Rotary microwave joint device

The invention relates to a rotary microwave joint device comprising a main circular waveguide constituted by two portions (10, 11) situated as extensions to each other and rotatable relative to one another about their axis of symmetry, each of said two portions (10, 11) being provided with at least one access which is orthogonal thereto, and mechanical means enabling a circularly polarized wave to be obtained in the main waveguide. The invention is applicable to space telecommunications.

The invention relates to a rotary microwave joint device. In orbiting 
satellites, antennas for telecommunications via relay satellites must have 
very good pointing capabilities, typically: 
EQU 0.ltoreq..sigma..ltoreq.120.degree. (elevation) 
EQU 0.ltoreq..phi..ltoreq.360.degree. (azimuth). 
BACKGROUND OF THE INVENTION 
There are two types of installation for the electronic transmission and 
reception equipment: 
in a first type the entire microwave transponder is situated behind the 
antenna; and 
in a second type intermediate frequencies are used to make it possible for 
only the power stages for microwave transmission, the low noise receivers, 
and the reception frequency converters to be installed immediately behind 
the antenna. 
Temperature control of both types of installation is very difficult, and 
draws heavily on the satellite's power consumption budget. 
In order to solve this problem, the invention makes it possible to 
integrate the electronic equipment for transmission and for reception of 
the platform of the satellite, by using a new rotary microwave joint 
device. 
In general, rotary joint devices make use of the circularly symmetrical 
properties of coaxial or cylindrical modes of propagation. As a result, 
they require transitions to be provided between access guides (for 
inlets/outlets) which operate with one type of propagation (rectangular 
guides, cylindrical guides) and the rotary joint itself. 
Matching conditions restrict the utilization bandwidth to a ratio of not 
more than about 1.5. In, contrast, a coupler in accordance with the 
invention does not have such frequency limitations. 
SUMMARY OF THE INVENTION 
The present invention provides a rotary microwave joint device comprising a 
main circular waveguide constituted by two portions each situated in the 
extension of the other and rotatable relative to one another about their 
axis of symmetry, each of these two portions being provided with two 
mutually orthogonal accesses which are also orthogonal to the walls of the 
waveguide, and an inlet hybrid coupler having its two outlets coupled to 
the two accesses of the first portion via two waveguides, the device 
further including an outlet hybrid coupler having its two inlets coupled 
to the two accesses of the second portion of the main waveguide via two 
waveguides. 
Advantageously, the two portions of the main waveguide have their outer 
ends as cutoff waveguides to constitute short circuit planes, the accesses 
being respectively situated in pairs in planes which are at predetermined 
distances from said short circuit planes. 
In a variant embodiment, the invention provides a device in which lowpass 
filters are interposed between the hybrid couplers and the accesses to the 
two portions of the main waveguide, and level with said accesses, and 
wherein the two cutoff guides are disposed at opposite ends of the main 
waveguide, with each of said cutoff waveguides being provided with two 
accesses which are orthogonal thereto and which are orthogonal to each 
other, an inlet hybrid coupler having two outlets coupled to the accesses 
of the first one of said cutoff waveguides and an outlet hybrid coupler 
having its inlets coupled to the accesses of the second of said cutoff 
waveguides, the first and second cutoff waveguides coupled to the main 
waveguide being closed at their free ends. 
In one particular embodiment, the invention provides a junction device 
provided, on either side of the junction, with: 
a corrugated portion; 
a corrugated/smooth transition; and 
a smooth portion.

