US2999988A

US2999988A - Resonant directional couplers

Info

Publication number: US2999988A
Application number: US416869A
Authority: US
Inventors: Pierre G Marie
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-03-23
Filing date: 1954-03-17
Publication date: 1961-09-12
Anticipated expiration: 1978-09-12
Also published as: FR1079880A; FR64770E

Description

p 1961 P. G. MARIE 2,999,988

RESONANT DIRECTIONAL COUPLERS Filed March 17, 1954 4 Sheets-Sheet 1 12 (2') 1256 730(1) Li'cfl)17 125/ 0) 4 6 6 t 6 6 I75 la 12-5) P) 10 1.1 712/24) 7517/0) INVENTOR. Pierre G. Marie PM, W W 011mm 1717M ATTORNEY-S Sept. 12, 1961 P. G. MARIE 2,999,988

RESONANT DIRECTIONAL COUPLERS Filed March 17, 1954 4 Sheets-Sheet 2 I4 13 20 t0 t1 1 L 20 i 22

Ta r0 r4

2,2 27 j 23 Fly. 3 F194 Fl 6 Fl 7 Hg. 8

INVENTOR.

Pierre 6. Marie BY VW' W ATTORNEYS Sept. 12, 1961 P. G. MARIE 2,999,988

RESONANT DIRECTIONAL COUPLERS Filed March 17, 1954 4 Sheets$heet 3 FIG. l5

INVENTOR. Pierre G. Marie I M, M, wmom f T /4 ATTORNEYS Sept. 12, 1961 P. G. MARiE 2,999,988

RESONANT DIRECTIONAL COUPLERS Filed March 17, 1954 4 Sheets-Sheet 4 INVENTOR.

Pierre 6. Marie PW, ,M,

Baum -4- Tow,

ATTORNEYS United States Patent 2,999,988 RESONANT DIRECTIONAL COUPLERS Pierre G. Mari, 16 Rue de Varize, Paris, France Filed Mar. 17, 1954, Ser. No. 416,869 Claims priority, application France Mar. 23, 1953 16 Claims. (Cl. 333-10) This invention relates to resonant directional wave guide couplers and more particularly to couplers which, from an input guide carrying a totality of electromagnetic energy spread over a wide band of frequencies, sort into each of a plurality of output guides the incoming energy lying within a distinct band of frequencies or channel lying within such wide band.

It is an object of the invention to provide a coupler of this type which will, given a totality of electromagnetic energy distributed throughout a wide band of frequencies and appearing as a progressive wave propagated down a principal guide, extract from this totality the fraction pertaining to a specified channel and pass it into one of the output guides without disturbing in the principal guide the flow of energy proper to the other channels.

A further object of the invention is to provide a coupler of the type mentioned comprising a single cavity resonator between the principal guide and each of the output guides.

A resonant directional coupler according to the invention includes a cylindrical resonator coupled between tworectangular guides. In such a coupler the energy entering as a TE wave through one end of a first one of the rectangular guides passes through the cylindrical resonator as a circularly polarized wave formed of two TE waves in quadrature relationship and emerges as a TE wave through one end of the second rectangular guide, if the frequency of the wave is close to the resonant frequency of the resonator.

A number of cylindrical resonators may be coupled at one end to the input rectangular guide and at their other ends to individual output rectangular guides receiving the energies of the separate channels. The couplers are directional in the sense that they are traversed by electromagnetic energy, when of the frequency appropriate thereto, along a path extending from a given end of the input rectangular guide to a specified end of the second rectangular guide. On the other hand the couplers are two-way devices in the sense that energy of such appropriate frequencies can pass through them in the opposite direction as well.

When for example the coupling system serves to mix in the principal guide, assumed to be coupled to a transmitting antenna, and which then constitutes the output guide, energies of particular Wave length ranges developed by oscillators coupled to the individual guides above referred to as output guides but which on the present assumption then constitute the input guides, it may be necessary to provide for unidirectional energy transmission only in order to prevent reflected waves from passing through the separate couplers with consequent modification of their associated oscillator frequencies, in the event of imperfect coupling of the antenna to the principal guide.

It is another object of the invention to provide such couplers with unidirectional properties, i.e. couplers such that they transmit energy passing from one end of the input rectangular guide in a selected direction to one end of the second or output rectangular guide, whereas they do not transmit energy of the same frequency in the opposite direction.

A further object of the invention is to provide such ice to a plurality of energies conveyed by rectangular channel guides having an optional direction with respect to the main guide, i.e., the direction of channel guides and main guide being not necessarily at right angles to one another.

Resonant directional couplers have already been proposed in which the input and output wave guides are coupled together by cavities of square cross section. Such cavities may support two independent modes of oscillation at right angles. By means of an appropriate coupling device these two modes may be caused to exist in phase quadrature. When so phased the combination of the two modes constitutes a Wave which resembles a wave of circular polarization. In the central region of the cavity the wave field pattern rotates Without deformation. This is however no longer true in the regions of the cavity outside the center thereof and it is not at all true in the corners thereof.

This explains why in the prior art couplers constructed according to this principle, it is necessary separately to match each of the two waves by means of an appropriate matching device such as an obstacle. The combination of the two matching devices however is adequate only to match one end of the cavity, either that connected to the input guide or that connected to the output guide. Consequently at least two cavities in series must be provided between the two guides.

A further object of the invention is the provision of a directional coupler in which each coupling element between the input and output guides comprises only a single cavity, which cavity requires no matching device within it.

couplers adapted to couple a wide frequency band of electromagnetic energy conveyed in a main rectangular guide According to the feature of the invention described in the fifth preceding paragraph there is introduced into the cylindrical resonator a body of a suitable ferrite, and there is produced within the resonator a permanent magnetic field directed along the axis of the ferrite body. Under these conditions the transmission through the resonator will no longer be bi-directional, and it is even possible by suitable adjustment of the field simultaneously to interrupt transmission in both directions.

The invention will now be further described with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a directional coupler according to the invention.

FIGS. 2a-2d are vector diagrams illustrating the possible modes of propagation in the coupler of FIG. 1.

FIGS. 3 and 4 are diagrams, useful in explaining the operation of the couplers of FIGS. 1 and 5, illustrating the transmission and reflection of plane Waves at semitransparent boundaries.

