US3177449A

US3177449A - Non-reciprocal ferrite switch with alternate conductive and resistive plates

Info

Publication number: US3177449A
Application number: US147945A
Authority: US
Inventors: Cho Akira; Kuroda Takaji
Original assignee: Nippon Electric Co Ltd
Current assignee: NEC Corp
Priority date: 1960-11-15
Filing date: 1961-10-26
Publication date: 1965-04-06
Anticipated expiration: 1982-04-06
Also published as: DE1200902B; GB942854A

Description

l5 r1l 6, 1965 AKIRA cHo ETAL 3,

NON-RECIPROCAL FERRITE SWITCH WITH ALTERNATE CONDUCTIVE AND RESISTIVE PLATES Filed Oct. 26. 1961 4 Sheets-Sheet 1 9- 28 POMR/ZAT/M 3/ 2/9/01? ART) 52.21%4P/17/N6 29 ,a f 27 swam/we Ell-WENT 24 25 POZAR/ZAT/ON 22 SEPAPA TING car 5 .2 (PAZ/ PART) ,9 3

(PR/0P APT) H 51). (PR/OP ART} 26 Hg. 50. 45 (PP/0P ART) (PM A APT) 26 BNWWM Agent April 6, 1965 AKIRA CHO ETAL NON-RECIPROCAL FERRITE SWITCH WITH ALTERNATE CONDUCTIVE AND RESISTIVE PLATES Filed 001.. 26. 1961 4 Sheets-Sheet 2 I nvenlor:

April 6, 1965 AKIRA CHO ETAL 3,177,449

NON-RECIPROCAL FERRITE SWITCH WITH ALTERNATE CONDUCTIVE AND RESISTIVE PLATES 4 Sheets-Sheet 3 Filed Oct. 26. 1961 F/g M /05 02 /02 I10 I07 I06 1/! 105 Inventor; A. CHO T. KURODA Agent Apnl 6, 1965 AKIRA CHO ETAL 3,177,449

NON-RECIPROCAL FERRITE SWITCH WITH ALTERNATE CONDUCTIVE AND RESISTIVE PLATES Filed Oct. 26. 1961 4 Sheets-Sheet 4 Fig. /7.

I nven lor; A.CHOT. KURODA Agent United States Patent 3,177,449 NON-RECIPROCAL FERRITE SWITCH WITH ALTERNATE CONDUCTIVE AND RESISTIVE PLATES Akira Cho and Takaji Kuroda, Tokyo, Japan, assignors to Nippon Electric Company Limited, Tokyo, Japan, a corporation of Japan Filed Oct. 26, 1961, Ser. No. 147,945 Claims priority, application Japan, Nov. 15, B69, 35/ 45,707 Claims. (Cl. 333-11) This invention relates to a microwave waveguide device and a microwave switching device employing a plurality of these microwave waveguide devices, and more particularly to a microwave waveguide device which can cause an electromagnetic wave that enters into the waveguide along the axial line thereof in either sense to pass therethrough without appreciable attenuation; and which under a predetermined condition can be in a matched state with respect to an electromagnetic wave which enters into the waveguide in one sense along the axial line thereof and in a short-circuited state with respect to another electro magnetic wave that enters thereinto in the other sense. The invention intends to utilize this type of device in a novel microwave switching device so as to transmit only waves that are incident from particular one or plural input terminals to an output terminal.

Microwaves have enjoyed an increasing popularity as a means for communication; now finding application in such diverse fields as multi-channel telephony, television relay, data transmission teletype, etc. Where practical it has been customary to include in the overall system both an operational and a standby transmitter. The output sides of the transmitters are connected to an antenna via a switching device; both transmitters being operated at all times. If the operational transmitter fails, the output of the standby is promptly switched over to the antenna so as to insure continuity of service.

Such a switching device must be capable of extremely rapid operation since any interval results in interrupted service. Although the intelligence may not be significantly impaired in speech transmission even if the interruption lasts as long as one second, an unintelligible communication may result in teletype or code transmission from this long a break in service especially where security gear is utilized in synchronization. Further in the case of numeric transmission particularly, the omission of only one numeral may result in a sequence loss.

Such a switching device must also have a high decoupling ratio. The decoupling ratio of a switching device represents the extent to which it can suppress the output of the spare transmitter when both the working and the spare transmitters are in operation, and it is intended that only the output power of the working transmitter be supplied to the antenna through the switching device. If the decoupling ratio is poor, a large amount of the output power of the spare transmitter will leak into the antenna distorting communication. This distortion becomes serious as the multiplicity of the channels increases.

