Microwave slot line ring hybrid having arms which are HF coupled to the slot line ring

A microwave ring hybrid on a dielectric carrier substrate is provided with connecting arms designed in microstrip technique. The ring of the hybrid comprises a slit line made in a conductive layer on the side of the carrier substrate opposite that on which the strip conductors of the microstrip lines for the connecting arms are disposed.

BACKGROUND OF THE INVENTION 
The present invention relates to a microwave ring hybrid whose connecting 
arms are designed in the microstrip technique and are provided on one side 
of a dielectric substrate. 
A ring hybrid of the above type is known, for example, from Siemens 
Zeitschrift 48 [Siemens Magazine] (1974), Addendum issue entitled 
"Nachrichten-Ubertragungstechnik" [communications transmission art], page 
162, FIG. 8. This ring hybrid is constructed completely in the microstrip 
technique on one side of a ceramic substrate. The connecting arms are 
galvanically, i.e. conductively, coupled so that, for example if the ring 
hybrid is used to connect two amplifier modules in parallel, additional 
networks to galvanically decouple the connecting arms, such as, for 
example, chip capacitors or fingers couplers must additionally be 
provided. These additional components may interfere with the symmetry and 
matching of the ring hybrids and may thus cause reflections and losses. 
SUMMARY OF THE INVENTION 
It is therefore the object of the present invention to design a microwave 
ring hybrid of the type whose connecting arms are designed in the 
microwave technique and are provided on one side of a dielectric substrate 
in such a manner that all connecting arms are galvanically separated from 
one another without the use of additional components. 
The above object is achieved according to the present invention by a 
microwave ring hybrid which comprises: a dielectric carrier substrate; a 
conductive layer disposed on one major surface of the substrate; a ring 
for the hybrid comprised of a annular closed slot line formed by a slit or 
slot in the conductive layer; and a plurality of connecting arms for the 
hybrid with each of the connecting arms being a microstrip line including 
a conductor disposed on the opposite major surface of the carrier 
substrate such that the slot line is coupled with each of the microstrip 
lines in a high frequency manner i.e., via the E-field component. 
According to various features of the invention, the high frequency coupled 
components of the connecting arms, in the form of microstrip lines, and 
the ring, designed as a slot line, intersect perpendicularly; the 
microstrip lines of at least two connecting arms extend into the region 
enclosed by the ring by a .lambda./4 section; and the microstrip line of 
one connecting arm has one line end extending into the region enclosed by 
the ring by a further .lambda./4 section or connected with the conductive 
layer on the opposite surface of the substrate, and its other line end 
projecting outwardly from the ring by a .lambda./4 section. 
Couplings between slot lines and microstrip lines are known, for example 
from Federal Republic of Germany Offenlegungsschrift (laid open 
application) DE-OS 2,607,634. However, that publication does not disclose 
a suggestion of how to realize a microwave ring hybrid with galvanic 
decoupling of all connecting arms without any additional decoupling 
measures. 
The present invention provides significant advantages in that, in spite of 
the galvanic decoupling of all connecting arms, all inputs and outputs of 
the ring hybrid are disposed on one side of the carrier substrate. Thus, 
the modules to be connected with the ring hybrid can all be disposed on 
one side of the carrier substrate. The slot line, which due to its 
unfavorable radiation behavior must not be coupled with radiation 
sensitive components, is disposed on the side of the carrier substrate 
facing away from these modules and thus provides hardly any interference. 
A further advantage is that the side of the carrier substrate on which the 
slot line is disposed is provided with a closed conductive layer except 
for the "interference location-slot line " and thus shields against 
radiation from the components connected with the ring hybrid in the 
direction of the carrier substrate. Adjacent microwave components can thus 
be brought into the vicinity of this conductive layer without being 
subjected to significant interference radiation. The packing density of 
microwave circuits can thus be increased considerably.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, there is shown a ring hybrid having four 
connecting arms which are designed in the microstrip technique. The four 
connecting arms include respective strip conductors 1, 2, 3 or 4 which are 
disposed on the top surface of a dielectric carrier substrate 5 whose 
bottom or other major surface is provided with a conductive layer 7 (FIG. 
2). Ring 6 of the ring hybrid comprises a closed annular slot line formed 
in the conductive layer 7 on the underside of the carrier substrate 5. To 
provide the desired coupling between the coupling arms and the ring, the 
conductors 1, 2, 3 and 4 crossover or intersect the ring 6 in the coupling 
region, preferably in a direction perpendicular to the circumference of 
the ring 6 as shown. The conductors 1, 2, 3 and 4 of the respective 
connecting arms are distributed over the circumference of ring 6, which 
has a total circumference of 3.lambda./2, (where .lambda. is the 
wavelength of the center frequency of the hybrid), in the manner of a 
conventional 180.degree. ring hybrid. That is, the spacing along the 
circumference of ring 6 between the the conductors 1 and 3 of two of the 
connecting arms is 3.lambda./4, and the conductors 2 and 4 of the other 
connecting arms each are spaced by .lambda./4 from the adjacent connecting 
arms on the circumference of ring 6. One end of the microstrip lines of 
the connecting arms including the conductors 1, 2 and 3 extends by 
.lambda./4 into the region enclosed by the ring 6, and thus provides for 
suitable transformation between the slot line and the microstrip lines in 
the coupling region. The line lengths of .lambda./4, 3 .lambda./4, 
3.lambda./2 may each by multiplied by a factor n(n=1, 2, 3, . . . ). The 
design configuration of the remaining connecting arm, i.e., the arm 
including the strip conductor 4, which is preferably equipped with an 
absorber, or resistance layer 12 may be effected in various ways. One end 
of the conductor 4, and thus of the resulting microstrip line, can extend 
into the region enclosed by the ringy be a .lambda./4 line section on one 
side of the ring crossover while the other end of conductor 4 projects 
outwardly by such a .lambda./4 line section from the line crossover. 