FIG. 5 is a perspective view of a coupler according to the invention including a single resonant cavity.

FIGS. 6-8 are plan views of irises which may be inserted into the circular wave guide portions of the couplers of the invention.

FIG. 9 is a perspective view of a coupler according to the invention including a plurality of resonant cavities.

FIG. 10 is a section taken on the line 1010 of FIG. 9.

FIG. 11 is a perspective view of a plurality of couplers according to the invention combined into a complete channel-selecting device according to the invention.

FIG. 12 is a perspective view partly broken away of a resonant unidirectional coupler according to the invention, together with a diagrammatic showing of certain associated circuit elements.

FIGS. 13a-13c are diagrammatic representations of the exchange of energy between the various ends of the guides making up the coupler of FIG. 12.

FIG. 14 is a diagrammatic illustration of the coupler of FIG. 12 shown connected between a transmitter, an antenna, and a high frequency radio receiver, and

FIG. 15 is a diagramamtic representation of a conventional lumped-elemen circuit equivalent to the directional coupler of FIG. 5.

Referring to FIG. 1, the input rectangular guide 1 is coupled to a circular guide 2 by means of a coupling aperture 3 formed in the broad side or width of the guide 1. All of the input energy is taken to be propagated down the guide 1 in the form of a progressive TE wave.

The aperture 3 is so located in theguide, that in the absence of coupling the progressive TE wave existing in the guide 1 will exhibit at that location a magnetic field which may be represented by a rotating vector of constant modulus and lying in the plane of the guide wall, the vector rotating about the center of the aperture. The equations of the magnetic field in the guide 1 are of the well known form:

H,=H sin cos (wt-13 16) in which b represents the base of the rectangular guide, H represents the magnetic field applied at the entrance of the guide parallel to the coordinate axis OZ, 0:, the angular frequency of a particular wave among the totality of energies being propagated, and the phase constant in the guide. fi is thus the quotient of 211- divided by the length of the wave in the guide. H and H are dephased by 90 with respect to each other, and their respective amplitudes represent the Cartesian coordinates of a vector rotating with angular velocity to and having a constant modulus under the condition:

This equation defines a quantity z which represents the distance between the edge of guide 1 and the center of the aperture 3 for a wave of given frequency. v

The sense of rotation of the magnetic field at the location of the aperture 3 is determined by the direction of propagation of the wave down the guide 1.

The guide 2 is positioned with its axis on the axis 4 of the aperture 3, and its diameter is such that the waves may exist therein only in the TE mode. The guide 2 is open at its lower end and may for example be soldered to the guide 1 except as to the portion 5 which extends beyond the edge of the guide 1 and which is closed by an appropriate metallic wall.

The currents circulating in the vicinity of the coupling aperture 3 may be represented as a plot of current lines 52 rotating without relative change among themselves about the common axis 4 of the aperture 3 and guide 2. The wave developed Within the circular guide 2 is consequently circularly polarized. The sense of rotation of the electric field of this wave of circular polarization is indicated by the arrow 6 and depends upon the direc tion of propagation of the TE wave within the guide 1.

It will be assumed in the following description that regardless of the type of guide and of wave propagation, the amplitude of a wave is equal to the square root of the power transmitted thereby. Having regard simply to the symmetry of the coupler and the linearity of the equations of propagation in the guides, it can be shown that if a wave of unity amplitude entering through the end 7 of the guide 1 develops a wave of amplitude p emerging through the end 8 opposite the end 7 and a circularly polarized wave of amplitude 1- ernerging from the end 9 of the circular guide 2 and rotating in the direction indicated by the arrow 6, reciprocally a circularly polarized wave of unity amplitude entering at the end 9 of the guide 2 and rotating in the sense of the arrow 6 will develop in the rectangular guide 1 a Wave of amplitude 1- moving toward the end 8 and a circularly polarized wave of amplitude p rotating in the sense of the arrow 6 and reflected toward the output end 9 of guide 2. No energy is propagated toward the end 7. Proof of this property of the structure of FIG. 1 may be made in the following fashion:

In FIG. 2a the arrow 10 represents the wave entering through the end 7, of unity amplitude, as indicated by the number 1 in parentheses in the figure. The arrow 11 represents the Wave of amplitude p emerging from the end 8, and the arrow 12 represents the circularly polarized wave of amplitude 1- rotating in the sense of the arrow 6 and emerging from the end 9.

In FIG. 2b the amplitudes and waves have been multiplied by the factor Consequently the wave entering through the end 7, represented by the arrow 10 has an amplitude of The wave emerging from the end 8 represented by the arrow 11 possesses an amplitude p /'r and the wave emerging throughthe end 9 represented by the arrow 12 possesses an amplitude 5p.

FIG. 20 symbolizes a state of affairs derived from that state of aifairs shown in FIG. 2a from a consideration of the field symmetry in the symmetry plane of the coupler (the plane containing the axis 4 and perpendicular to the axis of the rectangular guide). The representation of FIG. 2c further reflects a change of sign in the time factor in the equations of propagation and a multiplication of the amplitudes by the factor 1/1: I The eflect of the symmetry is to replace the unity amplitude wave entering through the end 7 by an output wave of amplitude p emerging through that end. Similarly the output wave emerging from the end 8 is replaced by an entering wave of unity amplitude passing through that end. The output wave emerging from the end 9 is unchanged. The change in sign for time results in replacing the wave emerging through the end 7 by a wave entering through that end and in replacing the wave entering through the end 8 by a wave emerging from that end and in replacing the wave emerging from the end 9 by a wave emerging through that end. Lastly, upon multiplication by the factor l/r a wave of ampltiude p/ 1' represented by the arrow 10 and entering through the end 7 together with a unity amplitude wave entering through the end 9 and represented by the arrow 13 produce a wave of amplitude 1/1- represented by the arrow 11 emerging through the end 8.