The switching device must moreover be of a constant resistance type, or of the type wherein the impedance remains unchanged no matter which transmitter is feeding the antenna. In other words, the impedance of the switching device must be matched .to the characteristic impedance of either transmitter whether or not that transmitter is being utilized at the moment. If the matching is not perfect, the impedance as seen from the output terminals of either transmitter will vary according to whether or not that particular transmitter is feeding the antenna, with the result that the modulation characteristics of the transmitters will vary. This will make it diffi cult to adjust the standby transmitter. Where a klystron is used as the transmitting tube the modulation characteristics deteriorate excessively with the result that adjustment of the transmitter in standby becomes impossible.

In addition, it is preferable that such a switching device be small in size and simple in construction.

Of the various switching devices heretofore proposed, the most common of the constant resistance type, is that which comprises as a switching element the device described in Bell Telephone Patents Nos. 2,748,353 and 2,887,664 wherein by means of a ferrite rod located in a magnetic field a Faraday rotation is induced in the electromagnetic wave. Such a switching device requires, as will later be described in greater detail, two orthogonal polarization separating circuits with the result that the decoupling ratio depends not only upon that of the switching element but also upon each polarization separating circuit. Inasmuch as it is generally difficult to obtain a high decoupling ratio between two orthogonal polarizations, the decoupling ratio of the polarizatin separating circuit is usually less than that of the switching element. Therefore, the decoupling of a conventional constant resistance type switching device has been poor.

An object of this invention is to provide a novel microwave waveguide device which can cause an electromagnetic wave that enters thereinto, along the axial line of the waveguide in either sense, to pass therethrough without appreciable attenuation in one condition; and which in a second condition is in a matched state with respect to an entering electromagnetic wave in one sense along the axial line of the waveguide and in a short-circuited state with respect to another entering electromagnetic wave in the other sense.

Another object of this invention is to provide a microwave switching device which is of a constant resistance type, works rapidly, has the highest possible decoupling ratio, and yet is small in size and simple in construction.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates schematically a conventional microwave switching device;

FIG. 2 shows the input polarization separating circuit viewed in the axial direction;

FIGS. 3a, 3b, and 3c show the switching element section of the waveguide, viewed in the axial direction, with various degrees of field rotation;

FIGS. 4a and 4b show the output polarization separating circuit viewed in the axial direction with various degrees of field rotation;

FIGS. 5, 6 and 7 show an axial section, cross section, and broken perspective views, respectively of an embodiment of the invention;

FIG. 8 shows the electric field direction in the waveguide;

FIG. 9 shows the waveguide device of the invention symbolically;

FIG. 10 shows the electric field in a circular waveguide;

FIG. 11 illustrates in perspective an insertion component with four pairs of plates;

FIG. 12 is a perspective view of an embodiment of a microwave switching device according to the invention;

FIG. 13 illustrates the device of FIG. 12 symbolically;

FIGS. 14 and 15 are top and side section views respectively of a portion of the device of FIG. 12;

FIG. 16 is a perspective view of a modified embodiment of FIG. 12 using circular waveguide, which nevertheless may still be shown symbolically by FIG. 13; and

FIGS. 17 and 18 illustrate symbolically two other examples of switching devices according to the invention.

Before entering upon a detailed description of the invention a conventional constant resistance microwave switching device, FIGS. 1-4, will be described in order to lay the groundwork for, and clarify the invention.

The switching device of FIG. 1 is so composed that it may transmit the output of a working and a spare transmitter (not shown) connected to

input terminals

21 and 22, respectively, through

input waveguides

23 and 24 respectively to an input polarization separating circuit 25. In the middle of a circular waveguide 26, at one end of which the polarization separating circuit 25 is formed, there is provided the conventional switching element 27 previously mentioned. At the other end of the circular waveguide 26, where an output polarization separating circuit 28 is formed, there are connected two

output waveguides

29 and 30. The waveguide 29 has an output terminal 31 connected to an antenna (not shown) while the waveguide is terminated in a non-reflective load (dummy load) at 32. The input polarization separating circuit 25 is, as shown in FIG. 2, formed by attaching to the circular waveguide 26 the

input side waveguides

23 and 24 so that the axial lines thereof may be perpendicular to each other and to the axial line of the circular waveguide itself. If the directions of the electric fields of the electromagnetic waves in the

input waveguides

23 and 24 are as shown by

arrows

33 and 34, respectively, two electromagnetic waves travel in the circular waveguide 26 along the axial line thereof, which are excited by the first-mentioned electromagnetic waves, the electric fields of which are shown by

arrows

35 and 36, respectively.

