarter-wave sections for this purpose. These sections enable conversions to be made from shunt to series but they have, however, the effect of increasing the bulk of the devices and of reducing the width of their operating band,
SUMMARY OF THE INVENTION An object of the present invention is to produce a magic T having a flat structure which avoids the drawbacks mentioned above.
In accordance with the invention, a hybrid octopole structure is assembled flat from a series T-structure and a shunt T structure, structure on a ceramic substrate which has a high dielectric constant and one of whose faces is metallized, this face being provided with two throughgoing, intersecting gaps forming a first, a second, a third and a fourth channel meeting at the point of intersection and constituting transmission lines for the propagation of wave energy, one of the lines having input means for connecting it to a source of such wave energy. The first channel is a coplanar line and the fourth channel is a slot line, these two channels being thus mutually decoupled or conjugate for the transmitted wave energy and being part of one of the gaps while the second and third channels. forming part of the other gap. are of the same structure as either the first or the fourth channel. i.e. coplanar or slot lines. In cither case, they form a shunt junction with the first and a series junction with the fourth channel.
BRIEF DESCRIPTION OF THE DRAWING Other objects, features and advantages of the invention will be pointed out in the following description given with reference to the accompanying drawings in which we have illustrated by way of example, several different embodiments. In the Drawing:
FIG. I relates to the prior art as already described;
FIG. 2 is a perspective view of a ribbon line;
FIG. 3 is a perspective view of a coplanar line;
FIG. 4 is a perspective view of a slot line;
FIG. 5 is a perspective view of a magic T comprising a combination of slot lines and a ribbon line;
FIG. 6 is a perspective view ofa magic T using a combination of a coplanar line and slot lines;
FIG. 7 is a perspective view of a magic T according to our invention incorporating a combination of ribbon lines and a slot line and FIG. 8 is a perspective view of a magic T incorporating a combination of coplanar lines and a slot line, and:
DESCRIPTION OF PREFERRED EMBODIMENTS.
As stated above although it has proved easy to produce shunt-T junctions using coaxial lines or known types of line having a flat structure such as three-plate lines or ribbon lines (microstrip), this has not been so in the case of series junctions, where coupling has to be accomplished by certain indirect methods, such as, for example, the use of quarter-wave sections arranged in a ring.
In accordance with the invention, the simultaneous use of lines of the coplanar and slot type enables hybrid-T junctions, and more particularly magic TS. to be produced as flat structures.
In general three main types of lines can be deposited onto a flat substrate by metallizing:
a. The ribbon line or microstrip, shown in FIG. 2, consists of a thin, flat, conductive ribbon 5 deposited on a layer of dielectric 6 which rests on a flat conductor 7 known as the ground plane. The distribution of the electrical field ?in such a line is symmetrical with respect to the plane of symmetry P of the line, this plane passing through the axis D of the ribbon.
b. FIG. 3 shows a so-called coplanar line. The ceramic substrate 6, which has a high dielectric constant, is made conductive by metallizing its upper face 9, for example, and a gap 10 is made in this conductive surface in which a conductive ribbon II is so positioned as to be symmetrical with respect to the central axis D of the unit. The coplanar line thus takes the form of a ceramic substrate coated with two ground-plane layers 12 and 13 which are separated by a gap 10 and bracket the central conductive ribbon II whose width is less than that of the gap. The electrical field of a wave propagated in the structure is-symmetrically distributed with respect to the plane of symmetry P of the line, as demonstrated by the arrows.
c. FIG. 4 shows a slot line, which is formed by making a slot 14 in the metallized face 15 of a ceramic substrate 6 of a high dielectric constant. This slot line thus comprises two conductor strips planes l7, l8 separated by a slot l4.
With this type of line, the electrical field of excitation of the slot is asymmetrical with respect to the plane of symmetry P of the line. We have found that, by combining the two last-mentioned types of lines as a fourchannel array on a substrate we can produce magic Ts realizing the aforestated object of our invention.
