Arrangement for coupling waveguide modes between two waveguides via a semiconductor element

An arrangement for coupling waveguide modes between two waveguides via a semiconductor element. The two waveguides each have a short-circuiting end wall and a common side wall constituting a common partition wall between the waveguides so that the two waveguides extend parallel to, and overlap one another at least over a partial length where they are separated from one another by the common side wall. The common partition wall is provided with a coupling aperture and the semiconductor element is inserted into the coupling aperture between the two waveguides and is in ground contact with the common partition wall. The semiconductor element has two connectng arms, one connecting arm extending as a coupling probe into one of the waveguides and the other connecting arm extending as a coupling probe into the other waveguide.

BACKGROUND OF THE INVENTION 
The present invention relates to an arrangement for coupling waveguide 
modes between two waveguides via a semiconductor element, with the 
semiconductor element being inserted into a coupling aperture in a 
partition between the two waveguides and being in ground contact with this 
partition. In such an arrangement the semiconductor element has two 
connecting arms, one of which extends as a coupling probe into one 
waveguide and the other of which extends as a coupling probe into the 
other waveguide. 
Such an arrangement is disclosed in a publication by I. Angelov, A. Spasov, 
I. Stoev, L. Urshev, entitled "Investigation of Some Guiding Structures 
for Low-Noise FET Amplifiers", European Microwave Conference 1985, pages 
535-540. This publication describes a high frequency amplifier whose 
amplifier element is a field effect transistor (FET). The FET is coupled 
in the manner described above to an input waveguide and to an output 
waveguide, both being disposed one behind the other along a common axis. 
This known arrangement has a drawback in that its structural length is 
unusually large, particularly if a multistage amplifier is involved. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an arrangement of the 
above-mentioned type which has very little attenuation and has the 
shortest possible structural length. 
The above and other objects are accomplished in the context of an 
arrangement for coupling waveguide modes between two waveguides via a 
semiconductor element as first described above, wherein, according to the 
invention, the waveguides each have a short-circuiting end wall and a 
common side wall constituting the common partition wall between the 
waveguides so that the two waveguides extend parallel to, and overlap one 
another at least over a partial length where they are separated from one 
another by the common side wall. 
Advantageously, in the arrangement according to the invention, the 
connecting arms serving as coupling probes of the semiconductor element 
may be very short. It is possible, therefore, to permit very thin 
connecting arms to extend freely into the waveguides without having to 
support them by special means. 
The overlap of input and output waveguides in the coupling range according 
to the invention has the advantage that it results in a considerable 
reduction of the structural length of the device, particularly in 
multistage high frequency amplifiers, compared to comparable prior art 
arrangements. 
The invention will be described in greater detail below with reference to 
an embodiment that is illustrated in the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a longitudinal sectional view of a microwave circuit, e.g. an 
amplifier, oscillator, mixer or the like, which includes an input 
waveguide and an output waveguide. Input waveguide 1, which is short 
circuited at its end wall 5, and output waveguide 2, likewise 
short-circuited at its end wall 6, are parallel to one another over a 
length of about .lambda./8 to .lambda./2 (.lambda.=waveguide wavelength) 
and are separated from one another in a region of overlap by a common side 
wall 3 on the broadside of the waveguides and common to both waveguides in 
the overlap region. Input waveguide 1 is coupled with output waveguide 2 
by means of a coupling aperture 4 provided in common side wall 3. This 
coupling aperture is spaced at about .lambda./16 to .lambda./4 from the 
inner surface of short-circuiting end wall 5 of input waveguide 1 and by 
the same distance from the inner surface of short-circuiting end wall 6 of 
output waveguide 2. 
An active semiconductor element 7 (e.g. a diode or an FET) of the microwave 
circuit is inserted into coupling aperture 4 between the two waveguides 1 
and 2 and is in ground contact with common side wall 3. A first connecting 
arm 8 of semiconductor element 7 projects into input waveguide 1 and there 
couples into semiconductor element 7 the mode of the input signal. A 
second connecting arm 9 of semiconductor element 7 projects into output 
waveguide 2 and couples into it the modes of the signal which have been, 
for example, amplified or multiplied in frequency by the semiconductor 
element. Connecting arms 8 and 9, which serve as coupling probes for 
semiconductor element 7, have a length that is about 0.3 to 0.8 times the 
length of the narrow side of the waveguide (i.e. about 0.15 to 0.35 cm at 
an operating frequency of 20 GHz). Because this requires only very short 
coupling probes, very thin and not very stable connecting arms can project 
freely into waveguides 1 and 2, respectively, and need no separate 
support. 
Connecting arms 8 and 9 of semiconductor element 7 are supplied with a 
direct voltage through coaxial feed-through 10 and 11 in the walls of 
waveguides 1 and 2, respectively. As shown by the view into input 
waveguide 1 in FIG. 2, the direct voltage is fed to connecting arm 8 of 
semiconductor element 7 through a thin wire 12 which passes through the 
waveguide perpendicularly to the E field. This type of direct voltage 
supply assures that the waveguide field is interfered with as little as 
possible and that the attenuation during coupling is relatively low. 
Matching the coupling between the waveguides and the semiconductor element 
can be effected in a simple manner by means of tuning screws 13, 14 and 
15, 16, respectively, which project into waveguides 1 and 2 through the 
waveguide walls opposite coupling aperture 4 in the vicinity of coupling 
probes 8 and 9. 
The arrangement shown in FIGS. 3 and 4 is identical with the 
above-described arrangement of FIGS. 1 and 2 except for the mounting of 
the semiconductor element and the configuration of the coupling probes. 
Therefore, the same reference numerals can be found in FIGS. 3 and 4 as 
are used in FIGS. 1 and 2. In the embodiment shown in FIGS. 3 and 4, a 
semiconductor element 7, which is not accommodated in a package, is placed 
onto a dielectric substrate 17. At one side, substrate 17 is provided with 
two conductor paths 18 and 19 which each have a length of about 0.3 to 0.8 
times the length of the narrow side of the waveguide and extend in 
opposite directions. Two contact terminals of semiconductor element 7 are 
connected with these conductor paths by means of bonding wires. Substrate 
17 is provided with two further conductive areas 20a and 20b with which 
the semiconductor element is grounded. This dielectric substrate 17, 
equipped with semiconductor element 7, is installed in coupling aperture 4 
so that its conductive areas 20a and 20b are contacted with common side 
wall 3 and its conductor paths 18 and 19 project into waveguides 1 and 2 
as coupling probes. 
The present disclosure relates to the subject matter disclosed in German P 
No. 36 03 454.1 of Feb. 5, 1986, the entire specification of which is 
incorporated herein by reference. 
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.