US2897457A

US2897457A - Resonant directional coupler with square guide

Info

Publication number: US2897457A
Application number: US595460A
Authority: US
Inventors: Pierre G Marie
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-07-04
Filing date: 1956-07-02
Publication date: 1959-07-28
Anticipated expiration: 1976-07-28
Also published as: FR1130115A

Description

P. G. MARIE July 28, 1959 RESONANT DIRECTIONAL COUPLER WITH SQUARE GUIDE Filed July 2, 1956 INVENTOR PIERRE G. MARIE By W -vc, W04 -w4 United States Patent Office RESONANT DIRECTIONAL COUPLER WITH SQUARE GUIDE Pierre G. Mari, Paris, France Application July 2, 1956, Serial No. 595,460 Claims priority, application France July 4, 1955 2 Claims. (Cl. 333-) The present invention relates to resonant directional couplers comprising two rectangular guides which are connected together by a circular guide stub forming a cavity resonator coupled to the former guides by systerns of slots and, more particularly, to resonant directional couplers of this type in which one of the rectangular guides is square.

In the specifications of U.S. applications Ser. No. 416,869 and 593,886, respectively, filed March 17, 1954, and June 26, 1956, in the name of the present applicant, for resonant directional couplers, directional couplers are described which comprise two identical rectangular wave-guides and a circular cavity resonator which connects them together, such that a traveling wave, which progresses in one of the rectangular guides in the TB mode and arrives in the region of junction between the said rectangular guide and the cavity resonator, has its electrical energy split into two parts. The first part (that which has trequencies outside the frequency band of the cavity resonator) continues to be propagated in the rectangular guide to beyond the junction with the cavity resonator. The second part of this energy (that which has frequencies within the frequency band of the cavity resonator) is radiated in the circular resonator through the intermediary of a system of special coupling slots in the form of a circularly polarized wave, which is constituted by two waves of the TB mode which are polarized perpendicularly and in quadrature. This circularly polarized wave, in turn, radiates in the second rectangular guide a wave of the TE mode, the

direction of propagation of which depends upon the direction of propagation of the incident wave in the first rectangular guide.

The system of coupling slots may be of two types. In the couplers of application Ser. No. 416,869, the slot systems comprise two crossed concentric slots, the centre of which is situated on the axis of the circular guide but is eccentric in relation to the axis of each rectangular guide. The result of this is that the structure of the coupler is asymmetric, the axis of the circular guide not meeting the axes of the rectangular guides. In the couplers of. application Ser. No. 593,886, the slot systems comprise two separate slots, one of which is longitudinal and the other is transverse in relation to the rectangular guide in which they have been made, and which are situated on one side and the other of the axis of the latter guide. The distances of the slots to the axis should have well defined values which are explained in the specification of the aforesaid application. In this case, the structure of the coupler is symmetrical in the sense that the axis of the circular guide meets the axes of the rectangular guides.

In both cases, the slots, which are supposed to be seen from the interior of one of the rectangular guides, have an asymmetry in relation to the axis of the guide either by both of them being on the same side or by being on one side and the other but with difierent directions of orientation and with unequal distances to the I 2,897,457 Patented July 28, 1959 axis. It follows from this that the small side of the rectangular guides should have a dimension which is less than (where X is the wave length in unbounded space of the wave which passes through the coupler) in order that, at the coupling position, the wave of the TB mode, which is propagated in the rectangular guide, should not give rise, at least partially, to a wave of the TE mode which has, in the rectangular guide, a direction of polarization which is perpendicular to the direction of polarization of the wave of the 'I'E mode.

Now, in certain applications, the couplers should have one of their rectangular guides square in order to be able to convey two TE waves which have their directions of polarization perpendicular. This is the case, for example, where a plurality of couplers of the aforesaid kind have a common square guide and form a multi-channel filter, all the channels or some of them being duplicated and used simultaneously for transmission and for reception. The electromagnetic energy relating to the transmitting channel arrives through a rectangular guide and is coupled, through the intermediary of a first directional coupler, with the square guide which leads it to an aerial with a certain direction of polarization, in accordance with the TB mode in said square guide. The electromagnetic energy relating to the receiving channel (assumed to have the same bandwith than the transmitting channel) arrives from the aerial through the square guide with a direction of polarization perpendicular to the preceding, in accordance with the TE mode in said square guide, and it is coupled with a rectangular guide of a second directional coupler. It appears that, in order to obviate any mixture of the energies of the channels, it is necessary that, at the junction positions between the square guide and the circular cavity resonators or guides of the directional couplers, no wave of the TE mode should be created by the wave of the TE mode and vice versa.