FIG. 2d represents the superposition of the two configurations represented in FIGS. 2b and 20. From an examination of this figure and bearing in mind the relation that it appears that to a unity amplitude wave entering through the end 9 (arrow 13 there corresponds a wave of amplitude 1 emerging through the end 8 (arrow 11 and a wave of amplitude p emerging through the end 9 (arrow 12 No energy emerges from the end 7 (arrow 10 From the preceding proposition it follows that if into a directional coupler such as that of FIG. 1, there is introduced through the end 7 of the rectangular guide 1 electromagnetic energy of TE form, the end 8 being terminated by the characteristic impedance of the guide and if there exist in the circular guide 2 both a wave excited through the coupling aperture 3 and directed toward the end 9 and a wave derived from the reflection of this latter wave at the end 9 and directed toward the coupling aperture 3, the two waves being propagated in opposite senses in the guide 2 being circularly polarized and having the same sense of rotation of their electric vectors, there will exist between the values t which measures the amplitude of the wave 10 entering through the end 7, r which measures the amplitude of the wave 11 emerging from the end 8, t; which measures the amplitude of the circularly polarized wave 12 passing from the coupling aperture 3 to the end 9, and r which measures the amplitude of the circularly polarized wave 13 passing from the end 9 toward the coupling aperture, the same matrix relation as that which obtains among the amplitudes of plane waves incident upon, transmitted through and reflected from a plane, semitransparent, non-absorbing surface of transmission coeflicient 1. This relation is Referring to FIG. 3, this matrix relation implies that if 14 is a plane, semitransparent non-absorbing surface receiving a wave 20 of amplitude t this incident wave will be divided into a transmitted wave 22 of amplitude t and a reflected wave 21 of amplitude r and that reciprocally an incident wave 23 of amplitude r will be divided into a transmitted wave 21 of amplitude r and into a reflected wave 22 of amplitude t FIG. represents the combination of two directional couplers of the type illustrated in FIG. 1. The first coupler comprises the rectangular guide 1 and the circular guide 2 coupled at the coupling aperture 3. The second comprises the rectangular guide 15 and the circular guide 2 coupled at the aperture 16. t and r represent respectively energy entering through the end 7 and emerging through the end 8 of the guide 1. t and r represent respectively energies of circularly polarized waves propagated in opposite directions through the guide 2. t and r represent respectively energy emerging through the end 17 and entering through the end 18 of the guide .15. Under these assumptions the distribution of energy in the combined double coupler is the same as the energy on the opposite sides of the

semitransparent surfaces

19 and 20 of FIG. 4.

The combination of

semitransparent surfaces

19 and 20 of FIG. 4 constitutes an interferometer of the Perrot and Fabry type. If the surfaces are strongly reflecting, only waves having such as wave length that the distance between the planes of the

surfaces

19 and 20 approximates an integral number of half wave lengths will be transmitted. Thus, disregarding losses The other waves not fulfilling this condition are reflected such that 1 is very small, and r is nearly equal to t a B y analogy, in the double coupler of FIG. 5 the waves having a wave length such that the height of the cylindrical guide 2 approximates an integral number of half wave lengths therefor in that guide will be transmitted with the result that:

2= o whereas the other waves not fulfilling this condition will be reflected so that r is nearly equal to t In FIG. 15, there is shown a diagrammatic representa tion of a conventional lumped-element structure equivalent to the directional coupler of FIG. 5. In FIG. 15 the resonant circuit comprising inductance 67 and capacity 68 connected in series represents the resonator 2 of FIG. 5 for one of its two TE modes of vibration, and the resonant circuit comprising inductance 69 and capacity 70 connected in series represents the same resonator 2 for its second TE mode. The transformers 71 and 72 represent the coupling holes between the resonator 2 and the currents which, in the

rectangular guides

1 and 15 of FIG. 5, flow in the direction of the guide axes, Similarly the transformers 7.3 and 74 represent the coupling holes between the resonator 2 and the currents which, in the

rectangular guides

1 and 15, flow perpendicularly to the guide axes. The currents in the resonant circuits 6768 and 69-70 are in quadrature relationship and whether one current lags or leads the other by a phaseshift results from the direction of propagation in lines7-8 and 17-18. The diagram of FIG. 15 is equivalent to a duplexer.

In the double coupler of FIG. 5 the value of t as a function of t and of fiequency is that of a simple cavity resonator, i.e. of a resonant circuit. A better selectivity with respect to wave length is obtained if there are pro vided within the circular guide 2 a plurality of cavity resonators tuned to the central frequency of the channel to be selected, these cavities being separated from each other by irises.

The form of these irises and their mutual separations may be specified by computations of the type used in the filtering of guided waves. It may however be noted that the circularly polarized waves propagated in both directions within the interior of the circular guide 2 are waves each made up of a pair of TE waves in quadrature and that the irises must be selected and positioned with due respect for the circular polarization present. To this end it is sufii'cient for them to have a repetitive symmetry at least threefold in nature. Most conveniently irises having a circular aperture may be employed.

FIGS. 6, 7 and 8 show other types of irises which may be employed to separate the cavity resonators. The iris 24 is inductive, the iris 25 is capacitive, and both possess fourfold repetitive symmetry. The iris 26 is capacitive and exhibits threefold repetitive symmetry. Apertures of the shape of the openings in the irises 24-26 may be substituted in place of the coupling apertures 3 and 16.

FIG. 9 represents a double directional coupler with three resonant cavities. The guide '1 in which the energy arrives from the end 7 and whose end 8 is connected by means not shown to the characteristic impedance of the guide, is coupled to the circular guide 2 through an aperture 27 having the shape of the opening in iris 26 of FIG. 8. The rectangular guide 15 from which the energy emerges from the end 17 and whose end 18 is coupled to the characteristic impedance of that guide is coupled to the circular guide 2 through an aperture 30 having likewise the form of the opening in the iris 26. The circular guide 2 is divided into three resonant cavities 39, 40 and 41 by means of

irises

28 and 29 of the form of the iris shown in FIG. 7. Each resonant cavity may be tuned by means of four plugs. In FIG. 9 there are illustrated

plugs

31 and 32 for cavity 39, plugs 35 and 36 for cavity 40 and plugs 37 and 38 for the cavity 41. Two additional plugs per cavity may be provided in diametrically opposite positions inasmuch as it is desirable to provide four plugs for tuning of cavities in which there exists a circularly polarized wave made up of two TE waves. Two plugs disposed each at one end of two perpendicular diameters would theoretically suffice, but this would destroy the symmetry of the circularly polarized wave.

FIG. 10 illustrates the four plugs 31-34 provided for tuning of the cavity 39.