If a magnetic field of predetermined intensity is impressed upon the switching element 27 in the direction of the axial line of the circular waveguide 26, the planes of polarization and hence the directions of the electric fields of the electromagnetic waves travelling in the circular waveguide 26 can be rotated in the desired sense by an amount of 90, so that the directions of the electric fields of the two electromagnetic waves may be as shown in FIG. 3a by

arrows

37 and 38. If the output polarizar tion separating circuit 28 is formed, as shown in FIG. 4a, by attaching to the circular waveguide 26 the

output waveguides

29 and 30 so that they may be parallel to the

input side waveguides

23 and 24, respectively, one of the electromagnetic waves in the circular waveguide 26, the direction of whose electric field is shown by an arrow 38 and is perpendicular to the axial line of the waveguide 29 which is connected to the antenna, will excite the waveguide 29, while the other, the direction of whose electric field is shown by arrow 37 and is perpendicular to the axial line of the waveguide 30 of the non-reflection end, will excite the waveguide 30. Therefore, the electromagnetic wave sent from the input terminal 21 is absorbed by the dummy load 32, and only the electromagnetic wave sent from the input terminal 22 is transmitted through the output terminal 31 to the antenna. If the magnetic field is not applied to the switching element 27, only the electromagnetic wave sent from the input terminal 21 is transmitted through the output terminal 31 to the antenna, while the electromagnetic wave sent from the input terminal 22 is absorbed by the dummy load 32. Thus the switching device of FIG. 1 can selectively transmit to the antenna either one of the electromagnetic waves applied to the

input terminals

21 and 22, by applying or not to the switching element 27 a magnetic field in the direction of the axial line of the circular waveguide 26. In order to supply the switching element 27 with such a magnetic field, it will be understood that an electric current of the desired sense and desired intensity is caused to ilow in a coil (not shown) wound about the circular waveguide 26 in the vicinity of the element.

Inasmuch as the sense of the Faraday rotation, of the plane of polarization of the electromagnetic wave, caused by a ferrite, is reversed by the reversal of the sense of the magnetic field, switching can be made by the reversal of the polarity of the electric current in the coil instead of making and breaking the coil current. More particularly the directions of the electric fields in the circular waveguide 26, of the electromagnetic waves which have passed the switching element 27, can be rotated (if the coil current is in the proper sense and of the required intensity) from the directions shown in FIG. 2 (by the arrows 35 and 36) by 45 as shown in FIG. 3b by

arrows

39 and 40, respectively. And thus, if the output polarization separating circuit 28 is formed as shown in FIG. 4b, by attaching to the circular waveguide 26 the

output waveguides

29 and 30 so that the axial lines of these waveguides are perpendicular to the

directions

39 and 40 respectively and to the axial line of the circular waveguide 26, only one of the two electromagnetic Waves in the circular waveguide 26 (the direction of the electric field of which is shown by the arrow 39) is transmitted through the waveguide 29 to the antenna. The other, moving in an electric field direction as shown by the arrow 40, that supplied from the input terminal 22, is absorbed in the waveguide 30. If the sense of the electric current in the coil around the switching element 27 is reversed, the two electromagnetic waves whose electric fields have the directions shown in FIG. 2 by the

arrows

35 and 36, after having passed through the switching element 27, will undergo electric field rotations of as shown in FIG. 30 by

arrows

41 and 42. Here the reverse is true and now only that wave supplied from the input terminal 22 is transmitted through the waveguide 29 to the antenna.

In such a conventional switching device which may switch the rotations of the planes of polarization between 0 and or between +45 and -45, the

polarization separating circuits

25 and 28 are indispensable. As has been previously described the decoupling ratio of a polarization separating circuit is poor. This is because the electromagnetic wave in the input side waveguide 23, for example, has in the neighborhood of the circular waveguide 26 not only the component whose direction is shown by the arrow 33 but also a component produced thereat in the direction perpendicular to the former direction, the ratio of these components giving the decoupling ratio. Although the decoupling ratio can be made considerably higher if the polarization separating circuit can be made completely symmetrical or if the method of excitation is carefully chosen, problems in manufacturing arise which are clilficult if not impossible to solve. In the higher frequency range, it is especially difficult to make the decoupling ratio large since the dimensions of the waveguide bccome correspondingly smaller.