Furthermore, in the couplers of the type described disclosed in the prior art, the coupling means are adapted to pick up from the rectangular guide two phase quadrature field components and to apply them to the circular cavity resonator in appropriate space relationship. The first field component to be picked up is either the transverse electric field component or the transverse magnetic field component which are cophasal. The second field component is the longitudinal magnetic field component, in phase quadrature with the two first. Now it is known that said last component has a phase which vary in the longitudinal direction of the rectangular guide and it results therefrom that the true phase quadrature relationship only occurs in 'a transverse plane. As the longitudinal magnetic field component is coupled through a longitudinal slot, the field fringing through the slot is not cophasal throughout said slot, which results in poor coupling versus frequency response.

The object of the invention is to construct a slot-andprobe coupling system between a rectangular guide (which may be square) and a circular guide, which is symmetrical in relation to the axis of the rectangular guide and is such that a wave of the TB mode in the rectangular guide gives rise to a circularly polarized wave in the circular guide.

Another object of the invention is to provide a slot and probe coupling system between a rectangular or square 3 by 90 and for applying them in parallel space relation ship to the circular guide.

Another object of the invention is to construct a multichannel filter comprising a plurality of directional couplers having a common square guide which is traversed by the energies of two waves having perpendicular directions of polarization in this square guide and the same band or hands overlapping with each other, relating to two communication channels, which ,enables the said channels to be separated.

The directional coupler of the invention comprises, essentially, a rectangular guide, a circular guide coupled to the former guide by a two-slot system, a square guide and means, for coupling the square guide and the circular guide, composed of a slot which is diametral with respect to the circular guide, transverse with respect to the square guide and symmetrical with respect to the longitudinal axis ofthe latter, a probe which is axial with respect to g ofthe magnetic field a a first m, wave in circular guide the circular guide, fixed to the latter by a radial conductive fixing rod and passes into the square guide at the center of the slot, and,'a tuning plug inside the circular guide and opposite the'end of the radial fixing rod, and a tuning plug inside the square guide and opposite the end of the probe.

The branching filter which may be made with couplers according to the invention comprises a plurality of directional couplers of the above mentioned type, the square guides of which are connected together and aligned with one anotherand the circular guides of which are connected either to one side of the square guide or to another side of the square guide which is perpendicular to the former side, according as to whether the said couplers are intended to extract from the total wave, which is propagated in the square guide, partial waves having a certain direction of polarization or the perpendicular direction of polarization.

The invention will now be described in detail with reference to the accompanying drawings, of which Fig. 1 represents a directional coupler according to the invention, and I Fig. 2 represents a multi-channel filter constituted by couplers of the type shown in Fig. 1.

Referring to Fig. 1, 1 is a square guide in which two traveling waves having directions of polarization indicated by the arrows 3 and 4 are propagated simultaneously. 9 is a circular cavity resonator or guide stub which is coupled with the guide 1 by a coupling system according to the invention and coupled with a rectangular guide 2 by a slot system comprising the slots 22 and 23 of the type described in the specification of US. application Ser. No. 593,886. Naturally, the system of coupling slots between the guides 8 and 9 could be of any'prior-art type, of the type of US. application 416,869 for example.

The coupling between the guide 1 and the circular guide 9 is effected by a single rectangular slot 5 which is terminated by two rounded portions and the longitudinal axis of which is in the cross-section plane of the square guide 1.

At the center of this slot and perpendicularly to this plane there is arranged a cylindrical rod 6 which constitutes a probe, the axis of which coincides with that of the circular guide 9. One of the ends of'the rod 6 is opposite a tuning plug 7 placed inside the square guide 1. The other end of the probe 6 is kept fixed to the wall of the circular guide 9 by a fixing conductive rod 8.

The axis of the rod 8 is perpendicular to the axis of the guide 9 and, consequently, to the axis of the probe 6. Situated in the extension of the axis of the rod 8 is a cylindrical rod 10 provided with a screw-thread. This rod is screwed into the guide 9 and its end, which is situated outside the guide, is provided with a milled head 11 which enables the said rod to be turned in order to make it pass, to a greater or smaller extent, into the circular guide 9.