FIG. ll represents a combination of four directional couplers of resonant cavity type according to FIG. 9. This combination is destined to son-t out the following channels:

(I) 3,700-3,720 mc.

(II) 3,740-3,760 mc. (I11) 3,780-3,800 mc. (IV) 3,8203,840 me.

All of these channels fall within a band of frequencies which may be collected by a receiving antenna and applied to the left end of the principal input guide 42. To this guide there are coupled four

circular guides

43, 44, 45, 46, coupled respectively to the rectangular guides "7 47, 48, 49, 50. Each circular guide is coupled to two rectangular guides by apertures such as the apertures 27 and 30 of FIG. 9. Each circular guide comprises three resonant cavities each having a height equal to a half wave length for a TB wave the circular guide of the mid frequency of the channel to be selected. If for example the circular guides 43-46 have a diameter D=6 cm., their out ofi wave lengths for TE waves are Assuming for the rectangular guides 37-41 the same cut oil wave length,

2b=l0.26 cm.

Hence b=5.13 cm.

Consequently the wave lengths of the waves in the circular guide and in the rectangular guides are the same. The properties of the coupler of FIG. 11 can then be In practice one may select for z an average value of 1.11 cm. and for the heights values slightly shorter than those indicated. Exact tuning is then obtained by means of the plugs.

The width b of the rectangular guides being fixed at a value approximately equal to 5.13 ms, the height a may no longer be arbitrarily chosen. For reasons of matching it is desirable to provide that:

A Z unmw 1 (2'3 b 3.76(2b) 2 Taking for A the median wave length of the entire band, i.e. 7\=8 cm. and taking for b and D respectively 5.13 and 6 cm., the value of a is 0.83 cm. in view of the fact that the value of the radial is unity.

In 'FIG. 11 the right end of the guide 42 and the near end of the guides 47-50 are provided with terminations 51 which may for example take the form of absorbing plates of carbon or similar material. The plates are provided with an oblique edge presented to the interior of the guides, and the plane of the plates is parallel to the height or small dimension of the guides.

The resonant cavities which make up each circular wave guide are tuned by means of plugs in order to transmit, for example to receivers which may becoupled to the guides 47 and 50, energies lying within the channels I-IV set out in the table.

It may be observed that the orientation of the guides 47-50 about the axes of their associated circular guides may be arbitrary inasmuch as circularly polarized waves possess rotational symmetry.

FIG. 12. illustrates a unidirectional coupler according to the invention. A plurality of unidirectional couplers of the type shown in FIG. 12 may be combined into a complete channel-selecting device according to the invention similar to that shown in FIG. 11 but having unidirectional transmission properties. The rectangular guides 1 and 15 are positioned parallel to each other in order to facilitate the following explanation. It is however to be understood that their orientation about the axis of the circular guide 2 may be arbitrary since '8 the waves propagated within the guide 2' are circularly polarized. The guide 2 is coupled to the

guides

1 and 15 by coupling apertures 3 and 16, respectively.

A rod of ferrite 53 is positioned coaxially within the guide 2, and a winding 54- is provided outside the guide. The rod 53 is positioned within the guide 2 by means of insulating disks 59 and 60 of polystyrene for example. The winding 54 is energized from a DC. source 55 controlled by a potentiometer 56. The current flowing in the winding 54 develops a unidirectional magnetic field parallel to the axis of the circular guide. 7

In the absence of this permanent magnetic field the resonant frequency of the cylindrical resonator 2 is the same for circularly polarized waves regardless of the sense of rotation of the electric vector thereof. However in the presence of the permanent axial magnetic field this is no longer true, and the two resonant frequencies corresponding to the two directions of rotation of the electric field are separate. The ferrites 'str'ongly exhibit the Faraday effect. This eifect, well known in optics, may be described as follows:

When a plane wave circularly polarized passes through a material subjected to a unidirectional magnetic field directed along the direction of propagation, the phase velocity (i.e. the optical index of the material) depends upon the direction of rotation of the electric vector. The difference between the index observed in the presence of the field and the index in the absence of that field increases with the intensity of the field and varies with the frequency of the incident wave.

The ferrites are metallic oxides of the general formula xFe O in which x represents a bivalent metal such as magnesium, nickel or cobalt. They combine the high resistivity of oxides with the ferromagnetic properties of iron. In view of this high resistivity relatively thick rods of this material may be positioned within a cylindrical guide without producing severe attenuation in wave propagation.

' Two T13 waves of the same amplitude in quadrature having their electric vectors mutually perpendicular on the axis of the guide 2 together form a circularly polarized wave. To the two possible directions of rotation of the electric filed along the axis of the guide there correspond two different phase velocities.

For a given unidirectional field let F be the resonant frequency of resonator 2 when the electric field rotates in the sense of the arrow 57, and let F be the resonant frequency when the electric field turns in the opposite sense indicated by the arrow 58. If the direction of rotation indicated by the arrow 57 is that of the circularly polarized wave developed in the resonator 2 when the energy enters through the end 7 of the guide 1, it will likewise be the sense of rotation of the circularly polarized wave when the energy enters through the end 18 of the guide 15. In fact, with the arrangement of FIG. 1 a symmetry of the fields with respect to the plane of symmetry perpendicular to the axis of the cylindrical guide preserves unchanged the direction of rotation of the electric field within the resonator 2.

On the other hand the sense of rotation of the circularly polarized waves developed when the energy enters through the end 8 of the guide 1 or through the end 17 of the guide :15 is that of the arrow 58. Indeed in these two cases the fields may be dreived from the two cases previously discussed by considerations of symmetry with respect to the plane containing the axis of the circular guide and perpendicular to the length of the rectangular guides, and this symmetry reverses the sense of rotation of the electric field in the resonator 2.

Thus if an electromagnetic wave has a frequency F it will traverse the resonator 2 if introduced at the

end

7 or 18, and it will not traverse it if introduced at the

ends

8 or 17. The possible energy transmissions between the

ends

7, 8 and 17, 18 for the frequency F are indicated by the arrows in FIG. 13 in which a diagonal arrow indicates passage of energy through the resonator 2.

Similarly a wave of frequency F passes through the resonator 2 if introduced at the

ends

8 or 17 and does not pass through it if introduced at the

ends

7 or 18. The possible transmission between the

ends

7, 8, 17 and 18 for the frequency F are indicated by the arrows in FIG. 13b.