Turning now to FIGS. 5 to 11 inclusive, an embodiment of the microwave waveguide device according to the invention will now be described.

As shown in FIGS. 5-7 rectangular waveguide 51 has contained therein a cylindrical ferrite rod 52, both ends of which are tapered to a sharp-point. The waveguide 51 has broad and narrow pairs of walls which are also known as the a and b walls, respectively. Contiguous to the rod on either side are two substantially

rectangular metal plates

56 and 57, the dimensions of which are such that the rod lays in a coaxial position with respect to the axial line 53 of the waveguide 51. The metal plates fit snugly between the outer cylindrical surface of the ferrite rod and the inner surfaces of the waveguide 51 that include the narrow walls. The two substantially

rectangular resistance plates

58 and 59 are similarly positioned at the other end of the rod, and may consist of any dielectric enameled with resistive film. In addition, the

metal plates

56 and 57 and the

resistance plates

58 and 59 are all in a plane which contains the axial line 53 and which is perpendicular to the b walls of the waveguide 51.

Edges

68 and 69 of the

metal plates

56 and 57, which are perpendicular to the edges contiguous the rod and waveguide are adjacent the end 70 of the cylindrical portion of the ferrite rod 52.

Edges

73 and 74 of the

resistance plates

58 and 59 which are perpendicular to the edges contiguous the rod and waveguide are similarly positioned with respect to the other end 75.

In order to support the

piece parts

52, 56, 57, 58, and 59, hereinafter referred to as the insertion component, in the manner explained above it has been found advantageous to introduce the insertion component (into the waveguide) between a pair of supporting

pieces

81 and 82 which are made of foamed polyethylene or the like. These supporting pieces are mirror images of each other and have such shape and dimensions that when put in a juxtaposed relation, they fill the air gap in the section of the waveguide containing the insertion component. The lengths of the supporting

pieces

81 and 82 in the direction of the axial line 53 of the waveguide 51 may be chosen so as only to meet the requirements for support. Although foamed polyethylene is preferable, because the dielectric constant thereof is nearly equal to that of the air and therefore it does not disturb the electrical characteristics of the waveguide 51, the supporting

pieces

81 and 82 may be made of other equivalent materials. Also, because of the proximity of the dielectric constant of polyethylene to that of air it is not requisite that the supporting pieces form-fit the insertion component and in fact they may be eliminated and replaced by any suitable means for supporting the insertion component.

Coil 83 is wound around the waveguide so as to pro duce a uniform magnetic field in the direction of the axial line 53 at least at the portion of the insertion component 80. Waveguide 51 is further provided with two

flanges

84 and 85 at both ends thereof to facilitate connections with other waveguides (not shown).

The electromagnetic wave which travels along the axial line of such a rectangular waveguide 51 is generally of H mode, and the direction of the electric field is, as shown in FIG. 8 by arrows 86, parallel to the abovementioned 1: walls and perpendicular to both the metal and resistance plates.

Such a waveguide device is shown diagrammatically by the symbol in FIG. 9, wherein an arrow 87 is in the direction from the flange 85 to the flange 84, or from the

resistance plates

58 and 59 to the

metal plates

56 and 57 of FIGS. -7.

When a magnetic field in the direction of the axial line of the waveguide device is produced by causing an electric current flow through the coil 83 thereof, the impedance of the device as seen in a first sense from the resistance plates to the metal plates (from the flange 85 to the flange 84) the sense shown by the arrow 87 of FIG. 9, is matched to the characteristic impedance of the waveguide and accordingly the device does not reflect the electromagnetic wave travelling in this sense, whatever direction the current may be flowing in coil 83. The impedance of the device as seen in a second sense opposite to the first, is a short-circuit and thus theoretically produces full reflection. When no electric current is caused to flow through the coil 83 and there is no magnetic field in the direction of the axial line 53, the waveguide device shows substantially the same characteristics as the waveguide itself, without the insertion component, with the result that an electromagnetic wave can pass through the waveguide device in either sense without substantial variation.