The slot 5 couples the transverse magnetic field parallel to arrow 4 in square guide 1 to the transverse component 9, said component'being parallel to the slot. The probe 6 and the rod 8 couple the transverse electric field parallel to arrow 3 in square guide 1 to the u'ansverse electric field of a second TE wave in circular guide 9, said last transverse electric field being parallel to the rod 8 and consequently to the slot 5. There are thus produced in the guide 9 two electromagnetic fields having rectangular patterns but which would be cophasal if no precautions were taken as the transverse magnetic field and the electric field in guide 1 from which they derive are cophasal.

In order to put these two fields into quadrature relationship, the screw 10 is turned so as to sharply detune the cavity as regards the second wave having its electric field parallel to the rod 8. Thus the phase of the vibration of said wave may be phase shifted by from the driving electric field phase in guide 1 (see for example "Principles of Microwave Circuits," by C. G. Montgomery et al., McGraw-Hill Book Company Inc., New York, 1948, page 226). The screw 10 is of little effect upon the first wave which has an electric field perpendicular to the screw and besides because it is located near the center of the cylindrical resonator and, as the resonator vibrates in the TB mode, the transverse magnetic field of the wave is almost zero at this point. The two fields having rectangular patterns and being apart in phase give rise to a TE mode circularly-polarized standing wave. It might be shown by a similar argument that such a standing wave produces in the rectangular 1 a traveling wave which progresses towards one end or the other according to the sense of rotation of said standing wave. Screw 7 serves to cancel the admittance due to the post 6, partially crossing the guide 1.

Referring now to Fig. 2, 12 is a square general guide, which is connected, at one end, to a pyramidal horn 13 and is terminated, at the other end, by a dissipative load 14. The pyramidal born 13 serves, at the same time, as a transmission aerial for a first communication channel with a direction of polarization parallel to arrow 3, and as a reception aerial for a second communication channel with a direction of polarization parallel to arrow 4. The dissipative load 14 is constituted by two small rectangular absorbent plates. On the side 15 of the square guide 12 is connected a directional coupler 17, the rectangular guide of which is terminated, at one end, by a dissipative load 18 and is connected, by its other end 19, to a transmitter (not shown) which produces the electromagnetic energy relating to the first channel.

Connected on the side 16 of the square guide 12 is a directional coupler 20, the rectangular guide of which is terminated, at one end, on a dissipative load 21 and is connected, by its other end 24, to a receiver (not shown) which receives the electromagnetic energy relating to the second channel.

Naturally, the number of directional couplers, which form the branching filter of Fig. 2, may be more than two.

What I claim is:

1. A directional coupler comprising a wave guide of square cross-section, a circular cavity resonator, a rectangular guide coupled to said circular cavity resonator by a two-slot system, coupling a circularly polarized TE mode standing wave in the circular cavity resonator to a TE mode traveling wave in the rectangular guide, and a coupling system between said square guide and said circular cavity resonator comprising a slot transverse with respect to the axis of the square guide and diametrical with respect to the circular cavity resonator coupling the trans verse magnetic field of a TE mode wave in the square probe, radial with respect to the circular cavity resonator and parallel to said slot, said probe and rod coupling the transverse electric field of the TB mode wave in the square guide and the transverse electric field of a second standing wave of the TB mode in said resonator and a tuning plug inside the circular cavity resonator and opposite the radial metallic rod, whereby said plug and rod detune the cavity resonator for the second standing wave, allowing said wave to be in quadrature relationship with the first standing wave.

2. A directional coupler comprising a general square guide conveying a TE mode wave and a TE mode wave, a first circular "cavity resonator coupled to a first face of said square guide by a first coupling system comprising a slot perpendicular to the general square guide axisand diametrical with respect to the circular cavity resonator, a probe coaxial with said resonator and entering through the slot inside the square guide, a metallic rod supporting the probe, radial with respect to the first cavity resonator and parallel to the slot of said first coupling system, and a tuning plug inside said first resonator and opposite the rod, afirst rectangular guide coupled to said first circular cavity resonator by a two-slot coupling system, a second circular cavity resonator coupled to a second face of the square guide perpendicular with the first face by a second coupling system identical with the first coupling system and a second rectangular. guide coupled to said second circular cavity resonator by a secondtwo-slot coupling system, whereby the energy of the TB mode wave is collected at one end of the first rectangular guide and the energy of the TB, mode wave is collected at one end of the second rectangular guide.

, References Cited in the file of this patent UNITED STATES PATENTS