If the frequency of the incident wave departs widely from the frequencies F and F no energy will pass through the resonator 2. The possible transmissions are then indicated by the arrows of FIG. 130. The absence of diagonal arrows indicates that the energy can pass down either of the guides 1 and but cannot pass from one to the other.

The properties just discussed are utilized in the device of FIG. 14 to protect an oscillator tube 61. The oscillator develops a band of frequencies centered on the frequency F and is coupled at the end 7 of a rectangular guide 1. By the mechanism of the

guides

1, 15 and 2 of FIG. 14 the oscillator 61 is protected against waves reflected by an antenna 62 coupled to the end 17 of the guide 15. Such reflections may occur for example when the antenna is not exactly matched in impedance to the impedance of the guide 15 throughout the range of wave lengths developed by the oscillator. Matched

terminations

63 and 64 are located at the

ends

8 and 18 of

guides

15 and 1. The energy developed by the tube 61 follows the path indicated by the arrow 65 and is radiated by the antenna 62. The energy reflected by the antenna follows the path indicated by the arrow 66 and is absorbed in the termination 64.

The coupler of the invention may serve as a duplexer in a radar receiver. The tube 61 of FIG. 13 then takes the form of a pulsed transmitter, and the termination is replaced by the radar receiver.

While the invention has been described in terms of specific embodiments, it is to be understood that variations readily occurring to the man skilled in the art are possible and that these variations fall Within the scope ofthe invention. Thus for example the guides 4750 may be connected to transmitters developing energy in the separate channels, and the guide 42 may then be connected to a transmitting antenna.

I claim:

1. A wave guide transmission system comprising a first rectangular wave guide adapted to support in the TE rectangular mode a plurality of electromagnetic waves of different frequencies lying within a frequency band divisible into distinct frequency channels, said guide having formed in a wide face thereof a plurality of apertures, a plurality of circular wave guides associable each with one of said channels, said circular guides being each afiixed at one end to said first guide coaxially about one of said apertures, and a plurality of secondary rectangular Wave guides each having an aperture formed in a wide face thereof, each of said secondary guides being aflixed to the other end of one of said circular guides with its aperture coaxially positioned relative to said one circular guide, said circular guides having each a height substantially equal to half a wave length, for waves of the TE circular mode propagated within such circular guides, corresponding to the median frequency of the associated one of said channels.

2. A wave guide transmission system comprising a first rectangular wave guide adapted to support in the TE rectangular mode a plurality of electromagnetic waves of different frequencies lying within a frequency band divisible into distinct frequency channels, said guide having formed in a wide face thereof a plurality of apertures having an electrical circular symmetry, a plurality of circular wave guides associable each with one of said channels, said circular guides being each afiixed at one end to said first guide coaxially about one of said apertures, a plurality of secondary rectangular wave guides the axes of which may have any direction parallel to the wide face of said first rectangular guide, each secondary wave guide having an aperture having an electrical circular symmetry formed in a wide face thereof, each of said secondary guides being affixed to the other end of one of said circular guides with its aperture coaxially positioned relative to said one circular guide, said circular guides having each a height substantially equal to half a wave length, for waves of the TE circular mode propagated within such circular guides, corresponding to the median frequency of the associated one of said channels, and means to terminate each of said rectangular guides at one end thereof with its characteristic impedance.

3. A wave guide transmission system comprising a first rectangular wave guide adapted to support in the TE rectangular mode a plurality of electromagnetic Waves of different frequencies lying within a frequency band divisible into distinct frequency channels, said guide having formed in a wide face thereof a plurality of apertures, a plurality of circular wave guides associable each' with one of said channels, said circular guides being each afiixed at one end to said first guide coaxially about one of said apertures, a plurality of secondary rectangular wave guides each having an aperture formed in a wide face thereof, each of said secondary guides being affixed to the other end of one of said circular guides with its aperture coaxially positioned relative to said one circular guide, one or more irises in each of said circular guides dividing the interior thereof into a plurality of resonant cavities, the cavities in each of said circular guides having a height substantially equal to half the guide wave length for a wave of the T13 circular'mode resonating within the cavities of such circular guide, said last-named Wave having the median frequency of the associated one of said channels, and a plurality of tuning plugs disposed in the walls of said circular guides communicating with each of the cavities formed by said irises.

4. A directional filtering Wave guide' coupler system comprising a principal rectangular guide adapted to support in the T13 rectangular mode a plurality of electromagnetic waves covering a wide frequency band divisible into distinct frequency channels, said guide having a plurality of apertures in a wide wall thereof centered respectively about points at each of which the longitudinal and transverse current components in said wall are for one of said channels of substantially equal magnitude and in phase quadrature, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and afixed at one end to said guide with the end adjacent said guide closed except at the said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the TE circular mode and having as their resonant frequencies substantially the median frequencies of said channels respectively, and a plurality of channel rectangular guides the axes of which may have any direction parallel to the Wide face of said principal rectangular guide, each channel guide being adapted to support waves within said band in the T13 rectangular mode and having each an aperture in one of its wide walls centered about a point at which the longitudinal and transverse current components in said Wall are for one of said channels of substantially equal magnitude and in phase quadrature, said channel rectangular guides being aflfixed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators respectively and with the ends of said cylindrical cavity resonators opposite said principal guide closed except across the apertures in said channel rectangular guides, whereby a plurality of waves falling within said wide frequency band and arriving in the TE rectangular mode from a given end of the principal rectangular guide give rise in each of said cavity resonators to a circularly polarized Wave having a given direction of rotation therein and falling within one of said channels and further give rise to a TE rectangular wave in each of said channel rectangular guides, the

wavesin said channel rectangular guides being propagated only toward a given end thereof.