FIG. shows a series-T structure formed by two slot lines at right angles to one another on a metallized face of a substrate 6. The other face of this substrate carries a ribbon 5 to enable the excitation of two channels 2 and 3 from a channel 1 in conjugate relationship with a channel 4, these channels being analogous to l, 2, 3 and 4 of FIG. 1.
The metallized upper surface of the substrate 6 constituting a ground-plane layer, forms two slot lines 14 and 140 which are perpendicular to one another and divide that layer into 3 parts, l6, l7 and 18. On the lower face 19 of the substrate is imprinted a ribbon 5 (drawn in broken lines) which forms with the groundplane layer 16 18 a ribbon line or microstrip of the type shown in FIG. 2. It will be noted that the end of the ribbon extends beyond the axis of the slot 140 by t\/4. lt will now be assumed that the slot line is excited via channel 1 by applying a potential difference across the edges of the slot 14. An electrical field ?is set up in the slot 14 acting as input means as shown by arrows fl, f2. This causes phase-opposed electrical fields el and 2 to be set up in channels 2 and 3 of slot 140 forming the series branches of a planar T structure, which may be a magic T assuming that there is continuity of the currents i1, i2 at the level of the junction with channel 1.
Under the above conditions, there is no coupling between the slot line 14 and the ribbon line 5 and thus between channels 1 and 4.
On the other hand, by exciting channel 4, that is to say the ribbon line, a current 14 is produced in the ribbon which excites identical potential differences in the slot 140 perpendicular to it and thus in the t wo channels 2 and 3, so that the electrical fields e4 in these arms have the same direction. The slotted line 140 is thus excited with an inphase wave by the ribbon line. The conditions set up are the same as those existing in the shunt junction of a T. Channels 1 and 4 are completely decoupled as in any magic T.
The M4 section is provided simply to ensure that arm 4 is fully coupled to arms 2 and 3.
FIG. 5 thus truly represents a magic T, produced as a flat structure, which has two mutually perpendicular slot lines and one ribbon line.
FIG. 6 shows a T structure according to our invention incorporating a coplanar line and slot lines.
This structure comprises again a ceramic substrate 6, having a high dielectric constant, whose upper surface is metallized. in this surface is formed a coplanar line, of the same type as that of FIG. 3, which comprises a conductive ribbon ll. centered on the axis of a wider gap 10. and mutually perpendicular slot lines 20 and 21. The four. channelsof this T structure are channels l, 2,3 and 4 terminating at the point of intersection of two throughgoingigaps in the. metallized face of the substrate.
.Channel 1, i.e. the coplanar line, is. for example, ex-
cited by a wave haying a symmetrical mode of propagatrical fields e21 and 022 in the two arms 2 and 3 are in phase. This channel I has the same electrical characteristics as the shunt channel of a T structure. The ribbon ll of the coplanar line may overlie a nonillustrated ribbon line on the lower non-metallized face of the ceramic substrate 6 so that there is total coupling between channel 1 and channels 2 and 3. This is only an example of matching and other means may be envisaged such as, for example, using inductances and capacitances to produce a tuned circuit. The absence of such a matching circuit would cause a relatively high degree of reflection of the mode propagated in channel I and would reduce accordingly the coupling to channels 2 and 3, but such a structure would nevertheless embody the principles of our invention.
lf channel 4 is excited by setting up a potential difference at its terminals, the electrical field e2 sets up 3 ual but phase-opposed electrical fields, i.e. WI and e20 as a result of the electrical continuity of currents [20 and at the junction with channels 2 and 3. The conditions set up here are the same those in the se ries channel of a T structure. Channels 1 and 4 thus appear completely decoupled.
The T structure in FIG. 6 truly represents a magic T wherein channel I is the shunt channel and channel 4 the series channel.
Another magic T, shown in FIG. 7, is a combination of a shunt T, produced from two mutually perpendicular ribbon lines with a slot.
The three arms of the T are formed by two mutually perpendicular ribbon lines 24 and 240; whilst the slot line 23 is defined by the metallized other face of the ceramic block 6.