Alternatively, as shown in FIG. 1, one end of the conductor 4 projects 
outwardly from the region enclosed by the ring 6 by a .lambda./4 section 
while the other end is connected to the absorber or resistance layer 12 
and then by means of a rivet 9 with the conductive layer 7 (see FIG. 2) on 
the underside of the carrier substrate 5. To compensate for series 
inductance in the absorber, the end portion of conductor 4 extending into 
the region enclosed by the ring 6 is equipped with a parallel capacitance 
in the form of a laterally extending strip conductor portion 10. 
FIG. 2, which is a sectional view of the ring hybrid of FIG. 1, shows the 
slot line 6 formed in the conductive layer 7. The width b (see FIG. 1) of 
the annular slit 6 with respect to the width a of the conductors 1-4 of 
the microstrip line has, as is known for 180.degree. ring hybrids, the 
ratio of a:b=2:1. As further shown in FIG. 2, tuning elements 8 may be 
provided adjacent the slot line 6 in the region where the respective 
conductors 1-4 of the crossover of the slot line 6. 
Tuning elements 8 may be screws which, according to FIG. 4, could be fixed 
in a housing 11. Housing 11 is in electrical contact with conductive layer 
7 and shows grooves 13 close to the annular slot 6, so that the annular 
slot 6 is only influenced by the screws 8. With the tuning elements 8, a 
better rf coupling of the high impedance slot and the strip conductors can 
be achieved. 
A ring hybrid according to FIG. 1 designed for a center frequency of 6 GHz 
attained a relative bandwidth of 15 %. The characteristic impedance of the 
microstrip lines is preferably selected to be 50 ohm. This results in a 
characteristic impedance of 71 ohm for the slot line 6. 
FIGS. 1 and 2, which are not drawn to scale, show a 180.degree. ring hybrid 
with the following specifications: 
The ceramic substrate 5 is formed of a composition of Al.sub.2 O.sub.3 with 
a relative capacitivity of (relative dielectric constant) of 
.epsilon..sub.r =9.8. The thickness of this substrate is 0.625 mm (25 
mil). Conductors 1-4 are of gold with a thickness of 5 .mu.m and a width 
of 0.53 mm. The .lambda./3 sections of conductors 1-3 within the ring have 
a length of 4.9 mm. The part of conductor 4 projecting out of the ring 
region has a length of .lambda./4 (4.9 mm). Within the ring region, 
conductor 4 is for convenient reasons 1 mm long and has a width of 0.53 
mm. The laterally extending strip conductor portion 10 is about 1.1 mm 
long and has a width of 0.2 mm. Between the end of conductor 4 and rivet 
9, FIG. 1 shows resistance layer 12 of tantalum nitride Ta.sub.3 N.sub.5, 
which is about 0.6 mm long and has a width of 0.53 mm. 
Conductive layer 7 is a gold layer with a thickness of 5 .mu.m. Slot line 6 
has a width of around 60 .mu.m. The diameter d of slot line 6 is given by 
the formula: 
##EQU1## 
wherein .lambda. is 24 mm. 
In connection with the above described embodiment, only a 180.degree. ring 
hybrid was shown. FIG. 3 shows an embodiment for 90.degree. ring hybrid. 
The conductors 1', 2', 3' and 4' of the connecting arms are distributed 
over the circumference of the ring 6', which is designed in the slot line 
technique, at equal distances of .lambda./4. The conductors of the 
connecting arms again cross over ring 6' perpendicularly. The conductors 
1', 2', 3' and 4' of the respective connection arms project by a 
.lambda./4 section into the region enclosed by the ring 6'. The lengths of 
conductors 1', 2', 3' and 4' on either side of the crossover depend on the 
application. FIG. 5 shows an application of a 90.degree. ring hybrid as a 
phaseshifter. An input signal is fed to conductor 2'. Conductors 3'and 
4'are of identical length and are coupled to identical impedances jX in 
series with varactors D. Conductor 3' will provide the phase shifted 
output signal. 
The characteristic impedance Z.sub.O of the microstrip lines including 
conductors 1', 2', 3' and 4' is assumed to be for example, 50 ohm. Widths 
of these conductors are again 0.53 mm. Ring 6', again formed in slot line 
technique on the underside of carrier substrate 5', is provided with slot 
line portions of various widths. The width b1 is around 80 .mu.m and the 
width b2 around 60 .mu.m. Between the crossovers of the connecting arms 
including strip conductors 1' and 2' as well as between the crossovers of 
the connecting arms including strip conductors 3' and 4', the width b1 of 
the slot line 6' is selected to be such that it has a characteristic 
impedance of, for example, 35 ohm. Between the connecting arms including 
the conductors 2' and 4' and between the connecting arms including the 
conductors 1' and 3', the width b2 of the slot line 6' is selected so as 
to provide a characteristic impedance of Z.sub.O, i.e. for example, 50 
ohm. In the region of the crossovers, tuning elements, such a elements 8 
of FIG. 2, may be applied as before. 
FIG. 6 shows a modified 180.degree. ring hybrid. Conductor 4 projects 
beyond the resistance layer 12 by a .lambda./4 section into the ring 
region, whereas the length of conductor 4 on the other side of the 
crossover is, as shown in FIG. 1, also .lambda./4. Resistance layer 12 and 
the laterally extending strip conductor portion 10 (capacitive stub) are 
the same as in FIG. 1. 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.