The theoretical reasoning behind the invention is presumably as follows. When no electric current flows through the coil 83, an electromagnetic wave having an electric field perpendicular to the

metal plates

56 and 57 and the

resistance plates

58 and 59 is not electrically affected by these plates and passes therethrough without any appreciable attenuation and reflection, but with only a slight loss caused by the ferrite rod 52. However, when an electric current flows through the coil 83, the direction of the electric field of the electromagnetic Wave which passes through the waveguide device is rotated in a sense determined by the sense of the electric current in the coil 83 on account of the Faraday rotation induced by the magnetic field at the ferrite rod 52. Which ever the sense of the rotation may be, the electric field takes on a component parallel to the surfaces of the plates and the electromagnetic wave is attenuated at the resistance plates and is reflected at the metal plates. Thus an electromagnetic wave which travels in the waveguide device in the first sense or from the resistance plates to the metal plates is absorbed at the resistance plates, while that which travels in the second sense is reflected by the metal plates. Due to the Faraday rotation of the electric field, the electromagnetic wave will take on an excess amount of this field component having a direction perpendicular to the b walls and the cutoff frequency of the waveguide 51 will approach the frequency of the electromagnetic wave. Therefore, the rotation is suppressed on one hand, and is forcibly caused on account of the Faraday rotation on the other hand, with the result that the electric field of the electromagnetic wave is in a forcibly rotated state. Thus it is possible to cause remarkable attenuation in an electromagnetic wave travelling in the waveguide in the first sense, if the shape, diameter, and length of the ferrite rod 52, the dimensions of the

metal plates

56 and 57, the dimensions and the resistances of the

resistance plates

58 and 59, and the relative positions of such piece parts are empirically varied for best results.

In an experimental example, the frequency of the elec tromagnetic wave which is caused to pass through the waveguide device was 7,000 me; the waveguide 51 was 15.8 mm. x 34.8 mm. in cross-section; the ferrite rod 52 was 7.5 mm. in diameter and about 60 mm. long; the number of turns of the coil 83 was 2,500 turns per 70 mm.; the exciting current was 450 ma; the

metal plates

55 and 57 were about 23 mm. x 13 mm., respectively; and the

resistance plates

58 and 59 were about 9.5 mm. x 13 mm. and had ohms/cm. respectively. The obtained attenuation was 40 db, and varied within the range 3550 db in accordance with variations in the ambient temperature and the exciting current.

In the embodiment previously described, a rectangular waveguide was used and the plates extended from the surface of the ferrite rod 52 to the inner surfaces of the guide. The rectangular waveguide may, however, be replaced by a circular waveguide or other waveguide which has any shape of cross-section; the

metal plates

56 and 57 and the

resistance plates

58 and 59 do not have to extend from the surface of the ferrite rod 52 to the inner surfaces of the rectangular waveguide or the inner surfaces of the waveguide of other form but may be placed, as the case may be, only between the surface of the ferrite rod and one of the inner surfaces of the waveguide. Also, the positions of the metal and the resistance plates relative to the ends of the ferrite rod 52 do not necessarily have to be as mentioned above but it is sufficient that they are positioned nearer to one end and the other end of the waveguide, respectively. The ferrite rod 52 may also deviate a little from the axial line 53 since this is not critical, but not too much since the attenuation will be affected. If the insertion component is so supported that the metal and the resistance plates are perpendicular to the b walls,

the waveguide device is as previously mentioned, in a earns r9 matched state with respect to an electromagnetic wave travelling therethrough in the first sense and in a shortcircuited state with respect to another electromagnetic wave travelling in the second sense when there is a magnetic field. When no electric current flows in the coil 83, an electromagnetic wave travelling in either direction passes through without substantial attenuation. If the insertion component is supported in a rectangular, circular, or other waveguide at a certain radial position, the waveguide device will give similar results depending upon the positioning of components with respect to the field. In this regard, it is to be noted that if the circular waveguide 88 shown in FIG. 10 is excited so as to propagate only the dominant mode H the direction of the electric field of the electromagnetic wave being determined by the mode of the excitation (e.g. shown by an arrow 89) the best result is obtainable when the circular waveguide is so excited that the direction shown by the arrow 89 is perpendicular to the plane of the metal and resistance plates of the insertion component. In contrast to the rectangular waveguide in which the Faraday rotation of the plane of polarization of the electromagnetic wave is a very particular phenomenon, the plane of polarization in a microwave waveguide device of the invention wherein a circular M waveguide is used is freely rotated in accordance with the intensity of the magnetic field.