5. A directional filtering wave guide coupler system comprising a principal rectangular guide adapted to support in the TE rectangular mode a 'plurality of electromagnetic waves covering a wide frequency band divisible into distinct frequency channels, said guide having a plurality of apertures in a wide wall thereof centered re spectively about points at each of which the longitudinal and transverse current components in said wall are for one of said channels of substantially equal magnitude and in phase quadrature, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and aflixed at one end to said guide with the end adjacent said guide closed except at the said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the TE circular mode and having as their resonant frequencies substantially the median frequencies of said channels respectively, said resonators further having as their heights an integral multiple of one-half the wave length corresponding to said median frequencies in the TE mode, and a plurality of channel rectangular guides the axes of which may have any direction parallel to the wide face of said principal rectangular guide, each channel guide being adapted to support waves within said band in the TE rectangular mode and having each an aperture in one of its wide walls centered about a point at which the longitudinal and transverse current components in said wall are for one of said channels of substantially equal magnitude and in phase quadrature, said channel rectangular guides being aflixed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators respectively and with the ends of said cylindrical cavity resonators opposite said principal guide closed except across the apertures in said channel rectangular guides, whereby a plurality of waves falling within said wide frequency band and arriving in the TE rectangular mode from a given end of the principal rectangular guide give rise in each of said cavity resonators to a circularly polarized wave having a given direction of rotation therein and falling within one of said channels and further give rise to a TE rectangular wave in each of said channel rectangular guides, the waves in said channel rectangular guides being propagated only toward a given end thereof.

6. A directional filtering wave guide coupler system comprising a principal rectangular guide adapted to support in the TE rectangular mode a plurality of electromagnetic waves covering a wide frequency band divisible into distinct frequency channels, said guide having a plurality of apertures in a wide wall thereof centered respectively about points at each of which the longitudinal and transverse current components in said wall are for one of said channels of substantially equal magnitude and in phase quadrature, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and affixed at one end to said guide with the end adjacent said guide closed except at the said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the TE circular mode and having as their resonant frequencies substantially the median frequencies of said channels respectively, said resonators further having as their heights an integral multiple of one-half the wave length corresponding to said median frequencies in the TE mode, at least two tuning stubs located in perpendicular radial planes in each of said cylindrical cavity resonators, and a plurality of channel rectangular guides the axes of which may have any direction parallel to the wide face of said principal rectangular guide, each channel guide being adapted to support waves within said band in'the TE rectangular mode and having each an aperture in one of its wide walls centered about a point at which the longitudinal and transverse current com ponents in said wall are for one of said channels'of sub stantially equal magnitude and in phase quadrature, said channel rectangular guides being affixed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators respectively and with the ends of said cylindrical cavity resonators opposite said principal guide closed except across the apertures in said channel rectangular guides, whereby a plurality of waves falling within said wide frequency band and arriving in the TE rectangular mode from a given end of the principal rectangular guide give rise in each of said cavity resonators to a circularly polarized wave having a given direction of rotation therein and falling within one of said channels and further give rise to a TE rectangular wave in each of said channel rectangular guides, the waves in said channel rectangular guides being propagated only toward a given end thereof.

7. A directional filtering wave guide coupler system comprising a principal rectangular guide adapted to support in the TE rectangular mode a plurality of electromagnetic waves covering a Wide frequency band divisible into distinct frequency channels, said guide having a plurality of apertures in a wide wall thereof centered respectively about points at each of which the longitudinal and transverse current components in said wall are for one of said channels of substantially equal magnitude and in phase quadrature, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and aflixed at one end to said guide with the end adjacent said guide closed except at the said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the TE circular mode and having as their resonant frequencies substantially the median frequencies of said channels respectively, said resonators further having as their heights an integral multiple of one-half the wave length corresponding to said median frequencies in the TE mode, at least one iris in each of said resonators dividing the interior thereof into a plurality of partial cylindrical cavity resonators, at least two tuning stubs in each of said partial cylindrical cavity resonators located in perpendicular radial planes of said resonators, and a plurality of channel rectangular guides adapted to support waves within said band in the TE rectangular mode and having each an aperture in one of its wide walls centered about a point at which the longitudinal and transverse current components in said wall are for one of said channels of substantially equal magnitude and in phase quadrature, said channel rectangular guides being aflixed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators respectively and with the ends of said cylindrical cavity resonators opposite said principal guide closed except across the apertures in said channel rectangular guides, whereby a plurality of waves falling within said wide frequency band and arriving in the TE rectangular mode from a given end of the principal rectangular guide give rise in each of said cavity resonators to a circularly polarized wave having a given direction of rotation therein and falling within one of said channels and further give rise to a TE rectangular wave in each of said channel rectangular guides, the wave of said channel rectangular guides being propagated only toward a given end thereof.

8. A directional filtering wave guide coupler system comprising a principal rectangular guide adapted to support in the TE rectangular mode a plurality of electromagnetic waves covering a wide frequency band divisible into distinct frequency channels, said guide having a plurality of apertures in a wide wall thereof centered respectively about points at each of which the longitudinal and transverse current components in said wall are for one of said channels of substantially equal magnitude and in phase quadrature, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and afiixed at one end to said guide with the end adjacent said guide closed except at the said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the TE circular mode and having as their resonant frequencies substantially the median frequencies of said channels respectively, a plurality of channel rectangular guides the axes of which may have any direction parallel to the wide face of said principal rectangular guide, each channel guide being adapted to support waves within said band in the TE rectangular mode and having each an aperture in one of its wide walls centered about a point at which the longitudinal and transverse current components in said wall are for one of said channels of substantially equal magnitude and in phase quadrature, said channel rectangular guides being affixed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators respectively and with the ends of said cylindrical cavity resonators opposite said principal guide closed except across the apertures in said channel rectangular guides, and means to terminate each of said principal and channel rectangular guides at one end thereof with its characteristic impedance.

9. A unidirectional filtering wave guide coupler system comprising a principal rectangular guide adapted to support in the TE rectangular mode a plurality of electromagnetic waves covering a wide frequency band divisible into distinct frequency channels, said guide having a plurality of apertures in the wide wall thereof centered respectively about points at each of which the longitudinal and transverse current components in said wall are for the median frequency of one of said channels of substantially equal magnitude and in phase quadrature, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and aflixed at one end to said principal rectangular guide with the end adjacent said principal rectangular guide closed except at said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the TE circular mode and having as their resonant frequencies the median fre quencies of said channels, a body of ferrite material supported coaxially within each of said cylindrical cavity resonators, means to generate in each of said ferrite bodies a magnetic field directed coaxially of said resonaators, and a plurality of channel rectangular guides adapted to support waves within said band in the TE rectangular mode and having each an aperture in one of its wide walls centered about a point at which the longitudinal and transverse current components in said wall are for the median frequency of one of said channels of substantially equal magnitude and in phase quadrature, said channel rectangular guides being affixed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators respectively and with the ends of said cylindrical cavity resonators opposite said principal guide closed except across the apertures in said channel rectangular guides, whereby a plurality of waves falling within said wide frequency-band and arriving in the TE rectangular mode from a given end of the principal rectangular guide give rise in each of said cavity resonators to a circularly polarized wave having a given direction of rotation therein and falling within one of said channels and further give rise to a TE rectan gular wave in each of said channel rectangular guides, the waves in said channel rectangular guides being propagated only toward a given end thereof, whereas waves coming from said given ends of said channel rectangular guidesdo not enter said cavity resonators.