MORE DETAILED DESCRIPTION 
The device in accordance with the invention comprises a main circular 
waveguide constituted by two portions 10 and 11 each lying in the 
extension of the other and rotatable relative to the other about their 
axis of symmetry .DELTA.. 
Two accesses 12 and 13 to the first portion 10 of the main waveguide are 
orthogonal thereto and orthogonal to each other. They are coupled via two 
waveguides 16 and 17 to the outlets 14 and 15 of a first hybrid coupler 18 
having a coupling coefficient of 3 dB. The inlets to the coupler 18 are 
connected to two waveguides 19 and 20. 
These two accesses 12 and 13 are situated at a distance d1 from a short 
circuit plane 21 provided by a cutoff waveguide. 
Two accesses 22 and 23 to the second portion 11 of the main waveguide are 
orthogonal thereto and orthogonal to each other. They are connected via 
two waveguides 27 and 28 to the inlets 24 and 25 of a second hybrid 
coupler 26 having a coupling coefficient of 3 dB. The outlets from the 
coupler 26 are connected to two waveguides 29 and 30. 
These two accesses 22 and 23 are situated at a distance d2 from a short 
circuit plane 31 provided by a cutoff waveguide. 
The short circuit plane 21 is situated at a distance d1 from the two 
accesses 12 and 13 so that all of the energy propagates along the main 
waveguide from the first portion 10 towards the second portion 11. In 
contrast, the short circuit 31 is situated at a distance d2 from the two 
slots 22 and 23 so that all of the energy from the slots 12 and 13 
propagates along the waveguides 27 and 28. 
At the junction plane P, electrical continuity is provided in conventional 
manner by mechanical contact between the facing ends of the portions 10 
and 11 of the main conductor. 
The waveguides providing the junction between the hybrid couplers (18, 26) 
and the main waveguides (10, 11) are rectangular waveguides. 
The inlet 19 of the two inlets to the hybrid coupler 18 receives a signal 
which is transmitted to both of the waveguides 16 and 17 and which serves 
to transmit a circularly polarized wave into the main waveguide via the 
two accesses 12 and 13 providing coupling therewith. 
In a variant embodiment of the invention shown in FIG. 2, use is made of 
the two cutoff waveguides 35 and 36 disposed at opposite ends of the main 
waveguide (10, 11) as shown in FIG. 1. 
In similar manner to the device shown in FIG. 1, two accesses 37 and 38 to 
the waveguide 35 are orthogonal thereto and orthogonal to each other. 
A hybrid coupler 39 has its inlets connected to two waveguides 40 and 41 
and has two outlets connected to two waveguides 42 and 43 which are 
coupled to said two accesses 37 and 38. 
Similarly, a hybrid coupler 45 having its outlets connected to two 
waveguides 46 and 47 has its two inlets connected to two waveguides 48 and 
49 which are coupled to two accesses 50 and 51 to the waveguide 36, said 
two accesses being orthogonal to the waveguide 36 and orthogonal to each 
other. 
The two cutoff waveguides 35 and 36 have their free ends 58 and 59 closed 
and situated at a distance from the access planes (37, 38, and 50, 51) 
such that all of the energy is transmitted firstly from the coupler 39 via 
the accesses 37 and 38 towards the junction and then from the junction 
towards the coupler 45 via the accesses 50 and 51. 
This circularly polarized wave of the main waveguide (10, 11) is excited 
without any obstacle in said main waveguide. As a result, if four filters 
(54, 55, and 56, 57) of the lowpass type are placed to put short circuit 
planes in the access planes (12, 13 and 22, 23), the device may be used 
for another frequency band capable of propagating in a waveguide diameter 
which is smaller than the diameter in the imaginary short circuit planes 
21 and 31 which are obtained by the cutoff waveguides. For use at higher 
frequencies, the diameters of the waveguides 35 and 36 are therefore less 
than the diameter of the cutoff waveguide. 
If the lowpass filters 54 and 55 have short circuit planes in the access 
planes 12 and 13, it becomes possible to operate using a second frequency 
band. 
The operation of a device in accordance with the invention and with the 
variant thereof is described above solely with respect to using one inlet 
to each of the inlet hybrid couplers (18, 39) and the corresponding single 
outlet from each of the outlet hybrid couplers (26, 45). 
However, the second inlet to each hybrid coupler may be used to convey a 
second signal at the same frequency as the signal conveyed by its first 
inlet. 
Thus, using the coupler device shown in FIG. 1, two same-frequency channels 
may be conveyed, and using the coupler device shown in FIGS. 2 and 3, two 
first frequency channels and two second frequency channels may be 
conveyed. 
The electrical contact between the two portions 10 and 11 of the central 
conductor may be provided by means of a coupling device shown in FIG. 4. 
This coupling device comprises three portions on opposite sides of the 
coupling plane P: 
a corrugated portion (60, 61); 
a corrugated/smooth transition (62, 63); and 
a smooth portion (64, 65). 
The electrical connection in the plane P takes place at the bottom of a 
corrugation. 
This type of connection provides good electrical continuity without 
requiring very good mechanical contact. 
Naturally, the present invention has only been described and shown by way 
of preferred examples and its component parts could be replaced by other 
equivalent parts without going beyond the scope of the invention. Thus, it 
is possible to offset the pairs of accesses which are coupled to the same 
waveguide by .lambda.g/2 where .lambda.g is the length of the wave guided 
in said waveguide, thereby obtaining better decoupling performance between 
said two accesses. 
It is also possible, in the coupler device shown in FIG. 1, to obtain a 
circularly polarized wave while using only one of the accesses 12 or 13 
and placing a polarizing obstacle in the first portion 10 of the main 
waveguide. 
Similarly, said circularly polarized wave may be extracted by using only 
one of the accesses 22 or 23 after placing a polarizing device in the 
second portion 11 of the main waveguide. 
When operating with polarizers, it is immediately obvious to extend the 
possibilities to two frequency accesses by using both of the accesses 12 
and 13 and both of the accesses 22 and 23 simultaneously. 
It is possible to generalize the transmission of twice two channels at two 
different frequencies provided by the device shown in FIG. 2 to n times 
two channels at n different frequencies, by providing n connections of the 
same type as those (10, 35 and 11, 36) shown in FIG. 2 at the free ends of 
the central waveguide.