The insertion component may, as shown in FIG. 11, be modified so that the ferrite rod 52 is included between two pairs of metal plates 90, 91, 92, 93 (which are similar to the

metal plates

56 and 57 shown in FIGS. 57) and two pairs of resistance plates 94, 95, 96 and 97 (which are similar to the

resistance plates

58 and 59 of FIGS. 5-7) similarly to the manner explained in connection with FIGS. 5 to 7 except that here the metal and resistance plates contact one another. If this modified insertion component is similarly supported in a rectangular waveguide and an electric current of required intensity is caused to flow in the coil 83, then the electromagnetic wave which travels through the waveguide device in the first sense undergoes considerable attenuation at the first set of resistance plates 96 and 97 and is reflected at the succeeding metal plates 92 and 93 to again undergo attenuation at the first resistance plates. In the same manner that part of the electromagnetic wave which leaks through is affected by the next set of resistance plates and metal plates eventually being totally absorbed, with the result that the impedance of the waveguide device seen in the first sense or from the flange 85 is in a matched state. In a like manner the waveguide device is in a short-circuited state with respect to the electromagnetic wave which enters in the second sense. It is to be noted. however, that the mere increasing of the number of pairs of metal and resistance plates does not necessarily result in greater attenuation and more perfect short-circuiting, but that such a waveguide device shows the best effects when the dimensions of these plates, the intensity of the electric current in the coil 83 and so forth are empirically varied for best results. It is not imperative that the plates be touching and gaps may be included between the metal and the resistance plates in the axial direction of the ferrite rod 52.

In the embodiment and modifications described above. the ferrite rod 52 was cylindrical and sharp-pointed at both ends. The ferrite rod, may however, instead of being cylindrical have the cross-section of any polygon. Electrically, both ends are preferably sharp-pointed, but this also is not a necessary condition though it gives better results. The greater length and the diameter of the ferrite rod 52 are, the less the strength of the magnetic field to be applied in direction of the axial line 53 by the coil 83 need be; but this variation is accompanied by an increase in the loss caused by the insertion com ponent. The diameter and the length of the ferrite rod are decided, therefore, by a compromise between the loss caused by the insertion component and the magnetic field to be applied.

The frequency range of the electromagnetic wave controllable with the microwave waveguide device of the invention depends on the maximum frequency of the electromagnetic wave at which the ferrite rod does not give appreciable loss and can effect the Faraday rotation. In any event the waveguide device can sufficiently achieve its purpose within the band of 1,000 Inc-5,000 mc., which is used in the present-day telecommunication.

Turning now to FIGS. 12 through 18 inclusive, a microwave switching device according to the invention will be described. It is to be noted here that, unless otherwise stated, the metal and resistance plates, of the microwave waveguide device, in the embodiments to be described are perpendicular to the electric field of the electromagnetic wave in the absence of a magnetic field.

The microwave switching device of the invention, which is perspectively shown in FIG. 12 and schematically shown in FIG. 13 by using the symbol of FIG. 9, is composed of a branch waveguide 101, which is preferably an E-branch waveguide, and the microwave waveguide devices 50 and 51' (similar to FIGS. 5-7) of the invention which are connected to the branch waveguide in such a manner that the metal plates of the insertion component of the waveguide devices are disposed inwardly; the flanges 84 and 84' are connected to

flanges

102 and 103 of the E-branch waveguide 101. The flanges and 85 which are positioned at both ends of the switching device of FIG. 12 serve as input terminals, while a flange 105 which is positioned at the end of an E-arm 104 serves as the output terminal.

As shown in FIGS. 14 and 15, which are a top view and a longitudinal sectional view of the portion including the E-branch waveguide 101, a metal plate 106 is placed in the E-arm 104 perpendicularly to the axial line thereof so as to leave a window 107 adjacent the metal plate 106, in order to provide the E-arm with susceptance. Another metal plate 113 having a member 112 is experimentally inserted into arm 110 in such a manner that the metal plate 113 may short-circuit the arm. The position of the metal plate 113 is adjustable in the direction of the axial line of the main arms 110-111 by means of the handle 112, so that the impedance of the main arms 110-111 as seen from the arm 111 to the arm 110 may be adjusted to the characteristic impedance of the main arms. The reason for this will be obvious later.