If the ribbon line 24 is excited by an electrical field e 24 the continuity of the currents i240 and 124i, at the junction with line 240 causes the electrical fields e240 and F274? in the two branches of line 240 to be in phase. The T thus produced from lines 24 and 240 behaves like a shunt junction.
If slot line 23 is excited by a potential difference at its terminals which s :ts up an electrical field 23 the currents mand 1230 which travel along the edge of the slot line generatelp line 240 hase-opposed fields at the junction, i.e. e250 and (T3? Channels 2. 3 and 4 thus form a series junction. It will be noted that the ribbon line extends beyond the axis of line 240 for a length M4 so as to ensure good matching and full coupling.
A further embodiment of a magic T according to the invention is shown in FlG. 8, this embodiment combining on the ceramic substrate 6 a shunt T formed from two coplanar lines and a slot line.
The two coplanar lines 25 and 250 as well as the slot line 26 are formed on the same metallized face of the ceramic substrate 6 by integral conductive ribbons. Again the arms of the complete structure are represented by channels 1, 2, 3 and 4 terminating at the point of intersection of two throughgoing gaps.
lf channel 1 is excited by applying a potential difference to its terminals. the distribution of the electrical field produced in line 25 is that shown by arrows j3.f4 in HO. 8. The fields j30 and f4) generated in the two branches of the coplanar line 250 are thus in phase with one another. The current :25 passing through the conductive ribbon of the coplanar line 25 divides into the two branches of line 250 and the direction of the field in these branches is shown by arrows f30 and I40 on one side and f3], and f4] on the other. Since these fields are in phase in the two line branches. the junction formed by the two coplanar lines is a shunt '11 The slot line 26 is formed in the same plane as the coplanar lines, which in this case is the metallized upper surface of the ceramic substrate 6. This slot line is, for example, excited by field At the junction with line 250, this field generates fieldsfS and f6 which are in phase opposition to the two branches of line 250. The current 1'26 passing through the conductive ribbon of line 250 excites fields which are oriented in the directions shown by arrowsfSO and f60 in the part of the gap of in line 250 remote from slot 26. The junction formed by lines 250 and 26 thus behaves like a series T.
It will be noted that the width of the slot line 26 must be relatively small in relation to that of the coplanar line, in order to avoid disturbances at the opening made in line 250 where line 26 joins it.
A number of flat structures forming magic Ts have thus been described which are obtained by joining together coplanar lines, slot lines and ribbon lines Through the disclosed embodiments may be modified without departing from the scope of the present ir1- vention it should be noted that it is not possible to obtain a T-structure by joining together a coplanar line and a ribbon line, since the modes which are propagated in this structure are symmetrical. without using complicated coupling means which our invention aims to eliminate.
What is claimed is:
l. A fiat hybrid-T structure comprising a dielectric substrate having a metallized face provided with two throughgoing, intersecting gaps forming a first, a sec- 0nd, at third and a fourth channel meeting at the point of intersection and constituting transmission lines for the propagation of wave energy, said first and fourth channels being mutually decoupled for said wave energy and forming part of one of said gaps, said first channel being a coplanar line, said fourth channel being a slot line decoupled from said coplanar line for said wave energy, said second and third channels being part of the other of said gaps and being of the same structure as one of the channels of said one of said gaps to form with said first and fourth channels a shunt junction and a series junction. respectively and input means for connecting a source of wave energy to one of said lines.
2. A hybrid-T structure as defined in claim 1 wherein said channels form a symmetrical orthogonal array 3. A hybrid-T structure as defined in claim 1 wherein said one of said gaps is wider in the region of said first channel than in the region of said fourth channel and is provided in said first channel with a narrower conductive ribbon terminating at said point of intersection.
4. A hybrid-T structure as defined in claim 3 wherein said other of said gaps has a width greater than that of said one of said gaps in the region of said fourth channel and is provided with a throughgoing narrower conductive ribbon integral with the ribbon of said first channel.
5. A hybrid-T structure as defined in claim 3 wherein said other of said gaps has a width less than that of said one of said gaps in the region of said fourth channel.