10. A unidirectional filtering wave guide coupler system comprising a principal rectangular guide adapted to support in the TE rectangular mode a plurality of electromagnetic waves covering a wide frequency band divisible into distinct frequency channels, said guide having a plurality of apertures in the wide wall thereof centered respectively about points at each of which the longitudinal and transverse current components in said wall are for the median frequency of one of said channels of substantially equal magnitude and in phase quadrature, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and affixed at one end to said principal rectangular guide with the end adjacent said principal rectangular guide closed except at said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the TE circular mode and having as their resonant frequencies the median frequencies of said channels, said resonators further having as their heights and integral multiple of one-half the wave length corresponding to said median frequencies in the TE mode, a body of ferrite material supported coaxially within each of said cylindrical cavity resonators, means to generate in each of said ferrite bodies a magnetic field directed coaxially of said resonators, and a plurality of channel rectangular guides adapted to support waves within said band in the TE rectangular mode and having each an aperture in one of its wide walls centered about a point at which the longitudinal and transverse current components in said wall are for the median frequency of one of said channels of substantially equal magnitude and in phase quadrature, said channel rectangular guides being alfixed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators respectively and with the ends of said cylindrical cavity resonators opposite said principal guide closed except across the apertures in said channel rectangular guides, whereby a plurality of waves falling within said wide frequency band and arriving in the TE rectangular mode from a given end of the principal rectangular guide give rise in each of said cavity resonators to a circularly polarized wave having a given direction of rotation therein and falling within one of said channels and further give rise to a TE rectangular wave in each of said channel rectangular guides, the waves in said channel rectangular guides being propagated only toward a given end thereof, Whereas waves coming from said given ends of said channel rectangular guides do not enter said cavity resonators.

11. A unidirectional filtering wave guide coupler system comprising a principal rectangular guide adapted to support in the T E rectangular mode a plurality of electromagnetic waves covering a wire frequency band divisible into distinct frequency channels, said guide having a plurality of apertures in the wide wall thereof centered respectively about points at each of which the longitudinal and transverse current components in said wall are for the median frequency of one of said channels of substantially equal magnitude and in phase quadrature, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and afiixed at one end to said principal rectangular guide with the end adjacent, said principal rectangular guide closed except' at said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the TE circular mode and having as their resonant frequencies the median frequencies of said channels, said resonators further having as their heights an integral multiple of one-half the wave length corresponding to said median frequencies in the TE mode, at least two tuning stubs located in perpendicular radial planes in each of said cylindrical cavity resonators, a body of ferrite material supported coaxially within each of said cylindrical cavity resonators, means to generate in each of said ferrite bodies a magnetic field directed coaxially of said resonators, and a plurality of channel rectangular guides adapted to support waves within said band in the TE rectangular mode and having each an aperture in one of its side walls centered about a point at which the longitudinal and transverse current components in said wall are for the median frequency of one of said channels of substantially equal magnitude and in phase quadrature, said channel rectangular guides being afiixed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators respectively and with the ends of said cylindrical cavity resonators opposite said principal guide closed except across the apertures in said channel rectangular guides, whereby a plurality of waves falling within said wide frequency band and arriving in the TE rectangular mode from a given end of the principal rectangular guide give rise in each of said cavity resonators to a circularly polarized wave having a given direct-ion of rotation therein and falling within one of said channels and further give rise to a TE rectangular wave in each of said channel rectangular guides, the waves in said channel rectangular guides being propagated only toward a given end thereof, whereas waves coming from said given ends of said channel rectangular guides do not enter said cavity resonators.

12. A unidirectional filtering wave guide coupler systern comprising a principal rectangular guide adapted to support in the T13 rectangular mode a plurality of electromagnetic waves covering a wide frequency band 7divisible into distinct frequency channels, said guide having a plurality of apertures in the wide wall thereof centered respectively about points at each of which the longitudinal and transverse current components in said wall are of the median frequency of one of said channels of substantially equal magnitude and in phase quadrature, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and aihxed at one end to said principal rectangular guide with the end adjacent said principal rectangular guide closed except at said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the T13 circular mode and having as their resonant frequencies the median frequencies of said channels, said resonators further having as their heights an integral multiple of one-half the Wave length corresponding to said median frequencies in the TE mode, at least one iris in each of said resonators dividing the interior thereof into a plurality of partial cylindrical cavity resonators, at least two tuning stubs in each of said partial cylindrical cavity resonators located in perpendicular radial planes of said resonators, a body of ferrite material supported coaxially within each of said cylindrical cavity resonators, means to generate in each of said ferrite bodies a magnetic field directed coaxially of said resonators, and a plurality of channel rectangular guides adapted to support waves within said band in the TE rectangular mode and having each an aperture in one of its wide walls centered about a point at which the longitudinal and transverse current components in said wall are for the median frequency of one of said channels of substantially equal magnitude and in phase quadrature, said channel rectangular guides being affixed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators respectively and with the ends of said cylindrical cavity resonators opposite said principal guide closed except across the apertures in said channel rectangular guides, whereby a plurality of waves falling Within said wide frequency band and arriving in the TE rectangular mode from a given end of the principal rectangular guide give rise in each of said cavity resonators to a circularly polarized wave having a given direction of rotation therein and falling within one of said channels and further give rise to a TE rectangular wave in each of said channel rectangular guides, the Waves in said channel rectangular guides being propagated only toward a given end thereof, whereas waves coming from said given ends of said channel rectangular guides do not enter said cavity resonators.