As has been described, the impedance of the microwave waveguide device as seen from its flange 84 which is the one nearer to the

metal plates

56 and 57 is in the short-circuited state when the coil 83 is excited. It follows therefore that it the length of the arm 110 is so chosen such that the position at which the microwave waveguide device is short-circuited will coincide with the position of the metal plate 113 at which the metal plate would match the impedance of the E-branch waveguide 101 and if the waveguide device 50 and the E-branch waveguide 101 are connected with each other, the impedance as seen from the arm 111 will be in a matched state when the coil 83 is excited. Assuming the absence of device 50 for the moment this leads to the result that, inasmuch as the microwave device 50 serves as a nonreflective termination with respect to an electromagnetic wave that has entered into the device from the flange 103 and has passed through the branch point and is entering the arm 110, the electromagnetic wave from the flange 103 is completely sent to the flange 105 of the E-arm 104. Inasmuch as the microwave waveguide device 50 will also serve as a dummy load directly for another electromagnetic wave that has entered into the device from the flange 85, the electromagnetic Wave initiating from there undergoes large attenuation and does not reach the flange 105. Although the object of the invention is partly attainable even if the position at which the microwave waveguide device 50 is short-circuited is not made to coincide with 9 the above-mentioned impedance-matching position of the metal plate 113, the best results will not be obtained since the impedance of the device seen from the flange 103 is not matched with the characteristic impedance of the device in the excited state of the coil 83 and so some of the electromagnetic wave is reflected.

Now with another microwave waveguide device 50 similarly connected to the E-branch waveguide 101 (in the above-mentioned manner) it will be appreciated that if the coil 83 is excited and the coil 83' is not, an electromagnetic wave from the flange 85 does not appear at the flange 105; only the electromagnetic wave from the flange 85 appearing there without any appreciable loss. If on the other hand coil 83 is not excited and only the coil 83 is, only the electromagnetic wave from the flange 85 is sent to the flange 105. In this manner the microwave switching device of FIG. 12 of the invention can selectively transmit one or the other of the output powers of two transmitters connected to the

flanges

85 and 85 which serve as the input terminals, respectively, to the flange 105 which serves as the output terminal.

The embodiment of the microwave switching device depicted above is of the constant resistance type, because the impedance of the device as seen from the input terminal 85 is always in match with the characteristic impedance of the microwave waveguide device 50 even though either or both of the coils 83 and 83' may be excited and because the impedance seen from the input termnial 85 also is similarly constant. The time required for switching is short, since the switching operation is performed by interchanging the excitation of the coils 83 and 83' to produce in either of the microwave waveguide devices 50 or 50' an axial magnetic field.

The coils 83 and 83' may be wound directly around the waveguides without loss of effectiveness, which fact makes it possible to reduce the whole dimensions of the microwave switching device and lessen the number of turns of the coils; with the result that the time required for switching is further shortened. Furthermore, the decoupling ratio between the input terminals 85 and 85' can be made sufficiently large, because the decoupling ratio of a polarization separating circuit which has been indispensable to the conventional switching device can be eliminated and because it is possible to design the

microwave waveguide devices

50 and 50 in such a manner that each of them may effect a very large attenuation to the electromagnetic wave entering thereinto from the flange 85 or 85' when the coil 83 or 83' is excited. If the microwave switching device according to the in vention is composed of rectangular waveguides, which are at least three in number and which lead to the working and spare transmitters and to the antennna, not only can the switching device he reduced in size and weight, but also the whole transmitting equipment can be reduced in size and weight since it is usual to employ rectangular waveguides at the output ends of both transmitters and at the input terminal of the antenna.

As has been previously described, the microwave waveguide device of the invention may be composed of a circular waveguide in place of the rectangular waveguide 51 shown in FIGS. -7. Referring to FIG. 16, which is a perspective view of another embodiment of a microwave switching device according to the invention it may be seen that

mircowave waveguide devices

50a and 50a are composed of circular waveguides. It is to be noted that instead of the

flange portions

84, 102, 84' and 103 (as in FIG. 12) integral waveguides are used; otherwise similar functioning part are designated with like numerals. Inasmuch as the most preferable result is 0btained when the

microwave waveguide devices

50 and 50 are excited in such a manner that the directions of the electric fields of the electromagnetic waves at the input terminals 85 and 85' are perpendicular to the metal and resistance plates,

rectangular waveguides

120 and 120 are connected to the ends of the circular waveguides so as to facilitate such excitation. This switching device performs the switching operation in a like manner to that of FIG. 12.

In the microwave switching devices so far described the direction of the magnetic fields produced by the coils 83 and 83' are substantially the same. Therefore, the magnetic field produced by one of the coils will, under some circumstances, affect the microwave waveguide device to which the other of the coils belongs. FIG. 17 shows another microwave switching device where this condition may be relieved. Here the

microwave waveguide clcvices

50 and 50 of the invention are so connected to the branch waveguide 101 that their axial lines are perpendicular to each other, thus eliminating any field interference.

Referring to FIG. 18 which is a symbolic system diagram of still another embodiment of the microwave switching device of the invention, the switching device 130 is so designed as to selectively transmit only one of the input powers supplied to more than three input terminals to the output terminal 105. In this switching device the

microwave waveguide devices

50, 50', 50", and 50' which have input terminals 85, 8S", and 85, respectively, and which are equal in number to the input power to be switched are connected to a branch waveguide 131 in such a manner that no two axial lines of the waveguide devices are aligned and that the abovementioned condition is satisfied.

Coils

83, 83', 83", and 83" of the Waveguide devices are so arranged (not shown) that it is possible to refrain from exciting any selected one of the coils into which the input power to be transmitted to the output terminal enters, and to excite all of the remaining coils. Such an arrangement is simply conceived and as it is well known it will not be gone into. It is to be understood that such a morethan-three-input switching device may also be obtained by providing the arm having the output terminal 105 of the switching device described with reference to FIGS. 12 through 17 inclusive, with another microwave waveguide device of the invention, thus pyramiding the devices.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention, as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A non-reciprocal waveguide device comprising: a waveguide, a ferrite rod disposed substantially coaxially in said guide, at least one pair of plates, each pair consisting of a conductive plate and a resistive plate, disposed successively along the axis of said rod between the surface of the rod and the inner surface of the guide such that a resistive plate is closer to one end of said rod and a conductive plate is closer to the other end of said rod, means for supporting said rod and plates, and means for applying an axial magnetic field to said rod.

2. A non-reciprocal waveguide device as set forth in claim 1 in which an even number of pairs of plates are provided and positioned in a plane passing through the rod axis and wherein said plates are positioned symmetrically in said plane on opposite sides of said rod such that symmetrically related plates have the same wave transmission characteristics.

3. A non-reciprocal waveguide device as set forth in claim 2 in which the waveguide has a rectangular crosssection and the plates are rectangular vanes and wherein said plane passing through the rod axis is perpendicular to the narrow walls of said guide.

4. A non-reciprocal waveguide device as set forth in claim 1 in which said rod has tapered ends and wherein the plates lie successively along the axis of said rod with in planes defined by the end portions of said rod less said tapered ends.

5. A non-reciprocal waveguide switching device comprising a branch waveguide having at least two input waveguide portions and an output waveguide portion; a non-reciprocal waveguide device as set forth in claim 1 positioned in each input waveguide section such that the conductive metal plate is disposed on the side nearest the branch waveguide junction and wherein the output waveguide portion is of finite length and is connected on a one to one ratio to each input portion, each nonreciprocal waveguide device being electrically displaced from the branch waveguide junction such that the characteristic impedance is seen when looking from an unenergized non-reciprocal device toward the junction when another non-reciprocal device is energized.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Goodwin, Proceedings of the IRE," January 1960, page 113.

Tomkins et al.: Journal of Applied Physics," Supplement to vol. 31, No. 5, May 1960, pages 1765-1775.

Claims

1. A NON-RECIPROCAL WAVEGUIDE DEVICE COMPRISING: A WAVEGUIDE, A FERRITE ROD DISPOSED SUBSTANTIALLY COAXIALLY IN SAID GUIDE, AT LEAST ONE PAIR OF PLATES, EACH PAIR CONSISTING OF A CONDUCTIVE PLATE AND A RESISTIVE PLATE, DISPOSED SUCCESSIVELY ALONG THE AXIS OF SAID ROD BETWEEN THE SURFACE OF THE ROD AND THE INNER SURFACE OF THE GUIDE SUCH THAT A RESISTIVE PLATE IS CLOSER TO ONE END OF SAID ROD AND A CONDUCTIVE PATE IS CLOSER TO THE OTHER END OF SAID ROD, MEANS FOR SUPPORTING SAID ROD AND PLATES, AND MEANS FOR APPLYING AN AXIAL MAGNETIC FIELD TO SAID ROD.