13. A unidirectional filtering wave guide coupler systern comprising a principal rectangular guide adapted to support in the TE rectangular mode a plurality of el'ec troma-gnetic waves covering a wide frequency band divisible into distinct frequency channels, said guide having a plurality of apertures in the wide wall thereof centered respectively about points at each of which the longitudinal and transverse current components in said wall are for the median frequency of one of said channels of substantially equal magnitude and in phase quadrature, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and aflixed at one end to said principal rectangular guide with the end adjacent said principal rectangular guide closed except at said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the TE circular mode and having as their resonant frequencies the median frequencies of said channels, a body of ferrite material supported coaxially within each of said cylindrical cavity resonators, means to generate in each of said ferrite bodies a magnetic field directed coaxially of said resonators, a plurality of channel rectangular guides adapted to support Waves within said band in the TE rectangular mode and having each an aperture in one of its wide walls centered about a point at which the longitudinal and transverse current components in said wall are for the median frequency of one of said channels of substantially equal magnitude and in phase quadrature, said channel rectangular guides being afhxed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators respectively and with the ends of said cylindrical cavity resonators opposite said principal guide closed except across the apertures in said channel rectangular guides, whereby a plurality of waves falling within said wide frequency band and arriving in the T13 rectangular mode from a given end of the principal rectangular guide give rise in each of said cavity resonators to a circularly polarized wave having a given direction of rotation therein and falling within one of said channels and further give rise to a TE' rectangular wave in each of said channel rectangular guides, the waves in said channel rectangular guides being propagated only toward a given end thereof, and means to terminate each of said principal and channel rectangular guides at one end thereof with its characteristic impedance.

'14. A directional filtering wave guide coupler system comprising a principal rectangular wave guide adapted to support in the TE rectangular mode a plurality of electromagnetic waves covering a wide frequency band divisible into distinct frequency channels, said guide having a plurality of apertures in a wide wall thereof centered respectively about points at distances from one edge of said wide wall substantially equal to b i 22 1; tan )\g wherein b is the width of the said principal rectangular guide and R is the wave length in said principal rectangular guide of the median frequencies in one of said channels, a plurality of cylindrical cavity resonators each arranged coaxially with one of said apertures and affixed at one end to said principal rectangular guide with the end adjacent said principal rectangular guide closed except at said aperture, said cylindrical cavity resonators having such diameters as to support waves within said channels respectively only according to the T E circular mode and having as their resonant frequencies the median frequencies of said channels, and a plurality of channel rectangular guides adapted to support waves said band in theTE rectangular mode and having each an aperture in one of its wide walls centered about a point at a distance from one edge of said wide 17 wall of said channel rectangular guide substantially equalto 1 tan wherein b is the width of said channel rectangular guide and X' is the wave length in said channel rectangular guide of the median frequency in one of said channels, said channel rectangular guides being aflixed to said cylindrical cavity resonators with their apertures coaxial with said cylindrical cavity resonators and with the ends of said cylindrical cavity resonators adjacent a channel rectangular guide closed except across the aperture in said channel rectangular guide.

15. A wave guide coupler system comprising a first rectangular wave guide adapted to support an electromagnetic wave in the T13 rectangular mode, said guide having an aperture in a wide wall thereof centered about a point at which the longitudinal and transverse current components of said wave in said wall are of substantially equal magnitude and in phase quadrature, a cylindrical cavity resonator aflixed at one end to said principal rectangular guide coaxially with said aperture with the end of said cavity resonator adjacent said guide closed except at said aperture, said cavity resonator having such a diameter as to support said wave only according to the TE circular mode, a body of ferrite material supported coaxially within said cavity resonator, a magnetic field winding disposed coaxially about said cavity resonator to apply a magnetic field to said ferrite body, and a second rectangular wave guide adapted to support said wave in the TE rectangular mode and having an aperture in one of its wide Walls centered about a point at which the longitudinal and transverse current components of said wave in said wall are of substantially equal magnitude and in phase quadrature, said second rectangular guide being afiixed to said cavity resonator with its aperture coaxial with said cavity resonators and with the end of said cavity resonator adjacent said second rectangular guide closed except across the aperture in said second rectangular guide.

16. A wave guide coupler system comprising a first 18 I rectangular wave guide adapted to support an electromagnetic wave in the TE rectangular mode, said guide having an aperture in the wide wall thereof centered about a point at which the longitudinal and transverse current components of said wave in said wall are of substantially equal magnitude and in phase quadrature, a cylindrical cavity resonator aflixed at one end to said principal rectangular guide coaxially with said aperture with the end of said cavity resonator adjacent said guide closed except at said aperture, said cavity resonator having such a diameter as to support said wave only according to the TE circular mode, and a second rectangular wave guide the axis of which may have any direction parallel to the wide face of said first rectangular guide, said second rectangular guide being adapted to support said wave in the TE rectangular mode and having an aperture in one of its wide walls centered about a point at which the longitudinal and transverse current components of said wave in said wall are of substantially equal magnitude and in phase quadrature, said second rectangular guide being aflixed to said cavity resonator with its aperture coaxial with said cavity resonators and with the end of said cavity resonator adjacent said second rectangular guide closed except across the aperture in said second rectangular guide.

References Cited in the file of this patent UNITED STATES PATENTS 2,473,274 Bradley June 14, 1949 2,602,859 Moreno July 8, 1952 2,606,248 Dicke Aug. 5, 1952 2,626,990 Pierce Jan. 27, 1953 2,667,620 Riblet Jan. 26, 1954 2,713,151 Farr July 12, 1955 2,714,707 Zabel Aug. 2, 1955 2,719,274 Luhrs Sept. 27, 1955 2,723,377 Cohn Nov. 8, 1955 2,795,763 Tillotson June 11, 1957 FOREIGN PATENTS 592,224 Great Britain Sept. 11, 1953 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No, 2 999 988 September 12,; 1961 Pierre Ga Mari It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7, line 4L9 for "radial" read radical column 8 line 75, for "FIGQ 13"" read FIG, 13a 3 column l4 line 14L for "and" read an line 46 for "wire" read wide same column 14 line 72 for "side" read wide column l5 line 27,, for "of" first, occurrence read for o Signed and sealed this 3rd day of April 1962.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents